Fenbendazole for helminths in backyard chickens: do regimens vs no treatment clear faecal egg counts and improve condition? — POSSIBLE

In backyard chickens with helminth burdens, do fenbendazole regimens vs no treatment clear faecal egg counts and improve condition?

Shelf #977 · gate-verified and approved by the developer

POSSIBLE: Fenbendazole regimens reduce worm burdens and faecal/excreta egg counts in chickens compared with no treatment, and the one randomised trial in genuinely backyard chickens also found better growth in treated birds. In Katoch 2012 (PMID: 23543701; 100 growing backyard chickens in Jammu, India, randomly assigned 50/50 to fenbendazole 7.5 mg/kg in drinking water or no treatment, 90-day field trial), mean weight gain was 1,617.6 ± 5.43 g (18.0 g/day) in treated birds vs 1,232.2 ± 7.28 g (13.7 g/day) in untreated controls — 385.4 g more, a 31.3% relative higher gain — and mean worm burden was 2.46 ± 1.14 vs 32.92 ± 6.12 (P < 0.05), a 92.5% relative reduction; no faecal egg count figure is reported for its trial groups. In Feyera 2021 (PMID: 34271320; 108 Ascaridia galli-infected cockerels randomised to 9 groups of 12, including an untreated control), fenbendazole worm-count efficacy was 97.2% relative as a single oral drench at 10 mg/kg and 88.7% relative in drinking water at 5 mg/kg over 5 days, untreated controls harboured significantly higher worm counts than every treated group (P < 0.0001), and excreta egg count reductions were consistent with the worm-count figures. In Abdelqader 2012 (PMID: 22463876; 150 A. galli-infected Lohmann chicks randomly allocated to 5 groups), the fenbendazole 50 mg/kg positive-control arm was the most effective treatment, reducing A. galli burden by 97% relative efficacy against the untreated control group. In the other field record in domestic (backyard-type) fowl, Saemi 2021 (PMID: 33557928; native chickens in northern Iran, randomly divided into groups of 30, with a placebo control of water plus dimethylsulfoxide), fenbendazole 5 mg/kg for 3 days gave a faecal egg count reduction efficacy of 83.7% (geometric mean 100 eggs per gram) vs levamisole 71.8% (199.6 eggs per gram), but the abstract reports that efficacy figure with P ≥ 0.05, and Capillaria spp. were the most resistant nematodes. At flock level, Tarbiat 2016 (PMID: 27514895; commercial laying-hen flocks randomly allocated to targeted fenbendazole treatment (1 mg/kg for 5 days, repeated when pooled counts passed 200 eggs per gram), conventional treatment, or no treatment) found cumulative pooled faecal egg counts significantly lower in the targeted-treatment flocks than in untreated flocks (P < 0.01), with cloacal egg counts and adult A. galli numbers also significantly lower at 35 and 45 weeks post placement. Design class (b): randomised allocation is established by carded records answering the fenbendazole-vs-untreated comparison in chickens (Katoch 2012, Feyera 2021, Abdelqader 2012, Tarbiat 2016), but no carded record states blinding or masked assessment, so class (a) is not met. The stamp is POSSIBLE, not LIKELY, because the backyard evidence is a single 100-bird growth trial with no egg-count result, one field trial's headline efficacy was non-significant (P ≥ 0.05), and the remaining quantified trials are in experimental or commercial birds; and the condition evidence is confined to weight gain in growing birds — no carded record measures body condition score, laying performance or survival. Tier C is not engaged: no mortality or survival claim is made. One-home cross-points: shelf #48 (coccidiosis vaccination in backyard poultry) and shelf #974 (toltrazuril vs amprolium for chicken coccidiosis) concern a different parasite (coccidia, not helminths) and different interventions, and share no record with this shelf. Drafted Nov 10, 2026 (VetMed build, topic #977); figures from the abstracts, fetched and verified at drafting.

Katoch 2012: randomised field trial in backyard chickens — fenbendazole 7.5 mg/kg in water gave weight gain 1,617.6 g vs 1,232.2 g in untreated controls over 90 days, with worm burden 2.46 vs 32.92

Randomised field trial with untreated control (record states randomly assigned), blinding not stated (publication types: Journal Article)

Who: Chickens: growing backyard chickens in a subtropical humid zone of Jammu, India. One hundred growing chickens aged 40 days were randomly assigned to two groups of 50 — treated with fenbendazole at 7.5 mg/kg body weight in drinking water, or untreated controls — in a 90-day field trial. Background necropsy of 125 free-range chickens from the area found 72.0% helminth prevalence (Ascaridia galli most prevalent, then Heterakis gallinarum, Capillaria spp., Cheilospirura hamulosa and four cestode species). Blinding is not stated. This is the one carded record conducted in flocks its authors call backyard chickens.

