Resumen

TORRES, René et al. Effect of grazing methods on modulated savannas: III. Weight changes of steers. Zootecnia Trop. [online]. 2004, vol.22, n.4, pp.333-346. ISSN 0798-7269.

The research was carried out in the Experimental Module at Mantecal, Apure state, Venezuela (7º35’ N and 69º10’ W), during the period 1984-1998, with the objective to evaluate the dynamic of weight changes of steers on hyperstational savannas with 5 months of water deficit and 5 months of excess of humidity. Two hundred hectares were assigned with similar proportions of upper, medium, and lower physiographic positions in the module to the following treatments: Continuous Grazing (CG), Deferred Grazing (DG) as the use of upper areas during the peak of the rainy season, the medium areas in the transition period rain-dry and dry-rain, and the lower areas during the dry period; and Deferred-Rotary Grazing (DRG) with similar grazing management than DG, but with three and six subdivisions in their medium and lower areas, respectively. The mean stocking rate was 0.50 AU/ha, constituted by herd cows and 12 steers of 220 kg of initial weight, which were changed annually and weighted every 45 days. Data were grouped in 1984-1989; 1990-1995, and 1997-1998 periods, considering the month of weight and analyzed as a completely random design. During the evaluated periods, there was not a significantly difference among treatments in the final animal weights. The mean weight was 85 kg/anim. and 48 kg/ha/year for first period. In the second period, it was 80.3; 76.8, and 88.7 kg/anim. and 37.7, 35.3 and 42.6 kg/ha/year in CG, DG, and DRG, respectively. During 1997 to1998 the productions were 121.1, 94.0, and 109.8 kg/anim. and 46; 36, and 42 kg/ha/year, in above order of treatments. At all times, the animals under CG lost weight for longest periods and significantly (P<0.50) than in DG, during dry season. Similarity between DG and DRG, when the later had a tendency to maintain the weight, resulting in greater efficiency in the dry period.

Palabras clave : savannas; grazing methods; steer; weight.