Resilience and lessons from studies in genetics of heat stress

Abstract Text:

Production environments are expected to change, mostly to hotter climates but also possibly more extreme and drier. This raises a question whether the current generation of farm animals can cope with the changes or should they be specifically selected for changing conditions. In general, genetic selection produces animals with smaller environmental footprint but also with smaller environmental flexibility. Some answers are coming from heat stress research across species, with heat tolerance partly understood as a greater environmental flexibility. Specific studies in various species show complexities of defining and selecting for heat tolerance. In Holsteins, the genetic component of heat stress on production approximately doubles in second and quadruples in third parity. Best production under heat stress is by cows with elevated body temperature, probably at a risk of increased mortality. In hot but less intensive environments, the effect of heat stress on production is minimal although the negative effect on fertility remains. Mortality peaks under heat stress and increases with parity. In Angus, the effect of heat stress is stronger only in selected regions, probably due to adaptation of calving seasons to local conditions and crossbreeding. Genetically, while the direct effect shows variability due to heat stress, the maternal does not, probably due to dams shielding calves from environmental challenges. In pigs, the effect of heat stress is strong in commercial but almost none in nucleus farms. This is partly due to lower pig density and better heat abatement in nucleus farms. Under intensive management, heat stress is less evident in drier environments because of more efficient cooling. A genetic component of heat stress exists but it is partly masked by improving management and selection based on data from elite farms. Genetic selection may provide superior identification of heat-tolerant animals but a few cycles may be needed for clear results. Also simple traits exist that are strongly related to heat stress, e.g., slick hair in dairy and shedding intensity in Angus. Defining resilience/robustness may be difficult especially when masked by improving environment. Under climate change, the current selection may be adequate if it 1) is accompanied by constantly improving management, 2) uses commercial data and 3) includes traits important under climate change such as mortality.

Keywords: G x E interaction, Animal stress, Robustness