Anticoccidial efficacy of drinking water soluble diclazuril on experimental and field coccidiosis in broiler chickens

Prophylactic and curative capacity of water soluble formulation of Diclazuril (Diclosol 1%) and feed additive form (Clinacox, 0.5%) were tested against Eimeria infection in broiler chickens. Such testing was performed both experimentally and in the field. Toltrazuril (Baycox, 2.5%) was used as reference control drug. Water soluble formulation of Diclazuril induced a marked inhibitory effect on the different stages of the parasite life cycle in experimentally infected treated birds especially when applied on the day when blood first appeared in the faeces [fifth day post-infection (d.p.i.)] as well as on the second day of blood dropping (6 d.p.i.). Both tested dosage levels of Diclazuril water soluble formulation in drinking water (5 and 10 ppm) showed the same effect in controlling coccidial infection and reducing the total oocyst numbers, lesion and faecal scores. Moreover, there was no significant difference in the efficacy of water soluble form of Diclazuril and the reference control drug (Toltrazuril, 25 ppm). In addition, testing the water soluble formulation (5 ppm) in naturally infected poultry farm (20,000 birds), showed the same anticoccidial effect observed when using Toltrazuril, as a treatment for coccidiosis. In conclusion, addition of Diclazuril at the dose of 5 ppm in the drinking water of naturally coccidia infected bird induced the same effect as 25 ppm of Toltrazuril as a treatment for coccidiosis in chickens.     

Anticoccidial efficacy of diclazuril against recent field isolates of Eimeria from commercial poultry farms

The anticoccidial efficacy of diclazuril, a novel anticoccidial agent, was titrated in laboratory experiments using recent field isolates of Eimeria. Fifty tests were conducted with six individual species isolates, and seven tests were done with a mixture of the six species. Results were based on intestinal lesion scores at necropsy, droppings scores, and weight gain. Diclazuril at 0.5 ppm was almost completely effective against E. tenella, E. acervulina, and E. mitis. Prevention of E. brunetti was better at 1.0 ppm than at 0.5 ppm. In birds infected with E. mitis. Prevention of E. brunetti was better at 1.0 ppm than at 0.5 ppm. In birds infected with E. maxima, diclazuril at 0.5-1.5 ppm significantly reduced lesion scores and droppings scores and improved weight gain, although lesions were higher than with other species. Oocyst shedding by E. maxima was almost completely prevented by 0.5-1.5 ppm. Lesion scores and droppings scores caused by E. necatrix or mixed infections were greatly reduced by 0.5 ppm of diclazuril, but 1.0 ppm was necessary to obtain full protection of weight gain. Results suggest that 1.0 ppm of diclazuril best prevents coccidiosis caused by six species of coccidia in chickens.     

Acquisition of immunity to Eimeria maxima in newly hatched chickens given 100 oocysts

The acquisition of immunity to Eimeria maxima by chicks infected 18 hr after hatch with a single dose of 100 oocysts was investigated. In the first experiment, birds were moved each day to clean cages in order to prevent the possibility of secondary infection resulting from ingestion of oocysts passed in their feces. Immunity was measured at 4 wk of age by calculation of oocyst production following challenge with 500 oocysts or weight gain following challenge with 100,000 oocysts. Large numbers of oocysts were produced by infected birds following challenge, although numbers were significantly less than those from birds that had been reared in the absence of infection (susceptible controls). The weight gain of infected birds following challenge was significantly greater than that of susceptible controls but less than that of unchallenged controls. Thus, only partial protection had been acquired, whether parasite replication or body weight gain was used to assess the extent of immunity development. In a second experiment, acquisition of immunity at 4 wk by chicks infected 18 hr after hatch with 100 oocysts of E. maxima and reared in floor pens in contact with their droppings was investigated. Infected birds produced no oocysts following challenge, and weight gains were not significantly different from the unchallenged controls, which indicates that full immunity had developed by 4 wk. It is concluded that if oocysts of Eimeria species are used to vaccinate day-old chicks, reinfection by oocysts present in the litter is necessary for the establishment of protective immunity.     

