堆型艾美耳球虫早熟株对常用抗球虫药的敏感性测定

The study was aimed to explore the sensitivity of Eimeria acervulina （E.acervulina） precocious strain to some common anticoccidials (diclazuril, toltrazuril, sulfamonomethoxine, dinitolmide, decoquinate, nicarbazin, maduramicin, salinomycin and oxytetracycline). The sensitivity of E.acervulina precocious strain to 9 kinds anticoccidials was assessed by using 4 indices: anticoccidial activity percentage (POAA), reduction of lesion scores (RLS), relative oocyst production (ROP) and anticoccidial index (ACI). The results of these sensitivity trials indicated that the four indices POAA, RLS, ROP and ACI of groups toltrazuril, sulfamonomethoxine, dinitolmide, decoquinate, nicarbazin, salinomycin and oxytetracycline were all negative; the ROP index of diclazuril group was positive, the other three indices were negative. The ROP and ACI indices of maduramicin group were positive, the other two indices were negative. The results showed that the Eimeria acervulina precocious strain was sensitive to diclazuril, toltrazuril, sulfamonomethoxine, dinitolmide, decoquinate, nicarbazin, salinomycin and oxytetracycline, it was partly sensitive to maduramicin.     

Comparative therapeutic effect of toltrazuril, sulphadimidine and amprolium on Eimeria bovis and Eimeria zuernii given at different times following infection in buffalo calves (Bubalus bubalis)

We compared the therapeutic effect of three anticoccidial drugs (toltrazuril, sulphadimidine and amprolium) in buffalo (Bubalus bubalis) calves experimentally infected with Eimeria bovis (E. bovis) and E. zuernii oocysts (3 x 104oocyst/calf). Buffalo calves (1.5-4 month old, 70-kg body weight) were randomly allocated into 3 groups (9 calves each). Group T was experimentally infected with oocysts and treated with toltrazuril (20 mg/kg BW twice orally at a 1-week interval). Group S was experimentally infected with oocysts and treated with sulphadimidine (125 mg/kg injected IM followed by half dose for 4 successive days). Group A was experimentally infected with oocysts and treated with amprolium (50 mg/kg orally for 7 successive days). Each group had three subgroups (three calves/subgroup) to represent timing of the drug administration: 1st day of coccidia infection (FD), onset of clinical signs of coccidiosis (CC), and onset of oocyst shedding into the faeces (OS). Clinical signs, body-weight gain (BWG) and number of oocysts per gram feces (OPG) were monitored daily for 35 days post-infection (DPI). The OPG were reduced (but the BWG was not different) in the T calves compared to S and A calves. Within the same group, treatment from the 1st day of infection reduced the OPG and increased the BWG compared to the later treatment timings.     

The effect of a metaphylactic treatment with diclazuril (Vecoxan) on the oocyst excretion and growth performance of calves exposed to a natural Eimeria infection

A multicenter field efficacy study was performed in six farms located in Belgium, France and Germany with a history of suspected coccidiosis outbreaks and the proven presence of Eimeria bovis and/or Eimeria zuernii. At each of these trial sites the calves were randomly allocated to two groups (T, treated; C, control) of similar size. In total, 231 calves were included in the study. Group T calves (n=116) were drenched with a single dose of diclazuril (Vecoxan, 1mg/kg body weight) close to the time of expected outbreak of coccidiosis (day 1 of the study period), group C calves (n=115) served as placebo-treated controls. Although E. bovis and/or E. zuernii were identified at all trial sites, clinical coccidiosis was only noted in 16% of the group C calves. At day 5 of the study period (4 days after treatment), faecal oocyst counts (opg, oocysts per gram) were substantially lower in group T ("short-term effect") compared to group C. At four trial sites, the respective values of groups T and C were significantly different (P=0.0132 to P=0.0001) in favour of group T. For the pooled data of all trial sites, this effect was highly significant (P<0.0001). The overall faecal oocyst counts from day 3 until day 21 of the study period ("Area Under the Curve") was significantly reduced in group T by 87.2-99.5% ("long-term effect") at five trial sites (P=0.0139 to P<0.0001). The pooled data revealed a highly significant effect of treatment on oocyst excretion over the observation period (P<0.0001). On five of the six trial sites, the average weight gain was higher in group T than in group C. On those trial sites, the average weight gain of group T calves exceeded that of the controls by 95-268g/day and by 2.0-6.0kg over the study period. This effect was statistically significant (P<0.01) at one trial site. Altogether the calves of group T gained on average 129g more weight daily than the controls (+2.7kg over the study period). For these pooled data, statistical analysis confirmed the positive effect of treatment of calves exposed to coccidiosis on growth performance (P=0.003). In conclusion, metaphylactic treatment with diclazuril efficiently controls coccidiosis in calves thus reducing environmental contamination with oocysts and preventing negative effects of natural exposure to coccidiosis on growth performance of calves.     

