INFLUENCE OF THE NAKED NECK GENE AND OF T HE FREQUENCY OF INSEMINATIONS ON REPRODUCTION PERFORMANCES OF HENS ACCORDING TO THE AMBIENT-TEMPERATURE

64 hens of each of the genotypes NaNa (homozygous Naked neck), Nana+ ( heterozygote) and na+na+ (normal plumage) issued from the same populat ion were distributed by half for each genotype in individual cages eit her at a constant ambient temperature of 21-degrees-C +/- 1-degrees-C, or at 31-degrees-C +/- 1-degrees-C. Then fertility and hatching rates were evaluated after artificial insemination with a fixed number of s permatozoa per hen and so as to equalize the average genotype of the e mbryos for each genotype of breeder hen. During the first period, the inseminations were repeated weekly, then in a second period half of th e females in each genotype and environment were inseminated weekly, th e other half twice a week. Finally eggs were collected two times for h ens on day 3 and 7 after insemination in order to estimate the number of spermatozoa trapped in the perivitelline membrane. The higher ambie nt temperature had a deleterious effect on the total number of laid eg gs, the hen-day laving percent and the percent of ''pause'' days. This was more marked in non-naked neck hens (significant genotype x temper ature interaction). Such a deleterious effect of high temperature was also obtained for fertile and hatched eggs both during the first and t he second period. More frequent inseminations improved fertility and h atchability, with no significant interactions with either ambient temp erature or genotype. After a single insemination, both fertility and h atching rates changed similarly in all genotypes and treatments. Morta lity rates were increased in heated birds with no significant effects associated with genotypes. Finally the trends observed for the effect of temperature and genotype on the number of spermatozoa in the perivi telline membranes agreed in qualitative way with fertility, showing an unfavorable effect of heat on these parameters. However this effect w as more marked in the na+na+ genotype, but the great variability of th is trait masked potential significant differences between genotypes.