Induction of a pause in laying by corticosterone infusion or dietary alterations: effects on the reproductive system, food consumption and body weight

A pause in laying was induced in hens by infusing 30 micrograms corticosterone/h, feeding diets deficient in calcium or sodium and by food and water withdrawal. In hens infused with corticosterone, food consumption remained high and body weight was unchanged, although liver weight doubled. The other treatments were associated with a decline in food consumption and a loss of body weight but liver weight was unchanged. The weight of the ovary was reduced most severely in hens infused with 30 micrograms corticosterone/h, but the number of follicles weighing more than 12 mg was not altered by any of the treatments. A decrease in the number of large, yolk-filled follicles was matched by an increase in the numbers of small follicles. All treatments resulted in an increase in the number of atretic follicles. All treatments produced an elevation of plasma corticosterone concentrations within the normal physiological range, and a decrease in plasma LH concentrations. These features may constitute part of the physiological mechanism causing regression of the ovary and the cessation of egg-laying, but they do not prevent recruitment of small follicles to the stage which precedes entry into the hierarchy of large, yolky follicles.

Feed restriction during the growing period, forced molt, and egg production

An experiment was conducted to examine postmolt laying performance of White Leghorn hens that had been subjected to feed restriction from 8 to 20 weeks of age. During the postmolt period, birds in all forced-molt (FM) groups consistently had higher percent hen-day egg production than the control birds. Within the FM groups, birds that had previously been restricted fed during the growing period at the rate of 70% of the control group's consumption (R70-FM) consistently had higher percent hen-day egg production during most of the postmolt period than the nonrestricted fed birds (Ad lib.-FM). Significant (P less than .05) improvements in albumen height and shell thickness were observed 4 weeks after the FM period. When premolt, molt, and postmolt periods were combined, R70-FM birds had the highest percent hen-day egg production and the best feed efficiency of any group.