Treatment with toltrazuril in a natural outbreak of coccidiosis in calves

Treatment with toltrazuril (Baycox) in calves naturally infected with several enteropathogenic agents resulted in a reduction in the mean number of Eimeria oocysts shed. The mean faecal consistency for the treated calves also differed significantly from that of the untreated calves. There was virtually no difference in weight gain in the two groups.     

Effect of subcutaneously administered diclazuril on the output of Eimeria species oocysts by experimentally infected rabbits

The effect of subcutaneously injected diclazuril on the output of Eimeria species oocysts was studied in experimentally infected rabbits. Diclazuril was administered either prophylactically at 0.5, 1 or 2 mg/kg bodyweight two days before each rabbit was inoculated with 20,000 oocysts of a mixed-species field isolate of Eimeria or therapeutically at 1, 2 or 4 mg/kg bodyweight five days after they were inoculated. The prophylactic treatments significantly reduced (P<0.05) the output of oocysts in faeces and the numbers in the rabbits' livers at all doses. The therapeutic treatment at 4 mg/kg also caused a significant reduction (P<0.05) in oocyst shedding, but the lower doses resulted in only a moderate reduction. The shedding of the pathogenic species Eimeria stiedae, Eimeria magna, Eimeria irresidua, Eimeria flavescens, Eimeria piriformis and Eimeria intestinalis was significantly reduced (P<0.05) in all the treated groups. The burden of oocysts in the livers of the therapeutic groups (4000 to 9000) were significantly lower (P<0.05) than in the inoculated but untreated control group (23,000), but higher than in the prophylactic groups (around 1000).     

杀球灵对鸡盲肠球虫病的治疗试验及作用峰期探讨

本试验用１０日龄公雏９６只,分为８个组。氯嗪苯乙氰用量为１×１０－６,其中６个组分别在感染后０,４８,７２,９６,１２０,１５４ｈ给药治疗人工感染１×１０５个柔嫩艾美耳球虫孢子化卵囊的雏鸡。结果表明杀球灵（Ｃｌｉｎａｃｏｘ）为高效抗球虫药物,兼有预防和治疗作用。作用于盲肠球虫的有性生殖和无性生殖阶段。     

5株柔嫩艾美耳球虫对4种抗球虫药的抗药性

选择260只19日龄雏鸡，随机分成26组，每组10只，研究柔嫩艾美耳球虫(E．tenella)南京株、凤阳株、扬州株、宣城株和蒙城株对地克珠利(Diclazuril)、马杜霉素(Maduramicin)、氯羟吡啶(C1opido1)、氯苯胍(Robenidine)的抗药性。每株球虫均设4个感染用药组、1个感染不用药组，另外设1个不感染不用药组。以POAA、RLS、ROP、ACI作为指标，判定5株球虫对4种药物的抗药性。结果表明凤阳株、扬州株和蒙城株分别仅对马杜霉素、氯苯胍、地克珠利敏感，南京株和宣城株对该4种药物均已产生不同程度的抗药性。提示目前在凤阳、扬州和蒙城地区可分别合理地使用马杜霉素、氯苯胍和地克珠利，对其它药物须减少或暂停使用。     

