Hatchery Losses in Flocks of Layer and Broiler Breeders Due to Feed Contamination with Nicarbazin and Narasin: A Case Report.

In the current study, we investigated decreased hatchability and increased embryonic mortality in two farms of layer breeders (flocks A1 and B1) and a farm of broiler breeders (flocks C1 and C2) from Austria, which also presented discoloration of eggshells in 2% of the eggs. After conducting clinical evaluations and the approval that the feed operator was common for flocks A1 and B1, and C1 and C2, it was decided to investigate the feed. Our findings revealed that the feed contained levels of nicarbazin and narasin up to five and 14 times, respectively, above the maximum limits allowed by the European Union for nontarget species. On the other hand, there were no significant abnormalities in vitamin levels, which were also described as the etiology of the noticed abnormalities. Switching to a noncontaminated feed resulted in the clinical signs and production parameters returning to expected ranges. This report emphasizes the significance of considering feed contamination by nicarbazin and narasin as a potential cause of hatchery losses in nontarget species, even in the absence of other clinical signs.

Reporte de caso- Pérdidas en la eclosión de parvadas de reproductoras ponedoras y pollos de engorde debido a la contaminación del alimento con nicarbazina y narasina: Reporte de un caso. En el presente estudio, se investigó la disminución de la incubabilidad y el aumento de la mortalidad embrionaria en dos granjas de reproductoras ponedoras (parvadas A1 y B1) y una granja de reproductoras de pollos de engorde (parvadas C1 y C2) de Austria, que también presentaron decoloración del cascarón en el 2% de los huevos. Luego de realizar evaluaciones clínicas y la aprobación de que el operador de alimento era común para las parvadas A1 y B1, y C1 y C2, se decidió investigar el alimento. Nuestros hallazgos revelaron que el alimento contenía niveles de nicarbazina y narasina de hasta cinco y 14 veces, respectivamente, por encima de los límites máximos permitidos por la Unión Europea para especies no objetivo. Por otro lado, no se observaron anomalías significativas en los niveles de vitaminas, lo que también se describió como la etiología de las anomalías observadas. El cambio a un alimento no contaminado provocó que los signos clínicos y los parámetros de producción regresaran a los rangos esperados. Este informe enfatiza la importancia de considerar la contaminación del alimento por nicarbazina y narasina como una causa potencial de pérdidas en la eclosión de especies no objetivo, incluso en ausencia de otros signos clínicos.

[Accidental feeding of the coccidiostat nicarbazin in layer breeder flocks - A case report]. / Versehentliche Fütterung von Legehennen-Elterntier-Herden mit dem Kokzidiostatikum Nicarbazin.

Following the accidental feeding of a compound feed containing the coccidiostat nicarbacin in layer breeder flocks (Lohmann Brown Classic), the birds displayed distinct clinical signs within a few hours. Mortality increased during the following 5 days, whereas laying performance and hatching rate of eggs during this period decreased markedly. Egg shell discoloration was observed as early as during the first day. As a consequence, an association between feeding of the coccidiostat nicarbacin and the observed symptoms was assumed. Recent studies indicate that Nicarbacin reduces the activity of aminolevulinic acid synthase type 1 (ALAS 1), which is responsible for the synthesis of protoporphyrin IX in the shell gland as main compound of brown egg shells. Reduced laying performance and increased mortality was likely due to nicarbacin-induced deregulated body temperature homeostasis and concomitant imbalances in acid-base status of the animals. The case reveals that the accidental feeding of nicarbacin to non-target animals such as laying hens and their parents may result in acute clinical symptoms. This highlights the necessity of appropriate care in handling feed additives and their premixes for specific non-target animals and should sensitize farmers and veterinarians.

Synergistic effect of a combination of nicarbazin and monensin against coccidiosis in the chicken caused by Eimeria spp.

