Cattle breed effects on the reactivity of cattle to a tannin-rich diet

Introduction: In regions suffering from soil erosion, feed resources for cattle are often scarce, and plants are often rich in antinutritional factors as a defence mechanism. One of the main antinutritional compounds are tannins. Seen that grass typically contains negligible amounts of tannins in comparison to trees and shrubs, it is suggested that grazers are less adapted to tannin- rich diets in comparison with browsers (Shimada, 2006). Cattle are typically considered grazers, but when looking into the grazing diet of zebu cattle in tropical regions, tannin levels are usually high. Therefore, this study was set-up to find indications whether zebu breeds historically grazing on tannin-rich diets have better adaptive mechanisms to cope with tannin-rich feed than crosses with Holstein. Materials and Methods: Four zebu cows and four zebu×Holstein crosses (>2/3 Holstein) were fed a diet with or without the tannin-rich plant ambabesa (Albizia gummifera) in a cross-over design with 8 days per period. On dry matter basis, Ambabesa contains 30% CP and 61% NDF. Cows were all female and 2-3 years of age, and fed at body weight basis. Blood samples were taken and plasma was stored until analysis. By means of a sponge, saliva samples were taken and stored until analysis. Plasma was analysed for the minerals Fe, Cu, Zn, Mn and S. Saliva was analysed for amino acids, with focus on proline as measure for protein-rich proteins (PRP), known to bind with tannins (Kim & Miller, 2005), but in general to look for typical deviations in amino acid pattern that can relate to other salivary protein secretion as described in cattle (Makkar et al., 1998). Results: Albizia gummifera was not readily ingested initially, and the cows needed an adaptation period. Zebu cows showed higher plasma Zn concentrations (p = 0.043) and a tendency for higher plasma Fe concentration (p = 0.083) in comparison to the Holstein breeds. Plasma Zn was positively correlated with plasma Mg and Ca. Amino acid analyses of the saliva samples were not yet available at the time of submitting this abstract. Conclusion: The higher plasma Zn in the zebus can point to better tannin-coping ability, seen that tannins can reduce the bio-availability of Zn (Lönnerdal, 2000). The association between plasma Zn and plasma Mg and Ca, can refer to the common inhibitory action of tannins on bivalent cations. The tendency for higher plasma Fe in zebus further supports this hypothesis, as it has been clearly demonstrated that Fe has a high affinity for tannins (South & Miller, 1998). These preliminary results suggest that not only browsing herbivores, but also grazers on tannin-rich vegetation can have adaptive mechanisms to tannins, and eventually other antinutritional factors