E. Gonzalez-Padilla,a R. Ruiz, D. LeFever, A. Denham and J. N. Wiltbank4 Colorado State University, s Fort Collins 80521
Summary
detected in 0, 94 and 93% for groups C, I and P, respectively. By utilizing estrogen and progesterone, it Tr/al 2. A group of 83 Limousin and appeared possible to mimic the changes Charolais crossbred heifers that had not shown occurring in blood hormone levels near heat during a 30-day observation period and puberty. This suggested the possibility of had no CL as diagnosed by rectal palpation induction of puberty in beef heifers. Four trials were given treatment I. By 4 days after implant were conducted to test this hypothesis and a removal, 93% of these heifers had shown heat fifth to explore the effect of treatment with and 56% became pregnant to the induced steroids in induction of estrus in suckling puberal estrus. Seventy-one percent of the anestrous cows. heifers were pregnant after a 28-day breeding Tr/al 1. At the Eastern Colorado Range Station, 45 Hereford, Angus-Hereford and period. Tr/a/ 3. At a research station in Sonora, Charolais-Hereford heifers were divided within Mexico, 158 prepuberal heifers were divided breed into a control group (C), Group I which into C and I groups. The percents in heat were received on day 1 a single IM injection of 5 mg 6 and 79 from 0 to 4 days; 28 and 84 from 0 to of estradiol valerate (EV) plus 3 mg of 25 days; and 38 and 84 from 0 to 48 days in 17a-acetoxy 11 beta-methyl 19 nor-preg-4ene 3, 20 dione (n0rgestomet), and a 6 mg ear the C and I groups, respectively. Pregnancy implant of norgestomet which was removed 9 rates were 4 and 43% after 4 days of breeding days later, and group P which received 5 mg of 11 and 58% after 25 days of breeding and 27 estradiol valerate, IM on day 6, daily IM and 73% after 48 days of breeding in the C and injections of 20 mg of progesterone from day 6 I groups, respectively. Tr/al 4. Thirty-four prepuberal Angus to day 10 and 2 mg of estradiol-17/~ on day 12. heifers, 9 to 10 months of age, were rectally By 4 days after implant removal, estrus was examined for ovarian activity and 18 were given treatment I while the other 16 served as Published with the approval of the Director of the controls. Eighty-nine percent of the treated Colorado State University Experiment Station as heifers were detected in estrus by 4 days after Scientific Series Paper No. 1964. the end of the treatment while 25% of the =All hormones and partial support for these experiments were kindly provided to us by G. D. controls showed heat in 18 days. Corpora lutea were detected by rectal palpation in 14 of the Searle, Co. of Chicago, Illinois. 3Present Address: INIP, Km 15% de la Cart., 16 treated heifers that showed heat. Mexico Toluca, Palo Alto, Mexico 10 D. F. Tr/al 5. To study the possibility of induction 4present Address: Texas A & M University, of fertile estrus in postpartum cows, a group of Agricultural Research Station, St. Rt. 2 Box 43C, 26 cycling and 32 anestrous lactating post Beeville, Texas 78102. SDepartment of Physiology and Biophysics and partum cows were given 6 mg of EV + 3 mg Department of Animal Sciences. norgestomet (IM) and 1 or 2 implants of 1110 JOURNAL OF ANIMAL SCIENCE,vol. 40, no. 6, 1975
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P U B E R T Y IN B E E F H E I F E R S . III. I N D U C T I O N O F F E R T I L E E S T R U S 1 2
PUBERTY OF BEEF HEIFERS
Introduction
Evidence shows that beef heifers bred to calve first at 2 years of age produce more calves in their lifetime than those calving first at 3 years of age or older (Pope, 1967; Donaldson, 1968; Morrow, 1969). Furthermore, heifers calving early the first time continue calving early in subsequent years and wean heavier calves (Burris and Priode, 1958; Short and Bellows, 1971; Lesmeister et al., 1973). However, under most practical conditions, a large proportion of heifers have not reached puberty at the start of their first breeding season as yearlings (Wilbank et aL, 1969; Arije and Wiltbank, 1971). Age at first estrus can be controlled to a certain extent by feeding (Wiltbank et al., 1965; Crichton et al., 1959; Amir et al., 1967; Short and Bellows, 1971; Deutscher, 1973); however, this is not the most economical approach in all situations and other alternatives are needed. Previous reports have shown a prominent role in progesterone in the onset of puberty (Gonzalez-Padilla et al., 1975a). It was also noted that corpora lutea formation and onset of the cyclic activity could be induced by progesterone and estradiol-17/3 injections in prepuberal heifers (Gonzalez-Padilla et al., 1974b). The purpose of this study was to evaluate the use of estrogens and progestogens for induction of fertile estrus in prepuberal heifers and anestrous post-partum cows under practical conditions. Materials and Methods
Trial 1. Fifty-seven Hereford, Hereford X
Angus and Hereford X Charolais yearling heifers (12 to 14 months old and 278 kg average weight) maintained at the Eastern Colorado Range Station were examined for the presence of corpora lutea (CL). Forty-five heifers which did not have CL were divided within breed into a control and two treated groups. In treatment ' T ' the heifers received on day 1 a single IM injection of 5 mg of estradiol valerate (EV) and 3 mg of 17,~-acetoxy 11 beta-methyl 19 nor-preg 4ene 3, 20 dione (norgestomet) and an implant of 6 mg of norgestomet in a hydron polymer that was removed on day 10. In treatment "P", the heifers received 5 mg of EV plus 20 mg of progesterone IM on day 6, daily injections of 20 mg of progesterone until day 10, and a 2 mg IM of estradiol 17/~on day 12. All heifers were maintained together in a small pasture with a sterile bull and were observed for estrus at 6-hr intervals during the first 5 days after implant removal in treatment I and twice daily thereafter until the end of a 45-day period of artificial insemination. Each heifer found in standing heat was inseminated 12 hr later. Pregnancy diagnoses was made 30 and 60 days after the end of the breeding season. Trial 2. A group of 70 crossbred Limousin and 15 grade Charolais heifers, ages 12 to 16 months and averaging 314 kg, were not detected in heat during the first 30 days of the breeding season. All were examined for the presence of CL. The 83 heifers which did not have CL were classified on the basis of follicular development as having follicles > 10mm or follicles < 10mm. All heifers received treatment I as outlined in Trial I. Heifers were bred 12 hr after being detected in heat, and pregnancy diagnosis was performed between 40 and 60 days after the last AI service. Trial 3. This trial was conducted at the "Centro de Investigaciones Pecuarias del Edo. de Sonora" in Mexico. A group of 91 Brangus (52 yearlings and 39 2-year-olds, averaging 263 kg), 38 Charolais (33 yearlings and five 2-year-olds, average weight 270 kg) and 29 Zebu crosses (14 to 18 months old and average weight 246 kg) that had not shown heat in. the last 30 days had their ovaries examined rectally and classified according to follicular development as described in Trial 2. They were stratified by breed, weight, age and follicular
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norgestomet each of which contained 6 mg of norgestomet. The implants were removed 9 days later. There were no differences due to the number of implants in occurrence of estrus or pregnancy rates. Within 5 days after implant removal, 96% and 87% of the cycling and anestrous cows were detected in heat, respectively. By the end of a 28-day breeding period, the pregnancy rate in the cycling and anestrous cows was 85 and 94% of the total, respectively. Utilizing this treatment, it would appear possible to induce fertile estrus in prepuberal heifers while further work is necessary in the post-partum cow.