A clinical study was made into the abilities of nicarbazin and monensin and a nicarbazin + monensin combination to control Eimeria acervulina, E. maxima, and E. tenella in chickens. When included in the feed, at concentrations of 40 ppm nicarbazin or 40 ppm monensin, these products showed partial efficacy evaluated by daily weight gain (DWG) but no activity judged by daily feed intake (DFI) or feed conversion ratio (FCR). By contrast, the combination of 40 ppm nicarbazin + 40 ppm monensin provided complete control of infection judged by greater DWG and DFI, and lower FCR. Monensin at a concentration of 40 ppm was ineffective in preventing lesions caused by all three species. Nicarbazin at a concentration of 40 ppm was unable to suppress lesions of E. acervulina and E. maxima but was able to suppress lesions caused by E. tenella. Nicarbazin 40 ppm + monensin 40 ppm suppressed lesions of all three species. RESEARCH HIGHLIGHTS Nicarbazin or monensin at 40 ppm gave only partial control of Eimeria spp. A combination of 40 ppm nicarbazin + 40 ppm monensin controlled DWG, DFI and FCR. Nicarbazin or monensin at 40 ppm did not suppress all Eimeria spp. lesions. Nicarbazin 40 ppm + monensin 40 ppm suppressed lesions of all three species.

Degradation of 4,4'-Dinitrocarbanilide in Chicken Breast by Thermal Processing.

Nicarbazin is one of the major anticoccidials used in broiler feeds. The compound 4,4'-dinitrocarbanilide (DNC) is the marker residue of concern left from nicarbazin in chicken meat. The effect of thermal processing on DNC content accumulated in chicken breast was assessed, and samples were analyzed by liquid chromatography-tandem mass spectrometry. Five conventional cooking methods were evaluated: boiling, grilling, microwaving, frying, and roasting. To ensure DNC in meat, broilers were fed nicarbazin without withdrawal period. All heating methods surpassed the 70 °C end point core temperature in chicken breast. Maximum DNC degradation was reached at 10 min for boiling, at 30 min for grilling, and at 2 min for microwaving, and no further reduction was observed for longer thermal processing time. Boiling was more efficient in reducing DNC (69%). Grilling, microwaving, and frying achieved on average 55% of degradation. The outcomes reported herein may be considered in decision-making regarding further review of maximum residue limits.

Blood Glucose Concentrations in Nicarbazin-Fed Broiler Chickens.

Four floor pen studies were carried out to evaluate the effects of nicarbazin (NIC) administration on blood glucose concentrations and the onset of hypoglycemia in broiler chickens. All tests involved continuous NIC feeding at 0, 100, or 125 ppm to 28 days of age. In each study, birds were reared at both standard environmental temperatures and at 3 C below this level. In addition, two studies were conducted in the presence of coccidial infection and two were carried out in noninfected broilers. At 26 days of age in each test, two birds per pen were bled by puncture of the brachial vein, and whole blood glucose concentrations were determined. Results indicated that the administration of NIC to broilers for 26 days had no effect on blood glucose concentrations, although graded levels of NIC tended to increase these values. In addition, no evidence of hypoglycemia was recorded in any of the trials. In a similar fashion, blood glucose was unaffected by environmental temperature and coccidial challenge. These findings support previous work showing that NIC administration does not influence blood glucose levels and indicate that the product is not involved when field diagnoses use reduced blood glucose and hypoglycemia as indicators of production anomalies.

Determination of the residue levels of nicarbazin and combination nicarbazin-narasin in broiler chickens after oral administration.

The depletion times of the anticoccidial nicarbazin administered individually and of nicarbazin and narasin administered in combination were evaluated by determining the presence and levels of 4,4'-dinitrocarbanilide (DNC), the marker residue for nicarbazin, and narasin residues in the muscle tissues of broiler chickens subjected to a pharmacological treatment. A high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was used. The results showed the presence of all anticoccidial residues; however, the DNC levels were higher when the nicarbazin was administered individually than when it was used in association with narasin throughout the experimental period. After six days of withdrawal, the DNC level following nicarbazin administration alone was lower than the maximum residue level (MRL) of 200 µg kg-1. However, when the nicarbazin was co-administered with narasin, the concentrations of DNC were lower than the MRL after four days of withdrawal. These results may be justified because the dosage of nicarbazin, when administrated individually, is greater than when it is used in combination with narasin. The levels of narasin were lower than the MRL of 15 µg kg-1 throughout the evaluation period. It was concluded that nicarbazin is rapidly metabolized from the broiler muscles up to six days of withdrawal since the DNC levels were lower than the maximum residue level (MRL) and the concentrations of narasin were lower than the MRL throughout the evaluation period.

