Response to Interruption with Short Photoperiod in Mid-laying of the native Hen

Abstract

Hen-day egg production, measured at 2-week intervals of the native hens interrupted with short photoperiod of 8 hours/day for 4 weeks before resuming long photoperiod of 15 hours/day (8L-15L group), tended to be higher than those of the native hens kept under continuous long photoperiod of 15 hours/day (Cont. 15L group). Significant differences (P<0.05) were, however, observed only at a few laying intervals. Though the hen-day egg production after resuming the long photoperiod of 15 hours/day of the 8L-15L group seemed to be improved, the cumulative egg production throughout the whole experimental period which included two rounds of exposure to the 4-week-short photoperiod and 12-week-long photoperiod cycle was not positively changed. It was only 56.0 eggs/hen/32 weeks compared with 57.4 eggs/hen/32 weeks (P>0.05) of the Cont. 15L group. Average feed conversion ratios of the 8L-15L group tended to be lower than those of the Cont. 15L group, with a significant difference (P<0.05) was observed only in round II of the experiment (7.2 vs 9.7) when the chicken grew older. Average egg weights were also improved (P<0.05) after a temporary interruption with the short photoperiod for 4 weeks. The 8L-15L hen had higher egg weights than the Cont. 15L hen (47.0 g vs 46.1 g in round I, and 47.8 g vs 46.9 g in round II). Increases in both albumen and shell actual weights were considered to be the cause of the greater egg weight. It was clear that the activity of the ovary and oviduct was changed according to the photoperiod the native hens received. Sizes and degree of development of both the ovary and oviduct of the 8L-15L group decreased tremendously when interrupted with the short photoperiod of 8 hours/day and then returned to even greater size with higher degree of development than of its counterpart, the Cont. 15L group, after resuming the photoperiod of 15 hours/day. Average fertility (percentage of live-fertilized eggs at 7 days of incubation) of the 8L-15L group was higher than (P<0.05) that of the Cont. 15L group (81.8% vs 75.3%).