Effect of Oral or Caecal Administration of Protein Supplements on Equine Plasma Amino Acids * † *Published as Miscellaneous Publication No. 679 with the approval of the Director, Agricultural Experiment Station, Contribution No. 9 of the Department of Animal Science and Agricultural Biochemistry, University of Delaware, Newark. †Part of this report was presented at the Third Equine Nutrition and Physiology Symposium, Gainesville, Florida, January 1973.