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Crude Protein for Diets Fed to Weaned Dairy Calves
The Professional Animal Scientist 24 (2008):596–603 ©2008 American Registry of Professional Animal Scientists
C rWeaned ude Protein for Diets Fed to Dairy Calves T. M. Hill,1 H. G. Bateman II, J. M. Aldrich, PAS, and R. L. Schlotterbeck Akey, Nutrition and Research Center, Lewisburg, OH 45338
ABSTRACT
INTRODUCTION
The concentration (as-fed basis) and source of protein in a diet for 4- to 12-wk-old weaned Holstein calves was evaluated. In Exp. 1, trial 1, 96 calves (8 wk old) were fed 1 of 4 diets containing 16% CP with soybean meal, 16% CP with soybean meal and modified expeller extracted soy protein, 18% CP with soybean meal, or 18% CP with soybean meal and modified expeller extracted soy protein, each blended with 5% hay in a 4-wk trial. There were no differences in performance because of CP concentration or source. In Exp. 1, trial 2, 96 calves (8 wk old) were fed either a 13.5, 15.0, 16.5, or 18.0% CP diet blended with 5% hay in a 4-wk trial. Calf ADG was maximized at 15% CP, whereas feed efficiency was maximized at 16.5% CP. In Exp. 2, 96 calves (4 wk old) were fed 1 of 2 diets arranged as 3 treatments in a 4-wk trial. The treatments were A) feeding a 16% CP diet for 4 wk, B) feeding an 18% CP diet for 2 wk followed by feeding a 16% diet for 2 wk, or C) feeding an 18% diet for 4 wk. No roughage was fed. Calf ADG tended to increase (4%) from treatments A through C. Diets for weaned calves should be 18% CP (63 g CP/Mcal ME) up to 8 wk old. Diets for calves from 8 to 12 wk old should be 15 to 16% CP (52 to 56 g CP/Mcal ME).
For calves less than 8 wk old, diets should contain between 17 and 18% CP when feeding either a conventional 20% CP or a moderate-accelerated 26% CP milk replacer or milk program (Akayezu et al., 1994; Hill et al., 2007). The dairy NRC (2001) suggests that energy, not protein, limits ADG in calves 55 to 100 kg BW receiving only a dry feed when the feed is greater than approximately 15% CP. Warner (1984) reviewed research published before 1984 and reported no advantage to using RUP sources in calf starter diets. In 6- to 12-wk-old weaned calves fed diets with 20 to 30% hay, Brown and Lassiter (1962) and Morrill and Dayton (1978) reported that the optimum CP concentration for a calf diet was between 11.7 and 15.4% CP. In 8- to 12-wk-old calves fed diets with 7.5% roughage, Veira et al. (1980) reported ADG and flow of nonammonia N to the abomasum increased as CP increased from 8 to 14%. Jahn and Chandler (1976) reported the ADG of calves from 8 to 20 wk old increased as dietary CP increased from 9 to 14.5% when the diets contained 11% ADF; however, ADG continued to increase as CP increased up to 17.5% when the diets contained 18 or 25% ADF. Jahn and Chandler (1976) noted that ADG was inversely related to ADF concentration of the diet. Zerbini and Polan (1985) compared soybean meal, cottonseed meal, corn
Key words: calf, crude protein, energy
1
Corresponding author: [email protected]
gluten meal, and fish meal as CP sources in 13.5% CP diets containing 26% hay for calves from 9 to 21 wk of age and observed no differences in ADG. However, Holtshausen and Crywagen (2000b) reported increased ADG in calves fed all concentrate diets from 12 to 20 wk old when a fish meal and corn gluten meal blend replaced sunflower meal in a 13% CP diet. The objectives of these experiments were to evaluate the performance of 4- to 12-wk-old weaned dairy calves fed diets with various concentrations (as-fed basis) and sources of CP that were equal in energy, minerals, and vitamins.
MATERIALS AND METHODS In Exp. 1, trial 1, 96 Holstein steer calves (2 blocks of 48 calves; 24 per treatment; 73 ± 3 kg; initially 8 wk old) were fed either a 16% CP diet based on soybean meal (16S), a 16% CP diet based on soybean meal and modified expeller-extracted soy protein (16SES; SoyPlus, West Central Soy, Ralston, IA), an 18% CP diet based on soybean meal (18S), or an 18% CP diet based on soybean meal and expeller soy (18SES; Table 1) in a 4-wk trial. The diets were formulated to have similar concentrations of DE, Ca, P, salt, Mg, added trace minerals, and added vitamins. These 4 diets were blended with 5% chopped grass hay and fed to the calves ad libitum with ad libitum water. These concentrations of CP were chosen for
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Table 1. Ingredient composition and analyzed nutrient composition of textured calf diets fed in each experiment1 Exp. 1, trial 1 Item Ingredient, % as fed Corn Oats Molasses Ingredients within pellet Soybean meal Wheat middlings Ca carbonate Fat Premix2 Dicalcium phosphate Salt Decoquinate3 Mg oxide SoyPlus4 Nutrient, % as fed DM CP Fat Ash Ca P
Exp. 1, trial 2
Exp. 2
13.5% CP 15.0% CP 16.5% CP 18.0% CP
16% CP 18% CP
16S
16SES
18S
18SES
45.00 25.00 3.00
45.00 25.00 3.00
37.00 25.00 3.00
37.00 25.00 3.00
52.00 25.00 3.00
48.00 25.00 3.00
44.00 25.00 3.00
40.00 25.00 3.00
45.00 25.00 3.00
37.00 25.00 3.00
17.59 4.76 1.38 0.89 0.75 0.91 0.60 0.05 0.07 0.00
3.83 4.10 1.36 0.09 0.75 0.84 0.60 0.05 0.07 15.31
21.75 8.64 1.46 0.99 0.75 0.72 0.60 0.05 0.04 0.00
4.73 7.83 1.44 0.00 0.75 0.63 0.60 0.05 0.03 18.94
13.30 4.11 0.71 0.40 0.75 0.63 0.60 0.05 0.07 0.00
16.80 4.01 0.74 0.40 0.75 0.61 0.60 0.05 0.06 0.00
20.60 4.20 0.77 0.40 0.75 0.58 0.60 0.05 0.05 0.00
24.10 4.71 0.80 0.40 0.75 0.55 0.60 0.05 0.04 0.00
17.59 4.76 1.38 0.89 0.75 0.91 0.60 0.05 0.07 0.00
21.75 8.64 1.46 0.99 0.75 0.72 0.60 0.05 0.04 0.00
86.8 16.0 4.0 5.3 0.84 0.55
87.3 16.3 4.3 5.1 0.80 0.53
87.1 18.1 4.0 5.2 0.86 0.56
87.6 18.2 4.2 5.0 0.82 0.54
87.9 13.6 3.5 4.7 0.63 0.49
87.9 15.0 3.5 4.9 0.64 0.46
88.0 16.4 3.4 5.1 0.66 0.47
88.0 18.1 3.4 5.3 0.67 0.49
88.3 16.2 3.8 5.5 0.85 0.53
88.0 18.4 4.0 5.7 0.82 0.51
1
Exp. 1, trial 1: diets contained 16 (16) or 18% (18) CP and either soybean meal (S) or soybean meal with modified expeller soy protein (SES); Exp. 1, trial 2: diets contained 13.5, 15.0, 16.5, or 18.0% CP; Exp. 2: diets contained 16 or 18% CP. Each diet was calculated from ingredient composition to be 3.3 Mcal DE/kg and 2.9 Mcal ME on an as-fed basis, based on NRC (2001).
2
Labeled concentrations were 0.04 g Se/kg, 800 kIU vitamin A/kg; Akey, Lewisburg, OH.
3
Concentration = 60 g/kg; Alpharma Inc., Fort Lee, NJ.
4
SoyPlus, West Central Soy, Ralston, IA.
evaluation based on reported optima for CP concentrations of diets fed to preweaned calves less than 8 wk old (Akayezu et al., 1994; Hill et al., 2006). The low treatment of 16% CP was below the optimum range of 17 to 18% CP, whereas the 18% CP treatment was within the range. The 2 CP sources were chosen because soybean meal is a commonly used ingredient that provides satisfactory ADG in calves, and the modified soy protein would allow for increased RUP and metabolizable protein without significantly altering the amino acid profile of the diet (Hill et al., 2006). The calves were housed in group pens (6 calves/pen) with pen space per calf of 5.5 m2 outside and 0.9 m2 inside for the 56-d trial. The inside pen space
was bedded with straw and there was no added heat. Calves were weighed, hip widths were measured, and body condition was scored initially and at the end of the trial (d 0 and 28). Feed offered and refused was weighed daily. Hip widths were made with a caliper. Calf BCS was based on a 1 to 5 system using 0.25 unit increments with 1 being emaciated and 5 being obese (Wildman et al., 1982). Scores were based on changes around the vertical and transverse processes of the spine as palpated by one experienced technician and ranged from 1.5 to 3.5. In Exp. 1, trial 2, 96 Holstein steer calves (2 blocks of 48 calves; 24 per treatment; 81 ± 2 kg; initially 8 wk old) were fed 1 of 4 diets (Table 2) that contained either 13.5, 15.0, 16.5,
or 18.0% CP in a 4-wk trial. The diets were formulated to have similar concentrations of DE, Ca, P, salt, Mg, added trace minerals, and added vitamins. These 4 diets were blended with 5% chopped grass hay and fed to the calves ad libitum with ad libitum water. Because there were no differences in ADG in trial 1 when 16 and 18% CP diet were fed, this wider range and lower minimum concentration of CP was evaluated. The calves were housed in group pens (6 calves per pen) and measurements were made as described in trial 1. Additionally, jugular vein blood samples were taken on d 0, 7, and 21 from 48 calves in 1 block. Serum was separated by centrifugation and analyzed for alkaline phosphatase (Tietz et al., 1983), creatinine (Whelton et al., 1994), glucose
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598
Table 2. Performance (28 d) of calves initially 8 wk old that were fed 4 diets containing either 16 (16) or 18% (18) CP and either soybean meal (S) or soybean meal with modified expeller soy protein (SES) in Exp. 1, trial 1 (as-fed basis) Item Pens, 6 calves/pen Initial BW, kg ADG, kg/d Intake, kg/d Feed efficiency CP intake, kg/d ME intake,2 Mcal/d g CP/Mcal ME consumed2 Initial hip width, cm Hip width change, cm Initial BCS3 BCS change3
16S
16SES
18S
18SES
SEM1
4 73.4 0.882 2.851 0.309 0.453 8.17 55.5 54.3 6.8 2.6 0.2
4 72.5 0.824 2.919 0.282 0.472 8.36 56.5 53.6 6.0 2.7 0.1
4 73.7 0.864 2.931 0.295 0.524 8.40 62.4 55.1 6.4 2.7 0.1
4 73.0 0.877 2.862 0.306 0.514 8.20 62.8 54.8 6.7 2.7 0.2
— 3.31 0.0293 0.2648 0.0334 0.0450 0.414 2.94 0.41 0.38 0.19 0.04
1
CP intake and g CP/Mcal ME consumed were greater for calves fed the 18% CP diets than for calves fed the 16% CP diets (P < 0.05); otherwise there were no differences (P > 0.05) for the main effects of CP concentration or source and there were no interactions (P > 0.05).
