The effect of stocking rate on the performance of beef cows and their progeny in the highland sourveld areas of Natal.

Abstract

In three separate. but related studies, the performance of weaner/replacement heifers, dry pregnant cows, and first calvers and mature cows and their progeny, at different stocking rates in the Highland Sourveld, was investigated. The study area was located in Bioclimatic region 4e in the Province of Natal, Republic of South Africa. In the first study, carried out over four seasons, the effect of winter and summer nutritional levels on the performance of replacement heifers, bred at two years of age, was investigated. The results of this study indicated that compensatory growth was a potentially important factor in reducing feed costs, but the degree of compensation was highly dependent upon stocking rate and the condition of the veld. The most economical regime for rearing heifers up to the mating stage was a low growth rate (0 - 0,25 kg/day) during the first winter (post weaning) followed by a low stocking rate (0,75 AU/ha) on summer veld. Treatment did not generally affect the number of heifers attaining puberty, nor their conception rates. Pregnancy rates as high as 96% were achieved. Treatment also had no apparent effect on subsequent calving rates. In the second series of experiments, the role of condition scoring as a management tool in the Highland Sourveld was studied. The condition score of the cow was shown to be an important factor determining conception rate and time of conception. Only 8% of the cows mated at a condition score of 1,5, conceived, whereas 80% conception rates were achieved when the cows were mated at a condition score of 3,0 - 3,5. The cost of improving a cow's condition from 1,5 to 3,0 was R108, whereas the cost of improving a cow's condition from 2,0 to 3,0 was R54. In the third study, carried out over nine consecutive seasons, the effect of stocking rate and lick supplementation on the performance of iactating cows and first calvers was investigated. Four stocking rates were applied - 0,83, 1,0, 1,25 and 1,67 cows plus calves per hectare. The very high stocking rate was terminated after four seasons because of a significant decline in both cow and calf performance, and the severe deterioration of the natural pasture. There was no benefit to either the cows or calves with access to a urea-based lick at the very high stocking rate, but at the low stocking rate (1,0 cow + calf/ha) the cows were in such a condition that the grazing season could have been extended, thereby saving on winter feed costs. First calvers produced weaners as heavy as those of the mature cows and were in similar body condition at the end of the grazing season. The excellent performance of the first calvers was attributed largely to the fact that they calved 3 - 4 weeks prior to the mature cows. The grazing behaviour of the first calvers and the mature cows, at the different stocking rates, was observed in the fourth study which was carried out over two consecutive seasons. There were no significant differences in the grazing time between the first calvers and the mature cows at any of the stocking rates. In all the treatments, the first calvers appeared to establish the grazing patterns, with the mature cows adopting a followership role. Alloparental behaviour was noted in the early part of both grazing seasons.