短链脂肪酸在生猪产业的研究与应用

短链脂肪酸是肠道微生物发酵产物,其对机体健康的影响已被广泛研究。本文就短链脂肪酸在国内外的研究进展,综述了其对猪肠道健康和代谢健康的有益影响以及在生猪养殖中的应用,旨在为新型饲料添加剂的开发与利用提供应用和理论依据。     

Effects of short-chain fatty acids and lactic acids on survival of Oesophagostomum dentatum in pigs

The direct influence of intracaecal infusion of short-chain fatty acids (SCFA) and lactic acids (LA) on already established Oesophagostomum dentatum infection in cannulated pigs was investigated. We tested the hypothesis that the previously discovered anti-parasitic effect of inulin is mediated through its metabolic products SCFA and LA by infusing into cannulated pigs these compounds in amounts approximating to those produced in the pigs large intestine and caecum during the metabolism of inulin. The experiment comprised of 18 pigs--2 groups of 9 pigs in each. The normal diet used in the experiment was based on barley flour with insoluble fibre from oat husk with added soybean meal, vitamins and minerals. After 2 weeks of adaptation to the diet all the pigs were inoculated with 6,000 infective larvae of O. dentatum. Six weeks later, surgery on all pigs was performed to install cannulas into caeci. At 7 weeks post-infection (p.i.) the SCFA and LA infusion was initiated in Group 1 (experimental) pigs; at the same time pigs in Group 2 (controls) were infused with saline. At week 10 p.i., all pigs were killed and their worm burdens determined. SCFA and LA infused pigs exhibited markedly reduced fecal egg counts and worm recoveries (98 and 92% reduction, respectively, compared to saline controls). The results from this study demonstrate that SCFA and LA have a significant negative influence on established O. dentatum infection in growing pigs. The results also show that the type of dietary carbohydrates fed and its intestinal degradation can yield metabolic by products that profoundly influence helminth survival.     

Effect of short-chain fatty acids on contraction of smooth muscle in the canine colon

OBJECTIVE: To determine effects of short-chain fatty acids (SCFA) on canine colonic smooth muscle. SAMPLE POPULATION: Colonic tissue obtained from 14 healthy dogs. PROCEDURE: Short-chain fatty acid (SCFA; acetate, propionate, and butyrate; 1 to 100 mmol/L)-induced contractions were compared with responses obtained with acetylmethylcholine (AMCh; 10(-4) mol/L). Roles of enteric neurons, cholinergic receptors, calcium stores in the sarcoplasmic reticulum, and extracellular calcium in the SCFA-induced responses were investigated by incubating muscle strips with tetrodotoxin (1 micromol/L), atropine (1 micromol/L), ryanodine (10 micromol/L), nifedipine (1 micromol/L), ethylene glycol-bis (beta-aminoethylether)-N,N,N',N'-tetra-acetate (EGTA; 0.1 mmol/L), or an extracellular calcium-depleted (zero extracellular calcium) solution prior to the addition of propionate or butyrate. RESULTS: Incubation with SCFA elicited isometric stress responses (0.25 to 2.15 x 10(4) N/m2) in colonic longitudinal smooth muscle. Maximal responses to butyrate and propionate (50 mmol/L) were 37 and 23%, respectively, of the maximal AMCh response. Acetate was least effective in stimulating contractile responses. Tetrodotoxin and atropine did not affect SCFA-induced contractions. Nifedipine and zero extracellular calcium solution abolished responses to butyrate and propionate, whereas EGTA attenuated (> 60%) but did not abolish those responses. Ryanodine did not affect SCFA-induced contractile responses. The SCFA did not affect colonic circular smooth muscle. CONCLUSIONS AND CLINICAL RESPONSE: The SCFA stimulate longitudinal but not circular colonic smooth muscle contractions via a direct effect on smooth muscle. The mechanism of the SCFA effect appears to involve the influx of extracellular calcium. These findings may account for some of the effects of fiber on canine colonic motility [corrected].     

