Abstract:In the world, the number one priority is to increase the egg production by breeding for increased persistency in lay. It means, the long life of commercial egg production farms can be extended to 90-100 weeks to achieve 500 eggs during a production period. It has been described in the previous reports that to reach the goal of long-life layer, a multifactorial approach including genetic, nutrition and design of housing system. But it seems that one of the angels of the square of the long-life theory has been neglected and it is physiology aspect of aging in birds. To achieve this target, the main challenge lies in keeping the layer in a good body condition until the end of the flock. The ovary is a major internal organ of the female reproductive tract that produce the gametes. Over 12000 oocytes are present in the ovary of the one-day old chick after hatching but about 5000 of initial recruitment follicles which are followed by hierarchal follicles that progress toward maturity. Therefore, it can be said the ovary has a natural potential to release more gametes during the long life of layer. There are several studies that explained the age-related- disorders in layer, low percentage of egg production, follicular atresia, low rate of follicular development, decline in clutch size are the main concerns at late laying period. The process of reproductive senescence in female birds is characterized by a gradual transition from regular reproductive cycles to irregular cycles to eventual acyclicity and ultimately a low or loss of egg production at the end of production period. The causes of these disorders are summarized in two subjects; 1: decreased age-related progesterone, testosterone and LH, 2: increased estrogen that cause hormonal imbalance status which primarily in fluence reproductive organ function. During ageing, increased estrogen with negative feedback on gonadotropins and decrease in preovulatory LH surge results to reduction in hypothalamic response to gonadal steroids and consequently irregular egg laying. There is a key point about the estrogen hormone. Although estrogen plays an important role in the female reproductive performance but it practically acts like a double-edged sword. The optimum concentration of estrogen is necessary for a normal egg production rate, but a high concentration of estrogen will have several side effects. There is now significant evidence to emphasis that reproductive hormones undergo significant changes with ageing. It has been confirmed that the LH and FSH responses to GnRH are attenuated with ageing. According to several reported researches, it is concluded that hormonal imbalance for testosterone, estrogen, FSH and LH is just a major suspected etiologic factor in causing low production in aged birds. Several investigators confirmed that the estrogen/testosterone and FSH/LH ratio as the independent predictors of reproduction performance in layer. The young birds or in peak of production that have no hormonal imbalances but the aged birds had the high imbalances in hormones during the late laying period. As age increased, average estradiol levels exhibited a linear increase and the elevated follicle-stimulating hormone/luteinizing hormone ratio is associated with low performance in aged breeder quails. Keeping the FSH/LH ratio constant at around 2.5 can be considered as a functional index for persistency of egg production in layer breeders.
