Introduction
Coccidiosis, a parasitic disease caused by protozoa of the genus Eimeria (Vermeulen et al., Reference VERMEULEN, SCHAAP and SCHETTERS2001), is one of the most frequently investigated enteric poultry diseases, mainly due to its ubiquity and severe negative impact on economic efficiency in the poultry industry. The infection follows the ingestion of one or more of seven Eimeria species that have been recognised as infecting chickens: Eimeria acervulina, E. maxima, E. tenella, E. brunetti, E. necatrix, E. mitis and E. praecox (Sharman et al., Reference SHARMAN, SMITH, WALLACH and KATRIB2010). Each species has its own characteristics with respect to prevalence, site of infection, pathogenicity, and immunogenicity. All species replicate in the epithelial cells of the intestinal lining, causing pathological changes varying from local destruction of the mucosal barrier and underlying tissue to systemic effects such as blood loss, shock syndrome and even death (Vermeulen et al., Reference VERMEULEN, SCHAAP and SCHETTERS2001). The traditional method of coccidiosis prophylaxis is routine use of feed coccidiostats. The rising drug resistance of Eimeria field strains (Chapman, Reference CHAPMAN1997) as well as public concerns about drug residues in poultry products (McEvoy, Reference McEVOY2001) are the main factors prompting the development and implementation of alternative strategies of coccidiosis control. Coccidia are immunogenic and primary infection stimulates the development of resistance to homologous challenge (Williams, Reference WILLIAMS1998). Therefore, it would seem obvious that increasing attention has been paid to anticoccidial vaccines whose function is to expose a bird to a low number of Eimeria oocysts in order to stimulate protective immunity against possible future infection (Williams, Reference WILLIAMS2002; Kitandu and Juranová, Reference KITANDU and JURANOVÁ2006). Generally, the vaccines are administered to young chicks up to 10 days old and birds must be reared on litter to ensure the recirculation of vaccine strains. It is thought that after two or three consecutive infections with a vaccine strain of Eimeria, solid species-specific immunity is built (Sharman et al., Reference SHARMAN, SMITH, WALLACH and KATRIB2010). Depending on the features of strains used, the live anticoccidial vaccines can be divided into virulent, attenuated or tolerant to ionophores. Non-attenuated vaccines are based on wild type strains with maintenance of their natural virulence. Reduced virulence of attenuated vaccines is accomplished by serial passage of parasites through embryonated eggs or, the most commonly used, by selection for precocity. Due to reduced prepatent time and reproductive potential, the use of precocious vaccinal strains results in less damage of intestinal epithelial cells in comparison with wild type strains (Vermeulen et al., Reference VERMEULEN, SCHAAP and SCHETTERS2001; Williams, Reference WILLIAMS2002). According to Chapman et al. (Reference CHAPMAN, CHERRY, DANFORTH, RICHARDS, SHIRLEY and WILLIAMS2002) live vaccines are the only practical alternative to coccidiostats and are considered to be more efficacious than Eimeria recombinant protein vaccines (Lee et al., Reference LEE, LILLEHOJ, JANG, LEE, BRAVO and LILLEHOJ2011b).