通扬球虫清对鸡球虫病的疗效试验

测定了通扬球虫清对鸡球虫病的疗效,三批试验结果显示,通扬球虫清高剂量组(甲基三嗪酮37.5mg/L饮水浓度,8天)和中剂量1组(甲基三嗪酮25mg/L饮水浓度,8天)的抗球虫指数始终在高效水平;中剂量2组(甲基三嗪酮25mg/L饮水浓度,2天)和通扬独霸组(地克珠利0.5mg/L饮水浓度,8天)的抗球虫指数相近,也属高效抗球虫范围;通扬球虫清低剂量组(甲基三嗪酮12.5mg/L饮水浓度,8天)的抗球虫指数属中等有效水平。综合各项指标及与通扬独霸组的药效相比,通扬球虫清在临床上选用25mg/L饮水浓度,连续饮用2天或2天以上切实可行。     

Economic benefits of prophylaxis with diclazuril against subclinical coccidiosis in lambs reared indoors.

One hundred and twenty weaned male lambs, naturally infected with Eimeria species, were used to assess the economic benefits of the prophylactic administration of diclazuril. They were randomly divided into four groups of 30 lambs on the basis of their bodyweight and output of oocysts. The groups were either left untreated (group 1), treated orally with a simple dose of diclazuril at 1 mg/kg (group 2), with two doses two weeks apart (group 3), or with sulphadimethoxine at 50 mg/kg for five consecutive days (group 4). No clinical signs of coccidiosis were observed in any of the groups. The output of oocysts was significantly reduced on day 7 after treatment in group 2, on days 7, 14 and 28 in group 3 and on days 7 and 14 in group 4. No significant differences were found between the treated and untreated groups for bodyweight, carcase weight and carcase classification. The mean fattening period was shorter for the treated lambs (52 and 55 days) than for the untreated controls (60 days). The average growth rate of the lambs treated twice with diclazuril and with sulphadimethoxine was improved and the feed conversion rates of the lambs treated once or twice with diclazuril were 7 per cent and 16 per cent better than that of the untreated lambs.     

Increased level of Eimeria sensitivity to diclazuril after using a live coccidial vaccine

Anticoccidial vaccine and an anticoccidial drug rotation program were compared to determine which program was more effective in producing coccidia populations sensitive of 1 ppm diclazuril. The study used an anticoccidial drug-sensitivity battery test (AST) to determine the baseline level of diclazuril sensitivity to field isolates of Eimeria spp. from seven broiler complexes that had used diclazuril. Based on percentage reduction in weight gain and lesion scores, 25% or fewer of the isolates were effectively controlled by diclazuril. Following the baseline sampling, four of the complexes switched to a nondiclazuril in-feed anticoccidial drug program and three of the complexes switched to a vaccination program for two broiler grow-out cycles as the sole coccidiosis-control program. This study demonstrated that the vaccine used (Coccivac-B) contained anticoccidial drug-sensitive strains. Eimeria isolates were subsequently collected from the identical houses and diclazuril AST results were compared with the baseline AST results. Following the two grow-out cycles, sensitivity of the isolates to diclazuril from the four complexes that continued to use in-feed anticoccidial drugs remained essentially unchanged. The isolates from the three complexes that switched to the vaccination program demonstrated a marked increase in diclazuril sensitivity, with 60%-100% of the isolates from each complex effectively controlled by diclazuril. Vaccination with the anticoccidial drug-sensitive strains produced a measurable increase in the level of sensitivity to diclazuril.     

