The impact of genetic selection for increased production on fitness traits of small ruminants

Abstract

Many sheep and goat breeds worldwide are subjected to high levels of selection emphasis to increase production of meat, milk and fibres. The continuous selection on a small number of traits have resulted in unintended consequences, mostly as adverse effects on the fitness of animals. Selection for increased dairy production led to an increase in mastitis incidence, while selection for increased meat yield impacted on the prevalence of MSTN and CLPG mutations. Reproduction efficiency is the single most important trait in any small ruminant production system. Selection for increased litter sizes in small ruminants has resulted in increased numbers of triplet and quadruplet pregnancies, with an associated increase in mortalities and reproductive wastage. To optimize a genetic response, a balanced approach should be followed to set breeding objectives that include some of these fitness traits. Selection for increased resilience to even one stressor (such as mastitis) could result in an improvement of overall robustness. As the accurate recording of health and welfare traits is currently a limitation, mitigation strategies should include the generation of novel phenotypes which could also be included in genomic solutions to address the current shortcomings of breeding programs.

HIGHLIGHTS • High selection pressure in some small ruminant breeds result in adverse effects. • Genetic antagonisms exist between production, fertility and health traits. • Balanced breeding objectives will achieve an optimized genetic response. • New technology can measure a range of different traits to provide novel phenotypes.