Effects of Transport Stress, Sex, and Weaning Weight on Postweaning Performance in Pigs

To examine the effects of transport, sex, and weaning weight on postweaning performance, pigs were weighed and blood was collected immediately before weaning (d 0; with or without a 3-h transport) and on d 1 and 7 postweaning. Corticosteroid-binding globulin concentrations decreased by d 1 and remained suppressed through d 7 regardless of transport. Cortisol concentrations in males increased from d 0 to 1 and then decreased to preweaning levels by d 7; females had higher preweaning cortisol levels that did not change on d 1 but that decreased by d 7 to lower levels than in males. The free cortisol index was elevated on d 1 in all groups but returned to preweaning levels by d 7. Low weaning weight was associated with lower corticosteroid-binding globulin concentrations and higher free cortisol index on d 1. White blood cell counts increased from d 0 to 1, and then decreased by d 7. The percentage and number of neutrophils as well as the neutrophil:lymphocyte ratio followed a similar pattern. Females had higher numbers of neutrophils than males on d 1. Low weaning weight was associated with greater numbers and percentages of neutrophils before weaning, but not after; weaning appeared to uncouple the relationship between BW and circulating immune cell populations. The stress caused by weaning was greater than that associated with transport and was, in part, related to weaning weight. Understanding how factors influence postweaning performance will yield new strategies to reduce their effects and increase uniform and efficient growth.