2
ME calculated as DE times 0.88 (NRC, 2001) for grower diet (2.9 Mcal/kg) and hay (2.1 Mcal/kg).
3
1 to 5 system with 1 = emaciated and 5 = obese.
(Kaplan, 1989), total protein (Weichselbaum, 1946), and urea N (Sampson et al., 1980). In Exp. 2, 96 Holstein steer calves (2 blocks of 48 calves; 36 per treat-
ment; 50 ± 1 kg; initially 4 wk old) were fed 1 of 2 diets (Table 3) arranged as 3 treatments in a 4-wk trial. The treatments were A) feeding the 16% CP diet 4 wk, B) feeding
the 18% CP diet for 2 wk followed by feeding the 16% diet for 2 wk, or C) feeding the 18% diet for 4 wk. The diets were formulated to have similar concentrations of DE, Ca, P, salt, Mg, added trace minerals, and added vitamins. The diets with fed to the calves ad libitum with ad libitum water. No roughage was fed. These treatments were selected because the optimum ADG was achieved with less than 18% CP diets in the 8- to 12-wk-old calves in Exp. 1. However, the optimum ADG was achieved with 17 to 18% diets in trials by Akayezu et al. (1994) and Hill et al. (2006) when feeding the test CP concentrations continuously from 0 to 8 wk of age. Thus, this trial was conducted to determine if and how soon after weaning calves could be changed to a lower CP diet. Calves were housed in 1.2 × 2.4 m individual pens bedded with straw in a curtain-sided, naturally ventilated barn with no added heat. Calves were weighed initially and weekly, and hip widths and body condition were scored initially, at wk 2, and at the end of the trial. Feed offered and refused was weighed daily. All trials used Holstein calves from a single dairy. The calves had been
Table 3. Performance (28 d) of calves initially 8 wk old that were fed 4 diets containing either 13.5, 15.0, 16.5, or 18.0% CP in Exp. 1, trial 2 (as-fed basis) CP, % as-fed Item Pens, 6 calves/pen Initial BW, kg ADG, kg/d Intake, kg/d Feed efficiency CP intake, kg/d ME intake,2 Mcal/d g CP/Mcal ME consumed2 Initial hip width, cm Hip width change, cm Initial BCS3 BCS change3
13.5
15.0
16.5
18.0
SEM
Quadratic1
4 80.9 0.998 3.073 0.325 0.418 8.80 47.4 22.5 2.0 2.7 0.2
4 78.9 1.093 3.062 0.357 0.457 8.77 52.1 22.3 2.2 2.7 0.2
4 79.1 1.113 3.034 0.367 0.493 8.69 56.7 22.0 2.2 2.7 0.3
4 83.2 1.111 3.172 0.350 0.567 9.09 62.4 22.6 2.2 2.8 0.2
— 2.14 0.0215 0.1037 0.0093 0.0169 0.308 1.85 0.06 0.07 0.06 0.09
— 0.78 0.02 0.62 0.03 0.01 0.69 0.01 0.38 0.04 0.59 0.43
P-value for the quadratic polynomial. The linear polynomial was also significant (P < 0.05) for each measurement that had a significant quadratic effect, but not for any other measurements. The cubic polynomial was not significant (P > 0.05).
1
2
ME calculated as DE times 0.88 (NRC, 2001) for grower diet (2.9 Mcal/kg) and hay (2.1 Mcal/kg).
3
1 to 5 system with 1 = emaciated and 5 = obese.
Crude protein for weaned dairy calves
fed 0.681 kg/d of a 26% CP, 17% fat milk replacer (Akey, Lewisburg, OH) and weaned at 4 wk. Calves also had been fed an 18% CP diet (similar to the 18% CP diet in Exp. 2; Table 1) and water ad libitum since 3 d of age. During this initial 4-wk period, calves were housed in 1.2 × 2.4 m individual pens bedded with straw in a curtain-sided, naturally ventilated barn with no added heat as in Exp. 2. Calves were castrated and dehorned at 3 wk of age. Vaccines and medical treatments were based on the recommendations of a veterinarian and described in Hill et al. (2006). All animals were cared for by acceptable practices as described in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999). Approximately 115% of the diets needed for each trial were made as one batch of feed in advance and samples were taken from every third bag (22.7 kg). Additionally, approximately 120% of the hay needed in Exp. 1 was set aside in advance of each trial and 2 samples were taken per bale (25 kg). Samples were composited and subsampled by treatment and analyzed (AOAC, 1996) for DM (oven method 930.15), CP (Kjeldahl method 988.05), fat (diethyl ether extraction, method 2003.05), ash (muffle furnace method 923.03), Ca and P (dry ashing, acid digestion, analysis by inductively coupled plasma spectroscopy, method 985.01). Additionally, the hay was tested for NDF with ash by the procedure of Van Soest et al. (1991) without sodium sulfite or α-amylase and for ADF with ash (Robertson and Van Soest, 1981). Experiment 1, trial 1 was analyzed as a randomized complete block (replication of trial) design using PROC MIXED of SAS (1999) as a 2 × 2 factorial arrangement of treatments. Concentration of CP (16 or 18%) was one factor and source of CP (soybean meal or soybean meal with modified expeller soy) was the other factor. Block and pen were random effects and concentration and source of CP were fixed effects. The experimental unit was pen.
Experiment 1, trial 2 was analyzed as a randomized complete block (replication of trial) design using the PROC MIXED of SAS. Block and pen were random effects and treatment was a fixed effect. Serum metabolite data were analyzed as repeated measures. Day was modeled as a repeated measurement using an autoregressive type 1 covariance structure. Measures from d 0 were included as a covariate for serum metabolites analyzed. When the overall F-test for treatment was significant (P < 0.05), linear, quadratic, and cubic contrasts were used to characterize the treatment means (concentrations of CP: 13.5, 15.0, 16.5, or 18.0%). The experimental unit was pen. Experiment 2 was analyzed as a randomized complete block (replication of trial) design using PROC MIXED of SAS. Block and pen were random effects and treatment was a fixed effect. The repeated measurements were modeled using an autoregressive type 1 covariance structure. The experimental unit was calf. When the overall F-test for treatment was significant (P < 0.05), a linear contrast to CP concentration in treatments (A lowest, B halfway intermediate, C greatest) and a contrast comparing treatment A with C were used to characterize the treatment means (A, B, C).
RESULTS AND DISCUSSION No initial measures of BW, hip width, or body condition were different among the treatment groups in the 2 experiments. No calves were treated for any sickness. No calves died or were removed from the experiments. In Exp. 1, trial 1, there were no differences in growth measures among the 4 treatments (Table 2). Hill et al. (2006) reported no differences in performance of calves from 0 to 8 wk old when fed 18% CP diets from these similar CP sources. Zerbini and Polan (1985) reported no differences in calf performance when they fed 9- to 21-wk-old calves 13.5% CP diets with 26% hay and compared soybean meal,
599 cottonseed meal, corn gluten meal, and fish meal as CP sources. However, when Holtshausen and Crywagen (2000b) fed all concentrate diets with 13% CP to 12- to 20-wk-old calves, they reported greater ADG in calves fed diets with a fish meal and corn gluten meal blend (high RUP) vs. sunflower meal (high RDP). The review of Warner (1984) reported no advantage to using RUP sources in calf starter diets. Likewise, a review of data published since 1984 by Hill et al. (2006) found that the performance of calves in trials fed soybean meal were typically equal to or greater than those fed other sources of CP and that there were mixed results with feeding sources of CP high in RUP. The lack of complete development of the rumen and its microbial population in preweaned calves may explain why there are no conclusive benefits to formulating starter diets with greater RUP or metabolizable protein concentrations. The RUP fraction of the CP source appears to decline with age of the young calf. Vazquez-Anon et al. (1993) estimated the RUP of the soybean meal to change from 58% at 2 wk postweaning to 31% by 8 wk postweaning. They also estimated the RUP of SoyPlus to change from 71% at 2 wk postweaning to 51% by 8 wk postweaning. Holtshausen and Crywagen (2000a) reported similar changes in feed degradation in the rumen with calf age. In Exp. 1, trial 2, calf ADG, feed efficiency, hip width change, and urea N responded quadratically (P < 0.05) to concentration of CP in the diet (Tables 3 and 4). Calves fed the diet with 13.5% CP had the lowest ADG (−9%), feed efficiency (−9%), and hip width change, indicating that 13.5% CP in the diet was deficient in CP. Whereas ADG appeared to plateau at 15% CP, feed efficiency appeared to plateau closer to 16.5% CP. Urea N appeared to increase from its lowest concentration in calves fed the 13.5% CP diet and to change its rate of increase in calves fed the diets with 16.5 and 18.0% CP. Serum concentrations of alkaline phosphatase, creatinine, glucose, and total protein did not
600
Hill et al.
