High environmental temperatures cause very serious economic losses to egg-laying farms.

In a recent post we discussed the negative effects of heat stress on egg quality. In today’s article, we will describe the impact of high environmental temperatures in hens (layers and breeders), male breeders and on the hatchability of fertile eggs.

1.Negative effects on the fertility of layers and female breeders

If exposed to high temperatures for several days, laying and breeding hens go through hormonal changes that ultimately result in a reduction of the fertility.

These hormonal changes take place through two pathways:

1. In the brain (hypothalamus), there is a reduction in the secretion of Gonadotropin-releasing hormone (hormone that controls the activity of other hormones related to ovulation) and of luteinizing hormone (the hormone that triggers ovulation).
2. In the ovary, there is a decrease of the amount of progesterone (hormone related to maturation of follicles). A reduction of the ovary weight and the number of large follicles is also observed during episodes of heat stress, so it is hypotized that the hormonal disfunction and the atrophy of the tissues may be related to poor blood flow in the ovary. We described the phenomenon of a reduced blood flow to the internal organs during heat stress in this article. 

2.Negative effects on the fertility of the male breeders

Broiler breeders are more sensitive to heat stress than females.

In this article we explained that chicken spermatozoa have an extremely high proportion of polyunsaturated fatty acids (PUFA). This particular lipid profile makes the spermatozoa very sensitive to the peroxidative damage caused by heat stress. For this reason, the administration of essential oils with high antioxidant properties and vitamin E is useful to restore fertility parameters (PhytoMax©)

Whenever male breeders are exposed to high environmental temperatures for a prolonged period:

• Spermatogenesis is decreased and fertility is reduced
• Semen volume is reduced
• In vivo sperm-egg penetration capacity worsens

3. Negative effects on the hatchability of fertile eggs

It has been demonstrated that the optimal temperature for incubation is 37.8ºC.

Heat stress (temperatures higher than 38ºC) during the incubation period has been shown to have a negative impact on hatchability and day-one-chick quality:

• Increased mortality of embryos during the incubation period.
• Embryos that survive show a higher percentage of malformations and abnormalities.
• The hatched chicks may be of sub-standard quality, showing lower weights at hatch, slower growth during the first week of life and a higher percentage of malformations.