The objective of this study was to investigate the effect of high and moderate summer ambient temperatures on testicular structures and endocrine profile of developing ram lambs. Twenty fall-born ram lambs were randomly divided into two groups: animals were kept outdoor (n=10) under ambient temperature (31-50 degrees C) or maintained indoor (26-32 degrees C) from May to October 2007. Daily maximum ambient temperature was recorded for both environments. Monthly serum testosterone and cortisol concentrations were compared between two groups throughout the experiment. The animals were slaughtered at the end of the study and their testes subjected to histopathology exam. The results showed that maximum outdoor ambient temperature was significantly higher than indoor. There was no difference between two groups on serum testosterone concentration. There was no effect on serum cortisol levels except in August and October. Histolopathological examination revealed a severe testicular degeneration with significant germ line degeneration without any impact on somatic cells. In conclusion, direct exposure of developing lambs during non-breeding season impairs testicular germ cells without significant effect on testicular endocrine function.
