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A model of litter size distribution in cattle
G L Bennett1, S E Echternkamp, K E Gregory
1U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NE 68933-0166, USA.
Journal of Animal Science
|August 5, 1998
Summary
Genetic selection for twinning in cattle may increase triplet births. A new model predicts triplet incidence, showing fewer than 5% triplets at 50% twinning and increased triplets above 60% multiple births.
Area of Science:
- Animal Science
- Reproductive Biology
- Genetics
Background:
- Genetic increases in cattle twinning rates can lead to higher-order births.
- Estimates for triplet incidence in high-twinning populations are lacking.
Purpose of the Study:
- To propose and validate a model for predicting litter size distribution in cattle.
- To assess the incidence of triplet births under genetically elevated twinning rates.
Main Methods:
- Combined empirical ovulation rate data from sheep with cattle embryo fate hypotheses.
- Modeled two phases of embryo loss: preimplantation (independent) and postimplantation (all-or-none).
- Validated model predictions against calving data from 5,142 cattle.
Main Results:
- Predicted <5% triplet births when 50% of births are twins/triplets.
- Above 60% multiple births, triplets significantly contributed to litter size increase.
- Model predictions closely matched observed triplet incidence (chi2 = 16.85, df = 14).
Conclusions:
- The proposed model accurately predicts triplet proportions in cattle with high twinning rates.
- The model can project efficiency changes from genetic twinning rate increases.
- Model also predicts conception rates influenced by ovulation and pregnancy outcomes.