Anticoccidial vaccination is not a new concept, and has been known and used since the 1950s, primarily in broiler breeder and replacement layer flocks (Lee et al., Reference LEE, BROUSSARD, FITZ-COY, BURKE, ECKERT, STEVENS, ANDERSON, ANDERSON and CALDWELL2009). Currently, numerous live anticoccidial vaccines comprising varied formulations of virulent or attenuated parasites of one or more species are commercially available (Shirley et al., Reference SHIRLEY, SMITH and TOMLEY2005). While many studies have proven their effectiveness (Danforth, Reference DANFORTH1998; Williams and Gobbi, Reference WILLIAMS and GOBBI2002; Lee et al., Reference LEE, BROUSSARD, FITZ-COY, BURKE, ECKERT, STEVENS, ANDERSON, ANDERSON and CALDWELL2009) and several vaccines have been used in broiler breeders, there has been a widespread reluctance to use them in broilers. The principal reason for this aversion are reports of poorer performance, measured as reduced weight gain and feed efficiency, in comparison with prophylactically medicated birds (Danforth, Reference DANFORTH1998; Williams, Reference WILLIAMS2002, Lee et al., Reference LEE, ECKERT, AMEISS, STEVENS, ANDERSON, ANDERSON, BARRI, McELROY, DANFORTH and CALDWELL2011a). Reduced performance as a consequence of anticoccidial vaccines is associated with mild coccidial infections (Lee et al., Reference LEE, ECKERT, AMEISS, STEVENS, ANDERSON, ANDERSON, BARRI, McELROY, DANFORTH and CALDWELL2011a) that could result in reduced absorptive surface area (Lehman et al., Reference LEHMAN, MORAN and HESS2009), malabsorption of nutrients and inflammation. Moreover, live vaccines are regarded as a predisposing factor for enteritis (Chapman et al., Reference CHAPMAN, CHERRY, DANFORTH, RICHARDS, SHIRLEY and WILLIAMS2002; Lehman et al., Reference LEHMAN, MORAN and HESS2009). Recovery and compensatory gain usually follow replication of vaccine oocysts in epithelial cells, but the relatively short time of broiler rearing is insufficient in some cases to compensate, prior to slaughter, for decreased weight gain due to virulent vaccines (Williams, Reference WILLIAMS1998; Lehman et al., Reference LEHMAN, MORAN and HESS2009). In this context, the concept of supporting the vaccination via the nutrition route in developing immunity, rebuilding the intestinal epithelium and maintaining high performance, is highly warranted.
Therefore, the aim of this paper is to review and discuss the results of recent broiler studies in which nutritional methods as performance- and/or immune-supporting factors were investigated with regard to the anticoccidial vaccination.
Dietary protein and amino acids level
Based on the information that increasing protein levels during periods of clinical coccidiosis has been shown to improve broiler performance (Sharma et al., Reference SHARMA, FERNANDO and SUMMERS1973). Lee et al. (Reference LEE, ECKERT, AMEISS, STEVENS, ANDERSON, ANDERSON, BARRI, McELROY, DANFORTH and CALDWELL2011a) conducted a series of experiments to study the effect of various protein levels in starter diets (from 20 to 24%) on the performance of broilers vaccinated with a live anticoccidial vaccine before subsequent challenge with mixed Eimeria spp. In this study, the authors noted deterioration of performance parameters as a result of vaccination during the pre-challenge period; however, this effect was ameliorated by increasing the protein level in the diet. The vaccination was found to be very effective in inducing protective immunity measured as improvement of body weight, feed conversion ratio and alleviation of the lesions after challenge with sporulated oocysts Eimeria acervulina, E. maxima and E. tenella. The authors concluded that the results identified vaccination as a valuable tool in the control of coccidiosis in broiler production and highlighted the importance of proper protein levels in starter diets to avoid performance decline accompanying anticoccidial vaccination. The results of the previous study of Lee et al. (Reference LEE, BROUSSARD, FITZ-COY, BURKE, ECKERT, STEVENS, ANDERSON, ANDERSON and CALDWELL2009), designed to compare live anticoccidial vaccine with the ionophoric salinomycin in broilers on two different four-phase feeding programmes varying in protein level, have shown that immunoprophylaxis, supported with appropriately formulated diets with increased protein levels during the starter period, lead to cumulative performances comparable to coccidiostats without affecting production costs.
The effectiveness of anticoccidial vaccines is related to proper immune function in birds, which in turn is associated with appropriate nutrition. Some amino acids, such as glutamine and arginine are, aside from their role as protein components, involved in regulation of immunity and have been recently investigated under conditions of anticoccidial vaccination (Perez-Carbajal et al., Reference PEREZ-CARBAJAL, CALDWELL, FARNELL, STRINGFELLOW, POHL, CASCO, PRO-MARTINEZ and RUIZ-FERIA2010; Mussini et al., Reference MUSSINI, GOODGAME, LU, BRADLEY, FISCUS and WALDROUP2012). Based on information regarding the stimulating effect of glutamine on the growth of villi, activity of the immune system and increased demand for this amino acid related to parasitic infestation, Mussini et al. (Reference MUSSINI, GOODGAME, LU, BRADLEY, FISCUS and WALDROUP2012) evaluated the response of coccidiosis-vaccinated broilers to different levels of glutamine supplementation (5.0, 7.5 or 10.0 g/kg) in the diet during the stages of immunity acquisition, i.e. up to 28 days of age, on performance and processing yield. As long as glutamine was supplied, the body weights in all experimental groups, regardless of supplementation level, significantly increased compared with control and this tendency, though not statistically confirmed, was also noted on the 42nd day of age. Another purpose of glutamine inclusion in the diet was to protect the muscle protein pool from increased catabolism in order to supply the glutamine to the gastrointestinal tract and immune system. The results of processing did not indicate a statistically confirmed effect of glutamine addition; however, important improvements (p=0.07) in breast meat yield were observed.
