Failure of stress and supplemental lighting to affect release of prolactin in swine.

Concentrations of prolactin (PRL) were quantified in blood serum collected by cannula from prepubertal gilts and by venipuncture from young boars. Subjecting the gilts to a 1-min experimental stress, which consisted of physical restraint with a snare, did not significantly affect serum PRL. However, injection of 50 micrograms thyrotropin releasing hormone (TRH) abruptly increased serum PRL within 5 minutes. In a second experiment with gilts, the stress of vascular cannulation did not increase serum PRL during the ensuing 4-hr period in comparison with concentrations in other gilts cannulated 90 min or 18 hr earlier. Venipuncture samples were obtained biweekly from boars exposed to natural lighting or to supplemental lighting that extended the photoperiod to 15 hr/day. Supplemental lighting did not affect serum concentrations of PRL of board during the period from 17 to 33 weeks of age. Thus, PRL release in swine was resistant to stress and to supplemental lighting, two factors which readily cause PRL release in other species. However, the PRL response to exogenous TRH was similar to that observed in other species.