Evaluation of Calf Starters Containing Different Amounts of Crude Protein for Growth of Holstein Calves1

Evaluation of Calf Starters Containing Different Amounts of Crude Protein for Growth of Holstein Calves1 J. M. AKAYEZU, J. 0. LINN, D.

E. OTTERBY, and W. P. HANSEN Department of Animal Science University of Minnesota St. Paul 55108 D. 0. JOHNSON West Central Experiment Station University of Minnesota Morris 56267

ABSTRACT

Abbreviation key: ADG = average daily gain, SP = St. Paul, WCES = West Central Experiment Station.

Several studies have reported on the appropriate protein percentages in calf starters for optimal growth of young calves (2, 4, 12, 15, 18, 19, 20). In many instances, starter diets containing various percentages of CP, ranging from about 13% to 218% in the DM, promoted similar BW gains (2, 4, 15, 20). But, in other cases, when incremental CP in starter diets was tested, live BW gains were improved when the protein content was 17 to 218% in the DM (2, 8, 19, 20). except when starter consumption was restricted (20). Crowley et al. (3) suggested that calf starters for dairy replacements should contain 15 to 20% CP in the DM (20% high quality protein if calves were weaned at 3 to 4 wk of age). The NRC recommendations for protein content in calf starter DM increased from 16% in 1978 (13) to 18% in 1989 (14), based on DMI of about 2.6% of BW. Field reports have suggested protein higher than NRC recommendations, but the beneficial effects of calf starters containing high amounts of protein have not been clearly shown. The objectives of this study were to evaluate the performance of young Holstein calves preweaning and immediately postweaning when they were fed calf starters containing different percentages of protein.

INTRODUCTION

MATERIALS AND METHODS

Received October 7, 1993. Accepted February 25. 1994. 'Published as Paper Number 20,841 of the Scientific Journal Series of the Minnesota Agricultural Experiment Station on research conducted under Minnesota Agricultural Experiment Station Project Number 1647.

One hundred twenty-four Holstein calves from University of Minnesota herds located at the West Central Experiment Station, Morris (WCES),and the St. Paul (SP)campus were used from d 4 to 56 of age. Within location, calves were blocked by sex and randomly assigned to one of four dietary treatments (A, B,

Holstein calves (n = 110) were used to evaluate the effect of calf starters containing 15, 16.8, 19.6, or 22.4% CP, DM basis (bets A, B, C, and D, respectively), on calf performance from d 4 to 56 of life. Preweaning druly gain tended to increase linearly as protein content of diets increased, averaging .37, .39, .38, and .44 kg/d for diets A, B, C, and D, respectively. After weaning, calves fed diet C gained the most (.86 versus .71, .75, and .79 kg/d for A, B, and D, respectively). Overall BW gains from d 4 to 56 averaged .54, .56, .62, and .61 kg/d for A, B, C, and D, respectively. Throughout the experiment, starter consumption tended to increase as CP content of diet increased. Under these conditions, maximum growth was supported by diet C (19.6% CP); no advantage was gained from higher (22.4%) protein content. Calf growth was moderate when calf starters of lower protein contents (15 or 16.8%) were fed. (Key words: calves, starter, protein)

1994 J Dairy Sci 77:1882-1889

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PROTEIN IN CALF STARTER TABLE 1. Ingredient composition of experimental diets. Diet' Ingredient

A

B

C

D

Corn, cracked

52.20 30.80 8.57 2.82 2.63 .72 .71 .22 .08 1.25

48.35 28.40 14.90 2.84 2.64 .61 .71 .22

44.45 26.04 21.24 2.85 2.65 .51 .7 1 .22

1.25

1.25

39.79 23.17 28.89 2.86 2.65 38 .71 .22 .08 1.25

(%, as fed)

oats

soybean meal Molasses, dry Tallow Dicalcium phosphate Limestone Trace-mineralized salt2 Vitamin premix3 Deccox-

.os

.os

*Diets A, B, C, and D were formulated to contain 14, 16.5, 19, and 22.5% CP, DM basis, respectively. vontained (grams per kilogram): Na. 381.6; Cl. 588.4; Co, .052; Cu, ,309; I, ,072; Fe, 2.062; Mn, 2.062; and Zn, 3.608. 3Contained (International Units per kilogram): vitamin A, 5,200,000, vitamin D, 1,600,000; and vitamin E, 19,800. 4Brand of decoquinate (active drug, 1 gkg; Rh8ne-Poulenc, Atlanta. GA).