Result: At the end of 90 days, mean body weight gain was 1,617.6 ± 5.43 g (18.0 g/day) in fenbendazole-treated birds vs 1,232.2 ± 7.28 g (13.7 g/day) in untreated controls — an absolute difference of 385.4 g, a 31.3% relative higher gain. Mean worm burden was significantly lower in treated birds (2.46 ± 1.14) than untreated controls (32.92 ± 6.12; P < 0.05), a 92.5% relative reduction. No faecal egg count figure is reported in the abstract for the trial groups.

Watch out: The only backyard-labelled carded record, and the only one measuring a condition outcome (weight gain in growing birds — not laying hens, body condition score or egg production). Worm burden is a mean count with wide variation in controls (± 6.12 on 32.92), the treated group's route was drinking water (the least reliable route in Feyera 2021), and no faecal egg count result is given for the trial, so this card supports burden and growth claims, not an egg-count percentage.

Katoch R, Yadav A, Godara R, Khajuria JK, Borkataki S, Sodhi SS. Prevalence and impact of gastrointestinal helminths on body weight gain in backyard chickens in subtropical and humid zone of Jammu, India. J Parasit Dis. 2012;36:49-52. PMID: 23543701. Registry ID: none in the record. MeSH: none in the record

Feyera 2021: randomised controlled trial — fenbendazole cleared 97.2% relative of Ascaridia galli worms as a 10 mg/kg oral drench and 88.7% relative in water (5 mg/kg over 5 days) vs untreated controls

Randomised controlled trial with untreated control, blinding not stated (publication types: Journal Article)

Who: Chickens: 108 cockerels experimentally infected with a field strain of Ascaridia galli, randomised into nine experimental groups of 12 (eight treatments and one untreated control), each drug given by oral drench or in drinking water. Fenbendazole was tested at 10 mg/kg as a single oral drench or 5 mg/kg in drinking water over 5 days; comparators were levamisole, piperazine and their combination at label doses. Blinding/masked assessment is not stated. These are experimental cockerels, not backyard hens.

Result: Ten days post treatment, untreated control birds harboured significantly higher worm counts (P < 0.0001) than all treatment groups. Based on geometric worm counts, percentage efficacies for the oral drench were 99.1% (levamisole), 96.3% (piperazine), 97.2% (fenbendazole) and 100% (combination), and for administration in water 96.4%, 93.7%, 88.7% (fenbendazole) and 97.7% respectively — all relative reductions against the untreated control burden. Excreta egg count reduction efficacies were consistent with the worm-count efficacies, with a strong positive linear association. Oral drenching caused a greater reduction in worm and egg counts than medication in drinking water (P < 0.05).

Watch out: A single parasite (A. galli), a single field isolate, experimentally infected young cockerels, and a 10-day endpoint — this does not measure other backyard helminths (Heterakis, Capillaria), reinfection over a season, or any condition outcome. In-water dosing was materially less effective (88.7% relative) than drenching the same drug.

Feyera T, Ruhnke I, Sharpe B, Elliott T, Shifaw A, Walkden-Brown SW. Comparative therapeutic efficacies of oral and in-water administered levamisole, piperazine and fenbendazole against experimental Ascaridia galli infection in chickens. Vet Parasitol. 2021;298:109514. PMID: 34271320. Registry ID: none in the record. MeSH: Animals · Anthelmintics*/therapeutic use · Ascaridia · Ascaridiasis*/drug therapy · Australia · Chickens · Feces · Fenbendazole*/therapeutic use · Levamisole/administration & dosage/therapeutic use · Male · Parasite Egg Count/veterinary · Piperazine/therapeutic use · Poultry Diseases*/drug therapy · Random Allocation · Treatment Outcome · Water/chemistry

Abdelqader 2012: in a randomised trial in infected chicks, the fenbendazole 50 mg/kg arm reduced Ascaridia galli burden by 97% relative efficacy — the best of any arm — vs untreated controls

Randomised controlled trial (publication type: Randomized Controlled Trial), blinding not stated; fenbendazole arm is the study's positive control

Who: Chickens: 200 one-day-old Lohmann Selected Leghorn chicks infected with 250 embryonated Ascaridia galli eggs; at 6 weeks of age 150 infected birds were randomly allocated into 5 equal groups — three citrus-peel extract doses (300, 600, 1200 mg/kg), fenbendazole 50 mg/kg as the positive-control treatment, and an untreated control group. Birds were euthanised 2 weeks post treatment and all intestinal worms collected. Blinding is not stated. (A parallel in vitro arm exposed 225 adult worms to fenbendazole, extract or vehicle.)

