Photoperiodicity, testicle development and sperm production in domestic fowl

Abstract

The reproductive capabilities of the cockerel are strongly influenced by daylength. Its variations strongly influence the age at which testicular development occurs, and consequently the age at sexual maturity. Both are advanced by increasing the daily photoperiods in growing cockerels. However the sperm production markedly declines after sexual maturity in cockerels submitted to long days, though they are known to allow high egg laying rates in the hen. By contrast, the adult sperm production may be well maintained under short constant days (e.g. 8L:16D), which induce delay in sexual maturity. Therefore there is an antagonism between photoschedules required to reach precocious sexual maturity and those able to maintain sperm production.

In the industry, adult broiler cockerels are raised under long days, together with the hens, to reproduce by natural mating. Many males (8 to 12 per 100 females) are used to compensate for the decline in their adult sperm production. They are furthermore submitted to restricted feeding, to prevent them from fattening and to stimulate their libido. However a number of deficient cockerels must often be replaced during the reproductive period. On an experimental basis, artificial insemination leads to a better management of males, through the use of specific photoschedules. It also permits the number of males to be reduced markedly by optimizing the use of semen to match the fertility requirements of hens. But artificial insemination is expensive and its technical requirements are rather hard to meet. It is therefore not in use for broiler production in countries where the cost of labour is high, even though it maximises profits in other domestic bird species.