Kumar, M Ravi, et al. “Effect of Undegradable Dietary Protein Level and Plane of Nutrition on Milk Yield and Serum Biochemical Constituents in Crossbred Cattle”. The Indian Journal of Animal Sciences, vol. 76, no. 9, Mar. 2011, https://epubs.icar.org.in/index.php/IJAnS/article/view/4355.