1. Recherches sur les Fonctions du Corps Jaune Gestatif;Ancel;J. Phys. Path. Gén.,1911
2. Ashton, J. (1930). The influence of geographical conditions on cattle development. Res. Dull. Mo. Agric. Exp. Sta. no. 141.
3. Bisschop, J. H. R. (1938). The relation between environment and animal breeding with special reference to the breeding of cattle in the semi-arid regions of South Africa, 13th Int. Vet. Congr., Zurich, p. 3.
4. Bonsma, J. C. (1940). The influence of climatological factors on cattle. Bull. Dep. Agric. S. Afr. no. 223.
5. Bonsma, J. C. (1943). Influence of colour and coat cover on adaptability of cattle. Fmg in S. Afr. Feb. reprint no. 2.