Relative Selection Efficiency Research Articles

RELATIVE MERIT OF SIB VERSUS OWN PERFORMANCE IN SELECTION FOR LEAN MEAT PRODUCTION IN SWINE

The relative selection efficiency (RSE) of direct selection for a trait of basic interest and indirect selection on an alternate trait was examined with consideration given to several population sizes, selection intensities and genetic parameters. Slaughter of litter samples resulting in a reduction of the population available for selection was associated with the direct but not the indirect selection procedure. Values of RSE increased with increasing values of the genetic correlation, but for any given value of the genetic correlation, RSE was inversely related to the heritability of the basic trait. Population size was important only for herds comprising fewer than 10 breeding females.Using predicted percent yield of lean cuts, (A), as the trait for direct selection with [Formula: see text] of 0.2, 0.3 and 0.4 and the live back fat probe, (B), as the trait for indirect selection, with [Formula: see text] and assuming a genetic correlaton between A and B of 0.6, it was demonstrated that, respectively 38, 19 and 9% faster genetic gains in the basic trait accrued from indirect as compared with direct selection. It is suggested that the inherent reduction in population size, coupled with other practical aspects associated with carcass testing, might make the indirect selection method preferable even when RSE is less than unity.

Effect of the Biometrical Relationship among Total Milk Yield, Milk Constituent Yield, and Per Cent of Milk Constituent on Response to Selection

The biometrical interrelationships among total milk yield, milk constituent yield, and per cent of milk constituent are considered. Formulas are developed which express the parameters of per cent constituent in terms of the parameters of total milk yield and milk constituent yield. Genetic and phenotypic statistics calculated directly from dairy cattle data agree with those obtained by application of the formulas.Formulas are presented for genetic gain in milk constituent yield by indirect selection on either total milk yield or per cent of milk constituent. These formulas show that genetic gains in milk constituent yield by indirect selection are determined by the means and genetic standard deviations of total milk yield and per cent constituent, the genetic correlation between these two traits and the heritability of either milk yield or per cent milk constituent.Relative efficiencies of three methods of selecting for either SNF yield or fat yield are compared in the population studied. Selecting for SNF yield using total milk yield was slightly less efficient than direct selection. However, the relative efficiency of indirect selection using per cent SNF was considerably lower. Loss in efficiency of indirect selection for fat yield, using total milk yield, is not greatly different from that using per cent fat.

Genetic and phenotypic parameters for body weight and greasy fleece weight at weaning in Australian Merino sheep

Genetic and phenotypic parameters for body weight and greasy fleece weight at weaning were estimated in a flock of Australian Merinos. Maternal handicaps were found to be more severe at weaning than at the older age of 15–16 months. Lambs born to 2-year-old ewes were 2–3 lb lighter in body weight at weaning and 0.2 lb lighter in greasy fleece weight than the offspring of adult ewes. Twin lambs were on the average 6–7 lb lighter than singles and cut 0.5 lb less greasy wool. Greasy fleece weight at weaning was found to be fairly highly heritable but only moderately repeatable. The repeatability and heritability of weaning body weight were both low. The genetic correlations estimated here were associated with appreciable sampling errors, but the estimates strongly suggested high and positive correlations between measurements at weaning and at 15–16 months for both traits. A general consideration of the relative efficiency of direct versus indirect selection, based on the information obtained in this study, leads to the conclusion that for greater genetic gains, mass selection for greasy wool weight and body weight at weaning should be carried out on measurements at 15–16 months of age, rather than at weaning.

Intra-Flock Genetic Merit under Floor and Cage Managements

THE increasing use of individual cages for laying birds raises a number of problems of significance to breeders. Among them is the question of the relative efficiency of selection for cage performance on the basis of floor records and vice-versa. The problem may be viewed as an example of the general situation in which the efficiency of direct selection for a trait is compared with the efficiency of another criterion of selection. Whatever may be the difference in heritabilities of the two traits, gains in one can be influenced by selection with respect to the other only if the genetic correlation between the two traits is different from zero. The usual estimates of this correlation are well known to be subject to extremely large sampling fluctuations. Nor, in the absence of knowledge of the distribution of these estimates, can one make a significance test whether its value is equal to …