THE EFFECT OF GENOTYPE ON PREDICTED LEAN YIELD IN HEAVY PIG CARCASSES USING THE HENNESSY GRADING PROBE, THE DESTRON PG-100 AND THE FAT-O-MEATER ELECTRONIC GRADING PROBES

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Abstract
One hundred and sixty-three carcasses from four genotypes (Lacombe, a halofhane-positive line, their F1 cross, and Yorkshire) at four weight classes ranging from 73 to 104 kg were evaluated by three electronic grade probes (Hennessy Grading Probe [HGP], Destron PG-100 [DGP]), Fat-O-Meater [FOM]). The two probes (HGP, DGP) in commercial use produced similar results for the prediction of lean yield. The carcass grading equations for the HGP and DGP were in close agreement with each other for predicted lean yield but they tended to increasingly underestimate the lean yield of carcasses as carcass weight increased. The halothane-positive line had predicted lean yields that were 4% less than actual, but pigs (i.e. Yorkshire) that are more typical of Canadian hog production still had predicted lean yield underestimated (1.5%), while predicted lean yield in the Lacombe was overestimated (1.1%). New prediction equations were developed which indicated no bias among the three probes, and were robust over a wide weight range. The addition of carcass weight reduced the residual standard deviation (RSD) for predicted lean yield from 1.913, 1.994 and 1.890 to 1.850, 1.875, and 1.797 for the HGP, DGP and FOM, respectively, while addition of a second probe site at the last rib further reduced the RSD to 1.725, 1.785 and 1.759. Furthermore the differences of the regression equations developed in the present study from those used by Agriculture Canada for grading hogs clearly illustrate the need to develop grading equations from animals that are representative of the population of pigs to be graded. Thus, there may be need to periodically reassess the grade probe equations as the genetic background changes or as carcass weight increases in the hog population. Key words: Electronic grading, market weight, genotype, halothane gene, Lacombe, Yorkshire