Rumensin-Free Milk – More Smoke and Mirrors

Marcela Martinez, Graduate Student
Gabriella Varga, Ph.D., Distinguished Professor
Department of Dairy and Animal Science
Penn State University

Introduction by Terry Etherton

In the talks I have been giving across the United States about the importance of biotechnology in animal agriculture, I have a slide with a list of technologies beyond rbST use that likely will be attacked. This is not based on the scientific evidence but rather is driven by the smoke and mirrors milk-marketing campaigns that differentiate milk in the grocery store by the use of “absence claims” on the label.

These absence claims are deceptive, misleading, and are designed to convey to consumers that conventional milk contains antibiotics, pesticides, etc. As I have written about extensively in my Blogs, this is not true!

Well, we can strike rumensin off my list since a small dairy in Washington (Sno-Fresh) is now selling milk with the label: “Free of Antibiotics, Rumensin, and rbST”. This defies logic.

For facts about what rumensin is, and that use in the dairy industry is FDA-approved and safe, read the Blog below written by Ms. Martinez and Dr. Varga. It is great!


Monensin sodium (Rumensin) is an ionophore that has obtained considerable success as a feed additive in the poultry, beef and recently in the dairy industries. Rumensin was first approved by the Food and Drug Administration (FDA) in 1971 for control of coccidiosis in broilers. On December 16, 1975, monensin was registered with the commercial name of Rumensin (Elanco Products Co., a division of Eli-Lilly, Indianapolis, IN) to improve feed efficiency in beef cattle (Tedeschi et al., 2003). In June 1996, Canada allowed the use of rumensin premix for lactating cows for coccidiosis control and in December 1997, a rumensin controlled released capsule (CRC) was approved to aid in the prevention of subclinical ketosis in dairy cattle (Duffield and Bagg, 2000). In October 2004, the FDA approved the use of rumensin in the United States to increase milk production efficiency in dairy cows (FDA, 2004). Before the approval of rumensin for dairy cows, this feed additive has been widely used in feedlots in U.S. to improve feed efficiency. Since its first introduction, rumensin has been widely used in the poultry, beef and recently in the dairy industry to improve animal health and performance. The use of rumensin reduces the incidence of illness in food animals which can help increase the safety of animal products for human consumption.

Ionophores are potent antimicrobial compounds that have the capacity to alter ruminal bacteria reducing the incidence of health issues related to the ruminal fermentation (e.g., bloat). Ionophores specifically target the ruminal bacterial population and they are not used in human medicine. Because of the complexity and high degree of specificity of ionophores, it appears that ionophores do not contribute to the development of antibiotic resistance to important human drugs. In recent years there has been concern about the use of antibiotics in animal feeds. This concern is based on the idea that animals fed antibiotics often have more antibiotic-resistant bacteria than those not fed antibiotics and that resistance can be transferred to other pathogens (Russell and Mantovani, 2002). It appears that ionophores do not promote the development of antibiotic resistance because of their complex nature and high degree of specificity.

The evaluation of human food safety is a meticulous process before a new drug is approved for food animals by the FDA. Toxicology data and residues of the drug are main factors evaluated before a new drug is approved for use in food animals. By doing this, consumers can consume products from animals that have been treated or received drugs approved by the FDA with confidence that the animal product is safe.

Bagg et al. (2005) fed 24, 72, 144, and 240 ppm rumensin to Holstein dairy cows and milk was evaluated for residues. Considering 24 ppm of rumensin as the recommended dose in dairy cows, this study evaluated 10 times this dose. The results from this study showed that there were no detectable rumensin residues (< 0.005 μg/mL) in any of the milk samples collected despite the use of highly sensitive assays. Results of this study confirm that food products derived from lactating dairy cattle receiving rumensin at recommended levels are safe for human consumption. Other studies (Dick et al., 1996 and Wilkinson et al., 1997) have also evaluated the presence of rumensin residues and none were found in milk.

