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

In each of 4 years, 94-116 mature cows had two 6-7-day-old embryos, produce d by the in vitro fertilisation of oocytes, inserted non-surgically into on e uterine horn of each cow. Starting 5 days before the expected date of cal ving, the cows were continuously observed and assistance at calving was pro vided 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 bor n to TC and SC, respectively). There was a higher incidence of assistance a t 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 signi ficant effect on the incidence of assistance at birth in SC. The TC in year s 2 and 3 had a high incidence of retained placenta at 48 h (70%) and a hig h incidence of assistance at birth (85%). In year 4, calving was synchronis ed 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 t reatment 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 p re-treated with OP. Continuous supervision over calving produced perinatal calf survival rates for TC that were similar to SC, despite the higher inci dence of assistance of TC at parturition. Hormonal synchronisation of calvi ng can halve the time required for continuous supervision of calving, but t he hormone treatments exacerbate the already high incidence of retained pla centa in TC. (C) 2001 Elsevier Science B.V All rights reserved.