If you’ve ever seen your animals eating soil, bones, feces or other unusual items, you probably took this as an indication that they may have a mineral imbalance. Yet many animal nutritionists will tell you, based on past studies, that ruminants are incapable of eating minerals in correct amounts to prevent or correct mineral deficiencies. But now we have new information. As our understanding of how animals choose what to eat has grown, we’ve been able to improve our experiments, adjusting them to take into account how animals learn about the foods they are eating.
One important change we made is allowing animals the opportunity to pair the flavor of a mineral with their recovery from a deficit of that mineral. The results of working with how animals learn shows us that yes, animals can detect their own mineral deficiencies and they will choose what to eat to get rid of the deficiency.
We have several studies by Utah State University’s Juan Villalba to thank for this new information. Juan looked at calcium and phosphorus deficiencies in lambs. In the first study, lambs avoided phosphorus (P) when it was fed in excess, and increased their preference for it when they were deficient in it. In another study, sheep on phosphorus-deficient diet increased intake of a Phosphorus supplement when they had a choice between a phosphorus or a calcium (Ca) supplement. He also found that sheep eating a calcium-deficient diet ate more of a calcium supplement than sheep fed a diet high in calcium.
But Juan had more than just the results of the trial showing him this answer. As he worked with the lambs, Juan saw them doing something we’d never seen. They licked and chewed the dirt not only in their own pens, but also in their neighbors’ pens. They ate their neighbors’ soil and feces, and licked their urine. What he realized was lambs in the study were randomly assigned to pens, so lambs on high phosphorus and low calcium diets were often penned next to lambs on low phosphorus and high calcium diets.
Juan took blood tests and found that the lambs’ blood mineral levels were normal, even though they were being fed deficient diets. He realized that the lambs had taken it on themselves to alleviate their mineral deficiency by licking urine and eating feces from their neighbors. When animals were separated by the kind of diet they were being fed, blood mineral levels dropped. Evidently, lambs were able to solve their mineral deficit as long as they had a source of minerals even if their solution was pretty disgusting.
Mineral nutrition is extremely complex. The amount of a particular mineral an animal will eat depends not only on the level of that mineral in the body but also on its interactions with other minerals. The body’s feedback mechanisms likely enable animals to make correct choices and maintain their mineral status. The study above indicates animals can correct for calcium and phorsphorus deficiencies.
If you’d like more information on this topic read the fact sheet: Mineral Nutrition: Are Animals Nutritionally Wise?
And check out this week’s Classic by NatGLC. We’ve got more on how animals choose what to eat, along with some videos of them doing some things you might not expect!
Villalba, J. J., F. D. Provenza, J. O. Hall, and C. Peterson. 2006. Phosphorous appetite in sheep: Dissociating taste from post ingestive effects. J. Anim. Sci. 84:2213–2223.
Villalba, J.J., F.D. Provenza, and J.O. Hall. 2008. Learned appetites for calcium, phosphorus, and sodium in sheep. J Anim Sci. 86:738-747.