In the southern hemisphere, foraging areas of cattle are affected by overgrazing and soil erosion resulting in decreased availability of grasses and increased amounts of browse plants high in condensed tannins (CT). This study aimed to identify biomarkers in free-ranging zebu cattle (Bos indicus) for the habitat degradation, based on their salivary and trace mineral response to dietary CT. Saliva and blood samples were collected from 60 randomly involved free-ranging zebu bulls in six study sites, which were further grouped into two regions based on the average CT concentration in the plants regularly consumed by the cattle. Jugular venipunctures for blood sampling and the swabbing technique for saliva collection were used. Plasma samples were analyzed for Cu, Zn and Fe. Saliva samples were analyzed for total amino acid concentrations. Average CT concentrations in the plants ranged between 0 and 166 g CT/kg dry matter (P <0.001). Higher CT levels were associated with reduced plasma Cu (P <0.05) whereas Fe was not affected (P > 0.05). In contrast to Cu, higher Zn concentration was found in the region rich in CT content (P <0.05). The proportion of proline of total amino acids, as main indicator of salivary proline-rich proteins in the saliva, was higher in the tannin-rich region (P <0.01). The ratio of proline to the sum of total amino acids was also higher in this region (P <0.001). Higher ratio of salivary arginine to ornithine was observed in the tannin-rich region (P <0.05), suggesting reduced ruminal protein synthesis due to reduced protein bio-availability. In conclusion, the increase in salivary proline concentration in free-ranging zebu cattle reflects the dietary CT load, which in turn suggests habitat degradation and lower availability of feed sources.
- proline-rich proteins