EFFECT OF LACTATION FEED-INTAKE ON ENDOCRINE STATUS AND METABOLITE LEVELS IN SOWS

Two experiments were performed to study the endocrine response of sows to changes in feed intake during lactation. The hormonal status of 24 ( exp. 1) and 15 (exp. 2) lactating sows subjected to different feed intakes was determined. During a 28-d lactation, the sows were full-fed (FF) or restrict-fed 3 kg d-1 (RF) of a diet formulated to contain 12.4 MJ DE kg-1 and 16 % crude protein. On days 2 and 28 postpartum, blood samples were collected by means of indwelling vena cava cannulae from 12 FF and 12 RF (exp. 1) and 8 FF and 7 RF (exp. 2) sows. Metabolic status was assessed by plasma assay for glycerol, free fatty acids, blood urea nitrogen, glucose and creatinine. Endocrine status was determined by plasma assay for growth hormone (GH), insulin, cortisol, prolactin, glucagon, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). On day 2 postpartum, there were no treatment differences (P > 0.05) in plasma concentrations of any of the components studied. On day 28 postpartum, the RF sows had higher (P < 0.05) plasma concentrations of glycerol and creatinine, nigher (P < 0.05) concentrations of GH and cortisol and lower (P < 0.05) concentrations of insulin than FF sows. Both mean plasma LH and FSH levels increased (P < 0.05) between days 2 and 28 of lactation. Furthermore, total LH and FSH secretion determined on day 28 was higher in FF than in RF sows (P < 0.05). It is suggested that the hormone changes associated with excessive catabolism in the RF sows during lactation could be functionally related to the difference in gonadotrophin secretion measured at the end of lactation.