Amprolium was first introduced in the poultry industry in 1960 in the US. Ever since it has been a very successful coccidiostat around the world with applications in feed and water.
One of the most important diseases in poultry is coccidiosis, caused by infections with a highly contagious intestinal parasite of the genus Eimeria. An effective way to target this parasitic disease is the use of coccidiostats, mixed into feed. The EU has regulated the use of coccidiostats in regulation No 1831/2003 (the feed additive regulation).
Amprolium hydrochloride (amprolium) is a synthetic coccidiostat that does not possess any antibacterial activity, making it suitable for antibiotic-free production systems. Amprolium is one of the few synthetic compounds for which the mode of action is clearly described: due to its close structural similarity to thiamine (vitamin B1), it acts as a thiamine antagonist and competes for the absorption of thiamine by the Eimeria parasites.
Thiamine analogues, such as amprolium, block absorption of thiamine and, as a result, cause starvation of the parasite due to thiamine deficiency. The thiamine transport system in the parasite is more sensitive to amprolium than that of the host, which explains why this coccidiostat is safe for use in chickens. It seems especially efficacious during schizogony (one of the three phases of the life cycle of Eimeria) as the demand for thiamine is at its highest then, thus allowing the development of an immune response.
Amprolium has been used intensively for a long time worldwide. To evaluate its efficacy after years of use, both in water (as treatment) and in feed (preventative) in the US, a meta-analysis on eight ASTs (anticoccidial sensitivity trials) was conducted. The Eimeria strains used to challenge the birds were collected in 2018 from eight different regions in the US. Each sample originated from a different state and/or complex and was composed of subsamples from multiple farms. Each strain was evaluated in an individual trial, conducted by the University of Georgia (US) using the same standardised protocol.
Birds reared in a clean environment until 12 days of age were allocated to different groups:
- uninfected untreated control (UUC)
- infected untreated control (IUC)
- infected treatment (IT)
The latter received amprolium in the feed at 125 ppm (registered dose) until the end of the trial. At 14 days of age, the birds were infected with the respective Eimeria strains collected from the different areas. At the end of the trials (seven days post infection), performance parameters were measured between day 12 (allocation) and the end (day 20).
Suitable for ABF systems
Meta-analysis of the different AST trials showed that amprolium significantly reduced the feed conversion ratio (FCR) from 1.88 to 1.65 and increased the average daily gain from 41.2 g to 46.7 g compared with the IUC, indicating that amprolium is able to overcome the negative effects caused by the coccidiosis infection (Figure 1).
These results confirmd the efficacy of amprolium to control coccidiosis under field conditions where the product was used extensively. In summary, amprolium (Coxam) has robust efficacy after many years of use and it is suitable for use in antibiotic-free (ABF) production systems.