EFFECTIVENESS OF SELECTION IN POULTRY
Abstract
Selection for eight week body weight was conducted for three generations in populations of effective population sizes (N(,e)) of 14.55, 7.27 and 3.64. Four replicate selected and control lines were observed in each effective population size. Selection intensity was kept as constant as possible in all population sizes. While the data showed considerable variability, in general there was a significant linear decrease in the mean cumulative gain as population size decreased and a linear decline in the gain per generation as the generation number increased. The importance of these results in the design and interpretation of selection experiments is discussed. A study of two generations of relaxed selection in three commercial crosses of chickens confirmed a previous report of an 11% to 15% decline in hen-day and hen-housed number of eggs. No additional loss in these traits occurred as a result of the second generation of relaxation. No significant change due to relaxation of selection was found for egg weight, body weight, age at 50% production, adult mortality or hatchability. An experiment was designed to estimate the interaction of dams by hatches, dams by sires in the same breed and dams by breed of sires. White Leghorn dams were mated to two White Leghorn sires and two New Hampshire sires and two hatches were measured for each sire. Two replicates were run each with different sires and dams. The traits observed were hatch of all eggs set, body weight at 8 weeks of age, age at first egg, percent production from first egg to 36 weeks of age, and egg weight at 32 weeks of age. No significant interactions were observed for any trait between dams and either breed of sire or sires in breed. The only significant interaction observed was that for dam by hatch for body weight at 8 weeks of age.
Degree
Ph.D.
Subject Area
Genetics
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