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The effects of natural antibiotic-alternatives on the health-related parameters and microflora of the digestive tract in individually versus group-penned piglets after oral infection with enterotoxige

Various sole or blended carboxylic acids or their salts are postulated as “biologically safer” alternatives than antibiotics. These products are claimed to improve the performance of piglets through an effect on the gut microflora and gut health. However, in healthy piglets, opportunistic pathogens exist as part of the intestinal ecology, and benefits seen in terms of the performance may not be detectable. To obtain a better discrimination of their potency in vivo, various infection models are postulated. This study aimed to evaluate the biological and physiological responses to sole or blended organic acidifiers for piglets being exposed to viro-bacterial infection when kept individually and groups. In total, 48 crossbred piglets after weaning at 28 days of age were placed in individual pens and allotted to four isoproteinic and isoenergetic dietary treatments: 1) a basal diet + 40 ppm avilamycin; 2) a basal diet; 3) a basal diet + 2% lactic acid; 4) a basal diet + 0.8% blended malic acid and Mg-citrate. Major ingredients used to formulate the basal diet were barley (24%), wheat (24%) soybean meal (16%), whey (15%), and fish meal (8%), whereas the contents of CP and ileal digestible lysine were 23.3 and 1.2%, respectively. The diets were offered ad libitum (controlled daily) in a dry form. On days 4 and 5 post-weaning, a half of the piglets from each dietary treatment was infected orally with RV 277 and ETEC serotype O149K91F4ac. The response of piglets to the dietary treatments and infection was monitored in terms of: visual monitoring of clinical health status, mortality, performance (feed intake, growth rate and feed conversion ratio),faecal consistency and faecal scour index, faecal shedding of haemolytic E.coli. Besides, on day 10 post-infection venous blood indices were assayed (heamogram), and afterwards the animals were euthanized to sample intestinal mucosa from the duodenum, jejunum and ileum, pancreas, and caecal digesta. Morphological indices (villus height and crypt depth in the jejunum and ileum) and activity of intestinal/pancreatic enzymes were determined. Each piglet was an experimental unit. The data were subjected to the ANOVA analysis of variance for the randomised block design. The significance of the differences between treatments was tested with the Student t-test at P < 0.05. As anticipated, the controlled oral infection with RV and ETEC was moderate (only 1 piglet died). However, in comparison to non-infected piglets, the infected piglets had a lower feed intake (FI) and average daily gain (ADG) at a worse feed conversion ratio (FCR), irrespective of the diet. The infected piglets had a greater (P<0.001) faecal scour index and significantly increased numbers of leukocytes number (+3.3 x 103/mm3), lymphocytes (+1.07 x103/mm3), neutrophiles (+1.9 x103/mm3) and eosinophiles (+0.07 x103/mm3). Besides, the challenging resulted in a higher (P<0.05) content of mucosal protein, whereas the activities of intestinal enzymes such as duodenal and ileal aminopeptidase N and ileal maltase were reduced. Pancreatic enzyme activities were unchanged, despite we found that 62% of the infected animals excreted haemolytic E.coli serotype K88 in faeces, and the infection increased (P<0.05) faecal shedding of haemolytic E. coli.The effects of dietary treatments on the performance, functionality the digestive tract and haemogram in infected or non-infected piglets were not statistically significant, and no interaction between these treatments and infection was found. Thus this may imply that the microbial load and the metabolic demands of the gut exposed to ETEC and RV might have been predominantly modulated by endogenous SCFA “liberated” from fermentable carbohydrates of this specific basal diet in the stomach and small intestine in amounts far exceeding the minimum inhibitory concentrations. In summary, the RV and ETEC infection negatively affected piglet's performance and health-related parameters, irrespective the diet. Antibiotic-free diets supplemented or not with these organic acidifiers, allowed obtaining comparable values as with avilamycin during the post-infective period.

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Animal Sciences Group Lelystad
Edelhertweg 15, PO Box 65
8200 AB LELYSTAD
Netherlands
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