Two-stage selection is a technique used in animal breeding to make the use of expensive measurements economically viable in a breeding programme. Selection candidates are first screened using inexpensive, but imperfect, predictors of their genetic merit. A selected subset are then evaluated using more accurate, but expensive, measurements and the final selection is made. This study compared the assessment of carcass composition traits using either computed tomography (CT) scanning or progeny testing (with 10 or 20 progeny per sire; PT10 and PT20, respectively) in the second stage of two stage selection systems using quantitative genetic theory. Stage 1 selection was assumed to be based on live weight and ultrasonic predictions of carcass merit. For a genetic correlation of 0.7 between ultrasonic and CT/PT measures, the economic return peaked for progeny test at $2.70 and $2.38 per commercial ewe when 10 and 5% of the male selection candidates were evaluated in PT10 and PT20, respectively. CT had a greater return at $3.52 per commercial ewe when 20% of the male selection candidates were evaluated using CT. The results show that given the moderate heritability of carcass composition traits, the reduction in generation interval and the lower cost of evaluation of CT outweighs the increased accuracy of selection and higher mating ratios associated with progeny testing.
Proceedings of the New Zealand Society of Animal Production, Volume 64, Hamilton, 212-216, 2004
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