DEVELOPING GENETIC RESISTANCE TO HEAT STRESS IN POULTRY
Another chicken production constraint in Africa that may be addressed by genetics is heat stress. Elevated temperatures and heat waves stress poultry, resulting in reduced productivity, anorexia, stress and mortality. Both meat type and egg laying chickens respond to heat stress in a similar fashion. Temperatures exceeding 35 C can cause heat stress in chickens, reducing nutrient utilization.
In meat birds this leads to reduced protein production and increased fat deposition while in layers there is reduced total egg production, reduced egg mass and decreased shell strength. Improved ventilation of poultry houses and feed additives, such as glucose, ascorbic acid, and glutamine can ameliorate some impact of heat. However, these options are not readily available to smallholder farmers in Africa.
Genetic factors influence the physiological response to heat stress. In layer-type chickens, divergent selection for tolerance to heat produced two lines that differed in survival time in heat. Also, different lines of chickens exhibit different, heritable responses to heat stress. Many specific genes have been shown to respond to heat stress in the chicken. With the possible exception of the Naked Neck gene, it is still uncertain which other genes play a direct role in the chicken’s ability to tolerate heat stress.
These observations clearly indicate that identifying alleles with different effects on resistance to heat stress is a feasible and attainable goal. The studies also suggest that some of the genes controlling thermal tolerance have pleiotropic effects on a variety of performance traits, so those relationships must be defined to accomplish overall improvement in important traits.