C, or D) in blocks of four by birth order. The experimental period was from October (WCES) or November (SP) 1990 to April 1991. Dietary treatments consisted of calf starters differing in protein contents. Starter diets were formulated to contain 14, 16.5, 19, or 22.5% CP (DM basis). The ingredient compositions of the calf starters used are in Table 1. Calves were fed fresh colostrum on d 1 of life. Calves were removed from the maternity pen within 24 h after birth and placed in their respective housing facilities. On d 2 and 3 of life, all calves received transitional milk. From d 4 to weaning, they were given fresh waste milk at 8% of birth BW daily in one feeding at WCES. At SP, they received 4 kg of 50% soured milk and 50% reconstituted milk replacer (Nutraseme@, 20% protein and 20% fat; American Agco, St. Paul, MN) daily in two feedings. In addition, at SP, when outdoor temperatures were <-18'C, liquid feeding was increased to 5 kg/d. Starters and water were offered free choice at both sites throughout the experimental period, and no hay was offered. Weaning occurred at or after 28 d of age, when daily starter consumption (averaged over 3 consecutive d) was 2.45 kg of DM. At WCES, calves were housed indoors in a heated and ventilated nursery with elevated individual stalls (.9 m high x .5 m wide x 1.5 m long) or outdoors in individual polyethylene

hutches (Poly DomesTM;Poly Tank Co., Litchfield, MN). These dome-shaped units were 2.16 m wide (base diameter) and 1.52 m high. Treatment groups were balanced for housing type. At SP, all calves were housed in outdoor individual wooden hutches (1.22 m high x 1.22 m wide x 2.44 m long). Calves were weighed on d 4 of life and weekly thereafter, again at weaning, and on d 56. Health data were also recorded. Amount of starter offered was recorded daily, and orts were weighed and recorded weekly. Any starter that was fouled was removed, weighed, and replaced with fresh starter. Starter diets were sampled weekly, and monthly composites were analyzed for CP by macro-Kjeldahl (l), for NDF and ADF using sequential analysis by methods of Goering and Van Soest (5) as modified by Van Soest et al. (22), and for ether extract by AOAC (1) procedures. Total ash was determined by ashing overnight at 550'C; the ash was then solubilized in 1 . W HCl, and the solution was analyzed for mineral contents by inductively coupled plasma atomic emission spectroscopy (Model QA 137; Applied Research Laboratories, Sunland, CA). In situ procedures were used to determine undegradable protein. Dacron bags (6 x 10 cm) with a mean pore size of 52 f 15 pm were filled with 0 or .5 g of feed sample, heat Journal of Dairy Science Vol. 77, No. 7, 1994

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AKAYEZU ET AL.

sealed, and incubated in the rumen of a lactating dairy cow fitted with a rumen cannula, and fed a 5050 forage to concentrate diet. Duplicate bags were incubated for 0, 2, 4, 8, 12, 16, and 24 h, on 2 consecutive d. The 0-h samples were soaked in water at 39'C for 15 min. Protein degradability was calculated according to methods of Mathers and Miller (11). Dietary undegradable intake protein also was calculated using NRC values (14) for feed ingredients. An analysis of covariance was performed using the general linear models procedure of SAS (17) for a completely randomized block design. Body weights on d 4 of life were used as the covariate. Preliminary tests on the data collected at WCES showed no significant interaction between diet and housing type; therefore, data from both experimental sites were pooled. Data from 14 calves were removed from statistical analyses because of death (4 calves), sickness (4 calves with prolonged diarrhea, 1 calf with complicated navel infection, and 3 calves with frozen extremities) that occurred early in the experiment, or because of abnormal growth throughout the experimental period, probably from congenital abnormalities (2 calves). Numbers of calves removed from treatments A, B, C, and D were 2, 4, 5, and 3, respectively, which resulted in assignment of unequal numbers of calves to the different treatments. The statistical model was

where = observed response, = overall mean, Ti = main effect of treatment, Sj = main effect of sex, (Ts)ij = treatment by sex interaction, Lk = main effect of experimental site, ('lT& = treatment by site interaction, (SL)),= sex by site interaction, = covariate (initial BW), and Eijklm = error term.

