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Actinobacillus seminis as a cause of abortion in an Australian sheep flock

Bruce Watt (Central Tablelands Local Land Service, Bathurst) and Helen Peam (State Veterinary Diagnostic Laboratory, Menangle)

Posted Flock & Herd March 2010


Actinobacillus seminis is a well known cause of epididymitis in Australian rams (Baynes and Simmons, 1960) and has also been reported as associated with metritis, polyarthritis (Higgins et al. 1981), posthitis and mastitis (Watt et al. 1970). There is a single report of A. seminis causing abortions in the UK (Foster et al. 1999).

Case history

The owner of a mob of 150 mixed age first cross ewes reported that 2-3 weeks prior to lambing (due to start mid September 2013), seven ewes aborted or produced stillborn premature lambs. The ewes were running in a pasture paddock in the Orange district of NSW and were supplemented with a mix of grain oats and manufactured sheep pellets.

Necropsy findings

A single, near term lamb with a crown rump length of 40cm was necropsied. The foetus was moderately autolysed with pulmonary atelectasis and blood stained subcutaneous oedema.

Image of post-mortem on sheep foetus
Figure 1. Foetus showing blood stained subcutaneous oedema
Image of post-mortem on sheep foetus
Figure 2. Abdominal and thoracic contents of the foetus

Laboratory Findings

Stomach contents and liver from the foetus were each cultured on sheep blood agar and incubated at 37° C in 5% CO2. A sparse predominant growth of gram-negative rods was obtained from the liver, and as part of a moderate mixed growth from abomasal contents. The bacterial isolate was catalase positive and oxidase negative. The isolate was further investigated by API32E (biochemical testing) which didn't result in a confirmed identification. Based on clinical history, colony morphology and a sparse biochemical profile Actinobacillus seminis was suspected. The isolate was PCR positive for A. seminis. These findings unequivocally demonstrate that the bacterium genealogically corresponded to A. seminis.


Actinobacillus seminis is a pleomorphic, gram-negative bacillus that is a well-known cause of epididymitis in Australian rams (Baynes and Simmons, 1960), and has been documented in the United States of America, South Africa, New Zealand, Hungary, Patagonia, the United Kingdom, Turkey, Kidney, and Spain. (Al-Katib and Dennis, 2009). A. seminis has also been reported in association with metritis, polyarthritis (Higgins et al., 1981), posthitis and mastitis (Watt et al. 1970). There are rare reports of A. seminis causing abortions in the UK (Foster et al. 1999), and South Africa (Van Tonder, 1973). The organism has been recovered from placenta and uterus of ewes after natural and experimental infections (Al-Katib and Dennis, 2009).

Subclinical cases have been known to persist for up to 4 years. This makes prevention and management of A. seminis a challenge. Al-Katib and Dennis (2009) recommended continual surveillance against the introduction of infected rams into a clean flock and identifying and removing infected animals. If A. seminis is suspected, testing by serology or by culture and PCR of semen or reproductive tissues can be used to confirm a diagnosis.

In the Australian context, epididymitis is the most important manifestation of A. seminis infection but this appears to be a sporadic problem which only sometimes causes significant wastage in some ram breeding flocks. Evers (1978) cautioned against a test and cull program based on A. seminis testing but advised culling on breeding soundness alone. While some Australian flocks may have attempted to eradicate A. seminis the authors are not aware of this. However, some seed stock producers who house rams have attempted to control A. seminis using shed hygiene (Mark Carter pers comm.) and some practitioners treat affected cases with broad spectrum antibiotics (McCann, 2010).

While the problem of stillborn lambs resolved, an examination of the ram flock may have also been useful. Unfortunately this was not practical in this case.


  1. Al-Katib and Dennis (2009) Ovine genital actinobacillosis: A review New Zealand Veterinary Journal 57(6):352-358
  2. Baynes and Simmons (1960) Ovine epididymitis caused by Actinobacillus seminis. Australian Veterinary Journal 36:545-459
  3. Evers JV (1978) Actinobacillus seminis infection in rams. Proceedings of the 61st Annual District Veterinarian's Conference, pp 49-53 www.flockandherd.net.au
  4. Foster G, Collins MD, Lawson PA, Buxton D, Murray FJ and Sime A (1999) Actinobacillus seminis as a cause of abortions in a UK sheep flock The Veterinary Record 144:479-480
  5. Higgins R, Godbout DE, Laselle F, Messier S, Couture Y and Lamothe P (1981) Isolation of Histophilus ovis from vaginal discharge in ewes in Canada Canadian Veterinary Journal 22:395-396
  6. McCann G (2010) Ram semen culture results, Proceedings of the 92nd Annual District Veterinarian's conference www.flockandherd.net.au
  7. Van Tonder EM (1973) Infection of rams with Actinobacillus seminis. Journal of the South African Veterinary Association 44(3):235
  8. Watt DA, Bamford V and Nairn ME (1970) Actinobacillus seminis as a cause of polyarthritis and posthitis in sheep Australian Veterinary Journal 46:515


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