Response of Holstein Cows to Corn Gluten Meal Used to Increase Undegradable Protein in Early or Later Lactation 1 J. B. HOLTER,2 and H. H. HAYES Department of Animal and Nutritional SCiences W. E. URBAN, JR., S. RAMSEY, and H. RIDEOUT Office of Biometrics University of New Hampshire Durham 03824 ABSTRACT

parity I cows and raised it in older cows. Data suggest that Lys may have been frrst-limiting, followed by TIe in early lactation and Met in late lactation, and that AA adequacy may be more important than undegradability in ration protein balancing. For most traits measured, treatment by parity interactions were significant, indicating that parity 1 cows did not respond in the same way as older ones to protein supplementation. (Key words: com gluten meal, undegradable protein, dairy cows)

Supplemental com gluten meal was used to raise CP by 1.1 to 1.5 percentage units and undegradable intake protein from 35 to 39% of CP in the com-based diet of parity 1 or greater Holstein cows to study effects of undegradability, parity, stage of lactation, and interactions on DMI, milk yield and composition, BW, and related traits during complete lactations. Cows were assigned at calving to treatments (n = 3D, 8 primiparous): control, supplement wk 1 to 8 postpartum (early), or supplement wk 9 to 44 postpartum (late). Total lactation means were not affected significantly by treatments. Supplementation with undegradable protein enhanced forage and, thus, total DMI in later lactation by pluriparous cows; it apparently spared BW loss wk 1 to 8 postpartum and enhanced BW recovery thereafter in first lactation cows with no effect in older cows. Effects of supplementation on milk yield were small, and they were negative in early lactation and generally positive in late lactation; effects were positive on fat test in early lactation for both parity categories but distinctly negative for parity 1 cows in late lactation. Supplementation of undegradable protein in late lactation also decreased milk protein content in

Abbreviation key: CGM = com gluten meal; VIP = undegradable intake protein. INTRODUCTION

Received September 30, 1991. Accepted January 22, 1992. IScientific Contribution Number 1742 from the New Ifanylshire Agricultural Experiment Station. 2(;orresponding author: J. B. Holter, Ritzman Laboratory, University of New Hampshire, Durham, NH 03824; phone 603-862-1338, Fax 603-862-3758. 1992 J Dairy Sci 75:1495-1506

Much research progress is being made in formulating nutritionally balanced diets for cows of unusually high milk yield Examples include the feeding of supplemental fat, oilseeds, or soaps to increase ration energy ~n­ sity in early lactation, increasing the proportion of undegradable or total protein in diets, and feeding animal and altered seed proteins to maximize rumen bypass of potentially limiting, essential AA. On-farm adoption of ~ese practices and concepts, however, sometunes leads to less than profitable responses; obvious reasons include substandard management, low herd yield potential, variable type and low quality of forages, and other limitations. In regard to balancing dairy rations on the basis of undegradable intake protein (VIP), Hoffman et al. (3) concluded that

1495

laboratory methods to measure UIP content of feedstuffs expediently and accurately need to be developed before diets can be formulated for UIP with confidence and before UIP interactions with other nutrients can be elucidated (p. 3474).

1496

HOLTER ET AL.

