After five generations of selection, a program aimed at developing lines differing in their minimum weight requirements for onset of sexual maturity (MinWtsxm) resulted in a difference of 500. g between the high and low MinWtsxm selected lines. At eight weeks of age, low line birds weighed significantly less and had significantly shorter shank length, with some indications of increased adiposity. Under ad libitum feeding from day of hatch, low line birds entered sexual maturity at an earlier age, lower body weight and higher fat content than high line birds. In other experiments, however, the difference in MinWtsxm was retained throughout lay and across molt. When S-5 birds were reared under restricted food intake levels and then fed varying fixed levels of food, they differed strongly in age at first egg, but there were no indications in the later production periods that the low line birds were laying at an optimum food intake below that of the high line birds. Egg number of the low line birds did, however, exceed that of the high line birds throughout the laying cycle. The converse was true for egg weight.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume X. Breeding programs for swine, poultry, and fish., , 293–298, 1986
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