Result: Fenbendazole was the most effective treatment in reducing A. galli burden, with 97% relative efficacy against the control group, followed by the citrus extracts at 1200 mg/kg (68%), 600 mg/kg (66%) and 300 mg/kg (5%); the 600 and 1200 mg/kg extract groups showed significant worm-burden reductions vs controls (P < 0.0001), while the 300 mg/kg group did not differ significantly from controls. A significant reduction in faecal egg count was observed 14 days post treatment only in the 1200 mg/kg extract group (P < 0.0001) as reported; the abstract does not give a separate faecal egg count figure for the fenbendazole arm.

Watch out: Fenbendazole was this study's reference arm, not its experimental question, and the dose (50 mg/kg, single) is far above the regimens in the other carded records — do not read it as a recommended backyard dose. Experimentally infected commercial-hybrid chicks, worm burden at necropsy only, and no faecal-egg figure reported for the fenbendazole arm in the abstract.

Abdelqader A, Qarallah B, Al-Ramamneh D, Daş G. Anthelmintic effects of citrus peels ethanolic extracts against Ascaridia galli. Vet Parasitol. 2012;188:78-84. PMID: 22463876. Registry ID: none in the record. MeSH: Animals · Anthelmintics/pharmacology* · Ascaridia/drug effects* · Ascaridiasis/drug therapy/parasitology/veterinary · Chickens · Citrus/chemistry* · Ethanol/chemistry* · Fruit/chemistry · Plant Extracts/chemistry/pharmacology* · Poultry Diseases/parasitology/prevention & control*

Saemi 2021: field trial in native (backyard-type) fowl — fenbendazole 5 mg/kg for 3 days gave 83.7% relative faecal egg count reduction efficacy, but at P ≥ 0.05; Capillaria was the most resistant genus

Field faecal egg count reduction trial with placebo control and random division, blinding not stated (publication types: Journal Article)

Who: Chickens: domestic native fowl in northern Iran. Of 45 domestic flocks, 20 were selected for faecal egg count reduction testing (April 2017-September 2018); infected chickens were randomly divided into three equal groups of 30 — fenbendazole 5 mg/kg body weight for 3 consecutive days, levamisole 16 mg/kg, or placebo control (water plus dimethylsulfoxide). In control-group flocks examined, 95.0% of birds were infected with gastrointestinal nematodes, with a geometric mean of 361 eggs per gram of faeces. Blinding is not stated.

Result: Fenbendazole showed a faecal egg count reduction efficacy of 83.7% (relative), with a geometric mean of 100 eggs per gram after treatment, and levamisole 71.8% relative efficacy (geometric mean 199.6 eggs per gram); the abstract attaches P ≥ 0.05 to both efficacy figures and states the fenbendazole-levamisole difference was not significant, while also stating both treatments led to significantly lower activity (the abstract's wording). Capillaria spp. were the most generally resistant nematodes, followed by Trichostrongylus spp. and Amidostomum anseris. The authors conclude fenbendazole was the better dewormer in these flocks but that resistance can be expected in poultry helminths.

Watch out: The closest record to backyard practice (native domestic fowl), yet its headline efficacy is reported with P ≥ 0.05 — treat 83.7% as a point estimate from a small field trial, not a proven flock-level effect, and note the abstract's internal tension between 'P ≥ 0.05' and 'significantly lower activity'. Mixed natural nematode burdens, not a single-species infection, and no condition or production outcome was measured.

Saemi Soudkolaei A, Kalidari GA, Borji H. Anthelmintic efficacy of fenbendazole and levamisole in native fowl in northern Iran. Parasit Vectors. 2021;14:104. PMID: 33557928. Registry ID: none in the record. MeSH: Animals · Anthelmintics/therapeutic use* · Drug Resistance · Feces/parasitology* · Fenbendazole/therapeutic use* · Iran · Levamisole/therapeutic use* · Parasite Egg Count · Poultry/parasitology* · Poultry Diseases/drug therapy*/parasitology

Tarbiat 2016: randomly allocated layer flocks — targeted fenbendazole treatment kept cumulative faecal egg counts significantly below untreated flocks (P < 0.01) and lowered adult Ascaridia burdens

Randomised flock-level treatment-strategy trial with untreated control (publication type: Randomized Controlled Trial), blinding not stated

Who: Chickens: commercial laying-hen flocks of two hybrids on a Swedish commercial farm, randomly allocated to targeted treatment (fenbendazole 1 mg/kg body weight for 5 days, started at 22 weeks post placement and repeated twice when pooled faecal egg counts passed the 200 eggs-per-gram threshold), conventional treatment (one fenbendazole treatment at 27 weeks), or untreated control. Pooled faecal egg counts were taken every second week; cloacal counts, worm fecundity and worm burdens were measured at 19, 35 and 45 weeks post placement. Blinding is not stated; these are commercial layers, not backyard flocks.

