title: Response of different commercial strains of laying hens to short total photoperiods in interrupted night experiments during days of 24 and 28 hours.
abstract: Experiments were conducted: as pilot experiments in which each experimental unit, replicated two or three times, consisted of 15 hens, as practical experiments in which each of four strains was replicated twice in two rooms containing 200 to 265 hens, and as commercial experiments in which each experimental unit consisted of 4 strains of 1000 hens but in which no replication occurred. Short total photoperiods were used in interrupted night experiments with 24-hr and 28-hr days. A light regimen of 2L:6D:2L:18D yielded similar results as 12L:16D for percent egg production, egg mass, egg shell breaking strength, and feed efficiency. Exposure to 28-hr days, in comparison with 24-hr days, resulted in a reduction of number of eggs produced but did not reduce egg mass produced. In one of four strains, the increase in egg size and reduction in number of eggs produced was significantly (P less than .05) less than in the other three strains, Under the 28-hr day regimens shell breaking strength was consistently greater (P less than .01) than under 24-hr light regimens. In an additional experiment, no relationship was found in egg breakage during transport between two populations of eggs that differed in eggshell breaking strength as a result of differences in light regimens received by the hens. Short (2L:10D:2L:10D or 2L:12D:2L:8D) and very short (2L:12D:1/4L:9 3/4D) interrupted night regimens generally yielded lower egg production than 16L:8D or 8L:10D:2L:4D light regimens. There was an indication that there might be strain differences in the response to the interrupted night regimen. Exposure to 2L:6D:2L:8D for 6 weeks at the start and 8 weeks at the end of an 11-month experimental period, with 16L:8D given during the remainder of the period, resulted in lower egg production during the last 8 weeks and no compensatory improvement in egg shell breaking strength or egg weight in comparison with continuous exposure to 16L:8D.
mesh_terms: D000818:Animals; D002645:Chickens / Q000235:genetics / Q000502:physiology*; D005247:Feeding Behavior; D005260:Female; D008029:Lighting; D009026:Mortality; D010058:Oviposition