Variation in the ovarian and plasma progesterone and estradiol levels of the domestic hen during a pause in laying.

Little is known about the physiological events occurring in the chicken ovary during a pause in laying, therefore the aim of the present study was to examine changes in sex steroid concentration in the follicle wall and blood plasma during cessation of egg laying. The experiment was performed on laying Isa Brown hens. Control hens were fed ad libitum whereas the experimental ones were subjected to a pause in laying by complete food deprivation for 5 days and water deprivation on 3 day followed by feeding every second day up to 9 day and then ad libitum. Blood samples were taken from the wing vein each day. The hens were decapitated on day 3, 6, 9, and 16. The ovary was isolated and the following follicles were dissected: white (1-2; 2-4; 4-6; 6-8 mm) and yellow preovulatory ones (F1-F3). Progesterone and estradiol were measured in the follicle wall and blood plasma by RIA methods. The hens stopped egg laying on day 4 and began egg restoration on day 14 of the experiment. Cessation of egg laying was preceded by a decrease in estradiol and progesterone levels in the ovary as well as in the blood plasma. The plasma level of these steroids began to increase 7 days before the start of egg restoration. Autopsy of the ovary showed that the atrophy of the chicken yellow preovulatory follicles during the pause in laying was accompanied by a significant increase in the total number of white follicles.

Attenuation by leptin of the effects of fasting on ovarian function in hens (Gallus domesticus).

Thirty-four-week-old laying hens received injections of recombinant chicken leptin to assess the role of leptin in avian ovarian function. In the first experiment, the hens (n=60) were divided into three groups: (i). fed ad libitum; (ii). fasted; and (iii). fasted + leptin. Hens were fasted for 5 days and those treated with leptin received 250 microg leptin kg-1 body weight twice a day, i.p. In the second experiment, the hens (n=72) were divided into four groups: (i). fed ad libitum; (ii). fasted; (iii). fasted + leptin given only during fasting (5 days); or (iv). fasted and leptin given during both fasting and 5 days of re-feeding (10 days). LH was measured in blood plasma, and progesterone and oestradiol were measured in blood plasma and the ovary by radioimmunoassay. Apoptosis was examined in the walls of the three largest yellow hierarchical follicles (F3-F1; F38-12 mm), and the granulosa layer of F3 follicles. The expression of leptin receptor in the granulosa layer of F2 and F1 follicles was barely detectable. This was in contrast to a much higher expression of leptin receptor maintained in the theca layer of F3-F1 follicles. The present results indicate that in chickens leptin might be involved in the adaptation to starvation due to attenuation of follicular apoptosis. The presence of leptin receptors in the ovary indicates the possibility of a peripheral effect of the hormone.