Crude Protein for Diets Fed to Weaned Dairy Calves

INTRODUCTION

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 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 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 ingrethent 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 m^sup 2^ 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 vita- mins. These 4 diets were blended with 5% chopped grass hay and fed to the calves ad libitum with ad libitum wa- ter. 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 cen- trifugation and analyzed for alkaline phosphatase (Tietz et al., 1983), crea- tinine (Whelton et al., 1994), glucose (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 treatment; 50 ± 1 kg; initially 4 wk old) were fed 1 of 2 diets (Table 3) ar- ranged 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 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 a-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, 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 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 Meal 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 Meal ME/d, 63.4 g CP/ Meal 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/ Meal 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 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 Dayton (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 40C). Predicted ADG at 200C (thermoneutral temperature) was limited by ME in Exp. 1 and 2. However, in the trials selected from the literature only 200C 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% 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.

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