Table 4. Selected serum constituents of calves initially 8 wk old that were fed 4 diets containing either 13.5, 15.0, 16.5, or 18.0% CP in Exp. 1, trial 2 (as-fed basis) CP, % as fed Item
13.5
15.0
16.5
18.0
SEM
Quadratic1
Urea nitrogen, mmol/L Creatinine, µmol/L Total protein, mmol/L Alkaline phosphatase, U/L Alanine aminotransferase, U/L Glucose, mmol/L
1.0 71.6 72.5 247 13.7 4.9
2.1 62.1 71.4 209 15.1 4.8
3.1 58.2 72.0 205 13.8 4.9
3.3 58.5 74.3 205 14.7 5.1
0.20 4.07 2.40 42.3 1.13 0.42
0.03 0.19 0.31 0.53 0.29 0.72
P-value for the quadratic polynomial. The linear polynomial was also significant (P < 0.05) for urea nitrogen, but not for any other measurements. The cubic polynomial was not significant (P > 0.05).
1
differ (P > 0.05) among treatments. The serum urea N and feed efficiency responses indicate that the diet with 15.0% was deficient in CP, but the 16.5% CP diet was adequate. The growth and urea N results of Exp. 1, trial 2 suggest the optimum CP concentration in the diet is between 15.0 and 16.5%. This is at the high range of work by Brown and Lassiter (1962) and Morrill and Dayton (1978), who reported the optimum concentration of 10.5 to 15% CP for 6- to 12-wk-old calves fed diets with 20 to 30% forage. In 8- to 12-wk-old calves fed diets with 7.5% roughage, Veira et al. (1980) reported ADG and flow of nonammonia N to the abomasum to increase as CP increased from 8 to 14%, but no plateau appeared. Jahn and Chandler (1976) reported the ADG of calves from 8 to 20 wk old to increase as dietary CP increased from 9 to 14.5% when the diets contained 11% ADF; however, ADG continued to increase as dietary CP increased up to 17.5% CP when the diets contained 18 or 25% ADF. However, in their study ADG was inversely related to ADF concentration of the diet. The data of Jahn and Chandler (1976) appear to disagree with those of Brown and Lassiter (1962) and Morrill and Dayton (1978) who fed high fiber diets and found the range of 10.5 to 15% CP to be the optimum. However, the data of Jahn and Chandler (1976) agree more with the data from trial 2 that showed the calves fed the 13.5% CP diet had
lower ADG and feed efficiency that calves fed the greater CP diets. In Exp. 2, ADG tended (P < 0.07) to increase linearly from treatment A (feeding the 16% CP diet 4 wk), to treatment B (feeding the 18% CP diet for 2 wk then feeding the 16% diet for 2 wk), to treatment C (feeding the 18% diet for 4 wk) in the 4- to 8-wk-old calves (Table 5). Research by Akayezu et al. (1994) and Hill et al. (2006) has shown that 17 to 18% is correct for the diet consumed by the 0- to 8-wk-old calf. The attempt in Exp. 2 to determine how soon calves that were fed an 18% CP diet could be switched to a 16% CP diet showed that 8 wk is likely the correct time. However, because the difference in ADG tended to be small (4%), switching calves sooner should not be a major risk to performance. Some general management recommendations provided to producers suggest not making diet changes around weaning (wk 4 in Exp. 2), a major time of stress to the calf. The calves (4 to 8 wk old, 62 kg average BW) fed by Akayezu et al. (1994) had similar postweaning (d 30 to 56) intake (1.51 kg starter diet/d, 0.263 kg CP/d, 4.44 Mcal ME/d, 59.2 g CP/Mcal ME) as the calves (4 to 8 wk old, 60 kg average BW) in Exp. 2 (1.63 kg starter diet/d, 0.284 kg CP/d, 4.49 Mcal ME/d, 63.4 g CP/ Mcal ME; Table 6). No roughage diets of similar ingredient and nutrient composition were fed in both trials. Because ADG was maximized with
the 17.4% CP diet fed by Akayezu et al. (1994), their diet was 59.2 g CP/ Mcal ME compared with the 63.4 g CP/Mcal ME in the 18% CP diet fed in Exp. 2. Otherwise, these 2 trials yielded similar results. In Exp. 1, trial 2, the maximal ADG was between the 15.0 and 16.5% CP treatments, which supplied 0.457 and 0.493 kg CP/d, respectively. The numeric difference in ADG between these treatments was only 0.020 kg/d (1.093 and 1.113 kg/d), whereas the difference in ADG between the 13.5 and 15.0% CP treatments was large (0.095 kg/d). This suggests that the requirement is likely closer to the 15.0% CP treatment that provided 0.457 kg CP/d than the 16.5% CP treatment, based on the response in ADG. Using NRC (2001) estimates, approximately 0.038 kg of CP is needed to support 0.100 kg of ADG above maintenance in the 95-kg-BW calf. These amounts are similar to difference in CP intake (0.039 kg CP/d) and ADG (0.095 kg/d) observed between calves fed the 14.5 and 15.0% CP treatments. Estimates from NRC (2001) suggest the 95-kg-BW calf requires approximately 0.500 kg of CP/d to support 1.1 kg of ADG. Calves fed the 15.0% CP treatment gained 1.093 kg BW/d when consuming 0.457 kg CP/d, or approximately 0.043 kg less/d than suggested by NRC (2001). Using feed efficiency or serum urea N data, the diet with 16.5% CP and supplying 0.493 kg CP/d appeared closer to
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Table 5. Performance (28 d) of A) feeding the 16% CP diet 4 wk, B) feeding the 18% CP diet for 2 wk and then feeding the 16% diet for 2 wk, or C) feeding the 18% diet for 4 wk to calves in Exp. 2 (as-fed basis) Item
A) 16%
B) 18%, then 16%
C) 18%
SEM
Linear1
Calves, n Initial BW, kg ADG, kg/d Intake, kg/d Feed efficiency CP intake, kg/d ME intake,2 Mcal/d g CP/Mcal ME consumed2 Initial hip width, cm Hip width change, cm Initial BCS3 BCS change3
24 50.2 0.635 1.611 0.394 0.248 4.44 55.8 18.4 2.0 2.3 0.2
24 48.3 0.651 1.572 0.416 0.258 4.34 59.6 18.1 1.9 2.3 0.3
24 50.5 0.661 1.627 0.406 0.284 4.49 63.4 18.3 2.1 2.3 0.2
— 0.84 0.0261 0.0634 0.0084 0.0106 0.178 2.38 0.14 0.09 0.03 0.03
— 0.33 0.07a 0.73 0.57 0.01 0.92 0.01 0.32 0.66 0.54 0.30
1
The P-value for the linear polynomial was P = 0.07. Other linear polynomials and the contrast constructed to compare treatments A to C for all of the different measurements were not significant (P > 0.05).
2
ME calculated as DE times 0.88 (NRC, 2001) for starter diet (2.9 Mcal/kg) and hay (2.1 Mcal/kg).
3
1 to 5 system with 1 = emaciated and 5 = obese.
optimum and more similar to estimates from NRC (2001). Brown and Lassiter (1962) and Schurman and Kesler (1974) reported 68- to 70-kg calves gaining 0.92 to 0.96 kg BW/d consumed 0.356 to 0.430 kg CP/d. These calves weighed less and were consuming 25 to 28% roughage diets compared with the calves in Exp. 1. Conversely, Veira et al. (1980) reported that heavier (131 kg BW) calves with faster ADG (1.22 kg/d) than the calves in Exp. 1 consumed 0.651 kg CP/d. In Exp. 1, trial 2, the optimum ADG was between 15 and 16.5% CP, which corresponded to 52.1 to 56.7 g CP/Mcal ME (Table 6). In Exp. 1, trial 1, the 16% CP diets were 55.5 and 56.5 g CP/Mcal ME. Schurman and Kessler (1974) fed 10.0, 12.6, and 22.8% CP diets and observed the best ADG with the 12.6 and 22.8% CP diets. The 12.6% CP diet contained 28% hay and was estimated to be 49 g CP/Mcal ME. The 14.2% CP, 7.5% roughage diet fed to 131-kg-BW calves in the Veira et al. (1980) trial that supported the maximum ADG had a 51.8 g CP/Mcal ME ratio. The 14% CP diet treatments that optimized ADG and fed by Brown and Lassiter (1962) and Morrill and Day-
ton (1978) contained 20 to 25% alfalfa hay and 54 to 56 g CP/Mcal ME. Gabler and Heinrichs (2003) fed 150-kgBW calves 60% roughage diets and observed the best numeric ADG and feed efficiency with a 59.1 g CP/Mcal ME ratio. Jahn and Chandler (1975) reported the best ADG in calves fed their lowest roughage diet (ADG declined as roughage increased), and that treatment was 14.5% CP and 57.1 g CP/Mcal ME. They also reported that with the higher roughage diets, ADG was maximized with more CP (17.5% CP) and a greater CP to ME ratio (75 to 82 g CP/Mcal ME) and attributed this to a need for more RDP. Concentration of roughage may explain why the older, heavier calves fed the 60% roughage diet by Gabler and Heinrichs (2003) appeared to require a greater CP to ME ratio diet than in other reports (Schurman and Kesler, 1974; Veira et al., 1980) and in Exp. 1. In the 5% roughage diets fed to 8- to 12-wk-old, 85- to 95-kgBW calves in Exp. 1, a 52 g CP/Mcal ME (at 15% CP in the diet) to 56 g CP/Mcal ME ratio (at 16% CP in the diet) appeared optimum. The younger 4- to 8-wk-old, 60-kg-BW calves in Exp. 2 appeared to need a greater ratio (63 g CP/Mcal ME).
