Prevalence of Johne's disease among cattle in Orkney

Challenges for the management of Johne's disease in the UK: Expectation management, space, 'free riding', and vet-farmer communication

Johne's disease in cattle is a significant global animal health challenge. Johne's disease is chronic, affecting the gastrointestinal tract of cattle and other ruminants and is caused by the bacteria Mycobacterium avium ssp. Paratuberculosis. Many countries have introduced schemes and programmes to try and control the spread of Johne's disease, including the UK. Despite efforts to control it, however, Johne's disease remains consistently ranked by UK producers as the top ranked disease negatively affecting productivity, indicating that schemes are not perceived to have solved the problem fully. Building on a global systematic review of the literature on barriers and solutions for Johne's disease control on-farm, we conducted an empirical study with over 400 farmers and 150 veterinary professionals across the UK. The study used workshops and semi-structured interviews to understand better the challenges dairy farmers and veterinarians face in implementing on-farm Johne's disease management schemes with the aim of identifying solutions. The study found that four main challenges are faced in the on-farm control of Johne's - (1) Management of farmer expectations around Johne's disease, with eradication near impossible, (2) Issues regarding space for segregation and the related economics of control (3) A 'free-riding' problem which can be influenced by the voluntary nature of control plans and (4) Challenges in vet-farmer communication, including levels of knowledge. Our findings have relevance for the control of Johne's disease in the UK and other countries, including for regions with voluntary and compulsory control programmes.

Genome-wide relaxation of selection and the evolution of the island syndrome in Orkney voles

Island populations often experience different ecological and demographic conditions than their counterparts on the continent, resulting in divergent evolutionary forces affecting their genomes. Random genetic drift and selection both may leave their imprints on island populations, although the relative impact depends strongly on the specific conditions. Here we address their contributions to the island syndrome in a rodent with an unusually clear history of isolation. Common voles (Microtus arvalis) were introduced by humans on the Orkney archipelago north of Scotland >5000 years ago and rapidly evolved to exceptionally large size. Our analyses show that the genomes of Orkney voles were dominated by genetic drift, with extremely low diversity, variable Tajima's D, and very high divergence from continental conspecifics. Increased d N/d S ratios over a wide range of genes in Orkney voles indicated genome-wide relaxation of purifying selection. We found evidence of hard sweeps on key genes of the lipid metabolism pathway only in continental voles. The marked increase of body size in Orkney-a typical phenomenon of the island syndrome-may thus be associated to the relaxation of positive selection on genes related to this pathway. On the other hand, a hard sweep on immune genes of Orkney voles likely reflects the divergent ecological conditions and possibly the history of human introduction. The long-term isolated Orkney voles show that adaptive changes may still impact the evolutionary trajectories of such populations despite the pervasive consequences of genetic drift at the genome level.

Phenotypic effects of subclinical paratuberculosis (Johne's disease) in dairy cattle

The effect of subclinical paratuberculosis (or Johne's disease) risk status on performance, health, and fertility was studied in 58,096 UK Holstein-Friesian cows with 156,837 lactations across lactations 1 to 3. Low-, medium-, and high-risk group categories were allocated to cows determined by a minimum of 4 ELISA milk tests taken at any time during their lactating life. Lactation curves of daily milk, protein, and fat yields and protein and fat percentage, together with log_e-transformed somatic cell count, were estimated using a random regression model to quantify differences between risk groups. The effect of subclinical paratuberculosis risk groups on fertility, lactation-average somatic cell count, and mastitis were analyzed using linear regression fitting risk group as a fixed effect. Milk yield losses associated with high-risk cows compared with low-risk cows in lactations 1, 2, and 3 for mean daily yield were 0.34, 1.05, and 1.61kg; likewise, accumulated 305-d yields were 103, 316, and 485kg, respectively. The total loss was 904kg over the first 3 lactations. Protein and fat yield losses associated with high-risk cows were significant, but primarily a feature of decreasing milk yield. Similar trends were observed for both test-day and lactation-average somatic cell count measures with higher somatic cell counts from medium- and high-risk cows compared with low-risk cows, and differences were in almost all cases significant. Likewise, mastitis incidence was significantly higher in high-risk cows compared with low-risk cows in lactations 2 and 3. Whereas the few significant differences between risk groups among fertility traits were inconsistent with no clear trend. These results are expected to be conservative, as some animals that were considered negative may become positive after the timeframe of this study, particularly if the animal was tested when relatively young. However, the magnitude of milk yield losses together with higher somatic cell counts and an increase in mastitis incidence should motivate farmers to implement the appropriate control measures to reduce the spread of the disease.

Mycobacterium avium subspecies paratuberculosis is widely distributed in British soils and waters: implications for animal and human health

In the first comprehensive geographical survey of distribution in Great Britain, Mycobacterium avium ssp. paratuberculosis (MAP) was detected in 115 of 1092 (10.5%) soil cores, in the range of 5 × 10(2) to 3 × 10(6) MAP cell equivalents (CE) g(-1) wet weight soil with the majority of the positive PCR reactions (n = 75; 65%) occurring around the limit of detection (500-5000 CE g(-1) wet weight soil). The distribution of MAP significantly increased from North to South and was significantly correlated with increasing cattle numbers over the same longitudinal axis. Similarly MAP occurrence significantly increased towards easterly latitudes although none of the parameters measured were associated. Comparisons of land use indicated that MAP was widely distributed in both farming and non-farming areas. Soil core samples taken from the rivers Wyre and Douglas catchments (Lancashire, UK) and river Tywi (South Wales) were negative for MAP. However, river monitoring showed a consistent presence of MAPs throughout those catchments over a 6-month period. We concluded that MAP is widely distributed within and outside the confines of the farming environment; its geographical distribution is wider than originally anticipated and; monitoring rivers describes the MAP status of catchment better than individual soil samples.