by Sanne Kure-Jensen
Dr. Darrell Emmick shared his experience with animal foraging behavior and explained how to train livestock to eat weeds. This talk was part of a workshop called ‘From We-Feeders to Weed-Eaters: Controlling Weeds through Animal Grazing’ hosted by Watson Farm in Jamestown, RI. Dr. Emmick also spoke at two similar workshops in Litchfield, CT and South Deerfield, MA. Joining him were experts from each state speaking on weeds and forage.
Animal Foraging Behavior
According to Dr. Emmick, animals learn what to eat through the interactions of two interrelated systems: affective and cognitive. The affective system operates without any conscious thought on the part of the animal, using feedback from osmotic, chemical, and mechanical receptors within the gut to evaluate the chemical and nutritional composition of foods eaten relative to the animal’s nutritional requirements. This is ‘Post ingestive feedback.’ If they feel good or energized after eating a certain food, they will eat it again. If they feel uncomfortable, bloated or sick afterwards, they are not likely to eat that food or plant again. The cognitive system uses information gained through the senses of sight, smell, touch, and taste, as well as social learning. Generally, babies eat what they see their moms eat. Animals also learn from other adventurous animals in their group.
Plant Nutrition vs. Toxins
A toxin is something that can make an animal sick. In small doses, toxins can act as a medicine. In large doses, toxins can kill. Dangerous or tolerated doses vary with animal age and health.
Healthy young plants grown in ideal conditions typically contain lower concentrations of toxins — alkaloids, terpenes, phenolics and glycosides — relative to nutrients such as protein, carbohydrates, lipids, nucleic acids. This often changes for the same plants growing in less than ideal conditions. Cool-season plants grown on hot dry southern slopes are most nutritious and least toxic during spring and fall.
Plant nutrients vary with time of day. Plants are typically less nutritious in the morning than at the end of the day.
Legumes always have more nutrition than grass, even in the morning. Most animals start their day with legumes. Animals switch over to grass or other forage when their ‘conditioned taste aversion’ kicks in. After a certain amount of a particular food, our bodies tell us it is time to add something new or for a different food altogether. This ‘conditioned taste aversion’ prevents animals from eating the same food all day, every day which helps balance nutrition and toxin intake.
Animals use protein and energy to process, eliminate or neutralize toxins in their digestive systems. When processing large levels of toxins, they produce less milk or put on less growth than with a diversified diet.
Almost all forage plants contain some level of toxin along with their beneficial nutrition. Plants develop lower nutritional quality and higher or dangerous levels of toxins when subject to herbivory (pest or livestock browsing) or stressed plants growing in harsh climates, extreme summer heat, poor soils or excessive shade.
Some toxins neutralize each other during digestion. The order plants or toxins are eaten matters to digestion, explained Dr. Emmick. Tall fescue contains alkaloids which upset rumen function and intake. Birdsfoot trefoil is high in tannins. If an animal eats tall fescue first, its intake will drop if later provided birdsfoot trefoil. If an animal eats birdsfoot trefoil first, intake will remain high when provided with tall fescue. The tannins in trefoil bind with the alkaloids and reduce their influence. There are many plant-herbivore interactions: nutrient-nutrient, nutrient-toxin and toxin-toxin interactions, which are just now being discovered.
Nutritional Needs of Cattle
Dairy animals need 16 percent crude protein. High quality pastures can offer 30 percent crude protein. Dr Emmick worked with Dr. Provenza in the Department of Wildland Resources at Utah State University studying animal grazing behavior and diet selection. In one study, they learned that dairy cows could self-select the foods with protein levels they need. If you feed them 11 percent crude protein in the barn, they will select high protein foods (clover) on pasture. If you feed then 21 percent crude protein inside, they will select low protein foods (grass) afterwards. Don Minto of Watson Farm confirmed that his cows know what they need. Minto described using a varied mineral free choice system allowing the animals to self-select their minerals rather than offering one single blend.
While Dr. Emmick appreciated the need to analyze forage quality, the results will vary considerably by season, temperature, moisture levels, time of day and life stage of plant. He said, “The cows will figure out what they need.” Computer models recommending feed blends are humans’ attempt to understand the animals’ dietary requirements. While these models offer a reasonable place to start, they are not as accurate as we would hope.
Training Livestock to Eat New Plants
Farmers can train their animals to eat new plants and weeds. Dr. Emmick recommends selecting one or more adventurous healthy animals. Harvest young, strong, healthy weeds. Mix a few into a bucket with favorite grains or in the barn with haylage. Dr. Emmick remembered being trained to eat mutton with mint jelly as a child. He recommended drizzling a little molasses over the top of unfamiliar weeds to make them appealing. Each day add a larger portion of the ‘weed’ to the mix. After a week to ten days, bring animas to a pasture with those same weeds. You can lightly spray the weeds with molasses for the first few days. The animals should be ‘trained’ to eat them.
Dr. Darrell Emmick is the former State Grazing Land Management Specialist with the USDA-Natural Resources Conservation Service in New York State. He can be reached via email at firstname.lastname@example.org or call 607-844-3211.
by Sanne Kure-Jensen