Coccidiosis in poultry: anticoccidial products, vaccines and other prevention strategies

Coccidiosis in chickens is a parasitic disease with great economic significance, which has been controlled successfully for decades using mainly anticoccidial products. However, large-scale and long-term use of anticoccidial drugs has led to the worldwide development of resistance against all these drugs. In order to minimize the occurrence of resistance, the rotation of various anticoccidial drugs in single and/or shuttle programmes is used. Unfortunately, this has not solved the anticoccidial resistance problem. Recently, live anticoccidial vaccines have been incorporated into rotation programmes, resulting in an increasing incidence of anticoccidial drug-sensitive Eimeria spp. field isolates, which may ameliorate the efficacy of anticoccidial drugs. Nevertheless, possible upcoming bans restricting the use of anticoccidials as feed additives, consumer concerns on residues and increasing regulations have prompted the quest for alternative coccidiosis control strategies. Although management and biosecurity measures could halt the introduction of Eimeria spp. to a farm, in practice they do not suffice to prevent coccidiosis outbreaks. Phytotherapy, aromatherapy and pre- and probiotics either show conflicting, non-consistent or non-convincing results, and have therefore not been applied at a large scale in the field. So far, live attenuated and non-attenuated anticoccidial vaccines have proved to be the most solid and successful coccidiosis prevention and control strategy. Despite the drawbacks associated with their production and use, their popularity is increasing. If with time, the immunogenicity of subunit vaccines can be improved, they could represent the next generation of highly efficient and low-cost anticoccidial strategies.     

Use of toltrazuril in pullet breeding flocks raised on floors with anticoccidial-free feed

In 28 replacement pullet flocks with flock size of 4,000 to 25,000 birds Toltrazuril (experimental preparation, 2.5% solution, approx. 7 mg/kg body weight) was administered for a period of two days in the drinking water for metaphylactic purpose and therapeutic use, respectively. All flocks were reared without anticoccidial feed additives. Exposition to Eimeria spp. was recorded by examination of faecal samples and intestinal scrapings. Clinical flock control was achieved by vets at eight to ten day intervals. Toltrazuril was characterized by short application period, rapid mode of action, significant reduction of oocyst shedding, good compatibility and acceptance thus proving superior to conventional chemotherapy of coccidiosis. The results suggest that, even without administration of anticoccidial feed additives. Toltrazuril is an effective agent for therapeutic use in acute coccidiosis. Under insufficient management and rearing conditions repeated metaphylactic application has to be considered.     

Pharmacokinetics of florfenicol after treatment of pigs with single oral or intramuscular doses or with medicated feed for three days

The pharmacokinetics of florfenicol, a structural analogue of thiamphenicol, were studied in six pigs after single oral and intramuscular doses of 15 mg/kg bodyweight, and after feeding them with medicated feed containing 250 mg/kg for three days, a concentration which provided approximately the same dose rate of the drug. The oral doses contained a specially prepared pelleted formulation of the drug. The bioavailability of the drug was similar for the oral and intramuscular doses. Florfenicol was absorbed rapidly from the feed and its concentration in plasma remained between 2 and 6 microg/ml - above the minimum inhibitory concentration values for common pig pathogens - during the three days.     

Free versus microencapsulated organic acids in medicated or not medicated diet for piglets

Aim of the study was to investigate the growth performance of weaned piglets fed either a medicated or not medicated diet supplemented with either a blend of formic and lactic (64/36) acids (FL, 11 kg/ton) or a microencapsulated blend of organic acids and flavors (T) (1 kg/ton, Tetracid®S, EU patent 1391155B1,Vetagro srl, Italy). 480 three-week old SCAAPAG × Goland piglets were fed four diets (4 pens of 30 piglets per diet): FL or T with or without the medication (M) comprising colistin 180 ppm + amoxicillin 600 ppm for the 1st phase and chlortetracycline 1000 ppm + sulphadiazine 1250 ppm + trimetoprim 250 ppm for the 2nd phase. The piglets received a two-phase diet (I:18% CP, 1.3% Lys, 7.5% CF and 2600 kcal/kg NE; II:18% CP, 1.2% Lys, 5.6% CF and 2400 kcal/kg NE). All data were analysed by ANOVA. After 49 days, animals fed the medicated diets had higher feed intake (+ 24.5% for group FL + M vs FL − M and + 22.3% for group T + M vs T − M; P < 0.01) and lower mortality (overall 1.2% for the medicated diets fed animals vs 9.2% for the non-medicated ones). Final weights were: 26.8 ± 1.0 kg, 25.7 ± 0.8 kg for FL + M, T + M, 20.9 ± 0.7 kg, 21.6 ± 0.8 kg for FL − M and T − M, respectively (P < 0.05). The medication resulted in maintaining animals in good health status. The microencapsulation technique allowed to lower the acids dose to be included in the feed by ten fold at least maintaining the same effects that a high dose can give without medication.     