Experimental production of rabbit mucoid enteritis

Rabbit mucoid enteritis (mucoid enteropathy) is a subacute fatal disease of weanling rabbits with unknown cause. Mucoid enteritis was experimentally produced by ligating the large intestines in rabbits. Of the rabbits with ligated cecum and those with ligated colon, 70% and 45%, respectively, had excessive production of mucus and passed large amounts of mucus with feces, closely resembling the naturally occurring mucoid enteritis. Injection of oxytetracycline into the cecum at the time of ligation prevented the development of mucoid enteritis, and injection of cholestyramine markedly reduced the frequency of the disease in the rabbits with ligated cecum.     

Intestinal flora studies in rabbit mucoid enteritis.

The clinical and bacteriological examination of spontaneous and experimental cases of mucoid enteritis on a large rabbit farm indicated that the mucin accumulations in the colon are a consequence of constipation. This opinion is supported by the results obtained following ligation of the proximal colon. These findings suggest that rabbit mucoid enteritis is not a specific disease entity but a general response to the factors which cause constipation. Studies of the bacterial flora of the gut in spontaneous and experimental cases suggest that while there is a notable increase in the number of coliforms and clostridia over the healthy controls, these organisms only play a secondary role.     

Large intestinal epithelium and short-chain fatty acids. Expected, unexpected, unexplained findings

Short-chain fatty acids (SCFA) are present in hindgut contents in high concentrations. SCFA are generated and also absorbed rapidly in the large intestine. Absorption results from diffusion of the undissociated and lipid soluble form or in exchange for bicarbonate. The controversial concepts concerning the extent of diffusion or the exchange for bicarbonate are partly due to contradictory findings and unequal mechanisms in different species and in different segments of the large intestine as well as in the different methods used. An almost neutral pH microclimate at the luminal surface is of importance for absorption of SCFA. The apical membranes of the epithelial cells in caecum and in proximal colon of guinea pigs are an substantial barrier for the diffusion of SCFA. After withdrawal of butyrate for only one hour from the perfusion or incubation solutions a massive apoptosis had been observed during the in situ perfusion of segments of guinea pig large intestine and also in in vitro studies with isolated epithelia in Ussing-chambers. In vitro apoptotic bodies and cells are emitted at the epithelial surface. However, in vivo induced by butyrate deprivation resident macrophages were tightly clustered below the surface epithelium. Aided by cytoplasmatic projections these macrophages phagocytose and transport apoptotic material from the epithelial intercellular spaces into their bodies. Obviously macrophages can be overloaded by this massive apoptosis, and some of the undigested apoptotic fragments are emitted into the lamina propria. Formation of a colitis ulcerosa may originate from these released undigested apoptotic bodies. Furthermore hints indicate aetiological interrelations between deprivation of butyrate and colon cancer. Butyrate-paradox denotes the contrarian effects on apoptosis and cell proliferation after addition or deprivation of butyrate in cultures of large intestinal tumour-cell-lines in comparison with the healthy, intact epithelium.     

大豆寡糖对肉仔鸡肠道pH值和盲肠短链脂肪酸的影响

在玉米-大豆浓缩蛋白型低寡糖基础日粮中分别添加0、0.50%、1.00%或2.00%的大豆寡糖,研究了不同添加量大豆寡糖对肉仔鸡肠道pH值和盲肠短链脂肪酸的影响。选用192只1日龄AA肉公鸡,随机分成4个处理组,每个处理设6个笼(重复),每笼8只鸡。结果表明:大豆寡糖对18、36日龄肉仔鸡十二指肠和空肠食糜pH值的影响无明显规律,各处理组之间无显著性差异(P0.05);随着大豆寡糖水平的增加,盲肠食糜pH值呈下降的趋势(P0.05),1.00%大豆寡糖添加组18、36日龄肉仔鸡盲肠食糜pH值为最低水平,且显著低于对照组(P0.05)。低寡糖日粮中添加不同剂量大豆寡糖,大幅度增加肉仔鸡盲肠食糜中乙酸和短链脂肪酸总量的浓度(P0.05);添加1.00%或2.00%大豆寡糖,显著增加18日龄肉仔鸡盲肠食糜中丁酸占短链脂肪酸总量的摩尔百分比(P0.05)。     

