The objective of this study was to evaluate the effects of protein sources and frequency of supplement offer on the intake and nutrient digestibility, on the concentrations of ammonia nitrogen (N-NH3), on rumen pH and on serum urea nitrogen concentrations in steers grazing pasture of Brachiaria brizantha cv. Marandu during the dry season. Five crossbred Zebu × Angus steers with initial live weight of 295 kg, castrated and fitted with rumen canullae were used in a 5 × 5 Latin square design. It was evaluated two isoprotein supplements, one with soybean meal (SM) and the other with high energy cottonseed meal, offered at two frequencies: every day (7 times a week), or 3 times a week (on Mondays, Wednesdays and Fridays); and a mineral mixture (MM). The supplementation increased the intake of CP, of ether extract (EE) and non-fibrous carbohydrates (NFC) in kg/day. The supplement with cottonseed meal increased the intake of ether extract. There was a positive effect of the three times a week supplementation on the intakes of total dry matter, of forage, of organic matter of forage, total carbohydrates (TC) and NDF. The supplementation reduced the digestibility of the NDF and increased the digestibility of the CP. The supplement with cottonseed meal reduced digestibility of NDF and total carbohydrates. Three times a week supplementation did not affect digestibility of the nutrients neither the rumen pH. Supplement intake increases concentrations of N-NH3, especially if it is carried out 3 times a week. Concentrations of urea nitrogen in the serum of growing steers increase.
frequency supplementation; pasture; rumen; supplement
