Cytotoxic activity of extracts from Hypochaeris radicata.

Pasture-associated stringhalt is an acquired equine disease characterized by peripheral neuropathy and hyperflexion of the pelvic limbs. The disease occurs most commonly during periods of drought in horses grazing pastures heavily contaminated by Hypochaeris radicata. We hypothesized that stringhalt is caused by neurotoxins elaborated by H. radicata in response to the stress of drought conditions. Supernates were collected from H. radicata that were stressed (or not) by immersion in copper chloride solution, then extracted with ethyl acetate and dried. Dilutions of extracts from stressed (SE) and control, unstressed (UE) plants were incubated with myelinating spinal cord cultures (MSCC) established from fetal Swiss mice, and with spinal ganglion cultures (SGC) and dermal fibroblast cultures derived from neonatal mouse tissues. Cytotoxicity in culture monolayers was evaluated both morphologically by microscopy and by release of lactate dehydrogenase activity into culture supernates. Three different SGC preparations were exposed to a single H. radicata extract and single preparations of fibroblasts and MSCC were exposed to three different extracts. Repin, a plant-derived sesquiterpene lactone neurotoxin, was included as a positive control. Significant dose-dependent cytotoxicity was seen within 24 h in all three culture types when incubated with SE or repin. Complete morphologic destruction of culture monolayers was induced by the highest concentrations tested of SE (100 µg/mL) and repin (30 µg/mL). Cytotoxic effect of SE was significantly greater than that of UE for all three cell types and was not due to copper contamination of the extract. This study has identified a cytotoxic activity in leaf exudates of H. radicata that was upregulated by the model stressor, copper chloride.

Focal premature physeal closure (hyena disease) in calves.

Focal premature closure of long-bone physes was the cause of conformational abnormalities that affected about 1% of a herd of dairy replacement calves. Affected calves were noticed to "bunny hop" by 3 months of age, and by 6 months of age, they developed abnormal conformation characterized by short pelvic limbs. This condition resembled "hyena disease," which has been described in dairy calves in Europe and Japan. With the exception of the aforementioned abnormalities and femoropatellar joint distention, a group of 5 affected calves examined were clinically normal. At necropsy, focal to almost complete closure of physes was found in the humeri, tibias, and femurs. Cause was not established for the condition; however, it was discovered that the calves had been given supplemental vitamin A/D3 in amounts greater than 10 times those recommended.

Effects of large doses of phenylbutazone administration to horses.

The effects of large doses of phenylbutazone were evaluated in clinically normal horses. The drug was given to 4 groups of 2 horses each at the rate of 30 mg/kg of body weight, orally, or 30, 15, or 8 mg/kg IV daily for up to 2 weeks. All horses became anorectic and depressed after 2 to 4 phenylbutazone treatments, and the horses given 15 or 30 mg/kg died on or between days 4 and 7 of treatment. A decrease in total blood neutrophil count occurred in all horses, and was associated with toxic left shift in horses given the 2 larger dosage schedules. The horses also had progressive increases in serum urea nitrogen, creatinine, and phosphorus concentrations, accompanied by decreasing serum calcium concentrations. There was a progressive decrease in total serum protein in all 8 horses. Gastrointestinal ulcerations, renal papillary necrosis, and vascular thromboses were the predominant postmortem findings.