By Dr Grant van Lelyvled
Technical and Marketing Manager for Ruminants, HIPRA Southern Africa
Contact details: e-mail firstname.lastname@example.org and telephone number (012) 348 1506
Mastitis causative agents, diagnostics and treatments
2.1 Microorganism and epidemiology
The mastitis causative agents include various viruses, yeasts and bacteria that are grouped as: environmental, contagious and secondary pathogens. There are some pathogens that possess the characteristic of all three categories depending on the situation.
Contagious organisms are well adapted to survive and replicate in the mammary gland, due to the evasive methods to limit the effects of the immune system or antibiotics. Causing chronic/reoccurring infections in a cow and/or herd. The prevalence of an IMI increases with the length in days in milk (occurrence throughout a lactation). There is a high infection risk (often exponential) and the transmission of the organism is mainly during milking and direct contact with infected cows. Biosecurity (quarantine, hygiene, etc.) helps to reduce or avoid the entry/consequences of these pathogens in the herd. Early detection and treatment (antibiotics and effective teat dips) can reduce cases.
The environmental organisms are mainly in the bedding (moist, contaminated with manure, etc.) and cause infection in the periods between milkings (animals resting in the contaminated environment). These organisms have a short rapid replication period due to the poor tropism for the alveolar cells in the mammary gland. Consequently causing short severe clinical cases.
- Pathogens with mixed aetiology
These pathogens can have contagious and environmental characteristics at the same time.
Detection and diagnosis of mastitis (clinical and subclinical) can be achieved by using simple daily routines [stripping and California Milk Cell Test (CMCT)] to the more expensive and specialist tests (bacteriology and PCR). To understand a farm’s situation a specific protocol should be developed, to allow for the necessary data to be collected and in turn result in the appropriate action to be taken. With the regular monitoring of parameters it will be easier to reduce, control and prevent mastitis.
The best approach is to record numbers and severity of cases, chronicity or duration of cases, treatments, etc. in the herd (the form referred to as a sanitary index).
Detection of clinical mastitis is based on 3 parameters. The methods of detection are subjective, but are practical and cheap tools in the management of udder health. The three parameters are: Milk appearance (colour and consistency changes), Udder condition (oedema, discolouration, uniformity, etc.) and Cow Habitus (depressed, anorexia, etc.). Depending on how many of the parameters are affected determines the grade of severity of the mastitis case.
In the case of subclinical mastitis, one does not have the physical parameters to monitor and one needs to use different tools to detect the chemical and physical changes in the milk.
2.2.1. Californian Mastitis Test (CMT) or California Milk Cell Test (CMCT)
The CMCT is a subjective test used to indicate elevated SCC in the milk and allows one to estimate the degree per quarter (Table. 3). The reagent interacts with the White blood cells in the milk, and this is observed as a change in viscosity (observed while swirling the panel). The degree of change is used to grade the likelihood of mastitis. Every animal should be tested at the beginning and end of each lactation, with regular intervals in between e.g. every 15 days if not monthly individual SCC is done). The test is done by firstly stripping the teats of residual milk (eliminating false positives), secondly allocating a set volume from each quarter to the respective well and finally an equal volume of reagent. This is agitated with a swirling motion. (Figure2.)
Manual elimination of milk from the teat cistern in order to prepare the udder (stimulation) and detect milk abnormalities (floccules, discolouration, etc.). This first jet of milk often contains a higher concentration of bacteria and elevated levels of Somatic cells, meaning it should not be used in the ISCC or bacteriology for diagnosis as the results will be skewed. Teat stripping is a good step to be incorporated in the pre-milking routine, because it is cheap and easy. Ideally this should be done before the application of pre-teat dips and care should be taken to prevent contamination of the milker’s hand, equipment and subsequent teats or udders that the milker comes into contact with. Stripping a teat should be done with a disinfected gloved hand to limit transmission of commensals or contagious bacteria.
2.2.3. Electric conductivity
Certain milking machines are adapted to collect a sample and measure the ions present in the milk (potential to conduct an electric current) due to the difference in salt concentration between infected and non-infected quarters. The problem with this tool is it is expensive and can result in false readings due to the sensitivity varying (constant calibration and maintenance) and other contributing factors (stress, heat, etc.).
- BTSCC (Bulk-Tank Somatic Cell Count)
An economic parameter used to determine the quality and value (penalties or bonuses) of milk. BTSCC does not indicate individual cow problems, but can be used in conjunction with other data to identify possible underlying problems (heat stress, machine calibration errors, etc.). The sample is to be taken from each bulk tank on the farm after a cooling period and a sufficient agitation (+/- 5min) period.
- ISCC (Individual Somatic Cell Count)
A great monitoring tool that should be done regularly. ISCC is an indicator of how the cow is reacting to an infection or stimuli. The ISCC can be used in the sanitary index to classify an animal as suffering from Mastitis (healthy cows have an SCC under 200,000 cells/ml). Cows with an ISCC above this threshold without clinical symptoms are considered infected and cows with an ISCC above this threshold and showing clinical signs have clinical mastitis. In heifers the threshold is 100,000 cells/ml instead of 200,000 cells/ml as threshold. Variations in ISCC can be the result of other factors (age, season, size of the herd, stage of lactation, etc.). The ISCC can be a composite sample of all four quarters or a sample per individual quarter depending on the data needed.
