Weather and pasture characteristics associated with outbreaks of perennial ryegrass toxicosis in southern Australia

Abstract

Severe outbreaks of toxicosis caused by the natural endophyte Neotyphodium lolii in perennial ryegrass (Lolium perenne L.) have occasionally resulted in heavy loss of livestock in Victoria and Tasmania. Meteorological records were examined from locations where acute toxicosis was recorded. High rainfall (>350 mm) in spring–summer was an obvious common feature; typically, it prolonged the period of high growth rate of pasture, increasing predicted spring–summer (September–March) growth (by ~36%) and increasing the predicted digestibility of organic matter of summer pasture (1 February) by 2.7% units (up to 55.6%). In years when severe toxicosis occurred, such rainfall was accompanied by dry, warm conditions in March and April, viz. mean maximum daily temperatures on the mainland of ≥21°C (March) and ≥18°C (April). During summer–autumn 2002, pastures from 10 Victorian farms on which acute perennial ryegrass toxicosis resulted in the loss of >7000 sheep/deer, were found to be dominated by perennial ryegrass. The ryegrass endophyte-produced toxins, ergovaline and lolitrem B, were detected in 74% and 100%, respectively, of composite faecal samples collected from acutely affected animals. The populations of perennial ryegrass all tested positive for Neotyphodium lolii endophyte, with a mean infection frequency of 90.5% (s.e.m. 1.81). The mean mycelial mass in basal tillers of perennial ryegrass was estimated at 66.00 (s.e.m. 3.40) from a sample of 20 plants, each of which was assessed on a scale of 1–5. Mycelial mass accounted for 19–20% of the variation in the concentration of ergovaline and lolitrem B in perennial ryegrass. Toxin concentrations in the plants where acute toxicosis was observed exceeded the tolerance levels for sheep (ergovaline 0.8 mg/kg; lolitrem B 1.8 mg/kg) in the minor (green) fraction of the plant in all but one affected pasture for ergovaline and all but two for lolitrem B. Maximum concentrations recorded were 4.3 and 4.6 mg/kg for ergovaline and lolitrem B respectively. Ergovaline increased in an asymptotic relationship with lolitrem B, which accounted for 45% of the variation in ergovaline. The concentrations of ergovaline and lolitrem B in the whole plant (green and dead fractions combined) were not greater than those recorded from randomly sampled pastures in earlier seasons, when only occasional mild cases of toxicosis were reported. Further examination of stored grass samples collected during the 2002 outbreak recently revealed unidentified peaks on the chromatograms for both ergovaline and lolitrem B; peaks that are not seen on chromatograms for toxic perennial ryegrass from New Zealand, where the expression of perennial ryegrass toxicosis is usually milder and rarely fatal.

Evidence of dehydration and electrolyte disturbances in cases of perennial ryegrass toxicosis in Australian sheep

“…5 Our clinical findings suggest that physiological stress caused by dehydration, altered gastrointestinal function and reduced mobility because of PRGT, exacerbated by environmental factors, will significantly reduce an affected animal's ability to maintain electrolyte homeostasis. 5 Our clinical findings suggest that physiological stress caused by dehydration, altered gastrointestinal function and reduced mobility because of PRGT, exacerbated by environmental factors, will significantly reduce an affected animal's ability to maintain electrolyte homeostasis.…”

“…31,32 In the kidneys and colon, BK channels play a role in excretion of potassium, particularly when levels are elevated. 5,9 Ergovaline may also play an important contributory role in exacerbating the dehydration in PRGT, as it has been shown to cause heat stress in a number of species, including ruminants. 5,9 Ergovaline may also play an important contributory role in exacerbating the dehydration in PRGT, as it has been shown to cause heat stress in a number of species, including ruminants.…”

“…3 Clinical signs range in severity from mild gait abnormalities and failure to thrive, to severe seizures, lateral recumbency and death. 4,5 A particular feature of PRGT in Australia is the occasional occurrence of large-scale sheep losses, suggesting other factors are influencing mortality rates compared with other PRGT risk zones such as North America and New Zealand. Clinical presentation is usually highly variable, with season, breed, sex, age and production status all affecting the severity of clinical signs in the flock or herd.…”

“…Clinical presentation is usually highly variable, with season, breed, sex, age and production status all affecting the severity of clinical signs in the flock or herd. 4,5 A particular feature of PRGT in Australia is the occasional occurrence of large-scale sheep losses, suggesting other factors are influencing mortality rates compared with other PRGT risk zones such as North America and New Zealand.…”

Physiological effects of endophyte-infected perennial ryegrass straw on female camels in the Middle East

“…(Reed et al, 2011;diMenna et al, 2012;Johnstone et al, 2011) The diagnostic criterion for this condition is determined by evaluation of the gait of an animal (Galey et al, 1991). Affected cattle, sheep, horses and alpacas exhibit an onset of muscle tremors, stiffness of gait during walking, base wide stance and gait progressing to clinical signs of ataxia or incoordination.…”