Variation in egg yolk cholesterol concentration between and within breeds of the domestic fowl.

1. The pattern of variation for egg yolk cholesterol concentration between 5 commercial egg layer lines and a cross of Gallus domesticus is described. 2. Yolk cholesterol concentration in the cross was lower than in the lines, and 6.7% lower than the midparent value. 3. It is proposed that the reduced yolk cholesterol concentration of the cross may be a consequence of heterosis, although sex-linkage and/or maternal effects cannot be discounted. 4. The difference between the cross and parental lines is consistent with a physiological relationship between yolk cholesterol concentration and rate of egg production, but not between yolk cholesterol concentration and yolk weight.