Evaluation of the Growth of Backfat Depth, Loin Depth, and Carcass Weight for Different Sire and Dam Lines1

The growth of 1,990 barrows and gilts of 3 sire and 2 dam lines was evaluated over 2 replicates. Pigs were weighed and ultrasonic backfat and loin depth measurements were taken at approximate 28-d intervals from 37kg BW to target BW of 113, 127, or 141kg. Carcass backfat and loin depths were measured with an optical probe. An exponential equation Y = exp(b0 + b1X + b2X2) + ai[exp(b0 + b1BW + b2BW2)]D (where Y is the value of the measurement; b0, b1, and b2 are regression coefficients; and D is a parameter) with a pig-specific random effect (ai) provided the best fit of the ultrasonic data to BW. The ultrasonic backfat depths were affected (P < 0.01) by replicate, dam line, and the interactions of replicate × BW and dam line × BW. The ultrasonic backfat depths of the gilts increased at a rate of 0.0077cm/kg BW gain at 40 kg BW to 0.0115 cm/kg BW gain at 135kg BW. Barrows had backfat growth rates of 0.0110 cm/kg BW gain at 40 kg BW, which increased to 0.0149 cm/kg BW gain at 115 to 125 kg BW. The ultrasonic loin depths were affected (P < 0.05) by replicate, sire line, and replicate × BW and sire line × BW interactions. Carcass backfat and loin depths were affected (P < 0.01) by replicate, sire line, dam line, target BW, sex, and the sire line × sex interaction. Pigs of different sire and dam lines have different rates of backfat and muscle growth, indicating differences in compositional growth.