Influence of restricted suckling and level of feed supplementation on postpartum reproductive performance of zebu and crossbred cattle in the semi-arid tropics

This study was carried out in central Tanzania on a group of 45 Zebu and 37 crossbred cows which were 4 to 10 years old. At calving time, the animals were allocated to one of the 4 treatment groups. In addition to free access to grazing for all cows in the study, in group H:AR (n = 18), cows were fe d a high level of concentrate supplementation (4kg/day) and calves were art ificially reared; in group H:RS (n = 24), cows were fed a high level of con centrate supplementation (4kg/day) and calves were only allowed restricted suckling up until the weaning age of 6 months. In group L:AR (n = 23) cows were fed a low level of concentrate supplementation (2kg/day) and calves we re artificially reared; and in group L:RS (n = 17) cows were fed a low leve l of concentrate supplementation (2kg/day) and calves were only allowed res tricted suckling up until the weaning age of 6 months. Milk progesterone wa s used as a means of determining the postpartum resumption interval (PRI) a nd the interval from parturition to conception (PCI). The overall PRI was 4 7.4 +/- 0.4 days and was significantly affected by breed but not by calving season, with crossbred cows exhibiting a shorter PRI than Zebu cows. The e ffect of the treatments was significant, with cows in the group H:AR displa ying a significantly shorter H:RI than those in the other groups, while cow s in group L:RS showed a significantly longer PRI than those in the other g roups. The overall PCI was 149.5 +/- 3.7 days, and was not significantly af fected by breed or calving season. The effect of the treatments was signifi cant, with cows in the group H:AR having a significantly shorter PCI than c ows in the other groups, while cows in group L:RS showed a significantly lo nger PCI. than those in the other groups. Crossbred cows had higher live we ights at calving (299.4 kg) than Zebu cows (272.6 kg), while all cows gaine d weight during the first 3 months after calving. The treatments had a sign ificant effect on weight gain, with cows in the group H:AR gaining signific antly more weight than those in the other groups. Cows which had high live weights at calving exhibited significantly shorter PRI and PCI than the lig hter cows. Animals which had gained more than 5 kg during the first month a fter calving, or which had gained more than 8 kg during the first 3 months after calving, showed significantly shorter PRI and PCI than cows which had gained less weight. The results show that the calf rearing system and the level of feed supplementation interact with each other and can influence th e postpartum anoestrous period in Zebu and Zebu crossbred cattle. Increasin g the level of nutrition in restricted suckling cows tended to improve the postpartum anoestrous period, but the positive effects of supplementation c ould not completely compensate for the negative effects of suckling.