Effects of melatonin on seasonal changes in reproduction of rams.

EFFECTS OF MELATONIN ON SEASONAL CHANGES IN REPRODUCTION OF RAMS' J. A. Fitzgerald2 and J. N. Stellflug Dubois, ID 83423 ABSTRACT

Three studies were conducted to determine the effects of exogenous melatonin (M) on changes in scrotal circumference (SC), fertility and reproductive hormone concentrations of rams. Rams were initially housed in barns with controlled photoperiod and given 16 wk of long (16L8D) or short (8L16D) days. In Studies I and 11, implants of M were given for 40 to 80 d beginning at maximal SC. Results showed that implanted rams had greater (P < .05) blood M concentrations than nonimplanted controls. However, M did not prevent testicular regression. In Study III, M was given to rams after testicular regression had occurred. Rams were implanted with M weekly for 6 or 4 wk, followed by a withdrawal period of 4 wk (6:4, 4:4 respectively). Results showed that M (6:4) stimulated (P < .05) testicular growth compared with nonimplanted controls. Treatment of rams with M for 8 mo did not affect LHRH-induced LH release (P > .05), but it reduced basal and LHRHinduced testosterone release (P c .05). Reproductive performance of rams in Studies I and 111was compared with that of nonimplanted rams. Fertility of M-treated rams in the spring from Studies I and III(86% to 91%) was similar to that in autumn (93%).Fertility of rams from Studies I and III exceeded (P < .05) that of nonimplanted rams in April (59% to 62%). Net lamb production from ewes mated in the spring was greater if rams were treated with M and(or) photoperiod. Key Words: Melatonin, Photoperiod, Testosterone, LH, Rams J. Anim. Sci. 1991. 693264-275

reproductive performance of rams (Haynes and Schanbacher, 1983). The effect on the male Seasonal anestrus in ewes lowers reproduc- can be observed by changes in fertility, lamb tive efficiency of flocks, and affects the crop and length of the lambing season (Fitzgerald, 1989). Controlling photoperiod improves fertility of rams (Schanbacher, 1979) 'The authors thank William Gardner Sr.. Mark but is limited as a management practice. Williams and Verne LaVoie for their technical assistance. Regulating reproduction with the hormone We also thank Gary Richardson for help with the melatonin (M) may be possible (Kennaway, statistical analysis. Hormones for RIA were kindly 1988; Reitec 1988). Questions, however, reprovided by Leo Reichert and the National Honnone and main regarding the appropriate treatment sePituitary Program. Regulin@ Limited (Level 12, 222 Kingsway South Melbourne Victoria 3205, Australia) and quence to administer it. Lincoln and Ebling Linton Staples generously supplied the melatonin and (1985) demonstrated that M stimulated testicuprovided assistance to conduct h e studies. Appreciation lar growth of rams but did not eliminate is also given to Jean Pelletier, Bruce Schanbacher, W. R. seasonal changes in testicular growth. Because Butler and Gary Moss for their comments. A preliminary report of these data was presented at the 1 lth Int. Cong. on M was delivered at a constant rate for 12 to 20 Anim. Reprod. and AI, Dublin, Ireland June 26-30, 1988. wk, the response to it may have become Mention of trade names of companies does not constitute refractory (Lincoln, 1980). Frequent changes an implied warranty by USDA or the authors. from a stimulatory to inhibitory photoperiod 2Rep.int requests to this author. may be more effective in preventing pho3ARS, U.S. Sheep Exp. Sta. torefraction (Pelletier and Almeida, 1986; Received August 14, 1989. Accepted June 28, 1990. Schanbacher, 1988). lntroductlon

264

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U.S. Department of Agriculture3,

