Long Term Selection for Small Body Weight in Japanese Quail II: Changes in Reproductive Traits from 60 to 65th Generations.

Abstract

Establishment of small body size poultry is an important strategy, which leads to effective management of bird-colonies and less feed consumption. And also it would be a useful experimental tool for elucidating an evolutionary mechanism causing the change in body size. In Saga University, a divergent selection for body weight at 6 weeks of age had been performed for 65 generations in Japanese quail. And three lines were established : large body weight (LL) line, randomly selected control (RR) line and small body weight (SS) line. Breeding of SS line started with the individuals selected from RR line (Okamoto et al., 1989a ; b). We have aimed to investigate the changes in reproductive traits during a long term selection for small body weight, and the results from 60 to 65th generations have been described in this report. Body weight of SS line was consistently smaller than that of RR line in every generation, and the following differences were observed over most generations. Fertility and hatchability in SS line were significantly lower than in RR line (P<0.01). The raising rate in early stage of growth after hatch tended to be lower in SS line than in RR line, but viability after sexual maturation in SS line remained at high level. Age at first egg in SS line was significantly delayed as compared with that of RR line (P<0.01), and total number of the eggs laid until 100 days of age in SS line was significantly lower than that of RR line (P<0.01). Total weight of the eggs laid until 100 days of age and average egg weight from 91 to 100 days in SS line were significantly lower than those in RR line (P<0.01). Genetic fitness (Falconer and Mackay, 1996) tended to decrease progressively in SS line though drastic increase was observed temporarily at 64th generation. Consequently, it has been concluded that long term selection for small body weight reduces genetic merits, particularly in reproductive traits such as fertility, hatchability, raising rate and sexual maturation, indicating that it is difficult to maintain the production of healthy adult birds at a higher level in the miniaturized line.