Efficacy of Novastat against Twelve Strains of Eimeria tenella and the Development of a Novastat-Resistant Strain

Focused review: The role of drug combinations for the control of coccidiosis in commercially reared chickens

“…There have been a few other attempts to select drug resistance to combinations. Thus, a decrease in sensitivity of E. tenella to Novastat was found after five serial propagations of a sensitive strain in the presence of suboptimal levels of the drug ( McLoughlin and Chute, 1973 ) and resistance to Maxiban could be developed after 11 serial passages of E. tenella in medicated birds ( Tamas and Wilks, 1989 ). However, Bafundo and Jeffers (1990) found that sixty generations of selection were required to develop resistance to Maxiban with E. acervulina, but only partial resistance developed after 52 generations with E. tenella .…”

“…Many studies have been conducted on the sensitivity of field strains to anticoccidial drugs but few for drug combinations (reviewed by Chapman, 1982 ; Cuckler et al, 1969 ; Ryley and Betts, 1973 ). Thus, of the early combinations, Novastat was unable to control field strains of E. tenella resistant to nicarbazin and other drugs ( McLoughlin and Chute, 1973 ). However, the combination has limited efficacy and therefore this was not considered to be acquired resistance ( Ryley and Betts, 1973 ).…”