Johne's disease
Bovine paratuberculosis (Johne's disease) is an endemic disease caused by Mycobacterium avium subsp. paratuberculosis (Map). Map is mainly transmitted between herds through movement of infected but undetected animals. The objective of a study by Biemans et al (2022) (Veterinary Researchhttps://doi.org/10.1186/s13567-022-01066-5) was to investigate the effect of observed herd characteristics on Map spread on a national scale in Ireland. Herd characteristics included herd size, number of breeding bulls introduced, number of animals purchased and sold, and number of herds the focal herd purchases from and sells to. These characteristics were used to classify herds in accordance with their probability of becoming infected and of spreading infection to other herds. A stochastic individual-based model was used to represent herd demography and Map infection dynamics of each dairy herd in Ireland. Data on herd size and composition, as well as birth, death, and culling events were used to characterise herd demography. Perhaps unsurprisingly, results showed that herds that both buy and sell a lot of animals pose the highest infection risk to other herds.
The single intradermal cervical comparative tuberculin (SICCT) test, which is used to determine bovine tuberculosis status as part of eradication schemes in the UK and elsewhere, has been reported to interfere with the results of the widely used enzyme-linked immunosorbent assay (ELISA) to detect antibodies against Map in milk. A better understanding of the relationship between the SICCT teat and Map tests could improve management and control of Johne's disease. The aim of a study by Nunney et al (2022) (Journal of Dairy Sciencehttps://doi.org/10.3168/jds.2021-21753) was to characterise the relationship between SICCT testing and milk ELISA performance and to assess whether the immunological response to the SICCT test is different for Map-infected cows and non-infected cows. Repeated Map milk ELISA test results of a cohort of 805 561 cows in the UK between 2010 and 2018 that had milk ELISA tests within 90 days of SICCT testing to identify cows likely to be infected were analysed. Having assessed, separately, cows deemed to be Map-infected and non-infected, the association between Map test results and proximity to SICCT testing were considered. The results were used to quantify the effect SICCT testing may have on performance of milk ELISA tests conducted soon after SICCT testing. At high prevalence levels (20%) of Map in the infected herd, overall accuracy of the milk ELISA is not reduced when testing occurs within 14 days from SICCT testing. Milk ELISA values of cows deemed to be infected were highest when Map testing was closer in time to SICCT testing, suggesting the SICCT test enhances antibody response for Map in infected cows. This corresponds to higher sensitivity of the Map milk ELISA when testing within 30 days of the SICCT test. For cows deemed to be non-infected, the effect of previous SICCT testing was delayed compared with infected cows, with Map milk ELISA values peaking at around 15 days post-SICCT test. For both, Map-infected and non-infected cows, interference from the SICCT test diminished 30 days after SICCT testing, suggesting post 30 days to be the most appropriate time for evaluating the milk ELISA for Map after SICCT testing. These results provide strong evidence that the effect of the SICCT test on serological response against Map is different for Map-infected versus non-infected cows and that, because of this distinct effect, it is possible to improve interpretation of Map milk ELISA test results, giving higher accuracy, by taking into consideration time since SICCT testing.
Surplus calves
To maintain its social license to operate, the dairy industry needs to account for public perspectives. Ritter et al (2022) (Journal of Dairy Sciencehttps://doi.org/10.3168/jds.2021-21425) assessed attitudes of members of the public toward the management of surplus calves not needed for milk production, and to assess how specific calf management practices might influence these attitudes. A mixed-methods questionnaire was developed and distributed online in the United States and Canada. After reading an introductory paragraph stating that surplus calves are generally used for meat production, participants were randomly allocated into groups and read one of four scenarios that described different surplus calf management practices in detail. The scenarios followed a 2×2 factorial design, and the factors that differed were the calf 's age at slaughter (≤2 weeks vs. ≥12 months), and whether the calf was separated from the cow at birth or later. Data representative of key census demographics from 998 participants were analysed. Overall, participants were slightly positive in their attitudes toward the introductory paragraph, and participants in the groups in which the calf was slaughtered after 12 months of age often specifically linked their acceptance of the practice to the fact that the calves' lives had a purpose (i.e. contributing to the beef supply). In contrast, only 3% of participants regarded a slaughter age of <1 month as appropriate. Participants in the groups in which calves were slaughtered within 2 weeks after birth had more negative attitudes, and these attitudes declined even further when the calf was separated from the cow soon after birth. Overall, results indicate that failure by the dairy industry to provide assurances that excess dairy calves have a reasonable length of life, and that this life has purpose, places the industry at odds with public values.