National Organic Standards Board 

Livestock Subcommittee Petitioned Material Proposal 

Fenbendazole 

July 21, 2020 

Summary of Petition: 

In July 2019, the NOSB received a petition requesting a revision to the annotation at 7 CFR §205.603 

(23)(i) to include the use of Fenbendazole for laying hens and replacement chickens intended to become 

laying hens. 

The targeted organisms of Fenbendazole are the parasitic roundworms Ascaridia galli and Heterakis 

gallinarum. Chickens infected with A. galli and H. gallinarum become unthrifty, weak and emaciated and 

exhibit weight loss proportional to the parasite load. Young birds are more susceptible to the parasites 

than are mature hens, but mature hens will exhibit significant loss of egg production when infected with 

A. galli and H. gallinarum. 

Histomoniasis, also known as Blackhead Disease, is a disease caused by infection with Histomonas 

meleagridis. The disease was named “blackhead disease” because one of the common symptoms 

observed in infected birds is a bluish or blackish appearance of the skin on their face, comb and wattles. 

The discoloration occurs because of excessive concentration of reduced hemoglobin in the blood or 

cyanosis. Flocks of laying hens frequently are infected during the late summer and fall, following heavy 

rainfall. This is due to the association of earthworms, who commonly surface from the soil after heavy 

rains. If the chickens eat earthworms which carry the cecal worm, Heterakis gallinarum, they will 

indirectly become infected themselves. 

Fenbendazole is an antiparasitic drug that works at the sub-cellular level preventing cell division. 

Benzimidazoles bind to the β-tubulin, inhibiting the cell’s microtubule assembly responsible for 

intracellular transport and required for mitotic cellular division. (McKellar and Scott 1990). In effect, it 

starves the parasite by causing intestinal cell disruption. Studies conducted by Sander and Schwarz 

1994; Yazwinski and Tucker 2008, Yazwinski et al, 2013, and Alvardo and Mozisek 2018 showed that the 

late-stage larvae and adult stages of A. galli and H. gallinarum treated with Fenbendazole showed 

significantly increased mortality, but hens treated with Flubendazole passed viable eggs that was not 

significantly decreased in numbers. According to the Merck Veterinary Manual, “The wide safety margin 

of benzimidazoles is due to their greater selective affinity for parasitic β-tubulin than for mammalian 

tissues.” (Merck, 2006) 

Fenbendazole was first approved in 1983 for use in cattle, including beef animals and dairy cows, as a 

treatment and control of several types of gastronomical worms, including: lungworms, stomach worms 

(brown stomach worm, barberpole worm and small stomach worm), and intestinal worms (hookworm, 

threadnecked intestinal worm, small intestinal worm, bankrupt worm, and nodular worm). 

A request was submitted to FDA by Ivervet, Inc. to expand the use of Fenbendazole to chickens. The FDA 

determined that the ADI (Acceptable Daily Intake) in humans is 40 ug/kg of body weight per day and the 

tolerance for Fenbendazole is 1.8 ppm expressed as the metabolite fenbendazole sulfone. In October 

2015, the FDA gave formal approval for the use of Fenbendazole in treatment and control of adult A. 

galli in broiler chickens and replacement chickens intended to become breeding chickens and for the 

treatment and control of adult A. galli and H. gallinarum in breeding chickens. The FDA allowed a total 

of 2.4 ppm residual of Fenbendazole in eggs with no withdrawal time from application. 

On January 15, 2018, the approval was extended for the use of Fenbendazole under the trade name of 

AquaSol for the treatment and control of adult A. galli in broiler chickens and replacement chickens and 

for the treatment and control of adult A. galli and H. gallinarum in breeding chickens and laying hens. 

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Fenbendazole was approved to be administered to conventional laying hens and replacement hens at 

the following rates: 

• 200 mg of fenbendazole/ml for oral administration via drinking water 

• Safe-Guard® AquaSol must be administered orally to chickens via the drinking water at a daily 

dose of 1.0 mg/kg BW (0.454 mg/lb.) for 5 consecutive days. 

Conventional poultry producers typically administer Fenbendazole to pullets (age 17 weeks of age) or 

before outdoor access is given to birds to ensure birds have no internal parasites before starting egg 

production. When birds receive access to the outdoors they come into contact with soil and in turn 

come into contact with internal parasites. Many producers find the need to re-treat their flocks after a 

period when birds have access to the soil and come into contact with many internal parasites. 

