Abstract

In the spring of 2006, 60 naturally infected hens obtained from a broiler-breeder farm in northwest Arkansas were used in a controlled titration study to determine the anthelmintic efficacy of albendazole in the treatment of both nematode and cestode infections. Albendazole was used at the dose rates of 0.0, 5.0, 10.0, and 20.0 mg/kg of BW, with all treatments given individually as an oral suspension on d 0 (split doses) and with necropsies for parasite collection conducted on d 7. There were 15 birds per treatment group. Statistically significant (P < 0.05) reductions in worm burdens from control levels were seen at the 5.0 mg/kg dose level for adult and larval stages of Ascaridia galli, Heterakis gallinarum, and Capillaria obsignata. A significant (P < 0.05) reduction in the numbers of Raillietina cesticillus (scolexes) from control group levels was seen only at the 20.0 mg/kg rate of treatment. For albendazole given at the rates of 5.0, 10.0, and 20.0 mg/kg, respective anthelmintic efficacies based on geometric means were 87.7, 91.2, and 98.2% (A. galli larvae); 100.0, 100.0, and 100.0% (A. galli adults); 96.9, 95.7, and 98.9% (H. gallinarum larvae); 92.7, 95.4, and 94.9% (H. gallinarum adults); 90.3, 91.3, and 95.1% (C. obsignata larvae and adults combined); and 73.1, 73.1, and 96.2% (R. cesticillus). No adverse reactions to albendazole were observed in this study.

Primary Audience: Flock Supervisors, Production Managers, Veterinarians

DESCRIPTION OF PROBLEM

Helminth infections of commercial chickens in the United States are greatly influenced in magnitude and incidence by management, bird age, production type, housing, and degree of effective veterinary or health-oriented intervention. Chemical intervention for nematode infections is conducted when the infections are diagnosed and deemed to be of a magnitude that may have economic implications, or when treatment is part of an existing program designed to prevent the emergence of significant nematodiasis. Cestode infections are invariably assessed as incidental, light, and warranting little concern, a fortunate consideration in light of the fact that no commercial product is available that provides both effective and economically feasible cestoci-dal activity.

Anthelmintic intervention in chickens is conducted either with piperazine or on a prescription basis with levamisole [1] or oxfendazole [2], with medication provided through the drinking system. Dose rates and durations used for these products have been sporadically reported in piecemeal fashion [3, 4, 5, 6, 7, 8, 9] or as the result of poultry company in-house appreciations of drug efficacies and worm burden sig-nificance. The current study was conducted to provide controlled study findings on the anthelmintic efficacy of albendazole for use in chickens, data that might serve to indicate the spectrum of activity and effective dose rates of alben-dazole for the off-label, veterinarian-prescribed treatment of chickens for the more common helminth parasitisms.

MATERIALS AND METHODS

Birds

All birds were obtained as adult hens from a northwest Arkansas broiler-breeder farm and scheduled for depopulation within the week. Birds were approximately 1 yr of age at acquisition. Although no exact history of prior treatment of the study birds could be obtained, it was certain that no benzimidazoles had been given the birds during their farm tenure. Prior to bird acquisition, infection status of the flock was determined by the necropsy and helminth quanti-fication of 3 randomly selected birds.

Study Schedule

Birds were obtained on d 7 prior to treatment on d 0 and acclimated at the research facility under housing, maintenance, and feeding conditions that prevailed for study birds until eventual necropsy. On d 0, birds were randomly allocated to treatment groups, penned according to treatment group, and treated accordingly. On d 7, all birds were euthanized for necropsy and parasite collection. Birds were weighed twice on d 0 (for the split-treatment doses) and once on d 6.

Bird Maintenance

For the entire study period, including necropsy, all birds were maintained according to procedures reviewed by the University Animal Use and Welfare Committee. Birds were housed in pens that were 7 × 15 ft, concrete floored with new shavings, and wire sided, at a density of 1 bird per 7 ft2 of floor space. Lighting was continuous, temperature was maintained at 75°F, feed and water were provided ad libitum, and forced-air ventilation was in operation throughout the trial.

