Influence of dietary energy and protein source on microbial protein synthesis, amino acid flow, and lactational performance in dairy cattle

Kelly D Cunningham, Purdue University

Abstract

Dietary energy and protein are the nutrients which are most limiting to high producing ruminant animals. These nutrients can affect ruminal fermentation, microbial protein synthesis, and amino acid flow to the small intestine and ultimately determine levels of production. Three cannulated animal studies and one lactation study were conducted to determine the effects of dietary energy and protein on ruminal fermentation, nitrogen and amino acid flows to the small intestine, and lactational performance in dairy cattle. In the first study, soybean hulls were used to replace traditional forage or concentrate feeds in diets fed to early lactation cows. Despite slightly lower levels of intake, ruminal fermentation, microbial protein synthesis, milk production, and milk component yields were similar for the control diet and diets containing soybean hulls. In the second study, increasing amounts of ruminally undegradable protein were fed to determine an optimal level of undegradable intake protein supplementation. Results from this study suggest that when diets contain greater than 5.7% undegradable protein the quantity of microbial protein synthesized in the rumen was decreased, however amino acid flows were not altered as the level of undegradable protein increased. Finally, a metabolism study and a lactation study were conducted to determine the ability of ruminally protected soybean meal to stimulate amino acid flow to the duodenum, milk production, and milk protein yield at two levels of crude protein. Despite lower dry matter intake in the metabolism study compared with the production study ruminally protected soybean meal increased amino acid flows and milk protein yields. In conclusion, these studies suggest that dietary energy and protein manipulations can effect the synthesis of microbial protein and the flow of amino acids to the small intestine, however, levels of production were not greatly improved by the dietary energy or protein changes described in these studies.

Degree

Ph.D.

Advisors

Cecava, Purdue University.

Subject Area

Livestock

COinS