Arginine (Arg) and vitamin E (VE) are well known for their immunomodulatory properties. Perez-Carbajal et al. (Reference PEREZ-CARBAJAL, CALDWELL, FARNELL, STRINGFELLOW, POHL, CASCO, PRO-MARTINEZ and RUIZ-FERIA2010) carried out a study to examine the concurrent effects of three levels of Arg and two levels of VE supplementation higher than those recommended by the NRC (1994) on the humoral and innate immune response of vaccinated broilers after challenge with a field mix of Eimeria oocysts. It was concluded that supplementation of 80 IU of vitamin E/kg of feed alone improves innate immune response measured as heterophil and monocyte oxidative burst. Those parameters were also improved by giving normal levels of VE (40 IU of VE/kg of feed) with 0.03% of Arg. The authors suggested that higher concentrations of plasma nitric oxide (NO) were associated with a stronger infection. Thus, birds vaccinated against coccidiosis and later challenged with a field mix of Eimeria spp. with a lower concentration of NO faced a less severe infection when fed diets with the combination of VE and Arg as mentioned above.
Mucosal response to vaccination implies an increase in mucin production, which is associated with an increased need for Thr, Gly, Ser and Pro. Mucins, high molecular weight glycoproteins, are the constituents of the protective mucus layer covering the epithelial cells of the gastrointestinal tract, regarded as the first line in defence against intestinal pathogens (Walk et al., Reference WALK, COWIESON, REMUS, NOVAK and MCELROY2011a). Lehman et al. (Reference LEHMAN, MORAN and HESS2009) tested dietary addition of gelatin, as a source of conditionally essential amino acids (CEAA) such as Gly, Ser and Pro, to the low- and high-protein-level feeds to assist recovery from a live oocyst vaccination. In this study, the performance results for the first three weeks and the entire (0-8 weeks) experimental period confirmed the detrimental effect of vaccination on birds’ early performance, which could not be compensated by birds at eight weeks of age. The gelatin addition ameliorated the negative vaccination response through the first three weeks through improvement of body weight gain and feed conversion ratio, but without reducing mortality. The lack of effect of gelatin inclusion on performance at three to six weeks of age may be, as the authors suggested, a sign of decreased intestinal requirement of CEAA for growth and mucin production in this period. It was concluded that conditionally essential amino acids Gly + Ser and Pro may be important factors in recovery from live anticoccidial vaccines, although the results did not indicated full recovery of weight gain by eight weeks of age.
Enzymes
The development of immunity induced by live anticoccidial vaccines is associated with the disruption of the epithelial layer and may, similarly to coccidiosis, result in reduced nutrient digestibility and absorption, e.g. Ca, P (Shaw et al., Reference SHAW, VAN GINKEL, MACKLIN and BLAKE2011). Phytase, an enzyme commonly used in commercial poultry feeding programs, is well known for improving growth performance and mineral utilisation, mainly due to the release of phosphate from phytic acid, making it available for absorption, and increasing the availability of other important minerals such as Ca. Phytase has been reported to significantly increase the proliferation of blood lymphocytes, increase production of both CD4+ (T-helper) and CD8+ (cytotoxic T) as well as intestinal IgA (Liu et al., Reference LIU, RU, COWIESON, LI and CHENG2008; Shaw et al., Reference SHAW, VAN GINKEL, MACKLIN and BLAKE2011), and reduce the antinutrient effects of phytate on mucin production and endogenous secretions (Walk et al., Reference WALK, WYATT, UPTON and McELROY2011b). These properties of phytase may promise a beneficial effect in vaccinated broilers; however, the results of the experiments discussed below are inconsistent. Shaw et al. (Reference SHAW, VAN GINKEL, MACKLIN and BLAKE2011) conducted a study to determine the effects of dietary phytase on a natural Eimeria challenge in naive and vaccinated broilers. Treatment combinations were created to include two dietary Ca-non phytate P (npP) levels (0.9% Ca, 0.45% npP; 0.7% Ca, 0.35% npP, 500 phytase), unchallenged versus challenged, and unvaccinated versus vaccinated groups of chicks. Challenge was accomplished through litter preseeded with Eimeria oocysts produced by birds orally infected with E. acervulina and E. tenella. The results indicated no effect, either of diet or vaccination, on the performance indices, although the challenge significantly affected those parameters irrespective of the vaccination. As the authors stated, phytase supplementation was unable to provide additional benefits to performance or P utilisation in birds which were vaccinated, subjected to a coccidiosis infection, or both.