PHOTOPERIOD AND RAM REPRODUCTION

265


This experiment evaluated the effects of M was fist given to rams in February, 6 wk on seasonal changes in reproductive perform- before breeding. A second implant was adminance of rams. Changes in scrotal circumference istered at the time ewes were joined with rams. (SC) and breeding performance were moni- Polypay ewes (n = 231) were allocated to 12 tored. We assessed the effect of chronic M pens and bred to individual rams from the four administration on the neuroendocrine axis by M and light control treatments. measuring LH and testosterone secretion after Study ZZ. Our objective was to determine an intravenous injection of LHRH. whether M would affect testicular regression of Polypay rams kept in barns under light control for over 1 yr. Changes in SC of four mature (2 Materials and Methods to 3 yr) Polypay rams were synchronized with Animal Management. Rams were initially artificial photoperiod (Figure 1, middle panel). kept in barns in which the daily photoperiod Measurements of SC were taken for two was controlled. Fluorescent lighting provided complete (nadir to nadir) cycles. At the 150 to 200 Ix of light at eye level of the rams. occurrence of the third expected peak in SC Lights came on at 0730 each day and went off under short days, rams were given at either 1530 for short (8L:16D) or 2330 for 40-d M implants. Characteristics of the cycle long (16L:8D) days. Rams exposed to long- of SC (nadir, peak and period) under the and short-day treatments (Fitzgerald et al. influence of M were compared with character1986) have predictable, cyclical changes in istics of the previous two control cycles for SC. This howledge was used to determine each ram. Period of a cycle was d e k e d as when to administer M in Studies I to III. Rams time, in days, between Occurrence of sequential were fed alfalfa hay (2.5 kg/head) outside peaks in sc. between 0830 and 1500 each day and then Study ZZZ. The objectives were to determine were retumed to the barn. Rams were trained whether M would stimulate testicular growth to serve an artificial vagina; ejaculates were and affect fertility of rams. Mature Polypay collected weekly by exposing rams to estrous rams (n = 15) were given 16 wk of artificial ewes held in stanchions. Scrotal circumference long days, at which time testicular regression measurements were made every 14 d by the occurred (Figure 1, lower panel). Five of these same technician using a scrotal measuring rams were shifted to short days at nadir SC tape. Three experiments evaluated the effect of and designated as controls. The remaining 10 M when administered at either peak SC (Study rams were implanted with M and remained on I and 11) or nadir SC (Study m). Figure 1 long days. In this study, we used M implants (18 mg) developed to release the hormone for depicts the design of these experiments. Study I. The objectives were to determine 10 rather than 40 d. These implants release M whether M would affect testicular regression at physiological nighttime concentrations of and fertility. Twelve mature (2 to 3 yr) 600 pg/ml in sheep (McPhee et al., 1986). Five Booroola crossbred rams were kept in a barn rams were given single implants at 7-d and exposed to an artificial photoperiod of intervals for 42 d, for a total of seven implants long followed by short days (Figure 1, upper each. The remaining five rams were given panel). Melatonin was administered during single implants at 7-d intervals for short days beginning at the expected time of 28-d for a total of five implants each. Twentypeak SC. Rams (n = 6) were implanted S.C. in eight days elapsed before implants were again the front shoulder with a single implant of M4 given to each treatment group (6 wk and 4 (18 mg). The M implant was developed as a wk). Rationale for testing the intermittent prototype that maintained jugular venous M treatment sequence was based on data reported concentration above 600 p g / d for 40 d (Reeve by Pelletier and Almeida (1986) indicating that et al., 1986). Control rams (n = 6) were not an 8-wk rotation of long and short days could implanted. Three implanted and three control attenuate seasonal changes in SC. By adminisrams were moved from short to long days at tering implants of M with a 1O-d release rate to the time of the initial implant of M. Melatonin rams in this study over a 6- or 4-wk period, the number of days (52 and 38) that rams were exposed to M approximated 8- and 5-wk periods of short days. The first implant was %egulu~ Limited, South Melbourne, Aust. given in December, 4 mo before an April

