A Look at the Recent Findings From Alltech Researchers

By Morgan Hart and Dr. Jamil Faccin

Essential oils (EO) are phytogenic feed additives used in pig diets primarily to support health.

The term “essential” refers to the plant’s essence or characteristic aroma and should not be confused with “essential” as used for nutrients such as amino acids. They are plant-derived extracts (e.g., black pepper, thyme, rosemary, garlic) containing bioactive compounds such as phenols (e.g., thymol, carvacrol, eugenol) and related terpenes (e.g., p-cymene).

These compounds have been widely studied for antibacterial activity and antioxidant effects, in part through membrane disruption and free radical scavenging (Zhai et al., 2018; Burt, 2004). Emerging evidence also suggests EO may influence immune function via interactions with gut microbiota, supporting reported improvements in growth performance and livability (Zhai et al., 2018).

In a review of 402 peer-reviewed studies spanning 14 feed additive categories in grow-finish pigs, Z.X. Rao et al. (2023) identified 20 studies evaluating EO. Across these, EO improved ADG (average daily gain) and feed efficiency by an average of 5.8% versus controls. Approximately 80% of EO studies reported positive performance responses, with 45% statistically significant and an additional 35% showing a trend or numerical improvement.

Although Rao et al. (2023) did not differentiate responses by specific essential oil blends (EOB), the Alltech Pork R&D team has recently conducted a series of commercial-scale trials evaluating a novel EOB (essential oil blend) (Olerix; Alltech, Inc., Nicholasville, Kentucky) to better define its application in nursery and grow-finish pigs.

In the first nursery study, presented at the 2026 ASAS Midwest Section Meeting (Soto et al., 2026), 1,008 pigs weaned at 13.2 lb were used in a 43-day trial.

Pigs were placed in pens with 28 pigs each and allotted to one of four dietary treatments with nine replicates per treatment.

Dietary treatments consisted of increasing EOB levels (0, 200, 400, and 600 ppm). Pigs were fed a commercial nursery program, formulated to meet or exceed the nutrient requirements of the NRC (National Research Council) (2012).

From day 0 to 21, pigs fed increasing levels of EOB improved (linear, P < 0.030) ADG and feed efficiency, with marginally (linear, P = 0.079) higher ADFI.

From d 21 to 43, feed efficiency was improved (linear, P = 0.001).

Overall (d 0 to 43), pigs fed increasing levels of EOB improved ADG (linear, P = 0.030, Figure 1), feed efficiency (quadratic, P = 0.040, Figure 2), and final BW (quadratic, P = 0.050). Furthermore, removals tended (linear, P = 0.057) to decrease as EOB inclusion increased.

Full value pigs by the end of the nursery, numerically (linear, P = 0.112, Figure 3) increased by >2% for pigs fed increasing levels of EOB compared to the control.

Following observed EOB benefits on health outcomes, a follow-up study was conducted using nursery pigs naturally infected with PRRS (Porcine Reproductive and Respiratory Syndrome) from the sow farm.

Due to several abortions and death losses, the farrowing sow group was reduced, resulting in pigs being weaned at an older age.

Upon arrival at the nursery, pigs averaged 18.0 lb and tested positive for PRRS with a Ct (cycle threshold) value of 23.2, indicating a high viral load. Pigs were placed in pens of 28 pigs each and allotted to one to four dietary treatments with nine replicates per treatment.

Treatments for this consisted of 1) control, 2) control + mannan-rich fraction (MRF is a proprietary technology of Alltech, Inc.), 3) control + EOB at 400 ppm, and 4) control + MRF + EOB.

Experimental diets were fed for the first 19 days post-weaning, followed by a common diet for all pigs. Although the overall growth performance did not differ among treatments (P > 0.10), total mortality (and therefore full-value pigs) showed an interesting response.

Pigs fed EOB had numerically lower mortality than pigs fed the control diet (1.14% vs 2.65%, P = 0.130, Figure 4).

