Effect of storage and composting on the fate of six coccidiostats in manure and litter of poultry

In poultry farming anticoccidial drugs are widely used as feed additives for the prevention and treatment of coccidiosis. The use of these compounds is strictly regulated and maximum residue limits (MRLs) have been set in matrices such as eggs, milk and meat in order to minimize the intake by humans.
There is however another possible exposure route that has not been taken into consideration yet. Because coccidiostats, and veterinary medicines in general, are often poorly absorbed, manure from treated animals may contain high concentrations of coccidiostats. Experimental studies have shown that the uptake of veterinary medicines into plants from soil containing contaminated manure may occur.
An animal trial was setup to collect manure (wet excreta) and litter (excreta + bedding material + feathers + wasted feed + wasted water) of broilers receiving diets supplemented with various coccidiostats. The feeding program consisted of six different diets and all pens received a standard diet with either none (control = treatment 1) or the respective coccidiostat (monensin, salinomycin, lasalocid A, nicarbazin/narasin or diclazuril) supplementation at the maximum allowed level.
A multi-residue method was developed and validated for the simultaneous detection, identification and quantification of the six coccidiostats in manure and litter. The manure and litter samples obtained from the animal experiments were analysed making use of the methods developed.
A part of the manure and litter samples obtained during the animal trial is used to determine the stability of the coccidiostats during storage of chicken manure and composting of chicken litter. The effect of composting was assessed at lab scale in composting bins filled with 10 kg fresh litter. The chicken litter had a sufficient high C:N ratio to facilitate the composting process. The measured temperatures in the bins initially varied between 15 and 21°C, which points at the absence of exothermic processes. The litters were sampled and analysed. The mass reduction varied between 20 and 32%, indicating litter decomposition in the bins, even if no temperature increase was observed. The results of this stability study show that in litter samples kept for 2 months at temperatures < 40°C coccidiostats concentrations are already reduced by 22 – 96%.
Afterwards, temperatures in the vessels used for the compost trial increased to temperatures > 40°C after mixing the litter with fresh grass clippings, and the composted litters were sampled again after this period with distinct temperature increase. The mass reduction in the second phase of the composting experiment ranged between 23 and 36%, indicating further decomposition of the litter mixed with grass clippings. Results on the reduction of coccidiostats in the exothermic phase of the composting process are presented.
In addition the manure samples, stored at room temperature and sampled after 34 days to assess the fate of the coccidiostats during manure storage, were analysed as well. Even for storage at room temperature, clear mass decreases of 26-33% were measured, indicating decomposition of organic matter in the manure. Results on the reduction of coccidiostats during storage of poultry manure are presented.