Oat bran and wheat bran impact net energy by shaping microbial communities and fermentation products in pigs fed diets with or without xylanase

Background: Dietary fiber can be fermented in gut of pigs and the end products of fermentation were short-chain fatty acids(SCFA). The SCFA had positive effects on gut bacteria and host immune system. In addition, SCFA can provide a part of available energy for pigs. However, there were limited reports on the relationship between dietary fiber, gut bacteria, and energy metabolism. Therefore, this study investigated how dietary fiber and enzyme addition impacted energy metabolism by acting on the microbial community and SCFA.Methods: Wheat bran(WB) was added to the corn-soybean meal-based diet at the levels of 12% and 27%, and oat bran(OB) at 15% and 36%. One of each diet was supplemented with or without 5000 U/kg feed of xylanase, so a total of 10 diets were allotted to 60 growing pigs(initial body weight: 27.2 ± 1.2 kg) using a randomized complete block design. The experiment was conducted in 10 consecutive periods using 6 similar open-circuit respiration chambers. Each pig was used for one 20-day period. During each period, six pigs were allowed 14 d to adapt to the diets in metabolic cages followed by 6 d(from d 15 to d 20) in respiration chambers to measure heat production(HP).Results: Pigs fed 36% OB diets had greater(P < 0.05) nutrient digestibility and net energy(NE) values compared to those fed 27% WB diets. Apparent digestibility coefficients of dry matter(DM) and crude protein(CP) were lower(P < 0.05) in pigs fed 27% WB diets compared with those fed 12% WB diets. Enzyme addition improved(P < 0.05)the NE values(11.37 vs. 12.43 MJ/kg DM) in diets with 27% WB. Supplementation of xylanase did not affect NE values for basal diets, OB diets and 12%WB diets. Compared with diets with 36% OB, pigs fed 27% WB-based diets excreted more total SCFA, acetate and propionate(expressed as g/kg feed DM) in fecal samples of pigs(P < 0.05).Pigs in the WB diets had greater proportion of phylum Bacteroidetes while phylum Firmicutes were greater in pigs fed OB diets(P < 0.05). Pigs fed WB diets had greater(P < 0.05) abundance of Succinivibrio and Prevotella, which were associated with fiber degradation and SCFA production.Conclusion: Our results indicated diets supplied by high level of OB or WB promote the growth of fiber-degrading bacteria. The differences in fiber composition between WB and OB led to differences in nutrient digestibility and bacterial communities, which were ultimately reflected in energy metabolism. Enzyme supplementation improved nutrient digestibility as well as NE values for 27% WB diets but not for other diets, which indicated that effects of enzyme were related to type and level of dietary fiber in diets.

Early osmotic adjustment responses in drought-resistant and drought-sensitive oilseed rape

The impact of osmotic stress on growth, physiolo- gy, and metabolism of winter oilseed rape （Brassica napus L.） was investigated by detailed analysis of biomass traits, hormone metabolites and osmolytes in two genetically unrelated drought-tolerant genotypes and two unrelated drought-sensitive genotypes. Seedlings were grown in vitro under controlled conditions and osmotic stress was simulated by applying a gradual treatment with polyethylene glycol （PEG 6ooo）, followed by hypo-osmotic treatment of variants used for metabolite determination. The results provide a basis for the identification of reliable selection criteria for drought resistance in oilseed rape. The in vitro cultivation system established during this study enabled effective discrimination of early osmotic stress responses between drought-resistant and -susceptible oilseed rape genotypes that also show large differences in relative seed yield under drought conditions in the field. Clear physiological and metabolic differences wereobserved between the drought-resistant and drought-sensitive genotypes, suggesting that osmotic adjustment is a key component of drought response in oilseed rape. Unexpected- ly, however, the drought-resistant genotypes did not show typical hormonal adjustment and osmolyte accumulation, suggesting that they possess alternative physiological mech- anisms enabling avoidance of stress symptoms.