P. J. Rajala-Schultz, W. J. A. Saville, G. S. Frazer, and T. E. Wittum. 2001. Association Between Milk Urea Nitrogen and Fertility in Ohio Dairy Cows. J. Dairy Sci. 84:482–489.
Article en anglès. Relació entre urea a la llet i fertilitat. JDSci 2001.
P. J. Rajala-Schultz, W. J. A. Saville, G. S. Frazer, and T. E. Wittum. 2001. Association Between Milk Urea Nitrogen and Fertility in Ohio Dairy Cows. J. Dairy Sci. 84:482–489.