Implications of Piglet Birth Weight for Survival Rate, Subsequent Growth Performance, and Carcass Characteristics of Commercial Pigs

The objective of this study was to analyze the effect of piglet birth weight on preweaning mortality, subsequent growth performance, and carcass characteristics. Individual records collected on 8,193 commercial crossbred pigs were used for analyses. A segmented regression model was used to analyze the effect of piglet birthweight on preweaning survival and a series of mixed models were used to analyze the effect of birth weight group on weights recorded at: weaning (n = 6,777), nursery exit (n = 4,806), and marketing (n = 1,417); HCW, and quantity of lean meat produced (n = 4,806). The effect of growth rate group defined during suckling (< 225 or ≥ 225 g/d) or the nursery phase (< 424 or ≥ 424 g/d) and the effect of growth group by birth weight group (< 1.0, 1.0-1.3, 1.3-1.6, and >1.6 kg) on growth and weight at later stages of production were also analyzed. Preweaning mortality, growth rate, BW, and carcass traits were adjusted to a standard age and daily gain (DG) of lean meat was calculated. Results of segmented regression analysis showed that the slope of preweaning mortality on birth weights below 1.03 kg differed (P<0.05) from the slope of preweaning mortality regressed on birth weights above 1.03 kg. The mixed model analyses showed a positive effect (P<0.05) of birth weight on age-adjusted nursery weight, finishing weight, HCW, quantity of lean meat produced, and lean DG. Growth rate during suckling had a greater impact on final market weight (P<0.10), wean-to-finish DG (P<0.05), and HCW (P<0.05) for piglets with a birth weight < 1 kg than for piglets in higher birth weight groups. However, growth rate during the nursery phase had a greater impact on HCW (P<0.05) quantity of lean meat produced (P<0.05), and lean DG (P<0.05) for piglets in the highest birth weight group (>1.6 kg) than for piglets in lower birth weight groups. In conclusion, piglets born weighing less than 1 kg were at a higher risk of preweaning mortality than piglets born weighing 1 kg or greater, but with fast growth during the suckling period, were able to achieve lifetime growth performance similar to that of piglets with birth weights above 1 kg. Taken together, later life performance was more impacted by growth rate during the suckling period than nursery period for low birth weight piglets and by growth rate during the nursery period, rather than suckling period, for high birth weight piglets.