Overbreeding

Overbreeding refers to breeding practices that excessively propagate individuals within a population to the point that genetic diversity declines and inbreeding increases. The term is used in discussions of domestic animal breeding, livestock production, and captive breeding of endangered species. It can arise from selection for uniform traits, rapid expansion of a pedigree line, or closed breeding populations where unrelated individuals are not introduced.

Causes include market demand for specific traits, economic incentives to maximize offspring numbers, and management systems that restrict gene flow by maintaining closed studbooks. Small founder populations and rapid generation turnover can exacerbate loss of genetic variation, making populations more susceptible to inbreeding.

Genetic consequences include increased inbreeding coefficients, reduced heterozygosity, and expression of deleterious recessive alleles. This can manifest as congenital defects, reduced fertility, lower litter viability, impaired immune function, and overall decreases in fitness and adaptability. Welfare concerns often accompany such outcomes in domesticated animals.

Mitigation strategies emphasize maintaining genetic diversity: larger effective population sizes, outcrossing or planned introgression, careful pedigree management, genetic screening for deleterious alleles, and independent oversight or registries. In endangered species, captive breeding programs aim to maximize genetic diversity while meeting conservation goals; in domestic breeding, many groups advocate responsible practices that balance trait selection with health and welfare.

Genetic metrics such as the effective population size and the inbreeding coefficient (F) are used to assess risk and guide breeding decisions.