Depending on the type of production or government rules relating to antibiotic-free product labelling and trade, there will be restrictions on the use of certain products, especially for the treatment of infections or coccidiosis control. Sick flocks should be treated or sacrificed, in order to comply with welfare regulations.
The meaning of antibiotic free products can cause some confusion, mainly because there is no official or international accepted description of what it is and how to classify different types of “antibiotic-free” products or production. Further complications come with anticoccidials for prevention of coccidiosis in poultry. In fact, in some countries they are classified as antimicrobials and as such they have to be withdrawn from “antibiotic-free” productions.
When decisions concerning the prevention or control of coccidiosis in poultry are based on the subjective scoring of macroscopic lesions, observed in the gut of a number of birds in a flock, several factors affecting the method should be considered. Proper selection of birds, a careful sampling procedure and sample handling along with an accurate judgment of lesions, are some of the most important methodological indicators for success in lesion scoring during a flock inspection.
1. Selection of the right birds in the right number:
Before necropsy, it is essential to check the history of vaccinations, treatments (anticoccidials in particular) and previous diagnoses of the flock to be sampled. It has been shown that the existence of gut lesions is not necessarily accompanied by clinical signs of coccidiosis in poultry (Williams et al., 2000).
The prerequisite for the control and treatment of coccidiosis in poultry is to correctly identify the presence of disease. Two of the most widely used methods for this purpose are the identification and enumeration of oocysts, and the identification of lesions in the intestine. Although egg identification and counting was described for decades, and has been used since then, it is important to consider some key aspects of the method to obtain valid results.
1) Be familiar with the morphology of the parasite:
Have skills to identify the Eimeria species is the main element to be considered for the success of the morphometric study of field samples. For this, it is convenient to train yourself using pure parasite suspensions obtained in the laboratory.
Prevention of coccidiosis in chickens with live vaccines means suspending the use of anticoccidials, but a reduction in other antibiotics has also been observed. Reduction in antibiotic use in animal production is currently one of the aims of the poultry industry. Antimicrobial resistance has become a global public health problem in humans and livestock and plans to reduce the use of antibiotics are being implemented by the authorities in most countries.
Obviously, chemicals and ionophores used to control coccidiosis should be considered as antibiotics because the parasites that are intended to be controlled with these products can develop resistance with prolonged use of these substances.
Coccidiosis – due to parasites of the genus Eimeria – is one of the most devastating diseases in poultry: a disease which has always being present in every poultry flock since the first chick appeared on the earth; in fact, Eimeria is an ever-present parasite that it is impossible to eradicate. For this reason, a coccidiosis prevention strategy needs to be put in place for each batch of chickens that arrives on a farm. Worldwide losses due to coccidiosis in poultry are estimated to be around US$1.5 billion/year.
From the 1950s the use of some chemical molecules has been implemented to prevent the effects of the several Eimeria species that cause the disease. Whereas the use of vaccines is quite commune in breeders, only between 5 and 6% of broilers in the world are actually vaccinated instead of being treated with anticoccidials.
The fight against coccidiosis in chickens means the adoption of different strategies depending of the type of bird. If we are managing long life cycle birds, we have to pay special attention to clinical Eimeria species that are able to generate a real coccidiosis process with macroscopic lesions and symptoms that will reduce the healthy status of the birds and will compromise the development of immunity against other diseases or cause the death of the birds.
However, when we are rearing standard, certified or even free-range broilers, the focus needs to be a different one. In these cases it will be difficult to find real clinical coccidiosis. Otherwise, the “silent” species – such as Eimeria praecox among others – will affect the intestinal mucosa and will reduce the capacity of a broiler for nutrient absorption. Dealing with subclinical species is essential in coccidiosis in chickens with a high growth rate.
The Eimeria species responsible for coccidiosis in the species Gallus gallus are: E. acervulina, E. maxima, E. mitis, E. praecox and E. tenella, which are responsible for the disease in short life-cycle poultry (broilers), and E. necatrix and E. brunetti, which, together with the above 5 species, are responsible for the occurrence of outbreaks in long life-cycle poultry (breeders and layers). They are all ubiquitous in their behaviour and vary in their pathogenicity.
There are seven Eimeria species that are responsible for avian coccidiosis, 5 of which cause the disease in broilers: E. acervulina, E. mitis, E. tenella, E. maxima and E. praecox.
Eimeria tenella is by far the most widely detected species on farms when routine lesion scoring is performed. However, it is well known that Eimeria infections very seldom occur with one single species of Eimeria, most of the time they are multiple. Let’s investigate what are the most prevalent species and how multiple infections usually occur.
As Eimeria tenella is probably the easiest species to detect by lesion scoring, a common belief is that this species is the most prevalent all over the globe. In fact, macroscopic lesions are amongst the most pathognomonic with blood or typical moulds in the caecum and common finding of bloody droppings in the litter.
Seven species of Eimeria (E. acervulina, E. brunetti, E. maxima, E. mitis, E. necatrix, E. praecox and E. tenella) are recognized to be causative agents of coccidiosis in chickens of the genus Gallus gallus. Until recently, Eimeria praecox was considered to be a non-pathogenic species unable to cause adverse effects in the host.
In fact, in 1970, when Johnson & Reid wrote the milestone article that for the first time standardized and described the scoring scale for lesions caused by all Eimeria spp., Eimeria praecox was not included. It was, and still is, well know that E. praecox is not able to provoke pathognomonic lesions like E. acervulina, E. brunetti, E. maxima, E. necatrix and E. tenella, however even then some researchers were investigating whether this species of Eimeria was truly non-pathogenic.