266

FlTZGERALD AND STELLnUG

Scrolal Implants

I

Hours of

Light

----I 3 Melatonin

N.12

16

3 Controls

8

3 Controls Ambient Photoperiod I

I

I

I

I

1

I

H o u r s 16 Of

Light 8

16

Hours of Light

N=5 LHRH Challenge

Breeding

0 Ambient 0

16

32

0 Photoperiod

48

64

80

96

Weeks Figure 1. Experimental design for Shdy I (upper panel), Study II (middle panel) and Study III (lower panel). Arrows indicate timing of melatonin treatment relative to scrotal circumference and photoperiod. Melatonin treatment as open bar in Study III.


of M for both 6- and 4-wk treatment groups was continued for 8 mo (May to December) after rams were removed from breeding. Breeding Pelformanee. Net lamb production of ewes mated to rams was determined for Studies I and III. In both Study I and ID, all ewes had been treated with M as described by

breeding trial. Before breeding, rams were ranked by semen quality and libido. Latency to serve an artificial vagina and average progressive sperm motility were the criteria considered. The top three rams from each M or control treatment then were randomly allocated to breeding pens for 32 d. Intermittent delivery


'Cambridge Medical, Billerica, h a .

known sample containing M was less than 10%. Plasma LH concentration was determined by RIA. The primary antibody (NIHanti-oLH-1) and ovine LH standard (NIHoLH-I3) were provided by the National Institutes of Health. The ovine LH used for radiolabeling (LFlR-1056-C2) was provided by Leo Reichert. Tracer was prepared by iodination of 2.5 pg oLH in a minimal volume of .5 M phosphate buffer (pH = 7.5) by the chloramine-t method (Greenwood et al., 1963). Separation of protein and salt fractions was done using Sephadex G-100 column chromatography and an elution buffer of .01 M phosphate-buffered saline (pH = 7.1) at 5°C. The low (90% of Bo) and high (5% of Bo) limits of detection of the assay were .25 and 7.0 ng, and the 50% intercept was 1.20 ng. Interassay CV averaged 12 f 3%. Plasma samples run at different volumes (100, 150, 250) showed parallel displacement of iodinated hormone in comparison to the standard curve, with mean CV of less than 3% for different plasma volumes assayed. Plasma testosterone was determined by RIA5. Steroids that showed major cross-reactivity with this antibody were 19-nortestosterone (15.5 %) , 5 -alpha-dihydrotestosterone (4.7%) and 17-methyl-testosterone (1.7%). Plasma from wethers was used to dilute testosterone standards. Low and high limits of assay detection were .1 and 20 ng; the 50% intercept was 1.0 ng. Plasma samples run at different volumes (50 or 100 pl) were parallel to the curve. Testosterone measured in unextracted, ovariectomized ewe plasma was below detection limits. Testosterone was determined in two assays (interassay CV c 10%) of plasma collected 48 and 60 min before and 48 and 60 min after the LHRH challenge during October, November and December (Study m). Statistical Analyses. The effect of M on changes in SC were analyzed by determining the best fit polynomial regression (Snedecor and Cochran, 1967). predicted values then were used to determine differences in peak or nadir circumference, days from peak to nadir and relative changes in SC. Differences in LH and testosterone concentration were analyzed by least squares methods for repeated measures (Gill,1978) with treatment, time and treatment x time considered in the model using the General Linear Models procedure of SAS (SAS, 1988). Animal within treatment was used as the error term to determine treatment differences. Treatment means were compared


