Gangrenous mastitis by Staphilococcus aureus is the most common cause of mammary disorders in sheep meat flocks in Spain. It is usually related to wounds made by lambs sucking strongly. Furthermore, the high infectivity of the process makes it very dangerous when one case appears in a farm.
In this paper it is described an outbreak of acute mastitis as a result of bite wounds in the udder in a pre-partum meat sheep flock is described.
The outbreak occurred on a Rasa Aragonesa sheep farm located in Huesca in northern Spain and caused the loss of 31 animals. The problem commenced when 390 pregnant ewes were segregated from the flock and divided into two groups to improve management of parturition. Although the flock was managed in an extensive system, the pregnant ewes were located indoors pre-partum. Assistance was requested by the farmer when he recognised that some of the ewes in one group showed gangrenous mastitis (Figure 1).
Clinical examination of the animals concluded that more than 40 animals had wounds of the teat, with 5 ewes developing gangrenous mastitis. In the following days seventeen more animals developed mastitis. The affected sheep were treated with penicillin G procaine (12.000 UI) and dihidroestreptomicine (12mg/kg) and all the ewes in the group received a dose of long-acting oxytetracycline (20mg/kg) to manage the outbreak. Twenty two animals died or were culled with gangrenous mastitis. After several days, no new cases of mastitis occurred on the farm, although a few additional animals presented with wounds involving the right teat (Figure 2).
Examination of the other group of pregnant ewes failed to detect additional mammary lesions. Further, we determined that the wounds in the teat of the affected animals were recent and occasionally presented with fresh haemorrhage. We concluded that the mastitis problem was a secondary complication of trauma to the teat. The nature of the teat injury suggested that the wounds had been caused by an animal that had incisors in the mandible but not in the maxilla. It was considered most likely that a sheep bite had caused the problem. Following this finding, the affected group was divided into subgroups in order to identify the 'biting' animal. However at that point no new cases were found until one month later when 9 lambing ewes were affected with gangrenous mastitis secondary to injured teats, occurring amongst the same batch of ewes that were previously affected. A detailed examination of the affected group was conducted and the culprit identified (Figure 3).
It is considered likely that new cases were not observed for several weeks during the lambing period because the animal which had caused the problem was distracted by the birth of its own lamb. The outbreak may have returned because of the death of the lamb. This case could be considered as an abnormal sheep behavior or as a pathology related to intensification. Although sometimes young sheep still suckle from their mothers and even caused them mastitis, this case report has been described because of its seriousness.