Genotype by type of housing interaction in populations of white leghorns under reciprocal recurrent selection

Genetic correlations were calculated between 1230 paternal half-sib progenies totalling 47,075 daughters housed in adjacent single cage and litter houses over a period of 9 years. The flocks were reciprocal Leghorn strain crosses under reciprocal recurrent selection. The genetic correlations between housing systems for egg weight, specific gravity and albumen height did not differ significantly from unity. Rate of lay to 305 d of age was correlated 0.70 and egg number for the same period o.81. The correlations for rate of lay and egg number for the total test period (7 to 10 months of lay) were o.81 and o-86, respectively. Body weight at maturity (four generations only) was correlated 0.86. No time trends in the correlations over the 9-year period were obvious. A three-way interaction between years, families, and housing for rate of lay was indicated because the correlations varied less within years than between years.