An observational study of factors associated with variation in growth rate in pigs
Variation in pig growth rate within a group of pigs has become a concern for pork producers because it increases fixed costs per pig marketed and makes all-in/all-out management practices difficult. The factors associated with weight gain variation on commercial farms have not been thoroughly studied. The purpose of this project was to determine the association between weights at weaning and eight weeks of age and specific management factors on commercial swine operations. This research was conducted on 2133 pigs from nine farms owned by commercial pork producers. The average weights at birth, weaning and eight weeks were 1.72 kg, 6.03 kg, and 14.83 kg respectively, and the coefficients of variation were 24.2% at birth, 24.9% at weaning and 26.3% at eight weeks of age. Heavier weaning weights were associated with larger birth weights (r 2 = 14.1%), age at weaning (r2 = 4.8%), and smaller litter size nursing the sow (r2 = 4.7%) (P < 0.001). There was an interaction between piglet birth weight and sow parity (r2 = 1.2%), and between sow parity and number of piglets nursing the sow (r 2 = 2.7%) (P < .001). Heavier eight-week weights were associated with larger birth weights (r2 = 2.4%), older age at weaning (r2 = 2.6%), and weaning weights (r2 = 8%) (P < 0.01). Birth weight, weaning weight and weaning age together account for 58% of the variation in eight-week weights. As birth weight increased by 0.5 kg, eight-week weights increased by 0.84 kg, pigs that were one kilogram heavier at weaning weighed 0.90 kg extra at eight weeks. Pigs were 0.25 kg lighter for each day weaned after 21 days of age. A field trial was conducted on a commercial farm that had a history of large variation in pig weight gain after weaning and evidence of ear lesions. The problem of lightweight pigs and pigs with ear lesions resulted in financial losses when pigs were sold at the end of the nursery phase. Access to water was investigated as a cause of these problems. Pigs given two water sources per 40 pigs had lower weight variation and better average daily gain than pigs with one water source.