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Abstract

The objective of this study was to evaluate the effects of supplementation of different level protein diets with rumen protected methionine and lysine on performance and ruminal parameters in Holstein dairy cows when in their early lactation. Twenty one dairy cows in their early lactations were assigned to three treatments in a randomized block design experiment of a 35-d duration period. Diets were: 1) High protein diet containing 17.5% crude protein (CP), 2) Moderate protein diet bearing 16% CP along with 12 gr/d of rumen protected methionine, 3) Low protein diet with 14.5% CP plus 14 gr/d of rumen protected methionine and also 5 gr/d of rumen protected lysine. Dry matter intake, milk production, 3.5% fat corrected milk (3.5% FCM), percent content of milk fat, molar concentration of rumen volatile fatty acids and ruminal fluid pH were not significantly affected by diets. However, experimental treatments significantly affected percent of milk protein, milk urea nitrogen and ruminal ammonia concentration (P<0.05). Results finally indicated that feeding 16% CP diet with rumen protected methionine can lead to a better performance, in comparison with the other experimental diets.

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