1. Comparison of Methods of Estimating Milk and Fat Production in Dairy Cows;Alexander;J. Dairy Sci.,1949
2. Ashton, E. D. 1956. Milk and Butterfat Recording. A World Survey. Technical Communication No. 3, Commonwealth Bureau of Dairy Science and Technology. Farnham Royal, Bucks, England.
3. The Accuracy of Various Methods of Estimating a Dairy Cow's Production of Milk and Butterfat;Campbell,1946
4. Dairy Cow Testing Throughout the World,1935
5. Kendrick, J. F. 1940. The Cow Tester's Manual. Misc. Publ. no. 359. USDA, Washington, D.C.