Plasma prolactin concentration in gilts reared in confinement

Plasma prolactin concentrations were determined in confinement-reared gilts, which were subsequently exposed to boars and/or relocated to pasture lots. At an average age of 181 days, an indwelling vascular cannula was surgically implanted, and 28 gilts were assigned randomly to either control (remained in confinement) or treatment (relocated to pasture) groups. Nine of the gilts in each group were exposed to a mature boar twice daily. Furthermore, the experiment was divided between April (n=17 gilts) and September (11 gilts). Blood samples were drawn at the time of surgical implantation and twice daily thereafter. Plasma concentrations of prolactin were quantified by validated radio-immunoassay procedures. Samples which were collected at surgery had significantly more prolactin than post-surgical samples in 25 of 28 gilts. The overall average for the post-surgical concentration of prolactin was 2.7 ng/ml, and there was no effect of continued confinement versus relocation to pasture lots. There was a tendency for boar exposure to reduce prolactin levels in relocated gilts but not in control gilts. There was also a tendency for plasma prolactin to be greater in September than in April, especially in control gilts. Overall these results indicate that plasma prolactin levels do not reflect the delay of puberty in confinement-reared gilts or the induction of puberty caused by relocation to pasture lots.