Donoho and Kline (1968) measured rumensin at zero withdrawal in chickens provided rumensin and no detectable residues (less than 0.025 ppm) were observed in muscle, liver and kidney. Fat contained 0.05-0.1 ppm at zero withdrawal but after one day withdrawal no detectable residues were observed. Same results were also observed by Okada et al. (1980) when chickens were fed the highest level of rumensin recommended and no detectable residues of rumensin were observed (less than 0.0125 ppm) in edible tissues after 2 days of withdrawal from rumensin. In 1982, Donoho et al. fed chickens with 14C-rumensin at a concentration of 110 g/ ton of feed for 4 to 6 d and found a rumensin concentration of radioactivity of 0.5 ppm in the liver, and less than 0.2 ppm in muscle, kidney and skin. Rumensin concentration in tissues declined with time and after 1-day withdrawal no rumensin residues (detection level of 0.05 ppm) were detected in fat or liver.

The Food and Drug Administration stated that meat and milk derived from dairy cattle fed rumensin are safe when animals are fed according to the approved label. Residue information in edible tissues from treated dairy cows confirmed the applicability of the zero withdrawal period already established for rumensin in beef cattle. Since rumensin is extensively metabolized, FDA waived the requirement to develop a regulatory method to detect residues in milk and meat from rumensin treated animals. Extensive chemistry and toxicology data have been developed to support the safe use of rumensin in cattle relative to residues in meat and milk. Based on toxicology and residue data, pre-slaughter withdrawal is not required for rumensin by the FDA. Therefore, it can be said that any small quantity of residual rumensin in food would not cause any adverse effects in humans. Scientific data indicate that meat and milk produced from animals treated with rumensin are safe for human consumption (Ipharraguerre and Clark, 2003).

An assessment was presented on the effects of rumensin residues present in edible tissues of cattle fed at the proposed upper level dose, on human intestinal flora. It was concluded that the amount of active rumensin residues present in the human colon is probably too low to produce any adverse effects on the human intestinal flora.

In conclusion, the safety of food products derived from lactating dairy cattle receiving rumensin at recommended levels for human consumption are safe and the consumer does not need to worry about health issues. Milk labels with claims of being rumensin-free need to be evaluated carefully by the consumers considering the scientific facts which prove that rumensin residues are not present in milk.


Bagg, R., G. H. Vessie, C. P. Dick, T. Duffield, J. B. Wilson, and J. J. Aramini. 2005. Milk residues and performance of lactating dairy cows administered high doses of Rumensin. Can J Vet Res. 69(3): 180–185.

Callaway, T. R., T. S. Edrington, J. L. Rychlik, K. J. Genovese, T. L. Poole, Y. S. Jung, K. M. Bischoff, R. C. Anderson and D. J. Nisbet. 2003. Ionphores: their use as ruminant growth promotants and impact of foof safety. Curr Issues Intest Microbiol. 2:43-51.

Dick, C. P., G. V. Vessie, J. W. Moran, and M. Coleman. 1996. The determination of Rumensin residues in cattle following the administration of two Rumensin controlled release capsules. Proceedings of the World Buiatrics Congress, Edinburgh. 254.

Donoho, A. L. and R. M. Kline. 1968. Antimicrobial agents and chemotherapy. American Society for Microbiology. Ann Arbor, MI. P. 763.

Duffield, T. F. and R. N. Bagg. 2000. Use of ionophores in lactating dairy cattle: A review. Canad. Vet. J. 41:388-394.

FDA. 2004. Monensin Sodium. In code of Federal Regulations, Section 21 CFR 558.335. p 68783. Revised November 26, 2004. Approved October 28, 2004 – Food and Drug Administration., Washington.

Ipharraguerre I. R. and J. H. Clark. 2003. Usefulness of ionophores for lactating dairy cows: a review. Animal feed and science technology. 106: 39-57.

Okada, J., I. Higuchi, and S. Kondo. 1980. Shokuhin Eiseigaku Zassahi. 21. P. 177.

Russell, J.B. and H. C. Mantovani. 2002. The bacteriocins of ruminal bacteria and their potential as an alternative to antibiotics. J. Mol. Microbiol. Biotechnol. 4:347–3

Tedeschi, L. O., D. G. Fox, and T. P. Tylutki. 2003. Potential environmental benefits of ionophores in ruminant diets. J Environ. Qual. 32:1591-1602.

Wilkinson, J. I. D., A. S. Kennington, K. M. Ehrenfried, J. W. Moran,and J. M. Buck. 1997. Human food safety with the use of Rumensin in lactating cows. In: Usefulness of Ionophores in Lactating Dairy Cattle. Proceedings of Symposium June 25 to 26, University of Guelph. 86.

Leave a Reply

Your email address will not be published. Required fields are marked *