It is about this time of year that farmers may notice a number of behavioural issues with their stock, along with declines in performance. Typical symptoms are grouping together particularly under shade, rather than being spread out across a paddock and around water troughs. Skin can peel 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. A severe symptom is ryegrass staggers, but loss of productivity and the behavioural traits described above, are more common and indicative of lower exposure levels.
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 largely as a result of heat stress, leading to lower feed intakes. Cattle can normally accommodate temperatures in excess of 30oC, but become uncomfortable at temperatures below 25oC when toxin levels are high, due to constriction of blood vessels, limiting blood flow near the skin reducing cooling ability.
The temperamental traits also arise because ergovaline 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 reduced immune function.
Youngstock tend to be more vulnerable than mature animals. Ergot alkaloids including ergovaline restrict production of prolactin in animals, a precursor for milk production, and important in reproduction and puberty development in young animals.
The most common response to exposure to endophytes is to limit access to the pasture, or grazing less harmful endophyte pastures. However, there is an increasing trend to use of mycotoxin binders, as these can adsorb the mycotoxins so reducing their absorption from the gastrointestinal tract.
Trials here and overseas have demonstrated that mycotoxin binders can reduce heat stress in sheep and cattle, 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 effects of ryegrass endophyte toxins, e.g. temperamental behaviour, staggers and heat stress.
Responses to mycotoxin binders occur very quickly usually with 24 hours, as they physically bind to the mycotoxins.
As featured in NZ Dairy Farmer
