Monensin sensitivity of recent field isolates of turkey coccidia

Attenuation of a drug-sensitive strain of a turkey protozoan parasite Eimeria meleagrimitis by selection for precocious development

An attenuated line of Eimeria meleagrimitis was established by repeated propagation of the parasite in 9-day old turkey poults and subsequent selection for precocious development. Following 20 passages, the prepatent period decreased from 120 to 104h. A series of experiments were conducted to evaluate the pathogenicity, immunogenicity and fecundity of the newly selected line. Judged by body weight gain, feed consumption and feed efficiency following infection, the attenuated line had appreciably reduced pathogenicity. Immunogenicity of the attenuated line was examined by infecting poults successively with incremental doses of 10(2), 10(3) and 10(4) oocysts at 0, 7, and 14 days of age respectively. No oocysts were detected following challenge with 5×10(2) oocysts, indicating that the attenuated line had retained immunogenicity. Fecundity was assessed by infecting two-week old birds with 5×10(2) oocysts of either parent or attenuated line. Oocyst production from 96 to 240h post-infection showed that the patent period of the attenuated line commenced earlier and was of shorter duration than the parent line.

Biological re-description of a genetically typed, single oocyst line of the turkey coccidium, Eimeria meleagrimitis Tyzzer 1929

For the purpose of re-describing the Eimeria species that infect the turkey (Meleagris gallopavo) and to establish benchmark biological information linked to genetic markers for each species, a strain of Eimeria meleagrimitis Tyzzer 1929 was obtained from a litter sample from a turkey farm in Minnesota, USA in 2008. Multiple pure lines were derived by infecting turkey poults with a single oocyst; one of these lines was then used to re-describe biological and morphological features of E. meleagrimitis in the turkey and to designate a neotype of E. meleagrimitis in the turkey. Oocyst morphometrics of this line matched those of this species as originally described by Tyzzer (Am J Hyg 10:269-383, 1929). Three asexual generations of merogony (the first generation of meronts large in size and the second and third generations small) were detected in the intestines before the onset of gametogony; no developmental stages were detected in the cecal pouches. No mortality was induced by this line of E. meleagrimitis even when turkey poults were infected with high doses of oocysts (up to 5 × 10(5) oocysts/bird) and despite the ability of E. meleagrimitis to induce severe mucosal damage in the upper and middle duodenum. Macroscopic lesions were characterized to provide a graded lesion scoring guide that should assist assessment of the severity of infections with this species in infected turkeys. The pathogenicity of the strain was investigated, and a significant reduction in weight gain and feed conversion ratio was observed with doses of 10(4) oocysts/bird or more. The maximum yield of oocysts in the feces was obtained when birds were inoculated with 5 × 10(3) oocysts.

Control of Coccidiosis in Turkeys with Diclazuril and Monensin: Effects upon Performance and Development of Immunity toEimeriaSpecies

The effects of diclazuril and monensin, when included in the feed of turkeys from 0 to 10 wk, upon performance and development of immunity to Eimeria species was investigated. Birds were initially inoculated with a low dose of oocysts of three species of Eimeria at 3, 5, 7, and 9 days of age in order to simulate a natural infection. Weight gain and feed intake from 0 to 6 wk of age was significantly greater in medicated birds compared with those that received no anticoccidial medication. Weight gain and feed intake from 6 to 10 wk was greater in birds that received diclazuril than in unmedicated birds. No differences in performance were evident after drug withdrawal from 10 to 16 wk. Immunity to Eimeria species developed by 10 wk in birds that received no anticoccidial medication but did not develop in those given diclazuril or monensin.

Effects of different concentrations of monensin and monensin withdrawal upon the control of coccidiosis in the turkey

The efficacy of different concentrations of monensin in turkeys exposed to field isolates of Eimeria and the effect of the withdrawal of monensin from their diet were investigated. Results of a battery study indicated that 66 ppm monensin was effective against three species of Eimeria in the turkey. In floor pens in which poults were exposed to infection, use of 59.5, 79.4, and 99.2 ppm monensin resulted in reduced mortality and improved feed conversion at 3 wk of age compared with birds that had received no medication. Poults given 59.5 ppm monensin weighed more and had a better feed conversion at 3 wk than poults given 79.4 or 99.2 ppm monensin, but at 10 wk no differences in the body weight or feed conversion of poults given different concentrations of drug were apparent. At 14 wk (and from 10 to 14 wk), poults that had been given 99.2 ppm monensin had a lower feed intake and weighed less than birds that had been given 59.5 ppm of the drug but there were no significant differences in feed conversion. There was no significant difference in the weight gain or feed conversion of poults from 10 to 14 wk of age whether monensin was present in the feed or had been withdrawn. No evidence of compensatory growth was found in the present study.

