CHANGES IN THE CHARACTERISTICS OF COMMERCIAL HOG CARCASSES IN CANADA

Over the 14-yr period 1969–1982 the proportion of commercial hog carcasses indexing above index 100 in the Canadian slaughter increased from 42.5 to 78.0 based on the 1968 index grid, and average fat (shoulder plus loin) was reduced by 10% on a weight constant basis. The fat reduction was equivalent to an increase in yield of trimmed retail product of 0.97 kg per carcass. Coincident with these changes was a progressive decline in the number of hog producers, with census numbers in 1981 approximately 25% of those recorded in 1966. Given the singular economic importance of carcass index it seems highly probable that the herds eliminated were those which, for reasons of genetics or management, were inferior in index performance. That genetics had a major role is suggested by the prolonged and linear nature of index improvement (2% per year). Provincial time trends for carcass weight, index and average fat were essentially parallel until April 1982, when the criterion of carcass fatness was changed from the sum of two fat measurements (maximum shoulder plus maximum loin) to the single measurement taken at the loin. Examination of sample survey data revealed statistically significant differences among provinces in the relative contributions of loin and shoulder fat to the sum of these two measurements with Ontario hogs tending to have more shoulder fat and less loin fat than hogs of the same carcass weight from other provinces. These differences could have resulted from systematic differences in measuring techniques; however, the fact that they were present in every sample is suggestive of regional genetic differences (e.g. breeds) in the hog populations. Key words: Hot carcass merit, population trends, genetic improvement