EFFECTS OF HEAT STRESS AND AGE ON GROWTH PERFORMANCE AND ENDOCRINE STATUS OF MALE RABBIT

Abstract

The effect of environmental temperature and age on plasma hormonal concentrations of testosterone (T), dihydrotestosterone (DHT}, cortisol (C), triiodothyronine (T3} and thyroxine (T4) were evaluated in 40 male Grimaud rabbits. Twenty animals were reared at 20ºC (TNT º = Thermic Neutrality Temperature) and the other 20 at 27 C (HST = Heat Stress Temperature). Far both treatments relative humidity levels averaged 77 % and the photoperiod was 8D:16L with a light intensity of about 40 lux. The animals were fed ad libitum with a commercial pelleted feed. Blood samples were collected from each ammal by intracardiac puncture at 71 and 85 days of age. No interaction effect between temperature and age was found. With regard to effect of temperature, the HST animals had a lower (P<0.01) final body weight (2325 vs 2555 g), daily gain (32. 7 vs 38.1 g) and feed intake (106 vs 126 g/d). The HST treatment significantly (P< 0.05) decreased plasma levels of T (1.01 vs 1.96 ng/ml, DHT (0.42 vs 0.73 ng/ml) and T + DHT (1.43 vs 2.66 ng/ml, but not the T/DHT ratio (2.69). TNT animals had higher (P<0.01) plasma levels of T3 (1.30 vs 1.01 ng/ml) and a lower (P<0.01) T 4/T3 ratio (32. 7 vs 41.3). The concentrations of C (18.9 ng/ml} and r 4 (41.0 ng/ml) resulted unchanged. The etfect of age in the older rabbits was a significantly higher (P<0.01) final body weight (2698 vs 2181 g) daily intake (123 vs 109 g) and feed/gain ratio (3.44 vs 3.12 g/g). No significant difference was observed in plasma concentrations of T (1.48 ng/ml), DHT (0.58 ng/ml), T/DHT (2.69) and T + DHí (2.05 ng/ml} in 71 and 85 days old rabbits. Age had no effect on C levels, which averaged 19.0 ng/ml. In blood samples of younger and older rabb1ts there was no difference in T3 (1.16 ng/ml}, T4 (41.0 ng/ml} values and T4/T3 ratio (37.0). Correlations and linear regression equations were also calculated far daily gain (DG}, digestible energy intake per unit of metabolic body weight (DET/MBW) and each hormone plasma level. Only the thyroid hormones showed significant correlations: T3 was positively (P<0.01) correlated with DG (r = 0.624) and DEI/MBW