Concentrazione plasmatica di T3 e T4 totali in capre in diversi stati fisiologici e con due differenti livelli di assunzione di energia

Total plasma T3 and T4 concentrations in goats at different physiological states as affected by the energy intake - The effects of two different concentrate levels on total plasma 3-3’-5-triiodothyronine (T3) and thyroxine (T4) concentrations in goats were investigated. Blood samples were taken from 20 goats fed hay ad libitum during the dry period (30 d and 3 d before oestrus, D1 and D2 respectively), pregnancy (13 wk, 17 wk and 21 wk of pregnancy, P1, P2 and P3, respectively) and lactation (5 wk and 13 wk after parturition, L1 and L2, respectively). Three weeks before blood sampling the goats were allocated, by means of a randomised block design, into two groups. Control group (C) was fed either 0.2 (in D1, D2, P1) or 0.4 Kg/head/d maize grain (in P2, P3, L1, L2). High energy diet group (H) was fed either 0.4 (in D1, D2 and P1) or 0.7 Kg/head/d maize grain (in P2, P3, L1 and L2). Plasma T3 concentrations were affected only by the sampling period, resulting significantly higher in P1 than in the dry period and in P3. In C goats, plasma T4 recorded in P1 and in L1 was significantly higher than that in P3. The variations of plasma T4 concentrations in H goats, throughout the different physiological states, did not result statistically significant. The decrease of plasma T3 and T4 during pregnancy in H goats was one month delayed. During the last two months of pregnancy, higher concentrate level induced higher plasma T3 and T4 concentrations in comparison to C. The effects of energy intake on thyroid hormone levels during late pregnancy could be justified by the negative energy balance that usually occurs in this period. The higher concentrate supply had no significant effect on milk yield nor on plasma thyroid hormone concentrations during lactation.