Use of oxibendazole for control of cambendazole-resistant small strongyles in a band of ponies: a six-year study

Oxibendazole (OBZ; 10 mg/kg of body weight) was administered to ponies at 8-week intervals to control strongylosis in a breeding band of Shetland-type ponies (n = 29 to 50) from October 1978 through September 1984. A similar use of cambendazole (CBZ; 20 mg/kg of body weight) in this band of ponies during the preceding 4-year period resulted in the survival of a CBZ-resistant population (S) of small strongyles. Effectiveness of OBZ treatments was monitored by pre- and posttreatment counts of the number of strongyle eggs per gram of feces (epg) and of the number of strongyle larvae per gram of feces (lpg). For the first 4 years of the 6-year period, epg and lpg counts were determined for 3 to 5 of the OBZ treatments; during the last 2 years, counts were determined for each treatment. For the 1st year, the mean reduction in epg was 96%. During the 2nd and 3rd years, mean reductions in epg were 80% and 81%, respectively. For the 4th and 5th years, mean reductions in epg were 69% and 43%, respectively. For the 6th year, the mean reduction in epg was 37%. Statistical analyses of the epg data, using the linear plateau method, indicated a significant increase in residual (surviving) strongyle infections after the periodic OBZ treatments, with a mean annual increase in survival of 10.3% for the 6 years. Changes in lpg were variable, but an overall loss of effectiveness of the OBZ treatments was evident. Only infective larvae of small strongyles were observed in the cultures; larvae of 2 species of large strongyles, Strongylus vulgaris and Strongylus edentatus, were conspicuously absent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Determination of the efficacy of pyrantel pamoate at the therapeutic dose rate against the tapeworm Anoplocephala perfoliata in equids using a modification of the critical test method

A total of 59 equids (54 horses and five Shetland ponies) were treated with pyrantel pamoate once, at the dose rate of approximately 6.6 mg base kg-1, during the period November 1985-January 1988. The drug was administered as a paste formulation (51 equids) intraorally or as a suspension formulation by stomach tube (eight equids). The purpose of treatment was to evaluate the activity of pyrantel pamoate (at the therapeutic dose rate) for removal of the tapeworm, Anoplocephala perfoliata, by a modified (24-h) critical test. The presence or absence of tapeworms was not determined for the equids before treatment. Twenty-three (39%) of the 59 treated equids were found to be infected with A. perfoliata (from one to 180 specimens per infected equid) at necropsy. Removals varied from 67 to 100% (average 88%) for the 18 infected equids treated with the paste formulation. For the five infected equids treated with the suspension, removals were 58-100% (average 75%). The combined average removal of A. perfoliata for both formulations was 87%. Two abnormal (triradiate) specimens of A. perfoliata were recovered; one from each of two different equids.     

Meckel's diverticulum in the horse

Meckel's diverticulum is a remnant of the vitellointestinal duct. It is through this duct that nutrients pass from the yolk sac into the midgut of the four-week-old embryo. In a review of 15,000 postmortem records at the University of Kentucky, Meckel's diverticulum was observed in five horses examined postmortem. In each case, the diverticulum was a factor in the animal's death. In light of these statistics, Meckel's diverticulum may not be as frequent a finding in the horse as has been previously considered.     

Segmental axonopathy of Merino sheep in New Zealand

AIM: To investigate an axonopathy of Merino sheep that caused progressive hindlimb ataxia and slight to moderate paresis, with the purpose of understanding its pathogenesis.

METHODS: Tissues were fixed in buffered paraformaldehyde or paraformaldehyde and glutaraldehyde, processed into wax and epoxy resin, respectively, and examined by light and electron microscopy. Fresh frozen spinal cord and trigeminal nerve roots were subjected to homogenisation, centrifugation and two-dimensional electrophoresis. Selected protein spots were identified using matrix-assisted laser desorption ionisation (MALDI) mass spectrometry.

RESULTS. By light microscopy, there were large pale foamy spheroidal axonal swellings affecting peripheral as well as central axons. By electron microscopy, these were shown to contain many membrane-bound vesicles. The main abnormalities in expressed proteins involved cytoskeletal elements and myosin heavy chain, the latter interpreted as associated with the molecular motor myosin Va.

CONCLUSIONS: The disorder is the same as that described in Merinos in Australia as segmental axonopathy, and believed to have an inherited aetiology. The lesions and protein changes indicate abnormalities of the cytoskeleton, its relationship with the myelin sheath, and myosin Va molecular motor. The consequence appears to be abnormal axonal transport and inability to maintain the integrity of axons and their myelin sheaths.     

Impact of a catastrophic hurricane on island populations

Lizard and spider populations were censused immediately before and after Hurricane Lili on islands differentially affected by the storm surge. The results support three general propositions. First, the larger organisms, lizards, are more resistant to the immediate impact of moderate disturbance, whereas the more prolific spiders recover faster. Second, extinction risk is related to population size when disturbance is moderate but not when it is catastrophic. Third, after catastrophic disturbance, the recovery rate among different types of organisms is related to dispersal ability. The absence of the poorer dispersers, lizards, from many suitable islands is probably the result of long-lasting effects of catastrophes.