Photorefractoriness in avian species – could this be eliminated in broiler breeders?

Testicular Growth and Comb and Wattles Development in Three Italian Chicken Genotypes Reared Under Free-Range Conditions

“…Broadly, they are reared under free-range conditions from 4-5 weeks of age, under natural variations of environmental temperature and relative humidity, photoperiod and light intensity. Among environmental parameters, day length and wavelength of light are very important factors for growth and sexual development in birds (Lewis and Morris, 2006;Tyler and Gous, 2012). The avian eyes allow poultry to be responsive to radiation below 400 nm and to see in ultraviolet light; the growth is primarily a response to wavelength, not to intensity, because growth generally decreases with increasing illuminance (Lewis and Morris, 2006).…”

“…Another important issue in birds is photorefractoriness, as the inability to respond sexually to an otherwise stimulatory day length: it terminates a breeding season after a period of time on long day lengths, and it is dissipated after exposure to short day lengths (Tyler and Gous, 2012). In fact, birds which are not restricted on feeding and exposed to about two months of short photoperiods (as in nature, by short winter day length) dissipate this condition; in this process T4 hormone is involved.…”

“…A consequence of bird photorefractoriness is seasonality: offspring are hatched when the most favourable environmental conditions occur to maximize the chances of survival. Partridge needs an exposition to short days for photorefractoriness to be dissipated (Siopes and Wilson, 1978), but some species dissipate photorefractoriness even if they are kept on long days, with a dissipation occurring at a slower rate (Tyler and Gous, 2012). In broiler breeders with no previous exposure to short day lengths sexual maturity is delayed (Lewis et al, 2004).…”

“…Age of sexual maturity is influenced by body weight, but the flock response to photostimulation can be variable, despite the uniformity in the target body weight (Lewis and Morris 2006;Lewis et al, 2007). In commercial hybrid genotypes, when a flock is photostimulated, a bimodal frequency distribution of age at maturity results from the advance in maturity of some birds and the delay in others (Tyler and Gous, 2012). Tyler and Gous (2012) stated that the response to early photostimulation is heritable.…”

“…In commercial hybrid genotypes, when a flock is photostimulated, a bimodal frequency distribution of age at maturity results from the advance in maturity of some birds and the delay in others (Tyler and Gous, 2012). Tyler and Gous (2012) stated that the response to early photostimulation is heritable. Lewis et al (2007) suggested that there are some genetic variations in the acquisition of photosensitivity.…”