Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 29, 1998
Publication Date: N/A
Interpretive Summary: Increased productivity from twin births in beef cattle is compromised by an increased incidence of dystocia and(or) retained placenta and their associated negative effects on calf survival and fertility. Subsequent pregnancy rate was 10.4% lower for dams birthing twins versus singles. Part of this reduction resulted from the increased incidence of retained placenta with twin births, which subsequently reduced pregnancy rate about 10%. Reproductive losses (i.e., about 9%) also resulted from increased fetal mortality or premature births in females gestating twins. The 10% lower pregnancy rate for fall- vs spring-calving dams of twins advocates the management of twin-producing cows in a spring-calving program and breeding in those months with increased ovulation rate; e.g., May-June. The shorter gestation length for dams with twin births and(or) retained placenta contributed to the longer interval from parturition to conception for these dams as all females were rebred on the same calendrical schedule However, > 90% of the dams with twins and(or) a retained placenta did express estrus during the breeding season. Thus, their lower pregnancy rate did not result from impaired ovarian folliculogenesis or failure to reinitiate estrous cycles within the breeding season. Increasing postpartum body weight and condition scores (e.g., supplemental dietary energy intake) hasten the return to estrus in both dams of singles and twins. However, increased body weight or condition score had no effect on fertility after twin births when body condition was adequate (i.e., body condition scores >/=5). In spite of the observed complications, twinning in beef cattle increased productivity sufficiently to compensate for these complications.
Technical Abstract: The effects of twinning, dystocia, retained placenta and body weight or condition score on postpartum reproduction were evaluated for 3,370 single and 1,014 twin births born from 1988 through 1994 in the twinning project at the Roman L. Hruska Meat Animal Research Center. Females were bred by AI for 40 d followed by 20 or 30 d of natural service with equal numbers bred and calved in spring and fall. Percentage of dams cyclic by the end o the AI period (94.4 +/- 1.3%) was not affected by type of birth. Pregnancy rate was lower after a twin birth than a single birth (69.8 +/- 1.6% vs 79.0 +/- .9 calving rate; P < .01); incidence of fetal mortality and(or) abortions was also increased with twin vs single pregnancies (12.4 vs 3.5%, P < .01). Dystocia associated with a single birth decreased the subsequent pregnancy rate (75.9 +/- 1.6 vs 83.8 +/- .8%, P < .01) but had no effect on conception after a twin birth (70.6 +/- 2.0 vs 68.6 +/- 1.9%, P > .1). Having a retained placenta decreased the subsequent pregnancy rate a mean of 10.3% (P < .05) but in only two of seven yr evaluated (retained placenta x year, P < .01). Females with a retained placenta (i.e., predominantly dams of twins) also had a shorter gestation length and an earlier calving date. The shorter gestation length for twins (276.1 +/- .3 vs 283.7 +/- .2 d, P < .01) contributed significantly to the longer interval from parturition to conception for twin births (94.4 +/- .9 vs 83.7 +/-.6 d, P < .01); whereas, conception date differed by only 2 d. In spite of the tendency for lower pregnancy rates and calf survival after twin births, twin-producing cows weaned 50% more calves.