P. J. Sharp

Ovarian morphology and rates of ovarian follicular development in laying broiler breeders and commercial egg‐producing hens

1. Ovaries from a light‐bodied egg laying strain and a broiler breeder strain were compared at 26 and 82 weeks of age. 2. The rate of lay in both strains was lower in the older hens. The 82‐week‐old hens were subdivided into good and poor layers: the poor layers produced eggs at about half the rate of the good layers. 3. The yellow‐yolky ovarian follicles in both strains were smaller, more numerous and more closely ranked in hierarchies in 26‐week‐old hens than in 82‐week‐old hens. 4. No marked differences were seen between the strains at 26 or 82 weeks of age in the sizes, numbers or hierarchical arrangements of yellow‐yolky ovarian follicles. 5. The ovaries from 82‐week‐old good and poor layers from both strains contained similar numbers of yellow‐yolky follicles. 6. After feeding a fat‐soluble dye, the number of days over which eggs containing dye were laid did not differ between 26‐, 52‐ and 113‐week‐old hens from an egg laying strain. However, fewer eggs with dyed yolks were laid by the older hens. 7...

Variations in plasma prolactin, thyroid hormones, gonadal steroids and growth hormone in turkeys during the induction of egg laying and moult by different photoperiods

1. Concentrations of prolactin, growth hormone, testosterone, progesterone, thyroxine and triiodothyronine were measured in the blood plasma of female turkeys during successive periods of egg laying, a decline in lay, a moult induced by a short photoperiod (6 light: 18 dark) and a resumption of egg laying induced by a long photoperiod (16L:8D). 2. Concentrations of prolactin, growth hormone, testosterone and progesterone were higher in laying birds than in birds which were moulting or not laying. 3. The concentration of testosterone, but not of the other hormones studied, increased significantly during the period of profuse moult. 4. Concentrations of the thyroid hormones did not change with the varying physiological condition of the birds. However, the concentration of thyroxine was depressed by the long photoperiod.

The effects of progesterone on oviposition and ovulation in the domestic fowl (Gallus domesticus)

1. Following an injection of 0.5 or 0.1 mg progesterone/kg between 0 and 6 h after ovulation, oviposition of the resulting egg was delayed by 1 to 11 h and occurred 26 to 31 h after injection, depending on the dose. The injection terminated the laying of a sequence of eggs by causing the next ovulation to occur a day late. The delayed ovulation occurred at the time normally expected for the first ovulation a sequence and became the first of a new sequence. 2. Following an injection of 0.5 or 0.1 mg progesterone/kg between 6 and 15 h after ovulation, oviposition of the resulting egg was generally delayed by between 15 and 28 h and occurred at the same time of day as the next ovulation, which was delayed as in the first experimental situation. Subsequent ovulations were resynchronised and followed at intervals according to the normal sequence established before the injection. 3. Injection of 0.5, 0.1 or 0.05 mg progesterone/kg between 12 and 9 h before expected ovulation advanced the oviposition of the egg already in the uterus (shell gland) by about 3 h. The succeeding ovulation was either advanced or blocked. 4. These observations suggest that the pre-ovulatory surge of progesterone is directly or indirectly involved in the timing of oviposition and ovulation.

The effect of reserpine on plasma LH concentrations in intact and Gona‐dectomised domestic fowl

Reserpine was found to inhibit the secretion of luteinising hormone when injected into intact and gonadectomised fowl at a dose rate which caused heavy sedation. This could indicate that reserpine or its derivatives should not be used for breeding poultry.

An assessment of the optimal range of dietary sodium for inducing a pause in laying

Laying hens were fed on a diet containing 0-9 g sodium/kg until 34 weeks of age, then groups were fed on diets containing 0-2, 0-3,0-4, 0-5, 0-6 or 0-9 g sodium/kg for 16 weeks before that containing 0-9 g sodium/kg was reintroduced for all birds. 2. Egg production and food consumption were depressed by the low-sodium diets in proportion to the dietary sodium content. 3. Birds receiving 0-3 to 0-6 g sodium/kg diet lost weight initially but subsequently gained weight; birds receiving 0-2 sodium/kg diet lost weight continouosly. 4. In birds receiving 0-2 g sodium/kg diet, the reproductive organs were completely regressed, whereas these organs resembled those of point-of-lay pullets in birds fed on 0-3 or 0-4 g sodium/kg. 5. When the control diet was reintroduced, birds which had received the low-sodium diets resumed normal egg production and food consumption and regained body weight. 6. The optimal range of dietary sodium for inducing a pause in egg laying is 0-3 to 0-4 g/kg.