Impaired antibody response and phagocytosis in goats fed a diet low in cobalt

Cobalt (Co) is utilized by rumen microflora to produce vitamin B₁₂. The aim of the present study was to determine whether feeding newly-weaned goats a diet containing low levels of Co results in impairment of neutrophil function, antibody production and/or lymphocyte proliferative responses. Forty, ten week old goats were fed a commercially-prepared concentrate (150 g/day) and Rhodesgrass hay ad libitum. This diet contained Co at <0.1 mg/kg dry matter. The goats were divided into a control group and a treated group (both n = 20). Goats in the treated group were supplemented with bi-monthly subcutaneous injections of 2 mg of hydroxycobalamin. Two months after weaning, the goats were immunized with keyhole limpet haemocyanin (KLH). A luminol-dependent chemiluminescence (CL) assay was employed to measure the oxidative respiratory burst of neutrophils during phagocytosis of zymosan A. The lymphocyte proliferative response to phytohaemagglutinin (PHA) and pokeweed mitogen (PWM) was assessed. The controls goats demonstrated a significantly lower antibody (IgG) response to KLH compared with the Co-supplemented goats that was apparent 1 week post immunization and was maintained for the 8 week observation period. Neutrophils from the Co-restricted group demonstrated significantly lower CL responses to opsonized zymosan A. Lymphocytes from the control and treated goats did not differ in their mitogenic responses to PHA and PWM. These results demonstrate that goats fed a diet low in Co exhibited impaired antibody and phagocytic responses.