Notably, most mortality occurred later in the trial while the pigs were receiving the common diet.

This data suggests a potential carryover protective effect in pigs challenged with PRRS and common secondary diseases.

The consistency of the nursery research described above, together with additional internal nursery evaluations, supports evaluating the EOB during the grow-finish period, where most of the feed cost in pig production resides.

In a study conducted in the EU, 1,024 pigs (49 lb initial BW (body weight)) were placed in pens with 16 pigs each and allotted to one to four dietary treatments with 16 replicates per treatment.

Treatments for this consisted of 1) control diet, 2) control diet + EU EOB (100 ppm), 3) control diet + US EOB (100 ppm), 4) control diet + US EOB (200 ppm).

The EU and US EOB versions were highly similar, with minor composition differences to comply with regional regulations.

Over 114 days, no differences were observed for ADG or ADFI (P > 0.10). However, the combination of numerically greater gain and lower intake resulted in a tendency (P = 0.056, Figure 5) for improved feed efficiency in pigs fed the EOB at any inclusion level or version compared with control pigs. This response corresponds to an estimated 10 lb/pig reduction in feed use over the study period. In an economic analysis, the US EOB at 100 ppm yielded a 2.96 ROI.

A key question was whether the EOB response could be replicated in a second grow-finish study in the US.

To address this issue, 2,171 pigs (85.5 lb initial BW) were placed 22 per pen and allotted to one of six dietary treatments with 16 replicates per treatment.

Treatments consisted of 1) negative control (no feed additives), 2) positive control (200 ppm copper as TBCC), 3–4) two pilot technologies unrelated to EOB, 5) EOB (100 ppm), and 6) EOB (200 ppm).

Although the differences were not statistically significant (P = 0.301), pigs that were fed 100 ppm EOB or high copper were numerically 1 lb heavier at the end of the trial compared with pigs fed the negative control and other treatments.

From a health perspective, a tendency (P = 0.058, Figure 6) for greater full value pigs was observed, with pigs fed 100 ppm EOB having greater survivability than control, technology A, and EOB 200 ppm pigs, with high copper and technology B being intermediate.

In an economic analysis, 100 ppm EOB generated a 2.89 ROI relative to the negative control and was more cost-effective than increasing copper inclusion in the grow-finish phase.

Across four controlled evaluations in nursery and grow-finish pigs, Olerix demonstrated consistent value through improvements in feed efficiency, throughput, and, in most cases, survivability-related outcomes.

Given that variability is one of the main concerns when adopting feed additives in diet programs, this level of consistency is particularly relevant.

Collectively, these results support positioning Olerix as a reliable nutritional tool in pig production, delivering measurable improvements in feed efficiency, full-value pigs, and return on investment.

References

Burt, S. Essential oils: Their antibacterial properties and potential applications in foods—A review. International Journal of Food Microbiology. 2004, 94, 223–253.

Rao Z.X., Tokach M.D., Woodworth J.C., DeRouchey J.M., Goodband R.D., and Gebhardt J.T. Effects of Various Feed Additives on Finishing Pig Growth Performance and Carcass Characteristics: A Review. Animals (Basel). 2023.13(2):200.

Soto J.A., Hart M.D., Cemin H.S., Faccin J.E.G., Hansen S.A., and Hansen E.L. Evaluation of a novel essential oil blend in nursery pig performance and health outcomes. Journal of Animal Science (Abs). 2026.

Zhai H.; Liu H.; Wang S.; Wu J.; Kluenter A.M. Potential of essential oils for poultry and pigs. Animal Nutrition, 2018, 4, 179–186.

Morgan Hart
Hubbard Feeds

Morgan Hart is a Swine Nutritionist for the Swine Technical Team at Hubbard Feeds, an Alltech company.

Dr. Jamil Elias Ghiggi Faccin
Alltech

Dr. Jamil Elias Ghiggi Faccin is a Pig Technical and Nutrition Specialist at Alltech.