Features
Focus on Sheep Mastitis
No sheep farmer needs to be reminded that mastitis causes heavy financial losses. Surveys show mastitis is the major reason for culling ewes (46%), well ahead of barrenness (37%). Added to this are the large number of ewes that die as a result of acute mastitis. And the damage doesn’t stop there. The costs of antibiotics, the labour associated with treatments and fostering, reduced lamb growth rates and increased lamb mortality ……the list goes on.
What is Mastitis?
Mastitis is an infection of the udder caused by micro-organisms, usually bacteria. They normally enter the udder via the teat canal and multiply rapidly in the milk. The udder becomes inflamed, hard and very painful. Abscesses form and irreparable damage is done to the tissues such that often the udder eventually sloughs off. Most cases occur in the first month of lactation when the udder is around peak milk yield. Acute cases are clearly seen at this time. Chronic mastitis occurs when the infection subsides leaving abscesses that form hard lumps in the udder and teat canal. Often these are not noticed until udders are inspected at weaning.
Subclinical mastitis, where there are no outward signs of disease, can affect 10-30% of ewes and causes a significant reduction in milk yield. This presentation is probably better appreciated in dairying flocks but may also explain some of the variation in lamb performance to weaning in commercial flocks.
We know quite a lot about the bacteria involved in cases of mastitis. Recent research has shown that approximately 80% of acute infections are due to either Mannheimia haemolytica or Staphyloccus aureus, the remaining 20% of cases involve environmental pathogens such as coliforms which are particularly prevalent in dirty and damp conditions. The main source of infection of M. haemolytica is the lambs’ mouth as it is only found on the teat when lambs are suckling.
Predisposing Factors and Minimising the Risks
Our knowledge of the factors which cause the micro-organisms to produce infection in the udder is sketchy. However, the incidence between flocks varies enormously and this gives us an insight into some of the predisposing factors. On this basis, the table below outlines the various factors and how you can try to reduce the incidence of mastitis.
PREDISPOSING FACTOR |
MINIMISING THE RISK |
PHYSICAL DAMAGE– lambs can cause physical trauma through vigorous suckling, head butting and teeth abrasions. Ewes rearing triplets or those not milking well, are particularly susceptible. ‘Shared’ suckling indoors or at very high stocking rates outdoors will also help to spread bacteria from ewe to ewe. |
ADEQUATE NUTRITION – ewes which are underfed either in late pregnancy or early lactation produce lower milk yields. Young or old ewes and those in poor body condition are most susceptible. Reduce stocking rates in lambing areas as lambs will be less likely to cross suckle and cause trauma. |
ENVIRONMENTAL –dirty lambing pens, cold, wind, wet weather, lush pastures or high fly populations are all implicated as potential factors. Research has also highlighted personal hygiene of those handling teats to check milk flow as a major factor. |
HYGIENE – dirty, wet bedding and dirty hands are major concerns. Cleanliness is essential for both pens and personnel. SHELTER / PROTECTION - from cold and wet. Udders and teats become chapped and sore and milk yields are reduced in bad weather. Provide shelter and avoid wet muddy conditions around feeders and in gateways. |
OTHER CONDITIONS– teat damage due to orf is commonly identified as a precursor. Dermatitis, will also increase the risk, particularly of S. aureus infection |
HEALTH PLAN – where orf is a known risk, discuss vaccination options with your Vet. Watch for early signs and isolate affected animals to reduce spread. Pay particular attention to new breeding stock. |
CONFORMATION - the shape and size of the udder may influence susceptibility. Long teats and deep udders, often associated with higher milk yields, tend to have larger diameter teat sphincters which may be easier for bacteria to penetrate |
SELECTION OF STOCK – where replacements are home-bred, select from ewes with good udder conformation and avoid those whose dams have been culled for mastitis. |
Detection and Treatment
Treatment is rarely totally successful, but early detection is the key to at least saving the ewe. Careful observation is essential. In the early stages of infection the affected ewe will be feeling unwell as her system tries to fight off the infection and the pain will often cause her to appear lame of stiff.
Consult your vet regarding treatments.
Most of the bacteria involved are highly susceptible (99%) to penicillin and ampicillin, 95% in the case of tetracycline. Supportive therapy in the form of IV fluids and anti-inflammatories can be used in acute cases. Dry ewe therapy may also be an option in problem flocks
Future Developments?
Any improvements in our ability to prevent mastitis are hampered by the very limited funds for research into the condition. Early indications from Australia, USA, Norway etc. are that breeding for resistance offers some potential. Vaccines are also being researched, in particular for dairy cows, which may offer a positive means of protection for ewes at some time in the future.
Footnote: this article first appeared in the Sheep Farmer magazine and is reproduced with their permission