Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: June 13, 1996
Publication Date: N/A
Technical Abstract: Increased incidence of triplet and higher births in cattle is regarded as an undesirable side effect of genetic increase in twinning. Estimates of triplets in populations with genetic levels of 40% or greater twinning do not exist because there are no such populations. However, predictions of triplets are needed to evaluate the potential impact of further genetic increases in twinning. Both empirical data and biological hypotheses were used to develop a prediction. Empirical data consisted of sheep ovulation rates and estimates of bovine losses of embryos in early and late phases of pregnancy. Ovulation rate was decreased from levels found in Romanov sheep to those of cattle. Biological hypotheses concerned the independent loss of embryos in early pregnancy and codependent failure of multiple embryos in late pregnancy. Pre-implantation losses were considered to be independent resulting in the loss of only the affected embryo. Post-implantation failure of an embryo was assumed to result in the loss of all embryos. It was also assumed that more than three embryos in one uterine horn resulted in the loss of all embryos. Data from heifers and from older cows calving from 1989 to 1995 were used to test predictions. This herd has been selected for twinning rate and multiple births ranged between 14 and 34%. Totaled over 14 cow age by year combinations, 3880 single, 1229 twin, and 33 triplet births were observed compared with predicted values of 3877.8 single, 1231.6 twin, and 32.4 triplet births. Prediction of triplet births was accurate (chi-square=16.85 with 14 df) within the range of available test data. Predicted triplet births at 35, 45, and 55% multiple births are 1.4, 3.2, and 6.6%, respectively. Predicted quadruplet births are .1% or fewer up to 55% multiple births.