Performance and anticoccidial effects of nicarbazin-fed broilers reared at standard or reduced environmental temperatures.

A series of 4 floor pen studies was conducted to evaluate the effects of environmental temperature modification on nicarbazin (NIC) responses in broiler chickens raised to 28 d of age. Birds were reared at either standard temperatures (recommended by the primary breeder for ages zero to 28 d) or at 3°C below this level. From placement to 28 d, birds were provided feeds containing zero, 100, or 125 ppm NIC, comprising a 2 × 3 factorial arrangement in each test. Two of the trials were conducted in the presence of an imposed coccidial challenge and 2 were conducted in healthy animals. At 18 and 28 d of age, performance was recorded; cloacal temperatures were measured at 7, 14, 21, and 26 days. Mortality data were collected daily and coccidial lesions were scored at 6 d post challenge. Results of these studies revealed that NIC improved coccidial lesion scores regardless of environmental temperature. In the absence of coccidial challenge, NIC depressed performance, but reductions in environmental temperature diminished the magnitude of these responses. Under conditions of coccidial challenge, NIC significantly improved body weight gains in both temperature environments. Compared to standard temperature conditions, lower environmental temperatures exerted a positive effect on feed conversion rates of NIC-fed broilers. Birds reared in the low temperature environment exhibited lower cloacal temperatures than standard environment groups throughout the test period. Irrespective of coccidial challenge, lower environmental temperatures significantly reduced nicarbazin mortality compared to standard temperature groups, resulting in a significant nicarbazin x temperature interaction. This finding indicates that temperature modification is a practical method for minimizing mortality over the course of 28-day nicarbazin usage.

Sensitivity of Eimeria field isolates in the United States: responses of nicarbazin-containing anticoccidials.

A series of studies were conducted to assess the drug sensitivity of 26 coccidial field isolates to the anticoccidial effects of nicarbazin (NIC) and narasin + NIC (NAR + NIC). Isolates were collected from typical broiler farms in the United States from 2003 to 2006, propagated once in the absence of anticoccidial medication, and then used to inoculate broilers that were fed nonmedicated rations or those containing NIC 125 ppm or NAR + NIC 80 ppm. Results of these sensitivity trials indicated that 81% of these coccidial isolates were sensitive to the effects of NIC, but only 22% of these coccidia were controlled by NAR + NIC. Studies conducted to evaluate performance responses to these drugs demonstrated that birds fed NIC gained more weight and utilized feed more efficiently than those receiving NAR + NIC. The results of 2 floor pen tests, conducted to confirm the results of the above sensitivity trials, demonstrated that NIC provided a greater level of protection from coccidiosis than NAR + NIC. Lower lesion scores and improved performance were recorded for birds receiving NIC compared with NAR + NIC. Results of these studies revealed that changes in the susceptibility of Eimeria spp. to the activity of NAR + NIC are evident. These changes appear to be associated with the reduction in ionophore sensitivity that has been documented in most areas of the world.

Comparison of nicarbazin absorption in chickens, mallards, and Canada geese.