Stellflug et al. (1988) to reduce seasonal effects of the ewe. To provide another comparison with lambing results collected from Studies I and III, net lamb production of Polypay ewes mated to rams in autumn or spring (rams not treated with M or artificial photoperiod) were summarized from production efficiency flock records at the U.S. Sheep Experiment Station from 1983 through 1987. Data summarized from autumn or spring mating using rams with no additional photoperiod or M treatment provided a baseline from which we measured the effect of spring mating of ewes either from Study I or III. All rams used for breeding under natural conditions during 1983 through 1987 were semen-tested (Hulet et al., 1965). Ejaculates were collected from rams and evaluated for motility and percentage of abnormal spermatozoa. After semen evaluation, the top third of the rams from each breeding group were randomly allocated to breeding pens of approximately 30 to 35 ewes for 28 d in autumn and 32 d in spring. Blood Collection. Blood samples were collected every 2 wk by jugular venipuncture of Booroola rams in Study I and Polypay rams in Study III to monitor differences in serum M concentration. These samples were collected between 0900 and 1200. To determine effects of chronic M administration on hormone secretion of rams from Study III, basal and LHRH-induced plasma concentrations of LH and testosterone were determined three times at 30-d intervals beginning 10 mo after the initial M implants had been given. Nonimplanted, 6:4 and 4:4 implanted rams were fitted with jugular cannulas 24 h before samples were collected. Blood samples were collected in October (Period l), November (Period 2) and December (Period 3) at 12-min intervals for 3 h. An injection of LHRH (NIH,500 ng, i.v.) then was given and 15 samples were collected. Plasma was immediately separated and frozen at 4 2 ° C . Hormone Assays. Serum M concentrations were determined by RIA (Rollag and Niswender, 1976). Samples from Study I and Study III were assayed in different years. Within each year, samples were analyzed in a single assay and the intra-assay CV of a

267

268

J?ITZ.GJBALD AND STPLLFLUG

TABLE 1. JiFFJXT OF MELATONIN IMPLANTS FOR 10 W K ON SCROTAL CIRCUMFERENCE (SC) AND INTERVAL FOR PEAK TO NADIR OF BOOROOLA RAMS IN STUDY 1' No. of rams

Melatonin

Short

Control

JJJnf3 Short

3 3 3 3

Long

sc

Pooled SE

mmb

Interval, db

283 276 269 28 1 7

159 162 155 149 11

'Data are means and pooled standard errors. %leans in a column do not differ (P > .05).

by using the least significant difference test. Differences in reproductive performance (fertility, lambs born and net production) between ewes lambing from Studies I and III and ewes lambing after mating to rams kept only in ambient photoperiod (no M treatment) in autumn or spring were compared using ANOVA. Results

Melatonin and Scrotal Circumference. Average daytime M concentration was approxi-

mately 60% greater (P < .05) in Booroola rams implanted with the hormone than in nonimplanted rams (Figure 2). Melatonin concentration of implanted rams exceeded (P < .05) that of nonimplanted control rams at wk 2 and 6 to 10 and approached significance at wk 4 (P .12). Data collected from Studies I and II (Tables 1 and 2), however, clearly show that M did not prevent testicular regression in either Booroola or Polypay rams. No differences (P > .05) were observed in days from peak to nadir or nadir SC. Photoperiod treatment beginning at peak SC had no effect

350

Control 0 Melatonin U

300

-

I

n

E

ii

250

Y

z -z

200

0

150

J

w 5

100

50

0

2

4

6 WEEKS

8

10

AVG

Figure 2. Average serum melatonin concentration of implanted and control Booroola rams from Study I beginning 2 wk after the initial melatonin treatment. Treatment means differed (P < .05) at 2 wk and at 6 to 10 wk.


Photo period

Treatment

269

PHOTOPERIOD AND RAM REF'RODUCTlON

TABLE 2. AVERAGE CHANGES IN PEAK AND NADm SCROTAL CIRCUMPERENCE (SC) AND LNTERVAL FROM PEAK TO NADIR SC OP POLYPAY RAMS FROM STUDY I P' No. of

Treatment

rams

1

Control Control Melatonin Pooled SE

4 4 4

2 3

Nadir,

peak, m b

m

365 364 355 9

321 323 321 7

b

Interval, db

134 137 130 7

9 a t a are means and pooled standard errors. keans

in column do not difk (P > .05).