1111
1112
GONZALEZ-PADILLA,WILTBANK AND NISWENDER TABLE 1. OCCURRENCE OF ESTRUS AND PREGNANCY RATES IN PREPUBERAL HEIFERS AT EASTERN RANGE STATION, TRIAL 1 Treatments
EV + Progesterone + Estradiol-17#b
Item
Control
No. heifers No. in heat after implant removal 0- 4 days 0-21 days 0-45 days No. pregnantd
14
16
15
0 (0) e e 0 (0) c 7 (50) e
15 ( 94)d 16 (100) a, 16 (100)a
14 ( 9 3 ) d 14 ( 9 3 ) d. 15 (100) a
o I olc 0c
8 ( 12(75)
1 (7) c
15 ( 94)u
11 ( 7 3 ) ~
1 (14) e
9 ( 56)d 3 ( 43)e 3 ( 75)c
3 (20) c 5 (42) c 3 (43) c
0- 4 d a y s 0.21 d a y s
0-45 days Pregnant/service First Second Third
a,
5(33)
c
aImplant con~i~ing 6 nag o f n o r g e s t o m e t for 9 days and i n j e c t i o n of 5 m g o f E V and 3 n ~ o f n o r g e s t o m e t o n d a y o f implantation. bsingle i n j e c t i o n o f 5 mg of EV plus daffy IM injections o f 2 0 m g of p r o g e s t e r o n e for 5 days; 2 mg o f estradiol-17/~ i~ected IM 48 hr after last p r o g e s t e r o n e . c,dValues in t h e s a m e r o w w i t h different supezscrlpts are significantly different. (P < .01). eValues in p a r e n t h e s e s are the peroent o f the t o t a l n u m b e r of h e i f e n in each group.
development into a control or treatment I groups. The AI breeding season lasted for 48 days in dry lot. Pregnancy diagnosis was made 60 days after the end of the breeding season. Tr/al 4. Thirty-four Angus heifers, 9 to 10 months of age and 250 kg average weight, that had not shown heat and had no evidence of CL as diagnosed by ovarian palpation, were divided into a control and a treated group. The treatment used was the same as in Trials 2 and 3. Observations for estrus were carried out for 18 days, ,~nd the ovaries of all heifers were examined rectally to ascertain if CL was present 16 days after implant removal. Trial 5. A group of 58 beef cows suckling calves (15 to 60 days old) were observed for estrus for 30 days prior to the start of the breeding season. Thirty-two of these cows failed to show estrus while 26 of them showed heat at least once. All cows were treated as described in Trials 2 to 4 except that the dose of EV was 6 mg and half of the cows in each group received two implants. Heat checks and artificial insemination were carried out for 28 days after implant removal, and pregnancy diagnosis was made 35 days after the end of the breeding season.
Statistical analysis. Chi square was utilized to test differences between groups in pregnancy rate and in proportion showing estrus. Results Trial 1. The results of Trial 1 indicate that fertile estrus was induced in prepuberal heifers (table 1). Ninety-four percent of the heifers in Group I and 93% of the heifers in Group P were detected in estrus between 24 and 72 hr post treatment, while none of the heifers in the control group showed estrus in the first 21 days post treatment. By the end of the 45-day breeding period, only 50% o f the control heifers had been in heat, as compared to 100% in the I and P groups. The percentspregnant after 4 days ofbreedingwere 50% and 13% for the I and P groups, respectively, and by the end of the 45-day breeding period, the pregnancy rates were 7%, 94% and 73% for the control, I and P groups, respectively. The main reason for the difference between treated and control groups was that only 50% of the control heifers had shown heat, by the end of the breeding season. The pregnancy rate at the induced estrus was lower in the P than in the I group; the reason for this difference is difficult to
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EV + Norgestomet + Implant a
1113
PUBERTY OF BEEF HEIFERS TABLE 2. OCCURRENCE OF ESTRUS AND PREGNANCY RATES IN PREPUBERAL HEIFERS TREATED WITH TREATMENT Ia, TRIAL 2
Follicles> 10mm no CL Follicles < 10mm no CL Total
No. 73
In heat by No. anestrous 4 days after after first implant removal observed heat c %
Pregnant (%) 1st
2nd
Service d
Serviced
Total in 28 Days e
97
5(7)
58
60
79
10
75
2(33}
33
50
50
83
93
7(9)
56
59
71
a l m p l a n t containing 6 nag of n o r g e s t o m e t for 9 days plus an i nj e c t i on of 5 mg of EV and 3 mg of nor~estomet o n day of i m p l a n t a t i o n . ~ by rectal e x a m i n a t i o n of the ovaries at the s t a rt of the t r e a t m e n t . eValues in parentheses indicate the percentage of those showing heat. dNo. Pregnant fNo. bred. eNo. Pregnant/No. heifers
ascertain since the treatments were different in more than one respect. It is thought that the heifers in the P group ovulated as most returned to heat in 17 to 24 days. The low fertility observed in the control heifers bred at their first estrus cannot be traced to sub-fertile semen or deficient AI techniques since the three groups of heifers were bred by the same technicians using semen from the same collection.
Trial 2. The results of the second trial, presented in table 2, also indicate that treatment I induced fertile estrus in prepuberal heifers. The first heifer was observed in estrus 18 hr after implant removal, and 93% of the heifers showed heat in the next 48 hours. The length of standing estrus was 12 to 18 hr in all but seven heifers (9% of those in heat) which were in standing heat from 24 to 48 hr and were bred twice during this period.
TABLE 3. ESTRUS OCCURRENCE AND PREGNANCY RATES IN PREPUBERAL HEIFERS AT SONORA, MEXICO, TRIAL 3 Treatment Controls Item
No. heifers In heat after implant removal (%) 0- 4 days 0-25 days 0-48 days
Follicular sizeb 10 mm
26
55
0 lld 19 d
9d 36 e 47 e
Treated a Total
Follicular sizeb I0 mm
Total
81
26
51
77
6 28 38
69 e 77 f 77 f
84 e 88 f 88 f
79 84 84
No. anestrous after first observed heat c 9 Pregnant (%)
0- 4 days 0-25 days 0-48 days
0
0 8d 19 d
3 (15)
5d 13 d 31d
3 (13) 4* 11" 27*
2 (10) 42 e 84 e 69 e
2 (4) 43 e 61 e 74 e
4 (6) 43* 58* 73*
a I m p l a n t containing 6 nag of n o r g e s t o m e t for 9 days plus an injection of 5 mg of EV and 3 "n~ of nor~estomet on day of implantation. ~ by rectal e x a m i n a t i o n of the ovaries at the start of the t r e a t m e n t . N o CL d e t e c t e d in any h e i f e r . CValues in parentheses are the percent of those showing heat by 25 days. 9d , e , f v a i n e s w i t h different superscripts in the same row are significantly di ffe re nt (P < .05). *Totals differ significantly (p < .05).
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Status of the ovariesb
1114
GONZALEZ-PADILLA, WlLTBANK AND NISWENDER
TABLE 4. PREGNANCY RATE IN TREATED AND NON TREATED HEIFERS, TRIAL 3 a Item
Treated b
31 42
65 51
S e c o n d service No. b r e d P r e g n a n t (%)
15 47
28 57
T h i r d service No. b r e d P r e g n a n t (%)
3 67
12 28
a N o significant d i f f e r e n c e s b e t w e e n treated and c o n t r o l in p r e g n a n c y rate in any service. b l m p l a n t of 6 mg o f n o r g e s t o m e t for 9 d a y s plus an injection of 5 mg of EV and 3 m g of n o r g e s t o m e t o n dlty o f implantation.