Nicarbazin (NCZ), a coccidiostat commonly used in the poultry industry, causes reduced hatchability and egg quality in layer hens at a concentration of 125 ppm (8.4 mg/kg) in the feed. Although this effect is undesirable in the poultry industry, NCZ could provide a useful wildlife contraception tool for waterfowl, particularly urban geese. We tested the absorption of NCZ in chickens (Gallus gallus), mallards (Anas platyrhynchos), and Canada geese (Branta canadensis) gavaged with 8.4 mg of NCZ/kg per bird each day for 8 d. Plasma levels of 4,4'-dinitrocarbanilide (DNC) differed significantly among species. Peak plasma DNC levels were 2.87 +/- 0.15 microg/mL, 2.39 +/- 0.15 microg/mL, and 1.53 +/- 0.15 microg/ mL in chickens, mallards, and Canada geese respectively. It took 6 d to obtain peak DNC levels in chickens as opposed to 8 d in mallards and Canada geese. The half life of DNC in plasma was 1.43 d in chickens, 0.72 d in mallards, and 1.26 d in Canada geese. Mallards eliminated 100% of plasma DNC 4 d post-treatment, whereas Canada geese eliminated 100% of plasma DNC 8 d post-treatment. Chickens had only eliminated 99% of plasma DNC 8 d post-treatment. Mallard plasma DNC levels were highly correlated with Canada goose plasma DNC levels. This research showed mallards are an ideal model species for the Canada goose for future reproductive studies on NCZ in a laboratory setting. However, levels higher than 8.4 mg/kg must be fed to waterfowl in order to obtain a plasma level comparable to chickens.

The Hymenolepis diminuta-golden hamster (Mesocricetus auratus) model for the evaluation of gastrointestinal anticestode activity.

A novel laboratory anticestode assay was developed using Hymenolepis diminuta in the hamster. The commercial anticestode compounds, praziquantel, bunamidine, and niclosamide were active against patent infections of Hymenolepis diminuta in golden hamsters (Mesocricetus auratus) when given orally at 3.125, 100, and 200 mg/kg, respectively. The gastrointestinal nematode anthelmintics, cambendazole and mebendazole, were active at 50 mg/kg. Rafoxanide (fasciolicide) was active at 25 mg/kg, the lowest level tested. The coccidiostat, nicarbazin, was active at experimental levels (800 mg/kg and up). The anthelmintic-ectoparasiticide (endectocide), ivermectin, was inactive against the tapeworm at 0.5 mg/kg, as expected.

Coccidiosis control by administering toltrazuril in the drinking water for a 2-day period.

A 56-day floor pen study was conducted to determine the appropriate time to administer toltrazuril (Baycox) (TOL) for control of coccidiosis in broiler chickens. Litter was seeded with field strains of Eimeria acervulina, Eimeria maxima and Eimeria tenella. On Days 0, 21, 35 and 56, all birds and feed were weighed. Starting on Day 14, weekly lesion scores and oocyst counts were performed. The treatments were 125 ppm nicarb (NIC) in the starter to 66 ppm salinomycin (SAL) in the grower with no TOL (NIC/SAL/no TOL), 66 ppm salinomycin in both the starter and the grower but no TOL (SAL/SAL/no TOL), or no in-feed medication with the following TOL treatment: TOL Days 2-3, TOL Days 6-7, TOL Days 10-11, TOL Days 14-15, TOL Days 18-19, and as control NM/NM/no TOL (NM). The withdrawal feed was nonmedicated. TOL was administered in the drinking water at the rate of 7 mg/kg body weight. Oocysts per gram litter and lesion scores showed a significant infection in the NM birds, which peaked about Day 21. The NIC/SAL gave excellent early protection but only moderate protection during the SAL phase. The final performance for the SAL/SAL was significantly less compared to all TOL and NIC/SAL birds. All TOL treatments but Days 2-3 provided good coccidiosis control with accompanying performance. The absence of clinical coccidiosis relapse during the last third of the growout along with moderate oocyst counts and low lesions was indicative of unimpaired coccidiosis immunity. It can be inferred from the overall results that the use of TOL as the sole anticoccidial for two consecutive days in the drinking water between Days 10 and 14 would be the best time for good coccidiosis control allowing full performance.

Coccidiosis control with toltrazuril in conjunction with anticoccidial medicated or nonmedicated feed.

