Inbreeding reduces the performance of livestock animals, a phenomenon known as inbreeding depression. But how large is the effect of inbreeding? And does the degree of inbreeding depression differ between traits? Researchers of the Animal Breeding and Genomics group of Wageningen University & Research performed a meta-analysis of 30 years of research to answer these questions.
The meta-analysis included 154 studies on 7 livestock species, published in the last 30 years. From these studies, the researchers extracted 2321 inbreeding depression estimates, which were defined as the change in performance for a trait (e.g. body weight, milk yield or fertility) per 1% increase in inbreeding, as illustrated in the figure below.
Inbreeding similarly affects all sorts of traits
To compare the degree of inbreeding depression across traits, estimates of inbreeding depression were expressed as a percentage of the trait mean. Across all studies and traits, a 1% increase in pedigree inbreeding decreased the mean trait value by 0.13%. There was no clear difference in the degree of inbreeding depression between trait groups (e.g. reproduction/survival traits, production traits or morphological traits).
Genomic inbreeding more powerful to detect inbreeding depression
Inbreeding is traditionally estimated from pedigree information, but can nowadays also be estimated using markers in the DNA of animals (so-called SNPs). Based on 12 studies in the meta-analysis, it was found that genomic inbreeding was more powerful to detect inbreeding depression than pedigree-based inbreeding.
Facilitating future comparisons across studies
To facilitate comparisons across studies in future, the researchers published the data set with 2321 inbreeding depression estimates. In addition, they provided recommendations on what information to report when publishing inbreeding depression estimates.