The Physiological Effects Of Feed Restriction On Reproduction In Female Breeders

Reproductive processes in females are the result of controlled interaction between the hypothalamus-pituitary and the ovary and can be influenced by environmental, selection, or nutritional effects.

A well-described effect of feed restriction in broiler breeder females is the reduction of ovary weight, the number of yellow follicles during lay, and the incidence of erratic ovipositions, defective eggs, and multiple ovula-tions.[4-6] Unrestricted access to feed leads to a low egg production rate and fewer settable eggs for incubation.[6] There is evidence that the observed disturbances in follicular growth, differentiation, and ovulation in animals fed ad libitum could be attributed to changes in the steroid-producing capacity and in the sensitivity of the follicles to locally produced growth factors (e.g., insulinlike growth factors, bone morphogenic proteins, transforming growth factor, etc.) in interaction with each other and with gonadotrophins. Moreover, selection for growth rate or body leanness may have changed ovarian gene expression for growth factors and their receptors.[7]

Besides these changes at the ovarian level, changes in the concentrations and/or pulsatility of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) may

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compared to animals fed ad libitum. It is possible that this increased sensitivity at the hypothalamic-pituitary level in feed-restricted animals contributes to the difference in laying performance between ad libitum-fed and restricted broiler breeder females.[9] In several studies, no significant improvement in fertility or hatchability due to feed restriction could be observed. Duration of fertility, however, appears to be significantly lower in hens fed ad libitum, probably due to sperm storage difficulties. Most of the problems concerning embryo viability and hatchability are related to the production of eggs with reduced eggshell quality. Such eggs exhibit an increased incidence of embryonic mortality. Double-yolked eggs represent a further loss, due to the poor embryo viability in multiple-yolked eggs.

Age (weeks)

Fig. 1 Body weight curves (top) and laying curves (bottom) of feed-restricted (res) and unrestricted (ad lib) broiler breeder females (Hybro G). (Data from Bruggeman, 1998.)

Age (weeks)

Fig. 1 Body weight curves (top) and laying curves (bottom) of feed-restricted (res) and unrestricted (ad lib) broiler breeder females (Hybro G). (Data from Bruggeman, 1998.)

be important factors explaining the alterations in follicular development and ovulation between broiler breeders fed different amounts of feed. Plasma LH/FSH ratio was increased by restricted feeding.[8] Moreover, the sensitivity of the pituitary to luteinizing hormone releasing hormone (LHRH) as well as to ovarian feedback factors (steroids, inhibin) is influenced by the nutritional level. After sexual maturation and establishment of lay, the long-term feed-restricted animals showed the highest responsiveness to both LHRH-1 and ovarian factors.

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