The aim of a study by Walk et al. (Reference WALK, WYATT, UPTON and McELROY2011b) was to evaluate three commercially available Escherichia coli 6-phytases, supplemented according to the manufacturer's matrix values, on the performance and bone ash of broilers exposed to a live coccidia oocyst vaccine. In this study, the vaccination increased the feed intake and body weight gain from days 0 to 21. The addition of phytase did not affect performance. The explanation of such positive performance indices as a result of vaccination is that the birds were housed in battery cages on raised wire floors with no access to excreta. This could prevent further oocyst cycling and interfere with the acquisition of immunity; thus intestinal damage may be slight in comparison to those reported in a floor pen environment. Therefore, according to the authors of the current review, the initial dose of vaccine oocyst should be regarded in this case as a short-term mild infection, not a vaccination, which in turn stimulated the compensatory gain.
A similar experimental design using brooder cages with wire floors was used by Walk et al. (Reference WALK, COWIESON, REMUS, NOVAK and MCELROY2011a) in another study which was conducted to determine the influence of single dietary enzymes (phytase, xylanase, protease) or their combination on performance, bone ash and number of goblet cells in the small intestine of broilers fed reduced Ca and P corn-soybean diet and exposed to a mixed Eimeria spp. live coccidia oocyst vaccine. In this study the vaccine dose of live oocysts did not affect the tibia ash but impaired performance by reducing feed intake and body weight gain without altering feed conversion ratio. The enzyme addition did not ameliorate the reduced performance induced by the vaccine. The effect of diet and vaccination on goblet cell number was varied, and dependent on diet, vaccination treatment, and diet × vaccination interactions as well as on bird age and intestinal segment. Briefly, on day seven, protease decreased, but in combination with phytase, increased goblet cells in the jejunum. On day 18, xylanase increased goblet cell numbers in the duodenum but, when combined with phytase, decreased their numbers in the jejunum of vaccinated broilers. As the authors suggested, a higher number of goblet cells in the small intestine may be a symptom of an increase in mucin secretion or an increase in goblet cell turnover.
A confirmation of the limited effect of the dietary enzymes on the performance of vaccinated birds comes from the results of a previous experiment conducted by Parker et al. (Reference PARKER, OVIEDO-RONDÓN, CLACK, CLEMENTE-HERNÁNDEZ, OSBORNE, REMUS, KETTUNEN, MAKIVUOKKO and PIERSON2007). The main assumption of the project was that dietary addition of exogenous enzymes such as amylase, protease, and xylanase to diets varying in protein content could improve intestinal gut health and live performance of chickens vaccinated and later infected with live oocysts by enhancing ileal digestibility of amino acids or modifying gut microflora. In this study broilers were also placed in wire cages, but paper was used as bedding for the first three weeks of age to ensure the recirculation of vaccine oocysts. Vaccination led to a significant reduction in performance as measured by feed intake and body weight gain; the dietary enzyme supplementation did not significantly change those parameters in the pre- and post-infection periods. Dietary enzyme supplementation of coccidia-vaccinated birds did, however, reduce the average intestinal lesions observed on the seventh day post-infection in three intestinal sections, especially in the caeca, and, as the authors suggested, this may be a result of modulation of caecal microflora.
