Birth weight threshold for identifying piglets at-risk for preweaning mortality

Abstract

The association of piglet birth weight (BtW) with early-life mortality risk is strongly supported by research of numerous studies reporting decreased preweaning piglet mortality as individual piglet BtW increases. The purpose of the present analysis was to identify a BtW threshold associated with reduced odds of preweaning survival. Observations from 2 studies with a total of 4068 piglets originating from 394 litters on 4 different commercial farms (3 European, 1 U.S.) were compiled for meta-analysis. Overall preweaning mortality rate across all farms was 12.2%. Data used in the analysis was weight of piglets within 24 h of birth and their corresponding survival outcome (dead or live) by weaning at 3 to 4 wk of age. A mixed effects logistic regression model was fit to estimate the probability of preweaning mortality based on BtW. A random effect of study was included to account for overall differences in mortality between the 2 studies. A piecewise linear predictor was selected to best represent the drastic decrease in preweaning mortality found as BtW increased in the range of 0.5 to 1.0 kg and the less extreme change in preweaning mortality observed for changes in weight above 1.0 kg. The model change point was determined by comparing model fit for BtW ranging from 0.5 kg to 2.0 kg based on maximizing the likelihood. A linear predictor equation was also generated to estimate the associated preweaning mortality probability associated with every 50 g of piglet BtW. Results indicated a 1.11 kg BtW change point in the log odds of piglet preweaning mortality, thus, implicating that every incremental change in BtW below 1.11 kg has a greater impact on mortality risk than incremental changes in BtW above 1.11 kg. Among the farms in this analysis, 14.9% of all piglets had BtW < 1.11 kg. These findings imply that interventions targeted at increasing the BtW of piglets having BtW less than 1.11 kg have tremendous potential to improve piglet preweaning survivability. A large percentage of the neonatal pig population falls below this weight threshold, and postnatal management strategies to decrease neonatal mortality should be directed toward these at-risk piglets.