Some optimum selection strategies and age structures with overlapping generations

Abstract

Genetic responses from selection strategies based on selection among all potential parents of the following year's crop were compared with those based on selection only within progeny crops. In the former group of strategies the duration of stay of an individual in the breeding herd is determined by the estimated breeding value of that individual, whereas in the classic model selected individuals of the same sex all remain in the breeding population for the same period. The former group of strategies, termed 'parent selection' strategies, were consistently superior in genetic response to the progeny selection strategies with a very large relative advantage under some conditions. The superiority of strategies that make more efficient use of genetic differences between own or parental age was greater among parent selection strategies than among progeny selection strategies. Similarly, increases in female to male mating ratios, fertility and survival rate generally resulted in larger increases in genetic response in the more efficient strategies. The effect of changes in number of male and female age groups differs markedly between strategies.

Determination of optimal selection policies

“…The conclusion that selection should be by truncation on expected breeding value agrees with those reached in other studies by COCHRAN (1951), HOPKINS and JAMES (1977), and GOFFINET and ELSEN (1984) from somewhat different viewpoints. Thus GOFFINET and ELSEN considered more general distributions and allowed for other factors such as herd effects, but did not explicitly include age effects due to genetic improvement.…”

Prediction of within-herd differences in total feed intake between growing pigs

“…Thus they found the proportion of young pigs tested in sire lines should be twice as high as in dam lines. Thirdly, within lines, giving priority to testing animals of higher predicted genetic merit based on pedigree information also increases genetic improvement (Hopkins and James 1977;). For the type of testing studied in this paper, where pigs can be recorded on an electronic feeder for a relatively short part of the total growth period, it would be useful to derive the balance between the number of pigs tested and the length of the recording period for each pig which maximises genetic improvement.…”

A deterministic multi-tier model of assortative mating following selection

“…A recurring issue in the recent history of animal breeding theory is the importance of incorporating selection history into selection strategies for populations when generations overlap. This was first demonstrated by Bichard et al (1973) and later extended by Hopkins and James (1977) in their Progeny Selection and Parent Selection strategies. It is now well known that a BLUP animal model takes account of the accumulated selection history, not of age groups as in the methods of Hopkins and James (1977) but of individuals by using the ancestral information in the numerator relationship matrix.…”