Evidence for Farming Initiative: Assessment of practices to reduce post-weaning diarrhoea in pigs without using zinc oxide

Weaning is an important transitional stage in pigs, and it is associated with environmental, social, and dietary challenges. Post-weaning diarrhoea (PWD) is a common health problem and one of the greatest challenges in pig production. Zinc oxide(ZnO) at therapeutic doses has been used since the early 1990s to reduce colonisation of pathogenic diarrhoea-causing bacteria during post-weaning of pigs in many parts of the world (Barbosa et al., 2019). However, there are concerns regarding the therapeuticuse of ZnO due to its association with the development and spread of antimicrobial resistance and with the potential risk to the environment. Hence, the EU has prompted the withdrawal of market authorisation of ZnO at therapeutic levels from the pig industry as of July 2022, with the UK set to follow in this direction. Indeed, the marketing authorisation has been removed in the UK as well as Europe, but a product that had been manufactured at the date of the withdrawal can be used in the UK until expired.Thus, alternative measures are being investigated to replace ZnO use in the control of PWD in pigs. Here, rapid evidence assessments were conducted to identify existing practices in pig production which have the potential and may be explored alone or supplemented with other practices to replace the therapeutic use of ZnO. To do this, systematic searches using PubMed, Web of Science, and Scopus databases were carried out to identifyrelevant scientific review articles published from 2010 to 2022. Manual searches in Google and Google Scholar targeted original research, grey literature, and technical information to complement the evidence that was collated from the reviews. Recovered publications were grouped into nutritional changes, management practices and immune status. In-depth analyses of the publications resulted in the identification of practices for each group to include nutritional changes (reduced crude protein intake, alternative sources of proteins, dietary fibre, feed additives), management practices (stress reduction, housing and pen layout, water quality, hygiene and biosecurity, delayed weaning and feeding regimes), and immune status (colostrum management, vaccination and antibiotic usage for Escherichia coli). Feed additives identified included probiotics, prebiotics, synbiotics, amino acids, enzymes, essential oils and plant extracts. Impact and narrative summaries for each practice were produced, and where appropriate, a return on investment was also developed. First and foremost, it is important to stress that, from the work conducted, it is evident that no other practices were as effective and inexpensive as ZnO in feed at therapeutic levels (2500ppm) in treating PWD in pigs. Put together, our analyses suggest that there are feed additives and nutritional changes that may be combined with other strategies to potentially (or at least partially) replace ZnO use in feed. The cost and effectiveness of the methods to mitigate against ZnO removal would largely depend on the degree of challenge and could differ from farm to farm, with better successes in one farm than another. On the other hand, management practices are comparatively more complex to implement but have the potential to prevent other diseases in addition to PWD, furtherimpacting survival and increasing growth rates. Immune status improvements, including colostrum management, are very effective in preventing PWD caused by pathogenic E.coli but can be costly due to the diagnostic workup and labour involved in its Page 2 of 116implementation. It is probable that the application of more than one practice at once has a synergistic effect, especially in the case of management practices. Further additional practices, such as phage therapy and genetic selection, have good prospects as alternatives for ZnO, albeit they are still in experimental stages and are not commercially available yet. Selection of the most appropriate practice(s) to implement would depend on the most significant factor causing PWD (i.e. nutritional vs infectious, or both) on each farm. Consequently, due consideration is required for the potential cost implications of the practice to be adopted. Hence, a working calculator is developed to allow farmers tomake an informed decision for each practice.