List of sources:
Cape of Good Hope. Civil service list, 1896.
Cape of Good Hope. Report of the Colonial Veterinary Surgeon, 1896, 1897.
Henning, M.W. Animal diseases in South Africa. Central News Agency, 1932.
Henning, O. Bacillus tuberculosis. Report of the Colonial Veterinary Surgeon (Cape of Good Hope), 1895, p. 49.
National Automated Archival Information Retrieval System (NAAIRS). http://www.national.archives.gov.za/naairs.htm Documents relating to Henning, Otto/Henning, O.
Obituary: Otto Henning. Journal of the South African Veterinary Medical Association, 1934, Vol. 5, pp. 69-71.
Posthumus, P.J. Past veterinarians in South Africa (10th edition), Vol. 2, [1992].
Register of veterinarians of the Union of South Africa and South-West Africa. Journal of the South African Veterinary Medical Association, 1929, Vol. 1(3), pp. 77-83.
South African bibliography to the year 1925. London: Mansell, 1979.