A 42-day broiler floor pen study was conducted comparing the anticoccidial efficacy of toltrazuril (Baycox) as a stand alone treatment and as an additional treatment to in-feed anticoccidial programs. Toltrazuril was administered on days 18 and 19 in the drinking water at 7 mg/kg of body weight. The treatments were 125 ppm nicarbazin (days 0-14) to 66 ppm salinomycin (SAL) (days 15-35) with and without toltrazuril, SAL (days 0-35) with and without toltrazuril, nonmedicated (NM) to SAL with toltrazuril, and NM with and without toltrazuril. The controls were NM noninfected and infected. The treatments were replicated in five blocks of eight pens each in a randomized complete block design. All withdrawal feed was nonmedicated. On day 14, birds, except noninfected, were exposed to coccidial oocysts (Eimeria acervulina, Eimeria maxima, and Eimeria tenella) seeded litter. On days 21, 28, 35, and 42, birds and feed were weighed, four birds per pen were coccidial lesion scored, and litter oocyst counts were performed. The coccidial infection in the NM infected treatment caused a significant (P < 0.05) coccidiosis infection. Coccidiosis was moderately controlled in the anticoccidial treatment birds without toltrazuril. Performance in the NM with toltrazuril was equal to or better (P < 0.05) than the anticoccidial programs without toltrazuril. Toltrazuril was equal to the noninfected birds in performance. Toltrazuril most completely eliminated all coccidial lesions and dramatically reduced oocyst shedding. The performance data, lesion scores, and oocyst counts showed that a 2-day treatment with toltrazuril successfully controlled the coccidiosis with no relapse of infection. Toltrazuril can thus be used for supplemental control with in-feed anticoccidials or as a primary anticoccidial with nonmedicated feed.

Efficacy of selected oral chemotherapeutants against Ichthyophthirius multifiliis (Ciliophora: Ophyroglenidae) infecting rainbow trout Oncorhynchus mykiss.

The chemotherapeutic efficacy of 6 in-feed compounds against Ichthyophthirius multifiliis Fouquet, 1876 was assessed using experimental infections of rainbow trout Oncorhynchus mykiss (Walbaum) fingerlings. Trial doses of 104 ppm amprolium hydrochloride or 65 ppm clopidol fed to fish for 10 d prior to infection significantly reduced the number of trophonts establishing in trout fingerlings by 62.0 and 35.2% respectively. In-feed treatments of infected trout with either 63 or 75 ppm amprolium hydrochloride, 92 ppm clopidol, or 38, 43 or 47 ppm salinomycin sodium for 10 d also significantly reduced the number of surviving trophonts by 77.6 and 32.2% for amprolium, 20.1% for clopidol and 80.2, 71.9 and 93.3% respectively for salinomycin sodium.

Alternative procedures for molt induction: practical aspects.

Shortening daylight (to 10.5 to 11 h/d) slightly reduced the rest period (the interval between last egg and first clutch), whereas feeding a low-protein diet during the 22-d period following 8 d of feed withdrawal (FW) (recovery period) markedly extended it. Feed withdrawal accompanied by a short-daylight regime and a long recovery period led to the best postmolt production. However, production per hen housed during the whole experimental period was only slightly increased. Thus, a long rest period may mask the positive effects of short daylight and recovery diet. At least 140 to 170 d were needed to enable the molted hens to compensate for the loss of eggs during the rest period. Therefore, under certain economic conditions, rearing of nonmolting hens for 640 to 700 d should be an economic consideration. Ten days of feeding of a diet containing 0.06% nicarbazin (NICR) arrested egg production and caused a 22-d rest period but not a typical molt. Few variables of production or shell quality were improved by NICR but to a lesser extent than by FW or Zn feeding. Five days of feeding on a high-Zn diet (20 g Zn/kg; HZn) improved postmolt performances similarly to FW. Ten days of feeding on a modest-Zn (2.8 g Zn/kg), low-Ca, and low-P diet (Zn-CaP) affected postmolt performances inconsistently. In one out of two trials (trial 2), the effects of Zn-CaP were similar to those of FW or HZn; in the other (trial 3), the effects were less pronounced, more time was required for egg arrest, and more eggs were laid occasionally during the rest period. In trial 2, only the Zn-CaP diet was accompanied by short daylight. In both trials, feed intake during the induction period was only slightly reduced. Zn feeding increased the yolk Zn content slightly in eggs laid during the induction period and at the onset of production. In trial 2, only Zn-CaP markedly increased yolk Zn of eggs laid during the first 5 d of production.

