## 2 Diversity of Gut Prokaryotes and the Principles of Microbiota Transfer
### Faecal Microbiota Transplantation as an Efficient Therapeutic Approach
Even though improving the digestive capabilities of ruminants can be achieved with transfaunation, some grazers--such as horses--are hindgut fermenters, and therefore standard FMT may be useful in their case. One study confirmed the effectivity of FMT procedures in reducing diarrhoea in horses [66]. Similar results can be seen in pig rearing, where FMT with was successfully utilised to increase average daily gains and decrease the diarrhoea susceptibility of piglets [67]; these results are especially intriguing because of the fact that while the piglets belonged to a crossbreed of Duroc \(\times\) Landrace \(\times\) Yorkshire, donor material was taken from local Jinhua variety. Another study introduced warthog FM to domestic pigs, which apparently resulted in increased resistance to African swine fever virus [68]. However, a different study found that FMT with highly feed-efficient pigs as donors significantly decreased growth rates, both in piglets subjected to FMT and in the offspring of FMT-treated sows [69]. Yet it is crucial to remark that the FMT procedure in this case involved the removal of the original gut microbiota by administration of an antibiotic cocktail followed by 36 h of fasting, and a similar routine was not applied to the control group, which might have substantially affected the end results. Nevertheless, all these findings highlight the importance of donor selection but show that FMT can be effective even when performed between individuals of different breeds or species, identifying promising avenues for future research aimed at conferring desirable traits on domesticated animals. In terms of the technical aspects of the procedure, traditional approaches to FMT therapy in human patients have been centred on utilising crude (often blended, sieved, and mixed with saline) donor faeces that were screened to obtain safe and effective transplant material [55]. However, other concepts have also been proposed, some of which are illustrated in Figure 1. A procedure dubbed \"washed faecal microbiota transplantation\" is based on repeated filtration, centrifugation, and resuspension of bacteria obtained from faeces, which is supposed to significantly decrease the amount of potentially toxic substances in the preparation and can apparently lower the occurrence rate of adverse effects after microbiota transplantation [70]. Other approaches--still classified as FMT without any additional designations in the name--include lyophilising bacterial suspensions and administering the powder inside capsules, with no apparent loss of efficacy [71]. There were also solutions that advocated for the usage of standardised, lab-cultured bacterial formulations that consisted of dozens of artificially selected strains of microbes; these preparations lack any perceived resemblance to faeces, potentially reducing the psychological discomfort of patients, and offer supreme control over their final composition [72]. There, perhaps, lies the future of FMT--selecting the crucial biological components of faeces to then culture, purify, and administer in a safe, controlled, precise, and repeatable manner. Capsules containing a carefully designed consortium of microorganisms could be fine-tuned by chemical alterations or coating to make them more suitable for feeding specific animals in order to achieve better yields. This includes hard, hydrophobic capsules for birds that exhibit pecking while scavenging for food or soft, hydrophilic capsules for aquatic animals such as fish. Naturally, the development of such products will have to be preceded by extensive research to identify the most suitable bacterial strains.