EFFECT OF THE STRESS OF INJECTIONS ON THE SERUM CONCENTRATION OF CORTISOL, PROLACTIN, AND GROWTH HORMONE IN GILTS AND LACTATING SOWS

Three experiments were conducted to determine the effect of subcutaneous injections of saline on serum concentrations of cortisol, prolactin and growth hormone in cycling gilts and lactating sows. In exp. 1, five crossbred cycling gilts were given one subcutaneous injection and blood was sampled during the preceding and following four hours. In exp. 2, blood samples were taken from six purebred lactating sows on a control day and on a day when they were injected with saline in a latin square design. Serum concentrations of cortisol, prolactin and growth hormone were monitored in exps. 1 and 2. In exp. 3, 11 purebred primiparous sows received subcutaneous injections twice daily from 5 to 25 d postpartum. Blood samples were collected for cortisol assay on days 5, 15 and 25. Serum cortisol concentrations increased significantly after saline injection in the three experiments, confirming that injections cause a stimulation of the hypothalamic-hypophyseal-adrenal axis in cycling gilts and lactating sows. When additional stressors such as handling and physical restraint were imposed prior to the injection, a release of prolactin and growth hormone was also observed in cycling gilts. The serum cortisol profiles of lactating sows repeatedly injected showed that their cortisol response to subcutaneous injections attenuated over days. Furthermore, these data indicate that the animals became readily acclimated to blood collection from a catheter within the first day of sampling. Key words: Cortisol, prolactin, growth hormone, stress, gilts, lactating sows