The pregnancy rate at the induced estrus was 56%, and after 28 days of breeding, 71% of the total heifers were pregnant. The degree of follicular development at the start of the treatment appeared to affect the response; a
TABLE 5. EFFECT OF BODY WEIGHT ON OCCURRENCE OF ESTRUS AND PREGNANCY IN PREPUBERAL HEIFERS IN TRIAL 3 Weight, kg
No. heifers
In heat 0-25 days (%)
180-220 Control Treated e Total
15 11 26
20a 64bc
221-260 Control Treated e Total
28 29 57
14a 75 c
261- 3 0 0 Control Treated e Total
26 22 48
38 a 100 d
301-340 Control Treated e Total
10 13 23
50b 100 d
341 Control Treated e Total
2 2 4
Pregnant 0-48 days (%) 20a 64 b
38
0a 54b 38
21 a 75b 44
30
73*
78"
27 a
35
87*
52 70 b
85b 43
50 50 100
42
82 b
30a 54b
100 100
31 18 a 65b
15 a 56b
70 b 100 c
100
23
47
67*
0-48 days (%) 13a 54 b
3a 57b
50 b 100 c
100 100
0-25 days (%)
78* 50 100
50
75
a,b,c,d,Values with different superscript in the s a m e c o l u m n are significantly different (P < .05). elrnplant c o n t a i n i n g 6 m g o f n o r g e s t o m e t for 9 d a y s and an injection of 5 mg o f E V a n d 3 m g o f n o r g e s t o m e t o n d a y o f implantation. *Different t h a n totals w i t h o u t superscript in the s a m e c o l u m n (P < .05).
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Control
F i r s t service No. b r e d P r e g n a n t (%)
smaller proportion of the heifers with follicles less than 10 ml had shown estrus and they had a lower pregnancy rate than heifers with follicles over 10 millimeters. It was also noticed that a higher proportion of heifers with follicles less than 10ram were not detected in heat a second time even though they were not pregnant at the induced estrus. These observations were not subjected to statistical analysis due to the small number of heifers with follicles smaller than 10 millimeters. Trial 3. In Trial 3, the occurrence of estrus was significantly affected by treatment, body weight, age and degree of follicular development, while pregnancy rate was only affected by treatment. Seventy-nine percent of the treated heifers showed estrus within 4 days after implant removal, and 84% had cycled by 25 days, while only 28% and 38% of the control heifers had shown heat after 25 and 48 days of breeding, respectively (table 3). The proportion of control heifers showing heat by 25 and 48 days was affected by the degree of
1115
PUBERTY OF BEEF HEIFERS
agreement with reports pointing out that body weight is a factor affecting the onset of puberty in beef heifers (Wiltbank et al., 1966, 1969; Arije and Wiltbank, 1971; Bellows, 1968). The effect of age was studied in the Brangus Heifers, since 52 of them were yearlings and 39 were 2-year-olds. A higher proportion of the 2-year-olds were detected in estrus by 25 and 48 days than in the yearlings (table 6). This effect may be confounded with weight, since 2-year-old heifers were heavier. Nevertheless, it is interesting to note in table 6 that the percent in heat and the percent pregnant after 25 days of breeding in the treated yearlings was higher than in the 2-year-olds in the control group (P < .01). Trial 4. Trial 4 was conducted in 9- to 10-month-old prepuberal Angus heifers to ascertain if I treatment was effective in younger animals. Table 7 show that 89% of the treated heifers showed estrus within 4 days from implant removal as compared to 25% of the control heifers showing heat by 18 days after implant removal (P < .01). Estrus in the treated heifers was synchronized with all being detected in heat in a 48-hr period. Unfortunately, observations for estrus were carried out for only 18 days, so it could not be ascertained if all these heifers kept on cycling. A rectal examination of the ovaries 16 days after implant removal revealed that 14 of the 18 treated heifers had corpora lutea, which would indicate that these heifers had started cycling. The degree of follicular development may
T A B L E 6. E F F E C T OF AGE ON O C C U R R E N C E OF ESTRUS AND PREGNANCY IN BRANGUS HEIFERS IN SONORA. T R I A L 3 In heat
Age Yearlings Control Treated a
Total Two-Year-Olds Control Treateda Total
No. heifers
0-25 days
(%)
Pregnant
0-48 days
(%)
0-25 days
0-48 days
(%)
(%)
28 24 52
28 b 71c 48
36 b 71c
3b 42 c
25b 54 c
52
21
38
20 19 39
40 b 100c 69
65 b 100 c 82
15b 63c 38
40 b 95c 67
a l m p l a n t containing 6 m g of n o r g e s t o m e t for 9 d a y s a n d an i n j e c t i o n of 5 m g of EV and 3 m g of n o r g e s t o m e t o n day of implantation. b,CValues with dittarent supel~cript in t h e s a m e age g r o u p and s a m e r are s i g n i f i c a n t l y d i f f e r e n t (P < ,05).
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follicular development at the start of the trial (P < .05); a similar trend was noticed in the treated group however, the difference was not statistically significant (P > .05). The interaction between ovarian status and treatment was significant (P < .01) for the number of heifers showing heat, indicating that the treatment induced heat even in animals with little follicular development. In this respect, Arije (1969) reported that daily injections of 20 mg of progesterone plus 40pg of estradiol17/3 for 16 days induced follicular development, estrus, ovulation, and cyclic activity in four of seven prepuberal beef heifers. As in the previous trials, the induced heat was at least as fertile as that of the controls. The data presented in table 4 shows that there were no differences in pregnancy rate at first service between treated and control groups nor between first and second service in the treated group. Because of the high proportion of heifers anestrus in the control group, only 27% of them were pregnant after 48 days of breeding, while 43%, 58% and 73% of the treated heifers were pregnant after 4, 25 and 48 days of breeding, respectively. Body weight affected the occurrence of estrus in control and treated heifers. A smaller proportion of heifers below 260 kg were detected in heat as compared to heifers above 260 kg (table 5). The same effect was observed in Trial 2 where the six heifers that failed to show estrus averaged 3 5 kg less than those showing heat. These observations are in
1116
GONZALEZ-PADILLA, WILTBANK AND NISWENDER T A B L E 7. O C C U R R E N C E O F E S T R U S IN P R E P U B E R A L A N G U S H E I F E R S
9 TO 10 MONTHS OF AGE, TRIAL 4
No. heifers No. heifers in heat after implant removalC 0- 4 days 0-18 days No. heifers with CL 16 days after implant removald
Treated a Follicular Size b < 10ram > 10ram Total 9 18 9
0 1(12)
0 3(37)
0 4(25)
7(78)** 7(78)**
9(100)** 9(100)**
16(89)** 16(89)**
Ie
1
2
6
8
14
a l m p l a o t cont'|hi--z_ 6 m g of n o r g e s t o m e t for 9 d a y s a n d a n i n j e c t i o n of 5 m g of E V a n d 3 m g of n o r g e s t o m e t o n d a y of i m p l a n t a t i o n . bD'.mgnosed b y r e c t a l e x a m i n a t i o n of t h e ovaries a t t h e s t a r t of t h e t r e a t m e n t . N o C L d e t e c t e d i n a n y heifer. CVmuea i n p a r e n t h e s e s are t h e p e r c e n t of the t o t a l n u m b e r of heifers in e a c h g r o u p . d T w o h e i f e m i n t h e c o n t r o l g r o u p c a m e i n h e a t o n d a y 16 a n d w e r e n o t p a l p a t e d . COne h e i f e r in t h e c o n t r o l g r o u p h a d C1 b u t was n o t d e t e c t e d i n h e a t . * * S i g n i f i c a n t l y d i f f e r e n t f r o m t h e c o n t r o l s (P < .01).
have affected the occurrence of estrus as trous at the start of the treatment or the observed in the previous trials; however, the number of implants used (P > .05). Eightynumber of animals was too small to utilize seven percent of the cows in the anestrous statistics and arrive at meaningful conclusions. group and 96% of the cows in the cycling group Trial 5. In Trial 5, the treatments utilized were detected in estrus by 5 days after were effective in synchronizing or inducing a treatment. The first cow showed estrus 36 hr fertile estrus i,n cows suckling calves (table 8). after implant removal, and all cows showing No significant differences were found in heat were detected within the following 72 percent of cows in heat or 'pregnancy rate hours. By the end of the 28-day breeding between cows classified as cycling and anes- period, 100% and 91% of the cows in the T A B L E 8. O C C U R R E N C E O F E S T R U S A N D P R E G N A N C Y R A T E S IN COWS S U C K L I N G C A L V E S , T R I A L 5.
