HETEROSIS AND OVERDOMINANCE FOLLOWING LONG-TERM SELECTION FOR BODY-WEIGHT IN JAPANESE-QUAIL

Although nonadditive genetic variation is more important in crosses among laying stocks than among meat stocks, development of special sire and dam lines to control the release of primary lines results in broilers being the product of three- or four-way crosses. Therefore, nonadditive genetic effects are important in meat stocks because of opportunities to combine stocks that complement each other. Four experiments were conducted to investigate heterosis and overdominance arising from crossing Japanese quail lines originating from the same base population and selected long-term (> 85 generations) for high 4-wk BW under different selection environments. The different selection environments were established by feeding different levels of CP (28 and 20%) and different levels of thiouracil (0 and .2%). Estimates of heterosis were high for hatch of total eggs (>25%) and liveability (12 to 47%), and low for hatch weight (2 to 4%). Overdominance estimates followed similar patterns but were of lower magnitude. Percentage heterosis estimates for BW were high at 1 wk (20 to 30%) and declined linearly to 5 to 10% at 4 wk when quail were fed 28 and 24% CP diets. Contrariwise, when fed low-CP (20%) diets, heterosis values were low initially and remained stable or increased across age. Data obtained from measuring feed intake and feed efficiency indicated that heterosis for BW was closely related to changes in feed intake. Heterosis values for feed intake closely followed those for BW, including the decline across age. Conversely, heterosis appeared to be absent for feed efficiency, except at 1 wk. Similar to heterosis estimates, overdominance estimates were high initially and declined across age and were more clearly demonstrated under the 24 and 28% diets. It was concluded that considerable heterosis is present for BW in Japanese quail following the crossing of lines selected long-term for high BW, but that it is dependent on both environment (diet) and age.