title: Adaptation of lactating cows to rations containing urea.
abstract: Effects of a progressive change in 6 wk from a urea-free concentrate to one providing .34 (medium) or .66 g (high) urea/kg body weight on jugular blood composition and animal performance were studied with 27 cows. Consumption of dry matter was not affected even at the high rate of urea intake. Milk production was maximum when after 6 wk daily intake of urea reached .34 g/kg body weight, but higher rates of urea intake decreased milk yield and milk fat content. Butyrate through caproate were lower in milk lipids of urea-fed cows than for controls. While medium urea increased stearate, the high rate elevated linoleate. Ammonia and urea in serum were increased by transition to the high urea intake. Nonessential amino acids of serum were increased during adaptation to the medium rate of urea consumption but decreased with the high rate. Transitions to medium or high urea intakes did not affect the essential amino acids of serum. Adaptation of 6 wk was preferable to 3 wk to reach a daily intake of urea of .34 g/kg body weight in cows producing up to 18 kg of milk per day.
mesh_terms: D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004032:Diet; D005260:Female; D007774:Lactation; D009584:Nitrogen / Q000097:blood / Q000378:metabolism; D011247:Pregnancy; D014508:Urea
chemical_list: D014508:Urea; D009584:Nitrogen