Trace micro-nutrients may affect susceptibility to bovine tuberculosis in cattle

Abstract

Bovine tuberculosis (bTB) is a continuing problem in British herds. Micro-nutrients are important for the maintenance of well-functioning immune system. The aim of this study was to determine whether the selenium, copper and vitamin B12 status of cattle was associated with Mycobacterium bovis ( M. bovis) infection. Between 2002 and 2005, 200 cattle (43% dairy, mean age 4.6 years), reactors according to the standard interpretation of the tuberculin test, and 200 in-contacts (41% dairy, mean age 4.4 years) non-reactors, which had been in contact with cattle with bTB, were selected from herds in England and Wales. Levels of the seleno enzyme glutathione peroxidase (GSHPx), copper and vitamin B12 were measured in blood. Confirmation of bTB infection was made by bacteriological culture and histopathology following a detailed postmortem. Levels of selenium and copper were also measured in a random sample of 63 livers. bTB was confirmed by culture/histology in 23/200 (11.5%) of in-contacts and 110/200 (55%) of reactors. In blood drawn at recruitment, GSHPx was lower in cattle with confirmed bTB compared to other cattle (geometric means 59.7 u/mL versus 78.9 u/mL red blood cells (RBC), p < 0.01). Vitamin B12 was similar (geometric means 161.5 pmol/L versus 165.5 pmol/L, p = 0.62) and copper was similar (geometric means 14.4 μmol/L versus 14.1 μmol/L, p = 0.55). In logistic regression models including all micro-nutrients simultaneously and controlling for age, sex, animal production class, herd size, number of reactors, postmortem laboratory and seasonal trends, lower levels of GSHPx (adjusted OR 0.42, 95% CI 0.21–0.81 per 100 u/mL RBC, p = 0.01) and higher levels of copper (adjusted OR 1.69, 95% CI 1.21–2.36 per 5 μmol/L, p < 0.01) were associated with an increased risk of confirmed bTB but there was no association with vitamin B12. There was evidence for a stronger association between confirmed bTB and GSHPx in in-contacts (adjusted OR 0.21, 95% CI 0.06–0.79 per 100 u/mL RBC) compared to reactors (adjusted OR 0.50, 95% CI 0.21–1.23 per 100 u/mL RBC) ( p = 0.08 for interaction). Lower liver copper was associated with a higher risk of confirmed bTB (adjusted OR 0.15, 95% CI 0.02–1.0 per 5000 μmol/kg dry mass, p = 0.05) but there was no association between liver selenium and bTB. Trace micro-nutrient status may affect susceptibility to M. bovis infection in cattle. Further studies are needed.