Effect of diet and season on steroid hormones in the ruminant.

The effects of diet and season on blood concentrations of progesterone and glucocorticoids in sheep and cattle are reviewed. Underfeeding tends to increase progesterone in sheep but the effects in cattle are equivocal. Sheep undergo seasonal anoestrus but there is very little evidence for circannual variations in progesterone in cattle. Glucocorticoids exhibit circadian rhythms. Levels are raised by several stressors such as handling, transport, venipuncture and impending slaughter. Undernutrition may result in the anticipated elevation of the catabolic hormone but seasonal variations in concentrations of glucocorticoids are not apparent.