Mastitis, defined as inflammation of the udder, has a multifactorial aetiology. Mastitis is one of the most significant health problems in dairy herds. Mastitis has important effects on both milk quality and animal welfare.
Mastitis impacts on milk quality in terms of increased somatic cell count and can reduce protein and fat levels.
The EU-wide upper legal limit for somatic cell counts in milk destined for liquid market is 400,000 cells/ml. Milk with a consistently higher (>3months geometric mean) cell count will not be sold by the milk purchasing dairy.
There are four main clinical presentations of mastitis recognised: acute toxic mastitis, mild/moderate clinical mastitis, sub-clinical mastitis and summer mastitis.
Consistently high SCC levels in a herd are usually a sign of high levels of subclinical mastitis. Most cases of subclinical mastitis are caused by contagious mastitis bacteria such as Staphylococcus aureus and to a lesser extent Streptococcus agalactiae, withStreptococcus uberis increasingly considered to cause chronic mastitis as well.
- Causes of Mastitis >
- Effects of Mastitis >
- Diagnosis of Mastitis >
- Treatment & Control of Mastitis >
Causes of Mastitis
Mastitis risk factors or disease determinants can be classified into three groups: pathogen, host and environmental determinants.
Mastitis pathogens
Whilst over 100 different micro-organisms have been identified as causative agents of mastitis, only a few species of staphylococci, streptococci and Gram-negative organisms are of economic or epidemiological significance.
Increased emphasis on somatic cell count reduction and targeting certain contagious micro-organisms (i.e. Streptococcus agalactiae) may have changed the relative importance of the principal mastitis pathogens in the national herd.
Low SCC herds may be more susceptible to environmental mastitis caused by Escherichia coli, which are becoming more important, whilst Str. agalactiae is rapidly disappearing. This phenomenon is coupled with apparent changes in the virulence of some pathogens (Str. uberis) and with the emergence of previously non-pathogenic or minor pathogens (coagulase-negative staphylococci) as mastitis causing pathogens.
There is also increasing evidence that bacteria that until recently have been considered non-pathogenic or opportunistic udder pathogens are becoming more common as primary mastitis pathogens. These bacteria include Corynebacterium bovis and coagulase negative staphylococci.
Major mastitis pathogens are classified as being either environmental or contagious.
Contagious mastitis pathogens
The contagious pathogens usually have a mechanism to adhere to the epithelial cells of the udder or to become intracellular, in order to protect themselves from the intramammary defence mechanisms. Staphylococcus aureus, Streptococcus agalactiae and Streptococcus dysgalactiae belong to this group of pathogens.
Some Staph. aureus strains also have the ability to remain intra-cellular and avoid both host natural defences and antimicrobials and may additionally produce beta-lactamase which inactivates penicillin.
Arcanobacterium pyogenes is an opportunistic, contagious mastitis pathogen. Mastitis caused by these microbes is often chronic and causes elevated SCC levels. These pathogens are primarily spread within the herd from cow to cow, with the biggest risk period being during milking, where bacteria can adhere to milking equipment or the milker’s hands.
Environmental mastitis pathogens
Environmental mastitis bacteria include a large number of both Gram-positive and Gram-negative species. Str. uberis, Str, equinus, Enterococcus faecalis and Enterococcus faecium of the Gram-positive species and Escherichia coli, Klebsiella spp., Enterobacter spp., Serratia spp. and Pseudomonas spp. of the Gram-negative are the most common environmental pathogens of the bovine udder.
Str. uberis and E. coli, however represent by far the largest proportion of the identified intramammary infections caused by environmental pathogens.
The significance of Str. uberis and E. coli has grown in the past 15 years as Str. agalactiae and S. aureus have been controlled successfully in many herds. It has also been suggested by various surveys that these pathogens, particularly E. coli, have become more significant in herds with low somatic cell counts.
Whilst it has been recognised that teat injuries, wet bedding and contamination with faecal material are important risk factors for E.coli mastitis, it has also been suggested that improvements in hygiene are not reducing E. coli mastitis incidence, as cows are becoming more susceptible to the disease. One of the reasons for the increased susceptibility is likely to be the increased milk flow capacity in cows, leading to milk leaking
Opportunistic udder pathogens
Opinions on the significance of Corynebacterium bovis as an udder pathogen vary greatly in the literature. Some workers suggest that, whilst intramammary infections with C. bovis cause increased SCC in affected quarters, the presence of this minor pathogen provides protection against major pathogens. Others, however, find no protective effect with some work suggesting an increased risk of infection with Str uberis or a coliform in a quarter infected with Corynebacterium spp or coagulase negative staphylococci at drying off.
