EFFECT OF THE NA (NAKED NECK) AND O (BLUE EGGSHELL) GENES ON EGG-PRODUCTION, EGG TRAITS AND FEMALE REPRODUCTIVE PERFORMANCES ACCORDING TO THE AMBIENT-TEMPERATURE

One-year laying hens were used, belonging to two dwarf (dw) brown-egg type lines from the same origin, one fixed for the Na (Naked neck) gene, the other with normal plumage. Within each line families with half of the progeny being heterozygous Oo+ (blue egg) and the other half o+o+, were chosen. The two lines and genotypes at the O locus were distributed in individual cages in two cells. One cell was maintained at a constant temperature of 21-degrees-C, the other at 31-degrees-C during a 4 month period, then the temperatures were exchanged between the two cells for a second period of the same duration. The laying rate, per cent hatchability over fertile or incubated eggs with articial insemination were recorded for each period, and some egg traits were measured only in one of the two periods. The main results concern the differences between the "Naked neck" and non-Naked neck lines and confirm a previous within family comparison between the NaNa and na+na+ genotypes. The beneficial effect associated with the "Naked neck" gene on female fertility and hatchability at high ambient temperature is found again, and a similar effect on laying rate with advancing age also likely. The "blue egg" gene increases egg shell and probably also egg shell membrane thickness at the two temperatures; this had no consequence on per cent cracked eggs which was low on the whole. The O gene was associated with no other effects nor specific responses to temperature.