Parasite control on thoroughbred studs

A survey of macrocyclic lactone efficacy in Australian cyathostomin populations

“…Shortly after the MLs became available on the Australian market, Rolfe et al (1998) reported an 11-week ERP following IVM treatment of horses on a NSW property, and ERPs of similar length, (9-13 weeks), were also reported in Belgium and the Netherlands (Borgsteede et al, 1993;Boersema et al, 1996;Demeulenaere et al, 1997). More recently, however, there have been a number of reports of reduced ERPs following IVM treatment and ERPs of less than 8 weeks have been reported from the UK (Dudeney et al, 2008;Relf et al, 2014;Hallowell-Evans et al, 2016), Germany (von Samson-Himmelstjerna et al, 2007), the USA (Little et al, 2003;Lyons et al, 2008b), and Sweden (Lind et al, 2007). In some of these studies, ERPs were as short as 4 weeks (Dudeney et al, 2008;Lyons et al, 2008b;Lyons et al, 2011) although there is a tendency for these shorter ERPs to reflect the time when strongylid eggs first reappeared in faeces following treatment, rather than when FECR (%) passed the 90% threshold as described earlier.…”

“…Reasons proposed for a shorter ERP in young horses include the resumption of development of a higher number of encysted larvae, and higher rates of re-infection as a result of a less developed immune response. Hallowell-Evans et al (2016) carried out resistance testing (FECRTs) and ERP measurements on Thoroughbreds in the UK and asserted that young stock showed reduced FECRs following treatment with PYR compared to adults on the same farm. The ERPs for IVM and MOX were 6 and 8 weeks, respectively, however data from mature horses was not collected for comparison.…”