Abstract

 A total ofthree hundred and sixty Isa Brown layers aged 85 weeks but 64 weeks in lay were used to investigate the organ changes and laying performance of forced-moult layers. The experiment was a 2 x 3 factorial arrangement in a completely randomized design with photoperiod and feed and water administration as factors. The combination of factors resulted to six treatments Tl, T2, T3, T4, T5 and T6, representing natural day length with feed and water, natural day length with water, natural day length without feed and water, reduced day length with feed and water, reduced day length with water and reduced day length without feed and water. Each experimental treatment was replicated 3 times with 20 birds per replicate. The treatments used to induce moult were imposed on the birds for 10 days after which the forced moult groups were supplied low protein moult diet for 50 days. At the end of this, they were returned to the same layers diet as the control birds. Parameters studied were plasma levels of progesterone, body weight, feather moult, follicular distribution, internal organs, egg production and egg quality. The results of the study showed that moulting hens had ruffled feathers, shriveled comb and wattle, yellowish tint on the beak and shank from day 10 of moult-induction until day 35. The forced moult groups lost body weight ranging between 50 to 400 g, during the period of moult-induction. The weight loss of T4 birds was significantly (P < 0.05) lower than those of the other moulted birds (T2, T3, T5 and T6). The control (Tl) and T4 showed little or no evidence of feather moult whereas T2, T3, T5 and T6 shed and later renewed their feathers during the moulting period. There were significant differences (P<0.05) between the weights ofthe different organs ofthe different groups during the forced-moult period. The liver tissues of birds in the different treatments showed normal histology by before moultinduction (day 0). On the contrary, the liver of the forced-moult groups showed different levels of degeneration between the different days of moult-induction with the level of degeneration increasing from days 7 to 49. The liver of moulting groups presented similar types of degeneration on the same days of sampling. By day 7 of moult-induction, the large yellow follicles ofthe forced moult groups (T2, T3, T5, T6) had been re-absorbed leaving the ovary with a cluster of atretic white follicles. By day 21 to 49 of moult-induction, the force - moulted hens started gradual re-establishment of their follicular hierarchy. By day 49, the number ofsmall white follicles in these groups was significantly greater (P < 0.05) than those of T1 and T4. The increased number of small white follicles in the forced moult groups ranging between 2482 and 3900 by day 21 to 49 of moult-induction was an evidence of the rejuvenation process following moulting. The plasma levels of progesterone in T2, T3, T5, T6, were from 0.5 to 0.6 ng/ml before moult-induction and decreased to 0 ng/ml by days 7 and 14. In T4 group, levels of progesterone decreased to 0.33 ng/ml by days 7 and 14 whereas T1 maintained an apparently constant level of progesterone throughout the period of study. There was no significant difference (P > 0.05) in the progesterone levels of all the treatment groups by day 42 to 56 of moulting period. The severity of the stress induced by moult procedures caused the cessation of lay in the forced moult groups T2, T3, T5, T6, within 3 to 30 days oftreatment. Percent hen-day production ofthe birds pre-moult was about 51 %. The forced moult groups attained a peak of 70 to 79 % in egg production after moulting whereas T1 decreased progressively with age. There were significant differences (P<0.05) in shell thickness, Haugh Unit, albumen height and yolk index between the different treatment groups at 3 months after moulting.