Higher incidence of Eimeria spp. field isolates sensitive for diclazuril and monensin associated with the use of live coccidiosis vaccination with paracox-5 in broiler farms

Twenty European Eimeria spp. field isolates were subjected to an anticoccidial sensitivity test (AST). The anticoccidial drugs tested were diclazuril (Clinacox) and monensin (Elancoban). The assay was performed in a battery cage trial. Infected medicated birds were compared with an unmedicated control group. Coccidial lesion scores and oocyst shedding were used as parameters. The results of the AST show that resistance is common amongst coccidiosis field isolates, especially Eimeria acervulina (68% and 53% resistance for diclazuril and monensin, respectively). Resistance is less frequent amongst Eimeria maxima (38% and 50% resistance for diclazuril and monensin, respectively) and Eimeria tenella isolates (23% and 38% resistance for diclazuril and monensin, respectively). A highly significant influence of the coccidiosis prevention program (live coccidiosis vaccination with Paracox-5 vs. anticoccidial drugs in feed) on the sensitivity patterns of Eimeria spp. field isolates for both diclazuril (P= 0.000) and monensin (P= 0.001) was found. Further, when looking at the single species and each anticoccidial drug level, significantly more sensitivity of E. acervulina for monensin (P= 0.018), E. maxima for diclazuril (P = 0.009), and E. tenella for diclazuril (P = 0.007) was found in isolates originating from vaccinated flocks. Moreover, for E. acervulina and diclazuril, E. maxima and monensin, and E. tenella and monensin a trend toward higher sensitivity of isolates for these products was found when live coccidiosis vaccination was applied. The present study shows that sensitivity for the anticoccidial drugs diclazuril and monensin is more frequent in Eimeria spp. field isolates originating from broiler farms where a coccidiosis vaccination policy is followed.     

Efficacy of salinomycin in treatment of experimental Eimeria bovis infections in calves

The efficacy of salinomycin for treatment of experimental Eimeria bovis infections was evaluated. In experiment 1, 18 calves were placed into four groups. Group 1 calves were nonmedicated controls; groups 2, 3, and 4 calves were given salinomycin (0.33, 0.66, and 1.00 mg/kg of body weight, respectively) in daily oral divided doses starting 2 or 3 days prior to E bovis inoculations and continuing until postinoculation day (PID) 21. Calves treated with 0.66 and 1.00 mg/kg (groups 3 and 4) passed substantially fewer oocysts than did control calves (group 1) or calves treated with 0.33 mg/kg (group 2). Group 1 control calves had typical signs of severe E bovis infections, whereas signs of infection in medicated calves were almost nonexistant. Experiment 2 was conducted as before, with 15 calves. Group 5 calves were nonmedicated controls; groups 6, 7, and 8 calves were treated with 0.5, 1.0, and 2.0 mg/kg, respectively. All group 8 calves and three of four group 7 calves had nearly complete suppression of oocyst excretions. The severity of the disease in the group 5 control calves was not as extensive as it was in group 1 control calves. In experiment 3, 16 calves were used. Group 9 calves were nonmedicated controls, whereas other calves were given salinomycin (2.0 mg/kg) during PID 3 to 7 (group 10), PID 8 to 12 (group 11), and PID 13 to 17 (group 12). Salinomycin therapy in group 2 calves resulted in substantial reductions in oocyst excretions and clinical signs.     

Chemotherapeutic efficacy of sulphadimidine, amprolium, halofuginone and chloroquine phosphate in experimental Eimeria bareillyi coccidiosis of buffaloes

Sulphadimidine, amprolium, halofuginone and chloroquine phosphate were administered to buffalo calves 10 days after experimental infection with Eimeria bareillyi. Animals given sulphadimidine or amprolium remained clinically normal and shed only a few oocysts in their faeces. Halofuginone was found partially effective and chloroquine phosphate completely ineffective in preventing faecal oocyst discharge and intestinal lesions. Sulphadimidine and amprolium treated calves gained weight, but chloroquine treated calves suffered progressive weight loss similar to that of infected untreated controls. No significant alterations of haematological values were observed either in the treated calves or in the untreated controls.     

