Plants and Plant Extracts to Replace Growth-Promoting Antibiotics in Farm Livestock Production
Published on 1 September 2010 in Sustainability and Communities
, Food, health and wellbeing
Introduction
Antibiotics were used as growth promoters in poultry, pig and ruminant livestock production for more than 40 years before their ban by the European Commission at the beginning of 2006. The ban followed one well documented instance in which a transmissible antibiotic resistance factor that originated in livestock receiving a relatively new growth-promoting antibiotic (GPA) found its way into a human pathogen. Thus, human infection caused by this pathogen would no longer be treatable by vancomycin, one of the most potent antibiotics remaining in the clinician’s armoury. While there is no suggestion that other GPA could compromise human health in this way, the Commission responded to strong consumer pressure and banned all GPA, thus lessening the environmental load of widespread antibiotic use as well as eliminating specific health risks. Other nations, including those in North America, took a more pragmatic view, however, banning only those GPA where risk was identified. As a consequence, EU livestock producers could be considered to be at a competitive disadvantage compared with those other nations.
Improved management practices can compensate at least partially for the absence of GPA. The Scandinavian countries, which banned GPA many years before the EU-wide ban was imposed, have pioneered the management approach. Alternative feed additives might provide a suitable alternative in less readily managed livestock systems. Among the most promising category of replacements is plant extracts. Several projects led by scientists at RINH have explored the potential of the plant kingdom as ‘feed additives’ rather than simply for their nutrient content.
Key Points
GPA promote more efficient livestock production in different ways in different animal species. In pigs, their main benefit is in preventing E. coli-caused diarrhoea immediately after weaning. In poultry, preventing necrotic enteritis caused by Clostridium perfringens is an important consequence of GPA use. In contrast, in ruminants growth promotion results from a combination of mechanisms, involving lower methane and nitrogen emissions and prevention of lactic acidosis.
Plants contain an abundance of chemicals that enable them to resist attack by microorganisms and insects. These ‘secondary compounds’ or ‘phytochemicals’ could potentially have useful growth-promoting effects in livestock via their effects on pathogens and other members of the gut microbial community. These phytochemicals include broad generic categories such as essentials oils, saponins and tannins, as well as specific small molecules numbering in the 1000s.
Research Undertaken
Scientists at the Rowett Institute of Nutrition and Health (RINH) have led several commercially driven projects, two international projects aimed at benefitting farmers in sub-Saharan Africa, and two major EC initiatives to discover plants and plant extracts that, when added to the feed, could improve feed efficiency in cattle and sheep.
Essential oils are small terpenoid molecules that are abundant in many plants. Their pleasant aromatic odour and antiseptic properties have been used by man for centuries. It was discovered that a commercial blend of essential oils had a growth-promoting effect that could be traced to effects on so-called ‘hyper-ammonia-producing’ bacteria in cattle and sheep, thus overlapping one of the mechanisms by which the banned GPA, monensin, increased the efficiency of nutrient retention in ruminants. The essential oils also inhibited the growth of some bacteria implicated in starch digestion, which may be a secondary effect of the essential oils additives.
Saponins were also found to be useful, both in commercial products and in some sub-Saharan forage plants. The saponins suppress the growth of rumen ciliate protozoa. The ciliates ingest and digest ruminal bacteria as their main source of nutrients. Saponins therefore prevent wasteful breakdown of bacterial protein in the rumen and consequently inhibit inefficient nitrogen retention. When protozoal activity can be suppressed, the animal lays down more tissue protein with no change in protein intake. This property fitted well with the International Livestock Research Institute’s ‘multipurpose trees’ project, where subsistence farmers in Ethiopia and throughout the sub-Saharan region were encouraged to use trees for shelter, fuel, soil enhancement and feed for their livestock. Using their foliage as a growth promoter added value to the system. The only problem with saponins is that, so far, their effect lasts only for a few days or weeks at most. Bacteria adapt to remove glycosyl linkages, converting saponins to their much less effective sapogenin parent compounds. More work needs to be done to investigate how this adaptive effect could be avoided. Alternating saponins-containing plants, where the saponin structure differs between the plants, on a weekly basis, for example, might be an effective means of circumventing the bacterial activities.
The EC-funded ‘Rumen-up’ project identified more than 20 plants that might be useful in improving ruminant livestock production from a total of 500 plants and plant extracts that were collected and screened. Some of the plants had known phytochemical contents that explained their effects. Some contained a high saponins content, useful in suppressing protozoa. Others inhibited dietary protein breakdown. Most of these contained a high concentration of tannins, phytochemicals already known to inhibit ruminal protein breakdown; a few others were also inhibitory, but via non-tannin compounds and therefore more novel, interesting and potentially valuable. Inhibitors of methane production and lactic acidosis were also discovered.
Rumen-up was considered successful in that an encouraging number of samples had positive effects. The EC therefore decided to extend the project to non-ruminant livestock and to applications in ruminants not covered by Rumen-up, using the same (re-collected) plant materials. The new project, ‘Replace’, recruited new partners expert in pig and poultry production. The precise results cannot be divulged in detail for IP reasons at this stage. However, the leaves and unripened fruits of one particular tree species, never before considered in animal nutrition, was found to be effective in both pigs and poultry, suppressing diarrhoea in the former and necrotic enteritis in the latter. Research is still under way to discover the exact phytochemical(s) that inhibit E. coli and C. perfringens. Patent protection should follow. Other plants affected the metabolism of dietary fatty acids by ruminal bacteria, such that milk from animals receiving these plants had a healthier fatty acid profile, with more polyunsaturated fatty acids (PUFA) and conjugated linoleic acids (CLA).
Policy Implications
Scotland’s National Food and Drink Policy (2009) seeks to improve the sustainability and availability of Scottish food for our population. Using plants rather than AGP in livestock production would improve the sustainability and efficiency of food production from farm livestock.
At a UK level, food security has been defined as ensuring the availability of, and access to, affordable, safe and nutritious food sufficient for an active lifestyle, for all, at all times. The fatty acid composition of food products, particularly derived from animals, is a central criterion of healthy food.
The rural economy of Scotland means that methane emissions constitute a higher proportion of her greenhouse gas emissions than other parts of the UK. Carbon taxation is being discussed as a serious option to limit GGE. The Scottish government, in its Climate Change (Scotland) Bill, has pledged to low its GGE by 80% by 2050. Some of these plants can suppress methane emissions
Fig. 1. Rumen ciliate protozoa. The ruminal microorganisms are so large that they can be seen with the naked eye. By consuming bacteria at a huge rate, they cause wasteful nitrogen retention in cattle and sheep.
Fig. 2. The Rumen-up concept.
Author
Professor John Wallace John.Wallace@abdn.ac.uk
Topics
Sustainability and Communities
, Food, health and wellbeing
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