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United States Department of Agriculture

Agricultural Research Service

Title: Effect of Increasing Ruminally Degraded Protein on Lactation Performance of Dairy Cows

Authors
item Baldwin, Ransom
item Kalscheur, K. - SO DAKOTA UNIV, UMD STUD
item Kohn, R. - UNIV OF MARYLAND
item Glenn, Barbara - FEDERATION OF ANML SCI SO

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 2002
Publication Date: N/A

Interpretive Summary: Dairy cows digest feed in a large fermentation vat, called the rumen, prior to absorbing nutrients further down the digestive tract. Sometimes part of the diet is not fermented in the rumen, this is important because it may change how much milk is produced and how much nitrogen is excreted. Nitrogen that is excreted on the ground has become a problem because there is often too much and it is a pollutant. Thirty-two lactating cows were used to determine if changing the amount of protein that is degraded in the rumen changed feed intake and milk production. Cows were assigned to diets which provided four concentrations of protein for rumen digestion but did not change rumen undegraded protein. Dry matter intake was significantly lower for diet 1, but was unchanged for diets 2, 3, and 4. Milk yield, fat yield, and protein yield all increased when cows were fed increasing amounts of protein for ruminal digestion. Milk fat and protein concentration each increased by 0.16 percentage units for cows fed diet 4 compared to diet 1. There was no difference in milk production and composition between Diets 3 and 4. Efficiency of nitrogen utilization declined linearly as the protien for digestion in the rumen increased. Milk urea N increased linearly when cows were fed increasing amounts of rumen digested protein, resulting in increased losses of nitrogen via urine. Lactation performance was improved when cows were fed increasing levels of rumen digested protein up to a point, thereafter however, milk production did not increase but N excreted went up.

Technical Abstract: Thirty-two multiparous and sixteen primiparous cows in midlactation were used to determine the effects of increasing dietary ruminally degraded protein (RDP) on intake, milk production, and milk composition. Cows were assigned to 1 of 4 diets in a replicated 4 × 4 Latin square design with 3- wk experimental periods. Diets fed provided four concentrations of dietary yRDP (% of DM) while rumen undegraded protein (% of DM) remained constant: 1) 7.4% RDP; 2) 8.5% RDP; 3) 9.8% RDP; and 4) 11.0% RDP. Diets contained 50% corn silage and 50% concentrate (DM basis). Ingredients within diets were equal across treatments except for changes in ground corn, soybean meal, and ruminally protected soybean meal (Soypass ). Dry matter intake was significantly lower for diet 1 (P<0.05), but was unchanged for diets 2, 3, and 4. Milk yield, fat yield, and protein yield all increased (P<0.05) when cows were fed increasing amounts of RDP. Milk fat and protein concentration each increased by 0.16 percentage units for cows fed diet 4 compared to diet 1 (P < 0.05). There was no significant difference in milk production and composition between Diets 3 and 4. As RDP increased, the efficiency of nitrogen utilization declined linearly. Milk urea N (P<0.001) increased linearly when cows were fed increasing amounts of RDP, indicating increased losses of nitrogen via urine. Lactation performance was improved when cows were fed increasing levels of RDP up to Diet 3. Additional RDP beyond 9.8% of diet DM did not significantly increase milk production but did increase N excreted.

Last Modified: 10/30/2014
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