Relaxin is not associated with poor milk yield in the postpartum sow

Porcine relaxin (pRXN) titers were measured in 109 plasma samples drawn between 24 and 120 h post-partum from good (n = 34), and poor (n = 25) milking sows and from sows (n = 12) exhibiting overt signs of hypogalactia located on six swine farms in Ontario. Mean plasma pRXN titers among the three groups at 24 h post-partum were not significantly different although there was considerable variation. By 48 h however, the pRXN titers had declined markedly in all groups and between 72 and 120 h, pRXN was cleared from the plasma of all sows examined except one hypogalactic animal that had a titer of 1.13 ng/mL at 96 h. These results suggest that, although pRXN may be identifiable in the corpora lutea during the puerperium, it does not contribute to either hypogalactia or poor lactational performance in sows. The data also encourage the view that pRXN could be used at farrowing without deleterious effects on suckling.