Dietary crude protein time-dependently modulates the bacterial community and metabolites and changes dietary nutrient efficiency in growing pigs.

The reduced nutrient digestibility of low-protein (LP) diets has been shown to be caused by the weakened fermentative capacity of the post-gut flora. The dynamic regulation of dietary protein contents on post-gut microbial population and fermentative metabolism is unclear. Twelve growing barrows (19.9 ± 0.8 kg) fitted with a T-cannula at the blind end of the cecum were randomly administered a high-protein (HP, 21.5% crude protein [CP]) diet or an LP (15.5% CP) diet for 28 d. The cecal content and feces were collected at d 1, 14, and 28 of the experiment for microflora structures and metabolite concentrations analysis. The nutrient digestibility coefficient and plasma biochemical parameters were also determined. Compared with the HP treatment, the LP treatment showed decreased plasma urea nitrogen concentration and apparent total tract digestibility of dry matter, gross energy, and CP ( < 0.01). In addition, urinary nitrogen losses, total nitrogen losses, and daily nitrogen retention in the LP treatment were lower than those in the HP treatment ( < 0.01), and the nitrogen retention-to-nitrogen intake ratio in the LP treatment was increased ( < 0.01). The HP group showed increased cecal total short-chain fatty acids (SCFA) concentration and fecal propionate, butyrate, and total SCFA concentrations ( < 0.05) on d 14 and 28, which may be mainly related to the elevated abundance of SCFA-producing bacteria, such as , , and ( < 0.05). Probiotics, such as , , and enriched in the LP treatment possibly contributed to reduced plasma endotoxin content. The differences in the abundances of almost all the above-mentioned flora appeared on d 28 but not d 14. Likewise, differences in the Simpson and Shannon indices and clustering patterns of the microbiota between treatments were also only observed on d 28. To sum up, in a time-dependent manner, the LP diet increased probiotics with gut-improving functions and decreased SCFA-producing bacteria, which may cause enhanced intestine health and reduced nutrient digestibility.