A comparison of three continuous and four shuttle anticoccidial programs

Continuous programs of a combination of narasin (40 ppm) and nicarbazin (40 ppm) (NaNi), narasin at levels of 60 and 70 ppm, and a 2 by 2 factorial shuttle design (NaNi or nicarbazin at 125 ppm, each for 27 or 28 days, followed by narasin at 60 or 70 ppm to termination), were compared with unmedicated controls for their anticoccidial efficacy and growth performance in nine broiler trials conducted in seven countries outside the United States. Cecal coccidial lesions were reduced only by treatments that incorporated nicarbazin either at the 40-ppm level in NaNi or at 125 ppm, whereas total intestinal lesion scores were reduced by all the anticoccidial programs tested. At Day 28, the three treatments containing NaNi and the treatment containing narasin at 60 ppm significantly improved weight gain and feed efficiencies over the two treatments containing nicarbazin at 125 ppm and the unmedicated controls. At termination all the anticoccidial programs significantly decreased the mortality rate and improved bird weights and feed efficiencies. Birds on the treatments containing NaNi either in the two shuttle programs or in the continuous program were significantly heavier than those on the two treatments containing nicarbazin at 125 ppm in shuttle programs.

Efficacy of different anticoccidials against experimental coccidiosis in large white turkeys

Two trials were conducted to compare the efficacy of currently approved anticoccidials for turkeys against challenge using a field isolate of mixed Eimeria species; E. adenoides, E. gallopavonis, and E. meleagrimitis. Poults in wire-floored cages were fed unmedicated diets from day-old to 3 wk of age. Diets were supplemented with either amprolium (AMP, 125 mg/kg), butynorate (BUT, 375 mg/kg), monensin (MON-60, 60 mg/kg; MON-100, 100 mg/kg), halofuginone (HAL; 3 mg/kg), zoalene (ZOA; 125 mg/kg), or sulfadimethoxine plus ormetoprim (SUL + ORM, 62.5 mg/kg and 37.5 mg/kg, respectively). After 2 days on the test diets, poults were individually weighed and inoculated with sporulated coccidial oocysts from the field isolate. Total fecal collections were obtained for Days 0 to 5 and 6 to 10 to estimate oocyst output. At 10 days postinoculation, the birds were individually weighed and killed to determine severity of intestinal lesions. The HAL and MON were most effective and AMP, ZOA, and SUL + ORM were least effective in maintaining weight and in reducing the severity of intestinal lesions. All the coccidiostats tested reduced oocyst passage, but poults fed HAL produced fewer oocysts. The results demonstrated differences in efficacy among anticoccidials with the more recently approved drugs providing the best protection against coccidiosis.

Anticoccidial effect of monensin against Eimeria mitis and Eimeria dispersa

Four chick and five poult trials were conducted in order to investigate the anticoccidial efficacy of monensin against Eimeria mitis in chickens and Eimeria dispersa in turkeys. The chicks were fed a basal diet with either 0 or 100 ppm of monensin. The poults were fed a basal diet with either 0 or 60 ppm of monensin. Two days after the initiation of each experiment, the chicks and poults were crop-intubated with oocysts of E. mitis and E. dispersa, respectively. A group was also included that was not infected and not medicated. Growth and feed intake were recorded. At 6 or 7 days postinoculation, the birds were killed by cervical dislocation and were scored for the incidence and severity of intestinal abnormalities. The Eimeria mitis infection reduced (P less than .01) gain and the feed:gain ratio, compared with uninfected birds; the E. dispersa infection only reduced (P less than .05) gain. Although well-defined, discrete lesions were not observed, marked intestinal abnormalities were noted in birds infected with either E. mitis or E. dispersa. Also, the infected, unmedicated birds had increased (P less than .01) intestinal scores compared with uninfected birds or those with infection but treated with monensin. Monensin eliminated the reduction in gain and feed efficiency seen in the infected birds. The infected birds fed monensin had intestinal scores, gain, and feed:gain ratios similar (P greater than .10) to those for the birds that were not infected and that did not receive medication.

