By Dr Balkar Bains
Coccidiosis control in commercial poultry has been heavily reliant upon the application of anticoccidial drugs via feed. The development of coccidia resistance to anticoccidial drugs was a common occurrence and problematic because coccidia were resistant to all chemical drugs within the same family.
Coccidiosis outbreaks frequently require treatment to minimize morbidity and mortality. Affected flocks experience poor growth rates and feed conversion efficacy, resulting in adverse economic consequences. There were concerted efforts in recent times to identify and implement better alternatives to the currently range of chemical anticoccidial drugs.
Types of anticoccidial combinations
Chemical and chemical anticoccidials
The concept of combinations of different drugs first commenced with chemical anticoccidials, to prolong the use of chemical compounds and overcome coccidia resistance. Combining two chemicals in practice proved to be effective in extending the efficacy period of several anticoccidials. However, chemical anticoccidials in combination were not completely effective in preventing resistance. The combination concept was based upon the principles of synergy or additive effects with some complementary mechanism of action of both compounds.
Initial success led to the development of several combination products made available to the poultry industry including Amprolium plus, Pancoxin, Rofenaid, Toltro and Lerbek (table 1). These products must be carefully managed to avoid the emergence of coccidia resistance.
Chemical and ionophore anticoccidials
In subsequent years, the concept of ionophore and chemical anticoccidial combinations was adopted most effectively to improve the efficacy of ionophore anticoccidials. This new concept was based upon the use of both ionophore and chemical anticoccidials at a lower dosage levels while maintaining the desired anticoccidial efficacy. The efficacy of these combinations does decline over time following continuous use under commercial conditions.
The most widely used commercially available products of this combination include Maduramicin + Nicarbazin and Narasin + Nicarbazin. The chemical compound Nicarbazin is used at a reduced dosage level and thus prone to the loss of efficacy particularly in the control of E. tenella. In addition, all limitations for the use of Nicarbazin in combination still apply.
Ionophore and ionophore anticoccidials
The combination concept appears to be more suited to ionophore anticoccidials. Ionophore combinations have greater potential for limiting coccidia resistance development compared with individual ionophore anticoccidials used at present. Ionophores belong to the same family of compounds and their mechanism of action against coccidia is similar. The loss of efficacy of ionophores under commercial conditions is gradual and often different with each coccidian strain.
These observations can be interpreted as being strengths or weakness of an individual ionophore. The identification of strengths offers a greater advantage in selecting ionophores for a specific application or known coccidia resistance problem in commercial flocks. The mechanism of action is coccidiocidal, yet it permits enough coccidia challenge to generate sufficient immune response that may enable the withdrawal of the anticoccidial from broiler feed after 35 days. The efficacy of ionophore combinations has been the subject of research in the past, which is reviewed here to evaluate the use of combinations under commercial conditions.
Efficacy of ionophore combinations
- In a controlled series of battery trials (Untewale & Schildknecht 1985) the efficacy of Monensin and Lasalocid was compared with uninfected unmedicated controls (UUC), infected unmedicated controls (IUC) and three combinations (normal inclusion rate of each ionophore is 100ppm):
- Lasalocid 75 ppm + Monensin 25 ppm
- Lasalocid 50 ppm + Monensin 50 ppm
- Lasalocid 25ppm + Monensin 75 ppm
Field isolates of coccidia in the challenge included E. acervulina, E. tenella and E. maxima. Results of the trial in table 2 (below), following E. tenella and E. acervulina challenge, show that the weight gain of chickens increased linearly as the proportion of Lasalocid increased in each treatment.
Similarly, the feed conversion also showed linear improvement. Results of E. maxima challenge in table 3 (below) shows that the combination improved both weight gain and FCR as the Lasalocid content of the combination increased.
- Anticoccidial efficacy of Salinomycin combination with other Ionophore anticoccidials at different ratios was evaluated (Wolfgang Raether and G. Dost 1985) in battery trials. For the challenge in this trial, strains of field isolated E. tenella 48%, E. brunetti 20% and E. acervulina 32% of unknown drug sensitivity. The significant findings of the trials were that Salinomycin and Lasalocid combination have an additive effect against coccidia as compared to other Ionophore combinations with Salinomycin. The authors concluded that the limited effect of some mixtures of Salinomycin and related ionophores might have resulted from reduced anticoccidial sensitivity due to prior use under commercial conditions. The results of the trials are summarized in table 4 below.
- Another trial (Research report) evaluated different dosage levels of combinations of Lasalocid plus Salinomycin (table 5, below), Lasalocid plus Maduramicin, and Maduramicin plus Salinomycin (table 6) against the challenge of mixed infection of E. tenella, E. acervulina and E. maxima from field isolates. Efficacy criteria included weight gain and FCR as percentage of uninfected unmedicated controls. The combination of Lasalocid and Salinomycin showed the best results when both compounds are used at 50% of the dosage currently used under commercial conditions.
- For the Maduramicin and Lasalocid combination the best results (table 6 below) were at the higher dosage of Lasalocid (67 ppm) inclusion, which were reflected in both weight gain % and FCR. Results for the Maduramicin and Salinomycin combination at 50% dosage inclusion level were comparable with other combinations.
Learnings on anticoccidial combinations
- It is generally agreed that continuous use of ionophore anticoccidials invariably results in some loss of efficacy as determined by commercial parameters. The rotation and shuttle programs are often used to recover loss of efficacy, which primarily is the FCR.
- The combination of two ionophore anticoccidials at dosage levels of 50% each offers an alternative that minimizes loss of efficacy.
- Combinations also provide the opportunity to use those ionophores that, when used in alone, are less effective against some coccidia strains.
- Combinations of those ionophores that experienced some loss of efficacy when used alone are likely to be less efficacious and may lead to a loss of efficacy after a short duration of use under commercial conditions.
- The low dosage of each ionophore in combination does offer less chance of tissue residues yet effectively controls coccidiosis.
- Caution must be observed in regards to toxicity and known side effects even if the levels are used in combinations are lower than used by single ionophores.
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