Secretory pattern of metabolic hormones in the lactating sow

Two experiments were conducted to monitor hormonal changes during lactation in crossbred sows (Pietrain x German Landrace). Sows were fed twice daily without weighing the remaining food. Number of piglets was not standardized. Plasma concentrations of growth hormone (GH), prolactin (PRL), insulin-like growth factor-1 (IGF-1), IGF-2, insulin (INS), triiodothyronine (T3), thyroxin (T4), free thyroxin (FT4), non esterified fatty acids (NEFA) and glucose (GLUC) were determined by RIA, EIA or enzymatically. In exp. A (n = 5 sows), blood samples were taken via permanent jugular cannula in weekly 24 h windows at 20 min intervals and 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 puncture of the ear vein 2 and 1 week before parturition, the 1st and 3rd-4th week of lactation and 1 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 after weaning to concentrations of 0.7 resp. 2.7 ng/ml. During lactation in 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 elevated during lactation for both pituitary hormones. Insulin levels showed a high individual variation.(ABSTRACT TRUNCATED AT 250 WORDS)