Divergent Selection for Feather Growth in Broiler Chickens

The objectives of this study were to estimate the genetic parameters of feathering and the response of the unselected trait, body weight, as a result of selection for feathering; also the correlated response of broiler production traits to selection for feather growth in the broiler progeny of different lines; and the response of the broiler progeny of the different lines under normal and high temperatures. The foundation stock consisting of 600 male and 600 female day-old grand parent chickens was selected from a population of thousands and supplied to the Poultry Husbandry Department by a hatchery of Ross Breeders Ltd., Scotland. Three groups of birds, including males and females, were selected for feathering on the basis of phenotype, insofar as 24/25 days of age feather pattern was concerned, as follows: Fast feathering, Slow feathering, and, a Control group, which was randomly selected. A grand total of 4023 pedigreed and 3042 broilers progeny from two generations were involved in the statistical analysis of this study. After two generations of selection, on average, males and females of the fast feathering line gained +.86 and +.65 units of back score; +4.2 and +7.25 mm of tail length; and +18.4 and +10.0 g of body weight while the males and females of slow group lost -.42 and -.43 units of back score; -2.2 and -3.9 mm of tail length; and -13.7 and -10.2 g of body weight, respectively, compared with the control group. On the basis of full-sib analysis, heritability of back score in the first generation was found to be .562+.072 and .458+.057 in the second generation. On the same basis, heritability of tail length was .599+.074 in the first and 0.568+.062 in the second generations while the heritability of .839+.078 and .713+.086 was found for body weight around 24 days of age in the first and second generations, respectively. There was a strong genetic correlation (.733+. 053) between tail length and back score, showing they can be a good substitution for each other. Also, there was a high genetic correlation between tail length and body weight (.605+.068). Considering this estimate, phenotypic selection for tail length might be worth considering in promoting a genetic improvement in feathering in the population of chickens carrying the K gene. The broilers produced from the first generation showed no signs of a significant difference between the selected lines as regards body weight and feed conversion. But there was a difference between males and females. Males tend to be heavier while females stored a higher percentage of abdominal-fat. However, when broiler progeny were reared under different temperatures still there was not any significant difference between lines but high temperature (3