Factors influencing endemic disease in the Northern Ireland sheep flock

Sheep scab, caused by infestation with the ectoparasitic mite, Psoroptes ovis, represents a significant economic and welfare burden for the Northern Ireland (NI) sheep industry. It is a highly contagious disease; concerted action is required to control its spread and impact and its eradication by 2031 is a priority target of the UK-wide Ruminant Health and Welfare Group. Control of scab offers many benefits for the industry, through improved animal health and welfare, fewer treatments, reduced environmental, and sustainability, concerns, reduced farmer costs and decreased selection pressure for anthelmintic resistance. This highly collaborative project brought together researchers from Moredun, AFBI, AHWNI, local vets and the NI sheep scab group and involved a significant degree of stakeholder engagement. It aimed to better understand the extent and spread of the disease in NI, investigate the barriers to control and then develop a tailored control strategy for sheep scab in NI. Farmers across NI who suspected sheep scab to be present in their flocks were encouraged to engage with the project. Following self-reporting to the project helpline, they were offered a free veterinary visit, diagnosis (using skin scrapes and blood testing) and appropriate treatment. Veterinary oversight of the prescription of organophosphate (OP) dips and macrocyclic lactone (ML) injectables was a feature of the initiative, allowing tailored treatments to be prescribed, advice to be given and follow-up to ensure treatment success. The project also aimed to improve general farmer knowledge and awareness of the disease. This was achieved through a series of six stakeholder events held across NI and attended by ~200 farmers and a veterinary CPD event attended by ~50 vets. We aimed to recruit 100 farmers, in total, 155 sheep farmers were engaged and of those, 105 participated. Of the participating flocks, 32 grazed one commonage area and were contacted as a pilot study of scab incidence in that area following the detection of several positive cases.

The project worked with 39 vet practices and 110 vet visits were performed. Blood samples were collected from 95 flocks, with 60 flocks returning positive results either by blood testing, skin scraping or both. Sheep scab was detected in 70% of the self-nominating (suspicious) flocks and in 28% of the pilot (non-suspicious) common grazing area flocks. All flocks in the common grazing area were offered OP dipping following the veterinary visit and blood sampling and overall, OP dipping was the treatment of choice for 72 flocks; injectable MLs were used in 16 positive flocks, 5 of which required subsequent dipping due to suspected treatment failure. Feedback from the project was gathered with a questionnaire, distributed to 108 flock owners and with 52 responses returned. Of these, 33 had positive scab results and overall, 81% indicated that they were willing to coordinate scab treatments with their neighbours. For future control, 65% would use an OP dip, 12% would use an injectable without blood testing, and 12% would blood test before treating. Every respondent thought that a programme dedicated to controlling sheep scab in NI would be helpful in the future and should either be funded through the NI Assembly/DAERA (67%) or shared government and industry contributions (33%). In summary, the project demonstrated a significant level of interest in dealing with sheep scab and the widespread geographical location of the disease across NI. Farmers willingly engaged with the project to avail of the knowledge exchange opportunities and veterinary involvement. Farmer feedback received following the project was highly favourable.

This study also explored the psychological and behavioural factors influencing farmers’ intentions to implement effective sheep scab control measures in NI. Quantitative data from a sample of 126 sheep farmers was statistically analysed using an extended theory of planned behaviour approach. Our analyses showed that attitude, perceived behavioural control, emotional effect, membership of Business Development Groups and higher education qualifications were statistically significant factors influencing farmers’ intentions to adopt sheep scab control measures. Other barriers to effective control included treatment costs, the time required to gather, test and treat sheep, lack of awareness of the economic impact of the disease, the convenience of ML use, concerns over dip disposal requirements, lack of sheep dip safety course provision in NI, lengthy withdrawal periods, DAERA restrictions, infection on neighbouring farms, reluctance to report infection and a lack of enforcement action in markets and abattoirs.

We also evaluated the impact of sheep scab on greenhouse gas (GHG) emissions at both the farm and NI levels, based on production losses and on modelling the effect of reducing and eradicating sheep scab from the NI flock on GHG emissions. This analysis showed that the main consequence of controlling sheep scab at the farm-level was an improvement in overall flock performance, leading to substantial reductions in the farm carbon footprint, with a 12% reduction for a typical lowland farm and a 6.6% reduction in an upland farm. Reductions at the NI-level would be more moderate, with the control of scab, offering a reduction of 4.267 Mt CO2e, representing 1.3% of NI sheep-related emissions.