Managing Endophyte Toxins in Perennial Ryegrass and Tall Fescue
The endophyte is a microscopic fungus that lives in plants (particularly significant in perennial ryegrass and tall fescue), and shares a natural, symbiotic relationship where it protects the host plant from environmental stressors such as drought, insects, nematodes and disease pathogens. Since it does not affect the appearance of the grass plant, its presence can be detected only by laboratory analysis.
Ergovaline and Lolitrom-B are two of the major toxins produced by the grass endophyte Neotyphodium spp. These toxins include neurotoxins and ergot alkaloids, some of which are closely related to LSD. The basic chemical structure of ergot alkaloids is very similar to dopamine, noradrenaline and serotonin. These three compounds are neurotransmitters, normally found in the body, that regulate a myriad of physiological traits such as appetite, cardiovascular function, endocrine activity, gastrointestinal motility, muscle contraction and temperature regulation.
Toxin production is closely related to environmental conditions but generally ergovaline levels increase during the hotter summer months, particularly when the pasture goes to seed and after later summer rains. The toxins are concentrated in the seed head, stem and crown of the plant. Lolitrom-B is not present in tall fescue, but more so in perennial ryegrass. This will differ from country to country.
The effects of these toxins will vary depending on the presences and concentrations but clinical signs can be very obvious. Apart from staggers, other common signs of ‘perennial ryegrass endophyte toxicoses’ (PRGT) or ‘endophyte ill-thrift’ include heat stress, temperament, ill-thrift and stiffness of gait. These can impact on most animals in the flock/herd, not just those with staggers. Ergovaline is an ergot alkaloid and as such can affect thermoregulation (causing heat stress), cardio-vascular function and hormone production (e.g. prolactin), reduced milk production and milk solids, reduced intake, scouring and temperament changes. Research is also suggesting that increased somatic cell counts in milk, infertility and immune dysfunction may also be affected.
Research in New Zealand has shown that sheep exposed to ergovaline showed signs of heat stress at temperatures around 23 degrees Celsius, whereas sheep not exposed did not show any signs of heat stress until temperatures rose to around 40 degrees Celsius. Subclinical levels of ergovaline can also be responsible for temperament changes in animals and show up as nervousness and psychotic behaviour as well as udder sensitisation.
Lolitrom-B is not present in tall fescue but is present in perennial ryegrass and is responsible for causing staggers (ryegrass staggers) in cattle, sheep and alpacas. Lolitrom-B is a neurotoxin and will affect the nervous system (ataxia and brain function) causing the ‘staggers’, and muscle control, including the smooth muscle of the digestive tract.
Tall fescue toxicosis has been present in the USA since the 1940’s after being introduced from Europe in the 1800’s. It is present across the eastern half of the US and is estimated that 90% of the pasture is infected with the fungal endophyte Neotyphodium coenophialum. In the US, the annual stock/production losses due to endophyte toxins are estimated at >$600M.
Although the presence of Neotyphodium spp. endophytes has been recognised in Japan and South Korea for the past 20 years, toxicoses problems have only been cause by imported hay and straw from the USA, Australia or New Zealand. The Japanese Black Cattle (Wagyu) are very sensitive to endophyte toxins.
In South America, the endopyte infection of pasture is fairly common and is mainly limited to Southern Brazil, Uruguay, Argentina and Chile. Research has shown that between 11-19% of samples were potentially toxic. Occurrences of toxicoses tend to occur in the older pastures and also tend to be related to tall fescue rather than perennial ryegrass.
Perennial ryegrass is the most predominate pasture used in the southern part of Australia and endophyte frequency in the older pastures average 90%. Australia usually experiences extreme cases of toxicoses every 5 years associated with hot dry summers which results in animal deaths, although the sub-clinical signs of perennial ryegrass toxicoses can be evident in most years. Unlike many other countries, the endophyte present can produce high levels of both ergovaline and Lolitrom-B. In Australia, the annual cost of endophyte toxins in the meat industry for stock/production losses is estimated at >$72M.
In New Zealand perennial ryegrass is the most productive and intensively grazed pasture and contains the endophyte Neotyphodium lolii. Although ryegrass staggers can be evident in late summer, sub clinical signs of ryegrass toxicoses can be evident from early summer when the plant goes to seed. Production losses of up to 9% in milk production are estimated for animals grazing endophyte infected pastures in New Zealand.
Some of the earliest descriptions of grass endophytes were made in Europe. However, when the connection between toxicoses and the ingestion of endophyte infected grasses were made in the USA and New Zealand, fescue and perennial ryegrass toxicoses were still unknown in Europe. In the current pastures, the newer cultivars of tall fescue and perennial ryegrass are infected by the endophyte, but in the permanent pastures and natural ecosystems the perennial ryegrass and tall fescue are commonly infected by Neotyphodium endophytes.
The endophyte association in pastures has been observed from the Mediterranean to Scandinavian countries and that the associations may be higher in drier climates.
Although high endophyte alkaloid levels are often recorded in European grasses, there have not been any distinctive cases of ryegrass staggers or fescue toxicoses reported in ruminants, except in France, however suspicious cases have been reported. Very often the sub-clinical symptoms experienced by animals are misdiagnosed with a magnesium deficiency or behavioural changes associated with hot weather.
FUSION is a new generation mycotoxin binder which may aid in reducing the direct effects of perennial rye grass toxicity. FUSION is a combination of both inorganic and organic binders which together may have a high affinity to bind the ergot alkaloids, with greater than 95% binding capacity in vitro. Commercial field results on dairy farms in Australia and New Zealand demonstrate a decrease in symptoms associated with PRGT within 24-48 hours after treatment.