Organic Summary: 

In May 2012, Fenbendazole was added to the National List for use in organic livestock, as specified at 7 

CFR § 205.603: 

In 2016 the NOSB recommended that the annotation for Fenbendazole be amended to include the 

following: 

• That parasiticides continue to be prohibited in slaughter stock. 

• That the milk withholding period after treatment with fenbendazole be changed from 90 days to 

2 days for dairy cows, and 36 days for goats and sheep. 

• That fleece and wool from fiber bearing animals be allowed to be certified organic even if use of 

parasiticides was necessary at some time in the animal’s life. 

• That fenbendazole be allowed without written order of a veterinarian. 

On Jan 28, 2019: The NOP issued a final rule: 

Paragraph (a)(23)(i) is revised to read as follows: Fenbendazole (CAS #43210-67-9)—milk or milk 

products from a treated animal cannot be labeled as provided for in subpart D of this part for: 2 

days following treatment of cattle; 36 days following treatment of goats, sheep and other dairy 

species. 

In addition, paragraph (b)(2) of § 205.238(b) is revised and paragraph (b)(3) is added to

§ 205.238(b) as follows: (b)(2) Dairy animals, as allowed under § 205.603; and (b)(3) fiber bearing 

animals, as allowed under § 205.603. AMS has reviewed and agrees with the NOSB

recommendation that § 205.238(b) be amended to clarify its use of parasiticides for dairy animals

and for fiber bearing animals. 

In Spring 2018, the NOSB recommended clarifying “Emergency” for use of synthetic parasiticides in 

organic livestock production. The following language was recommended for a rule change: 

Emergency treatment to allow synthetic parasiticide use in livestock: A livestock emergency is an 

urgent, non-routine situation in which the organic system plan’s preventive measures and veterinary 

biologics are proven, by laboratory analysis or visual inspection, to be inadequate to prevent lifethreatening illness or to alleviate pain and suffering. In such cases, a producer must administer the 

emergency treatment (§205.238(c)(7)). Organic certification will be retained, provided that such 

treatments are allowed under § 205.603 and the organic system plan is changed to prevent a 

similar livestock emergency in individual animals or the whole herd/flock in future years as required 

under §205.238(a).

Add this to § 205.238 (b)(4) Organic livestock as provided in §205.238 (b) (1), (2), and (3) and only in

the event of an emergency where management strategies have been proven insufficient to prevent 

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or control parasites within the accepted threshold for specific parasites, age and species of the 

animal. These management strategies include but are not limited to, grazing systems and living 

conditions that prevent infestation and re-infestation, forage height diversity, use of allowed nonsynthetic botanicals, biologics and minerals to maintain parasite levels below treatment thresholds, 

and could include monitoring and documentation of parasites through use of methods such as fecal 

monitoring and FAMACHA.

(23) Parasiticides—prohibited in slaughter stock, allowed in emergency treatment for dairy and 

breeder stock when organic system plan-approved preventive management does not prevent 

infestation. In breeder stock, treatment cannot occur during the last third of gestation if the 

progeny will be sold as organic and must not be used during the lactation period for breeding stock. 

Allowed for fiber bearing animals when used a minimum of 36 days prior to harvesting of fleece or 

wool that is to be sold, labeled, or represented as organic. 

(i) Fenbendazole (CAS #43210-67-9)—milk or milk products from a treated animal cannot be labeled 

as provided for in subpart D of this part for: 2 days following treatment of cattle; 36 days following 

treatment of goats, sheep, and other dairy species. 

In Fall 2019, the NOSB Livestock Subcommittee reviewed the petition to expand the annotation to allow 

Fenbendazole for use on laying hens and replacement chickens intended to become laying hens and 

submitted a discussion paper at the Fall 2019 NOSB meeting. Based on public comments from the Fall 

2019 NOSB meeting, the Subcommittee requested a technical report (TR) limited specifically to the use 

of Fenbendazole in laying hens and replacement chickens intended to become laying hens. The 

Livestock Subcommittee gave ten specific focused questions to the TR team concerning human health 

issues and regulatory issues, and asked the TR team to research any effective alternative methods to the 

use of Fenbendazole in controlling A galli and H. gallarinum worms in laying hens and replacement 

chickens intended to become laying hens. 

