SECRETION PATTERN OF GROWTH-HORMONE, PROLACTIN, INSULIN AND INSULIN-LIKE GROWTH-FACTOR-I IN THE PERIPARTURIENT SOW DEPENDING ON THE METABOLIC STATE DURING LACTATION

The aim of the study was to investigate the influence of different ene rgy levels during a 4-week lactation on the regulation of the metaboli c hormones somatotropin (GH), prolactin, insulin and insulin-like grow th factor-1 (IGF-1). A total of 21 crossbred sows (German Landrace X D uroc) were cannulated for daily blood collection from 3 weeks before p arturition until 2 weeks after weaning and for weekly window sampling (every 20 min for 10 h). Nineteen sows were given 2.8 kg food during l ate gestation, 5.0 kg food during lactation and 2.8 kg food per day af ter weaning and two sows were given food at a restricted level (3.0 kg ) during lactation. In the 19 sows, the different energy balance was i nduced by allocation of different numbers of sucking piglets to the re spective sows. One group of sows suckled seven piglets and served as a control (C; no. = 7) and another group suckled 10 to 12 piglets and w as energy deficient (D). After the study, the sows of the deficient gr oup were, based on their litter weight gain from parturition until wea ning divided into Io to (D-L; no. = 6) or high (D-H; no. = 6) litter w eight gain. The D-H sows lost move body weight during lactation than C and had lower glucose and higher nonesterified fatty acids levels bef ore morning feeding. GH and prolactin increased around parturition and their secretory profiles during lactation were altered by the frequen t sucking stimulus, whereby the access of the piglets to their dams wa s not controlled During lactation, GH and prolactin were highest in D- H sows. The results suggest a possible role of not only GH but also of prolactin in nutrient partitioning to the mammary gland just before t he start of lactation and for minimizing the adverse effects of a nega tive energy balance. Furthermore, insulin and IGF-I increased around p arturition in all sows. Insulin was higher before and after feeding an d the highest levels were found in C and D-L sows. The regulation patt erns of insulin and IGF-1 indicate that the lactating sow is able to m obilize enough energy from body reserves to prevent metabolic disorder s, even during a period with deficient energy supply. This is contrary to the regulation in the dairy cow, where the negative energy balance is coupled with a severe glucose deficit during phases of high milk y ield, which causes decreased levels of insulin and IGF-1. In the sow, the glucose intake with the food meets the glucose requirement for met abolic pathways also during a deficient lactational energy intake. The refore, in sows IGF-1 can be stimulated by increased GH levels via the GH receptor in the liver during a state of nutritional energy deficie ncy and the fact that sows can compensate a deficient metabolic state much better than cows is also reflected in the respective endocrinolog y.