Yij&

p

Id,

Orthogonal polynomials were used to examine linear, quadratic, and cubic effects. Results are reported as least squares means and pooled J o d of Dairy Science Vol. 77, No. 7. 1994

standard errors. Unless otherwise noted, significance was declared at P 5 .05. RESULTS

Nutrient compositions of the calf starters are in Table 2. Actual CP contents were slightly different from the targeted formulation, i.e., 15, 16.8, 19.6, and 22.4% for diets A, B, C, and D, respectively. Calculated undegradable intake protein values were similar among diets. Undegradable protein determined by in situ procedures was similar among starters but markedly different from calculated values. Calculated DE values of starters were similar to those recommended by NRC (14). Tables 3 and 4 summarize calf responses to the dietary treatments used in this study. There were no significant interactions involving diet. Calf weaning age, which was not affected by dietary treatments, averaged 30 d of life (Table 3). Average daily gain (ADG)from d 4 to weaning tended to increase linearly (P= .OS)as the CP content of the starters increased (Table 3). From weaning to d 56, ADG increased linearly Gp = .02) as dietary CP increased. Rates of BW gain were highest for treatments C and D, lowest for A, and intermediate for B. Calves receiving starter C gained 150 and 100 g daily more than calves fed diets A and B, respectively. Starter consumption was negligible for the first 2 wk of study, averaging c.2 kg/d at 18 d of age. Most calves were eating about .4kg of DM/d by 25 d of life and .6 kg/d at weaning. After weaning, starter consumption increased rapidly, averaging about 1.9 kg of DM/d at the conclusion of the trial (d 56 of life). Cumulative starter DMI linearly increased with increasing dietary CP contents through weaning (Table 3). However, total DMI (milk solids plus starter DM) were similar among treatments, and no linear trend was detected because the major proportion of the DM consumed during this period consisted of milk solids. During the postweaning period and over the entire experimental period, differences in amounts of starter or total DM consumed tended to increase linearly with increasing dietary CP content up to 19.5% CP (Table 3). Estimated digestible energy intakes (Table 4) followed the same trends as starter DMI in

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PROTEIN IN CALF STARTER TABLE 2. Nutrient composition of experimental diets. Diet1

Item

A

DM, % CP, % of DM Undegradable? % of CP Undegradable.3 % of CP NDF, % of DM ADF, % of DM Ether extract, % of DM Ash, % of DM Ca, % of DM P, % of DM K, % of DM Mg, % of DM Fe, ppm of DM Mu. ppm of DM Zn,ppm of DM Cu, ppm of DM DE2 M U g of DM

B

C

88.73 16.79 37.73 21.35 14.90 5.80 5.08 4.27 .69 .65

88.62 15.02 38.50 23.52 15.25 5.87

5.05 4.12 .73

.66 .77 .19 182.75 42.97 55.37 8.89 3.51

D 89.00 22.38 36.63 22.36 14.11 5.79 4.95 4.68 .68 .65 1.19 .24 174.60 40.26 54.99 9.69 3.56

88.97 19.55 37.15 21.09 14.94 6.00 4.71 4.46

.66 .65 1.02 .22 173.30 40.05 55.50 9.64 3.53

.90 .21 170.00 40.55 52.85 9.42 3.52

SD 1.87 .72

. . . .86 1.51 .70 .32 .49

.06

.04 .05 .01 34.06 3.10 4.91 2.73

...

lDiets A, B, C. and D were formulated to contain 14, 16.5, 19, and 22.5% 0,DM basis, respectively. ZDigestible energy and undegradable intake protein, percentage of CP. calculated using 1989 values of NRC (14) for the ingmhents used, assuming 89% DM (99% DM for fat). sundegradable protein (percentage of CP) determined by in situ procedures.

