Mastitis can be defined as ‘inflammation of the mammary gland’ and generally occurs as a result of bacterial invasion through the teat orifice and canal into the gland cistern.
Mastitis is a highly prevalent disease in dairy cattle, and one of the most important diseases affecting the world’s dairy industry.
Mastitis is a painful and debilitating condition which can lead to deterioration of animal welfare and may even result in the death of the animal.
Pathogens- the cause of mastitis
In most countries the major mastitis pathogens are Staphylococcus aureus, Streptococcus agalactiae, Streptococcus uberis and Escherichia coli. The word ‘major’ reflects their considerable impact on cow health, milk quality and productivity¹.
The main organisms associated with clinical mastitis in England and Wales are Strep. uberis and E. coli².
Minor bacterial pathogens are mostly associated with raised somatic cell counts or sub-clinical mastitis and may have a protective role in the udder against infection caused by major pathogens, Other organisms such as fungi and yeasts have also been identified as potential mastitis pathogens.
Source and spread
Mastitis can be subdivided into two categories, contagious and environmental, depending on the source of the infection. Understanding where mastitis causing bacteria come from (their source) and how they spread is relevant to define control strategies.
Contagious or Environmental
Contagious pathogens are found in the udder tissues and spread from cow-to-cow. Environmental pathogens originate from the cow’s surroundings such as bedding materials, manure and soil.
The primary source of contagious mastitis is an infected cow (or quarter) and transmission generally occurs from infected cow (or quarter) to uninfected cow (or quarter) during milking. Contagious pathogens adhere easily to the teat, colonise and invade the epithelium of the teat and mammary gland. Since the introduction of the ‘Five Point Plan’ (treating and recording all clinical cases, dipping teats in disinfectant after every milking, dry cow therapy, culling chronic cases and routine milking machine maintenance) in the 1960s great progress has been made in controlling contagious pathogens in the UK.
The primary source of environmental mastitis is the external environment (i.e. housing and bedding) in which a cow lives. Transfer of environmental bacteria occur either during milking, for example as a result of liner slip causing milk particles containing environmental pathogens being propelled against the teat end or in between milkings, when the cow is loafing or lying down. Environmental pathogens do not possess the same ability as contagious pathogens to adhere to and colonise the teat.
Pre-dipping and increasing hygiene in the environment will greatly reduce the number of environmental bacteria in the milk, and in doing so will also reduce the risk of environmental mastitis.
An extensive review of mastitis revealed that environmental pathogens predominate in the UK, but contagious pathogens remain an important issue in some herds².
Dry period or lactation
Mastitis pathogens can infect cows both during the dry period and when cows are lactating, and it is important to identify and recognise the source of these infections, as approaches to control, prevention and treatment of the pathogen's effects can differ according to whether the infection occurs when the cow is dry or in lactation.
Research has found the link between infection during the dry cow period and subsequent clinical mastitis and elevated somatic cell counts (SCC) in early lactation. Infection during the dry period is often inapparent until the cow develops mastitis or has raised somatic cell counts after calving. In some herds, over 60% of all clinical mastitis cases can be traced to bacterial infections that occur in the dry period³.
If more than 10% of cows calve in with a somatic cell count > 200,000 cells per ml or more than 1 in 12 cows have developed mastitis in the first 30 days of lactation, it is likely that infection is originating from the dry period.
An internal teat sealant such as OrbeSeal® reduces the risk of new infection entering the teat canal during the dry period, consistently preventing more than 1 in 3 cases of mastitis4.
The symptoms of mastitis will depend on the different presentations of disease.
In a case of clinical mastitis changes in the udder or milk can be felt or seen.
A per-acute/ acute clinical case is sudden by nature and associated with systemic symptoms (severely ill cow) such as fever, loss of appetite, dehydration and weakness. The affected quarter is red, swollen, feels hard and is painful. The milk produced is grossly abnormal and milk production is down.
A mild or sub-acute clinical case is the most common presentation of the disease, where symptoms generally tend to be mild inflammation in the udder and some changes in the milk such as flakes, clots or a watery appearance.
Chronic cases or recurring persistent cases have a long duration by nature. The infection may remain in a clinical phase indefinitely or may alternate between subclinical and occasional flare-ups of clinical phases.
A cow with subclinical mastitis doesn’t display any obvious clinical symptoms of disease or visible changes to her milk. However, inflammatory changes can be detected in her milk by laboratory tests such as somatic cell counts (SCCs) and the presence of micro-organisms (pathogens) in milk can usually be demonstrated by microbiological culture.
A subclinical cow, while appearing unaffected by the illness, may experience a reduction in yield potential due to the high SCC, and could represent a source of infection for other cows.
Treatment requirements will depend on the presentation of disease:
Strep. uberis and E. coli are the main mastitis bacteria causing clinical mastitis².
The high prevalence of Strep. uberis and E. coli indicate the need for broad spectrum therapy for initial mastitis treatment, combatting potentially fatal E. coli infections, whilst achieving good bacteriological cure rates against the other major pathogens in the herd.
Recurring persistent cases:
Nearly 90% of persistent mastitis cases are caused by Gram positive pathogens such as Staphs and Streps².
In the event first-line treatment fails, a follow-up treatment to target the most likely causes of persistent mastitis within the herd may be needed.
Mastitis remains one of the largest costs to the dairy industry and, along with fertility and lameness, represents the biggest cost to production in the majority of dairy herds in the UK.
Mastitis has an economic impact via:
Milk production losses/discarded milk
Veterinary and treatment costs
Reduced product quality/value
1. Zadoks RN, Fitzpatrick JL (2009), Changing trends in mastitis, Irish Vet. Journal 62, 59-70.
2. Bradley AJ, Leach KA, Breen JE, Green MJ (2007). Survey of the incidence and aetiology of mastitis on dairy farms in England and Wales, Vet Rec. 160, 253-258.
3. Green MJ, Green LE, Medley GF, Schukken YH, Bradley AJ (0202). Influence of dry period bacterial intramammary infection on clinical mastitis in dairy cows. J Dairy Sci. 85(10):2589-99.
4. Rabiee AR & Lean IJ (2013). The effect of internal teat sealant products (Teatseal and OrbeSeal) on intramammary infection, clinical mastitis, and somatic cellcounts in lactating dairy cows: A meta-analysis. J Dairy Sci; 96:1-17