Beef cattle

Estimating the Heritability of Beef Heifers' Ability to Rebreed at Two and Three Years of Age

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Abstract

One of the biggest economic losses to a commercial beef breeder is the culling of 2-year-old first calf heifers who fail to conceive after their first calving. A female who fails to breed after her first calf is an economic loss to an operation as she failed to provide enough calves to recoup her development costs. The objective of this study was to estimate the heritability of the heifer's ability to calve consecutively at two and three years of age. Records from 1,785 Angus cows from the Iowa State University McNay Memorial Research and Demonstration Farm in Chariton, Iowa were evaluated. Records from 1996 to 2022 were used to develop a binary phenotype for each dam (1 = successfully calved at ages 2 and 3, 0 = did not successfully calved at 2 and 3). Herd records indicated 69.6% of heifers who calved at age 2 also delivered a calf at age 3. Compared to an increase of 80.5% for cows who calved at 3 years of age and also calved at age 4. This illustrates the greater culling of dams between the ages 2 and 3. To estimate variance components, a 3-generation pedigree consisting of 12,081 records was used. Data were analyzed using a threshold animal model in the MCMCglmm package in R statistical software. The model included animal effect was included as a random effect and birthyear as the fixed effect representing the contemporary group. The resulting heritability for rebreeding from 2 to 3 years of age was 0.13 ± 0.06, with additive genetic variance estimated at 0.15 and residual variance fixed to 1. Indicating that 13.0% of the variation in heifer rebreeding among these dams was accounted for in genetic effects. This heritability is consistent with expected estimates for reproductive traits and does indicate that progress can be made through genetic selection. Estimates for the fixed effects of birth year were showed to be significant (P < 0.05) in the model as well. This would illustrate that year-to-year changes can occur by genetic and non-genetic factors. In conclusion, this study's results illustrate that there is a decrease in reproductive efficiency when it comes to heifers rebreeding after their first calf. The heritability shows that while environmental and other factors play a major role in this challenge, there can be progress made through genetic improvement. This can help improve overall productivity of females in the herd.

Keywords: 2026

How to Cite:

Condon, J., Phelps, S. & Culbertson, M., (2026) “Estimating the Heritability of Beef Heifers' Ability to Rebreed at Two and Three Years of Age”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286910. doi: https://doi.org/10.31274/wcgalp.24159

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