A second discussion paper was submitted by the NOSB in Spring 2020 to elicit more public comments on 

amending the 7 CFR 7 CFR §205.603 (23)(i) annotation to allow fenbendazole for use in laying hens and 

replacement chickens intended to become laying hens. 

Summary of Public Comments 

The NOSB Livestock Subcommittee received many public comments during the Fall 2019 and Spring 

2020 NOSB meetings. 

• Many of the public comments were focused on human health concerns resulting from the FDA 

allowance of 2.4 ppm residual of Fenbendazole in eggs when there is no withdrawal time. Some 

questioned the method that FDA used to determine the safety of the 2.4 ppm residual of 

Fenbendazole in eggs. One commenter was concerned that spent laying hens might end up being 

used for slaughter in soups, etc. That concern is not valid as the current annotation prohibits the 

livestock from being used as slaughter animals after treatment with Fenbendazole. 

• Some public commenters stated their concerns that the definition of “Emergency” had not been 

adopted by the NOP. They stated that without “Emergency” being adopted the use of Fenbendazole 

in laying hens and chickens intended to become laying hens was “ripe for fraud.” 

• Some commenters stated that “small producers with hens given more access to pastures” did not 

have problems with worms. Other producers countered by stating that the problems with worms 

being presence in hens and their eggs has significantly increased since producers had shifted their 

practices to meet the increased demand for eggs from hens with humane certifications for Free 

Range or Pasture Raised production models which requires 2.0-108.9 square feet per bird of 

outdoor access. When birds are out grazing, they are scratching and digging in the dirt for worms 

and in return picking up intestinal parasites. 

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• Certifiers and OTA took surveys of their poultry producers to determine if amending the annotation 

to allow use for laying hens would be of benefit to them. Results of the surveys suggested that the 

producers were experiencing issues with worms in eggs and that having the use of Fenbendazole on 

an emergency basis would be one more tool for them to utilize when needed. Other certifiers 

stated their clients were not having problems with worms in eggs. 

Technical Review Summary 

The TR addressed the specific questions asked by public commenters and the NOSB Livestock 

Subcommittee. 

• Health issues concerning the 2.4 ppm residual of Fenbendazole in eggs with no withdrawal 

period. The TR states that the ADI was established by the FDA based on extrapolation from 

adverse health effects found in a six-month oral toxicity study that fed Fenbendazole fed to 

laboratory dogs. Prior to the FDA’s 2018 approval of Fenbendazole for use in laying hens, the 

detection of any Fenbendazole residues in eggs was considered a violation (Marmulak et al. 2015). 

The TR found that infants and children are considered at a greater risk from exposure to veterinary 

drug residues than adults, because of their lower weight, growth and developmental stage which 

many risk assessment models do not include. The study also indicated increased risks to pregnant 

women and fetuses exposed to the drug (Boobis et al. 2017). In a study of food safety risks, 

Fenbendazole was rated as having a medium likelihood of occurrence (Bobkov and Zbinden 2018). 

In one human health study, five adult males were fed the equivalent of 2,500 eggs and 5,000 eggs 

respectively. There were no relevant changes in blood pressure, pulse rate, symptom list, selfrating scale, and clinical chemistry. (Rupp and Hajdu 1974, reported in Inchem 1998). 

Human trials were conducted in 1976 to determine whether Fenbendazole would be considered as 

treatment for human hookworms and pinworms. Fenbendazole was found to be effective with 

minor side effects of constipation and burning when urinating. Nevertheless, since that time 

Fenbendazole has not commonly been used to treat human infestations. 

Benzimidazoles (Fenbendazole) have been used as cancer chemotherapy agents and has been 

studied as a potential anti-cancer agent (Duan et al. 2013). Development of Fenbendazole is still in 

relatively early stages. Nothing was found in the scientific literature to suggest Fenbendazole 

residues in eggs would interfere with its use as a cancer treatment. 

