EFFECT OF SOURCE AND AMOUNT OF PROTEIN ON MILK-PRODUCTION IN DAIRY GOATS

Forty multiparous Alpine does (mean BW of 61.5 kg) were utilized in a 13-wk trial to investigate the effects of a TMR differing in CP amount (13 or 17%) and source (solvent-extracted soybean meal or heat-treate d soybean meal with or without urea) on lactational performance. Prote in supplements contributed 30% of the N in 13% CP diets and 50% of the N in 17% CP diets. All diets were isoenergetic (2.5 Mcal of metaboliz able energy/kg of DM) and were fed for ad libitum intake for the entir e trial. Mean DMI (2.88 kg/d), milk production (2.65 kg/d), milk fat ( 4.05%), milk protein (2.68%), milk lactose (4.54%), and milk SNF (7.81 %) did not differ among dietary treatments. Plasma urea N was greater (23.2 vs. 10.9 mg/dl) in does receiving the 17% CP diets; however, blo od hematocrit (27.4%), beta-hydroxybutyrate (843 muM, plasma glucose ( 68.8 mg/dl), NEFA (600 mueq/dl), and plasma total protein (74.5 g/L) w ere not significantly affected by treatment. The apparent absence of a dietary effect on lactational performance may be due to the high DMI of the does (4.7% when expressed as DMI per kilogram of BW) and high C P intake providing a surfeit of protein relative to requirements.