Although beyond the scope of these trials, the calf submodel in the NRC (2001) was used to predict ME and CP limiting ADG at ambient and thermoneutral temperatures for calves fed the optimum diets in Exp. 1 and 2 (Table 6). In each experiment, actual ADG greatly exceeded predicted ADG using ambient temperatures, especially in Exp. 1 where the ambient temperatures were low (−2 and 4°C). Predicted ADG at 20°C (thermoneutral temperature) was limited by ME in Exp. 1 and 2. However, in the trials selected from the literature only 20°C was used to predict ADG because ambient temperatures were not provided in the references. In the trials selected from the literature, predicted ADG from ME intake was not always limiting to CP intake, as in Exp. 1 and 2. Across Exp. 1 and 2 and the trials selected from the literature, predicted ADG using 20°C was not consistent with actual ADG.
IMPLICATIONS The literature reports the neonatal dairy calf fed milk or milk replacer should be fed an 18% CP diet (as fed). Current results suggest that the weaned calf should remain on an 18%
8 94 5.0 15.0 2.86 52.1 3.06 0.457 8.77 1.09
0.95 0.99 4
0.72
8 85 5.0 16.2 2.86 56.0 2.89 0.463 8.27 0.85
0.94 1.04 −2
0.64
0.70
0.94 1.10 4
8 95 5.0 16.4 2.86 56.7 3.03 0.493 8.69 1.11
0.56
0.56 0.65 20
4 60 0.0 18.4 2.90 63.4 1.63 0.284 4.49 0.66
18% CP
Trial 1, average Trial 2, Trial 2, of 16S, 16SES2 15.0% CP 16.5% CP
—
0.50 0.53 —
4 62 0.0 17.4 2.94 59.2 1.51 0.263 4.44 0.86
—
1.15 1.10 —
8 64 16.6 14.5 2.54 57.1 3.31 0.480 8.41 0.97
—
0.89 0.99 —
6 68 25.0 14.4 2.6 55.4 2.80 0.356 6.42 0.96
Akayezu et Jahn and Brown and al., 1994 Chandler, 1975 Lassiter, 1962
—
— — —
6 — 20.0 14.2 2.63 54.0 2.52 0.358 6.60 0.96
—
1.14 0.94 —
8 70 28.0 12.6 2.56 49.2 3.41 0.430 8.73 0.92
—
— — —
9 to 12 131 7.5 14.2 2.74 51.8 4.58 0.651 12.55 1.22
Morrill and Schurman and Veira et al., Dayton, 1978 Kesler, 1974 1980
2
Exp. 1, trial 1: diets contained 16 (16) or 18% (18) CP and either soybean meal (S) or soybean meal with modified expeller soy protein (SES).
Diet ME and predicted ADG were estimated using the NRC (2001) calf submodel. Predicted ADG were made at both thermoneutral (20°C input) and average ambient temperatures. Ambient temperatures were not reported in the trials selected from the literature. Predictions could not be made for the trial of Veira et al. (1980) because the BW exceeded 100 kg, the maximum BW allowed in the NRC calf submodel.
1
Initial age, wk Avg BW, kg Diet roughage, % Diet CP, % Diet ME, Mcal/kg g CP/Mcal ME Intake, kg/d CP intake, kg/d ME intake, Mcal/d ADG, kg/d Predicted ADG at 20°C (thermoneutral) ME supported, kg/d CP supported, kg/d Temperature, °C Predicted ME supported ADG at ambient temperature, kg/d
Item
Exp. 2
Exp. 1
Table 6. Calf and diet descriptions with measured and predicted ADG from the optimum diets in Exp. 1 and 2 and selected trials in the literature1 (as-fed basis)
602 Hill et al.
Crude protein for weaned dairy calves
CP diet with approximately 63 g CP/ Mcal ME until 8 wk old. Additionally, the 8- to 12-wk-old, 95-kg-BW calf fed 5% hay should be fed a 15% CP diet with approximately 52 g CP/ Mcal ME to optimize ADG, or a 16% CP diet with approximately 56 g CP/ Mcal ME to optimize feed efficiency.
LITERATURE CITED Akayezu, J. M., J. G. Linn, D. E. Otterby, W. P. Hansen, and D. G. Johnson. 1994. Evaluation of calf starters containing different amounts of crude protein for growth of Holstein calves. J. Dairy Sci. 77:1882. AOAC. 1996. Official Methods of Analysis. Vol. I 16th ed. Assoc. Off. Anal. Chem., Arlington, VA. Brown, L. D., and C. A. Lassiter. 1962. Protein-energy ratios for dairy calves. J. Dairy Sci. 45:1353. FASS. 1999. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. 1st rev. ed. Fed. Anim. Sci. Soc., Savoy, IL. Gabler, M. T., and A. J. Heinrichs. 2003. Dietary protein to metabolizable energy ratios on feed efficiency and structural growth of prepubertal Holstein heifers. J. Dairy Sci. 86:268. Hill, T. M., J. M. Aldrich, R. L. Schlotterbeck, and H. G. Bateman II. 2007. Protein concentration for starters fed to transported neonatal calves. Prof. Anim. Sci. 23:123. Holtshausen, L., and C. W. Crywagen. 2000a. The effect of dietary rumen degradable protein content on veal calf performance. S. Afr. J. Anim. Sci. 30:204.
Holtshausen, L., and C. W. Crywagen. 2000b. The effect of age on in sacco estimates of rumen dry matter and crude protein degradability in real calves. S. Afr. J. Anim. Sci. 30:212. Jahn, E., and P. T. Chandler. 1976. Performance and nutrient requirements of calves fed varying percentages of protein and fiber. J. Anim. Sci. 42:724. Kaplan, L. A. 1989. Glucose. p. 850 in Clinical Chemistry: Theory, Analysis, and Correlation. 2nd ed. L. A. Kaplan and A. J. Pesce, ed. C.V. Mosby Co., St. Louis, MO. Morrill, J. L., and A. D. Dayton. 1978. Factors affecting requirement and use of crude protein in calf starter. J. Dairy Sci. 61:940. NRC. 2001. Nutrient Requirements of Dairy Cattle. 7th ed. Natl. Acad. Press, Washington, DC. Robertson, J. B., and P. J. Van Soest. 1981. The detergent system of analysis and its application to human foods. p. 123 in The Analysis of Dietary Fiber in Food. W. P. T. James and O. Theander, ed. Marcel Dekker, New York, NY. Sampson, E. J., M. A. Baird, C. A. Burtis, E. M. Smith, D. L. Witte, and D. D. Bayse. 1980. A coupled-enzyme equilibrium method for measuring urea in serum: optimization and evaluation of the AACC study group on urea candidate reference method. Clin. Chem. 26:816. SAS. 1999. SAS Users’ Guide. Version 8 ed. SAS Inst. Inc., Cary, NC. Schurman, E. W., and E. M. Kesler. 1974. Protein-to-energy ratios in complete feeds for calves at ages 8 to 18 weeks. J. Dairy Sci. 57:1381. Tietz, N. W., C. A. Burtis, P. Duncan, K. Ervin, C. J. Petitclerc, A. D. Rinker, D. Shuey, and E. R. Zygowicz. 1983. A reference method for measurement of alkaline
603 phosphatase activity in human serum. Clin. Chem. 29:751. Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, non-starch polysaccharides in relation to animal nutrition. Symposium: carbohydrate methodology, metabolism and nutritional implications in dairy cattle. J. Dairy Sci. 74:3583. Vazquez-Anon, M., A. J. Heinrichs, J. M. Aldrich, and G. A. Varga. 1993. Effect of post-weaning age on rate of in situ protein disappearance in calves weaned at 5 weeks of age. J. Dairy Sci. 76:2749. Veira, D. M., G. K. Macleod, J. H. Burton, and J. B. Stone. 1980. Nutrition of the weaned Holstein calf. II. Effect of dietary protein level on nitrogen balance, digestibility, and feed intake. J. Anim. Sci. 50:945. Warner, R. G. 1984. The impact of protein solubility in dairy calf starters. p. 42 in Proc. Cornell Nutr. Conf. Feed Manufacturers. Rochester, NY. Weichselbaum, T. E. 1946. An accurate and rapid method for the determination of proteins in small amounts of blood serum and plasma. Am. J. Clin. Pathol. 16:40. Whelton, A. A., J. Watson, and R. C. Rock. 1994. Nitrogen metabolites and renal function. p. 1513 in Tietz Textbook of Clinical Chemistry. 2nd ed. C. A. Burtis and E. R. Ashwood, ed. W. B. Saunders Co., Philadelphia, PA. Wildman, E. E., G. M. Jones, P. E. Wagner, R. L. Bowman, H. F. Troutt Jr, and T. N. Lesch. 1982. A diary cow body condition scoring system and its relationship to selected production characteristics. J. Dairy Sci. 65:495. Zerbini, E., and C. E. Polan. 1985. Protein sources evaluated for ruminating calves. J. Dairy Sci. 68:1416.
