Direkte und maternale genetische Effekte und Umwelteffekte der Fruchtbarke it und Schlupfrate bei Legehennen

The main goals of layer breeding are a result of eeonomie eonditions. GOWE et al. (1993) reported that in egg stock seleetion programs the key traits are egg produetion rate, age at sexual maturity, viability at all ages, egg size, egg shell strength, feed effieieney as weil as fertility and hatehability. However, in praetiee, laying intensity is usually the main seleetion eriterion (WJ,;:ZYK, 1978; SEWALEM, 1998). On the other hand, the seleetion intensity (one of the faetors determining the genetie gain) depends on egg number as weil as fertility and hatehability. The reproduetive traits are known to be lowly heritable (FOERSTER, 1993; VAN KREY, 1993). It was indieated that environmental influenees (such as, pre-ineubation storage of hatehing eggs, maintenanee system) largely modi fies poultry fertility and hatehability (FAfRFULL and GOWE, 1987). Fertility is generally eonsidered a eommon trait of both parents (CRlTTENDEN et al., 1957), being a eonsequenee of the interaction of a male and a female gamete to produee a viable zygote. Hatehability is also determined by embryooie development andthus modified by "additional" matern al effeets (GowE et al., 1993; HARTMANN et al., 1997). These maternal effeets may be defined as any influenee on a progeny phenotype attributable (both in genetie and environmental terms) to the dam, other than the nucJear gene. Thus, these indireet (maternal) genotype effeets are divided into additive, dominance, additive by additive ete. The eonfounding of the two eontributions from the dam is eombined with the possibility of a eOITelation between the respeetive direet and matemal effeets. In Polish pedigree layer floeks, five traits (initial egg produetion, rate of initial egg production, body weight, egg weight and age at sexual maturity) are incJuded in the cJassieal seleetion index. This breeding strategy, whieh was deseribed by WJ,;:ZYK (1978) cJearly shows that the pedigree strains are only seleeted for produetive traits. In this ease, time genetie ehanges of the reproduetive traits (fertility and hatehability) ean be interpreted as a eOITelated response. The objeetives of this study were: i) to estimate the direet and matern al (indireet) additive genetie varianees as