Abstract
The objective of this study was to assess the sward canopy structure of Brachiaria brizantha cv. Marandu pastures maintained in three grazing intensities under continuous stocking system during the rainy season, along with the behavior and performance of grazing beef heifers supplemented with mineral salt or an energy/protein supplement. Three levels of forage allowance were assessed: 2.0, 2.5 and 3.0 kg of forage/kg of live weight, combined with two supplements (ad libitum mineral salt, and an energy/protein supplement at 0.3% of live weight/day, supplied daily). The experiment was designed as a randomized block study with two replications. The supplements did not influence the variables related to the canopy structure. Canopy height was greater at higher forage allowances during the late summer and early fall. Similarly, the stem mass was greater in pastures with higher forage allowances. Animals fed protein supplement spent less time grazing than animals supplemented with mineral salt. Stocking rate was higher in pastures with lower forage allowance levels, which increased the live weight gain per grazing area. Daily weight gain did not vary according to the forage allowance levels. The use of an energy/protein supplement did not affect the stocking rate; however, it increased individual live weight gain and live weight gain per grazing area compared with mineral salt supplementation. The use of energy/protein supplements is an efficient alternative to enhance animal performance and production under grazing systems during the rainy season
Highlights
The Brazilian beef cattle industry is primarily based on the use of pastures
In the pastures managed for a forage allowance of 2.0 kg of GFM/kg of LW, the allowance observed was close to the specified for all experimental periods (1.81 kg GFM/kg LW), while in paddocks with a forage allowance of 2.5 kg GFM/kg LW, the average allowance in the first three time periods was 2.44 kg GFM/kg LW; during the last period, there was a trend toward increasing allowance (3.29 kg GFM/kg LW)
Forage allowances were similar between supplement types (1.8, 2.7 and 3.3 in pastures that used mineral salt, and 1.8, 2.6 and 3.3 in those that used the energy/protein supplement); this was expected, since that the criteria used for the maintenance of forage allowance were the same in all combinations
Summary
The Brazilian beef cattle industry is primarily based on the use of pastures. In this setting, grasses belonging to the genus Brachiaria are extremely important, regardless of whether the production system used is intensive or extensive. Sollenberger et al (2005) proposed a new method to calculate forage allowance in kilograms of forage per kilograms of live weight This method consists of a mathematical formula that only considers the relationship between forage mass and stocking rate without including the effect of time, facilitating the use of the technique, since that estimates of forage accumulation are laborious and the results yielded often have low precision, especially under continuous stocking systems. Because this technique is easy to use, it allows the development of recommendations for pasture utilization, which may be adopted by producers to increase the efficiency of animal production under grazing systems
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