INFLUENCE OF PROTEIN PERCENT AND SOURCE ON COWS IN EARLY LACTATION

Four rations were compared in 68 lactating cows (17 per group) from 14 to 140 days postpartum. Treatments were negative control (12.5% crude protein of plant origin), positive control (16% crude protein of plant origin), urea (16% crude protein-75% from plant origin, 25% from urea in both urea-treated silage and in concentrate), ammonia-urea (16% crude protein-similar to urea except that silage was treated with ammonia). Mean daily milk yields, adjusted by covariance, from 3 to 20 wk did not differ and were 28.0, 29.0, 27.9, and 27.5 kg for the respective treatments. For wk 3 to 6 postpartum, high producing cows (over 25 kg during wk 2) from the positive control outyielded those on urea. Intakes of dry matter and calculated net energy did not differ between treatments but were generally higher for the negative control. Production of milk or composition of its major components did not differ. Rumen ammonia and urea of plasma reflected quantities of protein and nonprotein nitrogen fed. Milk yields of cows in early lactation were not significantly increased by added soybean meal or by nonprotein nitrogen to raise the crude protein of corn silage-type rations from 12.5 to 16%. © 1979, American Dairy Science Association. All rights reserved.