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Necrotic enteritis (NE) is described as a disease of high economical impact which affects health and welfare of broilers and may also pose a threat to public health. Therefore any predisposing factor to NE is regarded very important. The effect of stress factors attributed to management practices such as feed deprivation, high stocking density, heat stress, cold stress and vaccination with live attenuated anticoccidial vaccine on the pathogenesis of NE has not been studied adequately. Therefore, the objective of the present study was to validate the effect of the above mentioned management stressors on the pathogenesis of NE by the use of an effective experimental model. For this purpose five experiments were carried out. In each one of the four experiments 240 day old broiler chicks (Cobb 500) were randomly allocated into four experimental groups of 60 broilers each, while in the fifth experiment for the evaluation of vaccination with live attenuated anticoccidial vaccine on the patho ...
Necrotic enteritis (NE) is described as a disease of high economical impact which affects health and welfare of broilers and may also pose a threat to public health. Therefore any predisposing factor to NE is regarded very important. The effect of stress factors attributed to management practices such as feed deprivation, high stocking density, heat stress, cold stress and vaccination with live attenuated anticoccidial vaccine on the pathogenesis of NE has not been studied adequately. Therefore, the objective of the present study was to validate the effect of the above mentioned management stressors on the pathogenesis of NE by the use of an effective experimental model. For this purpose five experiments were carried out. In each one of the four experiments 240 day old broiler chicks (Cobb 500) were randomly allocated into four experimental groups of 60 broilers each, while in the fifth experiment for the evaluation of vaccination with live attenuated anticoccidial vaccine on the pathogenesis of NE, 300 day old broilers chicken were randomly allocated into five experimental groups of 60 broilers each. Each experimental group consisted of two replicates (subgroups). The experimental period for each experiment was set to 24 days. On day 16, 21, 22, 23 and 24, six birds per subgroup were euthanized. The examinations conducted at each sampling day included the gross lesion scoring of intestine, gizzard and liver, the histopathology of intestine and liver, the flotation of feces, the microscopic examination of wet smears from intestinal mucosa and content, the measurement of pH of intestinal content, the measurement of viscosity of contents of jejunum and ileum, the bacterial cultivation of C. perfringens from liver and swab samples of gizzard, duodenum, jejunum, and ileum and the quantification of C. perfringens in cecum. Moreover, broilers were weighed on day 1, 9, 16, 17 and 21, while feed conversion ratio was calculated for the periods of 10-16 days of age and 17-21 days of age. In order to reproduce the NE, an experimental challenge model using C. perfringens and tenfold dose of a live anticoccidial vaccine was adopted. Experimentally challenged birds were orally infected three times per day with 4x108 cfu C. perfringens for four consecutive days (days 17, 18 19 and 20). The used strain was resistant to rifampicin. For the induction of NE, at day 18 birds were also inoculated orally with tenfold dose of a live anticoccidial vaccine (Paracox TM-5) which consisted of oocysts of E. acervulina, E. maxima, E. mitis and E. tenella. Broilers in all groups were fed a specially formulated three phase ratio (starter 1-9d, grower 10-16d and finisher 17-24d), which included large quantities of wheat, rye and soya. In the finisher ration soya was replaced by fishmeal which acted as predisposing factor of NE. The use of antibiotic growth promoters and anticoccidial drugs was avoided. The aim of the first experiment was to investigate the effect of feed deprivation on the pathogenesis of NE in broiler chickens. The treatment groups used in this experiment were group N served as negative control, group SN where feed deprivation was applied, group P where birds were experimentally challenged with C. perfringens and tenfold dose of a live attenuated anticoccidial vaccine and group SP where birds were both experimentally challenged and suffered starvation. In groups where feed deprivation was applied, the feed was withdrawn at days 16, 17, 18 and 19 for 12 hours daily starting from 21:00 to 09:00. The results of the experiment demonstrated that starvation has a significant protective effect against the experimentally induced NE in broilers, by limiting the C. perfringens caeca counts and reducing the severity of the NE lesions. The objective of second experiment was to assess the influence of high stocking density as a predisposing factor in NE in broiler chickens. The treatment groups used in this experiment were control group N where birds were at normal stocking density (15 birds/m2) and not challenged, group DN where birds were raised at 50% increased stocking density from 1st day (30 birds/m2), group P where birds were raised at standard stocking density and challenged with C. perfringens and with tenfold dose of a live attenuated anticoccidial vaccine and group DP where birds were challenged and raised at increased stocking density as described above. The experiment provides evidence that high stocking density increased the frequency and severity of NE. The purpose of third experiment was to investigate the effects of heat stress on the pathogenesis of NE in broiler chickens. The treatment groups used in this experiment were group N served as negative control, group HN where heat stress (35oC) was applied, group P where birds were experimentally challenged with C. perfringens and with tenfold dose of a live attenuated anticoccidial vaccine, and group HP where birds were both experimentally challenged and suffered heat stress. In groups where heat stress was applied, temperature was increased from 25νC (the recommended temperature for broilers at the respective age) to 35νC at days 16, 17, 18, 19 and 20 for 12 hours daily starting from 21:00 to 09:00h. Heat stress predisposes broilers to the manifestation of NE, because it provokes the occurrence of NE lesions in non challenged birds and also caused further increase of the severity of lesions in challenged birds. The objective of fourth experiment was to assess the influence of cold stress on the pathogenesis of NE in broiler chickens. The treatment groups used in this experiment were group N served as negative control, group CN where cold stress (15 oC) was applied, group P where birds were experimentally challenged with C. perfringens and tenfold dose of a live attenuated anticoccidial vaccine and group CP where birds were both experimentally challenged and suffered cold stress as described above. In groups where cold stress was applied, temperature was decreased from 25νC (the recommended temperature for broilers at the respective age) to 15νC at days 17, 18, 19 and 20 for 12 hours daily starting from 9:00 to 21:00. The experiment provides evidence that cold stress increased severity of subclinical NE. The objective of fifth experiment was to assess the influence of live anticoccidial vaccine on the pathogenesis of NE in broiler chickens and to establish a more efficient experimental model for the reproduction of NE. The treatment groups used in this experiment were group N served as negative control, group PN where birds vaccinated at day 1 with live attenuated anticoccidial vaccine, group P where birds were experimentally challenged with C. perfringens and tenfold dose of a live attenuated anticoccidial vaccine, group M where birds were challenged with C. perfringens and E. maxima and group PM where birds vaccinated at day 1 and were challenged with C. perfringens and E. maxima. The study provides evidence that live anticoccidial vaccine decreased the frequency and severity of experimental NE. Furthermore, the challenge of birds with C. perfringens and E. maxima increased the frequency and aggregated the severity of NE lesions compared to challenge with C. perfringens and tenfold dose of a live anticoccidial vaccine. It is evident from our studies that among the management factors in intensive broiler production systems, high stocking density, heat stress and cold stress pose a significant predisposal role for the induction of NE, while feed deprivation and vaccination against coccidiosis act protectively against it.
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