Field studies (n=6) were completed on evaluation of activity of ivermectin (200 μg/kg) paste formulation against small strongyles in horses (foals, yearlings, and older animals) on a farm (Farm MC) in Central Kentucky in late 2006 and during 2007. A girth tape was used to estimate body weights which were then used to calculate the proper dose rate of ivermectin. The foals, yearlings, and some of the older horses were born and raised on the farm. However, most of the older horses which were not raised on the farm had been there for several years. The horse herd was given ivermectin exclusively, usually four times a year, since 1990. An exception was that during the foal's period of life fenbendazole, pyrantel pamoate, and oxibendazole were given occasionally besides ivermectin. Efficacy of drug activity was determined by pretreatment and posttreatment counts of strongyle eggs per gram of feces (EPGs). Culture of strongyle eggs in feces from some of the horses showed that only small strongyle larvae were present. The research included two studies (A and B) in foals (n=24) and four studies (C, D, E, and F) in yearlings (n=13) alone or with older horses (n=10). For each of the studies (B through F), there was a treated and a nontreated group. These groups were switched for each treatment, i.e., the treated group in one study was the nontreated group in the next study and vice versa. Eggs per gram of feces counts were determined at 1-or 2-week posttreatment intervals for 4 weeks for study A and 6 weeks for studies B through F. Also, for studies B, E, and F, counts of EPGs were done either two or three times during the third week posttreatment. The studies showed a similar posttreatment pattern of strongyle EPG counts beginning to return at about 4 weeks and increasing at 5 and 6 weeks posttreatment. Two horses in study E and one in study F had low EPG values toward the end of the third week posttreatment. The results of this ivermectin investigation showed that the strongyle EPG counts started returning about twice as quickly post-ivermectin-treatment of horses than when the drug was first marketed in the early 1980s.

Horse foals on five farms in Central Kentucky were used in field studies in 2007 evaluating activity of paste formulations of four compounds (fenbendazole-FBZ, ivermectin-IVM, oxibendazole-OBZ, and pyrantel pamoate-PRT) against internal parasites with emphasis on ascarids (Parascaris equorum). It has been well established the last few years that there is widespread resistance of P. equorum to ivermectin. The main purpose of the present research was to obtain current data on ascaridicidal activity of FBZ, OBZ, and PRT; also, to acquire further information on ascarid resistance to ivermectin. Additionally, data were documented on drug activity on small strongyles. Detection of ascarid and strongyle eggs in feces of foals was by a qualitative method (presence or absence) or a quantitative method (eggs per gram of feces). Strongyle eggs all were assumed to be from small strongyles. This is based on fecal cultures from horses on one farm and historic records from horses in this area on excellent deworming programs. A girth tape was used to estimate the body weight of each foal so that the appropriate dose rate of each drug could be given. Many of the foals were used in more than one cycle of treatments. Efficacy of the drugs, administered intraorally, was determined by calculating the average percentage reduction (% red.) of the number of foals passing eggs after vs. before treatment: (1) FBZ at 10 mg/kg was tested on four farms; 76 foals were examined, 50 with ascarid eggs (84% red.) and 62 with strongyle eggs (0% red.); (2) IVM at 200 microg/kg was tested on three farms; 58 foals were examined, 18 with ascarid eggs (0% red.) and 48 with strongyle eggs (100% red.); (3) OBZ at 10 mg/kg was tested on three farms; 181 foals were examined, 78 with ascarid eggs (94% red.) and 79 with strongyle eggs (0% red.); (4) PRT was tested on two farms, one farm at 1x (6.6 mg base/kg); 42 were foals examined, 16 with ascarid eggs (0% red.) and 33 with strongyle eggs (12% red.) and one farm at 2x (13.2 mg base/kg); 18 foals were examined, 13 with ascarid eggs (23% red.) and 15 with strongyle eggs (27% red.).

The objective of this article is to review knowledge on the hookworm Uncinaria lucasi Stiles, 1901 in northern fur seals, Callorhinus ursinus Linnaeus, 1758. Emphasis is placed on research on this host-parasite system in the Pribilof Islands, AK, USA where the bulk of the studies has been performed.

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