The VFA, also known as short-chain fatty acids, are produced in the gastrointestinal tract by microbial fermentation of carbohydrates and endogenous substrates, such as mucus. This can be of great advantage to the animal, since no digestive enzymes exist for breaking down cellulose or other complex carbohydrates. The VFA are produced in the largest amounts in herbivorous animal species and especially in the forestomach of ruminants. The VFA, however, also are produced in the lower digestive tract of humans and all animal species, and intestinal fermentation resembles that occurring in the rumen. The principal VFA in either the rumen or large intestine are acetate, propionate, and butyrate and are produced in a ratio varying from approximately 75:15:10 to 40:40:20. Absorption of VFA at their site of production is rapid, and large quantities are metabolized by the ruminal or large intestinal epithelium before reaching the portal blood. Most of the butyrate is converted to ketone bodies or CO2 by the epithelial cells, and nearly all of the remainder is removed by the liver. Propionate is similarly removed by the liver but is largely converted to glucose. Although species differences exist, acetate is used principally by peripheral tissues, especially fat and muscle. Considerable energy is obtained from VFA in herbivorous species, and far more research has been conducted on ruminants than on other species. Significant VFA, however, are now known to be produced in omnivorous species, such as pigs and humans. Current estimates are that VFA contribute approximately 70% to the caloric requirements of ruminants, such as sheep and cattle, approximately 10% for humans, and approximately 20-30% for several other omnivorous or herbivorous animals. The amount of fiber in the diet undoubtedly affects the amount of VFA produced, and thus the contribution of VFA to the energy needs of the body could become considerably greater as the dietary fiber increases. Pigs and some species of monkey most closely resemble humans, and current research should be directed toward examining the fermentation processes and VFA metabolism in those species. In addition to the energetic or nutritional contributions of VFA to the body, the VFA may indirectly influence cholesterol synthesis and even help regulate insulin or glucagon secretion. In addition, VFA production and absorption have a very significant effect on epithelial cell growth, blood flow, and the normal secretory and absorptive functions of the large intestine, cecum, and rumen. The absorption of VFA and sodium, for example, seem to be interdependent, and release of bicarbonate usually occurs during VFA absorption.(ABSTRACT TRUNCATED AT 400 WORDS)

Energy contributions of volatile fatty acids from the gastrointestinal tract in various species

Publisher Summary A great deal is known concerning the qualitative nutritional requirements of insects. The quantitative aspects of insect nutrition have, however, received less attention, and there have been few studies on the rates of intake and the efficiency of food utilization. In particular, relatively little is known concerning the intake, digestibility and efficiency of conversion of defined diets. Quantitative work with artificial diets has usually involved only measurements of the amount of a particular nutrient required per unit of diet. Insects as a group feed upon a remarkably diverse list of organic substances. At the same time most species show a high degree of specificity in their choice of food. It seems apparent that adaptive nutritional differences must be sought on a quantitative level and that a meaningful comparative nutrition of insects will not emerge until quantitative studies are emphasized. The determination of absolute requirements for dietary constituents depends upon the measurement of intake. Differences in food efficiency can be demonstrated only by measuring intake and growth. Digestibility should also be measured since it can be expected to vary widely with different foods. The efficiency with which digested food is used for growth will vary not only with the maintenance requirement for energy but also with the balance of nutrients.

The Consumption and Utilization of Food by Insects

Organic acids and their salts appear to be potential alternatives to prophylactic in-feed antibiotics and growth promoters in order to improve the performance of weaned piglets, fattening pigs and reproductive sows, although their growth-promoting effects are generally less than that of antibiotics. Based on an analysis of published data, the growth-promoting effect of formates, fumarates and citrates did not differ in weaned piglets. In fattening pigs, formates were the most effective followed by fumarates, whereas propionates did not improve growth performance. These acids improved the feedgain ratio of both weaned piglets and fattening pigs. In weaned piglets, the growth-promoting effects of dietary organic acids appear to depend greatly on their influence on feed intake. In sows, organic acids may have anti-agalactia properties. Successful application of organic acids in the diets for pigs requires an understanding of their modes of action. It is generally considered that dietary organic acids or their salts lower gastric pH, resulting in increased activity of proteolytic enzymes and gastric retention time, and thus improved protein digestion. Reduced gastric pH and increased retention time have been difficult to demonstrate, whereas improved apparent ileal digestibilities of protein and amino acids have been observed with growing pigs, but not in weaned piglets. Organic acids may influence mucosal morphology, as well as stimulate pancreatic secretions, and they also serve as substrates in intermediary metabolism. These may further contribute to improved digestion, absorption and retention of many dietary nutrients. Organic acid supplementation reduces dietary buffering capacity, which is expected to slow down the proliferation and|or colonization of undesirable microbes, e.g. Escherichia coli, in the gastro-ileal region. However, reduced scouring has been observed in only a few studies. As performance responses to dietary organic acids in pigs often varies, more specific studies are necessary to elucidate an explanation.

