Sex effects on fat hardness meter readings of market weight pigs
A portable fat hardness meter (FHM) was used to measure the firmness of the inner fat layer on a cross sectional surface over the second thoracic vertebra of pork carcasses. This was a 4-yr study with data collected on 141 barrows, 214 gilts and 270 boars. A statistical model, after adjusting for year and breed of sire (i.e., Lacombe, Landrace, Yorkshire), included sex, linear and quadratic covariates for carcass growth rate (i.e., carcass weight per day of age), a linear covariate for leanness (i.e., carcass fat thickness or dissectible lean) within sex, and a linear by linear covariate of growth rate by leanness, and was used to describe a response surface with fat hardness. No pigs in this study had extremely soft fat (i.e., FHM < 420). However, 4, 2 and 0% of the boars, gilts and barrows had very soft fat (i.e., FHM 420–619). While 10% of the barrows had extremely hard (i.e., FHM > 970) or very hard fat (i.e., FHM 930–970), only 1% of the gilts had very hard fat, and no boars were included in these classes. Relative to the FHM readings of gilts (i.e., 805 ± 6.2), boars (i.e., 780 ± 5.6) had softer fat (P = 0.0002) while barrows (i.e., 835 ± 7.4) had harder fat (P = 0.0001). The majority of boars had slightly soft fat (i.e., FHM 750–829) while gilts and barrows had slightly hard (i.e., FHM 830–889) fat. Regression coefficients for growth rate on fat hardness were homogeneous among the sexes. As growth rate increased fat hardness increased, but was attenuated by a negative quadratic term. Increased leanness was linearly antagonistically related with fat hardness. There were differential effects across sexes (P = 0.0261). As leanness increased, fat became softer among boars and gilts compared with barrows. A linear by linear interaction of growth rate with leanness attenuated this effect. Holding growth rate constant, a 25% reduction of carcass fatness would be expected to reduce fat hardness by 40, 35 and 20 points in boars, gilts, and barrows, respectively. While selection for increased lean growth may result in some degradation in fat quality, the trend towards marketing heavy pigs as they become leaner should be sufficient to offset this effect. Key words: Swine, carcass, grading, growth rate, fat, lean