ECONOMIC BENEFIT OF INCLUDING COMPUTED TOMOGRAPHY MEASUREMENTS IN A LARGE TERMINAL SIRE BREEDING PROGRAMME

Abstract

The marginal economic benefit of incorporating computed tomography (CT) into a terminal sire breeding programme was estimated for an operation with a 1400 ewe nucleus generating rams for use over 100,000 commercial ewes. A mating ratio of 1:80 was used for both flocks. Sires for the nucleus were used as ram lambs for a single year. Commercial rams were fast used as two-tooths for three years. Selection intensities for rams and ewes in the nucleus were 2.41 and 0, and generation intervals 1 and 3 years, respectively. Genetic and phenotypic parameter estimates from Waldron et al. (1992) and parametric bootstrapping were used to generate a probability distribution for breeding index improvement of carcass traits using selection based on CT relative to ultrasonics. The REVS used were +$6.00 and -$5.00 per kilogram of lean and fat, respectively. Internal rates of return (IRR) were calculated for the cumulative probability distribution. Twostage selection, using ultrasonics first and CT on a subset second, was optimised using “NEWSTAGE” (Wade and James 1996). The costs of ultrasound and CT scanning were set to $3 and $270 per head, respectively, for the NEWSTAGE analysis. A gene flow model was used to account for transfer of the improved genetics from the nucleus to the commercial flock. The optimal proportion of ram lambs to CT scan was determined to be 13 percent of rams born. For a single year’s investment (i.e. one year’s CT scanning) the cumulative net present value was positive by year three (evaluation occurred in year zero) and was near maximal by year ten. The risk of incorporating CT into a large terminal sire breeding programme was estimated as a 0.07 probability of making an IRR of less than ten percent.