- Diagnostic methods
Diagnosis is the identification of the causative agent (bacteriology or PCR in conjunction with other supporting data from the farm). The rest of the methods detect mastitis, but do not give a real diagnosis. Bacteriology identifies pathogens from the infected udder or from contaminated milk. The sensitivity and specificity (accuracy) of bacteriology is variable (growth medium and conditions, effects of antibiotic treatment and time span for the growth of certain bacteria, yeasts, etc.). The identification of the pathogen is not always serotyped or species specific (similar characteristics based on the physical and chemical properties of the Colony forming units (CFU). PCR is often more accurate due to typing of the organism.
2.2.5. Culture from bulk-tank
The bacteria isolated from the bulk tank can help identify possible problems and aid in determining the necessary corrective measures to be taken. One looks at the CFU and ranks the number of CFU/ml to determine the severity of infection or contamination. (Table 4.) The Bulk tank CFU/ml is an economic parameter, influencing the price obtained for milk and it is important for food safety. High levels of CFU/ml can result in the milk being declared unfit for human consumption and disposed of. These parameters are maintained by milk processing plants e.g. Clover, etc.
2.2.6. Individual culture
Culturing is an ideal tool to identify the predominant organisms present in the udder. The samples can consist of a composite or individual quarter milk samples. This can be used to establish a treatment protocol (drying off, inactivation a quarter, intra mammary treatment, retesting, and vaccination with STARTVAC®). Often cows with elevated SCCs have individual cow/quarter milk samples cultured. These results are often skewed by the incorrect sample collection, which result in overgrowths of an organism or contamination. Making the results useless. It is important to maintain a high standard of hygiene during the collection of the samples (disinfected gloved hands, alcohol swabs disinfecting the teat ends after cleaning the teat of all organic matter, correct handling of tubes (not to be placed in the mouth) and correct storage). (Figure 4.)
Real time Polymerase chain reaction (RT-PCR) is a new diagnostic tool. The method involves collecting a milk sample (bulk tank, mastitis group and individual cows) on an FTA card. The FTA card breaks down the bacterial cells to eliminate overgrowth or contamination. The RNA or DNA can be preserved for long periods. PCR eliminates some short falls associated with bacteriology (no growth, long incubation periods, identification of serotypes and storage and transport of samples). PCR speeds up the diagnostic process and has an almost 100% sensitivity and 100% specificity. The results obtained are can semi-quantitative. STARTCHECK is such a tool to identify the common pathogens involved in mastitis: S. aureus, CNS, E. coli and Coliform.
The importance with treating a mastitis case is to have the correct standard operating procedures. This will aid you to treat the correct cow (preventing over treatment, selecting the appropriate diagnostic or monitoring tool) and use the correct treatment (appropriate antibiotic, supportive treatment, isolation and culling). (Figure 6.)
The failure of treatment is due to host factors e.g. changes in parenchymal tissue (abscesses, inflammatory, etc.), drug factors (bioavailability and pharmacokinetic), environmental factors (stress, poor nutrition, poor milking routines, etc.), bacterial factors (biofilms, antibiotic resistance) and human factors (management and prevention methods e.g. vaccination, etc.).
The selection of antibiotics is very important and should maximise the curing rate of a cow’s IMI. The antibiotic should be selected using an anti-biogram. (Table 5.) The efficacy of the drug is influenced by the ability (bioavailability and pharmacokinetics) of the drug to reach (ion trapping, lipid solubility, inflammatory effect on the blood udder barrier) and maintain an effective minimum inhibitory concentration at the site of the infection. Additional supportive treatments for severe cases – oxytocin injections to aid in the milking out, intra-mammary infusion of dextrose, supportive vitamins and i/v fluids. Each type of mastitis should be handled differently (Figure 6.).
Teat canal infections generally self-cure, but can be treated with small amounts of antibiotics 3 times at 12 hourly intervals. Subclinical mastitis is normally treated at dry off but if treated during lactation intra mammary antibiotics are given 3 times at 12 hourly intervals. Sub-acute clinical mastitis is normally treated 4 times at 12 hourly intervals, with the occasional used of NSAIDs and parenteral antibiotics. Acute clinical mastitis is normally treated with intra-mammary antibiotics for five days and often treated with parenteral antibiotics. Per acute clinical mastitis needs to be treated aggressively and often supportive treatment for shock and salvaging methods used to save the udder (cannulas, teat amputation, or inactivation of the quarter). Chronic mastitis is treated with both intra-mammary antibiotics and parenteral antibiotics, NSAIDs and intra-mammary infusions of glucose (100 to 200 ml of 5% or 10% dextrose solution 3 time at 12 hourly intervals).
Ideally one should use a narrow spectrum antibiotic to limit resistance, side effects and maximise curing. The common trend is to use a broad spectrum antibiotic, due to ease and the lack of completing a full diagnosis. Depending on the results and number of treatments the cow could be dried off (inactivate a quarter) or culled (chronic cases not responding to treatment, etc.). Also a good thing to do would be contact a consultant like Inge-Marie Petzer.
- Hulsen, J., Lam, T. and Schukken, Y.H. 2013. Large her edition, Udder Health, A practical guide to first-rate udder health. Pages 5, 32, 50, 51 and 60.
- Calvo González-Valerio, M.T. 2014 Mastipedia. Chapter two. Laboratorios HIPRA, S.A. Avda la Selva, 135 170170 Amer (Girona), Spain.
- du Preez, J.H. (2000) Bovine mastitis therapy and why it fails Jl S.Afr.vet.Ass. Volume 71. Pages 201–208. Viewed on the 24/01/2015 <http://www.jsava.co.za/index.php/jsava/article/viewFile/714/688>