Calf survival from embryo transfer-induced twinning in dairy-beef cows and the effects of synchronised calving

In each of 4 years, 94-116 mature cows had two 6-7-day-old embryos, produced by the in vitro fertilisation of oocytes, inserted non-surgically into one uterine horn of each cow. Starting 5 days before the expected date of calving, the cows were continuously observed and assistance at calving was provided when required. In year 1, perinatal calf survival was similar in twin-calving (TC) and single-calving (SC) cows (98.1 versus 100% for calves born to TC and SC, respectively). There was a higher incidence of assistance at birth for TC (52%) than for SC (21%). In years 2 and 3, the calving of 30 SC and 33 TC was synchronised using an injection of Opticortinol (OP) 6-9 days before the injection of Estrumate and Dexol-5 (E+D). A further 34 SC calved naturally. Synchronised calving reduced the spread of calving from 16-25 to 8-9 days without reducing perinatal calf survival and had no significant effect on the incidence of assistance at birth in SC. The TC in years 2 and 3 had a high incidence of retained placenta at 48 h (70%) and a high incidence of assistance at birth (85%). In year 4, calving was synchronised in 16 SC and 21 TC with E+D and no pre-treatment with OP, while 15 SC were treated with both OP and E+D. There were no effects of the hormone treatment on perinatal calf survival and only small effects on the incidence of assisted births for SC. The incidence of retained placenta at 48 h was lower for SC pre-treated with OP (40%) than for SC (88%) and TC (76%) not pre-treated with OP. Continuous supervision over calving produced perinatal calf survival rates for TC that were similar to SC, despite the higher incidence of assistance of TC at parturition. Hormonal synchronisation of calving can halve the time required for continuous supervision of calving, but the hormone treatments exacerbate the already high incidence of retained placenta in TC.