TABLE 3. Performance of young calvcs fed starter diets of different CP contents. Diet1

Diet effects

SE

Item

A

B

C

D

Calves, no. BW on d 4, kg Weaning age,2 d Average gain,l kg/d d 4 to Weaning Weaning to d 56

30

27

26

27

40.0 30.6

41.0 30.5

40.6 29.7

41.6 30.2

d4tod56

Starter DMI,2 kg d 4 to Weaning Weaning to d 56 d 4 to d 56 Total DMI?.3 kg d 4 to Weaning Weaning to d 56 d4tod56

.37 .71

.39 .75

.54

.56

6.1

.38 .86 .62

Linear

Quadratic

Cubic

P

.44 .79 .61

.97 .67

.52

.71

.52

.08 .02

.02

c.01

.42 .10 .41

.38

.03

c.01 .07 .02

.99 .38 .42

.95 .17 .21

.03

.09 .34

44.0

39.2 45.3

6.7 44.1 50.8

7.2 41.7 48.9

.42 1.82 1.97

18.4 38.4 56.8

18.9 39.2 58.1

18.9 44.1 63.0

19.5 41.7 61.2

.22

.94

1.82 1.82

.07

38

.03

.39

.68 .17 .21

.22 .08

.59 .31 .31

38 .51 .91

.63 .90 .70

5.6 38.4

.a

Feed efficiency.23 (total DMl5W gain) d4toWeaning 2.14 Weaning to d 56 2.18 d4tod56

2.04

1.95 2.10 2.00

2.05 2.05 2.00

1.93 2.08 1.94

.07

Diets A, B. C. and D were formulated to contain 14, 16.5, 19, and 22.5% CP (DM basis), respectively. 2Means are least squares means covariately adjusted for BW on d 4. 3Total DMI = Milk solids plus starter DM, from weaning to d 56, total DMI = starter DMI.

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AKAYEZU ET AL

general. Interactions were significant for sex by site effects on starter DMI, total DMI, and estimated digestible energy intake from d 4 to weaning. Male calves at SP consumed less starter DM than male calves at WCES during this period. Additionally, females at SP consumed more total DM because they received more milk solids than females at WCES because of differences in liquid feeding regimen. At weaning, average daily protein intakes were greater for calves offered diets C or D than for those receiving diets A or B (Table 4). From weaning to d 56 and over the 53-d experimental period, daily protein intakes were different among all treatments and increased with increasing dietary protein content. Values for undegradable protein intakes postweaning using in situ values were 52.9, 54.7, 69.0, and 80.5 g/d for treatments A, B, C, and D, respectively. Feed efficiency (total DMVBW gain) (Table 3) and, thus, energy efficiency (Mcal digestible energykg BW gain) (Table 4) were not affected by dietary treatments during any of the

periods. Gross efficiency of protein utilization for growth, calculated as grams of protein intake per unit of BW gain, was not affected by treatments from d 4 to weaning flable 4). But, after weaning and from d 4 to d 56, CP intake per unit of BW gain increased linearly with increasing protein content of the diets. Male calves were heavier at d 4 than females (43.0 versus 38.6 kg, respectively), but weaning age, starter DMI, and total DMI were not affected by sex. Male calves gained faster (.43 versus .36 kg/d) and had greater feed efficiencies than females from d 4 to weaning. After weaning, ADG and feed efficiencies were similar among male and female calves. Table 5 indicates the type and incidence of health problems observed at both experimental sites. Values shown do not include calves removed from statistical analyses. Diarrhea was the most predominant health problem among calves, especially at SP. At this location, 13 calves had at least one episode of diarrhea lasting only 1 to 2 d, but 9 other calves had diarrhea persisting 23 d at each occurrence and

TABLE 4. Rotein and energy intake and efficiency of utilization for growth of calves fed starter diets of different CP contents. Diet effects

Diet'

Item

B

A

C

D

Calves, no. 30 27 26 CP intake,2 g/d d 4 to Weaning 151 156 169 Weaning to d 56 225 256 327 d 4 to d 56 188 205 248 Gross protein efficiency,*.3 g of CP intakekg of BW gain d 4 to Weaning 483 450 486 Weaning to d 56 328 353 401 d4tod56 360 375 417 Digestible energy intake.2~~ Mad 3.20 3.25 3.37 d 4 to Weaning Weaning to d 56 5.25 5.37 5.90 4.28 4.63 d4tod56 4.20 Energy efficiency,z Mcal of digestible energy/ kg of BW gain d 4 to Weaning 10.22 9.28 9.66 Weaning to d 56 7.65 7.39 7.23 d 4 to d 56 8.05 7.84 7.79 ~~

