Resumo
The effect of the thyroxine administration on body weight and on some physicochemical and histological characteristics of the Longissimus dorsi muscle was evaluated in gilts at 70 days of gestation. Twenty middle-sisters gilts, daughters of F1 females with a ¾ Landrace X » Large White, male were used. At 150 days of age, i.e., before first heat, the animals were randomly distributed into two groups: treated (n = 10) and control (n = 10). The treated group received a daily dose of 400μg of L-thyroxine (T4) in the diet until three days before slaughter and the control group received only diet. Before artificial insemination, blood was collected for determination of plasma total T4. The gilts were inseminated in the second estrus and slaughtered at 70 days of gestation. The initial and final body weight, daily weight gain and pH, water retention, and percentage of muscle fibers and stroma in the Longissimus dorsi muscle were studied. The means of all variables were compared by the Student t-test. Before insemination, the gilts showed clinical signs of hyperthyroidism, characterized by significant increase in plasma levels of T4, mild exophthalmos, and behavioral change characterized by aggression and agitation. There was not significant difference among groups according to the studied parameters. It was concluded that the daily administration of 400μg of thyroxine does not change the daily weight gain during the gestation, as well the pH, the water retention, and the percentage of muscle fibers and stroma of the Longissimus dorsi muscle of gilts at 70 days of gestation.(AU)