What’s Wrong With My Herd? Part 7: Mycotoxins and mastitis

Mastitis, a costly disease affecting the dairy industry worldwide, is a complex disease with many factors influencing its occurrence. Mycotoxins can increase the risk of mastitis and negatively impact milk production and milk quality.

Mastitis is an inflammation of the mammary gland, typically caused by an intramammary infection. Bacteria are the most common cause of mastitis in dairy cows, but other microorganisms have been isolated from the milk of quarters with mastitis including yeast, fungi, mycoplasmas, algae, and viruses. Physical trauma or chemical irritation can also cause mastitis.
There are multiple ways to classify cases of mastitis. The first major classification is the source of the pathogen (Table 1). Major contagious pathogens include Staphylococcus aureus, Streptococcus agalactiae, and Mycoplasma spp. Common environmental pathogens include Escherichia coli and Klebsiella spp. as well as environmental Streptococci including S. uberis and S. dysgalactiae. A third group exists, ‘skin flora opportunists’, which consists of the coagulase negative Staphylococci (CNS) species that colonize healthy teat skin.
The second classification of clinical vs. subclinical mastitis deals with the presentation of the disease. Clinical cases result in visible abnormalities of the milk and/or quarter, and range from mild to severe. Subclinical infections do not cause overt changes in the milk or quarter. Both mastitis types cause increases in somatic cell count (SCC). An elevated SCC often signals subclinical mastitis.
A third classification is acute vs. chronic mastitis. This has to do with the timing and duration of the disease. Acute cases are characterized by their sudden onset, but are often quickly resolved. Chronic cases continue over a longer period of time.

Table 1. Contagious and environmental mastitis

Contagious mastitisEnvironmental mastitis
ReservoirInfected mammary glandsThe cow’s environment including bedding/stalls/soil, manure, water and feedstuffs
ExposureSpread from cow-tocow via milking equipment, milkers’ hands or towels, flies and other vectorsConstant exposure exacerbated by heat and humidity


Economic losses stem from reduced milk production and decreased milk quality. Farmers must discard milk from cows with clinical cases of mastitis and from cows undergoing antibiotic treatment (according to withdrawal periods). Treatment and veterinary costs rise, as do labor costs.


Some of the main consequences of mycotoxin contamination in dairy cows in relation to udder health and milk production are: 

  • Reduced milk yield and quality
  • Toxic contaminants in milk, especially Aflatoxin M1
  • Increased risk of intramammary infections and mastitis
  • Altered milk composition

Reduced milk yield results from several factors, including a decrease in feed intake or feed refusal associated with certain mycotoxin contamination of the feed. Additionally, mycotoxins can alter rumen function, reducing nutrient absorption and impairing metabolism, which ultimately leads to reduced availability of the precursors needed for milk synthesis.

Addressing predisposing factors

Proper milking parlour management and milking routines are essential to limiting the risk of mastitis in a herd. The milking system must be well maintained, ensuring that properly functioning, clean equipment is used to harvest milk.
Good hygiene is critical. Clean sand is considered the gold standard bedding material, as inorganic materials do not support the growth of pathogens. The environment also influences mammary health as increased temperature and humidity better support pathogen growth in the cow’s surroundings. Additionally, heat stress reduces the cow’s resistance to infection.
Cows in negative energy balance, especially transition cows, are more susceptible to infection. Diets must meet vitamin and mineral requirements to support proper immune function. Coordinating the delivery of fresh feed while cows are in the parlour will entice cows to eat once they return to the pen after milking. This provides time for the teat ends to close while the cows remain standing at the feed bunk and limits exposure to pathogens following milking. Finally, feed should be monitored for the presence of mycotoxins and an effective mycotoxincounteracting product should be incorporated into the feed.
Many factors influence the development of mastitis, making mastitis control and prevention a constant challenge for dairy producers striving to produce high quality milk for consumers.

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