on scrotal changes of M-treated or control Booroola rams. Sperm concentration measured from weekly ejaculates ranged from 1.5 to 4.5 x lo9 cells per milliliter and was not affected by treatment. Changes in M concentrations and SC of rams from Study 111are summarized in Figures 3 and 4. Serum M averaged 514 f 135 and 583 f 87 pg/ml for the 6 4 and 4 4 implant groups and was greater (P < .05) than daytime concentrations of nonimplanted, control rams (193 f 37 pg/d). hplants of M affected (P< .05) SC when the hormone was administered during the nadir phase of the scrotal cycle. Average days from M treatment (150 d in Figure 4) to the initial peak in measured values (not smoothed line) in SC was 99 d for the 6:4 melatonin treatment group (Figure 4, bottom), fewer than the 117 d for the 4:4 (Figure 4, middle) and the 131 d for the nonimplanted controls (Figure 4, top). Sperm concentration (3.4 to 4.6 x 10s cells/ml) and motility estimates (58 to 70%) were similar among all treatments at the time of breeding. Because M (6:4) stimulated testicular growth, both M treatment sequences were continued for 8 mo (Figure 4). The 6:4 treatment regimen was particularly effective in maintaining SC during the summer when testes regressed in control rams. More frequent oscillations in SC were observed in treated than in control rams from 300 to 500 d after onset of treatments. Rams receiving the 4:4 treatment exhibited smaller peaks in SC than rams given the 6:4 sequence. Control rams had a typical breeding Season increase in SC in autumn and winter and at that time SC of controls exceeded SC of both the 6:4 and 4:4 implanted groups. Peak SC for control rams during December was similar to the peak circumference observed the previous year under light control. Peak circumference during December averaged nearly 3 cm less for rams given the 6:4 M treatment and nearly 1

cm less for rams given the 4:4 treatment than at the peak SC the previous year. Reproductive Performance. Table 3 summarizes lambing percentage, lambs born and net reproductive rate (% lambing x lambs born) for M and light-treated rams from Studies I and IQ and compares these results with data collected from previous autumn or spring breeding periods in which only nonimplanted rams were used as sires. In both Study I and Study 111 reproductive performance of ewes bred to either nonimplanted photoperiod control, or M-implanted photoperiod control rams was similar (P > .OS); therefore, these data were pooled. Percentage of ewes lambing after mating to r a m s given M or light treatments during spring was similar (P> .OS) to that for ewes mated in the fall. Treatment of rams with either light control or light control and M improved (P < .05) lambing percentage and overall net reproductive rate of ewes mated in the spring than in spring mating without ram photoperiodic treatment. Percentage of lambs born and net reproductive rate, however, were greater (P < .05) for ewes mated in the fall than for any spring breeding group. Plasma LH and Testosterone. Plasma LH and testosterone concentrations measured in rams from Study III are given in Figures 5 and 6. Plasma LH concentrations increased (P < .OS) within 12 to 24 min after injection of LHRH in all treatment groups. Peak LH was similar (P > .05) among treatments (2.6 to 2.7 ng/ml) but differed (P < .001) among periods. Increases in LH after LHRH were smaller during Period 3 (December, 2.1 ng/ml) than during Period 1 (October, 3.2) or Period 2 (November, 2.8). No treatment x period interaction was found. Basal testosterone differed among treatments and periods (Figure 6, P < .001). Basal testosterone increased twofold from October to November in control, nonimplanted rams and by December exceeded


Period

270

FI?zGERALD

AND STELLFLUG

700

6.4 600

=

4:4

400

300

200

100

0

I

I

IMPL I N

I

I

IMPL OU1

Figure 3. Average sexurn melatonin concentration of implanted and control Polypay rams from Study JJI. Determinations made for both the 6 4 and 4:4 treatment groups were averaged over samples taken every 2 wk during the initial three implants (in M) and withdrawal (out) periods. A nonimplanted control group (n = 5) is included for comparison. Melatonin concentration was higher (P < .OS) for implanted rams.

both M implant groups. Plasma testosterone concentration increased (P c .05) 48 to 60 min after LHRH and the treatment x period interaction (P < .001) affected the concentration after LHRH. Testosterone concentration after LHRH during Period 3 was lower in both M treatments than in controls. Testosterone concentration after LHRH was lower for 4 4 than for controls during Period 1 and was lower for 6:4 than for controls during Period 2.

