Egg Production is a Reflection of Ovarian Physiology: A Review PDF

Keywords

Egg production, oviposition, ovulation, ovarian function, follicular development modulators, aging

Abstract

Under ordinary daylight (14L: 10D), the occurrence of oviposition and ovulation in the domestic hen is normally restricted to an 8-10 h period of the day. The mechanism(s) which restricts the occurrence of oviposition and ovulation to a certain period of the normal day is not understood. Among factors proposed are a small daily surge of LH occurring at the onset of darkness; graded facilitatory influences associated with the open period; and products of post ovulatory follicles (POF). There is considerable evidence supporting the role of gonadotropin and progesterone on follicular growth and maturation and functional maintenance of the ovary in the hen. Recently, however, there is an ever-expanding list of factors that may be involved in establishing follicular growth and ovulation, currently including the germinal disc region, growth factors, macrophages, plasminogen activator, ornithine decarboxylase, inhibin, activin, follistatin, relaxin, arginine vasotocin, oxytocin, prostaglandines, vasoactive intestinal peptide, and their interactions. Based on the previous considerations and the data presented in this review, it may be suggested that control of follicular development in laying hens is the result of several physiological changes which still need to be determined. In conclusion, however, ovarian function of laying hens is the end result of a complex series of events accomplished by a major control (FSH, LH, P4) and its modulators (growth factors, inhibin, ornithine decarboxylase, etc). The role of these factors as potential modulators of follicular growth and ovulation needs further investigation. Egg production by laying hens declines with the progress of age. This decline in egg production with age is an indication of decrease of ovulation. Further, as the hen ages, the interval between ovulation increases and the result is a shorter sequence and a decrease in egg production. There is strong evidence for the role of proteolytic enzymes on follicular rupture in the domestic fowl. However, mechanism(s) controlling sequence termination is poorly understood. In this respect, there are several old theories for the explanation of the mechanism relating to sequence termination. Briefly, one of these systems regulates follicular maturation and the second system regulates the timing of the preovulatory surge of LH. Some recent data, however, suggest differences in follicular growth and maturation between genotypes of birds. It has also been suggested that the activity of the pituitary-ovarian axis in white laying hens is greater than that of brown laying hens. Additionally, the adrenal gland has been given a role in timing of ovulation in the hen.