Status at start of treatmenta, b Cycling Anestrous Item No. cows Cows in heat after implant removal, % 0- 5 days 0-28 days No. anestrous after first observed heat Pregnant, % 0- 5 days 0-28 days
1 implant 13
92 100 0 54 85
2 implants Total 13 26
100 100 1(8) 61 85
96 100 1(4) 58 85
1 implant 16
87 87 2(14) 56 75
2 implants Total 16 32
87 94 0 67 94
87 91 2(7) 62 84
a O b s e r v e d for e s t r u s twice d a l l y for 3 0 d a y s p r i o r t o t r e a t m e n t . b O n e or t w o i m p l a n t s of 6 nag of n o r g e s t o m e t for 9 d a y s a n d a n i n j e c t i o n of 6 m g of E V a n d 3 mg of n o r g e s t o m e t o n d a y of i m p l a n t a t i o n CValues in p a r e n t h e s i s ace p e r c e n t of t h e c o w s t h a t s h o w e d esters.
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Item
Control Follicular Sizeb < 10ram > 10ram Total 8 8 16
PUBERTY OF BEEF HEIFERS
Discussion. It is known that heifers calving early as two year olds continue calving early in subsequent years and wean more pounds of calf in their lifetime (Burris and Priode, 1958; Lesmeister et al., 1973). First calf heifers also take longer to return to estrus after calving than old cows (Wiltbank, 1972), which suggests the need for starting the yearling heifers' breeding season before that of the rest of the cow herd. However, a large proportion of heifers have not shown heat before the start of the regular breeding season (Wiltbank e t al., 1969; Arije and Wiltbank, 1971; Bellows, 1968) and therefore will be late calvers. Our results show that treatment I can be used effectively as a management tool to get a larger proportion of heifers pregnant early in the breeding season. This would particularly be important in heifers that do not receive enough supplemental feeding or are Zebu type heifers which have been reported to attain puberty at an older age than British heifers (Reynolds, 1967, 1972). In this respect, we made the observations in Trial 3 that none of the 14 control Zebu crossbred heifers showed heat during the 48-day breeding period, while 87% of 15 treated heifers in the same breed group were detected in heat and 73% of them became pregnant in 48 days. These results were not tabulated because the average weight of the Zebu crossbred heifers was lower than the other breeds and breed effect was confounded with weight. The fact that body weight significantly affected the response to the treatment indicates that optimum results can be obtained by a combination of I treatment and better feeding. However, our results are still far from allowing
specific recommendations as to how much feed would be required to optimize the results and the minimum age at which the treatment would be effective. Answers to these questions will probably be different for different breeds of cattle. With the type of cattle utilized in Trial 3, we found that response to the treatment was reduced in animals weighing less than 260 kilograms. However, in the Angus heifers of Trial 4, the treatment was effective in inducing estrus in heifers 9 to 10 months old weighing 250 kilograms. Based on the evidence presented, it appears that the treatment is effective in hastening the Final events leading to puberty. It has been suggested that in rats, the neural structures involved in the phasic release of LH are not responsive to progesterone and estradiol injections until about 10 days prior to the onset of puberty (Caligaris et at, 1972), and it is possible that our treatment may prove ineffective in heifers far from their expected data of puberty.
Literature Cited Amir, S., J. Kali, R. Volcani and R. Petlam. 1967. Early breeding in dairy heifers. Anim. Prod. 9:268. Arije, G. F. 1969. Puberty in beef heifers. M. S. Thesis, Colorado State University, Fort Collins. Arije, G. F. and J. N. Wiltbank. 1971. Age and weight at puberty in Hereford heifers. J. Anim. Sci. 33:401. Bellows, R. A. 1968. Reproduction and growth in beef heifers. A. I. Digest. January, 1968. Burris, M. J. and B. M, Priode. 1958. Effect of calving date on subsequent calving performance. J. Anita. Sci. 17:527. Caligaris, L., J. J. Astrada and S. Taleisnik. 1972. Influence of age on the release of luteinizing hormone induced by oestrogen and progesterone in immature rats. J. Endocrinol. 55:97. Crichton, J. A., J. N. Aitken and A. W. Boyne. 1959. The effect of plane of nutrition during rearing on growth, production, reproduction and health of dairy cattle. Anita. Prod. 1:145. Deutscher, G. H. 1973. Effect of nutritional levels of replacement heifer calves on their reproductive performanqe and productivity. Antelope range field sta. Buffalo, South Dakota. A-S series 73-10. Donaldson, L. E. 1968. The pattern of pregnancies and life-time productivity of cows in a Northern Queensland beef cattle herd. Australian Vet. J. 44:493. Gonzalez-PadiUa, E., J. N. Wtltbank and G. D. Niswender. 1975a. Puberty in beef heifers. I. The
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cycling groups and anestrous group, respectively, had been inseminated at least once. The pregnancy rate after 5 days of breeding was 58% and 62% for the cycling and anestrous groups, respectively. At the end of the 28-day breeding period, 85% and 84% of the cows in the cycling and anestrous groups, respectively, were pregnant. There is a possibility that the anestrous cows would have shown heat naturally before the end of the 28-day period, in which case the only thing the treatment accomplished was to hasten this event and allow two services per cow in a 28-day period.
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GONZALEZ-PADILLA, WILTBANK AND NISWENDER
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interrelationship between pituitary hypothalamic Cunha, A. Warnick and M. Koger (Ed.) Factors and ovarian hormones. J. Anita. Sei. 40:1091. affecting calf crop. University of Florida Press. Gonzalez-Padilla, E., G. D. Niswender and J. N. Short, R. E. and R. A. Bellows. 1971. Relationships Wfltbank. 1975b. Puberty in beef heifers. II. Effect among weight gains age at puberty and reproducof injections of progesterone and estradiol-17# on tive performance in heifers. J. Anim. Sci. 37:551. serum LH, FSH, and ovarian activity. J. Anim. Sci. Wiltbank, J. N., J. Bond, E. J. Warwick, R. E. Davis, 40:1105. A. C. Cook, W. L. Reynolds and M. W. Hazen. Lesmeister, J. L., P. J. Burfening and R. L. Blackwell. I965. Influence of total feed and protein intake on 1973. Date of first calving in beef cows and reproductive performance in the beef female subsequent calf production. J. Anim. Sci. 36:1. through second calving. U.S.D.A. Tech. Bull. 1314. Morrow, D. L. 1969. Factors affecting beef cow Wiltbank, J. N., K. E. Gregory, L. A. Swiger, J. E. production. M. S. Thesis, Colorado State UniversiIngalls, J. A. Rothlisberger and R. M. Koch. 1966. ty, Fort Collins. Effects of heterosis on age and weight at puberty Pope, L. S. 1967. Age at first calving and performance. in beef heifers. J. Anim. Sci. 25:744. In T. Cunha, A. Warnick and M. Koger (Ed.). Wiltbank, .l.N., C. W. Kasson and J. E. lngalls. 1969. Factors affecting calf crop. University of Florida Puberty in crossbred and straightbred beef heifers Press. on two levels of feed. J. Anim. Sci. 29:602. Reynolds, W. L. 1972. Factors affecting reproductive Wiltbank, J. N. 1972. Management program for performance in heifers. Proceedings - 21st and improving reproductive performance. Proceedings 22rid beef cattle short course. Texas A & M 21st and 22nd beef cattle short course. Texas A&M University, College Station, Texas. University, College Station. Reynolds, W. L. 1967. Breeds and reproduction. In T.