Cross resistance to the ionophorous polyether anticoccidial drugs in Eimeria tenella isolates from Czechoslovakia

Two field isolates of Eimeria tenella were isolated on farms where continuous outbreaks of coccidiosis in broilers had occurred over several years. The isolates were repeatedly tested for their sensitivity to ionophorous polyether drugs in floor pen trials lasting 7 wk. Hybro cockerels were inoculated with 25 x 10(3) oocysts/chicken at the age of 23 to 24 days. Total mortality, mortality caused by coccidia, live weights, feed conversion ratios, number of oocysts in litter, and titers of circulating antibodies against E. tenella were followed. Tested isolates were not controlled by the monovalent polyether drugs monensin, narasin, and salinomycin, but maduramicin, which is a monovalent monoglycoside polyether, and the bivalent polyether lasalocid controlled them effectively. This study indicates that coccidia that lose their sensitivity to a monovalent polyether drug lose the sensitivity to other monovalent polyethers, also, but might yet be effectively controlled by drugs from other classes of polyether antibiotics. This supports the hypothesis that there are differences in the mechanisms of anticoccidial activity of different classes of polyether antibiotics.

Anticoccidial efficacy of halofuginone in turkeys reared to market weight

Floor-pen studies were conducted in three geographic locations to study the efficacy of halofuginone (3.0 ppm in feed) against important species of coccidia in turkeys. Severe coccidiosis exposure was obtained in studies in Georgia and Colorado and mild coccidiosis in Wisconsin. Coccidiosis caused by contamination of the feed with oocysts of Eimeria adenoeides, E. meleagrimitis, and E. gallopavonis was almost completely controlled by halofuginone at 3 ppm, even though intestinal lesion scores and weight loss were high in two studies. Halofuginone was also highly effective in preventing buildup of infection in pens contaminated by indirect means (movement by caretakers through the pens, etc.). Weight gains and feed conversion were best in poults receiving halofuginone, whether directly or indirectly exposed. There was no evidence that halofuginone caused any untoward reactions in the poults, even though the drug was fed until turkeys reached market weight.

Drug resistance in avian coccidia (a review)

Drug resistance is now recognised as a major cause of the failure of drugs to control coccidiosis in the fowl. In this article, biological, biochemical and genetic aspects of resistance in Eimeria are reviewed and some of the problems that may limit progress in understanding the nature of resistance in coccidia are discussed.

Gordon memorial lecture. Coccidiosis control: past, present and future

Hygiene, management, chemotherapy and immunity all play a part in the control of coccidiosis. Under the conditions of modern intensive poultry rearing, special reliance is placed upon chemotherapy and since the introduction of the sulphonamides in 1939 a sequence of different types of drugs has been developed. At present the field is dominated by the ionophore antibiotics which have a special mode of action against the extracellular phases of the parasitic life cycle. Drug resistance is a continuing problem which has limited the effective life of most types of drug, although it has been most significant for particular compounds. So far it has not severely affected the efficacy of the ionophores. Immunity is involved in effective prophylaxis and the strong protective immunity which is a feature of most coccidial infections offers promise of a vaccination system. However, much more research will be necessary to bring this promise to fruition. Studies on immune mechanisms, antigenicity, biochemistry and in vitro cultivation may all contribute to the development of methods for controlling a series of infections which are an important obstacle to the development of modern husbandry methods.

The sensitivity of field isolates of Eimeria acervulina type to monensin

The sensitivity of 32 field isolates of Eimeria acervulina to 100 ppm monensin was investigated in birds inoculated with 10(6) or 10(3) oocysts. Isolates were obtained from broiler farms where monensin had been used (broiler isolates) and from breeder farms where the drug had never been employed (breeder isolates). The drug was not completely effective against breeder isolates. When broiler and breeder isolates were compared, monensin was less effective against the former irrespective of whether weight gain or oocyst production was used to measure the infection. It is likely therefore that resistance to monensin may have been acquired as a result of its use in broiler chickens. The drug had activity against broiler isolates, however with more prolonged use, fully resistant strains may eventually emerge.

Experimental development of monensin resistance in Eimeria meleagrimitis

The discovery of monensin-resistant field isolates of Eimeria meleagrimitis prompted an investigation of the ability of this parasite to develop monensin resistance in a laboratory selection experiment. A strain derived from a monensin-sensitive parent strain was intentionally selected for monensin resistance by propagation in monensin medicated turkeys in isolation, while the monensin-sensitive parent strain from which it was derived was cryogenically maintained as a genetic control. Comparison of the monensin sensitivity of the selected and parent strains demonstrated monensin resistance development in the selected strain by the fourth generation of selection. This is the first reported experimental development of monensin-resistant coccidia and suggests that unlike chicken coccidia, the turkey coccidium E. meleagrimitis possesses the ability to readily develop resistance to the polyether antibiotic anticoccidials under the appropriate conditions of drug exposure.