Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: February 6, 2006
Publication Date: July 7, 2006
Citation: Bennett, G.L., Allan, M.F., Cushman, R.A., Echternkamp, S.E. 2006. Observed and predicted numbers of single, twin, and triplet births in a cattle population selected for increased twinning [abstract]. Journal of Animal Science 84(Suppl. 1):203. Technical Abstract: A previously developed mathematical model to predict the distribution of single, twin and higher order calvings was tested in a cattle population selected for increased twinning to evaluate the model at high levels of multiple births. The original model was based on a distribution of ovulation rate (estimated from ewes because genetically high ovulating cows did not exist), an independent loss of preimplantation embryos, and a dependent, placental anastomosis caused loss of fetal litters. Unlike sheep, placental anastomosis occurs in most multifetus pregnancies in cattle. When it was developed, the model showed good agreement with actual distributions of singles, twins, and triplets for groups of females ranging from 13 to 35% multiple births in a cattle population selected for high twinning rate. This population currently averages about 50% multiple births. In 16 year-season groups from spring 1998 through fall 2005, there were 940 single, 823 twin, 67 triplet and two quadruplet calvings with calves born per cow ranging from 1.33 to 1.66 per year-season. In each year-season, the distribution of singles, twins, and triplets or more was predicted from the model based on observed average calves per cow. In total, 948.8 single, 804.0 twin, 78.8 triplet, and 0.5 quadruplet calvings were predicted by the model. Predicted and observed singles, twins, and triplets or more for the 16 year-season groups showed good agreement (chi-square = 18.17; df = 16; P = 0.31). Results validate the use of this model based on concepts of independent and dependent losses of embryos and fetuses for predicting distributions of singles, twins, and triplets in populations of cattle with high genetic levels of twinning.