title: Lactational responses to ruminally undegradable protein by dairy cows fed diets based on alfalfa silage.
abstract: Lactational responses to protein supplementation of diets containing 60% of DM as alfalfa silage were evaluated. Sixty muliparous Holstein cows were fed a covariant diet for the first 3 wk postpartum, blocked by calving date, and randomly assigned for 14 wk to one of six isonitrogenous (19.4% CP) diets. Diets were formulated with soybean meal, a blend of animal by-products, or both, and contained 5.0, 5.6, 5.6, 6.2, 6.1, and 6.8% ruminally undegradable protein (DM basis). Percentage of ruminally undegradable protein or source of supplemental protein did not affect 3.5% FCM (39.4 kg/d), milk fat yield (1.38 kg/d), milk protein percentage (2.83%), milk urea (7.66 mM), or plasma urea (8.91 mM). However, cows fed diets supplemented with soybean meal had higher DMI (26.2 vs. 24.7 kg/d), milk yields (40.4 vs. 39.1 kg/d), and milk protein (1.15 vs. 1.09 kg/d) yields, but lower milk fat concentration (3.42 vs. 3.53%) and body condition score (2.85 vs. 2.93) than cows fed diets containing a blend of animal by-products. The lack of response to ruminally undegradable protein was partially caused by higher than predicted DMI (5 to 15% above NRC predictions); all diets provided at least 1.3 kg of ruminally undegradable protein, and there was no beneficial effect from ruminally undegradable protein intake increases to 1.6 kg/d.
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706.
authors.forename: M A
authors.initials: MA
authors.lastname: Wattiaux
authors.forename: D K
authors.initials: DK
authors.lastname: Combs
authors.forename: R D
authors.initials: RD
authors.lastname: Shaver
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition; D001835:Body Weight; D002417:Cattle / Q000502:physiology*; D004044:Dietary Proteins / Q000008:administration & dosage / Q000494:pharmacology*; D005232:Fatty Acids, Volatile / Q000378:metabolism; D005260:Female; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology*; D008055:Lipids / Q000032:analysis; D000455:Medicago sativa; D008892:Milk / Q000737:chemistry; D008894:Milk Proteins / Q000032:analysis; D012417:Rumen / Q000378:metabolism*; D012820:Silage; D014508:Urea / Q000032:analysis / Q000097:blood
chemical_list: D001786:Blood Glucose; D004044:Dietary Proteins; D005232:Fatty Acids, Volatile; D008055:Lipids; D008894:Milk Proteins; D000641:Ammonia; D014508:Urea