Effect of fishmeal replacement with spray-dried animal plasma and colistin on intestinal structure, intestinal microbiology, and performance of weanling pigs challenged with Escherichia coli K99.

We evaluated spray-dried animal plasma (SDAP) as an alternative to antimicrobial medication with colistin sulfate in weanling pigs challenged with Escherichia coli K99. Forty-eight piglets weaned at 24 d of age were distributed into 12 pens, and each pen was assigned to one of four dietary treatments. All the piglets were given an oral dose of 5 x 10(7) cfu of E. coli K99 at weaning. The dietary treatments followed a factorial arrangement with two levels of SDAP (0 and 7%) and two levels of colistin (0 and 300 mg/kg of diet). The ADG and ADFI were measured on d 7 and 14 of trial. Three piglets from each treatment were killed on d 7 and 14 to remove the small intestine, and to obtain ileal and cecal digestive contents. The inclusion of SDAP improved ADG by 68 g (P < 0.05) and ADFI by 41 g (P < 0.10) in wk 1 of trial. During wk 2, SDAP improved ADG by 41 g (P < 0.10) and gain:feed ratio (G:F) by 25% (P < 0.01). On the other hand, whereas colistin had no effect on performance in wk 1, it improved ADG by 102 g (P < 0.01), ADFI by 62 g (P < 0.01), and G:F by 26% (P < 0.01) in wk 2. Over the 14 d of the trial, ADG was improved by 54 (P < 0.05) and 75 g (P < 0.05), and G:F was improved by 35 (P < 0.05) and 32% (P < 0.05) due to SDAP and colistin, respectively. There was interaction between colistin and SDAP for ADFI in wk 2 and between d 0 to 14 (P < 0.05), which indicates that their effects were not additive. The use of colistin was advantageous in the maintenance of the integrity of the intestinal mucosa of the pigs, as suggested by a small intestine that was 93 g heavier (P < 0.10) and with the tallest villi 106 microm longer (P < 0.10) than in pigs without colistin. The inclusion of SDAP in the diet favored the growth of lactobacilli in the ileum (P < 0.10) and the cecum (P < 0.05), whereas colistin reduced the number of enterococci in the cecum (P < 0.05) and of Escherichia coli both in the ileum and the cecum (P < 0.001). These results suggest that SDAP may be an alternative to medicated feed with antibiotics since it provided a level of protection against an experimental challenge with E. coli K99 similar to that obtained with colistin, an antibiotic of proven efficacy. The current situation in which the use of antimicrobials in animal feeding is being questioned should encourage further investigation into the use of SDAP as a means of preventing disease in pigs at weaning.