Probiotic bacteria and yeast cell products
Probiotic cultures consist of commensal bacteria with proven beneficial effects such as modulation of gut microbial communities through competitive exclusion of pathogens which, in turn, supports the development of beneficial microflora, along with having a positive impact on intestinal development and integrity as well as stimulation of mucosal immunity (Fuller, Reference FULLER1989; Williams, Reference WILLIAMS1998; Jin et al., Reference JIN, HO, ABDULLAH and JALALUDIN2000). Those properties make probiotics a potentially useful tool in support of coccidiosis immunoprophylaxis, whose effectiveness is conditioned by maintenance of a healthy intestinal tract and normal microflora (Dalloul and Lillehoj, Reference DALLOUL and LILLEHOJ2005). Only a limited number of studies, however, have been addressed to the evaluation of the combined protective effects of probiotics and anticoccidial vaccination.
The aim of the interesting experiments of Stringfellow et al. (Reference STRINGFELLOW, CALDWELL, LEE, MOHNL, BELTRAN, SCHATZMAYR, FITZ-COY, BROUSSARD and FARNELL2011) was to determine the effect of commercial probiotic Biomin PoultryStar (Biomin GmbH, Herzogenburg, Austria) supplementation and its capacity to modulate immune function in broilers relative to coccidiosis vaccination during the first 21 days of age. The probiotic consisted of lactic-acid- producing bacteria including Enterococcus faecium, Pediococcus acidilactici, Bifidobacterium animalis, and Lactobacillus reuteri, and was administered periodically via drinking water. The parameters of innate and adaptive immunity in cocci-vaccinated chickens were measured. Those experiments were varied with the dietary protein level (21.5 vs. 22%) but no increased immune function was observed with the higher protein diet. The effect of the probiotic and vaccine combination varied depending on the age of the birds; it was best observed on day 14, when probiotic in the water of vaccinated broilers induced a significantly higher oxidative burst of monocytes and heterophils and a significantly higher cell proliferation. These results, although not easy to explain, confirm the relationship between immune function and probiotic administration which, as the authors suggested, may offer increased protection at the time of vaccination or produce an adjuvant effect by modulating the host immune system.
Farnell et al. (Reference FARNELL, LEE, KLEIN, STRINGFELLOW, MOHL, BELTRAN, SCHATZMAYR, FITZ-COY, BROUSSARD and CALDWELL2009) also studied the immunopotential effect of the identical commercial probiotic cited above, using the same immune response parameters of vaccinated chickens in a 49-day experiment. The obtained results corresponded to those obtained by Stringfellow et al. (Reference STRINGFELLOW, CALDWELL, LEE, MOHNL, BELTRAN, SCHATZMAYR, FITZ-COY, BROUSSARD and FARNELL2011) and also indicated the immune-potentiating effects of probiotic bacteria and coccidiosis vaccine on the avian mucosa.
The other studies confirmed the beneficial effects of the probiotic Biomin PoultryStar on the other parameters connected with the evaluation of anticoccidial vaccines, such as performance indices, oocyst output and intestinal lesions in conditions of experimental infection with Eimeria spp. (Klein et al., Reference KLEIN, LEE, FARNELL, ODEN, POHL, MOHNL, BELTRAN, SCHATZMAYR, BROUSSARD, FITZ-COY and CALDWELL2009a; Reference KLEIN, LEE, FARNELL, ODEN, POHL, MOHNL, BELTRAN, SCHATZMAYR, BROUSSARD, FITZ-COY and CALDWELL2009b).
The aim of the earlier experiment of Pelícia et al. (Reference PELÍCIA, MENDES, SALDANHA, PIZZOLANTE, TAKAHASHI, GARCIA, MOREIRA, PAZ, QUINTEIRO and KOMIYAMA2004) was to evaluate the influence of combined use of probiotic and prebiotic, Enterococcus sp., mannan oligosaccharides (Colostrum Avis® and Simbiótico plus®; BioCamp Laboratórios Ltda, Campinas, Brasil) and vaccination as a substitute for chemoprophylaxis (antibiotic growth promoters and anticoccidial drugs) on performance, carcass and cut yields, qualitative traits of meat, development and score of lesions in Label Rouge broiler chickens raised in a free-range system and naturally exposed to coccidia. Any significant differences in the tested parameters between symbiotics and the other methods of bird health prophylaxis, which might indicate their comparative effectiveness in a free-range system, were noted.
