Effects of chronic lameness on the concentrations of cortisol, prolactin and vasopressin in the plasma of sheep.

Plasma cortisol, prolactin and vasopressin concentrations were measured by radioimmunoassay in blood samples from control and lame sheep. The lame sheep were all suffering from naturally occurring clinical cases of footrot and showed all the behavioural characteristics of chronic pain; they were scored for impairment of gait and pathology of the foot and divided into mild and severely lame groups. The severely lame sheep had increased plasma prolactin and decreased plasma cortisol concentrations. Plasma vasopressin was variable and showed no consistent changes with lameness. The relationships between plasma cortisol, prolactin and vasopressin may be a useful index in the assessment of animals experiencing chronic pain, when taken in conjunction with other measurements.