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

Although nonadditive genetic variation is more important in crosses am ong laying stocks than among meat stocks, development of special sire and dam lines to control the release of primary lines results in broil ers being the product of three- or four-way crosses. Therefore, nonadd itive genetic effects are important in meat stocks because of opportun ities to combine stocks that complement each other. Four experiments w ere conducted to investigate heterosis and overdominance arising from crossing Japanese quail lines originating from the same base populatio n and selected long-term (> 85 generations) for high 4-wk BW under dif ferent selection environments. The different selection environments we re established by feeding different levels of CP (28 and 20%) and diff erent levels of thiouracil (0 and .2%). Estimates of heterosis were hi gh 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 f or 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 fe d low-CP (20%) diets, heterosis values were low initially and remained stable or increased across age. Data obtained from measuring feed int ake and feed efficiency indicated that heterosis for BW was closely re lated to changes in feed intake. Heterosis values for feed intake clos ely followed those for BW, including the decline across age. Conversel y, heterosis appeared to be absent for feed efficiency, except at 1 wk . Similar to heterosis estimates, overdominance estimates were high in itially and declined across age and were more clearly demonstrated und er the 24 and 28% diets. It was concluded that considerable heterosis is present for BW in Japanese quail following the crossing of lines se lected long-term for high BW, but that it is dependent on both environ ment (diet) and age.