Cite as: Jacela JY, DeRouchey JM, Tokach MD, et al. Feed additives for swine: Fact sheets – prebiotics and probiotics, and phytogenics.
J Swine Health Prod. 2010;18(3):132–136.
Also available as a PDF.

Restriction on the use of in-feed antibiotics in many countries has fueled the interest in alternative products. A group of natural products known as phytogenics has been the focus of several studies in recent years.¹ Also referred to as phytobiotics or botanicals, phytogenics are plant-derived products used in feed to potentially improve pig performance. Aside from having antimicrobial activity, these products potentially provide antioxidative effects, enhance palatability, improve gut functions, or promote growth.¹ However, there is limited research validating their potential benefits for pigs.

What products are being used as phytogenic feed additives?

Phytogenics comprise a wide range of substances and thus have been further classified according to botanical origin, processing, and composition. Phytogenic feed additives include herbs, which are non-woody flowering plants known to have medicinal properties; spices, which are herbs with intensive smell or taste, commonly added to human food; essential oils, which are aromatic oily liquids derived from plant materials such as flowers, leaves, fruits, and roots; and oleoresins, which are extracts derived by non-aqueous solvents from plant material.¹ Two of the most common phytogenic substances evaluated in swine include the spices oregano and thyme.^1-5

How do phytogenic feed additives exert their claimed effects?

The mode of action of most phytogenic feed additives is still not fully understood. However, the following are some of the potential mechanisms by which they may improve performance.

Increased feed intake. The stimulatory effect of phytogenics on feed intake is due to the claimed improvement in palatability of the diet resulting from the enhanced flavor and odor, especially with the use of essential oils.⁶ However, the effect on feed intake of adding essential oils to pig diets is highly variable. In some phytogenic feed-additive studies,¹ the increased feed intake was found to be also influenced by the antibiotic supplemented in the diet. Other studies reported decreased feed intake with increasing inclusion levels of the phytogenic substance used.^4,7 The addition of phytogenic feed additives to pig diets may not affect feed intake in some instances^8,9 and even resulted in better feed efficiency in one study.⁸ Increased palatability of the diets associated with the addition of phytogenics also may be due to their anti-oxidative effects,¹⁰ which might contribute to preserving the desired organoleptic qualities of the diet.

Improved gut function. Improvement in gut function is mainly attributed to the possible stimulatory effect of phytogenic substances on digestive secretions, such as digestive enzymes, bile, and mucus.¹¹ However, limited evidence in pigs^12,13 exists to support this hypothesis, which is generally based on experiences derived from the use of spices in human nutrition. Phytogenic substances from certain herbs, spices, and their extracts have also been shown to have pharmacologic actions within the digestive tract, as evidenced by their relaxant and spasmolytic effects.^14-16

Anti-oxidative effects. Anti-oxidative properties of some phytogenic substances have been attributed to the phenolic terpenes in the essential oils.^17,18 Essential oils of plants belonging to the Labiatae family have been widely used as antioxidants in human and pet foods with high fat content.¹⁰ Plants high in terpenes include rosemary, oregano, and thyme.^1,10 However, whether they can be added in amounts sufficient to replace the effects of antioxidants commonly used in pig diets, such as ethoxyquin and butylated hydroxytoluene, remains to be seen.

Antimicrobial effect. The medicinal or antimicrobial properties of plant-derived substances have been well known for centuries.^19,20 This property is mainly attributed to the essential oils of these plants. Oregano and thyme are among those which have received a great deal of interest. These plants contain the monoterpenes carvacrol and thymol, respectively, and have demonstrated high efficacy in vitro against several pathogens found in the intestinal tract.^4,21,22 This suggests that phytogenic feed additives may be suitable replacements for in-feed antibiotics to improve pig health and growth performance, particularly during the first few weeks post weaning.²³ However, available research data^24,25 appear to be insufficient to support the claimed beneficial effects on health and pig performance. In one study,⁸ the addition of a commercial product containing a proprietary blend of phytogenic substances was associated with higher postweaning growth performance in nursery pigs than that observed in controls. However, growth performance was better in pigs fed diets containing antibiotics than in those fed the phytogenic test diets. In other studies^2,26 that evaluated the effects of oregano oil on nursery pig performance, pigs fed diets supplemented with oregano oil did not perform as well as pigs fed diets containing antibiotics.

Do phytogenics interact with other substances or compounds added to the diets?

While possible drug-herb interactions have been reported in humans,²⁷ most studies that evaluated the use of phytogenic feed additives in swine did not indicate any negative interaction with other supplements in the diets, such as antibiotics or organic acids.¹ However, negative interaction of phytogenic substances having astringent properties has been reported in one study, specifically due to partial denaturation of proteinaceous feed additives.¹

Are phytogenic feed additives totally safe?

Even though a product is said to be of natural origin, it is not necessarily better or safer than antibiotics or other synthetic feed additives. It is important to note that various antibiotics also are of natural origin. The fact that some herbs and spices also exhibit antimicrobial properties suggests that phytogenic feed additives may pose similar risks to producers and meat consumers. Similarly, potential overdose that may be harmful to the pig also is possible. All of these considerations warrant further investigation into the safety of phytogenic feed additives both for humans and animals.

Summary

Most beneficial effects claimed from using phytogenic feed additives are based on experience from the field of human medicine. Phytogenic feed additives, according to current research, will not replace the response observed with in-feed antibiotics during the nursery phase. Additionally, responses to feeding phytogenic additives have not been consistent among trials. Hence, more evidence is needed to confirm the apparent beneficial effects on pig performance before these products are added to swine diets on a regular basis. Finally, although these additives are considered “natural” products, they need to be carefully evaluated for potential interactions with other ingredients or other potentially negative effects.

References

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2. Neill CR, Nelssen JL, Tokach MD, Goodband RD, DeRouchey JM, Dritz SS, Groesbeck CN, Brown KR. Effects of oregano oil on growth performance of nursery pigs. J Swine Health Prod. 2006;14:312–316.

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*24. Main RG, Minton JE, Dritz SS, Tokach MD, Goodband RD, Nelssen JL. Evaluating cloves as a potential substitute for antimicrobials in nursery pig diets. Kansas Agric Exp Sta Prog Rep 880. 2001:32–34. Available at: http://www.ksre.ksu.edu/library/lvstk2/srp880.pdf. Accessed 11 January 2010.

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*Non-refereed references.