Effects of Supplemental Levels of Rumen-Protected Methionine and Lysine on Performance and Plasma Biochemical Indices of Lactating Holstein Cows

This experiment was conducted to investigate the effects of the supplementatl levels of rumen-protected methionine( RPMet) and lysine( RPLys) on performance and plasma biochemical indices of lactating Holstein cows under typical dietary condition in northern China. One hundred and sixty lactating Holstein cows in peak lactation period and with milk yield produced about 30 kg /d were selected and randomly allotted to four groups with 40 cows in each group. Cows in control group were fed a basal diet,and those in experimental groups were fed the basal diet supplemented with 13 g /d RPMet + 6 g /d RPLys( M13 + L6 group),43 g /d RPMet + 98 g /d RPLys( M43 + L98 group),and 74 g /d RPMet + 190 g /d RPLys( M74 + L190 group),respectively. The experiment consisted of a 10-day pre-experimental period and a 50-day experimental period. The results showed as follows: 1) dietary supplementation of RPMet and RPLys had no significant effects on dry matter intake( P 0. 05). 2) Milk yield,milk fat yield and lactose yield in M74 + L190 group were significantly higher than those in control group and M13 + L6 group( P 0. 05),while milk urinary nitrogen concentration was significantly lower than that in control group and M13 + L6 group( P 0. 05). 3) Compared with control group,plasma lysine concentration in M74 + L190 group was significantly increased( P 0. 05),while plasma urinary nitrogen concentration was significantly decreased( P 0. 05); plasma methionine and triglyceride concentrations in M43 + L98 and M74 + M190 groups were significantly increased( P 0. 05). In conclusion,under the typical dietary condition of northern China,the supplementation of RPMet and RPLys can improve performance of lactating cows in peak locating period,and the suitable supplemental levels of RPMet and RPLys for cows produced about 30 kg /d milk are 74 and 190 g /d,respectively.