The effect of photoperiod after photostimulation on male broiler breeder fertility.
Fertility in male broiler breeders may be controlled through a number of different methods, including lighting programmes. Currently in the poultry industry, male and female broiler breeders are reared under the same lighting conditions, as it is assumed that the males respond to light in a similar manner to females. However, the response to degree of photostimulation has not been as fully investigated in males as in females. The effects of different degrees of photostimulation, applied at 20 weeks of age, on the age at sexual maturity and the semen characteristics of male broiler breeders at the time of female sexual maturity, testosterone concentrations, secondary sexual characteristics and sperm-egg interactions were investigated. Results showed that males did not respond to light to the same extent as that seen in female boiler breeders, as ASM was not significantly affected by the degree of photostimulation applied as the males had probably spontaneously started spermatogenesis before photostimulation. This suggests that males could be photostimulated at a younger age than their female counterparts. A large amount of variation in individual male responses to degree of photostimulation was seen and this was possibly due to genetic variation as a result of selection pressure for meat and not fertility traits. Comb area was affected by the testosterone concentration and age but was found to be unrelated to semen characteristics. Semen characteristics were generally not affected by the final photoperiod apart from the semen concentration measured at female ASM. At 51 weeks of age, testes weights were affected by the degree of photostimulation with a trend of lower testes weights from birds on longer photoperiods which suggests the earlier onset of adult photorefractoriness in birds on longer photoperiods. Both testes and comb regression was evident by 51 weeks from at least one bird on each treatment which is concerning for the breeder industry where birds are usually kept for 60 weeks. The numbers of sperm trapped in the perivitelline layer of a hen’s egg, and the probability of the egg being fertile, were significantly affected by the photoperiod, age of the male and the time elapsed between artificial insemination and the laying of the egg. The impact of the degree of photostimulation on male broiler breeder fertility is an important topic for the poultry industry and is discussed.