超高效液相色谱-串联质谱法测定饲料中5种聚醚类抗球虫药的含量

本实验建立了超高效液相色谱-串联四级杆质谱法同时测定饲料中5种聚醚类抗球虫药含量的确认检测方法.试样经乙腈提取、石墨化碳黑固相萃取柱净化后,采用超高效液相色谱-电喷雾串联四极杆质谱法进行分离检测.色谱条件:ACQUITY UPLCTM BEH C18柱(2.1 mm×50 mmi.d.,1.7μm),流动相:甲醇-0.1%甲酸水溶液(85+15),等度洗脱,流速为0.3mL/min.采用正离子模式检测,外标法定量.结果表明,莫能菌素、马杜霉素、盐霉素、甲基盐霉素和拉沙洛西的浓度在1～500 mg/mL范围内线性良好,在10～100 mg/kg的添加水平务件下平均回收率为78.5%～91.2%,该方法的检测限(LOD)为10ug/kg,定量限(LOQ)为20 ug/kg.     

Carry-over of sulphadimidine in the faeces and urine of pigs fed medicated feed

In two experiments sulphadimidine-free pigs were placed in pens previously occupied by pigs fed a diet containing 100 ppm sulphadimidine. Faeces, urine and spilled feed had been removed by scraping the surface of the pens before the new pigs were introduced. The concentration of sulphadimidine in the tissues of the medicated pigs fell below 100 ng/g within 72 hours of withdrawal of the medicated diet and in the fluids the concentration fell below 500 ng/ml within 96 hours. The concentrations in the tissues of the pigs housed in the contaminated pens exceeded 100 ng/g for up to 24 hours but then fell to acceptable concentrations; the concentration of sulphadimidine in body fluids occasionally exceeded 500 ng/ml.     

Oxytetracycline pharmacokinetics in rainbow trout during and after an orally administered medicated feed regimen

The pharmacokinetic-pharmacodynamic predictor of antimicrobial activity for tetracyclines is reported to be the area under the concentration-time curve at steady state (AUC(ss)) divided by the minimal inhibitory concentration of the targeted pathogen. Here, we estimate AUC(ss) values for oxytetracycline (OTC) in serum of rainbow trout Oncorhynchus mykiss by using a destructive sampling study design. Seventy-two rainbow trout were fed OTC-medicated feed at 74.7 +/- 1.5 mg/kg (mean +/- SD) body weight (BW) by oral gavage for 10 consecutive days. Serum was collected from nine fish at 1, 3, 6, 8, 10, 12, 15, and 22 d after dosing began. Serum OTC concentrations were measured by high-performance liquid chromatography with a 0.01-microg/mL limit of detection. The average OTC AUC(ss) was 29.2 microg x h/mL and was estimated using nonlinear mixed-effects modeling and bootstrap resampling techniques. The elimination half-life was estimated as 85.0 h, and the fraction of steady state achieved was estimated as 0.85. The calculated AUC(ss) (24.8 microg x h/mL) following 10 d of oral dosing with 75 mg OTC/kg BW was less than the estimated AUC(ss). Results suggest that the pharmacokinetics of OTC exposure, including the AUC(ss), is better evaluated by using multiday dosimetry than by using a standard single-dose protocol.     