Experimental Treatments

There were 4 treatment groups with 15 birds per group (N compatible with World Association for the Advancement of Veterinary Parasitology guidelines requiring a minimum of 6 infected birds per treatment group on d 0). The treatment groups were albendazole (Valbazen) [10], delivered individually as a drench, at the rates of 0.0 (control group), 5.0, 10.0, and 20.0 mg/kg of BW. On d 0, each bird was weighed in the morning, given one-half of its calculated dose, and placed into its treatment group-specific pen. The above procedure was repeated in the afternoon (approximately 6 h after the morning treatment). This was to provide precise individual bird treatments and at the same time approximate daylong, in-water treatments that would be used in a commercial setting.

Parasite Recovery

Procedures used for parasite recovery were according to standard laboratory procedures as outlined in the World Association for the Advancement of Veterinary Parasitology guidelines for anthelmintic evaluation in poultry [11]. On d 7, all birds were euthanized by cervical dislocation and their intact intestines removed from the gizzard to the vent. Each intestine was cleaned of all mesentery and then opened lengthwise. Total contents and wash were collected and formalinized. Each intestine was then placed in water and refrigerated overnight before a final washing. All liquid from this soak and final wash was rinsed over a number 120 sieve (aperture of 125 μm) and the residue formalinized. Thus, from each bird the total contents and total soak were collected. With appropriate sieving, residue collection, and visual inspection, 80% of all collected material was inspected for adult Ascaridia galli. With appropriate sieving, residue collection, and stereoscopic examination of all residue, the remaining 20% of the collected material from each bird was inspected for all helminths and stages thereof. Counts reported herein are the sums, calculated worm totals, or both as obtained from the above counting procedures.

Statistics

All helminth counts were transformed by log10 (x + 1) transformation for generation of geometric means and 1-way ANOVA by using PROC GLM of SAS [12]. Treatment was the only effect in the model, and when found sig-nificant (P < 0.05), means were separated by repeated t-tests by using the LS MEANS options.

RESULTS AND DISCUSSION

No adverse effects of albendazole treatments were observed on bird appearance, behavior, apparent appetite, and weight gain. Animal intake was not monitored, but bird weights on d 0 and 6 were recorded. No significant differences in bird weights by treatment group were observed during the study (P < 0.05). Mean percentage weight gains by treatment group for the d 0 to 6 weighings were 5.5, 3.3, 4.9, and 7.9 for the ascending level of albendazole treatment groups. A longer posttreatment period of observation coupled with feed efficiency data would have been necessary to provide indications of worm burden detriment to animal performance and, indirectly, benefits of albendazole treatment.

The helminths found at necropsy and their levels of infection are presented in Table 1. Control bird infections were entirely consistent with those normally seen in adult broiler-breeders maintained on litter in Arkansas [13], with the highest levels of infection apparent for Capilla-ria obsignata and Heterakis gallinarum, and relatively light infections in evidence for Raillie-tina cesticillus and A. galli. These helminths are also the ones of greatest prevalence in Europe, regardless of production type [14]. In general, levels of the above helminths decreased with higher dosage rates of albendazole. Notable exceptions were infections by C. obsignata and H. gallinarum, for which individual bird infections of the greatest magnitude were seen in the 10.0 mg/kg treatment group, observations that are not out of the ordinary when efficacies are less than complete and infections are of great variability.

Geometric means of the helminth populations for each treatment group are given in Table 2. Significant (P < 0.05) reductions in nematode burdens (A. galli, H. gallinarum, and C. obsig-nata) from control bird levels were seen for albendazole at all dose rates (5.0 to 20.0 mg/kg). For R. cesticillus, significant reductions from control bird levels were apparent only at the 20.0 mg/kg dose level.

Percentage efficacies for albendazole, as derived from the geometric means, are given in Table 3. The standard formula for calculation of percentage efficacy is:

 

\begin{eqnarray*}&&\%\ efficacy\ =\\&&\frac{control\ group\ GM\ {-}\ treated\ group\ GM}{control\ group\ GM\ {\times}\ 100},\end{eqnarray*}

where GM is the geometric mean.

