Miscellaneous antinutritional substances
Alkaloids: Alkaloids represent a large and structurally diverse group of compounds present within angiosperm plants; the majority of alkaloids usually containing nitrogen in the form of a heterocyclic ring. Important classes of indole alkaloids include: the ergot alkaloids (ergotamine, ergocristine, etc.), the fescue alkaloids (ergovaline, ergosine, ergonine, lysergic acid amide), 3-methylindole (produced by rumen fermentation of tryptophan), and the beta-carbolines. Some of the more well known alkaloids include coniine (hemlock), nicotine (tobacco), atropine (deadly nightshade), cocaine (leaves of coca plant), quinine (cinchona bark), strychnine (seeds of Nux vomica), morphine (dried latex of opium poppy) and solanine (unripe potatoes and potato sprouts). Alkaloids are subclassified on the basis of the chemical type of their nitrogen containing ring. Alkaloids are formed as metabolic by-products. However, their characteristic bitter taste and accompanying toxicity generally help to repel insects and herbivores. Alkaloid containing plants should always be suspected of possibly being pharmacologically active and should be considered as a risk factor.
Alkaloid containing plants exact a heavy economic toll on livestock production. Such losses can be reduced or eliminated by recognizing plants containing alkaloids, understanding when livestock graze specific toxic plants, and knowing signs of potential toxicity. Grazing schemes can then be developed based on knowledge of the temporal and spatial dynamics of alkaloid concentration and consumption by livestock. Losses can be reduced by ensuring that livestock are not exposed or have limited exposure during periods of greatest risks.
Phytates: Phytic acid or the hexaphosphate of myo-inositol occurs naturally throughout the plant kingdom, and is present in considerable quantities within many of the major legumes and oilseeds, including soybean, rapeseed and cottonseed. Upto about 85% of the total phosphorus found in feedstuffs of vegetable origin, particularly the cereals, cereal by-products and oilcakes is present in form of phytic acid. Under most dietary conditions the phytate phosphorus is poorly utilized by monogastrics including poultry and, consequently, excreted via the feaces. Besides being an indigestible constituent the phytate phosphorus tends to act as an antinutritional factor in diet in that it possesses strong chelating properties thereby markedly reducing the bioavailability of several minerals. In many of the developed countries and a rapid advancement in fermentation technology, interest in application of phytase enzyme in improving phosphorus utilization by poultry has further been renewed.
Techniques have been developed for the removal of phytic acid from rapeseed,particularly during the preparation of protein isolates and concentrates. Approaches include the use of differential solubility between protein and phytic acid, membrane separation, enzyme treatment and ion exchange resin. But while phytic acid may be reduced during the preparation of protein isolates and concentrates, a better approach to the utilization of rapeseed may be the reduction of phytic acid in the seed before processing and consumption. Very little work has been done on the effect of the common processing methods such as cooking, autoclaving, microwave etc. on phytic acid in rapeseed probably due to the fact that rapeseed is not normally eaten as the whole seed. However, studies on legumes, cereals and other oilseeds showed that phytic acid is generally stable under ordinary processing conditions.
Theoretically, when phytic acid is hydrolysed by microbial phytase, all minerals bound to it should be released. Relatively, very little work has been done in India on the effect of phytase supplementation on the availability of minerals. Reports on this aspect suggested that contents of ash and minerals in tibia such as Ca, P, Mg, Zn and Fe were significantly higher in phytase supplemented layer diets. The economic production of phytase, through conveying phytase gene in the original wild Aspergillus strain on to the production strain resulting in a considerable increase in production efficiency, can be achieved.
Mycotoxins: Mycotoxins are poisonous chemical compounds produced by certain fungi that can occur in food have great significance in the health of humans and livestock. Since fungi produce them, mycotoxins are associated with diseased or mouldy crops; therefore, disease control is essential to eliminating this threat to food safety. The presence of mycotoxins in crops is not only a direct food safety problem but it threatens the competitiveness of agriculture in the world market and causes significant economic losses for many countries. The toxins can accumulate in maturing corn, cereals, soybeans, sorghum, peanuts, and other feed crops in the field and in grain during transportation. Although the adverse effects of feeding moldy feeds were long known by producers of red meat animals and poultry, a specific mycotoxin was not implicated. An outbreak of “Turkey X disease” in Great Britain in 1960 was traced to contaminated peanut meal from Brazil. Aflatoxin was indicated as the cause of death for more than 100,000 young turkeys and some 20,000 ducklings, pheasants, and partridge poults. This problem stimulated modern research on mycotoxins and the ecology of mycotoxin producing fungi. All species of animals appear to be susceptible, although susceptibility varies greatly from species to species and is due to different ways of metabolizing the mycotoxins.The most common food-borne mycotoxins include: deoxynivalenol/nivalenol; zearalenone; ochratoxin; fumonisins; and aflatoxins. Deoxynivalenol and nivalenol are produced by Fusaria species and are toxic to humans and animals. The main commodities affected are cereals. Deoxynivalenol (DON) is a frequent contaminant of grains such as wheat, buckwheat, barley, oats, triticale, rye, maize, sorghum and rice. Zearalenone (ZEN) is also produced by these species on maize and wheat and has been identified by the International Agency for Research on Cancer (IARC) as a possible human carcinogen. Another fusarium produced toxin, fumonisin B1 is found on maize and is suspected as being a human carcinogen. Fumonisin B1 is also toxic to pigs and poultry and causes equine eucoencephalomalacia, a fatal disease of horses.Genetically modified (GM) Bt corn, through the pest protection that it confers, has lower levels of mycotoxins: toxic and carcinogenic chemicals produced as secondary metabolites of fungi that colonize crops. In some cases, the reduction of mycotoxins afforded by Bt corn is significant enough to have an economic impact, both in terms of domestic markets and international trade. In less developed countries where certain mycotoxins are significant contaminants of food, Bt corn adoption, by virtue of its mycotoxin reduction, may even improve human and animal health.