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Adjusting Ration Protein as Lactation Advances

Dairy Pipeline: July 2000

Charles C. Stallings
Extension Dairy Scientist, Nutrition
Virginia Tech
(540) 231-4758

New study shows advantage of adjusting ration protein as lactation advances. A study in the May issue of the Journal of Dairy Science by Drs. Wu and Satter of the University of Wisconsin demonstrates the need for protein changes with stage of lactation and production level. Dr. Wu spent some time at Virginia Tech working with Dr. Carl Polan. The authors fed groups of cows differing amounts of protein in weeks 1 to 16 versus weeks 17 to 44. Crude protein in diets was 15.4 & 16.0%, 17.4 & 16.0%, 17.4 & 17.9%, and 19.3 & 17.9%. Cows were fed alfalfa silage, corn silage, high moisture corn, roasted soybeans, and expeller processed soybean meal. Cows were also on BST. Ration rumen undegraded protein was 33.5% of crude protein on the 15.4 and 16% protein diets, 35.8% on the 17.4 and 17.9% protein diets, and 37.6% on the 19.3% protein diet. The 44 week (308 day) lactation resulted in 3.5% fat corrected milk of 23,518, 25,582, 25,969, and 25,430 lbs. Clearly the low protein regime was not adequate to support production at the same level as higher protein. Also moving cows from 17.4% to 16.0% protein at week 17 resulted in a decrease of milk production compared to cows that stayed on 17.9% protein. Cows at 17 weeks were producing about 88 pounds of milk. By week 30 productions were similar between the two groups suggesting that 16% protein was adequate at this time and milk production had dropped to 75 pounds. The highest level of protein did not appear to be of benefit. The authors suggest that cows producing above 24,000 pounds of milk in a 305 day lactation should be fed approximately 17.5% protein that is 35 to 37% rumen degradable. As production declines protein can be reduced but to no less than 16%. This study does demonstrate that protein above 18% in the ration dry mater is questionable from an economic and environmental standpoint even for high producing cows. Also it is possible to reduce ration protein as milk production drops especially after 30 weeks of lactation.

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