Are all piglets born lightweight alike? Morphological measurements as predictors of postnatal performance

Birth weight (BiW) of pigs is a commonly used predictor of postnatal performance; however, it has been suggested that morphological measurements may be more reflective of the intrauterine environment and thus better predictors of postnatal growth. The aim of this study was to determine 1) whether morphological measurements, including ponderal index (PI), body mass index (BMI), and abdominal circumference (AC), could be used as predictors of postnatal performance and 2) if so, would they be better predictors than BiW and 3) would the same predictors apply to pigs of different BiW at different stages of their growth? Morphological measurements, BiW, and BW at d 28 and 70 were available for 731 pigs from experiments conducted over a 2-yr period. A series of linear models was used to determine predictors that affected growth performance from birth to d 28 and from d 28 to 70. For both light (LBiW; ≤1.25 kg) and normal BiW pigs (NBiW; 1.60 to 2.00 kg), BiW was not the best predictor of performance ( > 0.05); different variables for the growth periods considered applied to pigs with different BiW. For LBiW pigs BMI ( < 0.001) and AC ( = 0.0202) were the best predictors for d 1 to 28, and AC ( = 0.0317) and PI ( = 0.0450) were the best predictors from d 28 to 70, with pigs with a larger AC and higher PI/BMI more likely to have higher ADG pre- or postweaning. In contrast, the best predictor variables for NBiW pigs were AC ( = 0.0482) for d 1 to 28 and crown-rump length (CRL; = 0.0138) for d 28 to 70. Focusing on LBiW pigs with low ADG, BMI was the best predictor ( < 0.05) of growth for pre and postweaning, whereas for LBiW pigs with high ADG the best predictors were AC ( = 0.00132) from d 1 to 28 and BiW ( = 0.00601) from d 28 to 70, with increasing BMI, AC, and BiW associated with greater ADG. For NBiW pigs with high preweaning ADG, the best predictor consisted solely of AC ( 0.0210), but no morphological predictor variables were significant for NBiW pigs with low preweaning ADG. For d 28 to 70, the best predictor for NBiW pigs with low ADG was CRL ( = 0.0171), but for high ADG no predictor variables were significant. The present study showed that the morphology of piglets is more important than BiW when predicting the postnatal growth of pigs; however, which measurement is the most important depends on both the BiW and stage of growth. For small-sized pigs, these morphological measures may be considered as a decision-making tool by farmers when trying to identify potential poor performers.