Aspects Of Climate, Herbage Growth And Animal Production In A Semi-arid Area Of Kenya

Abstract

The results obtained from two major field experiments conducted on a natural range land sward in a semi-arid area of Kenya are presented and discussed in relation to other relevant work. In the cutting trial 15 different combinations of cutting height and frequency were used to examine the effects of defoliation on the productivity and persistence of the natural sward. Over 10 growing seasons even the most severe of the treatments, in which the sward was cut every three weeks at 5cm height did not appear to cause irreversible decline in sward vigour in the absence of the grazing animal. Highest overall herbage yields were obtained with the relatively severe defoliation treatment of six-weekly cutting at 5cm height. A multiple regression model relating the herbage production to rainfall in the present, previous and penultimate three-week periods before cutting accounted for 62% of the variation in yield. No advantage was found in using estimates of actual evapotranspiration rather than rainfall in the regression. The role of such a model in the prediction of long term forage productivity and potential animal performance is also discussed. The grazing trial examined the performance of groups of beef steers under set stocking at two. three. four and five hectares per animal. over an eight year period. Performance per animal was relatively unaffected by stocking rate. with an overall growth rate of about 350g live weight gain per day over the whole study period. Growth rate at anyone time was found to be directly relatable to sward condition. which in itself was related to climatic season. Evidence is presented that the crossbred animals used were very selective in their grazing. especially in the dry season. so that provided adequate forage was available within which selection could be effective. reduction in grazing intensity did not lead to improvement in diet intake quality or quantity. The difficulties of estimation of diet quality and intake levels are discussed in relation to the present and other relevant studies. particularly with reference to the use of internal markers for estimation of diet digestibility. The role of mathematical models in the examination of the climate/vegetation/animal complex is discussed and some of the problems associated with their use are examined. suggestions are made for areas of work considered to be priorities for future attention to assist in improving the management and animal productivity of the semi-arid areas. Attention is given to the need for research information to support the change in land use in such areas from low population-density nomadism to a sedentarised production system, which is required to support a higher level of human population