Responses in urea and true protein of milk to different protein feeding schemes for dairy cows.
Four multiparous Holstein cows were used in a 4 x 4 Latin square to investigate the effects of protein concentration, degradability, and quality on plasma urea concentration and milk N constituents. Diets varied in the amount and proportion of RDP and RUP relative to NRC requirements: diet 1, excessive RDP, deficient RUP; diets 2 and 3, balanced for RDP and RUP; and diet 4, excessive RDP, balanced for RUP. Diet 3 was formulated for optimal AA balance as predicted by the Cornell Net Carbohydrate and Protein System. Diets contained 34% corn silage, 19% alfalfa haylage, and 49% concentrate (DM basis). Concentrates varied in amounts of urea and soybean, corn gluten, and fish and blood meals. Concentrations of urea N and NPN in milk varied among diets: diet 1, 19 and 34 mg/dl; diet 2, 16 and 31 mg/dl; diet 3, 15 and 30 mg/dl; and diet 4, 23 and 39 mg/dl, respectively. Increases in NPN concentration were attributed to increases in the urea fraction of NPN. Intake of RUP and AA balance influenced milk true protein content; diet 1, 2.89%; diet 2, 2.90%; diet 3, 3.01%; and diet 4, 2.95%. the proportions of true protein and urea in milk are influenced by CP concentration, protein type, and protein quality.
Baker
L D
LD
Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348, USA.
Ferguson
J D
JD
Chalupa
W
W
D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D004044:Dietary Proteins / Q000008:administration & dosage*; D004063:Digestion; D005260:Female; D007774:Lactation; D008239:Lysine / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D008892:Milk / Q000378:metabolism*; D008894:Milk Proteins / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D012417:Rumen / Q000378:metabolism; D014508:Urea / Q000097:blood / Q000378:metabolism*
D004044:Dietary Proteins; D008894:Milk Proteins; D014508:Urea; D008715:Methionine; D008239:Lysine; D009584:Nitrogen