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  • Author or Editor: Sheila J. Gross x
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Objective—To determine whether conditions representing activities that are typical in the recreational use of horses, including transport to and from show grounds, stall confinement in unfamiliar surroundings, and light exercise, are associated with increased incidence of gastric ulcers in horses.

Design—Randomized controlled study.

Animals—20 client-owned horses.

Procedure—Horses had no gastric ulcers as determined by endoscopic examination on study day –1. Ten control horses were maintained on-site with no changes in management variables. Ten horses were transported via trailer for 4 hours on day 0 to another site, placed in individual stalls, fed twice daily, and exercised twice daily for 3 days. On day 4, they were transported back to the original site via trailer for 4 hours. On day 5, endoscopic examinations were performed on all horses to assess gastric mucosa status.

Results—Horses that were transported and housed off-site had a significantly higher incidence of hyperkeratosis and reddening of the gastric mucosa than control horses. Two control horses and 7 transported horses developed gastric ulcers by day 5. Ulcer scores of transported horses increased significantly from day –1, whereas ulcer scores in control horses did not change significantly from day –1.

Conclusions and Clinical Relevance—Activities that are typical in recreational use of horses were ulcerogenic, and ulcers in the gastric squamous mucosa can develop under these conditions within 5 days. ( J Am Vet Med Assoc 2005;227:775–777)

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in Journal of the American Veterinary Medical Association


To assess parasite control and weight gain after administration of an ivermectin sustained-release bolus over 135 days to calves grazing in the midwestern United States.


Replicated pasture study.


56 Bos taurus calves.


Calves were matched for body weight and randomly allocated to remain untreated or to receive an ivermectin sustained-release bolus before turnout on day 0. Calves were grazed by treatment group on 8 pastures (4 replicates). Body weights and fecal egg counts were recorded on days −1 and 28, and then at 28-day intervals until day 168.


Parasitism was not clinically evident prior to or during the study. In treated calves, mean fecal egg counts were at or near 0 at all posttreatment evaluations. Although the mean egg count exceeded 20 ova/g only once in control calves, the cumulative egg output was > 42 million/calf. For the treated group, it was < 0.1% of this number. Mean total weight gain was 33.9 kg (74.6 lb) greater for ivermectin-treated calves than for untreated control calves (P < 0.02); a 34% increase.

Clinical Implications

Fecal trichostrongyle eggs from calves can accumulate over a grazing season to provide enormous potential for augmenting pasture infectivity. An ivermectin sustained-release bolus (administered to calves being placed on pasture) controls parasitism, limits pasture infectivity, and can substantially influence growth by limiting the impact of subclinical parasitism. (J Am Vet Med Assoc 1997;211:754–756)

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in Journal of the American Veterinary Medical Association



To determine the efficacy of ivermectin (IVM) and milbemycin oxime (MBO) against induced heartworm infection, where monthly treatment is started 3 or 4 months after infection, and to monitor microfilaremia and antigenemia.


21 heartworm-naive Beagles.


Each of 21 dogs was given 50 infective larvae of Dirofilaria immitis by SC inoculation. One group of 5 dogs served as nonmedicated controls, 2 groups of 5 dogs received IVM at 6 μg/kg of body weight or MBO at 500 μg/kg for 12 months beginning at postinfection (PI) month 4, and 2 groups of 3 dogs received IVM or MBO for 13 months beginning at PI month 3. Blood collected at intervals not >1 month beginning at PI month 4 was examined for microfilariae and antigen. Dogs were euthanatized at PI month 16.


Adult worm counts, relative to controls, were reduced in the 4-month treatment groups by 95.1 (P < 0.01) and 41.4% for IVM and MBO, respectively. The difference between the IVM and MBO groups was significant (P < 0.01). Live worms were found in all MBO-treated (range, 8 to 27) and control dogs (range, 12 to 39) and in 3 of 5 IVM-treated dogs (range, 2 to 4). In the 3-month treatment groups, worm counts were reduced by 97.7 (P < 0.01) and 96.8% (P < 0.01) for IVM and MBO, respectively. Microfilariae were seen in all control dogs and in only 2 of the 16 treated dogs. The antigen response of MBO-treated dogs in the 4-month treatment group was only slightly weaker than that for control dogs. In all other treated dogs, this response was delayed and weaker.


Ivermectin is highly (≥ 95%) and significantly more effective than MBO against induced heartworm infection when 1 year of monthly prophylactic dosing is started 4 months after infection.

Clinical Relevance

In some cases of owner compliance failure, monthly administration of IVM gives a high level of protection against young adult heartworms. (Am J Vet Res1996;57:1189-1192)

Free access
in American Journal of Veterinary Research