Determination of 4,4'-dinitrocarbanilide (DNC), a component of Nicarbazin, in Canada goose (Branta canadensis) eggshells using high-performance liquid chromatography.

A method was developed using high-performance liquid chromatography to assay 4,4'-dinitrocarbanilide (DNC), the active ingredient in Nicarbazin, in eggshells collected from Canada geese fed a formulated feed fortified with Nicarbazin at doses of 0, 125, 250, and 500 microg/g. The method was developed using chicken eggshells fortified with DNC. The method was used to quantify DNC in both the shell-associated membranes and the calcified shell extracellular matrix. These values were compared to those obtained for a composite sample consisting of both the membranes and the calcified shell extracellular matrix. The validated method was used to quantify DNC in eggshells from geese fed fortified feed to ascertain the effect of Nicarbazin feed concentration on shell DNC concentration. DNC levels in the eggshells were highly correlated with feed dose.

Poly(methyl methacrylate) synthetic grit formulations sustain the delivery of nicarbazin, a contraceptive agent, in pest waterfowl.

Sixty-three mallards were fed one of ten poly(methyl methacrylate) based synthetic grit formulations containing varying concentrations of a proposed wildlife contraceptive (nicarbazin), plasticizer (acetyl tributylcitrate) and/or cross-linking agent (1,4-butanediol diacrylate). Release characteristics of the contraceptive agent were monitored for the purpose of developing a contraceptive formulation for control of pest waterfowl in urban settings. The addition of plasticizer increased the erosion rate (t(1/2)=0.97-2.85 days), cross-linking the polymer matrix slightly decreased the erosion rate (t(1/2)=4.45-5.05 days) and increasing the concentration of the contraceptive agent increased the erosion rate (t(1/2)=3.3 and 9.9 days at 60% and 7.5% active ingredient, respectively). The larger and smaller grit pieces had longer half lives at 11.0 and 11.6 days, respectively while the mid sized grit had a half life of 4.95 days. Control grit had a half life of 12.7 days based on weight loss. Analysis of blood and feces for monitoring release from the grit and approximate indirect plasma levels of the active ingredient proved feasible.

Comparison of an attenuated anticoccidial vaccine and an anticoccidial drug programme in commercial broiler chickens in Italy.

A live attenuated anticoccidial vaccine (Paracox) was compared with a nicarbazin-monensin anticoccidial drug shuttle programme in three crops of Italian broilers, comprising a total of 290,405 chickens. All birds received the antibiotic growth promoter avilamycin. No coccidiosis was evident during the trials, but the occurrence of oocysts in the litter demonstrated that a natural challenge was present. Vaccinated birds consistently performed at least as well as those treated with the anticoccidial drug shuttle. The final mean weights of vaccinated birds were significantly greater (P < 0.001) than those of birds treated with anticoccidial drugs, both for females at 36/37 days and males at 56 days. Feed conversion ratios, total mortality including culls, the proportion of rejects at the processing plant, and the moisture content of the litter were not significantly different between the two control methods. Growth curves showed that there was no post-vaccinal growth check in the vaccinated birds and no intolerance of the anticoccidial drug treatment. There was no overall seasonal effect, regardless of treatment, on the performance of the three crops reared from November 1997 to July 1998. These findings suggest that the use of this vaccine is likely to enable the replacement of anticoccidial drug shuttle programmes in broilers reared under conditions similar to those used in these Italian flocks.

Possible causes of nicarbazin residues in chicken tissues.

