Without more precise approach to analyze genetic parameters, improving egg production showing the plateau during several decades will be very difficult (Nordskog et al., 1974; Bnsley et al., 1978) and Sheldon(1980) pointed out the importance of molecular genetics for breaking the plateau in egg production.
At first Willham(1966) reported that partition of genetic components such as additive variance due to the individual's own genotype and maternal genetic variance due to the dam's genotype was important in analyzing the genetic parameter and determining the response to selection. Through analysis of genetic parameters following the Willham's model, Alschwede and Robinson(1971), Vaccare and Van Vleck(1972), and Hanrahan and Eisen(1973,1974) proposed for pig, poultry and mouse, respectively that the amount of genetic improvement seemed to be dependent upon interaction between additive and maternal genetic effects. Vaccaro and Van Vleck(1972) found that maternal genetic effects were important in determining the variation of all traits in chicks and also that the correlations of the additive and maternal genetic effects for most of the traits were calculated as negative. Silva et al.(1976) studied negative correlations between additive and maternal genetic effects could be considered as an aspect applicable to egg production in poultry.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 8. Symposia (2), , 825-830, 1982
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