In an alfalfa silage-based diet containing 18% CP with or without supplemental treated tallow, raising UIP from 33 to 36% of CP did not affect milk yield (-.2 to -.4 kg/d) or composition in primiparous or older Holstein cows (3). Soybean meal (solvent, 39.6% or expeller, 54.5% DIP in CP) was used to adjust ration VIP. The NRC (11) recommends that such rations contain 36% VIP with 17% CPo It is not unusual to misfeed (e.g., overfeed) CP by 1 percentage unit or more. Thus, in Hoffman et al. (3), the 18% CP diet containing lower DIP (33% of CP) may have met the UIP as well as the degradable protein requirements of cows, thereby accounting for no treatment response. This highlights the difficulty in practical implementation of the protein degradability system (3). Nevertheless, Majdoub et al. (10) lowered N solubility (a routine feed analysis) from 42 to 22% of total N in sorghum silagebased diets containing 15.3 or 12.6% CP and observed 21 and 14% increases in milk yield and no effect on milk composition. When diets high in ADF (22%) in wk 1 to 4 and low in ADF (11%) in wk 5 to 12 postpartum were fed to Holstein primiparous and multiparous cows, Zimmerman et al. (17) found no significant difference in milk yield (30.4 to 32.3 kg/d) for grass hay-based diets containing 22, 18, or 14% CP or for 22% CP diets based on alfalfa versus grass hays (32.0 vS. 30.4 kg/d) when ration ADF was 11 %. Yield and fat test were lower for cows fed the 14% CP, grass-based diet that contained 22% ADF. They (17) noted elevated plasma urea N as dietary CP increased: 17 to 19 mg/dl for the 18% CP, high and low ADF, grass-based diets and 23 to 25 mg/dl for the 22% CP, legume or grass diets. Such high plasma urea N concentrations generally are associated with lowered reproductive efficiency in cows. VanHorn et al. (15) compared yield responses in cows fed several ratios of alfalfa hay:corn silage and concluded that CP from alfalfa hay was less effective in supporting milk yield than that from soybean meal. These observations suggest that CP requirements for given yield may differ, depending on proportion of ration CP contributed by concentrate in legume-based versus com silage-based diets. Wohlt et al. (16) supplemented multiparous Holstein cows starting 22 d postpartum with soybean, fish, or com gluten meals (CGM) in Journal of Dairy Science Vol. 75, No.6, 1992

a 16% CP, com silage-based diet. They found higher and later peak milk yields with soybean and fish meals than with COM or with 12% CP negative control; the lower CP diet resulted in significantly lower milk yield but not in lower OM! through 18 wk of lactation. Yields of 4% FCM were not different among protein sources in 16% CP diets. The COMsupplemented diet maintained fat test similar to soybean meal but higher than fish meal (P < .02) during wk 4 to 18 postpartum, but it was inferior to soybean meal in maintaining high milk protein percentage during wk I to 9 postpartum. Postpartum BW nadir was about wk 10 and was most severe for cows fed negative control (12% CP) and COM diets and least severe for those fed fish meal. Percentage of CP in the DIP fraction was 38% for diets with fish meal and COM; corresponding values for fish meal and COM supplements alone varied from 41.7 to 49.0 and from 28.5 to 48.6%, respectively, between shipments (lots). These studies illustrate several important points. Use of book values for UIP probably has little meaning in formulating diets for specific herds. Quality of CP sources, ration degradable and DIP percentages relative to individual cows' requirements, type of forage in the diet, pattern of BW change, and stage of lactation all interact to influence milk yield and percentage and yield of milk constituents. Our objective was to use COM to raise ration CP and its content of UIP in early (wk 1 to 8) versus late (wk 9 to 44) lactation in primiparous and multiparous cows of average yield potential fed a com-based diet and to evaluate effects on milk yield and composition and on BW. MATERIALS AND METHODS

Holstein cows (n = 91) were blocked by parity (1 vS. >1) and assigned randomly at calving in a completely randomized design for complete lactations. They received control diet or supplemental CGM, substituted for equal weight of concentrate mixture, during early (wk 1 to 8) or late (wk 9 to 44) lactation. The amount of CGM fed was designed to raise ration CP by 1.0 to 1.5 percentage units and was equal to 10% of concentrate allocation during wk 1 to 8 and .45 kg/d during wk 9 to 44 postpartum.

