Cold exposure and mammary exchanges of circulating thyroxine and oestrone sulphate in the goat.

The effects of cold exposure on arterial and mammary venous concentrations of thyroxine and oestrone sulphate, and on mammary blood flow, were measured in goats during different stages of pregnancy and lactation. There were no significant differences in net mammary uptake of thyroxine in four non-pregnant lactating goats exposed for 30 h to cold (-3 +/- 2 degrees C) or control (20 +/- 2 degrees C) temperatures. Cold exposure for 30 h of six lactating goats (approximately 85 d pregnant) stimulated a net mammary release into the circulation of oestrone sulphate (mean 294 ng/min); plasma cortisol concentrations also increased. Cold exposure at approximately 30 d of pregnancy increased cortisol concentrations but had no effect on release of oestrone sulphate.