Efficacies below 90% are not considered therapeutic in the evaluation of anthelmintics for effectiveness [11]. With those criteria, all nematode populations were effectively reduced by albendazole at the dose rate of 5.0 mg/kg, with the exception of larval A. galli, which required 10.0 mg/kg for a reduction of ≥ 90%. Populations of R. cesticillus were reduced effectively by albendazole at the 20.0 mg/kg dose rate only (96.2% reduction). Given the high and extremely varied levels of Capillaria and Heter-akis that are common in broiler-breeders, and the marginally efficacious nature of albendazole at 5.0 mg/kg, the dose rate of 10.0 mg/kg would appear to be the indicated rate for use. Regardless of the dose rate of albendazole or any other anthelmintic, it is highly advisable that pre- and posttreatment helminth levels be determined in flocks to 1) monitor the levels of parasitism suffered by the birds, and 2) ensure effective removal of parasites by chemical intervention.

Helminth control in the poultry industry is extremely varied. Very little investigation or appreciation of worm significance relative to commercial chicken production exists, and studies in these areas are definitely needed. Further complicating the picture is the fact that no US Food and Drug Administration-cleared product for worm control is both available and efficacious, necessitating the use of products on a prescription basis and with piecemeal information relative to effective dose rates, regimens, and timing. Studies similar to the current one are needed for the products used most widely in an off-label manner for helminth control (e.g., levamisole and oxfendazole) so that effective dose rates relative to specific parasites might be established and used.

CONCLUSIONS AND APPLICATIONS

  1. Replacement broiler-breeder hens are consistently parasitized with a number of helminths, including A. galli, H. gallinarum, C. obsignata, and R. cesticillus.

  2. Albendazole is both safe and effective in the treatment of birds for these helminths.

  3. Additional studies investigating the significance of helminth infections relative to bird production, and determining the efficacies for other anthelmintics that are used in the commercial setting are indicated.

Table 1

Levels of helminths at necropsy (arithmetic)

  Albendazole, mg/kg of BW 
Helminth Parameter 0.0 (control) 5.0 10.0 20.0 
1Means are the arithmetic mean numbers of helminths per bird for the treatment group. 
Ascaridia galli 
    Adult Mean1 ± SE 5.4 ± 1.1 0.1 ± 1.1 0.0 ± 1.1 0.0 ± 1.1 
 Range 0–24 0–1 
 Percentage infected 73 
    Larvae Mean ± SE 11.7 ± 1.9 0.9 ± 1.9 1.3 ± 1.9 0.1 ± 2.0 
 Range 0–52 0–5 0–6 0–1 
 Percentage infected 80 47 33 14 
Heterakis gallinarum 
    Adult Mean ± SE 124.9 ± 36.1 2.8 ± 36.1 48.5 ± 36.1 0.9 ± 37.3 
 Range 1–749 0–11 0–720 0–10 
 Percentage infected 100 60 40 29 
    Larvae Mea3n ± SE 107.3 ± 43.1 4.3 ± 43.1 81.6 ± 43.1 3.9 ± 44.6 
 Range 0–373 0–14 0–1,195 0–21 
 Percentage infected 93 73 73 71 
Capillaria obsignata 
    Adults and larvae Mean ± SE 183.3 ± 57.6 26.6 ± 57.6 103.1 ± 57.6 12.8 ± 59.7 
 Range 6–811 0–232 0–1,430 0–85 
 Percentage infected 100 87 87 71 
Raillietina cesticillus 
 Mean ± SE 8.7 ± 4.8 8.4 ± 4.8 4.3 ± 4.8 0.2 ± 5.0 
 Range 0–54 0–120 0–55 0–3 
 Percentage infected 53 33 33 
  Albendazole, mg/kg of BW 
Helminth Parameter 0.0 (control) 5.0 10.0 20.0 
1Means are the arithmetic mean numbers of helminths per bird for the treatment group. 
Ascaridia galli 
    Adult Mean1 ± SE 5.4 ± 1.1 0.1 ± 1.1 0.0 ± 1.1 0.0 ± 1.1 
 Range 0–24 0–1 
 Percentage infected 73 
    Larvae Mean ± SE 11.7 ± 1.9 0.9 ± 1.9 1.3 ± 1.9 0.1 ± 2.0 
 Range 0–52 0–5 0–6 0–1 
 Percentage infected 80 47 33 14 
Heterakis gallinarum 
    Adult Mean ± SE 124.9 ± 36.1 2.8 ± 36.1 48.5 ± 36.1 0.9 ± 37.3 
 Range 1–749 0–11 0–720 0–10 
 Percentage infected 100 60 40 29 
    Larvae Mea3n ± SE 107.3 ± 43.1 4.3 ± 43.1 81.6 ± 43.1 3.9 ± 44.6 
 Range 0–373 0–14 0–1,195 0–21 
 Percentage infected 93 73 73 71 
Capillaria obsignata 
    Adults and larvae Mean ± SE 183.3 ± 57.6 26.6 ± 57.6 103.1 ± 57.6 12.8 ± 59.7 
 Range 6–811 0–232 0–1,430 0–85 
 Percentage infected 100 87 87 71 
Raillietina cesticillus 
 Mean ± SE 8.7 ± 4.8 8.4 ± 4.8 4.3 ± 4.8 0.2 ± 5.0 
 Range 0–54 0–120 0–55 0–3 
 Percentage infected 53 33 33 
Table 2