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Organic acids for performance enhancement in pig diets.

Since their discovery, antibiotics have been instrumental in treating infectious diseases that were previously known to kill humans and animals. However, their widespread use as an additive in animal feeds has raised concerns about the development of antibiotic‐resistant microorganisms. Increasingly, more microorganisms are becoming resistant to multiple antibiotics. A high proportion of the antibiotics added to animal feed is excreted in urine or manure. In some cases, as much as 90% of the antibiotic administered orally may pass through the animal unchanged. Once excreted in urine and manure, these antibiotics can enter surface and/or groundwater through nonpoint source pollution from manure‐applied lands. The literature shows that most of the antibiotics are strongly adsorbed in soils and are not readily degraded. An important environmental concern is the presence of antibiotics in sources of potable water. Except erythromycin and some sulfa drugs, most of the antibiotics found in surface waters have been only in minute quantities. In all cases, the amounts observed are in parts per billion ranges; 100‐ to 1000‐fold below minimum inhibitory concentration. Tetracyclines and penicillins, two of the most commonly used antibiotics in animal agriculture, have seldom been found in sources of potable water. There has been some reported presence of resistant bacteria in surface waters. This may have been from transport of resistant bacteria via animal or insect vectors, in airborne dusts, or simply water flow from some antibiotic‐rich setting such as manure lagoons. Direct toxic effects of antibiotics on plants and soil microflora and ‐fauna are unlikely because of the low concentrations at which antibiotics in manure are land‐applied. The indirect effects of antibiotics on the food web, however, cannot be discounted at this stage. Decrease in some components of the soil microbial populations due to manure‐applied antibiotics could cause loss of food sources for other soil organisms, which, in turn, could affect important soil microbial processes such as decomposition and mineralization. Also, repeated application of antibiotic‐laden manure can provide an environment in which selection of antibiotic‐resistant bacteria can occur. Prudent use of antibiotics to a bare minimum along with alternative methods that minimize development and proliferation of resistant bacteria need investigation.

Antibiotic Use in Agriculture and Its Impact on the Terrestrial Environment

In human and animal cells, Se plays an essential role in antioxidation and exerts an antiaging function but it is toxic at high dietary intake. To increase its intake in forage and foodstuffs, Se fertilization is adopted in some countries where soils are low in bioavailable Se, even though higher plants are regarded not to require Se. To test its ability to counteract senescence-related oxidative stress in higher plants, a pot experiment was carried out with lettuce (Lactuca sativa) cultivated with increasing amounts of H2SeO4. The yields harvested 7 or 14 weeks after sowing revealed that a low Se dosage (0.1 mg kg−1 soil) stimulated the growth of senescing seedlings (dry weight yield by 14%) despite a decreased chlorophyll concentration. The growth-promoting function was related to diminished lipid peroxidation. In young and senescing plants, the antioxidative effect of Se was associated with the increased activity of glutathione peroxidase (GSH-Px). In the senescing plants, the added Se strengthened the antioxidative capacity also by preventing the reduction of tocopherol concentration and by enhancing superoxide dismutase (SOD) activity. When no Se was added, tocopherols and SOD activity diminished during plant senescence. The higher Se dosage (1.0 mg kg−1 soil) was toxic and reduced the yield of young plants. In the senescing plants, it diminished the dry weight yield but not the fresh weight yield.

J.K. Loosli

Papers

The Stimulatory Effect of Sodium Butyrate and Sodium Propionate on the Development of Rumen Mucosa in the Young Calf

Influence of Purified Materials on the Development of the Ruminant Stomach

Changes in the Tissue and Volume of the Stomachs of Calves Following the Removal of Dry Feed or Consumption of Inert Bulk

A New Indicator Method for the Determination of Digestibility and Consumption of Forages by Ruminants

Adaptation to high concentrate feeding as related to acidosis and digestive disturbances in dairy heifers.