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 supplementing some protected amino acids on efficiency, health status and blood metabolites of dairy calves and to compare it with unprotected amino acids. methods: forty-eight 3-day-old holstein calves were randomly allocated to four treatments in a completely 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 immunoglobulin 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.