C rWeaned ude Protein for Diets Fed to Dairy Calves T. M. Hill,1 H. G. Bateman II, J. M. Aldrich, PAS, and R. L. Schlotterbeck Akey, Nutrition and Research Center, Lewisburg, OH 45338
ABSTRACT
INTRODUCTION
The concentration (as-fed basis) and source of protein in a diet for 4- to 12-wk-old weaned Holstein calves was evaluated. In Exp. 1, trial 1, 96 calves (8 wk old) were fed 1 of 4 diets containing 16% CP with soybean meal, 16% CP with soybean meal and modified expeller extracted soy protein, 18% CP with soybean meal, or 18% CP with soybean meal and modified expeller extracted soy protein, each blended with 5% hay in a 4-wk trial. There were no differences in performance because of CP concentration or source. In Exp. 1, trial 2, 96 calves (8 wk old) were fed either a 13.5, 15.0, 16.5, or 18.0% CP diet blended with 5% hay in a 4-wk trial. Calf ADG was maximized at 15% CP, whereas feed efficiency was maximized at 16.5% CP. In Exp. 2, 96 calves (4 wk old) were fed 1 of 2 diets arranged as 3 treatments in a 4-wk trial. The treatments were A) feeding a 16% CP diet for 4 wk, B) feeding an 18% CP diet for 2 wk followed by feeding a 16% diet for 2 wk, or C) feeding an 18% diet for 4 wk. No roughage was fed. Calf ADG tended to increase (4%) from treatments A through C. Diets for weaned calves should be 18% CP (63 g CP/Mcal ME) up to 8 wk old. Diets for calves from 8 to 12 wk old should be 15 to 16% CP (52 to 56 g CP/Mcal ME).
For calves less than 8 wk old, diets should contain between 17 and 18% CP when feeding either a conventional 20% CP or a moderate-accelerated 26% CP milk replacer or milk program (Akayezu et al., 1994; Hill et al., 2007). The dairy NRC (2001) suggests that energy, not protein, limits ADG in calves 55 to 100 kg BW receiving only a dry feed when the feed is greater than approximately 15% CP. Warner (1984) reviewed research published before 1984 and reported no advantage to using RUP sources in calf starter diets. In 6- to 12-wk-old weaned calves fed diets with 20 to 30% hay, Brown and Lassiter (1962) and Morrill and Dayton (1978) reported that the optimum CP concentration for a calf diet was between 11.7 and 15.4% CP. In 8- to 12-wk-old calves fed diets with 7.5% roughage, Veira et al. (1980) reported ADG and flow of nonammonia N to the abomasum increased as CP increased from 8 to 14%. Jahn and Chandler (1976) reported the ADG of calves from 8 to 20 wk old increased as dietary CP increased from 9 to 14.5% when the diets contained 11% ADF; however, ADG continued to increase as CP increased up to 17.5% when the diets contained 18 or 25% ADF. Jahn and Chandler (1976) noted that ADG was inversely related to ADF concentration of the diet. Zerbini and Polan (1985) compared soybean meal, cottonseed meal, corn
Key words: calf, crude protein, energy
1
Corresponding author: [email protected]
gluten meal, and fish meal as CP sources in 13.5% CP diets containing 26% hay for calves from 9 to 21 wk of age and observed no differences in ADG. However, Holtshausen and Crywagen (2000b) reported increased ADG in calves fed all concentrate diets from 12 to 20 wk old when a fish meal and corn gluten meal blend replaced sunflower meal in a 13% CP diet. The objectives of these experiments were to evaluate the performance of 4- to 12-wk-old weaned dairy calves fed diets with various concentrations (as-fed basis) and sources of CP that were equal in energy, minerals, and vitamins.
MATERIALS AND METHODS In Exp. 1, trial 1, 96 Holstein steer calves (2 blocks of 48 calves; 24 per treatment; 73 ± 3 kg; initially 8 wk old) were fed either a 16% CP diet based on soybean meal (16S), a 16% CP diet based on soybean meal and modified expeller-extracted soy protein (16SES; SoyPlus, West Central Soy, Ralston, IA), an 18% CP diet based on soybean meal (18S), or an 18% CP diet based on soybean meal and expeller soy (18SES; Table 1) in a 4-wk trial. The diets were formulated to have similar concentrations of DE, Ca, P, salt, Mg, added trace minerals, and added vitamins. These 4 diets were blended with 5% chopped grass hay and fed to the calves ad libitum with ad libitum water. These concentrations of CP were chosen for
Crude protein for weaned dairy calves
597
Table 1. Ingredient composition and analyzed nutrient composition of textured calf diets fed in each experiment1 Exp. 1, trial 1 Item Ingredient, % as fed Corn Oats Molasses Ingredients within pellet Soybean meal Wheat middlings Ca carbonate Fat Premix2 Dicalcium phosphate Salt Decoquinate3 Mg oxide SoyPlus4 Nutrient, % as fed DM CP Fat Ash Ca P
Exp. 1, trial 2
Exp. 2
13.5% CP 15.0% CP 16.5% CP 18.0% CP
16% CP 18% CP
16S
16SES
18S
18SES
45.00 25.00 3.00
45.00 25.00 3.00
37.00 25.00 3.00
37.00 25.00 3.00
52.00 25.00 3.00
48.00 25.00 3.00
44.00 25.00 3.00
40.00 25.00 3.00
45.00 25.00 3.00
37.00 25.00 3.00
17.59 4.76 1.38 0.89 0.75 0.91 0.60 0.05 0.07 0.00
3.83 4.10 1.36 0.09 0.75 0.84 0.60 0.05 0.07 15.31
21.75 8.64 1.46 0.99 0.75 0.72 0.60 0.05 0.04 0.00
4.73 7.83 1.44 0.00 0.75 0.63 0.60 0.05 0.03 18.94
13.30 4.11 0.71 0.40 0.75 0.63 0.60 0.05 0.07 0.00
16.80 4.01 0.74 0.40 0.75 0.61 0.60 0.05 0.06 0.00
20.60 4.20 0.77 0.40 0.75 0.58 0.60 0.05 0.05 0.00
24.10 4.71 0.80 0.40 0.75 0.55 0.60 0.05 0.04 0.00
17.59 4.76 1.38 0.89 0.75 0.91 0.60 0.05 0.07 0.00
21.75 8.64 1.46 0.99 0.75 0.72 0.60 0.05 0.04 0.00
86.8 16.0 4.0 5.3 0.84 0.55
87.3 16.3 4.3 5.1 0.80 0.53
87.1 18.1 4.0 5.2 0.86 0.56
87.6 18.2 4.2 5.0 0.82 0.54
87.9 13.6 3.5 4.7 0.63 0.49
87.9 15.0 3.5 4.9 0.64 0.46
88.0 16.4 3.4 5.1 0.66 0.47
88.0 18.1 3.4 5.3 0.67 0.49
88.3 16.2 3.8 5.5 0.85 0.53
88.0 18.4 4.0 5.7 0.82 0.51
1
Exp. 1, trial 1: diets contained 16 (16) or 18% (18) CP and either soybean meal (S) or soybean meal with modified expeller soy protein (SES); Exp. 1, trial 2: diets contained 13.5, 15.0, 16.5, or 18.0% CP; Exp. 2: diets contained 16 or 18% CP. Each diet was calculated from ingredient composition to be 3.3 Mcal DE/kg and 2.9 Mcal ME on an as-fed basis, based on NRC (2001).
2
Labeled concentrations were 0.04 g Se/kg, 800 kIU vitamin A/kg; Akey, Lewisburg, OH.
3
Concentration = 60 g/kg; Alpharma Inc., Fort Lee, NJ.
4
SoyPlus, West Central Soy, Ralston, IA.
evaluation based on reported optima for CP concentrations of diets fed to preweaned calves less than 8 wk old (Akayezu et al., 1994; Hill et al., 2006). The low treatment of 16% CP was below the optimum range of 17 to 18% CP, whereas the 18% CP treatment was within the range. The 2 CP sources were chosen because soybean meal is a commonly used ingredient that provides satisfactory ADG in calves, and the modified soy protein would allow for increased RUP and metabolizable protein without significantly altering the amino acid profile of the diet (Hill et al., 2006). The calves were housed in group pens (6 calves/pen) with pen space per calf of 5.5 m2 outside and 0.9 m2 inside for the 56-d trial. The inside pen space
was bedded with straw and there was no added heat. Calves were weighed, hip widths were measured, and body condition was scored initially and at the end of the trial (d 0 and 28). Feed offered and refused was weighed daily. Hip widths were made with a caliper. Calf BCS was based on a 1 to 5 system using 0.25 unit increments with 1 being emaciated and 5 being obese (Wildman et al., 1982). Scores were based on changes around the vertical and transverse processes of the spine as palpated by one experienced technician and ranged from 1.5 to 3.5. In Exp. 1, trial 2, 96 Holstein steer calves (2 blocks of 48 calves; 24 per treatment; 81 ± 2 kg; initially 8 wk old) were fed 1 of 4 diets (Table 2) that contained either 13.5, 15.0, 16.5,
or 18.0% CP in a 4-wk trial. The diets were formulated to have similar concentrations of DE, Ca, P, salt, Mg, added trace minerals, and added vitamins. These 4 diets were blended with 5% chopped grass hay and fed to the calves ad libitum with ad libitum water. Because there were no differences in ADG in trial 1 when 16 and 18% CP diet were fed, this wider range and lower minimum concentration of CP was evaluated. The calves were housed in group pens (6 calves per pen) and measurements were made as described in trial 1. Additionally, jugular vein blood samples were taken on d 0, 7, and 21 from 48 calves in 1 block. Serum was separated by centrifugation and analyzed for alkaline phosphatase (Tietz et al., 1983), creatinine (Whelton et al., 1994), glucose
Hill et al.