Summary
detected in 0, 94 and 93% for groups C, I and P, respectively. By utilizing estrogen and progesterone, it Tr/al 2. A group of 83 Limousin and appeared possible to mimic the changes Charolais crossbred heifers that had not shown occurring in blood hormone levels near heat during a 30-day observation period and puberty. This suggested the possibility of had no CL as diagnosed by rectal palpation induction of puberty in beef heifers. Four trials were given treatment I. By 4 days after implant were conducted to test this hypothesis and a removal, 93% of these heifers had shown heat fifth to explore the effect of treatment with and 56% became pregnant to the induced steroids in induction of estrus in suckling puberal estrus. Seventy-one percent of the anestrous cows. heifers were pregnant after a 28-day breeding Tr/al 1. At the Eastern Colorado Range Station, 45 Hereford, Angus-Hereford and period. Tr/a/ 3. At a research station in Sonora, Charolais-Hereford heifers were divided within Mexico, 158 prepuberal heifers were divided breed into a control group (C), Group I which into C and I groups. The percents in heat were received on day 1 a single IM injection of 5 mg 6 and 79 from 0 to 4 days; 28 and 84 from 0 to of estradiol valerate (EV) plus 3 mg of 25 days; and 38 and 84 from 0 to 48 days in 17a-acetoxy 11 beta-methyl 19 nor-preg-4ene 3, 20 dione (n0rgestomet), and a 6 mg ear the C and I groups, respectively. Pregnancy implant of norgestomet which was removed 9 rates were 4 and 43% after 4 days of breeding days later, and group P which received 5 mg of 11 and 58% after 25 days of breeding and 27 estradiol valerate, IM on day 6, daily IM and 73% after 48 days of breeding in the C and injections of 20 mg of progesterone from day 6 I groups, respectively. Tr/al 4. Thirty-four prepuberal Angus to day 10 and 2 mg of estradiol-17/~ on day 12. heifers, 9 to 10 months of age, were rectally By 4 days after implant removal, estrus was examined for ovarian activity and 18 were given treatment I while the other 16 served as Published with the approval of the Director of the controls. Eighty-nine percent of the treated Colorado State University Experiment Station as heifers were detected in estrus by 4 days after Scientific Series Paper No. 1964. the end of the treatment while 25% of the =All hormones and partial support for these experiments were kindly provided to us by G. D. controls showed heat in 18 days. Corpora lutea were detected by rectal palpation in 14 of the Searle, Co. of Chicago, Illinois. 3Present Address: INIP, Km 15% de la Cart., 16 treated heifers that showed heat. Mexico Toluca, Palo Alto, Mexico 10 D. F. Tr/al 5. To study the possibility of induction 4present Address: Texas A & M University, of fertile estrus in postpartum cows, a group of Agricultural Research Station, St. Rt. 2 Box 43C, 26 cycling and 32 anestrous lactating post Beeville, Texas 78102. SDepartment of Physiology and Biophysics and partum cows were given 6 mg of EV + 3 mg Department of Animal Sciences. norgestomet (IM) and 1 or 2 implants of 1110 JOURNAL OF ANIMAL SCIENCE,vol. 40, no. 6, 1975
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P U B E R T Y IN B E E F H E I F E R S . III. I N D U C T I O N O F F E R T I L E E S T R U S 1 2
PUBERTY OF BEEF HEIFERS
Introduction
Evidence shows that beef heifers bred to calve first at 2 years of age produce more calves in their lifetime than those calving first at 3 years of age or older (Pope, 1967; Donaldson, 1968; Morrow, 1969). Furthermore, heifers calving early the first time continue calving early in subsequent years and wean heavier calves (Burris and Priode, 1958; Short and Bellows, 1971; Lesmeister et al., 1973). However, under most practical conditions, a large proportion of heifers have not reached puberty at the start of their first breeding season as yearlings (Wilbank et aL, 1969; Arije and Wiltbank, 1971). Age at first estrus can be controlled to a certain extent by feeding (Wiltbank et al., 1965; Crichton et al., 1959; Amir et al., 1967; Short and Bellows, 1971; Deutscher, 1973); however, this is not the most economical approach in all situations and other alternatives are needed. Previous reports have shown a prominent role in progesterone in the onset of puberty (Gonzalez-Padilla et al., 1975a). It was also noted that corpora lutea formation and onset of the cyclic activity could be induced by progesterone and estradiol-17/3 injections in prepuberal heifers (Gonzalez-Padilla et al., 1974b). The purpose of this study was to evaluate the use of estrogens and progestogens for induction of fertile estrus in prepuberal heifers and anestrous post-partum cows under practical conditions. Materials and Methods
Trial 1. Fifty-seven Hereford, Hereford X
Angus and Hereford X Charolais yearling heifers (12 to 14 months old and 278 kg average weight) maintained at the Eastern Colorado Range Station were examined for the presence of corpora lutea (CL). Forty-five heifers which did not have CL were divided within breed into a control and two treated groups. In treatment ' T ' the heifers received on day 1 a single IM injection of 5 mg of estradiol valerate (EV) and 3 mg of 17,~-acetoxy 11 beta-methyl 19 nor-preg 4ene 3, 20 dione (norgestomet) and an implant of 6 mg of norgestomet in a hydron polymer that was removed on day 10. In treatment "P", the heifers received 5 mg of EV plus 20 mg of progesterone IM on day 6, daily injections of 20 mg of progesterone until day 10, and a 2 mg IM of estradiol 17/~on day 12. All heifers were maintained together in a small pasture with a sterile bull and were observed for estrus at 6-hr intervals during the first 5 days after implant removal in treatment I and twice daily thereafter until the end of a 45-day period of artificial insemination. Each heifer found in standing heat was inseminated 12 hr later. Pregnancy diagnoses was made 30 and 60 days after the end of the breeding season. Trial 2. A group of 70 crossbred Limousin and 15 grade Charolais heifers, ages 12 to 16 months and averaging 314 kg, were not detected in heat during the first 30 days of the breeding season. All were examined for the presence of CL. The 83 heifers which did not have CL were classified on the basis of follicular development as having follicles > 10mm or follicles < 10mm. All heifers received treatment I as outlined in Trial I. Heifers were bred 12 hr after being detected in heat, and pregnancy diagnosis was performed between 40 and 60 days after the last AI service. Trial 3. This trial was conducted at the "Centro de Investigaciones Pecuarias del Edo. de Sonora" in Mexico. A group of 91 Brangus (52 yearlings and 39 2-year-olds, averaging 263 kg), 38 Charolais (33 yearlings and five 2-year-olds, average weight 270 kg) and 29 Zebu crosses (14 to 18 months old and average weight 246 kg) that had not shown heat in. the last 30 days had their ovaries examined rectally and classified according to follicular development as described in Trial 2. They were stratified by breed, weight, age and follicular
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norgestomet each of which contained 6 mg of norgestomet. The implants were removed 9 days later. There were no differences due to the number of implants in occurrence of estrus or pregnancy rates. Within 5 days after implant removal, 96% and 87% of the cycling and anestrous cows were detected in heat, respectively. By the end of a 28-day breeding period, the pregnancy rate in the cycling and anestrous cows was 85 and 94% of the total, respectively. Utilizing this treatment, it would appear possible to induce fertile estrus in prepuberal heifers while further work is necessary in the post-partum cow.
