Persistent efficacy of doramectin pour-on against artificially induced infections of nematodes in cattle

Persistent efficacy of topical doramectin and eprinomectin against Ostertagia ostertagi and Cooperia oncophora infections in cattle

“…The duration of persistent efficacy of doramectin pour‐on against C oncophora and O ostertagi was longer than that described by Molento and others (1999), who observed a persistence of 28 and 35 days for C oncophora and O ostertagi , respectively. The duration of persistent efficacy for eprinomectin could not be determined in the present study, but it was less than 28 days against C oncophora and less than 35 days against O ostertagi.…”

“…Doramectin pour‐on is licensed in some countries for use in a chemoprophylactic system for nematode control in first grazing season calves given at turnout and again eight weeks later (Vercruysse and others 1998); the same chemoprophylactic design was used with eprinomectin pour‐on in some field experiments (Epe and others 1999, Dorny and others 2000). The duration of persistent activity of doramectin pour‐on has been reported to be 28 days and 35 days against Cooperia oncophora and Ostertagia ostertagi , respectively (Molento and others 1999); for eprinomectin it has been reported to be 21 days and 28 days, respectively, against the same nematode species (Eagleson and Langholff 1997). However, it has been demonstrated that trial design, parasite and/or host factors may affect the length of activity of macrocyclic lactones (Deroover and others 1997, Vercruysse and others 2000) and this may be the reason for the wide range of persistent efficacy described in literature for injectable formulations of these drugs.…”

“…DORAMECTIN and eprinomectin are macrocyclic lactones with a high efficacy against cattle strongyle nematodes (Shoop and others 1996, Conder and others 1998). They also show a persistence of activity of several weeks, which makes them particularly attractive for the strategic control of gastrointestinal nematodes in calves (Eagleson and Langholff 1997, Molento and others 1999). Both compounds are available as pour‐on formulations for easier administration.…”

Unexpected production loss caused by helminth parasites in weaned beef calves

“…The diagnosis of nematode parasitic gastroenteritis was also unexpected, because the calves had received pour‐on treatment with 0.5 mg/kg doramectin between six and eight weeks before the development of clinical signs. Pour‐on doramectin treatment should have protected the cattle against infection with O ostertagi , which is generally considered to be the primary cause of parasitic gastroenteritis in cattle (Armour 1974), for between 35 days (Molento and others 1999) and 42 days (Dorny and others 2000). The O ostertagi FWECs should therefore have been zero for at least 7.5 weeks after treatment.…”

“…This situation might arise if removal of O ostertagia from the abomasum modifies the acidity or biochemical environment within the proximal small intestine, enabling Cooperia species and N helvetianus to establish and survive in high enough numbers to become pathogenic (Vermunt and others 1996). Pour‐on treatment of the calves with 0.5 mg/kg doramectin should have afforded between 28 days' (Molento and others 1999) and 35 days' (Dorny and others 2000) protection against reinfection with Cooperia oncophora , but would have lacked efficacy against N helvetianus (Jones and others 1993). The poor persistence against reinfection with C oncophora that was observed in the first group of calves to be investigated could have arisen due to the presence of anthelmintic resistance, which has been confirmed in northern Europe (Coles and others 2008, Demeler and others 2007), or may simply reflect poor efficacy of pour‐on anthelmintic formulations (West and others 1994, Loveridge and others 2003, Sargison and others 2009).…”