Effect of dietary absorbable methionine and lysine concentrations on milk production and composition of dairy cows offered grass-silage based diets

Twenty-four autumn-calved cows, offered a grass-silage based diet, were use d to evaluate the influence of varying dietary concentrations of absorbable lysine and methionine. Cows were blocked on calving date and milk yield an d assigned to four treatments in a balanced latin square sequence. The trea tments consisted of primary growth unwilted grass-silage plus (1) 7 kg per cow per day of a by-product concentrate (C), (2) C plus 4.8 g absorbable DL methionine (MetDI) per day (CM), (3) C plus 4.8 g MetDI and 6.2 g absorbab le L lysine (LysDI) per day (CML) and (4) 7 kg per cow per day of a barley/ beet pulp/soyabean meal concentrate plus 7.7 g MetDI per day (BSM). The by- product concentrate consisted of maize distillers grains, maize gluten feed , unmolassed sugar-beet pulp and rapeseed meal. The amino acids (AA) were s upplied in a rumen-protected form (Smartamine(TM) RPAN Technology). Milk pr otein concentration (P < 0.001) and yield (P < 0.01) were higher on treatme nt CML and protein concentration was higher (P < 0.001) on treatment BSM co mpared to treatments C and CM. The BSM treatment gave a lower (P < 0.01) mi lk yield than CML. Casein concentration was higher (P < 0.01) on BSM than o n the other three treatments and was higher (P < 0.05) on CML than on C. Di rect supplementation with rumen-protected, absorbable lysine and methionine or provision of a concentrate made from LysDI rich raw materials (e.g, BSM ), balanced with rumen-protected methionine, were effective strategies to s upply the recommended LysDI and MetDI concentrations and increase milk prot ein production.