1111
1112
GONZALEZ-PADILLA,WILTBANK AND NISWENDER TABLE 1. OCCURRENCE OF ESTRUS AND PREGNANCY RATES IN PREPUBERAL HEIFERS AT EASTERN RANGE STATION, TRIAL 1 Treatments
EV + Progesterone + Estradiol-17#b
Item
Control
No. heifers No. in heat after implant removal 0- 4 days 0-21 days 0-45 days No. pregnantd
14
16
15
0 (0) e e 0 (0) c 7 (50) e
15 ( 94)d 16 (100) a, 16 (100)a
14 ( 9 3 ) d 14 ( 9 3 ) d. 15 (100) a
o I olc 0c
8 ( 12(75)
1 (7) c
15 ( 94)u
11 ( 7 3 ) ~
1 (14) e
9 ( 56)d 3 ( 43)e 3 ( 75)c
3 (20) c 5 (42) c 3 (43) c
0- 4 d a y s 0.21 d a y s
0-45 days Pregnant/service First Second Third
a,
5(33)
c
aImplant con~i~ing 6 nag o f n o r g e s t o m e t for 9 days and i n j e c t i o n of 5 m g o f E V and 3 n ~ o f n o r g e s t o m e t o n d a y o f implantation. bsingle i n j e c t i o n o f 5 mg of EV plus daffy IM injections o f 2 0 m g of p r o g e s t e r o n e for 5 days; 2 mg o f estradiol-17/~ i~ected IM 48 hr after last p r o g e s t e r o n e . c,dValues in t h e s a m e r o w w i t h different supezscrlpts are significantly different. (P < .01). eValues in p a r e n t h e s e s are the peroent o f the t o t a l n u m b e r of h e i f e n in each group.
development into a control or treatment I groups. The AI breeding season lasted for 48 days in dry lot. Pregnancy diagnosis was made 60 days after the end of the breeding season. Tr/al 4. Thirty-four Angus heifers, 9 to 10 months of age and 250 kg average weight, that had not shown heat and had no evidence of CL as diagnosed by ovarian palpation, were divided into a control and a treated group. The treatment used was the same as in Trials 2 and 3. Observations for estrus were carried out for 18 days, ,~nd the ovaries of all heifers were examined rectally to ascertain if CL was present 16 days after implant removal. Trial 5. A group of 58 beef cows suckling calves (15 to 60 days old) were observed for estrus for 30 days prior to the start of the breeding season. Thirty-two of these cows failed to show estrus while 26 of them showed heat at least once. All cows were treated as described in Trials 2 to 4 except that the dose of EV was 6 mg and half of the cows in each group received two implants. Heat checks and artificial insemination were carried out for 28 days after implant removal, and pregnancy diagnosis was made 35 days after the end of the breeding season.
Statistical analysis. Chi square was utilized to test differences between groups in pregnancy rate and in proportion showing estrus. Results Trial 1. The results of Trial 1 indicate that fertile estrus was induced in prepuberal heifers (table 1). Ninety-four percent of the heifers in Group I and 93% of the heifers in Group P were detected in estrus between 24 and 72 hr post treatment, while none of the heifers in the control group showed estrus in the first 21 days post treatment. By the end of the 45-day breeding period, only 50% o f the control heifers had been in heat, as compared to 100% in the I and P groups. The percentspregnant after 4 days ofbreedingwere 50% and 13% for the I and P groups, respectively, and by the end of the 45-day breeding period, the pregnancy rates were 7%, 94% and 73% for the control, I and P groups, respectively. The main reason for the difference between treated and control groups was that only 50% of the control heifers had shown heat, by the end of the breeding season. The pregnancy rate at the induced estrus was lower in the P than in the I group; the reason for this difference is difficult to
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EV + Norgestomet + Implant a
1113
PUBERTY OF BEEF HEIFERS TABLE 2. OCCURRENCE OF ESTRUS AND PREGNANCY RATES IN PREPUBERAL HEIFERS TREATED WITH TREATMENT Ia, TRIAL 2
Follicles> 10mm no CL Follicles < 10mm no CL Total
No. 73
In heat by No. anestrous 4 days after after first implant removal observed heat c %
Pregnant (%) 1st
2nd
Service d
Serviced
Total in 28 Days e
97
5(7)
58
60
79
10
75
2(33}
33
50
50
83
93
7(9)
56
59
71
a l m p l a n t containing 6 nag of n o r g e s t o m e t for 9 days plus an i nj e c t i on of 5 mg of EV and 3 mg of nor~estomet o n day of i m p l a n t a t i o n . ~ by rectal e x a m i n a t i o n of the ovaries at the s t a rt of the t r e a t m e n t . eValues in parentheses indicate the percentage of those showing heat. dNo. Pregnant fNo. bred. eNo. Pregnant/No. heifers
ascertain since the treatments were different in more than one respect. It is thought that the heifers in the P group ovulated as most returned to heat in 17 to 24 days. The low fertility observed in the control heifers bred at their first estrus cannot be traced to sub-fertile semen or deficient AI techniques since the three groups of heifers were bred by the same technicians using semen from the same collection.
Trial 2. The results of the second trial, presented in table 2, also indicate that treatment I induced fertile estrus in prepuberal heifers. The first heifer was observed in estrus 18 hr after implant removal, and 93% of the heifers showed heat in the next 48 hours. The length of standing estrus was 12 to 18 hr in all but seven heifers (9% of those in heat) which were in standing heat from 24 to 48 hr and were bred twice during this period.
TABLE 3. ESTRUS OCCURRENCE AND PREGNANCY RATES IN PREPUBERAL HEIFERS AT SONORA, MEXICO, TRIAL 3 Treatment Controls Item
No. heifers In heat after implant removal (%) 0- 4 days 0-25 days 0-48 days
Follicular sizeb 10 mm
26
55
0 lld 19 d
9d 36 e 47 e
Treated a Total
Follicular sizeb I0 mm
Total
81
26
51
77
6 28 38
69 e 77 f 77 f
84 e 88 f 88 f
79 84 84
No. anestrous after first observed heat c 9 Pregnant (%)
0- 4 days 0-25 days 0-48 days
0
0 8d 19 d
3 (15)
5d 13 d 31d
3 (13) 4* 11" 27*
2 (10) 42 e 84 e 69 e
2 (4) 43 e 61 e 74 e
4 (6) 43* 58* 73*
a I m p l a n t containing 6 nag of n o r g e s t o m e t for 9 days plus an injection of 5 mg of EV and 3 "n~ of nor~estomet on day of implantation. ~ by rectal e x a m i n a t i o n of the ovaries at the start of the t r e a t m e n t . N o CL d e t e c t e d in any h e i f e r . CValues in parentheses are the percent of those showing heat by 25 days. 9d , e , f v a i n e s w i t h different superscripts in the same row are significantly di ffe re nt (P < .05). *Totals differ significantly (p < .05).
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Status of the ovariesb
1114
GONZALEZ-PADILLA, WlLTBANK AND NISWENDER
TABLE 4. PREGNANCY RATE IN TREATED AND NON TREATED HEIFERS, TRIAL 3 a Item
Treated b
31 42
65 51
S e c o n d service No. b r e d P r e g n a n t (%)
15 47
28 57
T h i r d service No. b r e d P r e g n a n t (%)
3 67
12 28
a N o significant d i f f e r e n c e s b e t w e e n treated and c o n t r o l in p r e g n a n c y rate in any service. b l m p l a n t of 6 mg o f n o r g e s t o m e t for 9 d a y s plus an injection of 5 mg of EV and 3 m g of n o r g e s t o m e t o n dlty o f implantation.
