THE EFFECT OF SEVERAL DIFFERENT PHOTOPERIODS ON THE PERFORMANCE OF MEAT-PARENT GENOTYPES

Abstract

Approximately 4700 birds consisting of four commercial meat-parent genotypes were used in two experiments under six photoperiod treatments. In each experiment, the rearing photoperiod treatments consisted of (1) a constant 8-h period of light per day and (2) a constant 12.5-h period of light per day. In the first experiment birds reared on 8 h of light per day were subjected to three adult photoperiods: (A) increased from 9 h at 20 wk to 16-h constant photoperiod at 32 wk, (B) 16-h constant photoperiod from 20 wk to end of experiment, and (C) 10.5 h dark (D)–2 h light (L)–2D–9.5L. The group reared on the 12.5-h photoperiod were subjected to three adult photoperiods: (D) increased from 12.5 h of light per day at 20 wk to 17 h constant at 32 wk, (E) increased from a 12.5 h of light per day at 20 wk to 16 h at 22 wk, and (F) 10.5D–2L–2D–9.5L. Photoperiod treatments were the same in experiment 2 except that the adult treatments were introduced 1 wk earlier and treatments C and F were changed to 9.5D–2L–2D–10.5L. There were significant genotypic effects for practically all traits measured except mortality. Photoperiods D, E and F resulted in a significant delay in sexual maturity compared to A, B and C. Egg production tended to be higher for treatments A, B and C with treatment C supporting better general performance in experiment 2 than in experiment 1. The use of treatment C in experiment 2 resulted in performance equal to or better than other photoperiods. Interactions among genotypes and photoperiods were of no practical importance.