18 Heritability Estimates for Boer Goat Birth Weights

Abstract Historically, the North American Boer goat industry has focused on visual appraisal for genetic improvement with little objective data recording; however, birth weight and birth type have been recognized as important in Boer goat production systems. The objective of this study was to analyze Boer goat birth weight from a private cooperator to determine the heritability and potential implementation of a genetic evaluation for the trait. A total of 1254 birth weights were recorded between 2014 and 2021 on a breeding farm in Colorado. Given the dry climate, parturitions occurred from November until May depending on the year. There were 84 different sires and 301 unique dams represented in this dataset. All birthweights not collected within 24 hours of birth were excluded from the analysis. Birth weight averaged 3.73 ± 0.86 kg, with a variance of 1.64 kg2, and minimum and maximum birth weights were 0.68 kg and 6.35 kg respectively. The data were cleaned and organized by giving each animal a unique identifier, associated with birth date, sex, and different birth types (singles, twins, triplets, etc.). This was used to create contemporary groups made up of birth year, birth type and sex. A single generation pedigree was included in the evaluation as additional ancestry is still being accumulated from written records. This was an initial genetic evaluation of the dataset; therefore, embryo transfer kids were included in the analysis with no accounting for maternal genetic effects. We acknowledge this model approach has the potential to introduce bias into the evaluation due to the fact that embryo transfer kids experience different in-utero environments and are phenotypically heavier than natural service kids. For these reasons, the maternal genetic effect on birth weight was ignored in this initial analysis. Data were analyzed using a single trait, additive genetic effects animal model and the statistical software package ASReml 3.0. Fixed effects included in the model were birth year, birth type and kid sex. Individual animal was the sole random effect. The birth weight heritability estimate was found to be 0.41 ± 0.08. Comparatively, this is a high heritability when collated to additional estimates reported for other small domestic ruminants, such as sheep. These results provide a foundation for future studies which will include additional pedigree information, the addition of a maternal genetic effect and the exclusion of data from embryo transfer kids.