Economic returns from reducing backfat thickness in pigs by genetic and other means

Abstract

A major pig abattoir in Queensland grades carcases on the thickness of subcutaneous fat at three positions on the back. A model was developed for transforming grading results into a relationship between average fat thickness and average carcase price. This relationship was examined in a large sample of 60 to 70 kg carcases drawn from a year's killing. From highest to lowest, grades were designated GI, G2, G3 and G4. The distribution of carcases between grades was 84.0, 12.3, 3.5 and 0.2 per cent, the average fat thicknesses were 22.3, 27.8, 31.1 and 35.1 mm and average prices 111.0, 104.5, 96.0 and 81.0 c kg-1 respectively. A sigmoid relationship was found between fat thickness and price with the sampled population being close to the upper limit of price. The value of 1 mm reduction in fat thickness in the present population was estimated at 0.55 c kg-1. The same reduction in a population 1 standard deviation fatter was valued at 1.67 c kg-1. It was concluded that only populations fatter than the present one would be fully compensated for the increase in carcase lean which would accompany a reduction in back fat. Reference is made to the use of the derived relationship between fat thickness and carcase price in cost-benefit analyses and genetic improvement programmes.