1497

CORN GLUTEN MEAL

Forage was fed for ad libitum intake (6 to 13% recorded orts) and consisted of 63% ureatreated com silage OM and 37% wilted haycrop silage; wet weights were adjusted weekly based on OM measurements (Koster Crop Tester, North Randall, OR). Pelleted concentrate mixture contained 70.37% com meal, 7.85% com distillers dried grains with solubles, 7.5% CGM, 5.6% soybean meal, 3.0% cane molasses, and 5.68% minerals and vitamins. Composition of feeds and orts is shown in Table 1. The NEL estimates (11) for concentrate and CGM were 1.71 and 2.06 Mcal/kg of OM; estimates for com and haycrop silages, based on ADF, were 1.40 and 1.15 Mcal/kg of OM, respectively. Percentages of VIP in CP of feeds used were measured and were 54, 69, 56, and 30 for concentrate, CGM, com silage, and haycrop silage, respectively [CO G. Schwab, personal colmmmication; (1)], and essential AA profJJes of feedstuffs were measured and were from the same source. During the fIrst 8 wk postpartum, concentrate was fed to appetite with a ceiling, based on previous day's milk, of 1 kg!2.5 kg of milk for primiparous and 1 kg/2.0 kg of milk for pluriparous cows. This was to prevent low peak cows from overconsuming concentrate in relation to their needs. Sodium bicarbonate (57 g) was top-dressed on silage twice daily from calving until after peak of lactation. After wk 8 postpartum, concentrate was fed in standard declining fashion (adjusted weekly) for all treatments, based on total amount of grain consumed by each cow during wk 1 to 8 of lactation regardless of milk yield response (4, 6, 7); rate of decline was slower for parity 1 cows, as illustrated in Figure 1 and Table 2. Cows were fed and milked twice daily at 0500 and 1500 h in a conventional stanchion barn adapted for individual orts retrieval. Grain feeding was introduced 10 d prepartum and increased in .5- to .7-kg intervals to a maximum daily amount equal to .8% of BW at calving. Weights of milk, feeds, and orts were recorded daily, and biweekly a.m.-p.m. composites of milk were analyzed for fat (Babcock) and SNF (Golding bead test); milk was analyzed for protein (orange G dye binding); feeds were sampled every 2 wk and composited by 4-wk periods; and orts were sampled and composited by treatment every 4 wk. Each cow's BW was recorded prior to feeding and milking

once every 2 wk. Cows were exercised twice daily for 1 h in a paved, outdoor lot to observe reproductive behavior. Composites of feeds and orts were analyzed for proximate nutrients, ADF, NDF, and N solubility (in phosphatebicarbonate buffer). General herd health and reproductive efficiency were monitored. Oata were analyzed by ANOVA using SAS (13) for a completely randomized design with main effects of treatment, lactation (1 vs. >1), periods postpartum (1 through 11; split plot within main treatment), and all interactions. Significance was declared at P < .10 unless otherwise noted During wk I to 8 postpartum, diets were similar for control and late supplemented cows; thereafter, diets were similar for control and early supplemented cows. Thus, except for BW, figures were simplified by plotting period means for CGM-supplemented versus unsupplemented cows by parity category. RESULTS AND DISCUSSION

Com silage (fable 1) was high in soluble CP because of urea treatment, but concentrate mixture and CGM were low. Although we considered orts to consist principally of forages, it is apparent from their CP, fat, and fiber contents that parity 1 cows receiving CGM in early lactation rejected at least a small amount of CGM and that other supplemented cows had some concentrate, CGM, or both in their orts. Concentrate OMI (Figure I), as intended, was not significantly affected by treatments. Mean grain OMI for complete lactations of cows in parity 1 were 5.8, 5.7, and 5.8 kg/d for control and late and early CGM supplementations, respectively; corresponding means for pluriparous cows were 5.7, 5.8, and 5.5 kg/d Means for the entire lactation were remarkably similar among treatments and between parity categories. Pluriparous cows fed CGM in early lactation consumed 1.2 kg/d less grain OM than controls in wk 1 to 8 postpartum (period means not shown), thus reducing their allocation for the remainder of the lactation; this accounts for their lower grain intake means (5.5 vs. 5.7 and 5.8 kg/d) and the treatment by lactation effect (Figure I). Pluriparous cows were offered and consumed more grain in early lactation than parity I cows because of their Journal of Dairy Science Vol. 75, No.6, 1992

-

I

~ 00

0

..... 0

5'en

TABLE 1. Composition of forages (by harvest year), concentrate, com gluten meal (COM), and orts [by treatment! and lactation (l Ys. 2+)].

~.

Feeds and orts

Ether extract

n

Year

n

"< -J

~

CP

NDF

--(%)--

!'!-

:" Z ? P'

DM

Com silage plus .45% urea

(% of DM)

X

SE

X

SE

X

SE

25.6 28.0 29.8 25.4 27.8

1.1 .6 .3 .5

10.56 12.82 12.19 13.33 12.33

.49 .26 .23 .32

3.21 3.06 2.90 3.23 3.06

.12

1982 1983 1984 1985 Mean

6 13 13 6

1982 1983 1984 1985 Mean

5 13 13 9

30.9 29.8 33.2 34.4 32.1

1.1 .8 .7 1.9

14.52 13.04 13.45 13.16 13.39

.66 .76 .61 .55

4.63 4.38 3.85 3.38 4.01

Concentrate COM

37 2

89.8 89.8

.2

...

