Changes in the level of endogenous leptin, FSH, 17beta-oestradiol and metabolites during lupin-induced increase in ovulation rate in ewes

The aim of the study was to determine the changes in the plasma concentration of leptin during lupin feeding-induced increase in the ovulation rate (OR) in ewes. Additionally, alterations in the plasma level of glycogenic amino acids and glucose (as the factors influencing leptin secretion) and the levels of follicle-stimulating hormone (FSH) and 17beta-oestradiol (E-2) (as the hormones regulated by leptin and engaged in recruitment, selection and development of ovulatory follicles) were analysed. Ninety-six female Polish Lowland Sheep were used. All ewes were cyclic and synchronized with PGF2alpha. The ewes were divided into two groups: control (n = 48), fed only with hay, and experimental (n = 48), received additionally lupin (Lupinus angustifolius) grain as a high-protein and a high-energy supplement. They were given lupin from the second to 13th day of the oestrous cycle at increasing doses (150-750 g/day per ewe). On the 11th day of cycle blood samples for analysis of hormones, amino acids and total glucose concentration, were collected from the jugular vein. OR was determined by laparoscopy of ovaries on the sixth day of the following oestrous cycle. Mean OR of ewes supplemented with lupin grain (1.687 +/- 0.463) was 30.67% higher than that of control (1.291 +/- 0.454). In spite of the unchanged body mass, a significant increase (P < or = 0.05) in mean concentration of plasma leptin in the experimental ewes [2.17 +/- 0.15 ng/ml human equivalent (HE)] was found in comparison with control (1.42 +/- 0.12 ng/ml HE). A significantly (P < or = 0.05) higher plasma FSH level in the ewes fed lupin (105.21 +/- 5.87 ng/ml) compared with those fed hay (67.88 +/- 6.03 ng/ml) was also found. However, plasma level of E-2 decreased after lupin feeding. Moreover, in the ewes fed lupin the plasma concentrations of glucose and nine glycogenic amino acids (Gly, Ala, Val, Met, Leu, Ile, Tyr, Phe and Arg) were increased. It can be concluded that lupin feeding exerts the stimulatory effect on the OR in Polish Lowland Sheep. The increase in OR is connected with significantly higher plasma leptin level and coincident with rise in FSH, glycogenic amino acids and glucose concentration. In contrast, the level of plasma E-2 was significantly decreased in lupin-fed ewes.