Comparison of the simple breeding value model and the maternal effects model for genetic evaluation of Segurena lambs

Weaning weight in a single flock of 600 ewes and 40 rams was simulated thro ugh 30 consecutive lambings. The objective teas to compare the simple breed ing value model with the maternal effects model for lamb evaluation tinder the Segurena selection scheme. Three selection strategies were tested: sele ction on breeding values estimated by a simple breeding value model that ig nores maternal effects (method 1), selection on direct additive values only (method 2) or on the sum of direct and maternal additive values (method 3) , both latter methods utilizing a maternal effects model. Average values ob tained in the last lamb crop were about 18 kg for the phenotypic mean, abou t 5 kg for direct additive values and about -1 kg for maternal additive val ues, for all three methods. Average inbreeding coefficient of the last crop was more than 0.13 in method 1 but was less than 0.12 in the others. All d ifferences were not statistically significant (P > 0.05). Consequently, the simple breeding value model can be used for the genetic evaluation of wean ing weight of candidates for selection in the Segurena scheme. The effect o f variation in the magnitude of parameters was evaluated through four sets of parameters. Results showed that with a higher additive maternal componen t, method (3) would become increasingly necessary. The need far method (3) is accentuated with move negative additive covariance between direct and ma ternal effects. Thus, for higher maternal effects or more negative additive correlation, the use of the complete model (with maternal effects) becomes unavoidable. Varying population size, however, affects only the inbreeding accumulated, as long as the same methods of selection are used.