In many countries with intensive dairy production, coagulase negative staphylococci (CNS) have been identified as emerging mastitis pathogens, suggesting that increasing numbers of bacteria considered non-pathogenic, until recently, are capable of causing clinical intramammary infections.
Generally, it is accepted that the mastitis caused by these organisms is mild or subclinical. It has been suggested that the susceptibility of dairy cows to mastitis caused by CNS is a reflection of lowered resistance in the cow’s udder.
Effects of Mastitis
The effects of mastitis depend on the type occurring (see below)
Diagnosis of Mastitis
Acute toxic mastitis
This type of mastitis is often seen in cows in the period soon after calving and may be more frequent in cows with lower somatic cell counts. It is primarily caused by gram negative, endotoxin producing bacteria, such as E. coli, although in some cases Staphylococcus aureus can be the pathogen. This type of mastitis is very severe and will kill cows unless they are treated promptly.
The signs are primarily due to the endotoxin produced by the bacteria, causing the cow to develop endotoxic shock.
The cow will present as acutely sick, dull, and may be recumbent. They may have a high temperature or conversely may have a sub-normal temperature if in shock. The udder may show a variety of changes including swelling, heat, pain and the milk may look watery and discoloured though often not with ‘clots’.
Mild/moderate clinical mastitis
This type of mastitis is what is commonly recognised as a clinical case. The cow is often noticed at milking time to have a swollen udder, affecting one or more quarters, with visible changes in the milk.
There may be clots in the milk which can be more watery than normal. Often the cow is not systemically ill and appears bright and eating normally. She may have a slightly raised temperature and may show some signs of discomfort when walking due to a distended udder. A number of bacteria, mycoplasmas, yeasts and fungi can cause clinical mastitis.
Subclinical mastitis
This type of mastitis does not cause obvious visible changes to the milk, but there may be some chronic inflammatory changes to the udder detected as hardness or ‘knotty’ tissue on palpation of the affected quarter(s). If tested with a California Mastitis Test (CMT) there will be a reaction due to the increased somatic cell count of milk produced by cows with chronic subclinical mastitis.
Californian Mastitis Test (CMT)
This is a kit that will help the milker evaluate somatic cell counts in milk from different udder quarters immediately.
It will help the herdsman to recognise affected quarters when the obvious symptoms are mild or he can only see a "clot in the filter".
It is easy and quick to use, reliable and relatively cheap for what it does.
The reagent must not be allowed to freeze and needs to be warmed up in hot water if it is very cold. Several pathogens are associated with this type of mastitis, especially Staphylococcus aureus and Streptococcus uberis. This type of mastitis is important as cows can be a reservoir of infection for the rest of the herd, with pathogens spread during milking.
Additionally, the milk may have changes in the amounts of milk solids (protein and fat) present as well as a high cell count which, if present in a high proportion of cows in the herd may affect the bulk tank milk composition sufficiently to affect the price paid.
Lastly, and importantly, these cases may flare-up periodically and cause clinical disease with associated painful symptoms for the cow.
Summer mastitis
Classically, this type of mastitis is seen in dry cows in the late summer period and is associated with a spread of infectious mastitis-causing organisms by flies or by teat damage to dry cows. It can occur also in maiden heifers.
This type of mastitis is mainly due to a combined effect of several bacteria. Arcanobacterium pyogenes is the primary organism, but the severity of clinical signs depends also on the other, often anaerobic bacteria present which can include Peptococcus indolicus, Bacteroides melaninogenicus and Fusobacterium necrophorum and their production of endotoxin.
The clinical signs vary and in the early stages may not be seen as cows are not as easily observed when dry as when they are going through a milking parlour. However, the infection will spread rapidly and can cause severe swelling of the udder with a foul-smelling discharge or secretion from the affected quarter(s).
The cow may become very dull and depressed, especially if there is production of endotoxin and may develop a very high temperature. Severely affected cows may abort.
