1. Anon (1969 )-Report No. 19 of the Breeding and Production Organization, Milk Marketing Board of England and Wales. Thames Ditton, Surrey, U.K.
2. D. C. Blood (1974 )-Proc. Sixth Annual Convention American Association of Bovine Practitionerspp.162 -70 .
3. D. C. Blood, H. G. Rees, and R. S. Morris (1969 )-Vict. vet. Proc., 1969 , p.54 .