Sources of variation in purebred pig growth, live ultrasound backfat, and loin muscle area

The purpose of this study was to evaluate the extent how performance traits in purebred pigs, including days to 113.4 kg (D113), ultrasound backfat depth (BF), and loin muscle area (LMA), are affected by variation in birth weight (BTW) and weaning weight (WW). Data consisted of BTW and WW records (Duroc, n = 26,260; Landrace, n = 31,209; Yorkshire, n = 53,037), and off-test records (Duroc, n = 10,103; Landrace, n = 9,478; Yorkshire, n = 18,647). Mean piglet BTW and WW decreased as total born and number weaned increased (P < 0.05). Models included significant effects of parity, sex, farm, and random effects of contemporary group and sow. Covariates of BTW, BTW2, WW, and WW2 were included to evaluate their effects. Mean D113 for pigs from parity 1 dams were 2 to 3 d greater than pigs from parity 2 and 3 dams (P < 0.05). However, when BTW and WW were included as covariates to the model, D113 was not different for pigs from parity 1 dams versus older sows. Birth weight (linear and quadratic) and WW (linear and quadratic) accounted for approximately 20% of the residual variance in D113 within each breed. Backfat depth and LMA were affected (P < 0.05) by BTW and WW. However, inclusion of BF and LMA as covariates in the models produced only small reductions in residual variances. Pigs with lighter BTW and WW, are more common in parity 1 litters and large litters and had poorer postweaning growth, BF, and LMA than heavier pigs at birth and weaning.