598
Table 2. Performance (28 d) of calves initially 8 wk old that were fed 4 diets containing either 16 (16) or 18% (18) CP and either soybean meal (S) or soybean meal with modified expeller soy protein (SES) in Exp. 1, trial 1 (as-fed basis) Item Pens, 6 calves/pen Initial BW, kg ADG, kg/d Intake, kg/d Feed efficiency CP intake, kg/d ME intake,2 Mcal/d g CP/Mcal ME consumed2 Initial hip width, cm Hip width change, cm Initial BCS3 BCS change3
16S
16SES
18S
18SES
SEM1
4 73.4 0.882 2.851 0.309 0.453 8.17 55.5 54.3 6.8 2.6 0.2
4 72.5 0.824 2.919 0.282 0.472 8.36 56.5 53.6 6.0 2.7 0.1
4 73.7 0.864 2.931 0.295 0.524 8.40 62.4 55.1 6.4 2.7 0.1
4 73.0 0.877 2.862 0.306 0.514 8.20 62.8 54.8 6.7 2.7 0.2
— 3.31 0.0293 0.2648 0.0334 0.0450 0.414 2.94 0.41 0.38 0.19 0.04
1
CP intake and g CP/Mcal ME consumed were greater for calves fed the 18% CP diets than for calves fed the 16% CP diets (P < 0.05); otherwise there were no differences (P > 0.05) for the main effects of CP concentration or source and there were no interactions (P > 0.05).
2
ME calculated as DE times 0.88 (NRC, 2001) for grower diet (2.9 Mcal/kg) and hay (2.1 Mcal/kg).
3
1 to 5 system with 1 = emaciated and 5 = obese.
(Kaplan, 1989), total protein (Weichselbaum, 1946), and urea N (Sampson et al., 1980). In Exp. 2, 96 Holstein steer calves (2 blocks of 48 calves; 36 per treat-
ment; 50 ± 1 kg; initially 4 wk old) were fed 1 of 2 diets (Table 3) arranged as 3 treatments in a 4-wk trial. The treatments were A) feeding the 16% CP diet 4 wk, B) feeding
the 18% CP diet for 2 wk followed by feeding the 16% diet for 2 wk, or C) feeding the 18% diet for 4 wk. The diets were formulated to have similar concentrations of DE, Ca, P, salt, Mg, added trace minerals, and added vitamins. The diets with fed to the calves ad libitum with ad libitum water. No roughage was fed. These treatments were selected because the optimum ADG was achieved with less than 18% CP diets in the 8- to 12-wk-old calves in Exp. 1. However, the optimum ADG was achieved with 17 to 18% diets in trials by Akayezu et al. (1994) and Hill et al. (2006) when feeding the test CP concentrations continuously from 0 to 8 wk of age. Thus, this trial was conducted to determine if and how soon after weaning calves could be changed to a lower CP diet. Calves were housed in 1.2 × 2.4 m individual pens bedded with straw in a curtain-sided, naturally ventilated barn with no added heat. Calves were weighed initially and weekly, and hip widths and body condition were scored initially, at wk 2, and at the end of the trial. Feed offered and refused was weighed daily. All trials used Holstein calves from a single dairy. The calves had been
Table 3. Performance (28 d) of calves initially 8 wk old that were fed 4 diets containing either 13.5, 15.0, 16.5, or 18.0% CP in Exp. 1, trial 2 (as-fed basis) CP, % as-fed Item Pens, 6 calves/pen Initial BW, kg ADG, kg/d Intake, kg/d Feed efficiency CP intake, kg/d ME intake,2 Mcal/d g CP/Mcal ME consumed2 Initial hip width, cm Hip width change, cm Initial BCS3 BCS change3
13.5
15.0
16.5
18.0
SEM
Quadratic1
4 80.9 0.998 3.073 0.325 0.418 8.80 47.4 22.5 2.0 2.7 0.2
4 78.9 1.093 3.062 0.357 0.457 8.77 52.1 22.3 2.2 2.7 0.2
4 79.1 1.113 3.034 0.367 0.493 8.69 56.7 22.0 2.2 2.7 0.3
4 83.2 1.111 3.172 0.350 0.567 9.09 62.4 22.6 2.2 2.8 0.2
— 2.14 0.0215 0.1037 0.0093 0.0169 0.308 1.85 0.06 0.07 0.06 0.09
— 0.78 0.02 0.62 0.03 0.01 0.69 0.01 0.38 0.04 0.59 0.43
P-value for the quadratic polynomial. The linear polynomial was also significant (P < 0.05) for each measurement that had a significant quadratic effect, but not for any other measurements. The cubic polynomial was not significant (P > 0.05).
1
2
ME calculated as DE times 0.88 (NRC, 2001) for grower diet (2.9 Mcal/kg) and hay (2.1 Mcal/kg).
3
1 to 5 system with 1 = emaciated and 5 = obese.
Crude protein for weaned dairy calves
fed 0.681 kg/d of a 26% CP, 17% fat milk replacer (Akey, Lewisburg, OH) and weaned at 4 wk. Calves also had been fed an 18% CP diet (similar to the 18% CP diet in Exp. 2; Table 1) and water ad libitum since 3 d of age. During this initial 4-wk period, calves were housed in 1.2 × 2.4 m individual pens bedded with straw in a curtain-sided, naturally ventilated barn with no added heat as in Exp. 2. Calves were castrated and dehorned at 3 wk of age. Vaccines and medical treatments were based on the recommendations of a veterinarian and described in Hill et al. (2006). All animals were cared for by acceptable practices as described in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999). Approximately 115% of the diets needed for each trial were made as one batch of feed in advance and samples were taken from every third bag (22.7 kg). Additionally, approximately 120% of the hay needed in Exp. 1 was set aside in advance of each trial and 2 samples were taken per bale (25 kg). Samples were composited and subsampled by treatment and analyzed (AOAC, 1996) for DM (oven method 930.15), CP (Kjeldahl method 988.05), fat (diethyl ether extraction, method 2003.05), ash (muffle furnace method 923.03), Ca and P (dry ashing, acid digestion, analysis by inductively coupled plasma spectroscopy, method 985.01). Additionally, the hay was tested for NDF with ash by the procedure of Van Soest et al. (1991) without sodium sulfite or α-amylase and for ADF with ash (Robertson and Van Soest, 1981). Experiment 1, trial 1 was analyzed as a randomized complete block (replication of trial) design using PROC MIXED of SAS (1999) as a 2 × 2 factorial arrangement of treatments. Concentration of CP (16 or 18%) was one factor and source of CP (soybean meal or soybean meal with modified expeller soy) was the other factor. Block and pen were random effects and concentration and source of CP were fixed effects. The experimental unit was pen.
Experiment 1, trial 2 was analyzed as a randomized complete block (replication of trial) design using the PROC MIXED of SAS. Block and pen were random effects and treatment was a fixed effect. Serum metabolite data were analyzed as repeated measures. Day was modeled as a repeated measurement using an autoregressive type 1 covariance structure. Measures from d 0 were included as a covariate for serum metabolites analyzed. When the overall F-test for treatment was significant (P < 0.05), linear, quadratic, and cubic contrasts were used to characterize the treatment means (concentrations of CP: 13.5, 15.0, 16.5, or 18.0%). The experimental unit was pen. Experiment 2 was analyzed as a randomized complete block (replication of trial) design using PROC MIXED of SAS. Block and pen were random effects and treatment was a fixed effect. The repeated measurements were modeled using an autoregressive type 1 covariance structure. The experimental unit was calf. When the overall F-test for treatment was significant (P < 0.05), a linear contrast to CP concentration in treatments (A lowest, B halfway intermediate, C greatest) and a contrast comparing treatment A with C were used to characterize the treatment means (A, B, C).
RESULTS AND DISCUSSION No initial measures of BW, hip width, or body condition were different among the treatment groups in the 2 experiments. No calves were treated for any sickness. No calves died or were removed from the experiments. In Exp. 1, trial 1, there were no differences in growth measures among the 4 treatments (Table 2). Hill et al. (2006) reported no differences in performance of calves from 0 to 8 wk old when fed 18% CP diets from these similar CP sources. Zerbini and Polan (1985) reported no differences in calf performance when they fed 9- to 21-wk-old calves 13.5% CP diets with 26% hay and compared soybean meal,
599 cottonseed meal, corn gluten meal, and fish meal as CP sources. However, when Holtshausen and Crywagen (2000b) fed all concentrate diets with 13% CP to 12- to 20-wk-old calves, they reported greater ADG in calves fed diets with a fish meal and corn gluten meal blend (high RUP) vs. sunflower meal (high RDP). The review of Warner (1984) reported no advantage to using RUP sources in calf starter diets. Likewise, a review of data published since 1984 by Hill et al. (2006) found that the performance of calves in trials fed soybean meal were typically equal to or greater than those fed other sources of CP and that there were mixed results with feeding sources of CP high in RUP. The lack of complete development of the rumen and its microbial population in preweaned calves may explain why there are no conclusive benefits to formulating starter diets with greater RUP or metabolizable protein concentrations. The RUP fraction of the CP source appears to decline with age of the young calf. Vazquez-Anon et al. (1993) estimated the RUP of the soybean meal to change from 58% at 2 wk postweaning to 31% by 8 wk postweaning. They also estimated the RUP of SoyPlus to change from 71% at 2 wk postweaning to 51% by 8 wk postweaning. Holtshausen and Crywagen (2000a) reported similar changes in feed degradation in the rumen with calf age. In Exp. 1, trial 2, calf ADG, feed efficiency, hip width change, and urea N responded quadratically (P < 0.05) to concentration of CP in the diet (Tables 3 and 4). Calves fed the diet with 13.5% CP had the lowest ADG (−9%), feed efficiency (−9%), and hip width change, indicating that 13.5% CP in the diet was deficient in CP. Whereas ADG appeared to plateau at 15% CP, feed efficiency appeared to plateau closer to 16.5% CP. Urea N appeared to increase from its lowest concentration in calves fed the 13.5% CP diet and to change its rate of increase in calves fed the diets with 16.5 and 18.0% CP. Serum concentrations of alkaline phosphatase, creatinine, glucose, and total protein did not
600
Hill et al.
