Performance of dairy heifers in a silvopastoral system

The characteristics of the pasture and performance of dairy heifers were evaluated in a silvopastoral system (SPS) established with Brachiaria decumbens grass in a consortium with four tree species (105 trees/ha) and in a monoculture system of Brachiaria decumbens (MS). Thirty-two paddocks (0.5 ha/paddock) were used, sixteen for each system (SPS and MS). The paddocks were managed under rotational stocking, with seven days occupation and 35 and 45 days of rest during the rainy and dry seasons, respectively. The treatments were distributed in a randomised block design with two repetitions. The heifers used had an initial weight of 200 kg and a variable stocking rate as a function of the herbage allowance of 7.0 kg of DM/100 kg of body weight/day. The forage mass was estimated at each grazing cycle. For each sample, the DM, crude protein and neutral detergent fibre contents were determined as well as the in vitro dry matter digestibility (IVDMD). All animals were weighed every 35 days to estimate daily body weight gain and weight production per area. The forage dry mass, stocking rate and herbage allowance were similar between the systems studied, but they varied according to season. Average values of 2031 and 1100 kg/ha/grazing cycle, 1.6 and 0.8 AU (Animal unit = 450 kg of body weight)/ha and 7.2 and 5.0 kg DM/100 kg of body weight were estimated for the rainy and dry seasons, respectively. The values for crude protein content were higher in the SPS in the rainy season, while the NDF and IVDMD did not vary with raising system. The body weight gains per animal and per hectare in the dry season did not vary, but were higher in the SPS during the rainy season in the first and third experimental years. The annual body weight gains were also higher in SPS than in the MS. It was concluded that the SPS is more efficient for rearing dairy heifers than the MS due to the higher body weight gain per heifer and per area. (C) 2011 Elsevier B.V. All rights reserved.