|Peterson, A - UNIVERSITY OF MARYLAND|
|Kohn, R - UNIVERSITY OF MARYLAND|
Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: February 21, 2005
Publication Date: July 1, 2005
Citation: Peterson, A.B., Baldwin, R.L., Kohn, R. 2005. Effect of ruminally degraded protein source on production performance in Holstein cows [abstract]. Journal of Animal Science. 88(1)99. Technical Abstract: To evaluate the effect of two ruminally degraded protein (<b>RPD</b>) types (amino acids vs. non-protein N) eight early lactation Holstein cows were arranged in a repeated 4x4 Latin square design balanced for carryover effects with 21 d periods. All diets were isoenergetic (1.71 Mcal/kg) and had the same RUP content (5.6%). Cows were fed either a base diet containing 12.8% CP or one of three treatment diets containing 16% CP supplemented with urea, casein or both. Dry matter intake (<b>DMI</b>) was lowest for cows fed the base diet (16.8 kg/d) while cows fed the urea and urea/casein diets had the highest DMI at 18.8 and 18.6 kg/d, respectively (<i>P</i> < 0.05). Cows fed the casein diet consumed less than cows fed the urea diet (18.2 kg/d; <i>P</i> < 0.05) however this cannot be explained by apparent dry matter or NDF digestibility as they were not affected. Milk yield averaged 29.0 kg/d (SEM=2.6) for cows fed the base diet compared to cows fed the urea/casein diet which averaged 33.9 kg/d (<i>P</i> < 0.05). Cows fed the urea and casein diets yielded 32.9 and 32.6 kg/d of milk, respectively, which were not different from each other but were higher than the base diet and lower than the urea/casein diet (<i>P</i> < 0.05). Milk fat and protein percentages did not differ among treatments. Milk urea nitrogen (<b>MUN</b>) was lowest for cows fed the base diet averaging 6.6 mg/dl (<i>P</i> < 0.05) while MUN from cows fed the other diets averaged 12.5 mg/dl and did not differ from each other. Though the energy content of the diets was the same, the urea/casein diet may have provided a better combination of available ammonia and amino acids to the rumen microbes which may have increased microbial yield and therefore milk production. The type of RDP affects DMI and milk yield as cows may require both readily available amino acids as well as a source of ammonia for maximum yield.