Protein-losing enteropathy associated with cystic mucoid changes in the intestinal crypts of two dogs

Two dogs were emaciated and hypoalbuminemic due to protein-losing enteropathy associated with a severe, focal, mucoid, cryptal ectasia of the duodenum and marked villus atrophy. In one case, diseased portions of the duodenum were obvious endoscopically and were limited to discrete, focal areas in the small intestine, with apparently more undiseased tissue than diseased tissue being present. The signs and lesions in one dog resolved after initiating combination dietary and pharmacological therapy.     

Exogenous infusion of short-chain fatty acids can improve intestinal functions independently of the gut microbiota

The present experiment was conducted to investigate the effects of exogenously infused short-chain fatty acids (SCFAs) on the growth development and intestinal functions in a germ-free (GF) pig model. Twelve hysterectomy-derived newborn piglets were reared in six sterile isolators. All piglets were hand-fed Co60-γ-irradiated sterile milk powder for 21 d and then were switched to sterile feed for another 21 d. During the second 21-d period, GF piglets (n = 6) were orally infused with 25 mL/kg sterile saline per day, and SCFA piglets (n = 6) were orally infused with 25 mL/kg SCFAs mixture (acetic, propionic, and butyric acids, 45, 15, and 11 mM, respectively) per day. We observed the concentrations of SCFAs in serum and intestine, and the messenger ribonucleic acid (mRNA) abundance of G-protein-coupled receptor-43 in the ileum was increased (P < 0.05) in the SCFA group. Meanwhile, oral infusion of SCFAs enhanced (P < 0.05) the contents of glucagon-like peptide-2 in the jejunum and serum and tended to increase the villi height in the ileum (P < 0.10). Besides, the activities of lipase, trypsin, sucrase, lactase, Na⁺-K⁺-adenosine triphosphatase ([ATPase] P < 0.05), and Ca²⁺-Mg²⁺-ATPase (P < 0.10) were stimulated and the mRNA expressions of solute carrier family 7 (SLC₇A₁) and regeneration protein (REG)-ΙΙΙ γ in the jejunum (P < 0.05) were upregulated in the SCFA group. Additionally, SCFAs infusion downregulated the mRNA abundances of interleukin (IL)-1β and IL-6 in the jejunum, ileum, or colon (P < 0.05) and increased the counts of white blood cell, neutrophils, and lymphocyte in the blood (P < 0.05). Collectively, exogenous infusion of SCFAs might improve intestinal health through promoting intestinal development and absorption function, and enhancing intestinal immune function, and these effects were occur independently of the gut microbiota.     

Effect of short-chain fatty acids on pancreatic exocrine secretion in calves aged 2 weeks and 13 weeks

Effects of short-chain fatty acids on pancreatic exocrine secretion were studied under anesthesia in calves within 2 weeks of age (2-wks calves) given only whole milk and milk replacement and in which rumen fermentation has not begun yet, and in calves at 13 weeks of age (13-wks calves) weaned at 40 days of age and in which rumen fermentation has already begun. Basal rate of juice flow and protein concentration and amylase activity in pancreatic juice under basal condition were significantly lower in the 2-wks calves than those in the 13-wks calves. Intravenous administrations of acetate, propionate and butyrate stimulated pancreatic juice secretion and protein and amylase output in both groups of calves. Those responses were increased with increasing carbon number in the molecule of fatty acids. Although the response of amylase output (/kg of body weight) in the 2-wks calves was significantly less than that in the 13-wks calves, the response of juice flow and protein output (/kg of body weight) in the 2-wks calves were equivalent to or greater than those in the 13-wks calves. These results indicate that the characteristic of pancreas, being stimulated by short-chain fatty acids, in calves and probably in other ruminants is not generated on the process of postnatal development, but has been already acquired before rumen fermentation begins.     