• Fenbendazole Amounts in Eggs and Poultry 

The question was asked whether cooking eggs at the recommended cooking temperatures of 144-

158 F would eradicate the Fenbendazole residuals. The TR found that Fenbendazole fully degrades 

with peaks of 222.76 F, 447.24 F, 654.66 F and 862.07 F, all considerably higher than eggs are 

normally cooked for consumption. 

• Natural Alternatives to using Fenbendazole 

Organic livestock producers have historically and traditionally used a wide range of botanical and 

naturopathic remedies to control worms in poultry. One common natural remedy is the use of 

Diatomaceous Earth fed to the birds. The TR provided a table of several substances and 

methodologies historically used. Most but not all remedies are derived from plants commonly 

found in the U.S. The TR states that these remedies do not have efficacy or safety data on file with 

the FDA and are not labeled for internal use on animals. Many of these botanical remedies do not 

have scientific evidence of their efficacy and safety specifically to poultry internal parasites. At 

least one organic parasite management guide questions the scientific evidence supporting the 

efficacy of homeopathic remedies. 

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Studies show that sanitation of poultry runs is crucial. Pastures, yards and pens should be rotated 

frequently. It is not clear how long the rotation period in the runs is needed to break the parasitic 

cycle. Worm eggs may survive in pastures for over two years, and in some experiments, rotations 

did not significantly reduce infestation rates. Some studies indicated that DE could more 

effectively be applied to the litter as ovicides to prevent re-infestation of the parasites rather than 

fed in the poultry feed. The use of probiotics is showing some promise of helping eradicate the 

worm populations in poultry. 

The TR concludes that there is very little research looking at the effectiveness of the natural practices 

used by organic farmers to control worm populations. The efficacy and safety of these treatments are 

based largely on anecdotal information and not supported by peer-reviewed scientific research. 

Category 1: Classification 

1. Substance is for: _______ Handling ____X___ Livestock 

2. For HANDLING and LIVESTOCK use: 

a. Is the substance _______ Agricultural or ___X____ Non-Agricultural? 

Describe reasoning for this decision using NOP 5033-2 as a guide: 

b. If the substance is Non-agricultural, is the substance _____ Non-synthetic or __X__ 

Synthetic? 

c. Is the substance formulated or manufactured by a process that chemically changes a 

substance extracted from naturally occurring plant, animal, or mineral sources? [OFPA 

§6502(21)] If so, describe, using NOP 5033-1 as a guide: 

The manufacturing process for Fenbendazole was included in the March 2007 petition requesting 

the addition of Fenbendazole as an approved material under §205.603(a)(23)(i) of the National List. 

The Fenbendazole in AquaSol is now further processed whereby it is reduced in particle size to 

create a more stable suspension in drinking water. This further processing subjects the 

Fenbendazole to a wet-milling process whereby a 40 percent fenbendazole suspension is 

recirculated between a mixing vessel and wet-mill. Utilizing a rotating axis and milling beads, the 

wet-mill subjects the Fenbendazole particles to impaction and sheer forces, reducing the particle to 

a submicron size. Moreover, at the end of the manufacturing process Panacur AquaSol is a 20 

percent Fenbendazole suspension whereas Panacur Suspension 10% (Safe Guard in the US) is a 10 

percent suspension. 

3. For LIVESTOCK: Reference to appropriate OFPA category 

Is the substance used in production, and does it contain an active synthetic ingredient in the 

following categories: [§6517(c)(1)(B)(i)]; copper and sulfur compounds; toxins derived from bacteria; 

pheromones, soaps, horticultural oils, fish emulsions, treated seed, vitamins and minerals; livestock 

parasiticides and medicines and production aids including netting, tree wraps and seals, insect traps, 

sticky barriers, row covers, and equipment cleansers; or (ii) is used in production and contains 

synthetic inert ingredients that are not classified by the Administrator of the Environmental 

Protection Agency as inerts of toxicological concern? 

Fenbendazole is petitioned as a parasiticide. 

Category 2: Adverse Impacts 

1. What is the potential for the substance to have detrimental chemical interactions with other 

materials used in organic farming systems? [§6518(m)(1)] 

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Fenbendazole is insoluble in water and excreted after administration in feces. Because it is not 

soluble, there is little mobility of fenbendazole in soils, and a low risk of groundwater 

contamination. Laboratory tests show that radiolabeled fenbendazole is degraded with a halflife of 54 days. Although photo-degradation plays a role, degradation of fenbendazole in soil 

appears to be microbially dependent rather than photodegradative (Kreuzig et al., 2007). 