The pregnancy rate at the induced estrus was 56%, and after 28 days of breeding, 71% of the total heifers were pregnant. The degree of follicular development at the start of the treatment appeared to affect the response; a
TABLE 5. EFFECT OF BODY WEIGHT ON OCCURRENCE OF ESTRUS AND PREGNANCY IN PREPUBERAL HEIFERS IN TRIAL 3 Weight, kg
No. heifers
In heat 0-25 days (%)
180-220 Control Treated e Total
15 11 26
20a 64bc
221-260 Control Treated e Total
28 29 57
14a 75 c
261- 3 0 0 Control Treated e Total
26 22 48
38 a 100 d
301-340 Control Treated e Total
10 13 23
50b 100 d
341 Control Treated e Total
2 2 4
Pregnant 0-48 days (%) 20a 64 b
38
0a 54b 38
21 a 75b 44
30
73*
78"
27 a
35
87*
52 70 b
85b 43
50 50 100
42
82 b
30a 54b
100 100
31 18 a 65b
15 a 56b
70 b 100 c
100
23
47
67*
0-48 days (%) 13a 54 b
3a 57b
50 b 100 c
100 100
0-25 days (%)
78* 50 100
50
75
a,b,c,d,Values with different superscript in the s a m e c o l u m n are significantly different (P < .05). elrnplant c o n t a i n i n g 6 m g o f n o r g e s t o m e t for 9 d a y s and an injection of 5 mg o f E V a n d 3 m g o f n o r g e s t o m e t o n d a y o f implantation. *Different t h a n totals w i t h o u t superscript in the s a m e c o l u m n (P < .05).
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Control
F i r s t service No. b r e d P r e g n a n t (%)
smaller proportion of the heifers with follicles less than 10 ml had shown estrus and they had a lower pregnancy rate than heifers with follicles over 10 millimeters. It was also noticed that a higher proportion of heifers with follicles less than 10ram were not detected in heat a second time even though they were not pregnant at the induced estrus. These observations were not subjected to statistical analysis due to the small number of heifers with follicles smaller than 10 millimeters. Trial 3. In Trial 3, the occurrence of estrus was significantly affected by treatment, body weight, age and degree of follicular development, while pregnancy rate was only affected by treatment. Seventy-nine percent of the treated heifers showed estrus within 4 days after implant removal, and 84% had cycled by 25 days, while only 28% and 38% of the control heifers had shown heat after 25 and 48 days of breeding, respectively (table 3). The proportion of control heifers showing heat by 25 and 48 days was affected by the degree of
1115
PUBERTY OF BEEF HEIFERS
agreement with reports pointing out that body weight is a factor affecting the onset of puberty in beef heifers (Wiltbank et al., 1966, 1969; Arije and Wiltbank, 1971; Bellows, 1968). The effect of age was studied in the Brangus Heifers, since 52 of them were yearlings and 39 were 2-year-olds. A higher proportion of the 2-year-olds were detected in estrus by 25 and 48 days than in the yearlings (table 6). This effect may be confounded with weight, since 2-year-old heifers were heavier. Nevertheless, it is interesting to note in table 6 that the percent in heat and the percent pregnant after 25 days of breeding in the treated yearlings was higher than in the 2-year-olds in the control group (P < .01). Trial 4. Trial 4 was conducted in 9- to 10-month-old prepuberal Angus heifers to ascertain if I treatment was effective in younger animals. Table 7 show that 89% of the treated heifers showed estrus within 4 days from implant removal as compared to 25% of the control heifers showing heat by 18 days after implant removal (P < .01). Estrus in the treated heifers was synchronized with all being detected in heat in a 48-hr period. Unfortunately, observations for estrus were carried out for only 18 days, so it could not be ascertained if all these heifers kept on cycling. A rectal examination of the ovaries 16 days after implant removal revealed that 14 of the 18 treated heifers had corpora lutea, which would indicate that these heifers had started cycling. The degree of follicular development may
T A B L E 6. E F F E C T OF AGE ON O C C U R R E N C E OF ESTRUS AND PREGNANCY IN BRANGUS HEIFERS IN SONORA. T R I A L 3 In heat
Age Yearlings Control Treated a
Total Two-Year-Olds Control Treateda Total
No. heifers
0-25 days
(%)
Pregnant
0-48 days
(%)
0-25 days
0-48 days
(%)
(%)
28 24 52
28 b 71c 48
36 b 71c
3b 42 c
25b 54 c
52
21
38
20 19 39
40 b 100c 69
65 b 100 c 82
15b 63c 38
40 b 95c 67
a l m p l a n t containing 6 m g of n o r g e s t o m e t for 9 d a y s a n d an i n j e c t i o n of 5 m g of EV and 3 m g of n o r g e s t o m e t o n day of implantation. b,CValues with dittarent supel~cript in t h e s a m e age g r o u p and s a m e r are s i g n i f i c a n t l y d i f f e r e n t (P < ,05).
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follicular development at the start of the trial (P < .05); a similar trend was noticed in the treated group however, the difference was not statistically significant (P > .05). The interaction between ovarian status and treatment was significant (P < .01) for the number of heifers showing heat, indicating that the treatment induced heat even in animals with little follicular development. In this respect, Arije (1969) reported that daily injections of 20 mg of progesterone plus 40pg of estradiol17/3 for 16 days induced follicular development, estrus, ovulation, and cyclic activity in four of seven prepuberal beef heifers. As in the previous trials, the induced heat was at least as fertile as that of the controls. The data presented in table 4 shows that there were no differences in pregnancy rate at first service between treated and control groups nor between first and second service in the treated group. Because of the high proportion of heifers anestrus in the control group, only 27% of them were pregnant after 48 days of breeding, while 43%, 58% and 73% of the treated heifers were pregnant after 4, 25 and 48 days of breeding, respectively. Body weight affected the occurrence of estrus in control and treated heifers. A smaller proportion of heifers below 260 kg were detected in heat as compared to heifers above 260 kg (table 5). The same effect was observed in Trial 2 where the six heifers that failed to show estrus averaged 3 5 kg less than those showing heat. These observations are in
1116
GONZALEZ-PADILLA, WILTBANK AND NISWENDER T A B L E 7. O C C U R R E N C E O F E S T R U S IN P R E P U B E R A L A N G U S H E I F E R S
9 TO 10 MONTHS OF AGE, TRIAL 4
No. heifers No. heifers in heat after implant removalC 0- 4 days 0-18 days No. heifers with CL 16 days after implant removald
Treated a Follicular Size b < 10ram > 10ram Total 9 18 9
0 1(12)
0 3(37)
0 4(25)
7(78)** 7(78)**
9(100)** 9(100)**
16(89)** 16(89)**
Ie
1
2
6
8
14
a l m p l a o t cont'|hi--z_ 6 m g of n o r g e s t o m e t for 9 d a y s a n d a n i n j e c t i o n of 5 m g of E V a n d 3 m g of n o r g e s t o m e t o n d a y of i m p l a n t a t i o n . bD'.mgnosed b y r e c t a l e x a m i n a t i o n of t h e ovaries a t t h e s t a r t of t h e t r e a t m e n t . N o C L d e t e c t e d i n a n y heifer. CVmuea i n p a r e n t h e s e s are t h e p e r c e n t of the t o t a l n u m b e r of heifers in e a c h g r o u p . d T w o h e i f e m i n t h e c o n t r o l g r o u p c a m e i n h e a t o n d a y 16 a n d w e r e n o t p a l p a t e d . COne h e i f e r in t h e c o n t r o l g r o u p h a d C1 b u t was n o t d e t e c t e d i n h e a t . * * S i g n i f i c a n t l y d i f f e r e n t f r o m t h e c o n t r o l s (P < .01).
have affected the occurrence of estrus as trous at the start of the treatment or the observed in the previous trials; however, the number of implants used (P > .05). Eightynumber of animals was too small to utilize seven percent of the cows in the anestrous statistics and arrive at meaningful conclusions. group and 96% of the cows in the cycling group Trial 5. In Trial 5, the treatments utilized were detected in estrus by 5 days after were effective in synchronizing or inducing a treatment. The first cow showed estrus 36 hr fertile estrus i,n cows suckling calves (table 8). after implant removal, and all cows showing No significant differences were found in heat were detected within the following 72 percent of cows in heat or 'pregnancy rate hours. By the end of the 28-day breeding between cows classified as cycling and anes- period, 100% and 91% of the cows in the T A B L E 8. O C C U R R E N C E O F E S T R U S A N D P R E G N A N C Y R A T E S IN COWS S U C K L I N G C A L V E S , T R I A L 5.
