AN EVALUATION OF THE PRODUCTION POTENTIAL OF 6 TROPICAL GRASSES UNDER GRAZING .2. ASSESSMENT OF QUALITY USING VARIABLE STOCKING RATES

The potential quality of the 6 pasture grasses Setaria sphacelata var. sericea cvv. Nandi, Kazungula and Narok and var. splendida, Digitaria eriantha ssp. pentzii (pangola grass), and Pennisetum clandestinum cv. Whittet (kikuyu grass) was assessed in terms of liveweight gain of beef cattle, using a leader and follower grazing system. Pasture management was designed to provide adequate quantities of young leaf to the leaders throughout the year. This was achieved by rotational grazing and weekly adjustment of the number of followers, depending on quantity of feed available. Annual liveweight gain of the leaders (kg/steer.year) ranged from 135 (kikuyu grass) to 159 (cv. Narok) (540-636 kg/ha.year). Differences between grasses on an annual basis and over summer were not statistically significant (P = 0.12), although significant differences in liveweight gain of leaders were obtained during the winter. This was associated with differences between grasses in growth at lower temperatures, and in frost tolerance. Liveweight gain of the follower group was markedly higher for pangola grass and var. splendida (272 kg/ha.year) than for the other varieties (77-140 kg/ha.year). This difference was associated with differences in number of grazing days and in the superior liveweight gain per head of followers grazing pangola grass and splendida. Liveweight gain of leaders per annum was comparable for years 1 and 2 but fell dramatically from February to August in year 3. This was associated with high rainfall, reduced solar radiation, and a decrease in in vitro digestibility of plucked leaf of all setaria varieties but not of pangola or kikuyu grasses. The relatively low liveweight gains obtained in year 3 were not associated with any overall mineral or protein deficiency.