4 Matching Annotations
  1. Apr 2021
    1. Animals possess several mechanisms to negate or restrict the toxic or negative effects of plant compounds once i ngested. If a t oxin is eaten, it is in the animal's best interest to quickly get r id of it. Sheep, goats, a nd cattle can and will vomit in response to eating toxins, but it is rarely observed. Horses probably do not vomit except when near death, but commonly experience diarrhea. Diarrhea aids in rapid elimina- tion of toxins from the gut which can reduce absorption. In some episodes of diarrhea, there is a decrease in intestinal motility, further reducing t he absorption of toxins.
    2. With continued consumption of a plant containing a specific phytotoxin, the animal may gain an ability to overcome its negative effects because enzyme systems in animal tissue can increase their detoxification capacity and efficiency. Rumen microbes may also facilitate the ability of animals to adapt to diets high in phytotoxins. Microbial populations can change rapidly depending on th e substrates available fo r degradation. These "inducible defenses" could explain why herbivores often appear less sensitive to toxic or low quality plants with continued exposure. Nonetheless, adaptation does not develop to all toxins. The effects of many toxins are cumulative and animals may get progressively more poisoned as they continue to ingest plant material containing these toxins
    3. Once plant toxins are absorbed fr om the gut into the blood, they are often trans- ported to the liver. T he liver primarily, and secondarily the kidney, intestinal mucosa, lungs, a nd skin contain enzyme systems that metabolize or alter toxic compounds, rendering them inert. Ability to metabolize or reduce sensitivity to specific phytotoxins varies by herbivore species a nd individuals. For example, sheep can tolerate and detoxify more pyrrolizidine alkaloids than cattle, therefore it takes five times more tall larkspur (Delphinium occidentalis) to poison sheep compared to cattle
    4. Chemical reactions during ingestion may provide protection against the effects of some plant toxins. The ruminant's large forestomach is generally well adapted to bind, sequester, degrade, or detoxify plant toxins. The neutral p H of the rumen environment may modify a plant toxin or the toxin may be quickly diluted in the large volume of the rumen (e.g., ar ound 60 gallons for cattle). Of great significance for ingesting toxic plants is the massive number of rumen microbes that transform most phytotoxins into inert or less-detrimental compounds. For example, leucaena (Leucaena leucocephala) is a tropical forage legume that contains mimosine, a toxic amino acid. Mimosine i s detoxified by a group of rumen microbes and animals susceptible to mimosine toxicity can be cured by receiving a dose of the "mimosine- metabolizing" microbes. Rumen microbes usually reduce the toxic effects of plant compounds. However, in some cases, such as nitrates or cyanogenic glycosides, the rumen microbes convert a harmless compound into a deadly toxin.