Geometric means of helminths by treatment group

 Albendazole, mg/kg of BW 
Helminth 0.0 (control) 5.0 10.0 20.0 
a,bMeans on the same line with unlike superscripts are different (P < 0.05). 
Ascaridia galli 
    Adult 2.4a 0.0b 0.0b 0.0b 
    Larvae 5.7a 0.7b 0.5b 0.1b 
Heterakis gallinarum 
    Adult 37.2a 2.7b 1.7b 1.9b 
    Larvae 35.5a 1.1b 1.5b 0.4b 
Capillaria obsignata 
    Adults and larvae 77.4a 7.5b 6.7b 3.8b 
Raillietina cesticillus 2.6a 0.7ab 0.7ab 0.1b 
 Albendazole, mg/kg of BW 
Helminth 0.0 (control) 5.0 10.0 20.0 
a,bMeans on the same line with unlike superscripts are different (P < 0.05). 
Ascaridia galli 
    Adult 2.4a 0.0b 0.0b 0.0b 
    Larvae 5.7a 0.7b 0.5b 0.1b 
Heterakis gallinarum 
    Adult 37.2a 2.7b 1.7b 1.9b 
    Larvae 35.5a 1.1b 1.5b 0.4b 
Capillaria obsignata 
    Adults and larvae 77.4a 7.5b 6.7b 3.8b 
Raillietina cesticillus 2.6a 0.7ab 0.7ab 0.1b 
Table 3

Percentage efficacies for albendazole based on treatment group geometric means

 Albendazole, mg/kg of BW 
Helminth 5.0 10.0 20.0 
Ascaridia galli 
    Adult 100.0 100.0 100.0 
    Larvae 87.7 91.2 98.2 
Heterakis gallinarum 
    Adult 92.7 95.4 94.9 
    Larvae 96.9 95.8 98.9 
Capillaria obsignata 90.3 91.3 95.1 
Raillietina cesticillus 73.1 73.1 96.2 
 Albendazole, mg/kg of BW 
Helminth 5.0 10.0 20.0 
Ascaridia galli 
    Adult 100.0 100.0 100.0 
    Larvae 87.7 91.2 98.2 
Heterakis gallinarum 
    Adult 92.7 95.4 94.9 
    Larvae 96.9 95.8 98.9 
Capillaria obsignata 90.3 91.3 95.1 
Raillietina cesticillus 73.1 73.1 96.2 

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