Table 4. Selected serum constituents of calves initially 8 wk old that were fed 4 diets containing either 13.5, 15.0, 16.5, or 18.0% CP in Exp. 1, trial 2 (as-fed basis) CP, % as fed Item
13.5
15.0
16.5
18.0
SEM
Quadratic1
Urea nitrogen, mmol/L Creatinine, µmol/L Total protein, mmol/L Alkaline phosphatase, U/L Alanine aminotransferase, U/L Glucose, mmol/L
1.0 71.6 72.5 247 13.7 4.9
2.1 62.1 71.4 209 15.1 4.8
3.1 58.2 72.0 205 13.8 4.9
3.3 58.5 74.3 205 14.7 5.1
0.20 4.07 2.40 42.3 1.13 0.42
0.03 0.19 0.31 0.53 0.29 0.72
P-value for the quadratic polynomial. The linear polynomial was also significant (P < 0.05) for urea nitrogen, but not for any other measurements. The cubic polynomial was not significant (P > 0.05).
1
differ (P > 0.05) among treatments. The serum urea N and feed efficiency responses indicate that the diet with 15.0% was deficient in CP, but the 16.5% CP diet was adequate. The growth and urea N results of Exp. 1, trial 2 suggest the optimum CP concentration in the diet is between 15.0 and 16.5%. This is at the high range of work by Brown and Lassiter (1962) and Morrill and Dayton (1978), who reported the optimum concentration of 10.5 to 15% CP for 6- to 12-wk-old calves fed diets with 20 to 30% forage. In 8- to 12-wk-old calves fed diets with 7.5% roughage, Veira et al. (1980) reported ADG and flow of nonammonia N to the abomasum to increase as CP increased from 8 to 14%, but no plateau appeared. Jahn and Chandler (1976) reported the ADG of calves from 8 to 20 wk old to increase as dietary CP increased from 9 to 14.5% when the diets contained 11% ADF; however, ADG continued to increase as dietary CP increased up to 17.5% CP when the diets contained 18 or 25% ADF. However, in their study ADG was inversely related to ADF concentration of the diet. The data of Jahn and Chandler (1976) appear to disagree with those of Brown and Lassiter (1962) and Morrill and Dayton (1978) who fed high fiber diets and found the range of 10.5 to 15% CP to be the optimum. However, the data of Jahn and Chandler (1976) agree more with the data from trial 2 that showed the calves fed the 13.5% CP diet had
lower ADG and feed efficiency that calves fed the greater CP diets. In Exp. 2, ADG tended (P < 0.07) to increase linearly from treatment A (feeding the 16% CP diet 4 wk), to treatment B (feeding the 18% CP diet for 2 wk then feeding the 16% diet for 2 wk), to treatment C (feeding the 18% diet for 4 wk) in the 4- to 8-wk-old calves (Table 5). Research by Akayezu et al. (1994) and Hill et al. (2006) has shown that 17 to 18% is correct for the diet consumed by the 0- to 8-wk-old calf. The attempt in Exp. 2 to determine how soon calves that were fed an 18% CP diet could be switched to a 16% CP diet showed that 8 wk is likely the correct time. However, because the difference in ADG tended to be small (4%), switching calves sooner should not be a major risk to performance. Some general management recommendations provided to producers suggest not making diet changes around weaning (wk 4 in Exp. 2), a major time of stress to the calf. The calves (4 to 8 wk old, 62 kg average BW) fed by Akayezu et al. (1994) had similar postweaning (d 30 to 56) intake (1.51 kg starter diet/d, 0.263 kg CP/d, 4.44 Mcal ME/d, 59.2 g CP/Mcal ME) as the calves (4 to 8 wk old, 60 kg average BW) in Exp. 2 (1.63 kg starter diet/d, 0.284 kg CP/d, 4.49 Mcal ME/d, 63.4 g CP/ Mcal ME; Table 6). No roughage diets of similar ingredient and nutrient composition were fed in both trials. Because ADG was maximized with
the 17.4% CP diet fed by Akayezu et al. (1994), their diet was 59.2 g CP/ Mcal ME compared with the 63.4 g CP/Mcal ME in the 18% CP diet fed in Exp. 2. Otherwise, these 2 trials yielded similar results. In Exp. 1, trial 2, the maximal ADG was between the 15.0 and 16.5% CP treatments, which supplied 0.457 and 0.493 kg CP/d, respectively. The numeric difference in ADG between these treatments was only 0.020 kg/d (1.093 and 1.113 kg/d), whereas the difference in ADG between the 13.5 and 15.0% CP treatments was large (0.095 kg/d). This suggests that the requirement is likely closer to the 15.0% CP treatment that provided 0.457 kg CP/d than the 16.5% CP treatment, based on the response in ADG. Using NRC (2001) estimates, approximately 0.038 kg of CP is needed to support 0.100 kg of ADG above maintenance in the 95-kg-BW calf. These amounts are similar to difference in CP intake (0.039 kg CP/d) and ADG (0.095 kg/d) observed between calves fed the 14.5 and 15.0% CP treatments. Estimates from NRC (2001) suggest the 95-kg-BW calf requires approximately 0.500 kg of CP/d to support 1.1 kg of ADG. Calves fed the 15.0% CP treatment gained 1.093 kg BW/d when consuming 0.457 kg CP/d, or approximately 0.043 kg less/d than suggested by NRC (2001). Using feed efficiency or serum urea N data, the diet with 16.5% CP and supplying 0.493 kg CP/d appeared closer to
Crude protein for weaned dairy calves
601
Table 5. Performance (28 d) of A) feeding the 16% CP diet 4 wk, B) feeding the 18% CP diet for 2 wk and then feeding the 16% diet for 2 wk, or C) feeding the 18% diet for 4 wk to calves in Exp. 2 (as-fed basis) Item
A) 16%
B) 18%, then 16%
C) 18%
SEM
Linear1
Calves, n Initial BW, kg ADG, kg/d Intake, kg/d Feed efficiency CP intake, kg/d ME intake,2 Mcal/d g CP/Mcal ME consumed2 Initial hip width, cm Hip width change, cm Initial BCS3 BCS change3
24 50.2 0.635 1.611 0.394 0.248 4.44 55.8 18.4 2.0 2.3 0.2
24 48.3 0.651 1.572 0.416 0.258 4.34 59.6 18.1 1.9 2.3 0.3
24 50.5 0.661 1.627 0.406 0.284 4.49 63.4 18.3 2.1 2.3 0.2
— 0.84 0.0261 0.0634 0.0084 0.0106 0.178 2.38 0.14 0.09 0.03 0.03
— 0.33 0.07a 0.73 0.57 0.01 0.92 0.01 0.32 0.66 0.54 0.30
1
The P-value for the linear polynomial was P = 0.07. Other linear polynomials and the contrast constructed to compare treatments A to C for all of the different measurements were not significant (P > 0.05).
2
ME calculated as DE times 0.88 (NRC, 2001) for starter diet (2.9 Mcal/kg) and hay (2.1 Mcal/kg).
3
1 to 5 system with 1 = emaciated and 5 = obese.
optimum and more similar to estimates from NRC (2001). Brown and Lassiter (1962) and Schurman and Kesler (1974) reported 68- to 70-kg calves gaining 0.92 to 0.96 kg BW/d consumed 0.356 to 0.430 kg CP/d. These calves weighed less and were consuming 25 to 28% roughage diets compared with the calves in Exp. 1. Conversely, Veira et al. (1980) reported that heavier (131 kg BW) calves with faster ADG (1.22 kg/d) than the calves in Exp. 1 consumed 0.651 kg CP/d. In Exp. 1, trial 2, the optimum ADG was between 15 and 16.5% CP, which corresponded to 52.1 to 56.7 g CP/Mcal ME (Table 6). In Exp. 1, trial 1, the 16% CP diets were 55.5 and 56.5 g CP/Mcal ME. Schurman and Kessler (1974) fed 10.0, 12.6, and 22.8% CP diets and observed the best ADG with the 12.6 and 22.8% CP diets. The 12.6% CP diet contained 28% hay and was estimated to be 49 g CP/Mcal ME. The 14.2% CP, 7.5% roughage diet fed to 131-kg-BW calves in the Veira et al. (1980) trial that supported the maximum ADG had a 51.8 g CP/Mcal ME ratio. The 14% CP diet treatments that optimized ADG and fed by Brown and Lassiter (1962) and Morrill and Day-
ton (1978) contained 20 to 25% alfalfa hay and 54 to 56 g CP/Mcal ME. Gabler and Heinrichs (2003) fed 150-kgBW calves 60% roughage diets and observed the best numeric ADG and feed efficiency with a 59.1 g CP/Mcal ME ratio. Jahn and Chandler (1975) reported the best ADG in calves fed their lowest roughage diet (ADG declined as roughage increased), and that treatment was 14.5% CP and 57.1 g CP/Mcal ME. They also reported that with the higher roughage diets, ADG was maximized with more CP (17.5% CP) and a greater CP to ME ratio (75 to 82 g CP/Mcal ME) and attributed this to a need for more RDP. Concentration of roughage may explain why the older, heavier calves fed the 60% roughage diet by Gabler and Heinrichs (2003) appeared to require a greater CP to ME ratio diet than in other reports (Schurman and Kesler, 1974; Veira et al., 1980) and in Exp. 1. In the 5% roughage diets fed to 8- to 12-wk-old, 85- to 95-kgBW calves in Exp. 1, a 52 g CP/Mcal ME (at 15% CP in the diet) to 56 g CP/Mcal ME ratio (at 16% CP in the diet) appeared optimum. The younger 4- to 8-wk-old, 60-kg-BW calves in Exp. 2 appeared to need a greater ratio (63 g CP/Mcal ME).