2株柔嫩艾美耳球虫对5种抗球虫药的抗药性

选择130只21日龄雏鸡，研究了柔嫩艾美耳球虫（E.tenella)南京株和凤阳株对地克珠利（Diclazuril)、马杜霉毒（Maduramicin)、氯羟吡啶（Clopidol)、氯苯胍（Robenidine)和氨丙啉（Amprolium)的抗药性。试验鸡随机分成13组，其中每株球虫均设5个感染用药组，1个感染不用药组，另设1个不感染不用药组，每组10只鸡。以POAA，RLS，ROP，ACI作为指标。结果表明，2株柔嫩艾美耳球虫均对氨丙啉轻度抗药，对地克珠利敏感或轻度抗药，对氯羟吡啶中度抗药。对马杜霉和氯苯胍中度抗药或安全抗药。提示：目前在凤阳地区可合理地使用地克珠利和氨丙啉，对氯羟哟啶应慎用，对马杜霉素和氯苯胍须减少或暂停使用。     

Chemoimmunoprophylaxis against bovine tropical theileriosis in young calves: a comparison between buparvaquone and long-acting oxytetracycline

Eighteen seven to 21-day-old crossbred (Bos taurus cross Bos indicus) calves were allocated to four groups (A to D). Groups A and B each consisted of six calves and groups C and D three calves each. Each calf in groups A, B and C was inoculated with ground-up tick supernate (GUTS) equivalent to two infected acini prepared from Theileria annulata-infected Hyalomma anatolicum anatolicum. Each calf in group A was also given a single intramuscular injection of buparvaquone, 2.5 mg kg-1 bodyweight simultaneously with GUTS, whereas each calf in group B was given a single intramuscular injection of long-acting oxytetracycline, 20 mg kg-1 bodyweight following inoculation of GUTS. In calves of group A clinicopathological reactions were negligible, whereas in calves of group B mild to severe reactions were observed resulting in the death of three of the six calves. All the calves of group C (infected, untreated controls) died of acute theileriosis. All the surviving calves of groups A and B withstood a lethal homologous challenge given on day 30 after immunisation, indicating no difference in the immune status of the surviving calves of the two groups. Group D, challenge control, all calves died of theileriosis within 18 days of challenge.     

Estimation of the economical effects of Eimeria infections in Estonian dairy herds using a stochastic model

In this study, a stochastic predictive model stimulating a constant infection pressure of Eimeria was used to estimate production outcome, economic, and effects of treatment decisions in a dairy herd of 100 cows. The intestinal parasite cause problems mainly in calves, and is known to have long term effects on the growth rate, and in severe cases can result in mortalities. Due to the inconspicuous nature of the parasite, the clinical signs and sub-clinical manifestations it may produce can be overlooked. Acquired data from literature and Estonian dairy farms were implemented in the SimHerd IV model to simulate three scenarios of symptomatic treatment: no calves treated (NT), default estimate of the current treatment strategy (DT), and all calves treated (AT). Effects of metaphylactic treatment were studied as a lowering of the infection pressure. Delay in the age for beginning of insemination of heifers was the effect with the largest economic impact on the gross margin, followed by calf mortality and reduction in growth rate. Large expenses were associated with the introduction of replacement heifers and feeding of heifers as a result of the delay in reaching a specific body weight at calving. Compared to the control scenarios, with no effects and treatments of Eimeria, dairy farmers were estimated to incur annual losses ranging 8-9% in the balanced income. Providing metaphylactic drugs resulted in an increased gross margin of 6-7%. Purchase of new heifers compensated for some production losses that would otherwise have enhanced expenses related to Eimeria. The simulation illustrates how effects of Eimeria infections can have long lasting impact on interacting management factors. It was concluded that all three simulated symptomatic treatment regimes provided only small economic benefits if they were applied alone and not in combination with lowering of infection pressure.     