SE

Linear

Quadratic

.80 .91 .92

.5 1 .07 .09

.NO .22 .55

.66 .9 1 .56

.01

.77 39 .42

.59 .17 .19

.54 .47 .27

35 .48 .91

.66

177 360 267

3.97 9.02 6.30

c.01 <.01

480

.05

464

.02 .01

.9 1 <.Ol <.01

449

Cubic

P

27

3.37 5.73 4.52

.I7 .I2

9.13 7.39 7.64

1.09 .30 .26

.08

<.Ol

.07 .01

.87 .82

~

IDiets A, B, C, and D were formulated to contain 14, 16.5, 19, and 22.5% CP @M basis), respectively. 2Means are least squares means covariately adjusted for BW on d 4. 3The CP content of milk was assumed to be 3.5%;that of milk replacer was 20% (by manufacturer's specifications). 4Energy contents of 5.69 and 4.58 McaVLg of DM were used for milk (14) and milk replacer, respectively. Journal of Dairy Science Vol. 77, No. 7, 1994

PROTEIN IN CALF STARTER TABLE 5. Type and incidence of health problems observed among calves during the experimental period. ~~

Diet ltem

A

B

Calves, no.

30

27

Incidence Diarrhea 7 Navel infection 1 Swollen knees . . . Umbilical hernia . . . Pneumonia ...

C

26 (no. cases’)

6 2

8 1

1

. . .

.. ...

. . .

.

1

D 27

10 4 1 1 1

]Does not include calves removed from the study.

requiring treatment with electrolytes. Laboratory tests revealed the presence of a parasite, Cryptosporidium sp. in the feces of 2 of the 4 calves removed from the study. All cases of navel infection were observed at WCES among calves housed in the nursery, except for one case observed at SP. In addition, cases of frozen feet were also observed at WCES with calves housed outdoor in polyethylene hutches. DISCUSSION

Protein contents of milk and milk replacers were not analyzed but were assumed to be 3.5 and 20% CP, air dry, respectively. These assumptions probably influenced estimates of preweaning protein intake. The milk replacer was from one lot and probably did not vary greatly, but milk was from different cows and could have varied. Hence, estimates of CP intake are more precise postweaning than preweaning. Performance of calves during the postweaning period or over the 53-d experimental period suggests that protein intake did not limit growth in calves fed starter C or D. Maximum BW gains occurred with the starter diet that contained 19.6% CP in the DM, and no advantage was apparent from a diet of 22.4% protein content. Nitrogen intake may have been excessive in calves fed diet D. Nitrogen balance studies with starter diets ranging in CP from about 15% to about 22% of the DM showed that increased CP content >19.4% did not result in any further increase in N retention (15, 24), but fecal and urinary N excretion consistently increased (15). Results were similar

1887

when CP contents of starter DM ranged from 11.6 to 22.6% (24). Furthermore, Stobo and Roy (18) found no improvement in N retention when CP in starter DM was increased from 17.2 to 21.3%, but urinary N excretion almost doubled. These results are in general agreement with those of others (2, 10, 15, 20). In one study, Brown et al. (2) observed no improvement in BW gains, height at withers, and heart girth when calves were fed starters containing 13.5 to 26.6% CP in the DM from d 2 to 84 of life. Preston et al. (15) fed starters ranging from 16.4 to 21.7% CP in the DM, and found that BW gains were greatest with the starter containing 16.4% CP, but no differences were significant among treatments. Stobo et al. (20) fed starters containing 14.3, 18.7, or 24.2% CP to calves from 1 to 12 wk of age and observed no treatment effect on live BW gains, height at withers, and chest circumference. More recently, Luchini et al. (10) found no differences in BW at 84 d of age when calves were fed diets containing 19.3% CP from d 1 (weaning at 42 d of age), or 20.2% CP from d 1 or d 21 (weaning at 26 d of age), or 25.3% CP from d 21 (weaning at d 26 of age). Therefore, the evidence seems sufficient to indicate that the optimal amount of protein in calf starters to promote maximum growth of calves from birth to 8 to 12 wk of age is between 16.5 and 19.5% of the DM as long as starter consumption is adequate and starter formulation meets the energy requirements. Differences in amounts of undegradable protein consumed reflect differences in CP intake. More than 69 g/d did not appear to be beneficial in improving BW gain. Requirements for undegradable protein for calves of the ages used in this study are not given by NRC (14). For slightly older calves (3 to 6 mo), NRC (14) suggests higher undegradable intake protein than that fed in the present study. Schwartz et al. (21) concluded that NRC (14) undegradable intake protein values were too high for calves that were 3 to 6 mo of age. Because young calves are changing from preruminants to ruminants during the first 3 mo of life, determination of degradable and undegradable protein requirements is difficult. Quigley et al. (16) estimated that proportions of bacterial protein and dietary protein supplied to the small intestine were similar for Journal of Dairy Science Vol. 77, No. 7, 1994