Effect of ochratoxin A on Escherichia coli-challenged broiler chicks

A study was conducted to evaluate the effects of ochratoxin A (OA) on Escherichia coli-challenged broiler chickens. Day-old broiler chicks were separated into two groups of 92 chicks each, with one group fed a control mash diet, and the other fed a mash diet containing 2 ppm OA. On day 14, each group was further separated into two groups, with one group inoculated with E. coli O78 (1 x 10(7) colony-forming units/0.5 ml), whereas the other group was not inoculated with E. coli. After E. coli inoculation on day 14, four birds from each group were euthanatized at 1, 2, 3, 5, 7, 10, 14, and 21 days postinoculation. Escherichia coli infection caused dullness, depression, huddling, and diarrhea. Mortality was 14.3% in chicks infected with E. coli but fed no OA. Mortality increased to 35.7% in chicks fed OA and infected with E. coli. Decreased body weight and reduced feed intake were observed in chicks fed OA, and the effects were more pronounced in chicks fed OA and infected with E. coli. Increased serum levels of aspartate aminotransferase, alanine aminotransferase, uric acid, and creatinine and decreased levels of total proteins, albumin, globulins, calcium, and phosphorus were observed in OA-fed birds. Escherichia coli infection did not cause significant alteration in any of the serum biochemical parameters. The presence of OA in poultry rations increased mortality and the severity of an E. coli infection.     

Effects of Eimeria mitis on egg production of single-comb White Leghorn hens.

Single-comb white leghorn hens infected with either B4 or C2 strain of Eimeria mitis produced watery droppings as early as day 5 PI. E. mitis infection did not affect egg weight. However, specific gravities of the eggs produced by the hens infected with E. mitis were lower than those produced by the controls. Egg production was significantly reduced temporarily, but most birds returned to production within 14 days. Many of the birds that ceased to lay went through a complete-body molt (56% of the C2-infected hens and 20% of the B4-infected hens). Hens that ceased to lay regained considerable amounts of pigment in their skin, beaks, and shanks.     

Efficacy of Sarafloxacin in Broilers after Experimental Infection with Escherichia coli

Infections of chickens with Escherichia coli serotypeO78 can be treated with the antibiotic sarafloxacin. Three experiments were conducted on the administration of this drug to chickens that had been experimentally infected with E. coli. The birds were monitored for 10 days after infection for their average daily gain (ADG) and feed conversion ratio (FCR), and the post-mortem pathology was assessed. In the first experiment, sarafloxacin (20 mg/L, equivalent to 5 mg/kg live weight per day), given in the drinking water for 3 days after infection, led to a reduction in the mortality from 75% to 27%, but the ADG of the treated birds was still less than that of the uninfected controls. In the second experiment, when the sarafloxacin was administered at the same dose in the water but over only 2 h, there was also a considerable reduction in mortality, and the ADG and the FCR also improved significantly. In the third experiment, the dose dependence of the drug was tested. The birds were given 5 and 10 mg/kg per day sarafloxacin in each group, starting within 2 h after infection. This rapid administration of the drug completely prevented mortality, while the ADG and FCR were similar to those of the uninfected controls.     

Elevation of muscle and plasma 3-methylhistidine as a result of turkey coccidiosis

To assess muscle breakdown during avian coccidiosis, the level of the non-metabolizable amino acid 3-methylhistidine (3MH) was determined in muscle and plasma from turkey poults that received an infection with a field isolate containing a mixture of Eimeria species. The effect of increased levels of parasitism was evaluated at 6 days postinoculation (DPI) in birds receiving 2.5 x 10(4), 1 x 10(5), or 2 x 10(5) oocysts each. The changes in 3MH levels during recovery from acute infection were assessed at 6-29 DPI in animals given 1.9 x 10(5) oocysts per bird. In some experiments, uninoculated birds given the same amount of feed as infected birds (pair fed) were used to determine the impact of feed deprivation on weight loss and 3MH levels. Infected birds had significantly elevated plasma and muscle 3MH at 6 DPI after a single dose of Eimeria oocysts. The plasma and muscle 3MH returned to control levels after 14 DPI. The 3MH levels increased with increased dose of oocysts. Plasma and muscle 3MH levels were well correlated, and an inverse curvilinear relationship between weight gain and plasma 3MH concentrations levels was observed. Plasma and muscle 3MH levels were significantly elevated in pair-fed birds, but 3MH levels in infected birds were increased by 30% over pair-fed birds. The results suggested that muscle breakdown, as assessed by plasma and muscle levels of 3MH, increased during the acute stage of Eimeria infection in turkey poults.     

