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:
Peracute or gangrenous mastitis – This is characterised by severe depression, a fever which may progress quite quickly to a subnormal temperature, anorexia (hollow flanks), dehydration and a swollen mammary gland that is warm initially, progressing rapidly to a blue discolouration which feels cold (called black mastitis or blue bag). Milk from the affected gland may resemble serum (straw colour) or be blood-tinged and mixed with gas – accompanied by a foul odour. Affected animals quickly become incapable of standing and case fatality may reach 30% to 40% if animals are left untreated. If the animal survives the initial phase, the affected gland may rot away and fall out over a period of weeks. The bacterium most commonly associated with this syndrome is staphylococcus aureusm, although pasteurella multocida, pasteurella (mannheimia) haemolytica and E coli have also been reported.Acute mastitis – This syndrome is characterised by a warm, swollen, reddened, painful gland, with or without abnormal milk. The ewe may be detected as a lameness case due to the pain of the gland touching the leg as the ewe walks. Affected cases show depression, anorexia, fever and become unable to stand after a short period. The organisms listed under peracute mastitis above are also associated with acute mastitis. Chronic mastitis – This form of disease is often detected if sheep are examined at time of drafting for cull. Here, a previous case has gone unresolved and the udder has developed an internal lump caused by a fibrous nodule or abscess. The udder may also become shrunken and produce less milk with this syndrome. The pathogens most commonly associated with chronic mastitis include staphylococcus aureus and arcanobacterium pyogenes.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.
Lambing time: High standards of hygiene must be maintained when sheep are housed, as mastitis-causing agents thrive in dark, wet, warm bedding and when the ewe lies down, bacteria enter the teat easily as the gland is full of milk. Lambing pens should be maintained hygienically and lambing assistants should be very careful of hand hygiene when sampling udders for milk let-down after lambing or assisting suckling lambs that are slow to start. Good ewe nutrition and providing a clean lamb paddock are important factors in reducing the incidence of mastitis – avoiding prolonged periods in muddy or poached areas during the first six weeks of lactation. Animals should not be overcrowded. Lambs from mastitic ewes will often suck other ewes, spreading the pathogens around the flock. Isolating and treating affected ewes will help reduce the incidence of mastitis in a flock. Ewes should be fed in troughs rather than on the ground. Preventing respiratory disease in lambs may help to prevent mastitis, as pasteurella (mannheimia) hemolytica, a cause of pneumonia in young lambs, is a major cause of ewe mastitis. This can be effected through booster vaccination of ewes with pasteurella vaccine in late pregnancy and vaccination of the young lambs from three weeks old, with a booster four weeks later. Although the same organism is involved in pneumonic pasteurellosis in sheep, vaccination with these commercial pneumonia vaccines does not protect the vaccinated ewe against mastitis. Orf vaccination should be considered in flocks with a previous or recent history of infection.Weaning time: Proper management at weaning is important to ensure ewes’ milk production has declined adequately to reduce stress on the glands. After weaning, food and water should be restricted for one to two days to rapidly decrease milk production. Alternatively, some producers reduce water and all feed for the same period pre-weaning. The udders of ewes should be examined as soon as possible after weaning to facilitate decision-making on candidates for cull. Ewes with hard lumps in the udders should be culled as soon as possible after weaning, as they can potentially act as a source of infection to other ewes and in any event are poor producers of milk. 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.
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:
Peracute or gangrenous mastitis – This is characterised by severe depression, a fever which may progress quite quickly to a subnormal temperature, anorexia (hollow flanks), dehydration and a swollen mammary gland that is warm initially, progressing rapidly to a blue discolouration which feels cold (called black mastitis or blue bag). Milk from the affected gland may resemble serum (straw colour) or be blood-tinged and mixed with gas – accompanied by a foul odour. Affected animals quickly become incapable of standing and case fatality may reach 30% to 40% if animals are left untreated. If the animal survives the initial phase, the affected gland may rot away and fall out over a period of weeks. The bacterium most commonly associated with this syndrome is staphylococcus aureusm, although pasteurella multocida, pasteurella (mannheimia) haemolytica and E coli have also been reported.Acute mastitis – This syndrome is characterised by a warm, swollen, reddened, painful gland, with or without abnormal milk. The ewe may be detected as a lameness case due to the pain of the gland touching the leg as the ewe walks. Affected cases show depression, anorexia, fever and become unable to stand after a short period. The organisms listed under peracute mastitis above are also associated with acute mastitis. Chronic mastitis – This form of disease is often detected if sheep are examined at time of drafting for cull. Here, a previous case has gone unresolved and the udder has developed an internal lump caused by a fibrous nodule or abscess. The udder may also become shrunken and produce less milk with this syndrome. The pathogens most commonly associated with chronic mastitis include staphylococcus aureus and arcanobacterium pyogenes.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.
Lambing time: High standards of hygiene must be maintained when sheep are housed, as mastitis-causing agents thrive in dark, wet, warm bedding and when the ewe lies down, bacteria enter the teat easily as the gland is full of milk. Lambing pens should be maintained hygienically and lambing assistants should be very careful of hand hygiene when sampling udders for milk let-down after lambing or assisting suckling lambs that are slow to start. Good ewe nutrition and providing a clean lamb paddock are important factors in reducing the incidence of mastitis – avoiding prolonged periods in muddy or poached areas during the first six weeks of lactation. Animals should not be overcrowded. Lambs from mastitic ewes will often suck other ewes, spreading the pathogens around the flock. Isolating and treating affected ewes will help reduce the incidence of mastitis in a flock. Ewes should be fed in troughs rather than on the ground. Preventing respiratory disease in lambs may help to prevent mastitis, as pasteurella (mannheimia) hemolytica, a cause of pneumonia in young lambs, is a major cause of ewe mastitis. This can be effected through booster vaccination of ewes with pasteurella vaccine in late pregnancy and vaccination of the young lambs from three weeks old, with a booster four weeks later. Although the same organism is involved in pneumonic pasteurellosis in sheep, vaccination with these commercial pneumonia vaccines does not protect the vaccinated ewe against mastitis. Orf vaccination should be considered in flocks with a previous or recent history of infection.Weaning time: Proper management at weaning is important to ensure ewes’ milk production has declined adequately to reduce stress on the glands. After weaning, food and water should be restricted for one to two days to rapidly decrease milk production. Alternatively, some producers reduce water and all feed for the same period pre-weaning. The udders of ewes should be examined as soon as possible after weaning to facilitate decision-making on candidates for cull. Ewes with hard lumps in the udders should be culled as soon as possible after weaning, as they can potentially act as a source of infection to other ewes and in any event are poor producers of milk. 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.
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