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AKAYEZU ET AL.

calves at 2 wk postweaning and adult cows. Vasquez-Anon et al. (23) concluded that changes in degradability of protein in the rumen occurs rapidly after weaning. They used rumen-cannulated calves to determine disappearance of several protein feeds in the rumen at various times after weaning. Rates of degradation from the calf study were compared with in vitro values (obtained for the same feeds using a protease fiom Streptomyces griseus) and to in situ values obtained from adult cows. Vasquez-Anon (23) concluded that disappearance rates determined in cows or in vitro were not suitable for predicting rates of protein degradation in the rumens of calves. Hence, calculated and in situ values of undegradable protein for the starters used in this study may be suspect. Obviously, more work is needed in this area of protein nutrition for young ruminants. Mean live BW at 56 d of life were slightly lower than the guidelines suggested by Linn et al. (9) and the growth standards of herd replacements published by Heinrichs and Hargrove (6) or by Hoffman et d. (7) for calves of similar ages. Reasons for this result include possible differences in feeding management, experimental procedures, and genetic bases of the populations studied. Nevertheless, if 375 kg is considered to be the optimal BW of heifers at breeding (7) and if this BW is to be attained by 14 mo of age, then 2-mo-old calves with mean BW similar to those of calves fed diet A, B, and C in this study must gain at rates of 853, 844, and 839 g/d, respectively, fiom 2 to 14 mo of age. Similarly, if the target BW is to be attained by 15 mo of age, corresponding rates of gain are 787,779, and 774 g/d over the same period. These rates of gain are achievable under good management. However, several factors, such as DMI, palatability and energy content of starter diets, source and degradability of protein, and feeding management (restricted vs. ad libitum), may affect calf response to protein supplementation (4, 8, 12, 18, 20). CONCLUSIONS

In conclusion, current NRC recommendations (14) of 18% CP in the calf starter DM seems to be adequate for maximum growth of young calves. Calf starters containing higher Journal of Dairy Science Vol. 77, No. 7, 1994

amounts of protein offer no additional advantage, even when weaning occurs as early as 4 wk of life. Satisfactory growth of young calves fiom birth to 2 mo of age can be achieved by starters containing protein concentrations lower than the NRC (14) recommended level if DMI is adequate. This flexibility in protein level to achieve good calf growth should allow producers to adjust diet formulations to the most economic return with changing market prices. ACKNOWLEDGMENTS

Appreciation is extended to the dairy barn staffs at the WCES and SP for their cooperation and good calf care. The authors are grateful to G. D. Marx and H. Chester-Jones for help with the manuscript preparation. REFERENCES

