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Plants and their extracts and other natural alternatives to antimicrobials in feeds

Final Report Summary - REPLACE (Plants and their extracts and other natural alternatives to antimicrobials in feeds)

The aim of the REPLACE project was to examine plants, plant extracts and other natural materials as safe alternatives to Antimicrobial growth promoters (AGP). The candidates were derived from 500 samples of plant materials collected as possible feed additives for ruminants in addition to some natural materials likely to be useful in non-ruminants. Rumen-up samples, for which a large data set of background information and screening success existed, were re-collected to ensure fresh samples. They were tested for properties not screened in the Fifth Framework Programme (FP5), namely their possible impact on human and animal health (Escherichia coli, parasites), food quality (fatty acids) and efficient use of natural resources (increased forage use by ruminants). Researchers on pigs, poultry and fish, where the impact of antibiotic withdrawal is greatest, comprised the consortium. The intention was that, after identifying the most promising candidates for each target, a small number of samples would be taken to animal trials.

The project aimed to link fragmented research carried out with different animal species across Europe and provide a platform, via consultation with industry, farmers' and consumers' organisations, veterinarians, botanists, agronomists and economists, for the rational production of a new generation of natural feed additives. If the plans could be incorporated into livestock production, the main benefits would be a healthier, safer food chain, increased sustainability of animal agriculture and reduction in its detrimental effects on the environment.

The results of the project are stated below:

Pigs: All the REPLACE samples were screened for their influence on growth and survival of E. coli O149:K88 in pig ileum and stomach content, respectively. Promising samples were tested in growing pigs. Of these, three were identified to have great potential in controlling E. coli K88. They also appeared to have growth-promoting activity and to stimulate immune response. Two of the three plants had traditional uses in herbal medicine, though not in the control of diarrhoea in piglets. The third sample had no similar background in human or animal use. Experiments were carried out successfully in conventional and germ-free piglets, generating much information about production responses and the role of the immune system. Much effort was expended in trying to develop an in vitro model to work with another pig-gut pathogen, the obligatory intracellular Lawsonia intracellularis but it turned out to be unsuccessful.

Poultry - necrotic enteritis: All 500 REPLACE samples were screened for their effect on the growth in vitro of Clostridium perfringens, the bacterium that causes necrotic enteritis in poultry. Selected samples were then tested in two series of in vivo chicken trials showed that the birds were willing to eat diets amended with 1 % of the four most-promising tested additives, but the infection was not effective since the Cl. perfringens levels in the uninfected controls were too low. When the samples were retested in poultry kept on the floor, the basal level of infection was much higher. The selected samples were effective in controlling infection. Significantly, the most promising sample in the poultry trial (plant W) was the one identified to be most effective with piglets. The sample was re-tested in poultry receiving the 'provocative' diet, and compared with the effects of the antibiotic, salinomycin. Both plant W and salinomycin reduced clostridial counts and increased body weight in growth studies, however salinomycin increased growth rates with normal diets suggesting an influence on coccidial infection. Poultry trials in Oslo were carried out, with benefits in decreasing Cl. perfringens numbers being highly significant with three samples. There was no statistical / biological effect of the additives with respect to immuno-stimulation.

Poultry - campylobacter: 14 individual REPLACE samples showed high bactericidal activity against C. jejuni strain DSM 4688T. However, such was the overlap with samples that affected Cl. perfringens, that it was concluded that the animal pathogen work took priority, and although Campylobacter was important, it was measured only as a secondary consequence of measures that were aimed primarily at controlling Cl. perfringens. Measurements of C. jejuni numbers in production trials revealed that their numbers were significantly suppressed by Plant W.

Aquaculture: Samples were tested for their properties in trout. Two groups of promising samples were identified. Screening experiments were planned to explore the control of the fish parasite, Ichthyophtirius multifiliis, in trout fry. However, it proved impossible to sustain the parasite for long enough periods in the laboratory in order to carry out the screening. Seven studies were carried out with phytochemicals and plants from the REPLACE collection, and trials were performed with high precision in a commercial trout production farm. Positive effects of the essential oil compounds, carvacrol and alpha-pinene, on production parameters could not be detected under the conditions provided. Slightly lower ammonia concentrations in the presence of additives were observed.

Ruminants - fatty acid biohydrogenation: Screening the REPLACE collection for samples that had an antimicrobial effect on ruminal Fusocillus (now named Butyrivibrio proteoclasticus) but not Butyrivibrio fibrisolvens revealed six promising plants. However, when these plants were tested for their effects on biohydrogenation of linoleic acid in the mixed population, the effects were minor. The response was to shift the study to other candidate samples based on information from outside the REPLACE collection. One of these, Chrysanthemum, had some published evidence from in vivo experiments to show that cows consuming Chrysanthemum as a supplement produce milk with a healthier fatty acid profile. When tested in the systems, the Chrysanthemum produced results that had been hoped for with the rest of the collection. Only Chrysanthemum coronarium was effective, however, with two other Chrysanthemum species being ineffective.

Ruminants - gastrointestinal parasites: The project sought to find plants that might prove to be natural alternatives to chemical anthelmintics. A larval feeding inhibition assays identified a good number of promising samples, which were tested further in secondary assays, leading to a short list of five samples that are considered to be very promising. Most importantly, a novel biochemical mechanism for the control of parasites was discovered. A controlled efficacy test was conducted to determine the effects on the worm burdens of sheep administered bearberry, cowberry, olive, kelp and rockrose. Olive leaf proved to be the most effective plant product since in comparison to control samples it reduced egg counts by 50 %, worm burden by over 31 % and it also had a residual effect in faeces reducing larval yield by 67 %. It appeared to be most active against Haemonchus where it reduced the average contribution to egg count made by Haemonchus to 38 % compared to over 55 % in the controls. Olive also reduced the Haemonchus burdens by 42 % compared to controls and reduced overall larval yield by more than 65 %.

Collaboration and cooperation: Dialogue continued with the consortium Feed for Pig Health throughout the project. A joint public workshop was held in Denmark. The REPLACE consortium was aligned with an Australian one at the University of Western Australia, which was carrying out similar work using indigenous Australian plants as their collection. One particularly promising plant was identified as a result of this collaboration. It was not related to any of the species in the REPLACE collection, but it could be grown in Europe.