Yeast cell products are the next zootechnical feed additives that are being successfully used in poultry production. They are characterised by high nutritional value and beneficial effects on the intestinal environment by preventing the colonisation of the pathogenic microflora and immunomodulatory properties. The efficacy of these products has been thoroughly studied in broilers experimentally infected with coccidiosis, but there is very little information on the effect of yeast products used in conjunction with anticoccidial vaccines. Luquetti et al. (Reference LUQUETTI, FURLAN, ALARCON and MACARI2012) studied Saccharomyces cerevisiae cell-wall dietary supplementation (2 g/kg) as a factor potentially protecting the intestinal mucosa of broiler chickens vaccinated against coccidiosis. The results show very little interaction between yeast cell walls and vaccination in performance parameters. When S. cerevisiae cell wall was used to supplement the diet of vaccinated birds, a slight reduction in epithelial cell loss percentage and increased jejunal villus height were recorded.
The objective of another experiment was to evaluate the effect of mannan oligosaccharides (MOS), which are derived from outer cell walls of Saccharomyces cerevisiae, on coccidial lesion scores and live performance of broiler chickens vaccinated with a live coccidiosis vaccine and challenged with a mixture of three pathogenic strains of sporulated Eimeria oocysts (Nollet et al., Reference NOLLET, HUYGHEBAERT and SPRING2007). A coccidiosis-associated decrease in body weight gain between 1 to 15 and 15 to 22 d was significantly reduced by vaccination, irrespective of the MOS addition. The post-challenge (15-42 d) feed conversion ratio significantly increased in vaccinated birds, but the addition of MOS (2, 1, and 0.5 g/kg of starter, grower and finisher diet, respectively) effectively improved this parameter to the level obtained in the unvaccinated, unsupplemented birds. It was concluded that dietary MOS may therefore be considered beneficial when combined with live anticoccidial vaccine.
Phytogenic supplements
Herbal and other phytogenic substances are the most frequently investigated group of feed additives in birds vaccinated against coccidiosis. Recently, the efficacy of plant-derived anticoccidials in the control of avian coccidiosis has been thoroughly reviewed and discussed by Abbas et al. (Reference ABBAS, COLWELL and GILLEARD2012), although less attention has been paid to their effectiveness in combination with immunoprophylaxis.
Echinacea was one of the first herbs tested in vaccinated birds (Allen, Reference ALLEN2003), mainly due to its well-known immunomodulatory, antioxidant and anti-inflammatory properties (Zhai et al., Reference ZHAI, YI, WU, SENCHINA, WURTELE, MURPHY, KOHUT and CUNNIK2007). The aim of the experiment conducted by Allen (Reference ALLEN2003) was to determine whether dietary supplementation with a ground root preparation of Echinacea purpurea (1 or 5 g/kg) could enhance the immune response of broilers vaccinated and subsequently challenged with Eimeria ssp. in an experimental model using a commercial live vaccine preparation. To immunise only half and for challenge, an oocyst dose 1000 times the dose recommended by the vaccine producer were given. The herb was administered for the first two weeks only; this led to significant increases in body weight gain of vaccinated birds at 14 days of age, which ameliorated growth reduction due to vaccination. This positive effect persisted for the next two weeks. Supplementation with E. purpurea preparations had no significant effect on body weight gains of unvaccinated challenged chickens, but in vaccinated birds the addition of herbs significantly increased this parameter. Moreover, E. purpurea supplementation also significantly lowered total lesion scores but did not significantly modify the effects of vaccination and challenge on plasma carotenoids or NO2- + NO3-. The mechanism of Echinacea purpurea activity is unknown; however, the author suggested that it may stimulate the response of macrophages and natural killer cells to the antigens released from the live vaccine. It was concluded that echinacea has the potential for use as an adjuvant for live vaccines.
The essential oils of oregano, mainly carvacrol and thymol, have been known to exert antibacterial and anticoccidial activities (Giannenas et al., Reference GIANNENAS, FLOROU-PANERI, PAPAZAHARIADOU, CHRISTAKI, BOTSOGLOU and SPAIS2003). The positive effect of Origanum vulgare compound (Orego-Stim®), rich in thymol and carvarcrol, on performance parameters was also found in the research conducted on cocci-vaccinated broilers under an organic rearing system (Waldenstedt, Reference WALDENSTEDT2003). Supplementation with Orego-Stim® increased live weight and feed intake up to 48 days of age without affecting feed conversion ratio. The results indicated that oregano compounds and vaccine can constitute an effective part of the prevention of coccidiosis in alternative rearing systems (Waldenstedt, Reference WALDENSTEDT2003).
