Quantitative relationships between suckling-induced teat stimulation and the release of prolactin, gastrin, somatostatin, insulin, glucagon and vasoactive intestinal polypeptide in sows.

The pituitary hormones prolactin and oxytocin play important roles in the production and ejection of milk. In addition, some gastrointestinal peptides are released in response to suckling. During suckling, the piglets massage the udder of the sow both before and after let-down and the duration of suckling is correlated to the amount of milk produced by the sow. The aim of this study was to investigate whether there is a quantitative relation between the release of prolactin, gastrin, somatostatin, insulin, glucagon and vasoactive intestinal polypeptide (VIP) and the amount of stimulation of the sow's teats by the piglets. Repeated blood samples were drawn from three Swedish Landrace sows during three consecutive nursings by each sow on days 1, 3, 7 and 14 after parturition. The duration of massage by the piglets was noted, as was the number of piglets massaging. Hormone levels were quantified by radioimmunoassay. The release of prolactin, somatostatin, insulin, glucagon and VIP but not of gastrin were found to be significantly related to the amount of teat massage performed by the piglets during the first 2 weeks of lactation. The release was related to the duration of piglet massage or to the combined effect of duration and the number of piglets massaging but not to the number of piglets massaging per se. The basal level of prolactin was found to decrease during this time.