Selection in fat-tailed sheep based on two traits of fat-tail and body weight versus single-trait total body weight
2007
Nejati-Javaremi, A. (Tehran Univ., Karaj (Iran). Dept. of Animal Science) | Izadi, F. (University of Mazandaran, Sari (Iran). Dept. of Animal Science) | Rahimi, G. | Moradi, M.
The objective of the present study was to compare several selection strategies and to find a method of selection permitting improvement in body weight with possible decrease or, if possible, slight increase in fat tail weight. Stochastic simulation was used to produce a flock of 10 breeding rams and 250 breeding ewes with four lambs per ewe. A total of 1000 Iambs were produced for five consecutive non-overlapping generations. Data were simulated using a two- trait model. Both single trait and two trait models were used under phenotypic and genetic selection. In two-trait selection, economic weights were used to construct the selection indices. A range of covariance components was used for generating data and different sets of economic weights were applied to test the sensitivity of different selection strategies to these parameters. With low heritability for both traits, the least genetic trend was achieved for tail weight with phenotypic sele ction index. Highest aggregate genotype was obtained with two- trait genetic method. With increased heritability for tail weight and under single trait selection, an increase in total body weight fully coincided with increased genetic trend in fat tail weight. The highest aggregate genotype and the lowest genetic trend in fat tail weight were obtained when negative economic weight was applied to fat tail weight. When high heritability was used for simulation, the two-trait genetic selection model performed the best. However, when two-trait genetic evaluation is not practical, the best alternative would be to use two-trait phenotypic selection based on economic weights for the two traits.
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