山豆根多糖对感染PRRSV小鼠脾脏细胞因子水平的影响

探讨山豆根多糖对PRRSV感染小鼠脾淋巴细胞分泌细胞因子水平的影响。将70只昆明种小鼠随机分为7组(A组、B组、C组、D组、E组、F组、G组),每组10只,雌雄各半,依据前期已经建立氧化应激模型的感染条件,D组、E组、F组、G组小鼠于试验第1、2、3天分别采用口服、滴鼻和腹腔注射3种途径联合感染PRRSV病毒原液1.0mL/只,A组、B组、C组给予生理盐水1.0mL/只。第4、5、6天,A、D组小鼠分别腹腔注射生理盐水,0.2mL/10g。B组小鼠腹腔注射5.0mg/kg的脂多糖(LPS)溶液,C组、E组、F组、G组小鼠分别腹腔注射不同剂量的山豆根多糖(200、50、100、200mg/kg)。供试小鼠均于第14天处死,并取其脾脏制备匀浆。采用ELISA检测脾匀浆中TNF-α、IL-1β、IL-6、IL-8、IL-10和MCP-1等细胞因子的水平。结果显示,PRRSV感染小鼠后能升高小鼠脾脏匀浆内TNF-α、IL-1β、IL-6、IL-8、IL-10和MCP-1水平,50mg/kg~100mg/kg剂量的山豆根多糖能降低上述细胞因子的水平。结果表明,山豆根多糖能有效降低PRRSV感染小鼠脾脏细胞因子的水平。     

Effects of dietary vitamin E on chickens infected with eimeria maxima: observations over time of primary infection

Two trrials were conducted to define temporal changes in plasma D-alpha-tocopherol (AT) caused by infection with Eimeria maxima in chickens that consumed either low (25 ppm) or high (225 ppm) levels of dietary DL-alpha-tocopheryl acetate (VE-AC) from 1 day of age. In both trials, rates of weight gain were depressed between days 5 and 7 post-inoculation (PI) and were not influenced by the level of dietary VE-AC. Plasma AT was consistently depressed at 5 and 7 days PI in chickens consuming either level of dietary VE-AC. The pattern and degree of plasma AT depression correlated with those of plasma carotenoids. Plasma levels of NO2- + NO3- were significantly increased at 5 and 7 days PI. In trial 1, the average increase during that period was not as high in chicks consuming 225 ppm VE-AC, but in trial 2, diet had no effect on the degree of increase. Also, there were no consistent effects of dietary VE-AC on lesion scores or amount of oocysts shed. These results are in general accord with findings of earlier experiments, and we conclude that feeding high levels of VE-AC to broiler chicks from 1 day of age is not effective in mitigating the pathology, including weight gain depression and development of mucosal lesions, during E. maxima infections or in modifying immune response events associated with phagocytosis as indexed by plasma NO2- + NO3-. The likely basis for the ineffectiveness of feeding this fat-soluble form of vitamin E is that it is malabsorbed during E. maxima infection in the same manner as carotenoids and becomes less biologically available to infected tissues during the acute phase of infection.     

Effects of dietary tannic acid and vaccination on the course of coccidiosis in experimentally challenged broiler chicken

