Mechanisms underlying Phalaris aquatica "sudden death" syndrome in sheep

Twenty outbreaks of Phalaris aquatica "sudden death" syndrome in sheep were investigated between 1981 and 1991. Four were confirmed and one was suspected, to be a cardiac disorder; 5 were confirmed and 3 were suspected, to be a polioencephalomalacic disorder; the aetiology of the remaining 7 outbreaks could not be determined. Potentially toxic levels of hydrocyanic acid (20 to 36 mg/100 g) were measured in the 3 toxic phalaris pastures tested. The measurement of potentially toxic levels of nitrate nitrogen (2920 micrograms/g) in toxic phalaris pastures by others, was noted. It is suggested that phalaris "sudden death" syndrome could have as many as 4 different underlying mechanisms, and that these might reflect the presence in the plant of a cardio-respiratory toxin, a thiaminase and amine co-substate, cyanogenic compounds, and nitrate compounds.     

A novel nigrostriatal dopaminergic disorder in sheep affected by Tribulus terrestris staggers

An investigation was carried out into the pathogenesis of a unique locomotory disorder of sheep. Thirty sheep which had exhibited clinical signs for more than 15 months were examined for the presence of muscle atrophy, limb paresis, and spontaneous rotational behaviour. A single large dose of levodopa was administered to 12 normal and 12 affected sheep, and the drug-related effects of sedation and excitation were monitored continuously for three hours. The striatum was removed from eight normal and eight affected sheep and assayed for dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC). The findings of asymmetrical atrophy of pelvic limb extensor muscles, asymmetrical paresis of the limbs, a left:right dominance ratio of 50:50, spontaneous rotational behaviour, decreased response to levodopa loading, and decreased levels of DA (19 per cent reduction) and DOPAC (30 per cent reduction) in the striatum of affected sheep, were interpreted as indicative of a primary nigrostriatal dopaminergic disorder. It is suggested that a striatal presynaptic receptor malfunction has occurred.     

The pathogenesis of the nervous syndrome of Phalaris aquatica toxicity in sheep

The clinical signs displayed by 96 sheep affected by the nervous syndrome of Phalaris aquatica toxicity and 10 normal sheep injected intravenously with the phalaris alkaloid, 5-methoxy dimethyltryptamine (dose range 0.01 to 5.0 mg/kg), were observed. The distributions of phalaris indole-like cytoplasmic pigments in nuclei of the brains and spinal cords of 9 naturally affected sheep were determined microscopically. Based on the relationship between clinical signs and the central nervous system nuclei involved in their production, the distribution of phalaris indole-like pigments, and the pharmacology of dimethylated tryptamines, it is suggested that the nervous syndrome induced by Phalaris aquatica results from a direct action of phalaris alkaloids upon serotonergic receptors in specific brain and spinal cord nuclei.     

Experimental evidence that tryptamine alkaloids do not cause Phalaris aquatica sudden death syndrome in sheep

The acute toxicity for sheep of 3 alkaloids that occur in Phalaris acquatica was examined by intravenous and oral administration. The lowest tested dose rates that produced clinically observed signs were, for 5-methoxy dimethyltryptamine, 0.1 mg/kg body weight intravenously and 40 mg/kg orally; for gramine, 10 mg/kg intravenously and 500 mg/kg orally; and for hordenine, 20 mg/kg intravenously and 800 mg/kg orally. All induced the clinical signs observed in the nervous form of phalaris toxicity, but none induced the cardiac, sudden death, syndrome.     

The occurrence of phalaris staggers in sheep

Extract

Typical cases of the “staggers” syndrome associated with Phalaris tuberosa poisoning occurred at Invermay Research Station in October, 1954. It is being recorded because detailed records of pasture management and climatic conditions are available for the period when symptoms were seen, also the pasture composition of the Phalaris plot.     

Decreased plasma testosterone concentrations and weight gain in young bulls affected by ryegrass staggers

Ryegrass staggers caused a significant depression of plasma testosterone concentrations in prepubertal bulls, and the most severely affected animals had a marked reduction in liveweight gain.     

Decreased plasma testosterone concentrations and weight gain in young bulls affected by ryegrass staggers

Ryegrass staggers caused a significant depression of plasma testosterone concentrations in prepubertal bulls, and the most severely affected animals had a marked reduction in liveweight gain.     

Enzootic calcinosis in sheep: clinical signs and pathology.

Enzootic calcinosis in Corriedale sheep was characterized by degeneration and mineralization of elastic connective tissue of aorta, arteries, lung, and kidney and by ulceration of cartilage of joints of limbs. Results of serum chemical analysis revealed low Ca X P value and significantly low, but inconsistent magnesium concentration and normal inorganic phosphorus content. The Ca:P ratio in bone was low in affected sheep. Clinicopathologically, calcinosis of sheep at Mattewara, India, appeared to be similar to the disease described as Enteque seco in South America, Naalehu disease in Hawaii, Manchester wasting disease in Jamaica, and calcinosis in central Europe, Israel, and South Africa. The disease might be due to complex mineral imbalance, although the possibility of a plant poisoning has not been ruled out.     

Phalaris arundinacea as a cause of deaths and incoordination in sheep

Extract

An ovariectomized female terrier dog had two episodes of lead poisoning, confirmed by a laboratory, in June 1966 and in March 1968. In July 1968, when she was 11 years old, she was presented showing periodic vomiting and loss of condition. She appeared to respond to therapy with calcium EDTA for lead poisoning although the laboratory findings did not support this diagnosis.     

Relationships between metabolic changes and clinical signs in pregnant sheep given endotoxin.

Groups of four pregnant ewes were allocated to the following feeding and intravenous endotoxin treatments: fed, Escherichia coli endotoxin (50 micrograms/kg X 75), fed, saline, fasted, E. coli endotoxin (50 micrograms/kg X 75) and fasted, saline. Endotoxin administration resulted in depression, fever, hypoglycemia, hypocalcemia and a reduction in nonesterified fatty acid and ketone body concentrations. Depression correlated best with body temperature (r = 0.76), fasted sheep showed smaller increases in body temperature and were less depressed following endotoxin. Three of eight endotoxin treated sheep died, mortality was not related to rectal temperature but was associated with lactic acidosis. Hypoglycemia was not associated with either death or depression. Fed sheep that were unable to stand had lower serum calcium concentrations than standing sheep.     

Amino acid neurotransmitter release from cerebrocortical synaptosomes of sheep with severe ryegrass staggers in New Zealand

Enhanced unstimulated release of the excitatory amino acid neurotransmitters aspartic acid and glutamic acid was measured in cerebrocortical synaptosomes prepared from sheep showing severe symptoms of ryegrass staggers. A similar pattern of deviation from neurologically normal animals was seen whether the sheep had contracted the disorder naturally or whether they had been deliberately caused to develop the disorder by grazing specific pastures rich in endophyte infected ryegrass. Deranged neurotransmitter release may reasonably be involved in the chemical pathology of ryegrass staggers and the findings are in accord with the putative synonymy of lolitrem toxicosis and ryegrass staggers.