Results obtained by Oviedo-Rondón et al. (Reference OVIEDO-RONDÓN, CLEMENTE-HERNÁNDEZ, WILLIAMS and LOSA2005; Reference OVIEDO-RONDÓN, CLEMENTE-HERNÁNDEZ, SALVADOR, WILLIAMS, LOSA and STEPHAN2006a; Reference OVIEDO-RONDÓN, HUME, HERNÁNDEZ and CLEMENTE-HENÁNDEZ2006b) in subsequently performed studies with two essential oil blends, Crina® POULTRY or Crina® ALTERNATE, containing thymol, eugenol, curcumin and piperin, did not correspond with those mentioned above. The evaluated essential oil blends did not consistently promote better performance in cocci-vaccinated broilers (Oviedo-Rondón et al., Reference OVIEDO-RONDÓN, CLEMENTE-HERNÁNDEZ, WILLIAMS and LOSA2005), and even led to lower performance, higher lesion scores and oocyst counts in cocci-vaccinated birds (Oviedo-Rondón et al., Reference OVIEDO-RONDÓN, CLEMENTE-HERNÁNDEZ, SALVADOR, WILLIAMS, LOSA and STEPHAN2006a). The authors suggested that this negative effect may be due to the cytotoxic effects of phenolic compounds included in essential oils on the villus tips of the intestinal mucosa, thus affecting the development of immune response in vaccinated birds. The subsequent study concerned the influence of those essential oil blends on intestinal microbial ecology in respect to vaccination and infection with Eimeria spp. (Oviedo-Rondón et al., Reference OVIEDO-RONDÓN, HUME, HERNÁNDEZ and CLEMENTE-HENÁNDEZ2006b). While the anticoccidial vaccination resulted in small changes in intestinal microbial communities, stresses and coccidian infection resulted in drastic shifts. Supplementation with investigated essential oil blends modulated microbial communities in cocci-vaccinated broilers, preventing drastic shifts after a mixed coccidian infection (Oviedo-Rondón et al. Reference OVIEDO-RONDÓN, HUME, HERNÁNDEZ and CLEMENTE-HENÁNDEZ2006b).
The moderate effect of the combined use of vaccination and another essential oil blend was reflected in a recent study by Küçükyilmaz et al. (Reference KÜÇÜKYILMAZ, BOZKURT, SELEK, GÜVEN, EREN, ATASEVER, BINTAŞ, ÇATLI and ÇINAR2012). Supplementation with a specific essential oil blend in which the main active components were carvacrol, 1,8-cineole, camphor, thymol, α-fenchone, α-terpinyl acetate and sabinene was not able to ameliorate the deleterious effect of vaccination on performance. In the post-vaccination period, up to 18 days of age, poorer performance parameters were recorded in the vaccinated group in comparison to control and coccidiostat-supplemented groups; the addition of the essential oil blend did not lead to any benefits in this period. Following infection with a mixture of Eimeria spp., the performance in vaccinated birds was comparable to the coccidiostat-supplemented group and further addition of the essential oil blend resulted in no additional effect.
Another commercial phytogenic feed additive containing a blend of essential oils from oregano, anise, and citrus peel, Biomin P.E.P. 125 poultry (Biomin GmbH, Herzogenburg, Austria), was the subject of a study conducted under the conditions of a subclinical coccidial vaccine exposure (Reisinger et al., Reference REISINGER, STEINER, NITSCH, SCHATZMAYR and APPLEGATE2011). The experimental treatments included two doses of a coccidial vaccine (1x or 5x) and within every pen only half of the birds were vaccinated, whereas the remainder were naturally exposed through recycling of oocysts in the litter. Between days 14 and 27, among birds receiving the 1x dosage of coccidial vaccine, those fed essential oils had a 5.6% increase in body weight gain. In naturally-exposed birds with pen-mates given the 1x dosage of coccidial vaccine, birds fed essential oils had 12% longer villi than did unsupplemented birds, with 30% more goblet cells and 23% more goblet cells/10 μm of villus length. Though the evaluated essential oil blend did not yield any significant benefits in performance with respect to varying coccidial vaccine dosages or varied manner of exposure to vaccine oocysts, the physiological effect of this phytogenic additive supplementation on intestinal morphology may indicate an improved barrier against pathogens during a mild coccidial exposure.
