Ivermectin treatment of bovine psoroptic mange: effects on serum chemistry, hematology, organ weights, and leather quality

Unravelling Belgian Blue cattle farmers' adoption intention towards diagnostic tools: Integrating insights from behavioural economics and socio-cognitive theories

Macrocyclic lactone resistance in Psoroptes ovis mites, causing psoroptic mange, is emerging in beef cattle. Therefore, diagnostic tools that can indicate macrocyclic lactone resistance should be implemented at farms in order to control these parasitic infections and slow down emerging resistance. Unfortunately, the adoption of such tools remains relatively poor. This study explores which beliefs, and behavioural biases that misconstrue these beliefs, underlie farmers' adoption intention. Five semi-structured focus groups were conducted with Belgian Blue cattle farmers (n = 38). Inductive analysis revealed that farmers' positive attitudes towards acaricides use and risk perception towards acaricide resistance made them rather reluctant to implement diagnostic tools. In addition, farmers' susceptibility to acaricide resistance occurring on their farm was weakened by the optimism and availability bias. Deductive analysis revealed that economic reasons, usefulness of the diagnostic tool and contribution to animal wellbeing motivated farmers to adopt such tools (i.e., behavioural beliefs). However, the loss aversion and time discounting bias weakened farmers' beliefs related to economic reasons. The veterinarian was seen as the responsible actor for implementing diagnostic tools, while colleague-farmers' opinion related to the diagnostic tool was also valued (i.e., normative beliefs). The latter belief was strengthened by the bandwagon-effect bias. Farmers' beliefs about economic costs related to the diagnostic tool tended to hinder adoption intention, while the veterinarian's assistance motivated farmers to implement such tools (i.e., control beliefs). The loss aversion bias also strengthened farmers' control beliefs related to the diagnostic tools' perceived costs. As such, this article provides more insights into the (ir)rational factors shaping farmers' intention to adopt diagnostic tools. These insights might help animal health organisations to design communication strategies to stimulate the adoption of diagnostic tools on beef cattle farms.

New insights into the use of a mite count reduction test for the detection of therapeutic acaricide efficacy in Psoroptes ovis in cattle

When used for the evaluation of drug efficacy against Psoroptes ovis, the diagnostic performance of different sampling strategies for a mite count reduction test (MCRT) remains unclear. In the present study, a novel simulation framework was constructed that accounted for relevant biological features of P. ovis infestations in cattle and that was parameterized with field data from 16 farms (154 animals). Second, this framework was applied to explore the impact of study specific factors (number of animals, number of sampled lesions, and number of scrapings per lesion) and biological factors (mite infestation intensity and size of lesions) on the diagnostic performance of MCRT. Its outcome provided a basis to determine the diagnostic performance of MCRT when it was applied according to the World Association for the Advancement in Veterinary Parasitology (WAAVP) and the European Medicine Agency (EMA) guidelines, and to formulate recommendations to ensure a good diagnostic performance of the MCRT. For both guidelines, the MCRT allowed to correctly detect (power 80%) reduced and normal efficacy when the therapeutic efficacy was <70%, and ≥95%, respectively. The results highlighted a reliable diagnostic performance of the MCRT when performed as recommended by WAAVP and EMA for the detection of normal drug efficacy. When used for the detection of reduced efficacy, therapeutic efficacies between 70% and 90% could not be detected with sufficient reliability. The diagnostic performance can be improved by increasing the total number of skin scrapings (increasing the number of animals, number of sampled lesions and/or number of samples per lesion). In order to help researchers and veterinarians to optimize the design of the MCRT to their field settings, the findings were translated into a simple tool.

Resistance against macrocyclic lactones in Psoroptes ovis in cattle

Background

Psoroptic mange is an important disease in Belgian Blue cattle. Treatment failure of macrocyclic lactones against Psoroptes ovis has been reported, but clear evidence of in vivo resistance is lacking. This study assessed the efficacy of macrocyclic lactone products on 16 beef farms in Belgium and the Netherlands in vivo and in vitro.

Methods

On each farm a group of animals (n = 7–14) with psoroptic mange was treated with two subcutaneous injections of a macrocyclic lactone product with 7–10 days interval (15 farms) or a single injection with a long-acting macrocyclic lactone (1 farm). In vivo efficacy was assessed by the reduction in mite counts, clinical index (proportion of the body surface affected by lesions), the proportion of the animals with negative mite counts after the first treatment round and the number of treatment rounds needed to obtain zero mites counts in all animals. A mite population was categorized as sensitive when the mite count reduction after the first treatment round > 95% and the lower limit of the uncertainty interval > 90%. Resistance was detected when both parameters were below their threshold and suspected when one parameter was too low. In vitro knockdown and mortality were evaluated in a contact test.

Results

The proportion of the animals with negative mite counts after the first treatment round varied from 0 to 80%. All farms needed two or more treatments rounds to obtain zero mite counts on all animals. Clinical index only started to reduce after the second treatment round. Mite populations from three farms were categorized as sensitive, one as suspected resistant and 12 as resistant. No correlation was found between in vitro lethal dose 50 and knockdown dose 50 values and in vivo efficacy parameters.

Conclusions

Unambiguous treatment failure was detected on 12 out of 16 farms, confirming the presence of macrocyclic lactone resistance on Belgian Blue beef farms. In vitro parameters could not discriminate the farms based on their in vivo sensitivity. The mean reduction in mite counts and the lower limit of the confidence interval are proposed as parameters to identify acaricide resistance.