The influence of cobalt/vitamin B12 deficiency as a "stressor" affecting adrenal cortex and ovarian activities in goats.

Twenty 1.5 to 2-year old goats were made vitamin B12 deficient by feeding them cobalt-deficient diets for 23 weeks in order to determine the effects of a progressive deficiency on ovarian and adrenal cortex activities. At 1-day intervals, blood samples were collected for haematological study and plasma for vitamin B12, progesterone and corticosteroid radioimmunoassays. At 23 weeks, the adrenal cortex was taken for histological measurement and the pituitary gland and corpus luteum for LH and progesterone determinations, respectively. The regularity of the oestrous cycles was studied using teaser bucks. The goats receiving a cobalt-deficient diet presented irregular oestrous cycles (22.6 +/- 0.8 days; maximum deviation: 12 to 38 days), while those of the controls were 18 +/- 0.3 days (maximum deviation: 16 to 21 days). Low vitamin B12 concentration led to macrocytic and normochromic anaemia. The concentration of plasma progesterone augmented, but it decreased during the third and subsequent cycles in cobalt-deficient goats as compared to the controls. Plasma corticosteroids were persistently high in cobalt-deficient goats as compared to the controls, and pituitary LH was low in the deficient goats. It is suggested that an erratic endocrinological control mechanism led to irregular cycles, the action site being located in the hypothalamo-pituitary axis.