Ruiz, T. M., and E. Cancel-Medina. “Performance of Holstein Cows Fed Two Levels of Concentrate Supplementation and Ruminally Undegraded Protein.”. The Journal of Agriculture of the University of Puerto Rico, vol. 90, no. 1-2, Jan. 2006, pp. 9-26, doi:10.46429/jaupr.v90i1-2.2958.