18.82 66.82

.25

. ..

3.71 1.24

.

Parity I orts Control Early Late

30 25 27

34.7 35.0 34.5

1.0 .6 .8

13.80 15.50 16.90

.40 .64 .97

3.41 3.10 3.56

Parity 2+ orts Control Early Late

34 33 34

35.6 34.5 34.2

1.0 1.0 .9

12.82 14.15 14.75

.35 .51 .68

2.96 3.21 3.26

Haycrop silage2

...

Solubility of protein

ADF

.

..

.10 .09 .51

. .. .10 .20 .12

X · .. 47.92 49.23 53.58 49.51

·

..

· ..

-

X

SE

X

SE

· ..

29.25 26.73 28.77 32.67 28.76

.63 .26 1.13 .45

79.3 75.4 73.4 76.6 75.5

.8 .9 2.4 1.2

.54 .71

57.5 57.4 60.1 56.5 58.1

1.9 1.4 1.5 3.9

17.2 2.2

1.0

.08 1.52 .70

· .. · .. · ..

63.21 60.57 62.13

1.46 2.38

18.02 14.49

.60

.19 .08 .18

.09

.22

.11

..

.16 .13

(% ofCP)-

SE

39.51 40.19 40.58 38.16 39.78

... .66 1.30

· ..

5.77 8.32

...

51.19 49.51 47.44

1.87 1.73 3.08

31.14 27.96 29.47

.86 .77 1.06

49.50 50.30 48.82

1.96 1.76 1.90

26.46 27.49 27.01

.94 1.03 .95

.22

.

..

!Control, no additional COM fed; early, COM substituted for 10% of concentrate during wk 1 to 8 postpartum; and late, .45 kg/d of COM substituted for concentrate during wk 9 to 44 postpartum. 2Percentage of CP insoluble in acid detergent ranged from 3.8 to 12.5% for 40 samples; 2 samples exceeded 8.6%.

:=

0

i

~

~

1499

CORN GLUfEN MEAL

TABLE 2. Concentrate percentage in dietary DM, by parity category, trealment, and 28-d periods postpartum, for Holstein cows supplemented with com gluten meal to raise ration CP by 1.1 to 1.5 percentage units in wk I to 8 (early) or wk 9 to 44 (late) postpartum. Trealment(T) Lactation (L) I, n Control

Late

4 5 6 7 8 9 10 11

58.8 58.1 47.9 41.1 38.3 36.0 34.8 31.2 31.9 30.5 28.0

X

39.7

62.3 62.5 51.8 40.5 36.8 34.7 32.6 30.7 30.9 29.5 272 39.9

Periods (P)

=8

Lactation >1, n = 22

Early

Control

Late

59.0 56.5 48.2 40.1 37.0 35.7 33.2 31.6 34.9 34.3 31.1 40.1

68.3 70.9 57.5 42.1 29.1 23.7 20.3 14.5 11.9 12.4 13.2 33.1

SE 66.9 71.2 58.0 41.3 28.8 23.2 19.7 13.7 10.0 9.9 8.1 31.9

SE = 1.7 I

2

3

Early

Effect

P

T L p TxL TxP LxP TxLxP

NS

= 1.1 67.1 68.2 53.3 39.3 27.5 22.3 18.9 13.6 10.3 10.5 11.0 31.1

••••

•••• • •

••••

NS

INS (P > .10). • p < .05. ••••p

< .0001.

higher milk yield at that time, but they consumed less grain in later lactation because of their larger size, the resultant ability to consume DM, and their reduced need for energy to support growth. Mean ages at calving were 759 and 1499 d for cows in parities 1 and >1, respectively. The treatment by lactation category effect (Figure 1) apparently was associated with the slightly higher grain intake of pluriparous cows during the middle of lactation (wk 12 to 32), which was not observed in first lactation cows. Forage DMI (Figure 2) was higher (P < .05) for cows receiving CGM in late lactation, and the treatment by lactation number effect (P < .01) indicates that the response was greater in pluriparous cows. This effect was reflected in total ration DMI (Figure 3), which was higher for pluriparous cows receiving CGM supplement during wk 9 to 44 postpartum, but not consistently so for parity 1 cows (treatment by lactation number interaction; P < .01). The DMI of first lactation cows, in general, was remarkably level after wk 8 of lactation. This may be attributed to the higher proportion of concentrate (Table 2) in their diet than in that of older cows. Hawkins et al. (2) noted a significant positive effect of ration CP (18 vs.

