INFLUENCE OF GROWTH HORMONE-RELEASING FACTOR AND (OR) THYROTROPIN-RELEASING FACTOR ON SOW BLOOD COMPONENTS, MILK COMPOSITION AND PIGLET PERFORMANCE

Abstract

Two experiments were conducted using a 2 × 2 factorial design to determine the effect of porcine growth hormone-releasing factor (pGRF(1–29) NH2) and (or) thyrotropin-releasing factor (TRF) on the endocrine and metabolic status of sows as well as production performance during the lactation period. In exp. 1, sows were assigned to the following treatments: control (vehicle 3 mL, n = 6); pGRF(1–29)NH2 (20 μg kg−1, n = 7);TRF(1 μ kg−1, n = 7); pGRF + TRF (20 and 1 μg kg−1, respectively, n = 6). In the second experiment, 24 sows were equally distributed to the same treatments as in exp. 1 but the dose of TRF was increased to 9 μg kg−1. During lactation (28 d), releasing factors were administered subcutaneously at 10:00 h and 16:00 h from days 5 to 25, inclusively. Serum growth hormone (GH), thyroxine (T4) and prolactin (PRL) concentrations were assayed on days 5, 15 and 25. In both experiments, TRF stimulated T4 release on all sampling days. However, with advancing lactation and/or days of injection, basal and TRF-stimulated T4 levels decreased (P < 0.05). In the second experiment, GRF increased GH release on each sampling day while saline and TRF had no effect (P > 0.05). The GH response to GRF was higher (P < 0.05) on days 15 and 25 compared to day 5 and higher on day 25 compared to day 15. Also, in both experiments, TRF stimulated PRL release on all sampling days. With advancing lactation and/or days of injection, basal and TRF stimulated PRL release decreased (P < 0.05). In exp. 1, serum creatinine (P < 0.01) and blood urea nitrogen (P = 0.06) concentrations were decreased by GRF treatment while TRF treatment increased (P < 0.01) blood glucose and decreased (P = 0.07) serum cholesterol concentrations. In both experiments, milk yield, fat, protein and lactose contents were unaffected (P > 0.05). Piglet body weight gain and sow weight loss were not affected (P < 0.05) by treatments. Results showed that GRF increases the release of GH while TRF stimulates T4 and PRL release during lactation. However, none of these endocrine modifications influenced production performance. Key words: GRF, TRF, hormone, milk, sow, piglet