Dietary salt potentiates folliculogenesis and modulates the functionality of the oviduct in late production layers

Abstract

This experiment was conducted to investigate the effects of varied levels of inclusion of dietary salt on follicular development, gonadal morphometry and hormonal profile of laying chickens in their last phase of production. Four experimental diets were formulated with varied levels of dietary salt. The control diet had 0.25% salt, whilst the remaining diets had 0.50%, 0.75% and 1.00% levels of salt respectively. One hundred and twenty layers were randomly assigned to the four experimental diets each containing 30 birds replicated thrice with 10 birds per replicate. At the end of the eight weeks feeding trial, thirty-six birds were slaughtered and dissected. Their reproductive tract and ovaries were weighed, counted or measured accordingly while blood samples were collected to determine circulating estradiol, luteinizing (LH) and follicle stimulating (FSH) hormones. The results showed significant dietary effects (P<0.05) on the weight of ovary, the length of the infundibulum and number of follicles. Birds fed 1.00% dietary salt had the highest (P<0.05) weight of entire reproductive tract and ovary and also produced the highest number of pre-vitellogenic follicles. Layers in their late phase of production produced very high level of circulating estradiol that seemed to exert a negative feedback mechanism on FSH and LH especially at 0.75% inclusion of dietary salt. Conclusively, maintaining the dietary salt allowance of late production layers at 0.75% could be used as a management strategy to sustain them in production until it is economically favourable to dispose them off as spent layers.It was also discovered that high levels of circulating LH and FSH would not always translate to maximum egg production without optimum level of dietary NaCl.

Keywords: Dietary salt, follicles, gonadal morphometry, hormones, layers