Relationship of early laying, number and weight of laid eggs to fertility and hatchability of eggs in initial laying lines of hens
Abstract. The relationships between age of hens, number of laid eggs, egg weight on one hand and fertility and hatchability on the other were analysed during two periods of individual pedigree hatching. Altogether 1 369 hens originated from 9 selected initial laying lines of Bar Plymouth Rock (BPR) (3 lines), Rhode Island Red (RIR) (4 lines), Rhode Island White (RIW), and Sussex Light (SUL) breeds. A total number of 23 473 eggs from hens of all 9 aforementioned lines were set after being artificially inseminated. The total average hatchability of set eggs was 73.2 % and the average percentage of unfertilised eggs was 9.3 %. Positive correlations (rp =0.22 to rp =0.72; P<0.01) were found between the total number of eggs laid till the 240th day of age and the number of eggs produced at the beginning of the laying period in the all studied lines. There were negative correlations (rp =−0.03 to rp =−0.16; P<0.01) between the total number of eggs laid till the 240th day of age and the average egg weight (on the 222nd day of age). Zero to positive correlations existed between the total number of eggs laid till the 240th day of age on one hand and the number of hatching eggs, number of hatched chicks/hen and hatchability; the calculated values ranged from rp =−0.02 to rp =0.30 (P<0.01), from rp = −0.08 to rp =0.36 (P<0.01), and from rp =−0.09 to rp =0.30 (P<0.01), respectively. Correlations between the egg weight and number of hatched chicks/hen were negative to zero and their values ranged from rp =−0.19 (P<0.01) to rp =0.02. Correlations between the egg weight and hatchability were always negative (rp =−0.15; P<0.05 to rp =−0.04). Regarding the fact that there is a concurrent selection for an increased egg weight it can be said that this preference of smaller eggs is really counter-productive. A positive relationship between the number of hatching eggs/hen and the hatchability (rp =−0.02 to rp =0.39; P<0.01) was influenced by calculated negative correlations existing between the weight of eggs and the hatchability as well as between the weight of eggs and the number of laid eggs. As far as the hatchability is concerned, it can be concluded that in the aforementioned laying lines those hens are preferred, which produce more eggs of smaller size and that this fact obviously influences also the efficiency of selection for a greater weight of produced eggs.