| The purpose of this work was to examine the effectiveness of several replacements for antibiotics in broiler chickens using bacterial challenge models. For this work, pathogen challenge models were developed using three model pathogens; two human pathogens (Salmonella enteritidis and Campylobacter jejuni), and one poultry pathogen ( Clostridium perfringens). The first set of experiments involved the selection and use of 2 model probiotics; Bifidobacterium animalis and Lactobacillus fermentum. Oral administration of either probiotic did not significantly reduce (P < 0.05) the level of intestinal colonization by either S. enteritidis or C. jejuni in experimentally infected broiler chickens. The next set of experiments examined the effectiveness of orally administered, pathogen-specific antibodies obtained from hyperimmunizing laying hens in controlling bacterial infections with S. enteritidis, C. jejuni or Clostridium perfringens in broiler chickens. Regardless of the concentration, or mode of administration, anti- S. enteritidis hen-egg antibodies or anti-C. jejuni hen-egg antibodies were unable to significantly reduce (P < 0.05) the intestinal colonization by either pathogen in experimentally infected broiler chickens. Likewise, administration of anti-C. perfringens hen-egg antibodies did not reduce intestinal colonization by C. perfringens, and actually exacerbated the clinical outcome of this important poultry pathogen by significantly increasing (P < 0.05) intestinal lesions scores compared to negative control birds. Lastly, the effect of dietary protein source on intestinal C. perfringens populations was investigated. In broiler chickens experimentally infected with C. perfringens and fed diets which varied in the source of dietary protein, it was shown that birds fed fish meal, meat/bone meal, feather meal and potato protein concentrate had significantly higher intestinal C. perfringens counts than the birds fed corn gluten meal, soy or pea protein concentrates or the control diet ( P < 0.05). Further, it was shown that the glycine content of the diets and ileal contents was significantly, positively correlated with C. perfringens numbers in ileum and cecum. It is concluded that although the intervention strategies employed in these studies show promise, diet composition clearly had the largest effect on intestinal bacterial populations. Further studies are required to examine both the impact that diet and these intervention strategies have on the factors which control intestinal colonization by pathogens on a case by case basis. |