An experiment was carried out to assess the influence of tannic acid (TA) on integrity of the intestine in broiler chicks vaccinated against coccidiosis and challenged with the disease. In a 2 × 2 factorial design, the trial had five groups of 10 chickens each, including positive (group 2) and negative (group 1) controls. The chickens were kept on wood shavings and fed a commercial maize and soybean-based starter-grower diet. From day 1, groups 3 and 5 received TA (10 g kg(-1)) in their diet. On day 4, birds of groups 4 and 5 were vaccinated orally against coccidiosis with anti-coccidial vaccine, Livacox T?. Each dose of the vaccine contained 300-500 sporulated oocysts of each of Eimeria acervulina, Eimeria maxima and Eimeria tenella. On day 18, all experimental groups except for the negative (group 1) were challenged with 10-fold dose of Livacox T? to produce a mild coccidiosis infection. Faecal samples of individual birds were collected on day 23, and the number of faecal oocysts was determined. d-Xylose absorption test was also carried out on all birds on day 23. Immediately after d-xylose absorption test, all birds were killed humanely and the intestinal tract was removed, weighed and examined for gross lesions. Results showed that negative (group 1) and positive controls (group 2) had the highest and lowest levels of plasma d-xylose post-ingestion of the substrate, respectively. Vaccination and/or feeding TA raised the level of plasma d-xylose in infected birds, although this was not significant for TA-fed birds. Vaccination reduced but TA increased the total number of oocysts per gram of faeces. Birds of groups 2-5 had distinct intestinal lesions when compared with group 1. However, vaccination prevented intestinal lesions. Relative weights of intestinal parts were the lowest in group 1 and the highest in group 2. Vaccination but not TA reduced the relative weights of intestinal parts in infected birds. It was concluded that dietary tannins may reduce the efficacy of anticoccidial vaccines and alter the proper development of immunity against the disease.     

Efficacy of maduramicin against ionophore-tolerant field isolates of coccidia in broilers

Maduramicin ammonium was given at 2.5-8 ppm in the feed to broilers experimentally infected with coccidia recently isolated from broiler farms where ionophores had been used for several years. Infection pressure varied from mild to severe in five trials: mortality in unmedicated controls ranged from 0 to 59%, intestinal lesion scores were high, and weight gain was depressed by the infections. The cultures of Eimeria were partly resistant to ionophores: birds medicated with monensin at 100-121 ppm had only modest reductions in lesion scores and incomplete protection against weight loss or mortality. Control of infections by maduramicin was significant at 4 ppm but best at 5-7 ppm. Maduramicin was more effective than monensin or narasin, but about the same as salinomycin, in reducing lesions and mortality and in protecting performance. Maduramicin was well tolerated within the dose range of 5-7 ppm.     

Infection by Salmonella typhimurium, S. agona, S. enteritidis or S. infantis of chicks with caecal coccidiosis

Experimental infections of Salmonella typhimurium, S. agona, S. enteritidis or S. infantis were studied in chicks infected with Eimeria tenella. In all experiments, 4-d old birds were given 5 daily oral doses of approximately 10(4) salmonella organisms per bird. One day before this inoculation one group of birds received a single dose, in the range 1 X 10(4) to 4 X 10(4) sporulated oocysts of E. tenella per os whilst the other group was not inoculated and served as the control. Chicks were examined post morten 7, 10 or 14 d after receiving coccidia. With S. typhimurium infection, the number of salmonellas in the caeca of the E. tenella-infected birds was greater than in those infected only with salmonella. With S. agona and S. enteritidis, the counts of salmonella in the caeca and the numbers of birds positive for salmonella in the caeca and liver were greater in the E. tenella-infected birds. The rate of infection of S. infantis was not increased by caecal coccidiosis.     

Efficacy of diclazuril against turkey coccidiosis in dose-titration studies

Diclazuril, a new anticoccidial drug, was tested for its efficacy in turkeys against single Eimeria infections. Dose-titration studies indicated that diclazuril at dosages of 0.1, 0.5, 1, and 2 ppm was highly effective against the major pathogenic species-E. adenoeides, E. gallopavonis, and E. meleagrimitis-in terms of weight gain and suppression of lesions, abnormal droppings, and oocyst shedding.     

Efficacy of maduramicin ammonium against coccidiosis in turkeys under laboratory and floor-pen conditions

Experimental infections with field isolates of Eimeria meleagrimitis, E. adenoeides, E. gallopavonis, and E. dispersa in turkey poults were used to test the efficacy of maduramicin ammonium at 2.5-10 ppm in laboratory experiments. Infection with single or mixed species of coccidia reduced the weight gain of unmedicated infected controls and caused 18.1-65% mortality in two experiments. Maduramicin ammonium given at 5-7 ppm prevented mortality, significantly reduced droppings scores and oocyst passage, and improved weight gain to near that of the unmedicated uninfected controls. Maduramicin ammonium was tested at 4-7 ppm in a floor-pen trial lasting 10 weeks. Mortality from coccidiosis averaged 11.9% in unmedicated controls, compared with 0.6% with 4 ppm of maduramicin or no mortality with 5-7 ppm. Average weight gain and feed conversion at 10 weeks were significantly improved over unmedicated infected controls when maduramicin ammonium was given at 5-7 ppm. These results suggest that maduramicin ammonium is highly efficacious against field isolates of Eimeria in turkeys, especially within the range of 5-7 ppm in the feed.     