Although beyond the scope of these trials, the calf submodel in the NRC (2001) was used to predict ME and CP limiting ADG at ambient and thermoneutral temperatures for calves fed the optimum diets in Exp. 1 and 2 (Table 6). In each experiment, actual ADG greatly exceeded predicted ADG using ambient temperatures, especially in Exp. 1 where the ambient temperatures were low (−2 and 4°C). Predicted ADG at 20°C (thermoneutral temperature) was limited by ME in Exp. 1 and 2. However, in the trials selected from the literature only 20°C was used to predict ADG because ambient temperatures were not provided in the references. In the trials selected from the literature, predicted ADG from ME intake was not always limiting to CP intake, as in Exp. 1 and 2. Across Exp. 1 and 2 and the trials selected from the literature, predicted ADG using 20°C was not consistent with actual ADG.
IMPLICATIONS The literature reports the neonatal dairy calf fed milk or milk replacer should be fed an 18% CP diet (as fed). Current results suggest that the weaned calf should remain on an 18%
8 94 5.0 15.0 2.86 52.1 3.06 0.457 8.77 1.09
0.95 0.99 4
0.72
8 85 5.0 16.2 2.86 56.0 2.89 0.463 8.27 0.85
0.94 1.04 −2
0.64
0.70
0.94 1.10 4
8 95 5.0 16.4 2.86 56.7 3.03 0.493 8.69 1.11
0.56
0.56 0.65 20
4 60 0.0 18.4 2.90 63.4 1.63 0.284 4.49 0.66
18% CP
Trial 1, average Trial 2, Trial 2, of 16S, 16SES2 15.0% CP 16.5% CP
—
0.50 0.53 —
4 62 0.0 17.4 2.94 59.2 1.51 0.263 4.44 0.86
—
1.15 1.10 —
8 64 16.6 14.5 2.54 57.1 3.31 0.480 8.41 0.97
—
0.89 0.99 —
6 68 25.0 14.4 2.6 55.4 2.80 0.356 6.42 0.96
Akayezu et Jahn and Brown and al., 1994 Chandler, 1975 Lassiter, 1962
—
— — —
6 — 20.0 14.2 2.63 54.0 2.52 0.358 6.60 0.96
—
1.14 0.94 —
8 70 28.0 12.6 2.56 49.2 3.41 0.430 8.73 0.92
—
— — —
9 to 12 131 7.5 14.2 2.74 51.8 4.58 0.651 12.55 1.22
Morrill and Schurman and Veira et al., Dayton, 1978 Kesler, 1974 1980
2
Exp. 1, trial 1: diets contained 16 (16) or 18% (18) CP and either soybean meal (S) or soybean meal with modified expeller soy protein (SES).
Diet ME and predicted ADG were estimated using the NRC (2001) calf submodel. Predicted ADG were made at both thermoneutral (20°C input) and average ambient temperatures. Ambient temperatures were not reported in the trials selected from the literature. Predictions could not be made for the trial of Veira et al. (1980) because the BW exceeded 100 kg, the maximum BW allowed in the NRC calf submodel.
1
Initial age, wk Avg BW, kg Diet roughage, % Diet CP, % Diet ME, Mcal/kg g CP/Mcal ME Intake, kg/d CP intake, kg/d ME intake, Mcal/d ADG, kg/d Predicted ADG at 20°C (thermoneutral) ME supported, kg/d CP supported, kg/d Temperature, °C Predicted ME supported ADG at ambient temperature, kg/d
Item
Exp. 2
Exp. 1
Table 6. Calf and diet descriptions with measured and predicted ADG from the optimum diets in Exp. 1 and 2 and selected trials in the literature1 (as-fed basis)
602 Hill et al.
Crude protein for weaned dairy calves
CP diet with approximately 63 g CP/ Mcal ME until 8 wk old. Additionally, the 8- to 12-wk-old, 95-kg-BW calf fed 5% hay should be fed a 15% CP diet with approximately 52 g CP/ Mcal ME to optimize ADG, or a 16% CP diet with approximately 56 g CP/ Mcal ME to optimize feed efficiency.
LITERATURE CITED Akayezu, J. M., J. G. Linn, D. E. Otterby, W. P. Hansen, and D. G. Johnson. 1994. Evaluation of calf starters containing different amounts of crude protein for growth of Holstein calves. J. Dairy Sci. 77:1882. AOAC. 1996. Official Methods of Analysis. Vol. I 16th ed. Assoc. Off. Anal. Chem., Arlington, VA. Brown, L. D., and C. A. Lassiter. 1962. Protein-energy ratios for dairy calves. J. Dairy Sci. 45:1353. FASS. 1999. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. 1st rev. ed. Fed. Anim. Sci. Soc., Savoy, IL. Gabler, M. T., and A. J. Heinrichs. 2003. Dietary protein to metabolizable energy ratios on feed efficiency and structural growth of prepubertal Holstein heifers. J. Dairy Sci. 86:268. Hill, T. M., J. M. Aldrich, R. L. Schlotterbeck, and H. G. Bateman II. 2007. Protein concentration for starters fed to transported neonatal calves. Prof. Anim. Sci. 23:123. Holtshausen, L., and C. W. Crywagen. 2000a. The effect of dietary rumen degradable protein content on veal calf performance. S. Afr. J. Anim. Sci. 30:204.
Holtshausen, L., and C. W. Crywagen. 2000b. The effect of age on in sacco estimates of rumen dry matter and crude protein degradability in real calves. S. Afr. J. Anim. Sci. 30:212. Jahn, E., and P. T. Chandler. 1976. Performance and nutrient requirements of calves fed varying percentages of protein and fiber. J. Anim. Sci. 42:724. Kaplan, L. A. 1989. Glucose. p. 850 in Clinical Chemistry: Theory, Analysis, and Correlation. 2nd ed. L. A. Kaplan and A. J. Pesce, ed. C.V. Mosby Co., St. Louis, MO. Morrill, J. L., and A. D. Dayton. 1978. Factors affecting requirement and use of crude protein in calf starter. J. Dairy Sci. 61:940. NRC. 2001. Nutrient Requirements of Dairy Cattle. 7th ed. Natl. Acad. Press, Washington, DC. Robertson, J. B., and P. J. Van Soest. 1981. The detergent system of analysis and its application to human foods. p. 123 in The Analysis of Dietary Fiber in Food. W. P. T. James and O. Theander, ed. Marcel Dekker, New York, NY. Sampson, E. J., M. A. Baird, C. A. Burtis, E. M. Smith, D. L. Witte, and D. D. Bayse. 1980. A coupled-enzyme equilibrium method for measuring urea in serum: optimization and evaluation of the AACC study group on urea candidate reference method. Clin. Chem. 26:816. SAS. 1999. SAS Users’ Guide. Version 8 ed. SAS Inst. Inc., Cary, NC. Schurman, E. W., and E. M. Kesler. 1974. Protein-to-energy ratios in complete feeds for calves at ages 8 to 18 weeks. J. Dairy Sci. 57:1381. Tietz, N. W., C. A. Burtis, P. Duncan, K. Ervin, C. J. Petitclerc, A. D. Rinker, D. Shuey, and E. R. Zygowicz. 1983. A reference method for measurement of alkaline
603 phosphatase activity in human serum. Clin. Chem. 29:751. Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, non-starch polysaccharides in relation to animal nutrition. Symposium: carbohydrate methodology, metabolism and nutritional implications in dairy cattle. J. Dairy Sci. 74:3583. Vazquez-Anon, M., A. J. Heinrichs, J. M. Aldrich, and G. A. Varga. 1993. Effect of post-weaning age on rate of in situ protein disappearance in calves weaned at 5 weeks of age. J. Dairy Sci. 76:2749. Veira, D. M., G. K. Macleod, J. H. Burton, and J. B. Stone. 1980. Nutrition of the weaned Holstein calf. II. Effect of dietary protein level on nitrogen balance, digestibility, and feed intake. J. Anim. Sci. 50:945. Warner, R. G. 1984. The impact of protein solubility in dairy calf starters. p. 42 in Proc. Cornell Nutr. Conf. Feed Manufacturers. Rochester, NY. Weichselbaum, T. E. 1946. An accurate and rapid method for the determination of proteins in small amounts of blood serum and plasma. Am. J. Clin. Pathol. 16:40. Whelton, A. A., J. Watson, and R. C. Rock. 1994. Nitrogen metabolites and renal function. p. 1513 in Tietz Textbook of Clinical Chemistry. 2nd ed. C. A. Burtis and E. R. Ashwood, ed. W. B. Saunders Co., Philadelphia, PA. Wildman, E. E., G. M. Jones, P. E. Wagner, R. L. Bowman, H. F. Troutt Jr, and T. N. Lesch. 1982. A diary cow body condition scoring system and its relationship to selected production characteristics. J. Dairy Sci. 65:495. Zerbini, E., and C. E. Polan. 1985. Protein sources evaluated for ruminating calves. J. Dairy Sci. 68:1416.