Foraging Behavior

Summer 2007
by Diane Schivera

I attended two sessions presented by Frederick Provenza at the Pennsylvania Association for Sustainable Agriculture (PASA) conference this January. Both concerned ruminant eating and foraging behavior and biological reasons for this behavior.

In the introduction to his book, Provenza says, “Our work has shown how simple strategies that use knowledge of behavior can markedly improve the efficiency and profitability of agriculture, the quality of life for the manager and their animals, and the integrity of the environment.” When farmers study this fascinating topic and use Provenza’s methods, much of what he says becomes evident to them.

Palatability is a term that describes what and how much of a food an animal will eat. One side of the equation concerns postingestive effects. These are influenced by the chemistry of the food – i.e., nutrients and toxins in the food and the animal’s nutritional needs. The other side of the equation concerns flavor and includes odor, taste and texture. Feedback from postingestive effects will influence whether the animal likes or dislikes the flavor. If an animal eats a familiar meal with a novel food added, and if the food corrects a nutrient deficiency in the animal, the animal will like the flavor of the new food. Many people can relate to a reverse example: Consider how you feel when you get a stomach virus after eating a certain food. Even though you know that food is not what caused your illness, you still don’t like that food anymore. Likewise, if an animal feels sick for some reason after eating a particular food, the animal will associate that food with illness and won’t like the food anymore.

Variety in an animal’s diet is important for sustained consumption – partly because all food contains some toxin. Only a certain level of the toxin can be consumed before the animal will recognize that it will be harmed. Different plants contain different toxins that will detoxify each other if combined. Animals learn by postingestive feedback (positive and negative feedback from cells and organs) to eat these combinations in order to reduce the toxic effects and still meet their nutritional requirements. The other reason animals eat many different plants is to meet their nutritional needs or to correct a deficiency.

Sheep will graze clover rather than grass in the morning when they are hungry, because clover has a higher level of digestible protein than grass. After eating all clover, they satiate or acquire an aversion to the nutrients, soluble carbohydrates and proteins, toxic cyanide and/or the same flavor. In the afternoon they switch to grass, with its new flavor, lower nutrient levels and low cyanide (but higher concentrations of alkaloids). This variety also ensures that they will eat more over the course of the day.

Likewise, if an animal gets a high level protein ration in the barn, it will look for lower protein grasses in the pasture. The reverse will also occur. Excess protein causes a sharp decrease in palatability due to excess (and toxic) ammonia production in the rumen.

Animals will eat more new or toxic plants if they are fed a nutritionally adequate diet, because they are not trying so much to correct a deficiency. They will be encouraged to graze less-choice plants, which will help the biodiversity of pastures. Proteins will help balance plants that are high in tannins, and carbohydrates help animals digest such toxins as cyanogenic glycosides.

Choices help the animal meet its nutritional needs and reduce farmers’ costs and waste. Biochemical diversity provided through plant biodiversity will enable individuality, unlike a Total Mixed Ration (TMR). Research comparing TMR with free choice feeding of grains has shown that the latter will increase cows’ milk production by 11%; sheep will consume 25% more; and feed efficiency increased by 19% for beef cattle that were fed a choice of corn, alfalfa, barley and corn silage compared with a TMR; the choice diet reduced costs, too.

One way to encourage animals to feed on diverse plants is to seed pastures in blocks or strips. This allows animals easier access to patches of a specific plant, rather than having to sort through a larger area leaf-by-leaf, to meet their needs. Choice results in efficiency.

Learning to consume different feeds is easier when animals are young and more adventurous. Young animals will encourage their herd mates to eat more and to try new feeds or plants in the pasture. Additionally, research has shown that lambs fed wheat at a young age while with their mothers, compared with those fed wheat apart from their moms, for just one hour on each of five days will eat 10 times more wheat even three years later. A calf that is fed grain will eat it more readily as an adult. The same is true for pasture. Getting calves out to pasture with an adult, especially their moms, will produce cows that are good foragers.

This could be a way to control the bedstraw weed problem in Maine’s pastures. We could encourage animals to eat bedstraw by intensive grazing with their young in tow. Later in life these animals would be more likely to consume greater quantities of the difficult weed.

Whenever you sell an animal, it is helpful to send along some of the hay it is accustomed to eating; the familiarity will make its transition easier.

Many research projects have shown that animals take three years to adapt to a new environment and begin to thrive. Environments also take time to adjust to a management change. This is something for farmers who are transitioning to organic to remember.

Animals eat minerals and other nutrients to correct rather than prevent deficiencies. Animals eat for flavor, not color. In older trials, minerals were offered to animals in colors and were mixed with sodium, so the animals did not have a chance to respond to the mineral contents because their taste for sodium was saturated first. The mineral status and phase of development and production of the animal must also be taken into account. Some minerals are stored in the body, so a deficit response would not occur immediately.

With improved understanding of animal behavior, newer experiments are giving animals the opportunity to link the flavor of the mineral with the correction of a deficiency of that mineral. Sheep responded in recent studies by eating additional calcium and phosphorus when their diets were deficient in those minerals and when they were given the minerals separately. They even ate less phosphorus when the diet was calcium-deficient in order to achieve the correct balance.

Farmers who intensively rotate their pastures and have pastures with a varied population of plants can easily observe these behaviors in their animals. The animals are excited to move to new pastures. After they learn the routine, they become very easy to move. They love the variety, and eat and produce more.

For more information, see Foraging Behavior: Managing to Survive in a World of Change, by Frederick D. Provenza, $9.99 from This Web site has more information about animal behavior and feeding.

About the author: Diane is MOFGA’s organic livestock specialist. You can direct your questions to her at 568-4142 or [email protected].

Read Diane Schivera’s columns from previous issues:
Selenium: An Important Balance (Spring 2007; co-author Eric Sideman)
Record Keeping is Necessary for Livestock Producers (Winter 2006-2007)
Tips for Livestock Care (Autumn 2006)
Revitalizing Old Fields for Pasture and Hay (Summer 2006)

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