Anticoccidial activity of 9-(2-chloro-6-fluorobenzyl)-6-methylaminopurine and 9-(2-chloro-6-fluorobenzyl)-6-dimethylaminopurine against Eimeria tenella, E. acervulina, and E. maxima in battery trials

In a series of battery experiments utilizing 9-day-old White Leghorn male chicks, 9-(2-chloro-6-fluorobenzyl)-6-methylaminopurine (VM 6387) and 9-(2-chloro-6-fluorobenzyl)-6-dimethylaminopurine (VM 6736) showed remarkable anticoccidial activity against Eimeria tenella, E. acervulina, and E. maxima. The effective dose range was estimated from the results of the efficacy test against E. tenella on the basis of improvement of body weight gain and clinical signs of infection. The tests included dietary levels of 60-100 ppm of VM 6387 and 70-110 ppm of VM 6736. Both compounds gave good protection against E. acervulina and E. maxima at the same dose range. The sporulation of oocysts obtained from cecal contents of birds fed lower levels of VM 6387 was inhibited. Studies of the effects of VM 6387 on stages of the E. tenella life cycle demonstrated that the compound possesses remarkable activity at 1-5 days post-infection corresponding to the period of schizogony, as well as prolonged activity thereafter, when the parasite was undergoing gametogenesis.     

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.     

Protective effects of sugar cane extracts (SCE) on Eimeria tenella infection in chickens

The effects of oral administration of sugar cane extracts (SCE) on Eimeria tenella oocysts infection in chickens were studied with 2 different experiments. In Experiment 1, 3-week-old inbred chickens (MHC; H.B15) were inoculated into the crop with SCE (500 mg/kg/day) for 1 day or 3 consecutive days, and then challenged with E. tenella sporulated oocysts (2 x 10(4) cells/chicken). In Experiment 2, 1-week-old chickens were orally administered SCE at the same dose for 3 consecutive days, and then initially infected with E. tenella sporulated oocysts (2 x 10(3) cells/chicken). At 2 and 3 weeks of age, these chickens were immunized intravenously with the mixed antigens of sheep red blood cells (SRBC) and Brucella abortus (BA). At 4 weeks of age, chickens were challenged with E. tenella sporulated oocysts (1 x 10(5)/chicken). Challenged chickens with E. tenella oocysts showed markedly decreased body weight gain/day, severe hemorrhage and great number of shedding oocysts in feces and high lesion scores. Oral administration of SCE and initial infection with oocysts (2 x 10 (3)/chicken) resulted in a remarkable improvement in body weight gain/day, hemorrhage, the number of shedding oocysts and lesion score, compare to other infected groups. In addition, SCE-inoculated chickens with the initial infection showed a significant increase in antibody responses against SRBC and BA and also improvement in decreased relative proportions of Bu-1a(+) and CD4( )cells in cecal tonsil lymphocytes of E. tenella-challenged chickens. Cecal tissues of chickens administered SCE and initially infected with E. tenella oocysts showed lower numbers of schizonts, gametocytes and oocysts than those of infected control chickens. These results suggest that SCE have immunostimulating and protective effects against E. tenella infection in chickens.     

