Title page for ETD etd-12202011-165029

Type of Document Master's Thesis
Author Bell, Ashley Lorraine
Author's Email Address ashbell@vt.edu
URN etd-12202011-165029
Title Effects of reduced dietary protein and supplemented rumen protected amino acids on the nitrogen efficiency of dairy cows
Degree Master of Science
Department Dairy Science
Advisory Committee
Advisor Name Title
Hanigan, Mark D. Committee Chair
Escobar, Jeffery Committee Member
McGilliard, Michael L. Committee Member
  • nitrogen efficiency
  • milk production
  • protein synthesis
  • rumen protected amino acids
Date of Defense 2011-09-30
Availability unrestricted
Dairy cows are extremely inefficient at converting dietary nitrogen (N) to productive N. Approximately 25-30% of dietary N is used for milk protein while the remaining N is lost to the environment. According to National Research Council (NRC, 2001) recommendations, dairy cow rations are formulated in terms of metabolizable protein (MP) which often causes many amino acids (AA) to be fed in excess. A better understanding of protein and AA requirements could help to improve the nitrogen efficiency of dairy cows. The objective of this work was to examine the effects of feeding a low protein diet supplemented with rumen protected (RP) AA on production and N efficiency of dairy cows. Twenty-four Holstein and 24 Holstein x Jersey crossbred cows were used in a Youden square design consisting of 3 periods. Cows were randomly assigned to one of 8 treatments: 1) a standard diet containing 17% crude protein (+Con), 2) a 15% crude protein diet (-Con), 3) –Con plus RP methionine (+M, 16g/d), 4) –Con plus RP lysine (+K, 47g/d), 5) –Con plus RP leucine (+L, 181g/d), 6) –Con plus RP methionine and lysine (+MK), 7) –Con plus RP methionine and leucine (+ML), and 8) –Con plus RP methionine, lysine, and leucine (+MKL). Cows fed the –Con as well as the +MKL diet experienced a reduction in milk production and milk protein yield (P < 0.05). Dry matter intake decreased only for those animals on the +ML diet (P < 0.05). Milk urea N (MUN) decreased for all diets when compared to the +Con treatment (P < 0.05). In accordance with the decrease in MUN, N efficiency was numerically increased in the diets supplemented with RP AA, but this improvement was not significant. Phosphorylation of signaling proteins important for protein synthesis were also examined. Animals fed the +MK treatment increased phosphorylated and total forms of eukaryotic elongation factor 2 (eEF2) when compared to the +Con and –Con (P < 0.05), but this increase in abundance did not affect the ratio of phosphorylated to total abundance. Feeding dairy cows a low protein diet supplemented with RP AA has the ability to alleviate the loss in milk production associated with feeding a low protein diet as well as to increase nitrogen efficiency.
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