1Association of Official Analytical Chemists. 1980. Official Methods of Analysis. 13th ed. AOAC, Washington. DC. 2Brown. L. D., C. A. Lassiter, J. P. Everett, D. M. Se& and J. W. Rust. 1958. Effect of protein level in calf starters on thc growth rate and metabolism of young calves. J. Dairy Sci. 41:1425. 3Crowley. J., N. Jorgensen, and T. Howard. 1983. Raising dauy replacements. North Central Reg. E t . Publ. 205. Univ. Wisconsin. Madison. 4 Gardner. R. W.1968. Digestible protein requirements of calves fed high energy rations ad libitum. J. Dairy Sci. 51:888. 5G0ering. H. K. and P. J. Van Soest. 1970. Forage Fiber Analyses (Apparatus, Reagents, Procedures,and Somt application^). AMC. Handbook NO.379. A R S USDA, Washington, DC. 6 Heinrichs, A. J., and G. L. Hargove. 1987. Standards of weight and height for Holstein heifers. J. Dairy Sci. 70653. 7 Hoffman, P. C., D. A. Funk, and T.D. Syverud. 1992. Growth ratts of Holstein replacement heifers in selected Wisconsin dairy herds. Res. Rep. R3551. Univ. Wisconsin, Madison. 8 Leibholz, J.. and H.S. Kang. 1973. The crude protein requirement of tbe early-weaned calf given urea, meat meal or soya bean meal with and without sulphur supplementation. Anim. Rod. 17:257. 9Linn. J. G., M. F. Hutjens, W.T. Howard, L. H. Kilmw, and D. E. otterby. 1989. Feeding the dairy herd. North Ceneal Reg. f i t . Publ. 346.Univ. Minnesota, St. Paul. lOLuchini, N. D., S. P.Lane. and D. K. Combs. 1991. Evaluation of stattcr diet aude protein level and feeding regimen for calves weaned at 26 days of age. J. Dairy Sci. 743949. 11 Mathers. J. C., and E. L. Miller. 1981. Quantitath studies of food protein degradation and the energetic efficiency of microbial protein synthesis in the rumen

PROTEIN IN CALF STARTER of sheep given chopped lucerne and rolled barley. Br. J. Nutr. 45587. 12 Morrill, J. L., and A. D. Dayton. 1978. Factors affecting requiremnt and use of crude protein in calf starter. J. Dairy Sci. 61:940. 13National Research Council. 1978. Nutrient Requirements of Dairy Cattle. 5th rev. ed. Natl. A d . Sci., Washington, DC. 14National Research C o d . 1989. Nutrient Requkments of Dairy Cattle. 6th rev. ed. Natl. A d . Sci., Washington, DC. 15 Preston, T. R., F. G.Whitelaw, N. A. WLeod, and E. B. Philip. 1965. The nutrition of the early-weaned calf. VIII. The effect on nitrogen e n t i o n of diets containing different amounts of fish meat. Mi. Rod. 753. 16Quigley. J. D.. ID, C. G. Schwab. and W. E. Hylton. 1985. Development of Nmcn function in calves: nahue of protein reaching the abomasum.1. Dairy Sci. 68:694. 17SASISTAfl User's Guide: Statistics, Version 6.03 Edition. 1988. SAS Inst. Inc.. Cary. NC. 18 Stobo, I.J.F.,and J.H.B. Roy. 1973. The protein nutrition of the ruminant calf.4. Nitrogen balance studies on rapidly gmwing calves given diets of different protein content. Br. J. Nutr. 30:113.

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19 Stobo, I.J.F., J.H.B. Roy, and H. J. Gaston. 1967. The protein nutrition of the ruminant calf. I. The effect of protein content of the concentrate mixture on the performance of calves weaned at an early age. Anim. Rod. 9:7. 2OStob0, I.J.F., J.H.B. Roy, and H. J. Gaston. 1967. The protein nutrition of the ruminant calf. 11. Further studies on the effect of protein content of the concentrate mixture on the performance of calves weaned at an early age. Anirn. Prod. 9:23. 21 Swartz, L. A., A. J. Heinrichs, G. A. Varga, and L. D. Muller. 1991. Effects of varying dietary undegradable protein on dry matter intake, growth, and carcass composition of Holstein calves. J. Dairy Sci. 74:3884. 22Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstrach polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583. 23 Vasquez-Anon, M.,A. J. Heinrichs, J. M.Aldrich, and G. A. Varga. 1993. Effect of postweaning age on rate of in situ protein disappearance in calves weaned at 5 weeks of age. J. Dairy Sci. 76:2749. 24Whitelaw. F. G.,T. R. Preston, and R. D. Ndumbe. 1961. The nutrition of the early-weaned calf. 1. The effect on nitrogen retention of diets containing different levels of groundnut meal. Anim. Prod. 3:121.

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