that differences in M concentration accounted for the failure of M to affect SC in Studies I and II compared with Study III. Even though the concepts of duration, threshold and timing effects of M on reproductive function remain equivocal, several studies suggest that differences in M concentration alone do not mediate photoperiodic response in sheep (Bittman et al., 1983; Lincoln and Ebling, 1985; Stellflug et al., 1988). This study extends observations by Lincoln and Ebling (1985) and demonstrates that the Dlscusslon period of deliveIy and the phase of the scrotal Melatonin was more effective in switching cycle are important for long-term regulation. on reproductive activity after testicular regres- By using the 6:4 treatment schedule, we have sion than in preventing regression after peak shown for the first time that complete regresactivity occurred, as noted previously (Linwln sion of the testes can be attenuated in ambient and Ebling, 1985). The M concentrations in photoperiod. These data are similar to those blood were within the range of concentrations reported by Pelletier and Almeida (1986) and reported for this hormone and species during Schanbacher (1988) using photoperiodic cycles the dark phase of the photoperiodic cycle alone to regulate reproductive activity of Ile(Kennaway et al., 1977, 1982). Implants in de-France and Suffolk rams in confinement. Study III delivered consistently higher M Collectively these studies suggest that the soconcentrations than observed from rams moni- called short-day photorefiactoriness reported in tored in Studies I and II. It might be argued rams that are maintained on extended intervals


Control 0

500

271

PHOTOPERIOD AND RAM REPRODUCTION COWl'ROL

AMBIENT

16L:ED

,

I

San

June

___ 200

0

Dec 400

600

DAY 8

390 - 8 L : 380

16D 16L:8D ~ I E N T

111111111

-

340

330

320 310

-

-

-

300 -

m280 270

4 0

Ja

Dec

June I

I

200

400

600

DAYS WELATONIN 6:4 4w 390

3SO 370

E E

0 v)

360

350 340

330 320 310

300

0

LOO

200

600

DAYS

Figure 4. Average scrotal circumference (SC) of Polypay rams in Study JII.Means and standard error of means are depicted for actual measurements along with best fit polynomial predicted circumference. The correlation of actual to predicted circumference was .80 to -92(P < .001). 'Ihe broken, shaded bar in panels 2 and 3 depicts M treatment sequence. Time of breeding indicated by open bar.


280 270

272

Fll7GERALD AND STI3LLFLUG

TABLE 3. EFFECT OF PHOTOPERIODIC AND MELATONIN MANAGEMENT OF R A M S ON BREEDING PERFORMANCE OUT OF SEASON COMPARED WITH NORMAL FALL BREEDING No.of ewes

Breedin8

Ram

Sire

pens

treatment

breed

Percentage lambing

N0.d ltUllbS

Net rateb

Fall spring spring spring

777 685 95 1 231

24 21 27 12

Polypay Polypay Polypay Booroola

93' 62d 59d 91'

205' 173d 139

109 8od

18od

164e

SPm

339

9

None None None Photoperiod or melatonin (Study i ) Photoperiod 01 melatonin (Study III)

Polypay

86c

173d

14ge

191C

'Number of sires evaluated. Ram to ewe ratio calculated by dividing number ewes by number of breeding pens. b b production x percentage lambw. C94eMeausin a column that do not have a common superscript differ (P < .05).

