1. Brandsma, S. (1978) The relation between milking residual milk and milk yield. In Proc. Symp. on Machine Milking 17th Ann. Meeting. National Mastitis Council, Inc., Arlington VA, USA, p. 47.
2. Emmerson, M.A. (1941) Studies on the macroscopic anatomy of the bovine udder and teat Vet. Ext. Quart., 41, 80.
3. Gifford, W. (1936) The butterfat records of cows possessing supernumeraries compared with cows having the normal number of teats. Mo. Agric. Exper. Sta. Bull, 370, 42–47.
4. Hammond, J. (1927) The Physiology of Reproduction in the Cow. Cambridge University Press, Cambridge, UK.
5. Larson, B.L. (1985) Lactation. The Iowa State University Press, Ames, IA, USA.