2. What is the toxicity and mode of action of the substance and of its breakdown products or any 

contaminants, and their persistence and areas of concentration in the environment? 

[§6518(m)(2)] 

Fenbendazole toxicity was demonstrated in pigeons and doves leading the authors of the study 

to suggest a toxic etiology for fenbendazole in birds of the order Columbiformes treatment 

(Howard et al., 2002). 

The fate of Fenbendazole in manure and manured soils has been studied under laboratory and 

field conditions. In pig manure, benzimidazoles disappear slowly. After a 102-day incubation 

period, 80% Fenbendazole remains. The latter was accompanied by 4% of the corresponding 

metabolite fenbendazole-sulfoxide. Fenbendazole-sulfoxide remains in clay soil samples after 54 

days (Kreuzig et al., 2007). 

Excreted Fenbendazole and Ivermectin residues in cattle dung pats do not significantly affect 

adult dung beetles or adult dipteran flies; however, excreted Ivermectin produces toxic effects 

on the larval development of the same dung-colonizing families of insects, while Fenbendazole 

lacks such toxic effects (Strong et al., 1995). 

Fenbendazole does not appear to hinder rapid disappearance and mineralization of cattle dung 

pats in pastures and does not appear to affect the role that earthworms play in this process. 

3. Describe the probability of environmental contamination during manufacture, use, misuse or 

disposal of such substance? [§6518(m)(3)] 

Fenbendazole is manufactured by a process that requires petrochemicals such as benzene and 

various amines. These are considered toxic compounds. 

4. Discuss the effect of the substance on human health. [§6517 (c)(1)(A)(i); §6517 (c)(2)(A)(i); 

§6518(m)(4)]. 

Fenbendazole is not generally considered toxic to humans at regulated doses (FDA, 1995). 

5. Discuss any effects the substance may have on biological and chemical interactions in the 

agroecosystem, including the physiological effects of the substance on soil organisms (including 

the salt index and solubility of the soil), crops and livestock. [§6518(m)(5)] 

Fenbendazole is insoluble in water, is not a leachate, binds tightly to soil and is not expected to 

migrate in soil. The only route for fenbendazole to enter the environment is through animal 

excretion or spillage. Fenbendazole degrades in soil through microbial and photodegradative 

processes, taking up to 60 days (Hoechst-Roussel Agrivet, 1995) 

6. Are there any adverse impacts on biodiversity? (§205.200) 

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Fenbendazole can break into albendazole. However, there is a low likelihood of physiologic 

effects. (pg 5 TAP) 

Category 3: Alternatives/Compatibility 

1. Are there alternatives to using the substance? Evaluate alternative practices as well as nonsynthetic and synthetic available materials. [§6518(m)(6)] 

While diatomaceous earth (DE) is utilized widely and effectively as a control for external 

parasites, its effectiveness as an internal control has not been reputably documented. 

Diatomaceous earth has no effect on lungworm and is not very appetizing to poultry. It may also 

be a lung irritant. Given that the level of dust is already quite high in barns, diatomaceous earth 

does not seem appropriate when the animals are fed indoors. The main motivation for adding 

diatomaceous earth to rations should not be to control internal parasites. 

2. For Livestock substances, and Nonsynthetic substances used in Handling: In balancing the 

responses to the criteria above, is the substance compatible with a system of sustainable 

agriculture? [§6518(m)(7)] 

Parasiticide use has been tolerated in organic livestock production on a limited basis to alleviate 

animal suffering. This has almost been, without exception, part of an integrated system of 

animal health management and requires documentation of a number of approaches other than 

intervention. 

National List Motion: 

Motion to amend the listing for fenbendazole to include: Fenbendazole-for use in laying hens or 

replacement chickens intended to be laying hens at 7 CFR §205.603 (23)(i). 

Motion by: Sue Baird 

Seconded by: Kimberly Huseman 

Yes: 4 No: 2 Abstain: 0 Absent: 0 Recuse: 0 

Approved by Sue Baird, Livestock Subcommittee Chair, to transmit to NOP July 22, 2020 

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