Abstract:
The objectives of the present research were to study the factors that influence postpartum reproductive characteristics of suckling beef cows in extensive production systems in Mozambique and to develop new management strategies to improve their reproductive efficiency. The effects and interactions between post-partum BW, BCS, age and parity number on plasma concentrations of estradiol, progesterone, creatinine, urea and cortisol around oestrus and the related conception rates of Bos indicus cows in extensive production system were analysed as well as the minimum BCS at the beginning of breeding to maximise the subsequent conception rates. Thirty-five days prior to the breeding season cows were synchronised using Crestar. During the second oestrus after synchronisation, 18 blood samples were collected per animal for hormonal analysis, from 24 hr before oestrus to 24 hr after oestrus. The hormonal pattern of estradiol and progesterone around oestrus were similar to that observed in Bos taurus cows under intensive conditions. Conception rates of cows in the experimental group were 90.5%. Better results on estradiol pattern and conception rates were related to a BCS of ≥ 2.5 and it was thus concluded that the post-partum management of extensive Bos inducus cows should aim to achieve at least a BCS of 2.5 at the beginning of the breeding season. Twelve-hour and 48-hr calf removal were conducted separately to evaluate their effects on conception rates of Bos indicus beef cows in extensive production systems and to quantify the related effects on calf-weaning weights. The 12-hr calf removal was performed from 45 days post-partum to the beginning of the breeding season, and the 48-hr calf removal was performed preceding the onset of the breeding season. It was concluded that 12-hr calf separation at night enhance the energy balance (3%), increases the conception rates (80%) and improves the calf-weaning weights, whereas 48-hr calf removal increases conception rates (76%) and does not affect calf weaning weights. Both calf removal management strategies concentrate conceptions in the early part of the breeding season and stress the importance of the effect of BCS and estradiol on conception rates in Bos indicus beef cows in extensive production systems.
