Concentrações plasmáticas de testosterona, triiodotironina (T3) e tiroxina (T4) em bodes submetidos ao estresse calórico / Plasma concentrations of testosterone, triiodothyronine (T3), and thyroxine (T4) in bucks submitted to heat stress

Para verificar o efeito do estresse calórico (EC) nas concentrações plasmáticas de testosterona, triiodotironina (T3) e tiroxina (T4), oito bodes, das raças Saanen (n=4) e Alpina (n=4), foram mantidos em câmara bioclimática, sob condições de termoneutralidade (13,0ºC a 26,7ºC) durante 30 dias e, após um período (60 dias) de descanso, submetidos ao EC (23,7ºC a 34,0ºC) por 30 dias. Para minimizar as variações sazonais nos perfis hormonais devido ao fotoperíodo, durante toda fase experimental, incluindo a de adaptação em condições de termoneutralidade (30 dias), o fotoperíodo foi controlado utilizando-se alternância de dias longos (16h de luz e 8h de escuro) e de dias curtos (8h de luz e 16h de escuro) a cada 30 dias. As amostras de sangue foram coletadas duas vezes por semana durante cinco semanas. No conjunto das raças, o EC não influenciou (P>0,05) as concentrações de testosterona (1,8±0,2 vs 1,3±0,2ng/ml) e nem a de T4 (52,7±2,8 vs 50,0±2,8ng/ml). Houve declínio (P<0,01) das concentrações de T3 nos animais submetidos ao experimento (1,3±0,1 vs 1,0±0,1ng/ml), mas a redução foi observada somente nos bodes Saanen. Em ambas as raças, as concentrações de T3 e T4 variaram (P<0,01) conforme o dia da coleta das amostras de sangue. O EC foi suficiente para produzir uma resposta fisiológica com redução das concentrações plasmáticas de T3 em bodes das raças Saanen, mas não da raça Alpina, assim como não foi capaz de alterar os níveis plasmáticos de testosterona e nem de T4.

To verify the effect of heat stress (HS) on plasma testosterone, triiodothyronine (T3), and thyroxine (T4) concentrations, eight Saanen (n=4) and Alpine Brown (n=4) bucks were kept in climate chamber under thermal neutral conditions (13.0ºC to 26.7ºC) for 30 days. After a resting period (60 days), the same bucks were submitted to heat stress (23.7ºC to 34.0ºC) for another 30 days. To neutralize the seasonal variations of hormonal profiles throughout the period, the photoperiod was controlled every 30 days altering long (16 hours of light and 8 hours of darkness) and short days (8 hours of light and 16 hours of darkness). The blood samples were collected twice a week during five weeks. In both breeds, there was no effect of HS (P>0.05) on plasma concentrations of testosterone (1.8±0.2 vs 1.3±0.2ng/ml) and T4 (52.7±2.8 vs 50.0±2.8ng/ml). There was a decline (P<0.01) of plasma T3 concentrations (1.3±0.1 vs 1.0±0.1ng/ml) after HS treatment, but this reduction was only evident in Saanen bucks. In both breeds, the plasma concentrations of T3 and T4 varied (P<0.01) according to the day of blood sample collection. The HS was sufficient to provoke a physiological response with reduction of plasma concentrations of thyroid hormones mainly of T3 in Saanen bucks, but not in Alpine ones. The HS did not affect the plasma testosterone and T4 levels.

Hematobiochemical changes and antioxidant status of heat stressed rabbit bucks and its amelioration using chromium picolinate

This study was conducted to evaluate the effect of dietary chromium picolinate on heat stressed NewZeland White rabbit [NZW] bucks. Forty five NZW rabbit bucks were used in this study and divided into 3 equal groups. The first group was kept in an ambient temperature of 18 +/- 0.5 °C and relative humidity [RH] of 62 +/- 0.5% corresponding to the thermo neutral zone of this species and kept as control normal group. While the second and third groups were exposed to heat stress by establishing an ambient temperature of 35.5 +/- 0.5 °C and relative humidity of 68 +/- 0.5% for 5 hours / day for 3 consecutive days. The second group was kept as heat stressed group, while the third group was given a diet supplemented with chromium picolinate 1200 microgram/kg diet. Whole blood and serum samples were collected from all groups just after heat termination, 1, 3 and 7 days post heat stress. The results of this study revealed that heat stress [HS] elicited significant decrease in body weight in addition to significant increase in rectal temperature and respiration rate and significant decrease in body weight. HS produced significant decrease in red blood cell count, hemoglobin concentration, packed cell volume, total leukocytic count, lymphocytes and monocytes beside significant increase in heterophil and heterophil / lymphocyte ratio. Moreover, HS elicited significant decrease in serum total proteins, albumin and globulin in addition to significant increase in serum urea, creatinine and glucose. Also, HS lead to significant increase in serum Cortisol besides significant decrease in serum thyroid hormones. Regarding the effect of HS on antioxidant status, HS lead to significant increase in serum malondialdehyde [MDA] concentration with significant decrease in serum concentration of antioxidant vitamins [E, C and A] and trace elements [Iron, Zinc, Copper and chromium]. Chromium supplementation restored the abovementioned parameters towards the normal control values. It is concluded that chromium picolinate supplementation 1200 microgram/kg can be considered protective management practice in rabbit diet, alleviating the detrimental effects of HS