Since the United States initiated the Veterinary Feed Directive (VFD) in January 2017, which limits the use of crucial antibiotics in farm animals, researchers have been exploring alternative ways to maintain the health of young pigs, particularly after weaning. Various products, including organic acids, enzymes, probiotics, antimicrobial peptides, medium-chain volatile fatty acids, spray-dried plasma products and essential oils (also known as photogenic plant products), are being investigated as substitutes for antibiotics in swine rations. This review consolidates the findings from studies that tested selected essential oils and dissects evidence suggesting that these products could emerge as viable alternatives for antibiotics. They offer the potential for consistent availability within the industry, high safety factors for pigs and consumers, cost-effectiveness and environmental friendliness. Despite mixed results, the use of essential oils by pig producers in the European Union for several years underscores the need for further research and understanding. However, the potential of essential oils to revolutionize pork production is a promising prospect.
Essential oils are defined as natural bioactive compounds that are derived from plants. They include aromatics, volatile (change in chemical structure and overall usefulness) and oily liquids extracted from materials such as seeds, flowers, leaves, buds, twigs, herbs, bark, woods, fruits and roots. Essential oils that have been fed to pigs in multiple research studies include carvacrol, thymol, citral, eugenol and cinnamaldehyde, which are derived from thyme, lemongrass, clove, nutmeg, cinnamon, basil, oregano and hay leaf.
While essential oils are natural bioactive compounds derived from plants, their oily and volatile nature presents challenges in pig diets. These challenges include their effectiveness within diets and their absorption into the pig’s gut. While scientists don’t completely understand how essential oils work in the intestines, they believe they help reduce inflammation and protect the gut. This means essential oils might help lessen some of the problems caused by E. coli, which can upset a pig’s immune system and cause diarrhea after weaning. The need for further research to fully understand the potential of essential oils in pig diets is not just critical; it’s urgent and of utmost importance.
In the United States, research with essential oils for sows, nursery pigs, and grow finishers is increasing (discussed in greater detail below). Although some studies have noted improved feed palatability and intake, contributing to overall growth performance, a clear path to their widespread adoption by pork producers has not been delineated. In addition to the lack of definitive information around the pharmacodynamics effects (i.e., the relationship between dose and the mechanistic beneficial actions), key challenges facing the use of essential oils in pork production include some potential regulatory concerns, high inclusion costs, formulation, and effective delivery methods. The current gaps in knowledge underscore the need for further research on the use of essential oils in pork production.
Sows
Essential oils have been tested in sow diets to increase overall reproductive performance and key performance indicators typically measured in these studies include sow feed intake, number of piglets born alive, and sow milk production. Sows with essential oils in their feed have shown small but significant indications of improved gut health compared to untreated controls regarding intestinal lining changes (especially microvilli density and length), lymphocyte proliferation and various blood parameters. Significant improvements in sow health or performance have accompanied these changes in gut morphology in some studies. For instance, a study in 2009 reported that supplementation of a blend of essential oils from 10 days before the estimated farrowing date through weaning improved early lactation feed intake in sows, decreased sow weight loss during the first week of lactation and enhanced piglet body weight at weaning. A study involving 2,100 sows reported that they had higher voluntary feed intake, lower annual mortality rate (4.0% vs. 6.9%), reduced sow culling rate during lactation (8% vs. 14%), increased farrowing rate (77.0% vs. 69.9%), increased number of live born piglets per litter (10.49 vs. 9.95) and decreased stillbirth rate (0.91 vs. 0.81). However, another study noted that 70 second-parity sows fed oregano essential oil blend during gestation and farrowing did not increase piglet growth or immune responses.
Nursery Pigs
Most research on essential oils in pigs has been directed toward nursery pigs due to the dietary changes…
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