Feeding a diet with a decreased protein content reduces both nitrogen content in the gastrointestinal tract and post-weaning diarrhoea, but does not affect apparent nitrogen digestibility in weaner pigs challenged with an enterotoxigenic strain of Escherichia coli

This study evaluated possible nutritional and physiological mechanisms to explain why feeding a diet of decreased protein content reduces PWD. A total of 48 male pigs weaned at 21 d (initial BW 6.9±0.11kg; mean±SEM) was used in a 2×2×2 factorial arrangement of treatments with the respective factors being: (1) PL (HP 239g/kg vs. LP 190g/kg CP); (2) presence or absence of an ETEC challenge; and (3) duration of feeding after weaning until euthanasia (D; 7 d vs. 14 d). No dietary antimicrobial compounds were used, and diet LP contained crystalline AA including isoleucine and valine to achieve an ideal AA pattern. Pigs were offered the experimental diets on an ad libitum basis. Feeding a LP diet decreased total N intake, ileal N flow, PUN and NH₃-N contents at the ileum and all sites in the large intestine (P<0.05-0.001), but did not alter (P>0.05) the AID of N and AA at either d 7 or d 14, except for serine which was lower in pigs fed the LP diet (P<0.001). Feeding diet HP increased the incidence of PWD, and ETEC infection increased PWD only in pigs fed the HP diet (PL×ETEC interaction, P<0.05). Pigs fed diet HP had more PWD at d 7 but not at d 14 after weaning (PL×D interaction, P<0.05). Experimental ETEC infection increased (P<0.001) faecal Escherichia coli score compared to non-infected pigs, and decreased AID of some AA at d 7 (ETEC×D interaction, P<0.05-0.001). Feeding diet LP reduced the molar proportion of BCFA in the caecum and proximal colon (P<0.001 and P<0.05, respectively), but total VFA concentrations in this organ were unaffected by PL (P>0.05). Pigs fed diet LP had decreased pH in the jejunum and ileum (P<0.05 and P<0.01, respectively), while ETEC infection increased pH in the caecum and proximal colon at d 7 (ETEC×D interaction, P<0.05). Feeding diet LP did not alter GIT weight, but ETEC infection adversely affected the proportional weight of the GIT at d 7 (ETEC×D interaction, P<0.01). The PL did not alter small intestinal morphology and growth. These results suggest that feeding a LP diet immediately after weaning reduces the flow of N into the large intestine, thereby decreasing protein fermentation without altering apparent AA digestibility at the ileum.