Modelling the impacts of pasture contamination and stocking rate for the development of targeted selective treatment strategies for Ostertagia ostertagi infection in calves

摘要: A simulation study was carried out to assess whether variation in pasture contamination or stocking rate impact upon the optimal design of targeted selective treatment (TST) strategies. Two methods TST implementation were considered: 1) a fixed percentage herd according given phenotypic trait, 2) individuals that exceeded threshold value for trait. Four traits, on which base average daily bodyweight gain, faecal egg count, 3) plasma pepsinogen, 4) random selection. Each method (fixed treatment) and determinant criteria (phenotypic trait) assessed terms benefit per R (BPR), ratio weight gain change frequency resistance alleles (relative an untreated population). The strategy investigated by setting initial 100, 200 500 O. ostertagi L3/kg DM herbage; at low (3calves/ha), conventional (5 calves/ha) high (7 rates. When treating herd, treatments pepsinogen selection identified as most beneficial (i.e. resulted greatest BPR) all levels Conversely when administered values ADG beneficial, best overall