Two experiments were carried out to investigate possible causes of nicarbazin residues in broiler chicken tissues. The first experiment was designed to establish whether feeding nicarbazin as stipulated in the product license can result in 4,4'-dinitrocarbanilide (DNC) tissue residues exceeding the JECFA MRL (200 micrograms/kg). It was shown that the MRL was exceeded in the livers of broilers housed on deep litter, but not in those of broilers housed on wire flooring. Muscle DNC concentrations were well below the MRL. The higher residual tissue concentrations in birds housed on deep litter were attributed to faecal recycling. The second experiment was to establish the relationship between nicarbazin-contaminated withdrawal ration up to the point of slaughter and DNC residues in the tissues of broilers that had not been previously exposed to nicarbazin. Tissue DNC concentrations were found to be proportional to feed concentrations. The housing method caused no significant difference in tissue residues. Meal containing nicarbazin at a concentration of 2.4 mg/kg or greater caused liver DNC residues above the JECFA MRL. Violative residues may, therefore, occur in chickens not exposed to nicarbazin during rearing, but fed withdrawal ration contaminated at 2.4 mg/kg or greater, or in chickens housed on deep litter and fed nicarbazin-medicated meal according to the product license even when the withdrawal ration is nicarbazin-free.

Residual activity of anticoccidial drugs in chickens after withdrawal of medicated feeds.

Seven anticoccidial drugs commonly used in poultry (diclazuri), monensin, salinomycin, halofuginone, nicarbazin, robenidine, amprolium, and lasalocid) were tested for residual activity after withdrawal. In each test, the products were given at the recommended level to cages of 10 broiler chickens. Oral inoculation with coccidia was given after withdrawal of medication. Birds pretreated with 1 ppm of diclazuril and inoculated with Eimeria tenella after drug withdrawal had normal weight gain and very low lesion scores. Residual activity depleted gradually over several days, as shown by higher lesion scores when medication was withdrawn for up to 3 days before inoculation. Similar results were observed when young birds were inoculated with a mixture of E. tenella, E. maxima and E. acervulina, and also when birds were given diclazuril to market weight (6 weeks of age) and inoculated with a mixture of six species of Eiméria (The above species plus E. brunetti, E. mitis, and E. necatrix) after withdrawal of medication for 2 days. In contrast, there was no evidence of residual anticoccidial activity with nicarbazin, halofuginone, lasalocid, amprolium, salinomycin or monensin. Overall, the residual activity was unique to diclazuril.

Evaluation of the efficacy of Eimeria maxima oocyst immunization with different strains of day-old broiler and roaster chickens.

The performances of three different strains of male and female broiler or roaster chickens immunized at 1 day of age with a drug-resistant field isolate of Eimeria maxima were evaluated in battery and floorpen immunization trials. No difference in immunization potential was seen between these strains or sexes of day-old chickens immunized with 2500 oocysts/bird of E. maxima and challenged at 10 days of age with 25,000 oocysts/bird of the same isolate in two separate battery trials. All immunized birds showed significant protection for the parameters of weight gain and midintestinal lesion scores at 7 days post challenge (PC) when compared with nonimmunized challenged controls. In two separate floorpen trials, one broiler bird strain (designated strain 2) immunized by the same procedure and challenged at 21 days of age with the equivalent of 25,000 oocysts/bird of the same isolate showed significant protection for weight gain and lesion scores at 7 days PC when compared with nonimmunized controls. Birds in these same floorpen experiments immunized with E. maxima and then fed three different anticoccidial shuttle diets (narasin and nicarbazin 90 grams/ton (g/t) in starter feed and narasin 72 g/t + roxarsone 45.4 g/t in grower feed; nicarbazin 113 g/t in starter feed and narasin 72 g/t + roxarsone 45.4 g/t in grower feed; and monensin 100 g/t in starter and grower feed) showed no interference with elicited immunity with E. maxima challenge for the same parameters measured. No significant difference was seen between any floorpen immunized bird groups for total weight gain at trial terminations (49 days of age).