Effect of Protein Level in Milk Replacers on Growth and Protein Metabolism of Dairy Calves

Abstract

Summary Three trials were conducted with two-day-old calves to study the minimum protein level required in milk replacer rations to support normal growth and protein metabolism. Two growth studies were conducted, using a total of 72 calves from two to 72 days of age in Trial 1 and from two to 86 days of age in Trial 2. A metabolism study was conducted with 16 calves. In Trial 1, replacers were fed containing 30.5, 24.1, 18.7, and 15.2% protein. Growth results indicated that the calves fed the three higher protein replacers made comparable growth, but the calves fed the 15.2% protein replacer grew at a slightly slower rate. Similar results were obtained in the second trial when 29.7, 26.2, 23.5, 19.6, and 16.6% protein replacers were fed. In both trials, calves fed the lowest protein replacers grew at slower rates than the calves fed the other protein levels. This was particularly true from two to 49 days of age. When the growth results of the two trials were combined, resulting in replacers of approximately 30, 24, 19, and 16% protein, the average daily gains of calves fed the combined replacers were 0.68, 0.80, 0.73, and 0.60lb per day, respectively. The growth rate of the calves fed the 24% replacers was significantly greater than the calves fed the 16% replacers. Results of the metabolism studies showed that the coefficients of digestibility decreased as the protein content of the replacers decreased; this was particularly true with crude protein and crude fiber. Metabolism data indicated little difference among rations in total nitrogen excretion, but nitrogen retention and the per cent of nitrogen retained decreased significantly as the protein content of the milk replacers decreased. The protein content of the milk replacers had little effect on the blood constituents studied, except urea-nitrogen and serum protein nitrogen. These two constituents decreased as the protein content of the replacers decreased. Results of these studies indicate that calves can make normal growth when fed milk replacer rations containing approximately 24% protein and that their growth rates are equal to calves fed higher levels of protein. Results also indicate that the protein level could be decreased to approximately 19% without seriously affecting the growth rate of calves.