Browsing by Author "Horst, P."

In 3 experimental runs, the influence of genotype X temperature interactions on the reproductive traits (sexual maturity, egg production, fertility, hatchability, and chick production) of hens of a broiler breeder dam line carrying major genes for dwarfism (dw-) and frizzle (F) was investigated. In experiments 1 and 2, the hens were caged individually under hot (30 degrees C) and temperate (19 degrees C) temperatures, from wk 18 to 72 of age, whereas in experiment 3, hens were kept under moderate temperature (24 degrees C). Hens in experiment 1 were heterozygous for the frizzle gene, and those in experiments 2 and 3 were homozygous, both with and without the dwarf gene. Hens without the above-mentioned major genes (ffDw-) served as control lines. In experiment 1, the frizzle gene (Ff) had no significant effect on sexual maturity, egg production, fertility, hatchability, and chick number under the 2 environmental conditions. In experiment 2, there was a significant interaction between feathering genotype (FF) and environmental temperature for all traits except sexual maturity. Under heat stress, there was a distinct reduction in all reproductive traits except sexual maturity for normally feathered hens compared with frizzle-feathered hens, whereas under temperate conditions, egg production and number of chicks of the FF genotype were reduced and sexual maturity was delayed. In experiments 1 and 2, the dw- gene showed a depressive effect on the growth of hens. In experiment 1, the interaction between dwarf genotype and environmental temperature for egg production was significant. Under temperate conditions, the egg production of dwarf hens was inferior to that of normally sized birds, whereas under hot temperatures, the egg production of the 2 body sizes did not differ. In experiment 2, for sexual maturity, egg production and fertility locus X locus interactions could be determined. The genotype combining the 2 major genes (FFdw-) proved to be inferior to the normally feathered dwarf type (ffdw-) for laying performance but superior in fertility. Under the conditions in experiment 3, the egg production of dwarf birds was significant reduced.

High ambient temperature is a major factor for diminishing reproductive performance of broiler parent stocks. Homozygous naked neck (NaNa) broilers, which possess a higher adaptation to heat due to a reduction of feather coverage, exhibited higher growth rates and meat yield. This study was conducted to investigate the influence of genotype x temperature interactions on the reproduction traits of heavy broiler dams caused by different feathering genotypes induced by naked neck gene (Na). In an additional experiment, the effect of Na gene on embryonic activity using oxygen uptake was examined. Normal-feathered (nana) and NaNa hens were maintained in separate cages under high (30 degrees C) and moderate (19 degrees C) temperatures, with RH of 55% from the 18th to 72nd week of age. Egg production, fertility, hatchability, and the time of embryonic mortality were recorded. In comparison with the NaNa genotype, the nana hens showed clear performance depressions under thermal stress with respect to egg production (63%), fertility (20%), hatchability, and number of chicks (72%). Under temperate ambient temperature, there were no differences in laying performance and fertility between both genotypes, with the exception of hatchability due to an increase in embryonic mortality as a result of the Na gene and consequently in the complex trait number of chicks. The early embryonic mortality of eggs laid by nana hens exposed to heat stress is clearly higher than of eggs by nana hens kept under temperate ambient temperature. In contrast, there were no significant differences in early embryonic mortality of eggs of NaNa birds kept under high and temperate environmental temperatures, demonstrating that heat stress leads to reduced early embryonic livability. Embryonic mortality in the late developing stage is significantly increased, and the homozygous genotype is much more affected than the heterozygous embryo. The possible reason for the Na gene-induced embryonic mortality is still not clear. In this investigation, it is shown that the phenomenon cannot be explained by the oxygen consumption.