Selection for hyaluronic acid production traits: direct and correlated responses in two White Leghorn lines selected for cockerel comb size

Hyaluronic acid (HA) is a polysaccharide preferably extracted from cockerel combs and used for medical purposes, mainly eye surgery. One way of increasing the production of HA from cockerels is to increase the size of the combs. The aim of this work was to study comb development and quantify direct and correlated responses for comb size at different ages and comb weight in two lines of White Leghorn selected for comb size at two different ages. Two lines were created, one selected for comb size at 16 weeks of age (CS16) (line E = early comb development) and the other for comb size at 29 weeks of age (CS29) (line A = adult comb size). There were between 500 and 800 birds of each line and generation and the lines had been selected for five generations. Cockerels in line E developed the combs at an earlier age and had smaller 29-week combs compared with the cockerels in line A. Genetic gain for the selection trait in generation five, measured in relation to line means in generation 1, was 58% in line E and 36% in line A. The corresponding correlated response for CS29 and comb weight (CW) in line E was 28% and 25% respectively, while for CS16 and CW in line A it was 46% and 35%. The results indicated that it is possible to increase cockerel comb size at both 16 and 29 weeks of age through selection.