Result: No flock became infected until after 16 weeks post placement. Cumulative pooled faecal egg counts at the end of the study were significantly lower in targeted-treatment flocks than in both conventional-treatment and untreated flocks (P < 0.01); the abstract gives no egg-count values or percentage reduction. Cloacal faecal egg counts and the number of adult Ascaridia galli in targeted-treatment flocks at 35 and 45 weeks were significantly lower than in the other flocks. Repeated targeted treatment did not affect worm fecundity, though a worm density-dependent increase in fecundity was observed.

Watch out: A strategy comparison (when to treat) at flock level in commercial layers, not an individual-bird efficacy trial in backyard hens, and its abstract reports significance without egg-count numbers. Its untreated arm is what makes it eligible here; its fenbendazole dose (1 mg/kg for 5 days) is the lowest regimen among the carded records.

Tarbiat B, Jansson DS, Tydén E, Höglund J. Comparison between anthelmintic treatment strategies against Ascaridia galli in commercial laying hens. Vet Parasitol. 2016;226:109-15. PMID: 27514895. Registry ID: none in the record. MeSH: Animals · Anthelmintics/administration & dosage/pharmacology/therapeutic use* · Ascaridia/drug effects*/physiology · Ascaridiasis/drug therapy/parasitology/veterinary* · Chickens/parasitology* · Cloaca/parasitology · Feces/parasitology · Female · Fertility/drug effects · Intestines/parasitology · Male · Parasite Egg Count/veterinary · Poultry Diseases/drug therapy*/parasitology

Synthesis: fenbendazole cuts worm burdens by about 89-97% relative in controlled chicken trials, lowered flock egg counts vs untreated, and improved weight gain in the one randomised backyard trial — POSSIBLE

Synthesis

Who: Synthesis of the five cards above (Katoch 2012, 100 backyard growing chickens; Feyera 2021, 108 cockerels; Abdelqader 2012, 150 chicks; Saemi 2021, 90 native fowl in 3 groups from 20 flocks; Tarbiat 2016, commercial layer flocks) and of the near-miss records documented in the result, fetched at drafting and deliberately not carded as claim-carriers.

Result: (1) Worm/egg clearance: three randomised records with untreated controls agree on large relative reductions — 97.2% worm-count efficacy for a 10 mg/kg drench and 88.7% in water (Feyera 2021), 97% burden efficacy at 50 mg/kg (Abdelqader 2012), a 92.5% relative lower mean worm burden in backyard birds (2.46 vs 32.92, Katoch 2012), and significantly lower cumulative flock egg counts under targeted treatment (Tarbiat 2016); the one other field trial in backyard-type native fowl found a smaller, non-significant 83.7% relative egg-count efficacy, with Capillaria the most resistant genus (Saemi 2021). (2) Condition: exactly one carded record measures a condition outcome — Katoch 2012, in growing backyard chickens, found 385.4 g more weight gain over 90 days in treated birds (1,617.6 vs 1,232.2 g); no carded record measures body condition score, laying performance or survival, so condition claims rest on that single growth result. (3) Near-misses not carded: Feyera 2022 (PMID: 35431079; 229 free-range layers) found fenbendazole 10 mg/kg attained the ≥90% desired efficacy cut-off by worm and egg count reduction, but its design compared anthelmintics with no untreated control group described, so it is cross-pointed, not carded; Ssenyonga 1982 (PMID: 6750887; Uganda poultry) reported faeces became egg-negative by day 7 after the last fenbendazole feed treatment and 100% efficacy against Ascaridia galli and Heterakis gallinarum at 10 mg/kg at post-mortem, but no control group is described in its abstract; Taylor 1993 (PMID: 8310628) compared two in-feed fenbendazole dose rates for Capillaria in breeder hens (efficacies 92.3% and 99.3%) with no untreated arm. (4) Design class (b): randomisation established, blinding not established in any carded record. One-home check at drafting: none of PMIDs 23543701, 33557928, 34271320, 27514895, 22463876, 35431079, 6750887 or 8310628 appears in any other pack on disk; shelves #48 and #974 are coccidiosis questions (different parasite) and share no record with this shelf.

Watch out: All relative efficacies are reductions against untreated control burdens or egg counts in the same study — they are not cure proportions for an individual backyard hen, and in-water or in-feed administration, mixed Capillaria burdens, and reinfection from range litter will all pull field performance below the drench-trial figures. The condition evidence is a single weight-gain result in growing birds; do not extend it to laying performance, body condition score or survival in adult backyard hens.

Synthesis of Saemi Soudkolaei A et al. PMID: 33557928; Feyera T et al. PMID: 34271320; Tarbiat B et al. PMID: 27514895; Abdelqader A et al. PMID: 22463876; Feyera T et al. PMID: 35431079. Registry IDs as on the individual cards (none in the records).

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