Abstract
Response in a modified reciprocal recurrent selection scheme for egg production was evaluated considering variable family sizes and genetic correlation between purebred and crossbred half sisters. The criteria of selection of purebred breeders included pullet's own performance, purebred full and half sisters and crossbred half sister's performance. Heritability of egg production of crossbreds (aggregate genotype) and purebred's was assumed to be 0.2 and genetic correlation between purebred and crossbred half sisters (rpc) as 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, -0.1, -0.2, -0.3, -0.4, -0.5 and -1.0. Number of dams per sire to produce purebred and crossbred progenies assumed to be 5, 6, 7, 8, while number of purebred female progeny (Np) and crossbred progeny (Nc) per dam were considered to be 3, 4, 5 and 6 in each case. Considering phenotypic variance as unity, selection indices were constructed for different combinations of dams and progeny for each value of rpc. Following selection index theory, response in crossbred and purebred for egg production was computed. Results indicated that response in crossbreds depended mainly on crossbred family size and also on magnitude of rpc irrespective of its direction, and response was greater with large crossbred family size than the purebred families. Correlated response in purebreds depends both on magnitude and direction of rpc and was expected to be greater with large purebred family size only. Inclusion of purebred information increased the accuracy of selection for crossbred response for higher magnitude of rpc irrespective of its direction. Present results indicate that desirable response in both crossbred and purebred performance is a function of rpc and family sizes. The ratio of crossbred and purebred family sizes can be optimized depending on the objective of improving the performance of crossbreds and/ or of purebreds. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 1 : 8-12)
Highlights
Reciprocal recurrent selection (RRS) exploits non-additive genetic variance and additive variance (Cress, 1966; Hill, 1971; Bell and moore, 1972) and is suitable for low heritable trait like egg production in poultry.Arthur (1986) pointed out the modern layer breeding systems generally use RRS or some modification of it to improve performance of the cross
Bell (1982) emphasized that genetic correlation between the means of purebred and crossbred half sibs is a reliable indicator of the relative emphasis to give to purebred versus crossbred informations when selecting for crossbred performance For low or negative rpc RRS is advantageous over within line selection (WLS) for improving crossbred performance
Singh and Kumar (1994) and Wie and van der Werf (1994) have detailed the methodology to combine different sources of informations for a trait considering as two traits for purebreds and crossbreds simultaneously to maximize the genetic response in crossbreds under modified reciprocal recurrent selection (M-RRS)
Summary
ABSTRACT : Response in a modified reciprocal recurrent selection scheme for egg production was evaluated considering variable family sizes and genetic correlation between purebred and crossbred half sisters. Heritability of egg production of crossbreds (aggregate genotype) and purebred’s was assumed to be 0.2 and genetic correlation between purebred and crossbred half sisters (rpc) as 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, -0.1, -0.2, -0.3, -0.4, -0.5 and -1.0. Correlated response in purebreds depends both on magnitude and direction of rpc and was expected to be greater with large purebred family size only. Inclusion of purebred information increased the accuracy of selection for crossbred response for higher magnitude of rpc irrespective of its direction. Present results indicate that desirable response in both crossbred and purebred performance is a function of rpc and family sizes.
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