Date of this Version
The increased twinning frequency (Le., approximately 25%) in the U.S. Meat Animal Research Center twinning project has resulted in additional management requirements to achieve survival of twin calves and timely rebreeding of their dams. Previously, neonatal survival of twin calves (Le., within 24 hr after calving) was about 82% compared to 97% survival for singleborn calves. Although twin calves are smaller at birth than single-born calves (34.3 vs 44.8 kg), the incidence of calving difficulty (dystocia) is increased in twin pregnancies (35% vs 23% for twins vs singles, respectively) due to abnormal positioning of the calves within the uterus. The dystocia further increases mortality of twin calves (27% with vs 5% without dystocia). Secondly, the production of twin births results in lower conception rates (71% for twins vs 85% for singles) and a longer postpartum infertility period (95 vs 85 days, respectively) regardless of rearing one or two calves. Precalving diagnosis of twin fetuses would enable dietary supplementation to increase maternal energy stores and increase awareness of calving difficulty. Greater obstetrical assistance at calving should reduce the effects of dystocia and nutrition on calf survival and rebreeding performance of the dam. Previously employed methods to identify twin pregnancies were: 1) measurement of estrone sulfate in maternal blood, 2) determination of number of corpora lutea and fetuses by laparoscopy, and 3) determination of fetal number by rectal palpation of the uterus. The objective of this study was to evaluate ultrasonography for diagnosing twin pregnancies in cattle. Increased prepartum nutrition and timely assistance at calving could then help reduce neonatal calf mortality and postpartum infertility associated with twin births.