14%) on DMI when cows (presumably pluriparous) were fed a com-based diet supplemented with soybean meal, and they noted higher DMI in a 14% CP diet in which CGM and blood meal replaced soybean meal. The forage and DMI responses of pluriparous cows agree with results of Robinson et al. (12) when

,/ '

- - No supplement - - - - Corn gluten meal Treatment 1, respectively. Milk fat percentage (Figure 7) was higher for parity 1 than for older cows and was higher

C0t!in9 BW. klJ Loc'afton: , r Control 588 655 ----- Late 590 693 .._ - Ea,ty 527 668 Treatment (n (P < .0000 T_L(P1

Early

69 658 94 100 98

Control Late

Parity 1

Early

Control Late

Parity >1

Early

22 22 23 8 8 8 578 604 589 524 540 493 -.25 -.18 -.43 .32 .46 .36 18.00 18.75 17.73 14.85 14.94 15.00 2.46 3.02 3.04 3.05 2.50 2.60 34.2 35.6 34.6 21.0 22.4 20.3 28.7 30.9 31.8 20.7 20.4 20.6 98 95 96 87 88 89 16.94 16.92 18.46 15.16 16.20 14.96 35.3 35.3 39.4 34.7 38.9 35.1 77 1026

lOS 94 102

Periods 9 and 10 (wk 33-40)

Periods 5 and 6 (wk 21-28)

77

77

1024 104 94 102

1013 105 114 104

46 654 96 88 103

50 668 103 105 103

46 654 96 88 101

Control Late 22 594 .25 16.90 2.47 24.3 22.4 90 14.33 35.0 35 714 97 91 92

22 628 .32 17.34 2.50 25.0 23.0 91 15.40 38.4 39 746 103 107 94

Parity >1

Parity 1

Early 23

600 .07 17.20 2.49 24.6 22.5 94 14.23 35.0 33 725 100 90 92

Control Late 8 564 .50 15.35 2.37 18.8 19.4 87 14.63 35.1 40 655 98 92 105

8 588 .57 14.89 2.30 18.0 17.6 90 15.87 38.9 44 562 109 111 107

Early

Control Late

Early

8 529

22 618

23 614

.50 14.95 2.45 17.0 17.6 92 14.84 35.1 44 571 104 93 106

.32 14.15 1.93 13.5 13.6 93 13.45 35.0 17 430 109 97 102

22 654

.11 14.69 1.97 14.0 14.8

99 14.60 39.2 21 467 119 118 103

.32 14.20 1.94 14.4 14.3 91 13.37 34.9 15 452 105 97 104

wt/wt Arg

His De Leu Lys Met PIle

1br Val

3.74 2.75 2.34 3.55 1.19 2.34 3.37 2.56 2.48

3.77 2.74 2.31 3.55 1.16 2.34 3.35 2.54 2.45

3.85 2.92 2.48 4.00 1.20 2.61 3.68 2.71 2.63

3.58 2.54 2.13 3.33 1.06 2.23 3.13 2.34 2.25

3.74 2.64 2.22 3.48 1.11 2.32 3.27 2.39 2.35

3.89 2.84 2.39 3.98 1.13 2.64 3.63 2.63 2.54

3.26 2.67 2.34 3.28 1.22 2.07 3.18 2.50 2.46

3.50 2.94 2.58 3.87 1.28 2.46 3.64 2.77 2.72

3.28 2.69 2.36 3.30 1.23 2.08 3.21 2.52 2.49

2.91 2.57 2.30 3.06 1.22 1.88 3.02 2.43 2.42

3.13 2.81 2.49 3.58 1.27 2.22 3.42 2.65 2.64

2.85 2.55 2.29 3.02 1.22 1.85 3.00 2.42 2.41

3.10 2.65 2.34 3.19 1.23 1.99 3.14 2.49 2.47

3.85 3.34 2.95 4.36 1.48 2.73 4.12 3.16 3.13

3.63 3.03 2.66 3.69 1.39 2.33 3.60 2.84 2.81

3.19 3.20 2.94 3.60 1.61 2.10 3.68 3.06 3.10

3.32 3.42 3.14 4.24 1.62 2.51 4.12 3.28 3.31

2.95 3.01 2.79 3.37 1.53 1.96 3.45 2.88 2.93

(')

