Effects of grazing systems on pasture production and quality of Brachiaria brizantha and liveweight gain of lambs .

Abstract

Grazing cycle beyond parasite survival time can reduce the level of parasite contamination, but at the same time it may depress the quality of available forage for animal production . A study was conducted to evaluate the effects of grazing management systems on the production and quality of Brachiaria brizantha and the performance of lamb grazing this pasture . A total of 72 male lambs aged from 3 to 4 months were used . The lambs were divided into 3 groups and randomly allocated to receive one of the following grazing treatments : GMl-pastures were grazed for 6 weeks and then rested for 6 weeks, GM2-pastures were grazed for 1 week and then rested for 6 weeks, and GM3-pastures were grazed for 12 weeks and then rested for 12 weeks . The herbage mass measured before and after grazing was greatest (P<0.01) forGM3. Canopy compositions before grazing   as not different (P>0 .10) among the three grazing methods, while after grazing, the proportion of stem fraction was highest and leaf fraction was lowest for GM3 (P<0 .01) . The in vitro dry matter digestibility (IVDMD) of plucked samples were not different (P>0 .10) among the grazing methods. The crude protein (CP) concentration was lower (P<0 .05) for GM3 as compared for GM 1 and GM2, and a difference of two percentage unitmay be of biological important. The changes in IVDMD and CP concentration of the plucked samples collected throughout grazing cycle remained reasonably steadily . Average daily gains (ADG) were low and not different (P>0 .10) across grazing treatment and ranged from 29 to 35 g. It was concluded that a 12-week grazing cycle while could increase the herbage mass of Brachiaria brizantha did not decrease feed intake, the digestibility and the crude protein concentration of the consumed forage . Therefore, this gazing system could be considered as a means to control parasite establishment on pastures.

 

Key words : Grazing systems, herbage mass, forage quality, sheep