SECRETORY PATTERN OF METABOLIC HORMONES IN THE LACTATING SOW

Two experiments were conducted to monitor hormonal changes during lact ation in crossbred sows (Pietrain x German Landrace). Sows were fed tw ice daily without weighing the remaining food. Number of piglets was n ot standardized. Plasma concentrations of growth hormone (GH), prolact in (PRL), insulin-like growth factor-1 (IGF-1), IGF-2, insulin (INS), triiodothyronine (T3), thyroxin (T4), free thyroxin (FT4), non esterif ied fatty acids (NEFA) and glucose (GLUC) were determined by RIA, EIA or enzymatically. In exp. A (n=5 sows), blood samples were taken via p ermanent jugular cannula in weekly 24 h windows at 20 min intervals an d additionally once daily for 6 weeks during lactation and for 3 days after weaning. In exp. B (n=24 sows), blood was collected by needle pu ncture of the ear vein 2 and 1 week before parturition, the Ist and 3r d-4th week of lactation and 3 and 2 weeks after weaning. GH (0.8 ng/ml ) and PRL (10.2 ng/ml) increased with onset of lactation (3.3 resp. 91 .5 ng/ml), remained at high levels (2.5-2.8 resp. 39-41 ng/ml) during the 2nd and 3rd week, declined slowly thereafter and considerably afte r weaning to concentrations of 0.7 resp. 2.7 ng/ml. During lactation i n 4 of 5 sows in exp. A, the typical episodic secretory pattern of GH and PRL was lost due to frequent suckling. Basal values, as known from non lactating sows, were not reached and number of pulses was elevate d during lactation for both pituitary hormones. Insulin levels showed a high individual variation. Mean values did not change significantly throughout lactation (0.8-1.2 ng/ml), but tended to be lower at the en d of lactation and after weaning (0.8-1.0 ng/ml). NEFA levels were hig hest in the 2nd week of lactation (0.9 mMol/l) and decreased steadily thereafter and after weaning (0.2-0.3 mMol/l). IGF-1 increased from 77 ng/ml 2 weeks before parturition to 144 ng/ml at parturition, remaine d high (467-552 ng/ml) for 4 weeks and declined to 249 ng/ml after wea ning. IGF-2 increased from the 1st to the 3rd week of lactation (350 r esp. 430 ng/ml), remained at that plateau and decreased after weaning (300 ng/ml). T3 (0.7-0.9 ng/ml), T4 (25-32 ng/ml) and FT4 (10-13 pg/ml ) did not change. In conclusion, the secretory patterns of metabolic h ormones esp. increased IGF-1 - may indicate a regulatory mechanism tha t can help the sow to reduce her protein mobilization during lactation .