0

~

Cl

~ Z

~

ICom gluten meal (COM, substituted for concentrate) supplemented to raise ration CP by 1.1 to 1.5 percentage units during wk 1 to 8 (early) or wk 9 to 44 (late) postpartum. 2Intake of NEL as multiple of maintenance NEL (.080 Mca1/kg of BW 75 ). 3NEL in diet x lOO/NEL required for maintenance, milk, and BW change (11); NEL (megacalories per kilogram of DM): concentrate, 1.71; COM, 2.06; com silage. 1.56; and baycrop silage. 1.08. 4cp in diet x l00/CP required for maintenance, milk, and BW change (11); same for undegradable (UIP) and degradable (DIP) intake protein. 5Milk protein composition from Jacobson et aI. (8) and feed composition from C. O. Schwab (personal communication).

....

lit

0

\N

1504

HOLTER ET AL.

TABLE 4. Effect of treatments l on monthly somatic cell score of milk of Holstein cows.

Treatment

Monthly sample postpartum

IH.9

2.0-3.9

1 2 3 4 5 6 7 8 9 10 11

50 75 67 52 57 52 45 48 37 32 42

41 18 23 38 37 38 45 31 44 41 33

9 7 7 10 6 10 10 14 19 23 25

40 31 42 29 38 35 39 50 57 36 50

12 23 6 3 3 7 19

54 28 46 43 46 48 31 34 46 50 80

15

Somatic cell score 4.0-5.9

6.0-9.0

n

Cows (%) Control

X Early

1 2 3 4 5 6 7 8 9 IO 11

X Late

1 2 3 4 5 6 7 8 9 10 11

IO

X

81

16 4 13 10 7 10 3 7 8 0

25 26 31 31 29 29 31 30 30 25 14

8 II 4 0 0 3 7 0 7 0 0

26 28 28 30 28 29 29 29 28 18 5

10

10 16 21

81 23 36 39 33 39 38 52 41 29 33 20

22 28 30 29 30 29 29 29 27 22 12

14

86 32 42 39 58 52 48 39 33 23 40 29

0 0 3 0 0 0 0 7 0 4 0

20

25 11 23 14 10 10 24 18 17 0 19

lAdditional protein as com gluten meal fed wk 1 to 8 (early) or wk 9 to 44 (late) postpartum.

at levels below three times that required for maintenance. Primiparous cows apparently were less adequate in NEL throughout lactation than older ones, despite the higher proportion (40 vs. 32%) of concentrate in their diet (Table 2); however, BW curves (Figure 6) were reasonably normal for cows expected to recover part of their body energy reserves, to continue their growth, or both during the subsequent dry period. There were no obvious differences among treatments in regard to N&. adequacy, despite higher forage DMI by COM-supplemented, older cows (Figure 2). Journal of Dairy Science Vol. 75, No.6, 1992

Ration CP (Table 3) was increased by 1.1 to 1.5 percentage units, and CP in the DIP fraction was increased from 35 to 39% with COM supplementation as intended; this practice resulted in improved CP adequacy during mid and late lactation in both parity categories, but not during wk 1 to 8 postpartum. In early lactation, milk protein yield apparently was related linearly to CP adequacy of the diet in first lactation cows. Perhaps this was because parity 1 cows were slightly underfed CP compared with those in parity 2 or higher. Estimated DIP generally was below recommended (11) amounts except when cows were supple-

1505

CORN GLUTEN MEAL

TABLE 5. Effect of additional dietary CP in early or late lactation on measures of breeding efficiency in first lactation and older Holstein cows.

Treatments Additional CP postpartum 1 Breeding traits

First lactation Not bred Conceived fust service Conceived second service Conceived third to fifth service Bred but no conception Older cows ~t~d

Conceived fIrSt service Conceived second service Conceived third to fifth service Bred but no conception Overall services per conception Overall cows bred but no conception, %

Control 1~2

3n In 3n On

Early

Late

I~

2n In 4n on

1m

3m

12/21 6/21 2/21 1/21

6/19 4/19 7/19 2/19

1.8 3.6

2.3 7.7

4/23 7/19 5/19 4/19 3/19 1.7 19.2

1Early = wk 1 to 8, late = wk 9 to 44 postpartum; com gluten meal was CP source. 2Number of cows out of total cows.