柔嫩艾美耳球虫扬州分离株对8种抗球虫药的抗药性

将柔嫩艾美耳球虫(Eimeria tenella)扬州分离株感染14日龄苏禽黄羽肉鸡,设立8个用药组、1个感染不用药对照组和1个不感染不用药对照组,以相对卵囊产量、病变记分减少率、最适抗球虫百分数和抗球虫指数为指标对该虫株对盐霉素、马杜拉霉素、球痢灵、氯羟吡啶、氨丙啉、尼卡巴嗪、甲基三嗪酮、地克珠利等8种常用抗球虫药的抗药性进行了综合评定,分析了该地区球虫的抗药性及对策。结果表明,该虫株对甲基三嗪酮敏感,对氨丙啉具有中度抗药性,对盐霉素、马杜拉霉素、球痢灵、氯羟吡啶、尼卡巴嗪、地克珠利等其他6种药物具有完全抗药性。提示目前在扬州地区甲基三嗪酮抗球虫疗效最好,氨丙琳效果稍差,应合理使用,盐霉素等其他6种药物应慎用、减少或暂停使用。     

Sub-clinical parasitism in spring-born, beef suckler calves: epidemiology and impact on growth performance during the first grazing season

Sub-clinical parasitism in spring-born single suckled beef calves was investigated from the middle of their first grazing season until weaning or housing later the same year. The study was conducted on four beef suckler herds in southern England over a 3-year period and involved a total of 334 spring-born beef suckler calves and their dams. The animals were grazed extensively on pastures naturally infected with nematode larvae. At the start of each period of observation, faecal samples were taken from calves and cows and subjected to routine worm egg counts; calves were re-sampled at the end of the grazing season.In July in each year and at each location the calves were ranked by initial weight within sex, paired according to rank and randomly allocated to either an untreated control group or a group in which the calves were each treated with an ivermectin sustained-release (SR) bolus. The calves in both trial groups, and their dams, were grazed together until weaning or housing. The calves were weighed at the initial allocation and at the end of the study. The adult cows were not treated with any anthelmintic during the study.The faecal nematode egg counts (FECs) conducted in July showed that the suckler cows were excreting worm eggs at low concentrations: range 0-100 eggs per gram (epg), with one individual count of 500epg, 88% of the cows sampled had counts of <50epg. Similarly, the counts from the calf samples were fairly low in July: range 0-250epg, 73% of the calves sampled had counts of <50epg. By the end of the grazing season, the faecal samples from the untreated control calves showed higher values: range 0-650epg, with only 58% having an epg of <50.The average rate of daily liveweight gain in the untreated heifer calves was 0.79kg per day, the corresponding figure for the heifer calves treated with the ivermectin SR bolus in mid-summer was 0.88kg per day; the difference of 90g per day was significantly different (P=0.0118). The average rate of daily liveweight gain in the untreated bull calves was 0.91kg per day, the corresponding figure for the bull calves treated with the ivermectin SR bolus in mid-summer was 1.01kg per day; the difference was significantly different (P=0.0169).     

Prevalence of Cryptosporidium, Giardia and Eimeria infections in post-weaned and adult cattle on three Maryland farms

The prevalence of Cryptosporidium, Giardia and Eimeria, in healthy, asymptomatic, post-weaned and mature cattle was investigated on three Maryland farms. One farm, a dairy research facility, had 150 multiparous Holstein milking cows; 24 were examined and Cryptosporidium andersoni was detected in three (12.5%) but neither Giardia nor Eimeria was detected. The second farm, a commercial dairy, had 57 multiparous Holstein milking cows and an equal number of heifers. Of 19 cows examined, C. parvum, Giardia duodenalis, and Eimeria bovis and/or E. ellipsoidalis were detected in two (10.5%), two (10.5%) and one (5.26%) cow, respectively. Of 23 heifers examined, C. parvum, Giardia, and E. bovis and E. ellipsoidalis, was detected in two (8.7%), four (17.4%), and five (21.7%), heifers, respectively. The third farm, a beef cattle breeding and genetics research facility, had 180 7- to 9-month old purebred black Angus. Of 118 examined for C. parvum and Giardia, 34 (28.8%) and 44 (37.3%) were positive, respectively, of 97 examined for E. bovis and/or E. ellipsoidalis 32 (33.0%) were positive. These findings, based on a method with a minimum detection level of 100 oocysts of C. parvum/g of feces, which underestimates the number of infected cattle, clearly demonstrate the presence of low level, asymptomatic infections in post-weaned and adult cattle in the United States and indicate the potential role of such cattle as reservoirs of infectious parasites.     

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.