Changes in heterosis under within‐line selection or reciprocal recurrent selection: an experiment on early egg production in Japanese quail

Abstract

Introduction In much animal production, commercial animals are crossbreds from closed lines or breeds under long‐term directional selection. Therefore it is desirable to be able to predict heterosis gains over the generations as it is done for genetic progress under within‐line selection. However, heterosis is the phenotypic expression of a complex phenomenon which may involve several types of genetic effects like dominance and epistasis. In animal breeding, basic quantitative genetics theory indicates that heterosis should be proportional to (squared) differences in gene frequency between populations (e.g. F alconer and M acK ay 1996), and it has been found approximately correct, so it is commonly used for planning crosses. Under that type of heterosis, however, selection towards the same objective in two populations should bring gene frequencies closer, and therefore it should eventually decrease heterosis. On the other hand, reciprocal recurrent selection designed to increase genetic distance between lines should eventually achieve maximum heterosis (O llivier 1982). Some experiments reviewed by brun (1982) have already compared genetic progress under within‐line and reciprocal recurrent selection, but they did not focus on comparing the trend of heterosis with generations between the two selection methods. Also, heterosis was monitored periodically in some selection experiments on poultry, and results were reviewed by F airfull (1990). They were somewhat contradictory, but they generally failed to relate genetic progress to loss of heterosis under within‐line selection. Moreover, in commercial production, as purebreds and crossbreds are not contemporaries and are generally maintained under very different management systems, estimations of heterosis and of the evolution of crossbred advantage over the generations may be difficult to obtain. Using the Japanese quail as an experimental animal, the present work was initiated specifically to follow the changes in heterosis brought about by selection for a single heterotic trait, early egg production (M invielleet al. 1995). For that purpose, two selection methods expected to have opposite effects on heterosis, directional within‐line (or individual) selection and reciprocal recurrent selection, were applied for 13 generations in four quail lines started from two different origins, and trends of heterosis in the selected character and in weight and egg traits were evaluated.

Effects of Different Selection Methods Using Body Weight on Egg Yield Parameters in Japanese Quail

“…This is even more so in the negative correlation between body weight and egg production. This situation should be considered in the development of quail parent lines (Kocak et al, 1995;Minvielle et al, 1999;Yahaya et al, 2009). It is reported that the long-term selection for body weight in quails has resulted in a decrease in egg production and an increase in egg weight.…”

Analysis of reproductive traits in crosses among maternal lines of rabbits

“…The second explanation considers that V and H lines, both have a very high prolificacy, higher than line A, and consequently low differences in the frequencies of the genes affecting prolificacy and then low heterosis, as suggested by the theory of dominance for heterosis, could be expected [7]. The results obtained by Minvielle et al [19] in quails were, however, contrary to this expectation, because the heterosis did not diminish with the progress of the selection programme. Another result contrary to the second explanation was obtained by García and Baselga [10,11].…”

“…Because the usual methods are based on within line selection, as opposed to reciprocal-recurrent selection, direct performance of the crossbred does is improved. Furthermore, it is expected that the initial heterosis expressed in the cross will be maintained along the generations of selection and that the genetic progress obtained selecting the maternal lines will be capitalised on top of the heterosis [16,19,23] and expressed in the crossbred does. In this sense, a very important point is to check if the heterosis is actually maintained.…”

Genetic parameter estimates of growth curve and reproduction traits in Japanese quail

“…Much of the genetic improvement studies on quails have focused on early egg number or BW at fixed ages in which the phenotypic mass selection is considered. Information on quail lines selected for meat or egg production is extensive (Marks, 1990), but the data on heterosis in quail are rare (Chahil et al, 1975;Minvielle et al, 1999). Contrary to commercial broiler production, crossbreeding of highly selected lines have been rather little use in quail production.…”