Contrary to our study, Shanmugasundaram et al. (2012) reported that broiler chickens raised on used litter had an increase in IL1 and IL4 transcripts, but a decrease in IL10 transcripts in cecal tonsils compared with those raised on fresh litter. Different cytokine levels seen in these two studies may reflect different genetic background of chickens, age of chickens, gut commensals, and other environmental factors such as diets and litter contaminants. Especially, the latter study suggested that higher IL1 mRNA expression was indicative to a low level of chronic inflammation in the cecal tonsil that was exposed to pathogenic or nonpathogenic bacteria. Furthermore, we sampled mid-intestine of 28-d-old chickens raised on litter where 10 broiler flocks had already been grown while Shanmugasundaram et al.
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