Treatment & Control of Mastitis
Host determinants
Many factors influence the incidence of mastitis, which will only be named here:
- Genetic resistance
- SCC
- Cow and udder conformation
- Milk yield
- Nutritional status
- Age of host
- Stage of lactation and dry cow treatments
- Other diseases (particurarly ketosis, milk fever, lameness and post-puerperal endometritis/metritis are closely associated with mastitis incidence)
Several management practices can minimise mastitis occurrence:
- Vaccination
- Milking hygiene
- Disinfection of teats before and/or after milking
- Treatment of teat injuries
- Udder cleanliness
- Stockmanship
Milking machine and milking technique
Milking machine faults and poor milking techniques are probably among the main environmental risk factors for mastitis, alongside housing hygiene.
Unstable or excessive vacuum, faulty pulsation, liner slippage for various reasons and teat cup hygiene contribute to mastitis risk by either damaging the patency of the teat canal or by causing pathogenic organisms to enter the teat canal during milking.
Following milking the teat canal remains open for up to 45 minutes after milking. A recommended husbandry practice is to prevent the cows from lying down until the teat canal has closed, to prevent bacterial penetration. One of the easiest ways to do this is to provide access to feed and water for the cows after milking.
The Five Point Plan For Control of Mastitis in Dairy Herds
- Routine post-milking teat dipping.
- Prompt treatment of clinical mastitis with antibiotics.
- Blanket antibiotic dry cow therapy for the whole herd.
- Culling of cows with chronic mastitis.
- Milking machine maintenance with annual testing.
Treatment of toxic mastitis
Cows with toxic mastitis are often in, or at risk of endotoxic shock. Therefore treatment should include administration of supportive therapies. The cow may require administration of fluids, and the use of hypertonic saline intra-venously can be very effective in increasing the circulating blood volume, although it is imperative that the cow either drinks water herself or is given water (30- 50 litres depending on size of cow) by stomach tube following use of hypertonic saline.
Additionally, the use of non-steroidal anti-inflammatories (flunixin meglumine) can relieve pain help reduce the pyrexia if present and can help combat the endotoxins.
Administration of antimicrobials is also advised as the cow’s immune system will be severely compromised at this time. Above all, cows should receive plenty of nursing, including frequent turning if recumbent and frequent stripping out of the affected quarter(s) to help remove the altered milk which will contain endotoxin.
Antibiotic therapy
Antibiotic therapy should be encouraged in the treatment of mastitis caused by Streptococcus agalactiae as this pathogen is zoonotic and is easily eradicated from a herd. When this pathogen is identified in an organic herd an eradication plan should be implemented.
All licenced antibiotic preparations for mastitis treatment require milk withdrawal periods.
Alternative therapies
A multitude of mastitis therapies have been used before and after the advent of antibiotic therapy. These include the use of frequent stripping, herbal udder ointments and liniments, massage, phytotherapy, diet changes, clay therapy and homeopathy.
The use of oxytocin combined with frequent stripping is a more "modern" alternative therapy. Most alternative therapies are aimed at helping the cow’s own defence mechanisms to clear the infection rather than attacking the pathogen directly as is the case with antibiotics.
Mastitis therapy and pain relief
An important aspect of mastitis therapy is the alleviation of inflammation in the udder. Swelling and subsequent pain associated with clinical mastitis can cause considerable discomfort to the cow.
Antibiotic preparations offer no immediate relief from pain.
Whilst the inclusion of steroid anti-inflammatory components in intramammary preparations has very little effect on the inflammation, systemic use of non-steroidal anti-inflammatory agents, can have a beneficial effect on the inflammatory process in acute mastitis.
Prevention and treatment of mastitis in dry cows
Routine DCT of all cows, independent of their udder health status, has been criticized for potentially contributing to the development of antimicrobial resistance on farms.
Using an internal teat sealant can provide protection against new infections in the dry period but it is important to emphasise that this will not specifically ‘treat’ existing infections.
Selection of cows for use of ITS is therefore important, as only those cows with no current infection at drying off should be considered. It is recommended that cows with a cell count of consistently <200,000 cells per ml at drying off and no previous cases of clinical mastitis should be selected.
However, these criteria are difficult to meet in the field and a modification of the selection criteria, based on the knowledge of the individual farm can be utilised.
This info was adapted from Defra’s Compendium of Animal Health & Welfare in Organic Farming, which is a collaborative effort led by Duchy College, Cornwall with VEERU at The University of Reading and The Faculty of Veterinary Medicine, University of Glasgow.
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