Most sheep farmers have encountered mastitis on a sporadic basis in their flock. However, occasionally the disease manifests in outbreak form, while in other flocks it arises on a frequent or on-and-off basis in individual sheep. In this article, we will examine the factors that can contribute to an elevated incidence of mastitis, the clinical syndromes, how to treat it and, most importantly, how to avoid and control it.
As mastitis involves inflammation of the mammary gland, it can be caused by physical injury, but more commonly by bacteria which invade the mammary gland.
The bacteria most frequently involved are pasteurella (including mannheimia) species, streptococcus spp, staphylococcus spp and coliforms such as E coli. Many of these organisms are normal residents of the mouth and teats of a sheep and as such are spread readily by suckling lambs. This is one of the reasons why mastitis is more common in ewes during the period shortly after lambing until post-weaning.
Factors influencing incidence
Ewes are more susceptible to mastitis if they have some damage to their teats, such as shearing cuts, over-suckling by lambs where milk production is poor or from viral infections such as orf. Mastitis is also more common in ewes raising multiple lambs or breeds that produce a lot of milk.
Many of these factors are controlled by genetics, which as a result is recognised as a risk factor. Different issues can influence mastitis incidence in sheep suckling lambs to those producing milk for human consumption as management and milking practices become an important part of the equation in the latter.
Some farms experience few cases of mastitis – the most common cause of introduction of infection into a flock is thought to be the purchase of chronically infected ewes. Transmission of infection may occur by cross-sucking in lambs, by the hands of stock-people during handling of the udder or from a contaminated environment.
Ewes in wet, dirty or crowded conditions also show higher incidence – thought to be due to exposure to high concentrations of the bacteria that initiate mastitis.
The causal agents of mastitis in sheep include staphylococcus aureus, streptococcus spp, coliforms including E coli and pasteurella (mannheimia) haemolytica. While research is lacking regarding strain typing of the bacteria that cause mastitis in sheep, a lot of the culprits also cause mastitis in cows and as a result co-grazing with cows could potentially be a risk factor for increasing mastitis in sheep.
Clinical signs
Three clinical syndromes are recognised in ewe mastitis as follows:
Finally, there is a subclinical form of mastitis that may be difficult to identify. The udder may be firm and hot and lambs of affected ewes may have poor growth rates, with occasional deaths of twin lambs.
The swollen glands are often without other signs and may be detected by an astute stockperson when gathering sheep. This form of mastitis will progress to more severe disease if left untreated. Poor weather or inadequate nutrition may trigger the progression from sub-clinical to clinical mastitis.
Treatment
Ewes with mastitis should be segregated from the rest of the flock and treated with antibiotics. It may be necessary to manually feed their lambs.
If multiple cases of mastitis arise, it is important that the causal bacteria are determined in order to choose the best treatment options. Milk samples must be carefully taken to avoid contamination and submitted fresh or frozen to the local regional veterinary laboratory.
Advice on sampling technique and the most appropriate initial drugs to use should be sought from your local veterinary practitioner.
Some cases of mastitis can be treated with intra-mammary lactating cow antibiotics. Unfortunately, none are licensed for use in ewes so, at the very least, standard meat and milk withdrawal periods apply.
Where clinical signs are severe, antibiotics may also be administered by injection and it is important that the drugs selected are effective. Again, advice should be sought on drug choice from your local veterinary practitioner.
Treatment should be continued for several days. Non-steroidal anti-inflammatory drugs with pain-relieving action may also be prescribed and are thought to improve the clinical success in some cases.
Control
Mastitis can be controlled with good management, especially at two stages – after lambing and at weaning.
In summary, attention to detail and addressing all possible risk factors can significantly reduce the risk of disease in flocks affected with high morbidity. Your local veterinary practitioner can advise you best in this regard.