Cows Eating Dirt

“Hey Doc, waddya got for cows eatin dirt?”

Originally printed in the Oct 2007 issue of the
Progressive Dairyman.  Used here by permission.


“Hey, Doc, my cows are eating dirt. Waddya got for that?

A few years ago, I posed this question at several dairy seminars in the Midwest: “Do your animals chew on wood or eat dirt if they have the chance?”  A few said their cows would chew on wood.  Almost all indicated their cows would eat dirt if available.  One fellow said that he had to haul in dirt around the foundations of his buildings to replace the soil his cows had eaten over a period of years.  Strangely enough, a few even told of their cows licking or drinking from urine puddles if they could get to them.  As bad as that sounds, it is even more alarming when conventional opinion regards this eating behavior as being almost normal because it is so common.  It’s the “everybody’s doing it, so it must be OK” syndrome. And it may be “normal” in the sense that it is appropriate, compensatory behavior for animals forced to subsist on a mineral deficient ration. Eating dirt and other abnormal appetites are attempts to secure some vital element or attain some nutritive balance that is not otherwise present in their diet. It should be considered a warning signal that something is amiss in the ration.

To examine the problem from a holistic viewpoint, let’s go back in time and look at the effect of domestication on today’s dairy cattle.  Most authorities agree that primitive cattle or Aurochs (Bos taurus primigenius) were first domesticated about 8000 years ago. Before domestication, cattle lived a lifestyle similar to that of bison in the American west. They were free to roam over wide, naturally fertile areas. Specific imbalances of soil in one area would be offset by excesses or adequacy of the same element in other areas. A multitude of different plants were available. Many plants had the ability to absorb and concentrate different minerals and trace mineral giving the grazers even greater nutrient options. Thus, over a period of time they could seek out and obtain balanced mineral and nutritional needs.   Predators strengthened the genetic pool by culling the weak and unfit.

It’s a lot different today.  Dairy cattle have been genetically modified to produce at levels never intend by nature, increasing their need for minerals.

Ever more restrictive confinement limits their ability to seek out and consume adequate diets. In a natural grazing situation herbivores probably had hundreds of different plants from which to choose.  Today they are limited to 6 or less: grass, alfalfa, corn, soybeans, cottonseed and maybe some oats or barley. Seeds and grains in the amount currently fed are detrimental to dairy cow health. Cow are ruminants and need a high-forage diet!

Crop quality has declined. Every crop harvested or animal removed from a farm or ranch takes with it a finite amount of life supporting nutrients. Major elements can be replaced but it is difficult to restore a natural balance that includes high organic matter, adequate trace minerals, and vibrant biological life. Intensive NPK fertilization results in higher yields at the expense of nutritive values and mineral content in the crops.


A total mixed ration (TMR) is the industry standard feeding strategy that purports to provide, in one total mix, all the nutrition required by the ‘average’ cow in the group. This concept fails to consider the individuality of each animal’s nutrient requirements. No two animals have the same needs.  Variables such as breed, age, pregnancy, stage of lactation, weather, season of the year and others have a marked influence on the need for mineral supplementation. With a TMR probably no one animal will get exactly what it needs. A few may get pretty close but many will be lacking in some nutrients while others will have excesses. This limits their production, eventually depresses their immune response and ultimately may result in various herd health problems. Eating dirt, if available, is their way of responding to these imbalances.

Unfortunately, mainstream nutritionists tend to downplay the ability of animals to balance their nutritional needs.  Anyone who doubts that cattle can make valid nutritional choices needs to watch cows graze in a mixed pasture. They do not just mow grass like a lawn mower, but pick and choose each mouthful. They avoid eating the bright green grass surrounding ‘cow pies’ in the pasture but will search the fence-rows for weeds that concentrate various essential trace minerals. Given the chance, they will balance their nutritional needs during each feeding period.

 The following incident illustrates another aspect of this ability. Weather had made it a bad year for crop quality.  In late winter, a good client called me about two problems. His cattle were eating excessive amounts of mineral and his heifers would abort a live calf about 10 days before they were due to calve.  The calf would live, but the heifer would usually die. Focusing first on his mineral problem, he decided to try a “cafeteria” mineral program in which each mineral was fed separately. He had to carry each bag of mineral through his cow-lot to get to the mineral feeder.  His first few trips were uneventful. Then suddenly several of the normally docile cows surrounded him, tore a bag of mineral from his arms. chewed open the bag and greedily consumed the contents … a zinc supplement.    

Within a week after the mineral change, consumption returned to normal and his remaining heifers calved normally.  Apparently, the previous year’s stressful growing season had resulted in crops that were deficient in zinc or perhaps high in zinc antagonists.  His mineral mix was high in Calcium with only small amounts of zinc.  Their quest for zinc impelled them to over-eat the mixed mineral. Excess calcium interferes with zinc absorption. Every mouthful they took increased the imbalance and escalated their need for zinc.   Inevitably, metabolic problems began in the most vulnerable group - young, growing heifers in the last stages of pregnancy.  Finally they just gave up and checked out ... all for want of a few grams of zinc.  .

If your cows are eating dirt or if you just want to experiment; give your cows a chance to participate in their own diet formulation. Do not change your current ration, but do provide separate free-choice sources of these 6 items: salt, bentonite, bicarb, a basic mixed mineral with a  2 to 1 Ca/P ratio, one with a 1 to 2 Ca/P ratio and kelp.  Cows with rumen acidosis will prefer bicarb or bentonite. The separate sources of Ca and P allow them to adjust that critical ratio. If they lack trace minerals they may also eat a lot of kelp. If kelp consumption remains high you may want to provide separate sources of some of the trace minerals. There are commercial companies that provide a broad range of separate free-choice minerals and trace minerals.

We should use our nutritional knowledge to formulate dairy rations, but also rely on the nutritional wisdom of animals to fine-tune their individual needs. It doesn’t hurt to have two opinions ... one from your nutritionist’s computer and one from the real experts, your cows.  I will leave it to you to decide which one is the most reliable.