الكاتب: Multiple References

The experiment was conducted during two years in a herd of Mertolengo cattle kept at pasture. In both years, cows (n = 141) were treated with a progestagen plus equine chorionic gonadotrophin (eCG) to synchronize the oestrous cycle. In year 1, cows were randomly allocated to three groups: i) artificial insemination (AI); ii) transfer of an embryo into the uterine horn contralateral to the corpus luteum seven days after AI (AI+ET); and iii) bilateral embryo transfer (2ET). Embryos were produced in vitro (IVP) and frozen in ethyleneglycol to allow the direct transfer after thawing. In year 2, cows were allocated to groups AI or AI+ET (only single ovulating cows in this group). In year 1, the calving and twinning rates were similar for the three groups (overall: 46.4 % and 11.5 %, respectively) and, in group AI+ET the survival of ET-derived embryos was negatively affected by the presence of double or multiple ovulations. In year 2, the calving and twinning rates of group AI+ET were 41.5 % and 52.9 %, respectively. In both years, the fertility rate of treated cows at the end of the breeding season was similar to that of the remaining untreated cows in the herd. Compared to single calving cows, twin calving cows had a significantly shorter gestation lenght, lower birthweight of calves, higher perinatal mortality of calves, and longer intercalving interval and decreased fertility in the subsequent breeding season. These results suggest that although Mertolengo cows can successfully carry and rear twins under the traditional management system, the economic efficiency of twinning is negatively affected by calf losses and by delayed rebreeding and reduced fertility of the cows. These negative effects may be overcome by management changes but the benefit of these changes needs to be evaluated.