Impacts of Reducing Protein Content in Milk Replacer on Growth Performance and Health of Young Calves

SIMPLE SUMMARY: The appropriate protein percentages in calf milk replacer (MR) is a key factor in determining the optimal growth of young calves. We hypothesized that elevated MR feeding with a lower protein content may not negatively affect the performance, metabolic traits, and health of the calves. The question on is: how much protein is required by calves in order to achieve an intended growth rate? In the present study, the average daily gain was similar between both groups fed MR of 19% and 22% protein, although crude protein intake was reduced in the group fed MR of 19% protein. Even though the mean dry matter content in the feces of group fed MR of 19% protein was partly lower, the incidence of diarrhea was not greater in this group. Both groups fed MR of 19% and 22% protein had very great serum insulin-like growth factor 1 (IGF-1) concentrations. This confirms that both groups, i.e., also the animals fed with a crude protein-reduced MR, were adequately supplied with nutrients. Furthermore, the lower serum urea concentration in the 22% protein in MR calves indicates that they probably had a greater body protein accretion and the proportion of amino acids for energy supply was lower than in the 19% protein in MR calves. Thus, the urea content in the blood serum indicated that a higher protein intake during the pre-transition period is feasible with a higher protein content in the MR. ABSTRACT: In the present study, a drinking amount of 10 L of milk replacer (MR) was allowed to dairy calves in order to approach the natural drinking behavior. The question is: how much protein is required by calves in order to achieve an intended growth rate? For this reason, sixty-eight pre-weaned Holstein calves were divided into two groups and fed with 10 L/d of MR containing either 22% protein (MR22) or 19% protein (MR19) at an almost comparable energy intake. Effects on performance, metabolic status, and health were compared. Feed intake, growth performance, and health status were monitored during the pre-transition, transition, and postweaning phase (until 157 d of age). Total feed intake, and intake of MR, body weight (BW), and average daily gain (ADG) were not significantly different between MR22 and MR19 during the entire experimental period (p > 0.05). At d 42, calves in MR19 group showed greater serum levels of growth hormone (16.2 vs. 22.2 ng/mL; p = 0.02), insulin-like growth factor 1 (262 vs. 291 ng/mL; p = 0.03), and urea (2.86 vs. 3.04 mmol/L; p < 0.01). The results of the present study suggested that when high amounts of MR are provided, the protein content in MR can be reduced to 19% without any adverse effects on growth performance as well as on health status of dairy calves.