Coccidiosis vaccines – can isoquinoline alkaloids help?
Over 3 billion US$ annual costs are caused by coccidiosis worldwide, of which 0.5 billion are spent on anticoccidial drugs – everyone in the poultry industry has read these numbers time and again. They underline the severity of the ubiquitous parasitic infection with Eimeria spp. that has been causing clinical and subclinical losses in chicken production for many decades.
Anticoccidial drugs and their limitations
Chemical drugs to prevent coccidiosis have been on the market since the 1950’s and ionophores were introduced around 20 years later. These two types of drugs are still the most widely used products in the broiler industry to prevent coccidiosis, although they come with some disadvantages. Eimeria quickly build resistance against chemicals, therefore one drug should not be used for more than one grow-out period. In fact, it is common practice to use one compound per feeding phase, not only switching between chemical coccidiostats, but also rotating between chemicals and ionophores.
Just as it happened with antibiotic growth-promoters in the early 2000’s, the use of anticoccidial drugs might come under closer scrutiny due to public pressure to cut down medical treatments in livestock. While several anticoccidials are currently registered as feed additives in the European Union, in the US, ionophores are classified as antimicrobials. Therefore, they cannot be used in antibiotic-free production systems, so that fewer products are available to these producers in their rotation programs.
Vaccines – an alternative to drugs?
Coccidiosis vaccines are live vaccines that rely on the principle of creating immunity against coccidiosis through the controlled exposure to low dosages of infective Eimeria strains. Though vaccines are very effective, they also entail some difficulties: immunity is built only against the Eimeria species which are contained in the vaccine, while chemicals and ionophores work against all Eimeria and, in some cases, also against some bacteria. Furthermore, for immunity to develop, the birds need to undergo a mild infection which causes a decrease in productivity and is a potential predisposing factor for secondary infections. The productivity loss can be compensated if the grow-out period is long enough, i.e., at least 42 days. Vaccines registered in the European Union impose lower pressure on the birds, because they contain attenuated Eimeria strains. These strains have a shortened life cycle and produce a lower oocyst output; therefore, they cause less intestinal damage and immunity develops faster. However, these vaccines cost considerably more than the non-attenuated vaccines. The higher cost of vaccines compared to anticoccidials as well as the danger of productivity losses are the reasons why vaccination in conventional European broiler production is uncommon, while it is a standard procedure in organic production and in the rearing of layers and breeders.
A few details need to be considered for the technique of vaccine application: Immunity against coccidiosis only develops after 3-4 full life cycles of Eimeria, involving the developmental stages of the parasite inside the host and outside. Therefore, the environment of the broiler house needs to be beneficiary for Eimeria, i.e., the litter must not be too dry (≥ 20 % humidity). On the other hand, hygiene is of utmost importance, because the infection pressure from field strains of Eimeria should be kept to a minimum until immunity is fully developed. When applying the vaccine, the barn’s lighting regime should also be considered, because light encourages preening, ensuring a faster and homogenous uptake of the spray-on vaccine.
Notwithstanding the complexity of coccidiosis vaccine use, considering the limitations of anticoccidial drugs, vaccines might become an increasingly interesting alternative. For example vaccines can help to restore the sensitivity of the field population of Eimeria towards the anticoccidial drugs. Vaccines are a valuable tool to raise healthy broilers in organic farming where no anticoccidial drugs are allowed. But they can also be used in conventional production, preferably in systems with a longer grow-out.
When using vaccines, it is advisable to support the birds against the side-effects of coccidiosis vaccines: subclinical inflammation and intestinal damage. Certain feed additives can help to alleviate these effects. Isoquinoline alkaloids (IQs) are secondary plant metabolites that can support broilers in stressful conditions. The following results show that IQs are a valuable addition for broilers that are vaccinated against coccidiosis.
Vaccinated broilers show a lower body weight gain than non-vaccinated birds until Day 44 of production (Figure 1). This shows that the stress of vaccination affects the birds until the late grower or finisher phase. It takes the vaccinated birds until day 53 to reach a higher body weight than the non-vaccinated control birds (Figure 2). On the other hand, vaccinated broilers that additionally receive IQs already match the performance of control birds on day 44 (Figure 1) and achieve the highest final body weight at the end of the production period (Figure 2).
The supplementation of IQs not only improves the body weight of the broilers but also leads to a significantly better feed conversion as shown in Figure 3.
These results can be explained by taking a closer look at physiological parameters like gut integrity and inflammation. Coccidiosis vaccines harm the gut epithelium, thereby impairing the barrier function of the gut wall. By adding the molecule Fluorescein Isothiocyanate-Dextran (FITC-Dextran) to the feed, the gut integrity can be evaluated. FITC-Dextran is not absorbed in a healthy intestine, because the molecule is too large to pass through the epithelium. However, when the gut wall is damaged, FITC-Dextran passes through and can be detected in the blood serum. Figure 4 shows that the serum-concentration of FITC-Dextran is significantly higher in vaccinated broilers than in non-vaccinated birds, indicating a deterioration of the gut epithelium. However, in vaccinated broilers supplemented with IQs, the serum levels of FITC-Dextran are comparable to the negative control.
To assess the impact of the vaccine on the animals’ acute phase immune reaction, the serum-concentration of the inflammation marker TNF-α can be measured. Figure 5 shows that the TNF-α levels of vaccinated broilers supplemented with IQs are close to the levels in the control group, while the levels are significantly higher if birds are vaccinated but do not receive IQs.
It can be concluded that the inflammation level is lower in the IQ group and the gut integrity is significantly higher than without IQ supplementation. An improved gut barrier and immune status lead to a better growth performance and a higher feed efficiency. Therefore, the addition of IQs can help producers who are searching for alternatives for anticoccidial drugs to raise healthy birds with coccidiosis vaccines.
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