Effects of dietary urea levels on milk protein fractions of Holstein cows

• Published in: Animal feed science and technology Vol. 140; no. 1; pp. 191 - 198
• Main Authors: Aquino, A.A., Lima, Y.V.R., Botaro, B.G., Alberto, C.S.S., Peixoto, K.C., Santos, M.V.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 2008; [New York, NY]: Elsevier Science; Elsevier
• Subjects: Animal productions; Biological and medical sciences; Casein; cow feeding; crude protein; Dairy cow; dairy cows; energy intake; Feed and pet food industries; Food industries; forage; Fundamental and applied biological sciences. Psychology; Holstein; milk composition; milk protein percentage; Milk urea nitrogen; net energy for lactation; Non-protein nitrogen; nonprotein nitrogen; protein supplements; regression analysis; soybean meal; sugarcane; Terrestrial animal productions; true protein content; Urea; Vertebrates; Whey protein; Dairy cow; Urea; Non-protein nitrogen; Casein; Milk urea nitrogen; DM; RUP; Whey protein; CP; NPN; RDP; Farming animal; Dairy cattle; Non protein nitrogen; Vertebrata; Milk protein; Mammalia; Cow milk; Ureas; Artiodactyla; Ungulata
• ISSN: 0377-8401; 1873-2216
• DOI: 10.1016/j.anifeedsci.2007.03.005

The aim of this study was to evaluate the effects of substituting soybean meal for urea on milk protein fractions (casein, whey protein and non-protein nitrogen) of dairy cows in three dietary levels. Nine mid-lactation Holstein cows were used in a 3 × 3 Latin square arrangement, composed of 3 treatments, 3 periods of 21 days each, and 3 squares. The treatments consisted of three different diets fed to lactating cows, which were randomly assigned to three groups of three animals: (A) no urea inclusion, providing 100% of crude protein (CP), rumen undegradable protein (RUP) and rumen degradable protein (RDP) requirements, using soybean meal and sugarcane as roughage; (B) urea inclusion at 7.5 g/kg DM in partial substitution of soybean meal CP equivalent; (C) urea inclusion at 15 g/kg DM in partial substitution of soybean meal CP equivalent. Rations were isoenergetic and isonitrogenous—160 g/kg DM of crude protein and 6.40 MJ/kg DM of net energy for lactation. When the data were analyzed by simple polynomial regression, no differences were observed among treatments in relation to milk CP content, true protein, casein, whey protein, non-casein and non-protein nitrogen, or urea. The milk true protein:crude protein and casein:true protein ratios were not influenced by substituting soybean meal for urea in the diet. Based on the results it can be concluded that the addition of urea up to 15 g/kg of diet dry matter in substitution of soybean meal did not alter milk protein concentration casein, whey protein and its non-protein fractions, when fed to lactating dairy cows.