Long-term effects of contrasting forage allowances on sward structure and cattle performance in native grasslands of the biome Pampa

Abstract

Extensively managed systems in the Pampa biome present suboptimal zootechnical performance, which can be improved by adjusting grazing intensity. The long-term effects of grazing intensities on vegetation structure and animal production were observed in an experiment that was established in 1987 in Eldorado do Sul, Rio Grande do Sul State, Brazil. Treatments consisted of forage allowances (FA) of a native grassland: 4, 8, 12, and 16% (kg DM/100 kg BW), and a variable allowance of 8–12% (8% in spring and 12% during rest of the year), in a randomized complete block design with two replicates. Evaluated variables were sward height (SH) and herbage mass (HM) of the lower stratum (between tussocks), tussock cover (%), average daily gain (ADG), and live weight gain per hectare (Gha).  Long-term maintenance of FA resulted in contrasting sward structures, with increasing SH and tussock cover from the lowest to the highest FA (4, 5, 7, 8, and 9 cm; and 2, 28, 31, 37, and 44%, respectively, for the 4, 8, 8–12, 12, and 16% FA treatments – annual average). Herbage mass decreased from highest to lowest forage allowance: 1778, 1535, 1428, 1238 and 818 kg ha-1 for treatments 16, 12, 8-12, 8 and 4% FA, respectively. Average daily gain (ADG) was greater under 8–12%, 12%, and 16% FA (0.2 kg animal⁻¹ day⁻¹) compared to 8% FA (0.1 kg animal⁻¹ day⁻¹). The 4% FA significantly compromised ADG (0.03 kg LW animal⁻¹ day⁻¹). For Gha, the 8–12% FA presented best performance (166 kg LBW ha⁻¹ year⁻¹) . The greatest live weight gains were recorded in spring (48 kg LW ha^-1) followed by summer (36 kg ha^-1) seasons (average of treatments). Structural control provided by adjusting grazing intensity to 8–12% FA favored both animal individual performance and production per area in natural grasslands of the Pampa biome.