Effect of Feed Restriction and I.C.I. 33, 828 on Delaying the Sexual Maturity and Laying Performance of Meat-type Pullets

Abstract

For the farmers and hatcheries of keeping parent stock of broiler, the establishment of techniques to keep them with less expenses of feed and obtain more hatching eggs per bird is extremely important. For this purpose, sexual maturity should be delayed artificially to get larger eggs from the beginning of the lay.Feed restriction during growing period is a useful and most commonly used technique to delay onset of lay. Another method using a drug effective to block release of gonadotrophic hormone from anterior pituitary is also often used experimentally. The drug, I.C.I. 33, 828, is produced by Imperial Chemical Industry in England.The present report is the result of three comparable methods of treating growing pullets of breeders with restricted feeding, fasting and administration of I.C.I. 33, 828. The experiment was carried out with 201 pullets of New Hampshire _??__??_ × Rhode Island Red _??__??_ hatched on December 16, 1966. Feed restricted group was divided into three sub-groups:Treatment No. 1 (Skip-a-day)-fed every other days for 88 days from 60 to 147 days of age.Treatment No. 2 (Fasting A)-fasted for 6 days from 120 to 125 days of age.Treatment No. 3 (Fasting B)-fasted for 6 days from 134 to 139 days of age.Three other groups were treated with I.C.I. 33, 828. They received the compound of I.C.I. 33, 828 at 0.002%, 0.004% and 0.008% levels in the feed for 30 days from 134 days of age when 10 birds of 151 pullets started to lay. The birds belong to control group were fed ad libitum without the drug.1) Average body weight of skip-a-day group was 77% of that of control at the time the treatment terminated, and after that it recovered slowly until 230 days of age when there was no significant difference between them. Whereas in Fasting A and B groups, the body weight at the end of the treatments were 79% and 87%, of that control and once they were returned to full feeding, they recovered to the level of control immediately within 2 and 1 weeks, respectively.2) Feed consumption of skip-a-day was 73.4% of the control during the treatment period. However, no difference was observed in the consumption from 148 to 182 days of age. After release from fasting at Fasting A & B, there was no significant difference in feed intake from the control group. The groups treated with I.C.I. 33, 828 consumed 73-79% of the control during the treated period and the more the amount of the drug in feed, the more reduced feed consumption.3) Sexual maturity of pullets was significantly delayed by feed restriction and the administration of I.C.I. 33, 828. Mean ages at the first egg of the control was 149.2 days and experimental groups were delayed 6-22 days from the control. Fasting A & B showed almost same sexual maturity and the difference in age of fasting did not affect on the age of the maturity. The groups treated with I.C.I. 33, 828 showed delayed sexual maturity and the more the dose the later the maturity. 0.002% and 0.004% of I.C.I. 33, 828 could not depress to become the maturity completely even during the treatment period, and some of the birds started to lay before the treatment finished. Especially in the group of 0.002%, 15 birds out of 25 laid during the treatment, although the production during the period was as low as 1-3 eggs per bird in 10 days. Only 0.008% level could prevent onset of lay perfectly during the period of medication.4) Feed restriction and treatment with I.C.I. 33, 828 had marked effects upon enlarging egg size. Significantly larger egg sizes, 0.8-5.7gr. larger than the control, were obtained in the treated groups except in Fasting A. Those significantly large egg sizes could not be maintained until 230 days of age when there was no difference in the size between the groups.5) There was no significant difference between the groups in egg productions until 500 days of age and during 365 days of laying period after 1st egg.