Effects of Marandu pastures heights and sources of energy supplements on the weights gains per animal and per area
The study aimed to evaluate forage allowance based in sward heights, and energy supplementation from different sources in the weight gain of young Nellore bull yearling in pastures of Urochloa brizantha cv Marandu. Grazing system was continuous with variable stocking (put and take animals) to maintain the sward height during the rainy season. Three pasture heights (15, 25, 35 cm) were combined with three supplementation strategies (Mineral mixture, protein/energy supplement based in corn meal, and protein/energy supplement based citrus pulp) distributed in eighteen paddocks (Two pasture replications). Both energy/protein supplements contained 19.0% of crude protein, and were supplied at 0.3% of body weight/day. Experiment was conducted from January to April. Forage mass, and animal body weight were determined monthly to calculate the forage allowance. One hundred and eight animals (259 +/- 20 kg) were grazed for 122 days and weighed at the beginning and the end of the trial. Total dry matter intake was evaluated using modified lignin LIPE® (eternal marker), and indigestible neutral detergent fiber (internal marker). The type of supplementation did not influence (P > 0.05) any pasture variable evaluated during the experimental period. To maintain pastures heights it was necessary to adjust the stocking rate that decreased linearly (6.64, 5.03 and 4.08 UA/ha-1) in response to the treatments (15, 25 and 35 cm, respectively). Forage allowance, and dry matter intake increased linearly (P < 0.05) in response to the pasture heights, or forage allowance. Gain per unit of land showed a quadratic response associated to lowest weight gains per unit of land (6.94, 6.38, and 5.37 kg/ha/day) in response to pasture heights (forage allowance), but there was a positive response in individual animal weight gain (0.694, 0.874 and 0.953 kg/day). Protein/energy supplementation increased (P < 0.05) weight gain per area and per animal. Citrus pulp provided greater (P < 0.05) stocking rates (5.4 AU/ha), but corn was similar (5.3 AU/ha) to both mineral (5.0 AU/ha) and citrus pulp. Pasture management at 15 cm during the rainy season resulted in highest stocking rate, and consequently more weight gain per area. However, lowest forage allowance reduced forage intake, average daily weight gain, and final body weight at the end of the rainy season. It was concluded that the pasture energy/protein supplementation (0.3% BW) provides a balance between gain per area, per animal, and low risks to pasture degradation and maximum productivity in the system.
Keywords: Beef cattle, supplementation, weight gain