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Mycotoxins and Poor Performance:

February 22, 2022

Mycotoxins and Poor Performance:

About this time of year, farmers may notice several behavioural issues with their stock, along with declines in performance. This can occur with both cows in milk and with replacement heifers. Typical symptoms are grouping together, mainly where shade is available, instead of spreading out across the paddock and around water troughs. Peeling of the skin can occur in severe cases. Such behaviour and symptoms are often attributed to biting flies or facial eczema but are more likely to be associated with ryegrass toxicity.

Perennial ryegrass toxicity results from endotoxins produced by an endophyte (Neotyphodium lolii) present in many older ryegrass pastures. The most common and recognisable symptom is ryegrass staggers, but more commonly results in subclinical loss of productivity and the behavioural traits described above.

Another feature is an increase in temperamental cows, that kick off cups during milking. Most farmers and vets say they don’t see actual grass staggers, but are more likely to have observed these behaviour traits. The loss of production arises primarily due to heat stress, leading to lower feed intakes. Cattle can normally accommodate temperatures over 30°C, but become uncomfortable at temperatures below 25°C when high toxin levels. The reason for this loss of tolerance is constriction of blood vessels, which limits blood flow near the skin, thus reduces cooling ability. The temperamental traits arise because ergovaline also increases neurotransmission, resulting in increased udder sensitivity. Local observations have indicated declines in milk production of affected cows of 5-10%. Increased somatic cell counts in milk, infertility and immune function, and lower milk fat and protein levels, have been reported by overseas research.

Youngstock tend to be more vulnerable than mature animals. Ergot alkaloids including ergovaline restrict the production of prolactin in animals, which is a precursor for milk production, and important in reproduction and puberty development in young animals. One way to assess the risk of ryegrass toxicity is to test pasture levels, as levels higher than 0.8 mg/kg DM for ergovaline and 2 mg/kg DM for lolitrem B are considered a potential risk (Oregon State University). Urine analysis can provide an alternative diagnostic tool for assessing the challenge from ergot alkaloids, as they are metabolised relatively quickly and excreted via the urine.

The most common response to exposure to endophytes is to limit access to the pasture or graze less harmful endophyte pastures, e.g. AR1 and AR37. However, there is an increasing trend toward using mycotoxin binders, as these can adsorb the mycotoxins, reducing their absorption from the gastrointestinal tract.

Australian trials have demonstrated that mycotoxin binders can reduce heat stress in sheep and significantly increase growth and reproduction on pastures containing sub-clinical levels of ergovaline and lolitrom-B.

Some dairy farmers and veterinarians in New Zealand have also reported rapid alleviation and suppression of the affects of ryegrass endophyte toxins, e.g. temperamental behaviour, staggers and heat stress.

Responses to mycotoxin binders usually occur quickly within 24 hours, as they physically bind to the mycotoxins.

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