No abstract

The inhibitory influence of the suckling stimulus on resumption of cyclicity post partum was elucidated for dairy cows by Oxenreider (1968) and for beef cattle by Short et al. (1972). In the traditionally managed herds in West Africa calves suckle their dam initially to stimulate milk let down, the cows are then milked and the calf is allowed to suckle the residual milk. Under such management calves normally suckle their dams for the entire lactation (mean 420 days, s.d. 138.6) as reported by Agyemang et al. (1990).In a trial to study milk conversion in the calf described by Agyemang et al. (1993) cows were allocated at calving to either a group in which they were milked the traditional way (n = 20), or to a group where calves were not allowed to suckle except for the first 4 days (n = 16). In the latter group milk let down was stimulated by oxytocin injection before morning and evening milking. All the cows were managed in the same herd and calved within a range of 2 months to avoid bias due to seasonal or nutritional influences. A fertile bull was always present in the herd.This study continues the work by Agyemang et al. (1993) by analysing the subsequent calving records of the dams to determine the differences in calving interval (CI) between the groups of suckled and non suckled cows.A summary of the data is given in Table I and these were analysed using the Wilcoxon 2 sample test. It was found that 60% of the non suckled cows had a CI of less than 390 days while 60% of the suckled cows had not calved by 480 days postpartum. The difference in the mean between the 2 groups of 138 days in favour of the non suckled group is highly significant (P < 0.01).The fate of 6 animals (37.5%) of the non-suckled group was not known and could not be determined in retrospect. Since these could have been cows with a very high CI a comparison was also made between the mean CI of the non-suckled group and 62-5% of the best animals of the suckled group revealing a reduced mean CI of 50 days in favour of non-suckled cows, 456 days and 406 days respectively.