Hervás, G., P. Frutos, A. R. Mantecón, and F. J. Giráldez. “Effect of the Administration of Quebracho Extract on Rumen Fermentation and Diet Digestibility in Sheep”. Spanish Journal of Agricultural Research, Vol. 2, no. 1, Mar. 2004, pp. 63-71, doi:10.5424/sjar/2004021-61.