Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2006
Publication Date: 4/1/2007
Citation: Brito, A.F., Broderick, G.A. 2007. Effects of different protein supplements on milk production and nutrient utilization in lactating dairy cows. Journal of Dairy Science. 90:1816-1827. Interpretive Summary: Protein supplements are usually the most costly ingredients in the diets fed to dairy cows. When too much protein is fed, or protein is used inefficiently, dairy cows will excrete most of the excess nitrogen resulting from protein catabolism in the urine. Urinary nitrogen is the most polluting form of excretory nitrogen. Soybean meal is the principal protein supplement fed to dairy cows in the U.S. However, a number of other oilseed meals, such as cottonseed meal and canola meal, are less expensive and could be used to replace soybean meal as the dietary protein supplement. Urea is a much cheaper source of dietary “crude protein” than any of the oilseed meals commonly fed to dairy cows and has often been used to replace part of the protein in the cow’s diet. We conducted an experiment to compare urea, soybean meal, cottonseed meal, and canola meal as protein supplement for lactating dairy cows. Diets were composed of alfalfa silage, corn silage and high moisture corn, typical ingredients fed to dairy cows in the U.S. Except for the source of protein supplement, all diets were the same and contained 16.5% total protein. Yield of milk and milk components was 20 to 35% lower, and urinary nitrogen excretion substantially greater, when cows were fed supplemental protein as urea rather than one of the 3 oilseed meals. The value of lost milk yield was much greater than the cost savings when urea was fed. Also, cows fed canola meal rather than cottonseed meal produced more milk protein and milk fat, while fat and protein yield was intermediate in cows fed soybean meal. Canola meal was the least expensive source of supplemental protein among the 3 oilseed meals. This research indicates that there are substantial differences in the value of proteins fed to U.S. dairy cows and that urea is ineffective as a protein supplement in diets based on alfalfa and corn silages and corn grain. This research also shows that dairy farmers could save money, and at the same time maximize production, by feeding canola meal as the supplemental protein.
Technical Abstract: Sixteen (8 ruminally cannulated) multiparous and 8 primiparous lactating Holstein cows were used in 6 replicated 4 x 4 Latin squares to test the effects of feeding supplemental protein as urea, solvent soybean meal (SSBM), cottonseed meal (CSM), or canola meal (CM) on milk production, nutrient utilization and ruminal metabolism. All diets contained (% of dry matter) 21% alfalfa silage and 35% corn silage plus: 2% urea plus 41% high moisture shelled corn (HMSC), 12% SSBM plus 31% HMSC, 14% CSM plus 29% HMSC, or 16% CM plus 27% HMSC. Crude protein was equal across diets, averaging 16.6%. Intake and production were substantially reduced, and milk urea, blood urea, and ruminal ammonia were increased, on urea versus the diets supplemented with true protein. Although intake was lower in cows fed SSBM compared to CM, no differences were observed for milk yield among SSBM, CSM, and CM. Yields of fat and protein both were lower on CSM than on CM, while SSBM was intermediate. Milk urea and milk protein content also decreased when CSM replaced SSBM or CM. Diet did not affect ruminal VFA except that isobutyrate concentration was lowest on urea, intermediate on CSM, and greatest on SSBM and CM. Urinary excretion of urea N and total N was greatest on urea, intermediate on SSBM and CM, and lowest on CSM. Apparent N efficiency (milk N/N intake) was lower on CSM than on the SSBM diet. Overall, production and N utilization were compromised when high yielding dairy cows were supplemented with urea rather than true protein and the value of the true proteins, from most to least effective, was in the order CM > SSBM > CSM.