Use of the gas production technique to estimate the nutritive value of condensed tannins-containing shrub species from a mountain area in northern Spain

Abstract

Pasture production in the mountain areas of northern Spain is restricted by low temperatures in winter and by high temperatures and lack of rainfall in summer. In such conditions, animals consume substancial amounts of shrub species to meet their feeding requirements. Despite their potential as feed resources, most shrubs contain high levels of anti-nutritional factors such as tannins. Recent studies on condensed tannins (CT; Barry & McNabb, 1999) point out the importance of considering their dosage-dependent effect: while species containing moderate concentrations of CT can exert beneficial effects on protein metabolism in ruminants, high dietary CT concentrations are clearly detrimental for the animals. The aim of the present experiment was to study the nutritive value of some shrubs from a grazing mountain area of the province of León (north of Spain), using the in vitro gas production technique, and examine its relationship with their CT content.