|Kalscheur, K - SD STATE UNIVERSITY|
|Glenn, B - BIOTECH INDUSTRY ORG|
|Kohn, R - UNIVERISTY OF MARYLAND|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2005
Publication Date: January 1, 2006
Citation: Kalscheur, K.F., Baldwin, R.L., Glenn, B.P., Kohn, R.A. 2006. Milk Producton of Dairy Cows Fed Differing cConcentrations of Rumen Degraded Protein. Journal of Dairy Sci. 89:249-259. Interpretive Summary: Rumen degradable protein (RDP) is a chemical characteristic of feedstuffs that is recognized to impact the nitrogen (N) economy of the lactating dairy cow. The objectives of this experiment were to determine the effects of feeding RDP below predicted requirements on milk production, milk composition, Dry matter intake, and feed efficiency and to determine the effect of dietary RDP on N utilization efficiency and N excretion in lactating dairy cows. Forty-eight cows were fed four diets differing in rumen-degraded protein in a repeated Latin Square design. Cows underfed rumen-degraded protein produced less total milk, milk fat and milk protein than cows fed to recommendations. This experiment confirms current feeding recommendations for optimal milk production but more importantly quantifies the expected amount of lost milk production as a result of underfeeding protein in this form. Knowing the quantity of milk lost from underfeeding protein will aid producers and nutritionists in balancing the economic and environmental risks and benefits of underfeeding and overfeeding protein.
Technical Abstract: Thirty-two multiparous and sixteen primiparous Holstein cows in mid lactation averaging 126 days in milk were used to determine the effects of rumen degraded protein (RDP) on intake, milk production, and milk composition. Cows were assigned to diets in a repeated Latin square design with 3-wk experimental periods. Diets were formulated to provide four concentrations of dietary RDP (6.8, 8.2m 9.6, and 11.0% of dry matter (DM)) while rumen undegraded protein remained constant (5.8% of DM). Diets contained 50% corn silage and 50% concentrate (DM basis). Ingredients within diets were equal across treatments except for ground corn, soybean meal, and ruminally protected soybean meal. Dry matter intake was reduced for the lowest RDP diet, but was unchanged for other diets. Milk yield, fat yield, and protein yield all increased linearly when cows were fed diets greater RDP. Milk fat and protein concentration each increased by 0.16 percentage units for cows fed 11% RDP compared to 6.8% RDP. For the three most deficient diets, milk protein yield increased by 0.29 g/d for every 1 g/d increase in RDP. As RDP increased, the efficiency of N utilization declined linearly. Milk urea N increased linearly when cows were fed increasing amounts of RDP, indicating increased losses of N via urine. These data show an environmental benefit from underfeeding RDP to dairy cows but at a high financial cost.