Interesting results were obtained when tannic acid (10 g/kg of feed) and attenuated anticoccidial vaccine were applied in broiler chickens challenged with experimental coccidiosis (Mansoori and Modirsanei, Reference MANSOORI and MODIRSANEI2012). Tannins had been previously reported to exert anticoccidial activity and ameliorate the negative impact of coccidiosis; however, their combination with vaccine against coccidiosis considerably reduced their effectiveness. While the vaccination provided protection against coccidiosis, as demonstrated by higher plasma concentrations of d-xylose (a parameter of intestinal integrity and ability to absorb nutrients), lower oocyst output, intestinal lesion scores and intestinal relative weights of intestinal parts, supplementation with tannic acid resulted in a decrease in all these indices. The authors explained these results as the effect of a possible disturbance in the development of immunity induced by the vaccine by altering the life cycle of the precocious Eimeria strains included therein, and advised not to use attenuated coccidiosis vaccines and dietary tannins at the same time.
A promising effect was obtained by Guo et al. (Reference GUO, KWAKKEL, WILLIAMS, SUO, LI and VERSTEGEN2005) after applying polysaccharide extracts originating from the mushrooms Lentinus edodes and Tremella fuciformes or the herb Astragalus membranaceus in conjunction with live vaccine. Generally, polysaccharides may act as immune enhancers or immunomodulators and could affect both innate and adaptive immunity, including cellular and humoral responses. The positive effect of the above extracts as a source of polysaccharides on the cellular and humoral immunity of E. tenella-infected broilers had also been confirmed in a previous study (Guo et al., Reference GUO, KWAKKEL, WILLIAMS, PARAMENTIER, LI, YANG and VERSTEGEN2004). The extracts were supplemented only from eight to 14 days of age, but in conjunction with the vaccine significantly enhanced body weight gain of chickens infected (at 18 days of age) with E. tenella in comparison with the vaccinated and infected group, despite the fact that extracts largely increased oocyst excretion of droppings during the primary postvaccination response (Guo et al., Reference GUO, KWAKKEL, WILLIAMS, SUO, LI and VERSTEGEN2005).
Conclusions
The usage of anticoccidial vaccines has been proven to be a successful tool in the control of coccidiosis; however, reports of a temporary deterioration in performance due to vaccination has resulted in a widespread reluctance to use them in broilers. Hence, methods to eliminate or ameliorate this effect are needed. Nutrition is a promising approach in this context and it was assumed that a beneficial outcome of nutritional factors in cocci-vaccinated broilers may be achieved through the identification and satisfaction of the nutritional requirements of vaccinated chickens, a stabilising effect on intestinal microbiota, maintenance of intestinal integrity, improvement in the digestibility and absorption of nutrients, and immunostimulation. The results of the studies discussed in the current review indicate a particular role for the appropriate level of protein in the diet administered directly after vaccination and the positive effect of probiotics, yeast derivatives, herbal or mushrooms extracts with immunostimulating properties. Some of the feed additives that were successful in case of subclinical or clinical coccidial infection have been proved to be ineffective when used in conjunction with live anticoccidial vaccines. It is important to take into consideration that acquisition of immunity through live cocci-vaccination requires two or three consecutive infections with vaccine oocysts. Thus factors with anticoccidial properties resulting in disruption of the parasite life cycle may adversely affect the efficacy of coccidiosis immunoprophylaxis. Moreover, the experimental design of studies whose purpose is to demonstrate the effect of nutritional factors should include the appropriate conditions for recirculation of vaccine oocysts which will result in the acquisition of immunity, along with all the potentially negative consequences of live oocyst vaccination.
In conclusion, the data presented in the current review indicate that feed additives with immunostimulating properties and proper protein level in the diet may have a beneficial effect in cocci-vaccinated broilers. However, in order to overcome the reluctance to use anticcocidial vaccination in broilers, further studies are needed to determine solutions that will effectively support the acquisition of immunity in cocci-vaccinated birds as well as prevent deterioration of performance due to vaccination.
