Interaction Between Crude Protein Level and Rumen Protected Amino Acids in Starter Diet on Performance of Dairy Calves

BACKGROUND: A limited number of studies have investigated the inclusion of amino acids in calf starter. OBJECTIVES: This study was aimed to evaluate different levels of crude protein in starter and supplement- ing some protected amino acids on efficiency, health status and blood metabolites of dairy calves and to com- pare it with unprotected amino acids. METHODS: Forty-eight 3-day-old Holstein calves were randomly allocated to four treatments in a complete- ly randomized design. Dietary treatments were (1) 18% Crude Protein starter without Amino Acid, (2) 18% Crude Protein with 0.0340% protected lysine and 0.016% protected methionine, (3) 18% Crude Protein starter with 0.215% un-protected lysine and 0.012% un-protected methionine, (4) 22% Crude Protein without Amino Acid. All calves received the same amount of whole milk, weaned on day 56; the study was finished on day 70. RESULTS: Calves in treatment 4 had the greatest starter intake, weaning weight and final weight (P<0.05) but their feed efficiency was not different among treatments. There were no significant differences in Immu- noglobulin G, total protein and Lysine and Methionine concentration in blood (P>0.05). Health score (eye, ear, nose and respiratory score), was not different among treatments but the fecal score revealed a significant difference (P<0.05). Starter diet with 22% Crude Protein resulted in higher serum urea concentration (P< 0.05) CONCLUSIONS: Results of the present study indicate that, the performance of calves received protected or un-protected amino acid in starter was not different. Also, higher Crude Protein levels in diet did not lead to a better gain to feed ratio.