Status at start of treatmenta, b Cycling Anestrous Item No. cows Cows in heat after implant removal, % 0- 5 days 0-28 days No. anestrous after first observed heat Pregnant, % 0- 5 days 0-28 days
1 implant 13
92 100 0 54 85
2 implants Total 13 26
100 100 1(8) 61 85
96 100 1(4) 58 85
1 implant 16
87 87 2(14) 56 75
2 implants Total 16 32
87 94 0 67 94
87 91 2(7) 62 84
a O b s e r v e d for e s t r u s twice d a l l y for 3 0 d a y s p r i o r t o t r e a t m e n t . b O n e or t w o i m p l a n t s of 6 nag of n o r g e s t o m e t for 9 d a y s a n d a n i n j e c t i o n of 6 m g of E V a n d 3 mg of n o r g e s t o m e t o n d a y of i m p l a n t a t i o n CValues in p a r e n t h e s i s ace p e r c e n t of t h e c o w s t h a t s h o w e d esters.
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Item
Control Follicular Sizeb < 10ram > 10ram Total 8 8 16
PUBERTY OF BEEF HEIFERS
Discussion. It is known that heifers calving early as two year olds continue calving early in subsequent years and wean more pounds of calf in their lifetime (Burris and Priode, 1958; Lesmeister et al., 1973). First calf heifers also take longer to return to estrus after calving than old cows (Wiltbank, 1972), which suggests the need for starting the yearling heifers' breeding season before that of the rest of the cow herd. However, a large proportion of heifers have not shown heat before the start of the regular breeding season (Wiltbank e t al., 1969; Arije and Wiltbank, 1971; Bellows, 1968) and therefore will be late calvers. Our results show that treatment I can be used effectively as a management tool to get a larger proportion of heifers pregnant early in the breeding season. This would particularly be important in heifers that do not receive enough supplemental feeding or are Zebu type heifers which have been reported to attain puberty at an older age than British heifers (Reynolds, 1967, 1972). In this respect, we made the observations in Trial 3 that none of the 14 control Zebu crossbred heifers showed heat during the 48-day breeding period, while 87% of 15 treated heifers in the same breed group were detected in heat and 73% of them became pregnant in 48 days. These results were not tabulated because the average weight of the Zebu crossbred heifers was lower than the other breeds and breed effect was confounded with weight. The fact that body weight significantly affected the response to the treatment indicates that optimum results can be obtained by a combination of I treatment and better feeding. However, our results are still far from allowing
specific recommendations as to how much feed would be required to optimize the results and the minimum age at which the treatment would be effective. Answers to these questions will probably be different for different breeds of cattle. With the type of cattle utilized in Trial 3, we found that response to the treatment was reduced in animals weighing less than 260 kilograms. However, in the Angus heifers of Trial 4, the treatment was effective in inducing estrus in heifers 9 to 10 months old weighing 250 kilograms. Based on the evidence presented, it appears that the treatment is effective in hastening the Final events leading to puberty. It has been suggested that in rats, the neural structures involved in the phasic release of LH are not responsive to progesterone and estradiol injections until about 10 days prior to the onset of puberty (Caligaris et at, 1972), and it is possible that our treatment may prove ineffective in heifers far from their expected data of puberty.
Literature Cited Amir, S., J. Kali, R. Volcani and R. Petlam. 1967. Early breeding in dairy heifers. Anim. Prod. 9:268. Arije, G. F. 1969. Puberty in beef heifers. M. S. Thesis, Colorado State University, Fort Collins. Arije, G. F. and J. N. Wiltbank. 1971. Age and weight at puberty in Hereford heifers. J. Anim. Sci. 33:401. Bellows, R. A. 1968. Reproduction and growth in beef heifers. A. I. Digest. January, 1968. Burris, M. J. and B. M, Priode. 1958. Effect of calving date on subsequent calving performance. J. Anita. Sci. 17:527. Caligaris, L., J. J. Astrada and S. Taleisnik. 1972. Influence of age on the release of luteinizing hormone induced by oestrogen and progesterone in immature rats. J. Endocrinol. 55:97. Crichton, J. A., J. N. Aitken and A. W. Boyne. 1959. The effect of plane of nutrition during rearing on growth, production, reproduction and health of dairy cattle. Anita. Prod. 1:145. Deutscher, G. H. 1973. Effect of nutritional levels of replacement heifer calves on their reproductive performanqe and productivity. Antelope range field sta. Buffalo, South Dakota. A-S series 73-10. Donaldson, L. E. 1968. The pattern of pregnancies and life-time productivity of cows in a Northern Queensland beef cattle herd. Australian Vet. J. 44:493. Gonzalez-PadiUa, E., J. N. Wtltbank and G. D. Niswender. 1975a. Puberty in beef heifers. I. The
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cycling groups and anestrous group, respectively, had been inseminated at least once. The pregnancy rate after 5 days of breeding was 58% and 62% for the cycling and anestrous groups, respectively. At the end of the 28-day breeding period, 85% and 84% of the cows in the cycling and anestrous groups, respectively, were pregnant. There is a possibility that the anestrous cows would have shown heat naturally before the end of the 28-day period, in which case the only thing the treatment accomplished was to hasten this event and allow two services per cow in a 28-day period.
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interrelationship between pituitary hypothalamic Cunha, A. Warnick and M. Koger (Ed.) Factors and ovarian hormones. J. Anita. Sei. 40:1091. affecting calf crop. University of Florida Press. Gonzalez-Padilla, E., G. D. Niswender and J. N. Short, R. E. and R. A. Bellows. 1971. Relationships Wfltbank. 1975b. Puberty in beef heifers. II. Effect among weight gains age at puberty and reproducof injections of progesterone and estradiol-17# on tive performance in heifers. J. Anim. Sci. 37:551. serum LH, FSH, and ovarian activity. J. Anim. Sci. Wiltbank, J. N., J. Bond, E. J. Warwick, R. E. Davis, 40:1105. A. C. Cook, W. L. Reynolds and M. W. Hazen. Lesmeister, J. L., P. J. Burfening and R. L. Blackwell. I965. Influence of total feed and protein intake on 1973. Date of first calving in beef cows and reproductive performance in the beef female subsequent calf production. J. Anim. Sci. 36:1. through second calving. U.S.D.A. Tech. Bull. 1314. Morrow, D. L. 1969. Factors affecting beef cow Wiltbank, J. N., K. E. Gregory, L. A. Swiger, J. E. production. M. S. Thesis, Colorado State UniversiIngalls, J. A. Rothlisberger and R. M. Koch. 1966. ty, Fort Collins. Effects of heterosis on age and weight at puberty Pope, L. S. 1967. Age at first calving and performance. in beef heifers. J. Anim. Sci. 25:744. In T. Cunha, A. Warnick and M. Koger (Ed.). Wiltbank, .l.N., C. W. Kasson and J. E. lngalls. 1969. Factors affecting calf crop. University of Florida Puberty in crossbred and straightbred beef heifers Press. on two levels of feed. J. Anim. Sci. 29:602. Reynolds, W. L. 1972. Factors affecting reproductive Wiltbank, J. N. 1972. Management program for performance in heifers. Proceedings - 21st and improving reproductive performance. Proceedings 22rid beef cattle short course. Texas A & M 21st and 22nd beef cattle short course. Texas A&M University, College Station, Texas. University, College Station. Reynolds, W. L. 1967. Breeds and reproduction. In T.
