The effect of cobalt dietary restriction on goats immune responses

Eugene H. Johnson*, Khalid Al-Habsi, Rashid Al-Busaidi, Mohammed Al-Abri. Impaired antibody response and phagocytosis in goats fed a diet low in cobalt. Small Ruminant Research 140 (2016) 27–31.

Why they did it

Small ruminants, such as sheep develop serious clinical signs of vitamin B12 deficiency when they are fed diets containing low levels of cobalt. While it has been assumed that the dietary requirements for cobalt are the similar in goats, these animals have shown to be fairly resistant to disease relating to B12 deficiency. Previous researchers showed that goats with low serum vitamin B12 exhibited higher coccidian counts compared to supplemented animals. A separate study noted that deficient goats were more susceptible to Ostertagia spp, allucidating to the fact that the immune system may be compromised. The aim ofthe present study was to investigate innate and adaptive immune responses in goats exposed to low levels of dietary Co by studying the respiratory burst of neutrophils as an indicator of phagocytic function, antibody production to immunisation and lymphocyte proliferative responses to mitogen stimulation.

What they did

Forty, 10 week old male goat kids were randomly allocated into a control or treatment group at weaning. The kids were fed a diet consisting of Rhodes grass hay (Chloris gayana) ad libitum and 150 g/day per head of a commercially prepared ruminant concentrate. r. Goats in the treated group received subcutaneous injections of 2 mg of hydroxycobalamin at weaning and bi-monthly thereafter throughout the duration of the study. This treatment regimen has been shown to maintain serum vitamin B12 concentrations within established reference values.

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.

What they found

The control 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.

Take home message

Goats fed a diet low in Co exhibited impaired antibody and phagocytic responses. Consequently low levels of serum vitamin B12 might result in animals suffering impaired immunity and potentially being more susceptible to infectious diseases.

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