of stimulatory photoperiod (Almeida and Lincoln, 1984) can be prevented by the appropriate photoperiodic sequence using either light control or M. We did not test whether the onoff sequence of M delivered to the rams at peak circumference would have been more effective than the constant delivery of the hormone in overcoming short-day refraction. However, SC decreased in rams only treated with long or short days at peak circumference. This suggests that the response to either a stimulatory or inhibitory photoperiodic signal at peak SC is less effective than that observed if the signal is given after testicular regression. Testosterone secretion and scrotal size are highly correlated (Schanbacher and Ford, 1976). The effect of intermittent M treatment for 6-wk periods may have prevented the testes from achieving maximal size, which would have culminated in a more drastic reduction in SC, characteristic of the normal seasonal changes observed for the ram. Perhaps M treatment for 6 wk followed by withdrawal of the hormone established a different set point for the feedback regulation of the testes. Testosterone concentration was lower in rams given intermittent M for 8 mo and may be indirect evidence for a different set point. These data are similar to observations by Almeida and Pelletier (1988) in which seasonal changes in scrotal size of rams exposed to frequent contrasts of long and short days were attenuated and were correlated with lower testosterone and LH concentrations. The observation that peak LH after the injection of LHRH declined from October through December coincident with growth of the testes to

peak circumference suggests that feedback inhibition by the testes occurred. The reduction in peak LH after LHRH and the pattern of the response curve is similar to that described by Lincoln and Short (1980) at a similar phase of the testes cycle in the Soay ram. Because LH secretion after LHRH did not differ between treatments, the site at which differences in feedback sensitivity might occur is likely to be at the hypothalamus. Photoperiodic management of rams can improve semen quality (Pelletier et al., 1987) and increase fertility of the flock bred out of season. Photoperiod or the combination of photoperiod and M treatments given to rams in this experiment also were effective in improving reproductive performance of ewes bred in the spring. Although lambing rate was improved, the percentage of lambs produced per ewe was higher during fall breeding. Thus, ovulation rate and embryo survival of ewes treated with M in the spring might be two limiting factors. Although rams implanted with M were not tested for fertility during the summer, we suggest that rams given the 6:4 sequence of hormone would have had improved performance because of the maintenance of testes size above that of nonimplanted control rams from June through August. Rams in which the scrotal cycle has been "captured" by the combined use of photoperiod and M can be kept outdoors without complete regression of the testes. Thus, extensive management of the ram, not entirely dependent on confinement in photoperiod barns, might become an attractive alternative for producers. Further experiments are needed, however, to determine


Breeding season

273


Period 3

u

3.0

Period 1 Period 2 Period 3

-E

c

0

96

0

96

0 I [3

\

2.0 Y

5 1 .o

- 96

3.0

-E

-f

T 4

6:4 Period 1 Period 2 Period 3

0 I

o

LHRH

A

500 ng

\

ul

c Y I

2.0

A

1

I I o A

1 .o

- 96

-48

0

48

96

MINUTES Figure 5. LHRH-induced LH release measured in rams from Study ill. Data are shown for the three sampllng periods from October (Period 1) through December (Period 3). Upper, middle and lower panels are control, 4- and &wk M treatments. reqectively. No treatment differences were observed (P > .05). Peak LH secretion was lower (P < .05) in December.


- 96

274

FI'IZGJ3UU.D AND STELLFLUG

30

28 -

Control

n

26 -

6:4 4:4

["""I

n

24 -

\

22 -

0 C

w

18

0

16

a W c

v1

0

c in

w

c

rn

8 I

1.

20 -

Y

2

POST LHRH

PRE LHRH

14 12 -

a

'Ia a

4

2 0

1

2

3

PERIOD

1

2

3

PERIOD

Figure 6. Average plasma testosterone concentration of rams from Study III. Data are m m m a n' z d by treatment and period of collection. Concentrationbefore (left) and after (right) LHRH is depicted. Means within a period that differ (P < .05) are shown as a,b.