Effect of medicated feed on tracheal infection and population of Mycoplasma gallisepticum in chickens

Six-week-old broilers were fed 50 g tylosin/ton, 400 g chlortetracycline (CTC)/ton, or unmedicated feed and then challenged intratracheally with R strain Mycoplasma gallisepticum (MG). Feed-grade antibiotic medication did not prevent infection, but medication did lower the number of isolations from treated birds compared with controls. Only tylosin significantly lowered MG counts in the trachea. The log10 ID50 of birds receiving tylosin, CTC, or unmedicated feed were 5.8, 4.4, and 2.9, respectively. Six-week-old leghorns were placed on the three diets described previously and challenged with the R strain of MG. Birds were sacrificed at various times up to 10 weeks postchallenge (PC). Compared with the control diet, the tylosin-medicated diet significantly reduced the tracheal MG count from day 1 to 4 weeks PC, whereas the CTC-medicated diet significantly lowered the tracheal MG count only at 3 days PC. In all groups, the MG count gradually declined after 1 week PC; by 8 weeks PC it was essentially the same in all groups. It was concluded that continuous medication has the potential for reducing MG tracheal populations only during the initial phase of an outbreak.     

免疫调节剂对球虫感染鸡的免疫学指标的影响

为探讨免疫调节剂对鸡球虫病的免疫反应调节作用，设计并进行了免疫调节剂对球虫感染鸡的免疫学指标的影响的研究。测定指标包括：淋巴细胞玫瑰花环细胞形成率、淋巴细胞转化率、红细胞免疫复合物花环形成率、红细胞Ｃ３ｂ受体花环形成率、脾脏重／体重相对重；血清中ＩｇＧ，ＩｇＭ，ＩｇＡ的ＥＬＩＳＡＰ／Ｎ值。试验结果表明：胸腺素、黄芪多糖和卡介苗等免疫调节剂可提高球虫感染鸡的淋巴细胞玫瑰花环形成率、淋巴细胞转化率。     

Differences between the anticoccidial potencies of monensin in maize-based or wheat-based chicken diets

Experiments were carried out to investigate why the anticoccidial ionophore monensin is more potent against the coccidiumEimeria tenella in chickens fed on a maize-based diet (as in the USA) than in chickens fed on a wheat-based diet (as in the UK). The explanation seems to be that the pathogenicity ofE. tenella is lower in maize-fed chickens than in wheat-fed chickens, whether monensin is present in the diet or not. Possible reasons for this are suggested. The better survival of maize-fed birds may be partly due to protective effects of the higher concentrations of vitamins A and E derived from their diet. Furthermore, the higher concentrations of niacin and riboflavin in wheat than in maize may enhance coccidial pathogenicity. These opposing factors might combine to cause equivalent infection levels to produce more severe coccidiosis in chickens fed on a wheat-based diet than on a maize-based diet.     

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.     

Differential compensatory growth in swine following control of feed intake by a high-alfalfa diet fed ad libitum or by limited feed

Seventy-two castrated male four-way composite (Chester White x Landrace x Large White x Yorkshire) weanling pigs (17 kg initial BW) were used to determine the compensatory response of specific organs and whole body following a 3-wk period of restricted energy intake imposed by ad libitum-feeding an 80% alfalfa meal diet or pair-feeding an adequate corn-soybean meal diet to attain equal weight loss. Six pigs were killed at d 0 to provide baseline data. Six pigs from each diet group (control, C; alfalfa, A, restricted, R) were killed at d 21, after which all remaining pigs were fed C ad libitum to 35 d, 105 d or 126 d. Six pigs per group were killed at 35 and 105 d and four per group were killed at 126 d. Organ weight and carcass data were recorded for all pigs at all time intervals. Regression of organ and trimmed lean tissue weights on time was tested for linearity (d 1 to 126 for C and d 21 to 126 for A and R except d 35 to 126 for gastrointestinal tract traits for A and R); differences in organ weights between C, A and R at d 21 and d 35 were tested by a two-way analysis of variance. There was no evidence of a compensatory growth response to dietary energy restriction for 21 d except for rate of change in weights of liver and kidneys and backfat depth from 21 to 126 d and of gastrointestinal tract components from 21 to 35 d. Specific organs may exhibit compensatory growth over different time spans in young pigs in the absence of observable weight compensation at the whole-animal level.     

肉鸡饲料消化不良的原因和防治

春夏季节时，常有养殖户反映20～60日龄多的肉鸡出现粪便中残留饲料小颗粒，粪中可见玉米小颗粒。当肉鸡饲料出现消化不良时，养殖户就抱怨饲料质量太差。但是这个问题在不同的养殖户．导致的原因不同，要考虑很多因素：