Evaluation of the effects of short-chain fatty acids and extracellular pH on bovine neutrophil function in vitro

OBJECTIVE: To investigate the effects of short-chain fatty acids (SCFAs) and pH on neutrophil oxidative burst, phagocytosis, and morphology after exposure to acetate, propionate, butyrate, or succinate at pH 5.5 and 6.7. SAMPLE POPULATION: Neutrophils isolated from bovine blood samples and Porphyromonas levii, Prevotella spp, and Bacteroides fragilis isolated from lesions of cattle with acute interdigital phlegmon (foot rot). PROCEDURES: Bacteria were cultured in strictly anaerobic conditions. Bacterial SCFA production was measured with high-performance liquid chromatography. Neutrophils were isolated, stimulated with phorbol 12-myristate 13-acetate (PMA) or opsonized zymosan (OZ), and incubated with dihydroethidium or dichlorofluorescein diacetate to measure production of O(2)and H(2)O(2), respectively. Phagocytosis was assessed after exposure to serum-opsonized bacteria. Cellular morphology was assessed with differential staining. RESULTS: All bacteria produced at least 3 of the 4 SCFAs. Production of both O(2) and H(2)O(2) was markedly curtailed in PMA-stimulated neutrophils exposed to SCFA at pH 5.5, compared with production at pH 6.7. Succinate caused a significant dose-dependent decrease in O(2) production at pH 6.7 in OZ-stimulated neutrophils. Monoprotic SCFAs elicited a significant increase in H(2)O(2) production in OZ-stimulated neutrophils at pH 6.7 but a significant decrease at pH 5.5. Monoprotic SCFAs significantly increased phagocytosis at pH 6.7 but decreased phagocytic activity at pH 5.5. Cellular necrosis was observed in cells exposed to SCFAs at pH 5.5. CONCLUSIONS AND CLINICAL RELEVANCE: Establishment and persistence of anaerobic bacteria in cattle with foot rot infection may result in part from neutrophil dysfunction secondary to the effects of bacterially secreted SCFA in acidotic microenvironments.     

Testing the efficacy of medium chain fatty acids against rabbit colibacillosis

Enteropathogenic Escherichia coli (EPEC) represents a major cause of lethal diarrhea in young mammals. Although the pathogenicity mechanisms of EPEC are now well understood, the intrinsic and environmental factors that control the expression of EPEC virulence remain largely unknown. In the rabbit, suckling reduces pups' sensitivity to EPEC infection. Hence, we have hypothesized that uncharacterized factors present in doe milk may mediate this protection. Medium chain fatty acids (MCFA), known to possess antimicrobial properties, are highly abundant in doe milk. We demonstrate that caprylic acid exhibits a clear bacteriostatic effect in vitro against the rabbit EPEC strain E22 (O103:H2:K-), in a dose-dependent manner. In vivo, the dietary inclusion of triglycerides of MCFA did not however reduce the sensitivity of young rabbits challenged with this EPEC strain. The mortality and fecal excretion of EPEC were not reduced, and the bacterial adhesion to ileum was not inhibited. Amount of MCFA reaching the ileal level might have been too low and/or their association to other milk antimicrobials may have been required to observe a positive effect on disease evolution in a context of a highly virulent challenge.     

The effect of various anionic salts on ruminal pH and short-chain fatty acids in non-pregnant and non-lactating cows

AIM: To evaluate whether the different anionic salts used in the prevention of parturient paresis have an impact on the ruminal pH and the production of short-chain fatty acids (SCFA) in mature non-pregnant, non-lactating cows.

