Seasonal Infertility on boars: Heat stress
Causes
Seasonal infertility occurs mainly in summer and results from the effects of day length and high temperature (heat stress). In fact, the reduced conception is caused partly as a result of a decrease in semen quality and libido in the boar. Some research has proven that there are negative effects of high temperature as well as of high humidity on volume of the ejaculate and total sperm production.
Treatment and prevention
The adverse effects on boar semen quality can be overcome by the supplementation of the boar diet with the micronutrients, vitamins and the necessary essential amino-acids to maximize its sperm production. For example, detailed studies found that the treatment with L-carnitine enhanced the number of mature sperm in ejaculates from boars under stress situations. Besides, betaine added to the diet tends to increase its total sperm production at summer months.
You can find more information through these links related to heat stress and reproduction:
http://www.pigprogress.net/Health/Health-Tool/diseases/Seasonal-infertility-/
http://www.thepigsite.com/articles/4376/heat-stress-in-boars/
http://www.nationalhogfarmer.com/reproduction/2015-research-review-heat-impacts-boar-fertility
