EFFICIENCY OF GAINS AND CARCASS CHARACTERISTICS OF SWINE OF 2 DEGREES OF FATNESS SLAUGHTERED AT 3 WEIGHTS

Barrows and gilts (200) were slaughtered at 100, 113 and 127 kg live wt. The sample was comprised of 36 litters, of which 6 litters within each breed of sire (Duroc, Hamsphire and Yorkshire) were classified as fat litters (2.36 cm) and 6 litters classified as lean litters (2.16 cm) on the basis of litter mean backfat probes taken at 68 kg live wt. Growth traits were evaluated from 9 wk of age until the designated slaughter weight. Carcasses from the 1st replication (18 litters) were evaluated for percentage separable lean, fat and bone and those from the 2nd replication (18 litters) were evaluated for percentage closely trimmed lean cuts. The fat and lean groups had similar carcass length, longissimus muscle area and percentage closely trimmed lean cuts. The fat group had significantly thicker backfat, lower percentage separable lean and a higher percentage separable fat than the lean group. The 3 weight groups had similar average daily gains and feed efficiencies for the total test period. As slaughter weight increased from 100-127 kg there was an increase in carcass backfat thickness (P < .05) and longissimus muscle area (P < .01). Percentage separable lean, fat and bone of carcass were similar at each of the 3 slaughter weights. The 127 kg group tended to have lower percentages closely trimmed lean cuts than the 100 and 113 kg groups which had similar percentages. The effect of slaughter weight on growth and carcass traits differ from findings reported earlier for swine of different genetic background.