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Essential oils have multiple desirable properties which can have beneficial effects on animal performance, such as finishing pigs, when added to their rations.
Phytogenic substances have characteristic tastes and aromas and can exert multiple effects in the digestive tract. Their effects include stabilization of proper digestion and improvements in finishing pig performance. Phytogenic feed additives with standardized essential component composition are necessary to achieve expected and appropriate effects on feed palatability and performance of pigs.
Phytogenic feed additives are herbal preparations from plants which have beneficial properties beyond their organoleptic and olfactory properties. Plants containing these substances have a long tradition in human diets where they have been used for centuries as culinary spices as well as for aiding digestion and stabilizing health. Phytogenic substances used in animal nutrition can be categorized as follows:
• Processed aromatic plants (e.g. herbs, spices)
• Parts of plants (leafs, seeds, fruits, roots)
• Extracts made of plants or plant parts
Today, essential oils are gaining prominence as animal feed additives.
What are Essential Oils?
Essential oils are generally understood to be liquid preparations from of aromatic plants that have notable beneficial effects on maintaining animal performance. The oils are the substances responsible for the fragrance and plants may contain 0.01 – 2 per cent essential oils. The oils tend to accumulate in specialized parts of the plants, e.g. leaves (eucalyptus, cinnamon leaf oil, patchouli), bark (cinnamon), seeds (caraway, anis, pepper), bulbs (garlic), roots (ginger, vetiver) or in fruit peels (lemon, orange). Although essential oils are not thought to be vital to the plant’s existence, there is much speculation about their role and advantages the plants gain from their production:
• Attractant for pollinating insects
• Protection against herbivores
• Protection against bacteria and fungi
Composition of Essential Oils?
The composition of essential oils is very complex as most essential oils contain hundreds of substances, some of which are present in higher concentrations than others. Some of these substances have been shown to exert different biological activities, such as antimicrobial, antiviral or antioxidant. The table below gives some examples of a number of different substances with different activities found in different herbs and spices:
Antioxidative substances can delay oxidation of feed ingredients (e.g. fats, oils), hence preventing degradation and increasing shelf life.
Essential Oils as Feed Additives
Plants expressing essential oils contain the active components in extractable concentrations. The standard method of extracting essential oils is by steam distillation. Furthermore, the composition of essential oils is influenced by cultivar within plant variety, climatic conditions and time of harvest. Blending oils from different batches of plants is a practical method to compensate for the different concentrations between batches and assure oil with a standardized composition and quality, which is prerequisite for consistent efficacy.
Improved Pig Performance
Essential oils can be used effectively in finishing pig diets due to their sensory properties and biological activities. This is demonstrated in a trial where grower-finisher pigs were fed diets supplemented with essential oils at dosages of either 125 or 500 g/ton. Pigs fed diets containing the essential oils had improved weight gain and feed conversion while feed consumption was not affected compared to performance of pigs fed unsupplemented diets.
Combination of Essential Oils
Pigs have a sophisticated sense of taste and smell; therefore, particular attention must be paid to the palatability of feed, particularly at times of feed change where changes to strong or unpleasant tasting or smelling feeds should be avoided. Better feed acceptability can be achieved through suitable combinations of essential oils by, for example, covering bitter tasting substances with sweet-fruity aromas. Basically, essential oil products should contain a mixture of components which are effective in the gastro-intestinal tract, and have appropriate sensory properties. The earlier animals are fed diets with phytogenic substances, as a general rule, the better the effects expected.
Application in Practice
Single essential oils and mixtures of essential oil are used in pig finishing diets. Oregano, thyme, clove, garlic oil or their primary active components are often used in these preparations. Usually essential oils are mixed into the compound feed directly in the feed mill or via a premix at the farm. Thus, precise mixing equipment is needed for good distribution of the essential oils in the diet since inclusion rates are relatively small.
Influence on Digestion
Essential oils can exert beneficial effects on digestion, particularly in times of enhanced stress. Feed change is such a stress factor, which often results in a decrease of feed consumption and occasional intestinal disorders. In these conditions, essential oils can have a stabilizing effect, hence maintaining feed consumption and preventing digestive dysfunctions. Feed conversion is usually affected more adversely than feed intake. Increased protein digestibility and improved feed conversion was shown in trials with weaning piglets fed a blended (oregano, anise and citrus oil) essential oil product (Zitterl-Eglseer et al., 2008). Application of this blend of essential oils in pig diets resulted in an improvement of daily gain and feed conversion ratio by 6.5 and 6.1 per cent, respectively. Additionally, lower NH4+ concentrations were determined in the slurry of these pigs, indicating better protein utilization and subsequent reduced ammonia emissions, thus having a beneficial effect towards the environment.
Dr. Tobias Steiner, BIOMIN Holding GmbH