PORK CARCASS GRADING: THE MAGNITUDE OF BREED AND SEX BIASES IN THE PREDICTION OF MEAT YIELD FROM A SINGLE FAT MEASUREMENT

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Abstract
The magnitude of breed and sex biases in the prediction of meat yield using a single fat measurement was investigated under commercial conditions. Warm carcasses (n = 174) originating from four purebreeds (Yorkshire, 24 boars, 17 gilts; Landrace, 22 boars, 27 gilts; Hampshire, 24 boars, 15 gilts; Duroc, 21 boars, 24 gilts) weighing close to 80 kg were assessed for fat thickness at the maximum loin with a ruler (current Canadian carcass grading measurement) and at the last rib 70 mm from the midline with a Hennessey Grading Probe. All carcasses were evaluated for retail and lean yield 24 h post-slaughter. At the same carcass weight (78.7 kg), significant differences in both retail and lean yield were found (Hampshire > Landrace; boars > gilts), which largely reflected breed and sex differences in fattening. At the same loin fat thickness (25 mm) breed bias in retail yield amounted to 23 g/kg carcass, while sex bias amounted to only 2 g/kg carcass. At the same last rib, fat thickness breed bias in retail yield was reduced to 12 g/kg carcass, while sex bias increased to 4 g/kg carcass. The effect of changing sites of fat measurement from the loin to the last rib in this study resulted in a substantial reduction in breed bias (1.81 kg to 0.98 kg of retail yield), but to increased sex bias (0.15 kg to 0.28 kg of retail yield). Similar trends were found when lean yield was used as the base instead of retail yield. Prediction equations for retail and lean yield were found to be more precise using last rib fat thickness than those using the maximum loin fat measurement. It was concluded that breed bias would be reduced if last rib fat thickness was used to predict the meat content of pork carcasses. Key words: Boar, breed, gilt, pork grading, pork carcass, meat yield