Two trials wereconducted to investigate different protein and energy sources in multiple supplementsfed to growing crossbred bulls. In the first experiment, performance of 20 crossbredgrowing bulls averaging 17 months of age and 265±18 kg of body weightwas evaluated in the dry season. Animals were maintained in 1.5 ha paddocksof Brachiaria brizantha with supplements being offered daily in a proportionof 0.75% of the body weight. A completely randomized design with a 2 x 2 factorialarrangement was used. Supplements contained whole soybean (WSB) or whole cottonseed(WCS) as the protein sources and rice bran (RB) or wheat bran (WB) as the energysources. No significant differences on the average daily weight gain (ADG),final body weight (FBW), and total weight gain were observed among diets inthis trial. The ADG and FBW averaged 0.589 and 318.2, 0.530 and 317.2, 0.620and 319.6 and 0.606 kg/day and 323.6 kg for animals fed supplements containingWSB/WB, WSB/RB, WCS/WB, and WCS/RB, respectively. The objective of the secondstudy was to estimate the carbohydrate fractions of the pasture and that ofthe feeds used in multiple supplements as well as their digestion rates usingthe gas production technique. Forage had higher indigestible fraction (C) andlower potentially degradable fraction (B2) compared to the supplements.Among supplements, WCS had the lowest C fraction while WSB and WB had the highestproportion of non-fiber carbohydrates (NFC). Although WCS had the highest contentof C fraction, it also showed the fastest rate of digestion of the B2fraction. Digestion rate of NFC were: 35.06, 14.86, 17.83 and 58.80, respectivelyfor RB, WB, WSB and WCS. The choice of each protein and energy source will dependon market price and availability because there were no significant differencesamong treatments. The structural carbohydrates (B2 e C) are responsiblefor the high concentrations of total carbohydrates in Brachiaria brizanthaduring the dry season, which averaged 80%. It was observed variations in thecarbohydrate fractions as well as in the degradation rates across supplements.