mented with CGM. Estimated intake of degradable protein was close to requirement except for pluriparous cows in midlactation. One might tentatively conclude that UIP adequacy was related to FCM yield in pluriparous cows during all three stages of lactation, but only during wk 1 to 8 in first lactation cows; perhaps growth interfered with this relationship in heifers after wk 8 of lactation. Gross examination of the ratio of essential AA in the feed consumed to that estimated (8) in the milk secreted has precedence (8), but critical evaluation requires measurement of AA flow to the small intestine; however, relative treatment effects on these ratios were of interest, using assumptions that ruminal alterations of feed AA and microbial contributions to intestinal AA were similar among treatments. Our data suggest that Lys may have been frrst-limiting for all cows throughout lactation and that the apparent second-limiting AA were fie in early lactation and Met in mid and late lactation; these findings support the more direct AA passage studies of Schwab (14) in regard to Lys and Met in multiparous cows. In a previous study (5) using a combased diet, pluriparous cows maintained a positive body protein balance as ration CP was reduced from 19 or 21% to about 13.5%, below which the balance was negative; over this range of CP contents, milk protein percentage declined with decreasing ration CP

percentage, but milk yield (40 kg/d) was not affected. Data from pluriparous cows in the present study agree with that of Holter et al. (5). Our results also agree with those of Janicki et al. (9), who fed pluriparous cows diets rich in com during wk 6, 10, and 14 postpartum and found that increasing the insolubility of CP from 52 to 60% did not significantly increase milk yield or change its composition and that increasing the ration CP from 13.6 to 15.3% significantly (P < .01) reduced milk yield (32.4 vs. 35.2 kg/d). In all cases, body protein balances were substantially positive, and the higher CP diet resulted in significantly and unnecessarily higher body protein balance (363 vs. 258 gld), thus reducing NEL available for milk synthesis. Udder health, as monitored by monthly SCC (fable 4), was not evaluated statistically, but means suggest that, on a herd basis, supplementation of CGM to increase the DIP content of CP slightly reduced (81 vs. 86%) the proportion of cows with somatic cell score below 4.0. There were not enough cows in parity 1 to evaluate effects of treatments on breeding efficiency (fable 5). For older cows, 57% of controls conceived on first service compared with 32 and 37%, respectively, of those supplemented early (wk 1 to 8) and later in lactation with CGM to raise ration CP by 1.1 to 1.5 percentage units. Although data were limited, we postulated a carry-over effect of Journal of Dairy Science Vol. 75, No.6, 1992

1506

HOLTER ET AL.

early CP supplementation because most cows were first bred more than 56 d postpartum. Failure to conceive after repeated breedings was somewhat more prevalent in cows fed supplemental cp after wk 8 postpartum. Nevertheless, results are consistent with the generally held idea that overfeeding CP relative to requirements or feeding CP that is too degradable adversely affects reproductive performance in dairy cows. CONCLUSIONS

Considering our study and those cited (2, 5, 9, 14, 16, 17) in which com silage, grass haycrop, or both constituted the primary forage and com was a major component of concentrate, most cows in most (average) herds may not respond to simply increasing CP percentage or proportion of DIP (should its routine measurement become practically feasible) using a com-based protein supplement; rather, producers in regions where com is dominant in dairy rations should consider feeding diets with CP lower than is the usual practice but supplemented with rumen undegradable, but highly digestible, rich sources of Lys, Met, and fie. Schwab (14) suggested that the method of choice would be supplementation with mmenprotected specific AA. It also is clear that primiparous cows that have a significant growth requirement, in addition to maintenance and milk yield needs, may not respond to a herd supplementation policy in the same way as older cows. This implies that scientists should include primiparous cows in feeding studies and should monitor yield and BW or body condition responses through complete lactation following early lactation supplementation treatments. Otherwise, expensive supplement packages, thus developed, should be sold selectively only to producers with herds and feeding programs for which a profitable response is likely. ACKNOWLEDGMENTS

Authors thank C. G. Schwab and K. Cunningham for sharing AA and degradability data; J. Whitehouse and C. Wagner for animal care and attention to research protocol; S. Blanchard for feed analyses; and L. Emmons, K. Kelley, and J. Warren for manuscript preparation. Journal of Dairy Science Vol. 75, No.6, 1992

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