THE PRODUCTION PARAMETERS INFLUENCING THE COMPOSITION AND STRUCTURE OF PASTORAL CATTLE HERDS IN A SEMIARID AREA OF KENYA

The size and composition of three herds belonging to Maasai pastoralis ts were monitored for more than 5 years (1990 to 1996). Animals were c ategorized as either suckling calves, weaned heifers, weaned males or breeding females. The dates of entries and exits were used to estimate the total number of observed animal days for each category. Fertility rates of breeding females and mortality and disposal rates for each c ategory were estimated using animal days as the denominator. Herd diff erences were tested using contingency tables. Age to first calving and calving intervals were estimated and examined using analysis of varia nce tests. The patterns of births and deaths were seasonally influence d. The mean annual calving rate of all breeding females was 65.6% and for females excluding first calvers was 46.9%. No herd effects were ob served. The mean observed interval between calvings was 609 days and t he calving interval, calculated from the parturition rate, was 649 day s with no herd differences. Mean age at first calving was approximatel y 4 years with no herd differences. Mean annual mortality rates were 8 .9% for breeding cows, 7.8% for weaned males, 6.7% for weaned heifers and 22.1% for calves. The mean annual culling rate of cows teas 10.8% and the sale rate of heifers and weaned males was 12.9% and 41.5% resp ectively. The mean age at disposal of heifers was 655 days and of stee rs was 801 days. Herd sizes were shown to fluctuate annually with no o bvious trend between herds. The main determinants of production identi fied were the effect of seasonally poor nutrition on the rate of repro duction and the effect of season, herd mobility and disease on mortali ty. The study describes production levels that can be used to predict future changes to the system. The results are discussed in terms of th e factors influencing and their relevance to pastoral development. The findings are compared with those observed in other, similar areas.