Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 29, 1998
Publication Date: N/A
Interpretive Summary: Productivity of the beef cow is low relative to other meat-producing animals, birds and fish. Furthermore, 65% of the feed resources for beef production provide for maintenance of the breeding herd. Twin births provide an opportunity to increased productivity (53.1% increase in total live calf birth weight, 58.4% increase in total 200 d weight and 65.2% more ecalves weaned), but part of the increase is compromised by an increased incidence of dystocia, retained placenta and lower fertility. A comparison between 3370 single and 1014 twin births revealed a twofold increase in incidence of dystocia with twins (46.9 vs 20.6%, twin vs single), primarily due to abnormal presentation of one or both twin calves (37.0% of twin births). Thus, advanced diagnosis of twin pregnancies by ultrasonography aided in implementing early obstetrical assistance. Dystocia associated with single births diminished with age of dam and reduced subsequent pregnancy rate 8%; whereas, dystocia with twins was unaffected by age of dam and had no effect on conception. Twins increased the incidence of retained placenta significantly (27.9 vs 1.9%) as a result of a shorter gestation length for twins. Shorter gestation lengths (7.6 days) with twins compensated for increases in length of the anestrous period as percentage of dams reinitiating estrous cycle was unaffected by type of birth (94.4%). Having a retained placenta reduced subsequent pregnancy rate about 10% and was a major contributor to lower pregnancy rates after twin vs single births (69.8 vs 79.0%). Although twinning in cattle increases the incidence of dystocia and retained placenta and tends to lower pregnancy rate, the 1.5 times more calves weaned provide an opportunity to increase productivity with intensive management.
Technical Abstract: Maximal productivity from twinning in beef cattle is constrained by increased dystocia and retained placentas, longer postpartum interval, and lower conception rate. Incidence and cause(s) of these physiological differences, and their impact on subsequent reproduction, were evaluated for 3370 single and 1014 twin births from 1988 to 1994 in a population of cattle selected for twin births. Equal numbers of females were bred and calved in the spring and fall. Twinning increased (P<.01) the incidence of dystocia (46.9 vs 20.6%, twin vs single); primarily due to abnormal presentations of one or both calves at parturition (37.0 vs 4.5%, respectively). Contrary to twin births, first- (40.5%) and second- (22.7%) parity dams with a single birth had more (P<.01) dystocia than older dams (13.4%). Incidence of retained placenta was higher (P<.01) for twin vs single births (27.9 vs 1.9%) and in the spring vs the fall calving season (18.3 vs 11.4%), and was associated with a shorter (P<.01) gestation length. The shorter (P<.01) gestation length for twins (276.1 vs 283.7 day, twin vs single) increased the interval from parturition to conception (94.4 vs 83.7 day, respectively; P< .01); whereas, conception date differed by only 2 day. Percentage of dams cyclic during the AI period was unaffected by type of birth (94.4%). Pregnancy rate was higher after a single birth than a twin birth (79.0 vs 69.8%; P<.01), reduced by dystocia when associated with a single birth (75.9 vs 83.8% with vs without; P<.01) and decreased 10.3% (P<.05) by a retained placenta. Although twinning increases the incidence of dystocia and retained placenta and tends to lower pregnancy rate, twin births wean 1.5 times more calves and provide an opportunity to increase productivity with intensive management.