Experimental inoculation of pigeons (Columba livia) with Mycobacterium bovis

The purpose of this pilot study was to determine if pigeons (Columba livia) are susceptible to infection with Mycobacterium bovis by either oral or intratracheal inoculation and to assess their possible role in the lateral transmission of bovine tuberculosis. Six pigeons were orally inoculated with 1.3 x 10(5) colony-forming units of M. bovis, six pigeons were intratracheally inoculated with the same dose, and six pigeons served as noninoculated controls. The study continued for 90 days postinoculation (PI), with groups of birds necropsied at 30-day intervals, and fecal samples and tissues were collected for mycobacterial culture. Two pigeons, one intratracheally inoculated and one orally inoculated, shed M. bovis in their feces at 1 day PI, and one intratracheally inoculated bird shed M. bovis in its feces 60 days PI. Whereas no illness or weight loss was present during the course of the study, 2 of 12 inoculated birds exhibited microscopic lesions of mycobacteriosis, and the organism was isolated from tissues of three inoculated birds. Pigeons are susceptible to infection with M. bovis after high dose inoculation and can shed the organism in their feces for up to 60 days PI; intratracheally inoculated birds appear more likely to become active fecal shedders of M. bovis. Although these were high dose inoculations under experimental conditions, pigeons may potentially play a role in the lateral transmission of bovine tuberculosis between infected and uninfected mammalian hosts.     

J亚群禽白血病病毒与禽网状内皮增生症病毒共感染对肉鸡生长和免疫功能的抑制作用

1日龄网鸡感染J亚群禽白血病病毒(ALV-J)以及共感染禽网状内皮增生症病毒(REV)后,肉鸡生长发育明显受阻,体重增重明显下降(P＜0.05),法氏囊、胸腺明显萎缩(P＜0.05),在用新城疫疫苗免疫后,感染组血清中新城疫抗体效价显著低于对照组(P＜0.05);在ALV-J和REV共感染后,这种抑制作用更为明显(P＜0.01).ALV J单独感染后,鸡对传染性法氏囊病病毒(IBDV)弱毒疫苗免疫后的抗体反应与对照组没有明显差别,但ALV-J与REV的共感染可明显延缓鸡对IBDV弱毒疫苗免疫的抗体反应.     

Dose-response effects of diclazuril against pathogenic species of ovine coccidia and the development of protective immunity

Twin lambs at pasture with their ewes, were divided into seven groups of 10 lambs. One group of 10 lambs served as a non-infected, untreated control. Five groups of 10 lambs were infected with 10,000 oocysts of Eimeria crandallis and 10,000 oocysts of Eimeria ovinoidalis when they were 3 weeks old (day 21 of the study). This produced a good level of infection with high oocysts production and diarrhoea in the lambs. Fourteen days after the primary, artificial challenge (day 35) four of these groups were treated with oral diclazuril at 0.25, 1.0, 2.0 or 4.0mg/kg. Diclazuril treatment was highly effective, dramatically reducing symptoms of diarrhoea and reducing faecal oocyst output by 79.7%, 97.3%, 99.4% and 99.5% respectively in the treated groups within four days. Two weeks post-treatment, and 28 days after the primary coccidial challenge (day 49 of the study), five groups of lambs were re-challenged with 100,000 oocysts of E. crandallis and 100,000 oocysts of E. ovinoidalis (secondary challenge). A group of lambs which had received neither the primary coccidia infection, nor drug treatment (susceptible controls) were also given the secondary challenge. All lambs given the secondary challenge produced high numbers of coccidia and exhibited varying degrees of diarrhoeic faeces. The lambs, which had previously received the higher doses of diclazuril at 2.0 and 4.0mg/kg, developed clinical signs of coccidiosis. These lambs were completely susceptible despite having received the early primary immunising infection of coccidia on day 21. The effects of the secondary challenge were more severe in the groups dosed with the two highest levels of diclazuril than in the susceptible control lambs, which had presumably been exposed to continued low levels of pasture contamination and had acquired a limited degree of immunity from this exposure. It would appear that treatment at the higher dose levels not only eliminated most of the oocysts from the primary challenge but also adventitious infection derived from the grazing paddocks. In contrast, lambs which had received the two lower drug levels of diclazuril (0.25 and 1.0mg/kg) whilst producing large numbers of oocysts, had only transient diarrhoea following secondary challenge. It was concluded that when used as a metaphylactic treatment, diclazuril works rapidly and is effective within four days of administration. Overall, a single dose of diclazuril at either 0.25-1.0mg/kg appears to be highly effective in the control of coccidiosis in young lambs at pasture whilst allowing the development of protective immunity against subsequent heavy coccidia challenge.