METHODS: Eleven Holstein-Friesian crossbred cows were administered 2,000 mEq of either one of three chloride salts, viz CaCl₂, MgCl₂, or NH₄Cl; four sulphate salts, viz CaSO₄, CaSO₄ with a grain size of 10 µm, MgSO₄, or (NH₄)₂SO₄; two combinations of anionic salts, viz CaCl₂+MgSO₄, or CaSO₄+NH₄Cl; NaCl; or water, via a ruminal cannula over a 14-day treatment period. The salts and controls were assigned in an 11 × 11 Latin square, and the cows were distributed randomly. Ruminal fluid was collected four times in each treatment period for monitoring the ruminal pH, and four times a day at Days 7 and 14 for monitoring any changes in the concentrations of SCFA.

RESULTS: Feeding anionic salts did not change the ruminal pH, total concentration of SCFA, or distribution pattern of the main SCFA acetic acid, propionic acid, butyric acid or valeric acid (p>0.05).

CONCLUSIONS AND CLINICAL RELEVANCE: Feeding anionic salts has no negative side effect on the ruminal pH and concentrations of SCFA in mature non-pregnant, non-lactating cattle. Impaired function of the rumen due to the feeding of anionic salts is not likely.     

Modulation of Na+ transport across isolated rumen epithelium by short-chain fatty acids in hay- and concentrate-fed sheep

The effect of increasing concentrations of short-chain fatty acids [SCFA; mixture of the Na+ salts of acetic acid (62.5%), propionic acid (25.0%) and of butyric acid (12.5%)] on Na+ transport of sheep rumen epithelium was studied in vitro. The conventional Ussing chamber method was used for measuring Na+ transport rates (22Na+), short-circuit current (Isc) and tissue conductance (GT) of isolated rumen epithelium. SCFA in the buffer solution on the mucosal side caused a linear increase of Jnet Na+ from 1.14, to 1.22, 1.78 and 2.50 microeq/cm2/h in hay-fed sheep at 0, 15, 40 and 80 mmol/l SCFA, respectively. In a second study, the effect of higher SCFA concentrations [0 (control), 80, 100 and 120 mmol/l] was investigated with epithelia from two groups of sheep. One group was subjected to hay ad libitum, whereas the other received concentrate feed (800 g/day in equal portions at 7.00 am and 3.00 pm) and hay ad libitum. Epithelia from concentrate-fed sheep again showed a significant (p < 0.05) and linear increase in Jnet Na+ at 80, 100 and 120 mmol/l. However, in hay-fed sheep, the difference in increase among 80, 100 and 120 mmol/l SCFA was not significant, indicating that, above 80 mmol/l SCFA Jms and Jnet exhibit saturation. Moreover, Na+ fluxes (Jms and Jnet) were generally higher in concentrate-fed than in hay-fed sheep at all SCFA concentrations and significant differences were observed at 100 and 120 mmol/l SCFA. The obtained results confirm the effect of SCFA on Na+ transport and are in agreement with studies regarding feeding regimes and electrolyte transport in the rumen. The important new observation is the increase of Na+ transport in concentrate-fed sheep even at high concentrations of SCFA (100 and 120 mmol/l). The enhanced activity of the Na+/H+ exchanger at these SCFA concentrations supports the assumption that the capacity for regulating the intracellular pH by extrusion of protons is increased, suggesting an adaptation in concentrate-fed sheep. This adaptation could prevent possible disturbances of epithelial functions (transport and barrier) under conditions of increased SCFA absorption.     

Effect of feeding selected short-chain fatty acids on the in vivo attachment of Salmonella typhimurium in chick ceca.

Two groups of 20 chicks each were fed 1% fatty acid continuously starting at 1 day of age, while a control group of 20 chicks received unsupplemented feed. At 2 days of age, chicks were inoculated orally with 1 ml of Salmonella typhimurium (1 x 10(6) colony-forming units/ml). Ceca were obtained from six chicks of each group at 7, 14, and 21 days of age. At 14 days of age, formic and propionic acids had statistically reduced Salmonella recovery by 2.56 logs and 3.09 logs, respectively, compared with controls. At 21 days of age, both test groups showed significant reductions of approximately 3.6 logs compared with controls. There were no statistical differences in body weights among the groups at 21 days of age.