toxins in plants
- i found some evidences in deer nutrition that the toxin issue in plants is missunderstood .
toxines in plants are there to regulate food intake and are as detrimental at higher concentration than they are at too low concentration .they are especially there to help to regulate intake of nutrients in proportion of one's metabolic needs of the moment ( tolerance to toxines change in accordance of body's needs for nutrients associated with them )
they realised in farming deer that some toxines were needed to be added to their artificial feeding.
we can expect that the effort in plant breeding to remove toxins ( volontarelly or not ) might have a detrimental effect on human nutrition also .( "the need" for supplements might have a source here)
extracted from http://www.deer.rr.ualberta.ca/library/lessonwild/quebec.htm
The other important difference between most domestic forages and natural browse is plant chemistry, particularly the content of tannins and other secondary compounds that are often quite high in natural diets (Ayres et al., 1997). ....
They can be toxic to ruminants. Condensed tannins possess carbon-carbon bonds that are not susceptible to cleavage upon hydrolysis. They bind strongly with protein and carbohydrates (Barry & McNabb, 1999).
In both domestic and wild ruminants, tannins at moderate to high levels decrease digestibility and voluntary intake (Van Hoven, 1984; Robbins et al., 1987a,b), liveweight gain (Barry & McNabb, 1999), and mineral absorption, and may damage the intestine or liver. ...
( now some attention to beneficial propreties of one toxine in plants .jc)
Although most attention has been directed to understanding tolerance of animals to tannins, recent work points to a number of beneficial effects at moderate concentrations (e.g. <5% dry matter) (Barry & McNabb, 1999; Hoskin et al., 1999).
Tannins may act as a natural detergent to reduce bloat (Tanner et al., 1995; McMahon et al. 2000). Their antioxidant properties may protect proteins, carbohydrates, and lipids from oxidative damage during digestion (Hagerman et al., 1998). Tannins reduce dependence on synthetic anthelmintics in sheep (Niezen et al., 2002) and farmed deer (Hoskin et al., 2000). Tannins are less effective for nematodes such as Trichinella spiralis that bury into the digestive mucosa (Butter et al., 2001). Tannin-protein complexes in the rumen may reduce the fermentation of forage protein to ammonia, increasing the quantity of protein digested in the small intestine, thereby augmenting biological value (Waghorn et al., 1987, 1994; McNabb et al., 1996).
Condensed tannins react with plant protein to form tannin-protein complexes which are insoluble and stable at pH 3.5-7.0, but dissociate and release protein at pH < 3.5, that of the abomasum (Aerts et al., 1999; Barry & McNabb, 1999).
Herbivores are able to closely regulate intake of tannins or protective substances such as polyethylene glycol (Provenza et al., 2000). Roe deer actively select diets which are high in tannins and regulate the concentration of hydrolysable tannins quite precisely at about 2.8% at least on certain diet combinations (Tixier et al., 1997; Verheyden-Tixier & Duncan, 2000). Purified bark tannins up to levels of 10% dry matter increase voluntary intake of white-tailed deer and mule deer (Figure 3) and may improve performance of mule deer (Figure 4).
Figure 3. Voluntary intake by mixed groups of white-tailed and mule deer of pelleted feeds containing 5% or 10% bark tannins compared with control pellets (Hudson, unpublished).
Figure 4. Body weights of mule deer and white-tailed deer maintained on pelleted containing 0% and 5-10% bark tannin (Hudson, unpublished).
Deer might be expected to respond positively to even higher levels of tannins than do conventional farm livestock. This appears to be the case with red deer (Min et al., 1997; Adu et al., 1998). Hoskin et al. (1999) reported lower autumn live weight gain and carcass weight achieved from weaner deer grazing chicory (Cichorium intybus) (total CT concentation: 0.26% DM) or pasture (0.26% DM) compared with deer grazing sulla (Hedysarum coronarium) (5.10% DM). Odocoileine deer that are more specifically adapted to browse diets may have still higher optimum levels.
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