Genetic aspects of heat stress in pigs expressed in fertility traits

The number of pig breeding programs has reduced in recent years. This leads to a small number of pig breeding companies producing pigs for many different environments. Therefore, pig breeding programs have to breed pigs capable of facing heat stress challenges during their productive life. Management practices such as cooling offer one option to reduce heat stress and warrant performance during hot seasons. A more sustainable alternative is to breed sows for improved heat tolerance. When evaluating breeding goals for dam lines we were confronted with different appreciation of two dam lines by pig producers in the Netherlands (temperate climate) and in Spain (warmer climate).These two dam lines, differed in the relationship between ambient temperature and reproductive performance. One of the dam lines showed no influence of temperature on performance, the other showed a decrease of 0.1 piglet per 1°C increase in ambient temperature. In a subsequent study, estimates of heritability reinforced the idea that genetic selection for sow heat stress tolerance is possible. Genetic correlations between reproductive performance in a temperate climate and reproductive performance in a hot climate tend to be unfavourable. In other words, improving reproduction traits without taking heat tolerance into account will lead to animals which have higher performance under temperate conditions, but which are also more sensitive to heat stress.