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

Abstract

HighlightsStocking rate effect on design of targeted selective treatments (TST) was evaluated.Initial pasture contamination effect on the design of TST was evaluated.Different phenotypic traits and methods of selection for treatment were addressed.Benefit was assessed as weight gain/frequency of resistant alleles in helminths.Treatment according to threshold triggers of average daily gain was most beneficial.

The Economic Impact of Parasitism from Nematodes, Trematodes and Ticks on Beef Cattle Production

“…Treatment failure due to AR can have greater economic impact on cattle producers than no treatment because treatment costs are added to continued production losses [86]. Alternative strategies for effective and sustainable helminth control, designed to limit production losses due to nematode infection while maintaining the efficacy of available anthelmintics, have been investigated [138][139][140][141][142]. Two such strategies are targeted treatment (TT), wherein the whole herd is treated based on knowledge of the risk or severity of infection, and targeted selective treatment (TST), wherein only certain individual animals within the herd are treated, such as those with high parasite loads or poor parasite tolerance, or simply animals randomly selected for treatment, with the remaining herd left untreated.…”

“…The untreated animals contribute anthelmintic susceptible parasites (known as refugia) to the pasture. This population of susceptible parasites is intended to help slow AR selection pressure and thereby prolong anthelmintic efficacy [138][139][140][141][142].…”

“…are more pathogenic than Cooperia spp., the identity of both parasite species present and the resistance profile is needed. Strategies such as targeted treatment or targeted selective treatment may help slow AR [140,141,[194][195][196][197][198]. Increased costs associated with the testing necessary to implement TST must be considered [140].…”

Refugia-Based Strategies for Parasite Control in Livestock

“…Many models have been developed, each with their own emphasis and objectives and across several scenarios, including both cattle and small ruminants, and evaluating both TT and TST regimes and parasitologic, pathologic, or performance-based decision criteria (see examples 12,18,19,20,21,22,23,24,25 ). Although differences in the parameters of each of the models exist, the one common element is that in almost all cases they demonstrate the importance of providing refugia to assist in slowing the development of anthelmintic resistance.…”