Two experiments were conducted aiming to evaluate the effect of amounts of supplement on the intake, digestibility, body weight gain and microbial synthesis efficiency in beef cattle. Four Holstein-Zebu steers fistulated in the esophagus, rumen and abomasum with an average of 250 kg of body weight were used in experiment 1. The supplement was made up cottonseed meal, ground corn grain, mineral mixture and urea/ammonium sulfate. The diets were: control (salt) and supplements levels of 0.33, 0.66 and 1.00% of body weight (BW). Maximum intake of dry matter (DM), neutral detergent fiber (NDF) and total digestible nutrients (TDN) were estimated at 1.09, 0.73 and 1.20% of BW, respectively. It was observed a linear intake increase to organic matter (OM), crude protein (CP), ether extract (EE) and non-fiber carbohydrates (NFC) intake as supplement offer increased. The total digestibility from DM, OM, CP, EE and NDF increased linearly with the intake of supplement but no affected on microbial efficiency. Nineteen Zebu steers aging 18 months and mean body weight of 320 kg were used in experiment 2. The diets were: maintenance, control (salt), and the daily supplement offer of 1, 2 and 3 kg. It was observed linear increase in DM, OM, CP, EE, NDF and NFC intake as supplement offer increased. Maximum intake of TDN, diet TDN content and average daily gain (ADG) were estimated to occur as 2.88, 2.62 and 2.69 kg of supplement offer, respectively. A quadratic effect was observed for total digestibility in all diet components. The microbial efficiency was not influenced by diet supplementation. The neutral detergent fiber digestibility is highest for a intake of approximately 1.5 kg of the supplement/day, which results in the best response to the ADG obtained with the intake of 400 g of CP.
digestibility; intake; microbial efficiency
