To examine the inhibitory effect of whole grain paddy rice diet (WPR) feeding on the colonization of Campylobacter jejuni in the cecum of broiler chicks, we performed the following examination. Sixty female broiler chicks (14 days of age) were allocated into two groups, thirty birds were fed a ground corn diet (GC) as a control group, and 30 chicks were fed WPR as an examination group. After feeding with the different diets for 16 days, six chicks were selected from each group (12 chicks in total), and each chick was inoculated with 2×10 3 colony-forming units of C. jejuni GTC03263. Forty-eight hours after the bacterial inoculation (the birds continued to be fed with the corresponding diets after the bacterial inoculation), the chicks (six from each group) were killed and dissected to detect bacterial colonization in the cecum. The other six chicks were dissected to weigh the chick gizzard and to measure the pH of its contents. No bacterial colonization was observed in the cecum of chicks in the WPR group, whereas bacteria were found in the cecum of five of six chicks in the GC group. The average ratios of gizzard weight to body weight of the WPR-fed chicks was significantly higher than that of the GC-fed chicks, whereas the average pH value of the gizzard contents was not different between the two groups. These results suggest that WPR feeding in broiler chicks has a positive effect on development of the gizzard muscle and grinding activity of the gizzard. Increased grinding activity may eliminate the regional differences in pH within the gizzard, resulting in less bacterial survival in the gizzard and then less bacterial colonization in the cecum of WPR-fed chicks than in GC-fed chicks.

We previously reported that a diet containing 65% paddy rice suppressed the colonization of Campylobacter jejuni in the cecum of broiler chicks, suggesting that this type of diet has positive effects on upper gastrointestinal tract function in broilers. To reveal the possible mechanisms involved in this antibacterial effect of the whole-grain paddy rice diet, we performed experiments comparing the digesta passage rate in the crop and gizzard, the development of gizzard, and the pH distribution in the gizzard between groups of chicks fed two different diets, such as ground corn and whole-grain paddy rice. During these experiments, we made the following observations: the chicks in the group fed the whole-grain paddy rice diet had more developed gizzards and significantly larger crop content than the chicks in the group fed the ground corn diet. The chicks fed the whole-grain paddy rice diet retained the digesta in the crop for much longer and had less variation in the pH values in the gizzard than those fed ground corn. On the basis of these observations, we concluded that the hardness of the rice hull in whole-grain paddy rice leads to a larger amount and longer retention of content in the crop, as well as the uniformity of the internal pH of the gizzard, by promoting gizzard activity. We speculate that the hardness of the rice hulls promoted the grinding activity of the gizzard, resulting in the long retention time of the digesta in the crop and uniformity of the internal pH of the gizzard, which may sterilize or suppress Campylobacter growth in the gastrointestinal tract of broiler chicks.