Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/30/2007
Publication Date: 12/1/2007
Citation: Echternkamp, S.E., Thallman, R.M., Cushman, R.A., Allan, M.F., Gregory, K.E. 2007. Increased calf production in cattle selected for twin ovulations. Journal of Animal Science. 85(12):3239-3248. Interpretive Summary: Reproductive rate for beef cattle is low relative to other meat-producing species. Twin births provide an opportunity to increase rate and efficiency of reproduction in beef cattle, and most bovine females have the uterine capacity to gestate twin fetuses to term. Twin ovulations are the first prerequisite for fraternal twin births. The continued long-term selection for twin ovulations in the MARC Twinner population has increased the frequency of twin ovulations and births as well as the frequency of triplet ovulations and births; calves/parturition increased from 1.34 in 1994 to 1.56 in 2004. However, some of the potential gain from the production of two calves is compromised by reduced calf survival at birth (-8%), lighter individual body weights for twins at birth (-21%) and weaning (-14%), and an increased incidence of dystocia associated with abnormal presentation of twins within the birth canal. Although most bovine females have the uterine capacity to gestate twin fetuses to term, twin calves gestated in separate uterine horns (bilateral twins) have greater neonatal survival, heavier birth weight (especially male calves), and a longer gestation length than both twins located in the same uterine horn. Bilateral twins also had less calving difficulty, which increased their survival. Calf survival was also greater for bilateral versus unilateral triplets. In contrast, survival to weaning was similar for single, twin, and triplet calves. Total weaning weight/parturition for single, twin, and triplet births was 217.7 ± 2.5, 328.3 ± 3.2, and 378.4 ± 15.0 kg, respectively. The sex ratio of male:female (0.52:0.48) at birth did not differ from the theoretical 1:1 ratio for single or twin calves, indicating that the in utero survival of a twin fetus was not affected by the sex of the other twin fetus. Results from this study reconfirm experimental results that the production of twin births has the propensity to increase reproductive efficiency in beef cattle by 20 to 30%. Because of increased dystocia and neonatal calf mortality, triplet births provide little additional production benefits compared with twin births.
Technical Abstract: The effects of increasing fetal numbers and their distribution between the left and right uterine horns on calf survival, calf BW at birth and weaning, gestation length, dystocia, and calf sex ratio were evaluated for single (n = 1,587), twin (n = 2,440), and triplet calves (n = 147) born to primiparous and multiparous females in the MARC Twinner population between 1994 and 2004. Cattle were distributed equally between spring and fall breeding seasons. Fetal number and distribution in utero were determined by real-time ultrasonography at 40 to 70 d post-breeding. For cows and heifers combined, number of calves/parturition increased from 1.34 in 1994 to 1.56 in 2004. Gestation length was 6.8 d shorter (P < 0.01) for twins compared with singles (277.5 ± 0.2 vs. 284.3 ± 0.2 d) and 12.7 d shorter for triplets (271.6 ± 0.8 d). Survival and BW of individual calves at birth decreased (P < 0.01) but total calf BW/dam increased (P < 0.01) as fetal number increased from single to triplet births. Twins resulting from bilateral twin ovulations had increased (P < 0.01) survival and BW at birth, a longer (P < 0.01) gestation length, and less (P < 0.01) dystocia than twins resulting from unilateral twin ovulations. Calf survival and BW at birth were 97.2 ± 0.3% and 48.0 ± 0.1 kg for singles, 92.0 ± 0.4% and 39.0 ± 0.2 kg for bilateral twins, 83.2 ± 0.4% and 36.7 ± 0.2 kg for unilateral twins, 73.8 ± 1.4% and 30.6 ± 0.7 kg for bilateral triplets, and 51.9 ± 3.2% and 31.7 ± 1.6 kg for unilateral triplets. Birth weight of single calves increased 0.51 kg for each additional day of gestation length vs. 0.38 kg/d for individual twins. Calf birth weight increased (P < 0.01) with age of dam from 2 to 4 yr. Twin and triplet births had a greater (P < 0.01) incidence of dystocia than single births. Ratio of male:female calves (0.52:0.48) at birth was not affected by type of birth. Postnatal calf survival was similar for all three types of birth. Total progeny BW at weaning for single, twin, and triplet births was 217.7 ± 2.5, 328.3 ± 3.2, and 378.4 ± 15.0 kg, respectively (P < 0.01). Although most bovine females have the uterine capacity to gestate twin calves, decreased survival and BW of unilateral twins and all triplets indicate that their growth and development may have been compromised by uterine crowding.