whether treatment of rams with M under these conditions would allow a lower ram to ewe ratio than that normally achieved in untreated rams. lrnpllcatlons

secretion. Biol. Reprod. 30143. Almeida, G. and J. Pelletiex. 1988. Abolition of seasonal testis changes in the ne-de-France ram by short light cycle: Relationshipto luteinizing hormone and testosterone release. Theriogenology 29:681. Bittman,E. L., F. J. Karsch and I. W. Hopkins. 1983.Role of the pineal gland in ovine photoperiodism: Regulation of seasonal breeding and negative feedback effects upon luteinizing hormone secretion. Endocrinology 113:329. Fitzgerald,J. A. 1989. The role of the male. In:h c . Symp. Sheep Reproduction, July 10-1 1,1989. Colorado State Univ., Fort Collins. SID, Denver, CO. Fitzgerald, J. A., J. N. Stellflug and C. F. Parker. 1986. Comparison of testicular parameters of Polypay. Rambouillet and Columbia rams in a controlled photoperiod. J. Anim. Sci. 63(Suppl. 1):173 (Abstr.). GiU, J. L. 1978. Design and Analysis of Experiments in the Animal and Medical Sciences.Vol. 2. Iowa State Univ.

Seasonal breeding is a significant factor that determines reproductive efficiency of sheep. Most emphasis in controlling the reproductive process has focused on the ewe. Methods to improve male reproductive performance also have an impact on breeding efficiency. Use of confinement barns to regulate seasonal breeding has limitations. This study suggests that melatonin, which affects reproductive hormone Press, Alms. secretion and maintains scrotal size for a Greenwood, R C., W.M.Hunter and J. S. Clover. 1963. The prolonged period under ambient photoperiod, preparation of a 1311-labekdhuman growth hormone of a bigh specific radio activity. Biochem. J. 8 9 114. may be of practical value in management of a Haynes, N. B. and B. D. Schanbacher. 1983. The control of flock. reproductiveactivity in the ram. In: W.Haresign (Ed.) Sheep Production. Butterworths, London. p 431.

Literature Cited Almeida, O.F.X.and G. A. Lincoln. 1984. Reproductive photorefractoriness in rams and accompanying changes in the patterns of melatonin and prolactin

Hulet,C. V., W. C. Foote and R L. Blackwell. 1965. Relationshipof semen quality and fertility in the ram to fecundity in the ewe. J. Reprod. Fertil. 9311. Kennaway, D. J. 1988. Short and long-term effects of manipulation of the pinealhnelatonin axis in ewes.


-E

I


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Seasonal changes in serum testosterone in adult rams.

The effects of melatonin and light treatment on the reproductive performance of yearling Suffolk rams.

Melatonin and male reproduction.

Effects of melatonin agonists and antagonists on reproduction and body weight in the Siberian hamster.

Seasonal changes in sexual activity and serum levels of LH and testosterone in Finnish Landrace and Suffolk rams.

Melatonin: a "Higgs boson" in human reproduction.

Reproductive effects of placing micro-implants of melatonin in the mediobasal hypothalamus and preoptic area in rams.

Seasonal changes in serum melatonin in women with previous breast cancer.

Seasonal variations in the response of the testis and LH levels to hemicastration of adult rams.

Effects of melatonin on aluminium-induced neurobehavioral and neurochemical changes in aging rats.

Melatonin administration enhances the reproductive capacity of young rams under a southern Mediterranean environment.

Regulation of seasonal reproduction by hypothalamic activation of thyroid hormone.

Effects of polychlorinated biphenyls on poultry reproduction.

Effects of melatonin on vertebrate circadian systems.

The influence of phototherapy on serotonin and melatonin in non-seasonal depression.

Effect of immunization against melatonin on seasonal fleece growth in feral goats.

Comparative analysis reveals the underlying mechanism of vertebrate seasonal reproduction.

Short-term chlordecone toxicity in rats including effects on reproduction, pathological organ changes, and their reversibility.

Seasonal effects on gene expression.

RFRP Neurons - The Doorway to Understanding Seasonal Reproduction in Mammals.

Light-induced plasma melatonin suppression in seasonal affective disorder.

Effects of fescue toxicosis on reproduction in livestock.

Melatonin and the circadian system: contributions to successful female reproduction.

Role of the thyroid gland in seasonal reproduction. III. Thyroidectomy blocks seasonal suppression of gonadotropin-releasing hormone secretion in sheep.