Effects of Rumen-Protected Methionine and Lysine Supplementations on Growth Performance and Carcass Chemical Composition of Holstein Bulls

This experiment was conducted to investigate the effects of rumen-protected methionine( RPMet)and lysine( RPLys) supplementations on growth performance and carcass chemical composition of Holstein bulls,and to discuss the feasibility that RPMet and RPLys instead of part protein of diet. Tw enty five Holstein bulls aged about 12 months with similar body weight and body measurements were selected and divided into 5groups with randomized experiment design,and each group included 5 Holstein bulls. The control group was fed a basal diet,the experimental groups were fed the basal diet added with RPMet 15 g / d( M15 group),RPLys 30 g / d( L30 group),RPMet 15 g / d + RPLys 30 g / d( M15 + L30 group) and RPMet 15 g / d +RPLys 30 g / d( meanw hile dietary crude protein content was low ered by 2. 20 %)( LCP group),respectively. Adaptation and experimental periods lasted for 10 and 150 d,respectively. The results show ed that compared with control group: 1) dry matter intake was not affected by RPMet and RPLys supplementations( P 0. 05); L30,M15 + L30,LCP groups significantly increased final weight and average daily gain( P 0.05),and the values reached the highest in M15 + L30 group,but they were not significantly different from those in LCP group( P 0. 05); M15 + L30 and LCP groups significantly decreased feed to gain ratio( P 0.05),and M15 + L30 group had the minimum value,but the difference betw een M15 + L30 and LCP groups was not significant( P 0. 05). 2) Chest girth and carcass crude protein content in M15 + L30 and LCP groups were significantly increased( P 0. 05),while there was no significant difference betw een the tw o groups( P 0. 05). 3) M15 + L30 and LCP groups significantly increased carcass essential amino acid contents including threonine,leucine and arginine( P 0. 05),and the differences betw een the tw o groups were not significant( P 0. 05); M15 + L30 group significantly increased isoleucine content( P 0. 05); M15 +L30 and LCP groups had significantly higher non-essential amino acid contents including aspartate,serine,glutamic acid,glycine,alanine,cystine and proline and total amino acid content( P 0. 05); L30 and M15 +L30 groups had significantly higher tyrosine content( P 0. 05),but there was no significantly difference betw een the tw o groups( P 0. 05). It is concluded that dietary supplementations of RPMet and RPLys can improve growth performance and increase carcass protein and amino acid contents of Holstein bulls,and the supplementation of RPMet 15 g / d + RPLys 30 g / d can instead part of dietary crude protein( 2. 20 %).