There are number of reasons why animals won't eat certain plants. Novelty is a big reason. If mom didn't eat the plant chances are her offspring won't either, especially if there are plenty of alternative foods to eat. This section overview why animals don't eat many plants.
Principle: Animals avoid plants because they are unfamiliar, low in nutrients, contain toxins or a combination of these reasons. If plants do not cause death, birth defects, or obvious signs of poisoning, animals can be trained to eat most plants. Caution: Managers should never force animals to eat plants if they don't know why the animal is avoiding them.
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Reasons Animals Avoid Certain Plants:
Foods High in Toxins - Most of the time animals avoid plants that are high in toxins and they do a good job of regulating their intake of toxins, but sometimes they make mistakes. Read Why livestock die from eating poisonous plants.
Poor Quality Foods - Simply exposing young animals with their mothers to poor quality feeds increases intake later in life. For example, cows exposed to ammoniated straw with their mothers for 60 days during their first 3 months of life maintained a higher body condition, produced more milk, lost less weight, and bred back sooner than cows with no exposure to straw as calves. The differences occurred even though the experienced cows had not seen straw for five years and they persisted for at least three years after both groups of cows were fed ammoniated straw in winter.
High levels of fiber and low levels of protein are the main reasons ruminants limit their intake of poor-quality roughages. Distention of the rumen and losses of nitrogen limits the amount of poor-quality forages animals can eat. Experiences early in life improves digestion of poor-quality roughage. Young lambs raised on mature weeping lovegrass (a poor-quality roughage) ate more sorghum hay (another poor-quality roughage), digested sorghum hay and recycled urea (nitrogen) more efficiently than lambs reared on fresh oats (high-quality roughage). The differences between these two groups of lambs lasted for at least nine months. Thus, experiences early in life result in lasting physiological changes that enable animal to perform better in harsh environments.
- Diet mixing: Increasing Intake of Unpalatable Plants
- Livestock as a Tool FOR Biodiversity in the Sagebrush Steppe
Photos of cows eating weeds on this page by Kathy Voth. Weeds are from top to bottom: Canada thistle, Spotted knapweed, Leafy spurge and Distaff thistle