In the world of livestock and perhaps especially goats, numerous mineral programs exist. Most folks offer a pre-mixed mineral and supplement lack as needed in the form of additives like kelp or through injections, boluses, gels etc. Some goat owners offer individual minerals free choice. The individual, free-choice programs are based on the idea that goats are nutritionally wise and can select what they need and when they need it. But is that true? How DO ruminants learn what to eat? Here’s what we’ve learned so far.
Taste is the most important factor in deciding, followed by texture and odor. Both formal studies and simple observations have shown that ruminants learn what to eat through social learning (observing and copying dams and herdmates) as well as from biological feedback after consuming those foods. That means that the animal learns primarily through trial and error. If it eats this particular shrub and experiences negative consequences (rumen upset for example) the animal will then, in theory, associate the taste of that shrub with the rumen upset and not eat it again, or at least not eat large amounts of it.
In my research, Dr. Fred Provenza and Dr. Richard Holliday are among the most avid champions of free-choice, individual mineral feeding and nutritional wisdom. Even their observations and studies on the topic illustrated that the animals did not seek out certain minerals until they were deficient, sometimes severely deficient, or imbalanced. This suggests that animals eat to correct, not prevent deficiencies. In a goat-specific study, Provenza concluded “that the relative amounts of different foods ingested within a meal, and the salience of the flavors of those foods, are both important variables that cause goats to distinguish between novel foods that differ in postingestive consequences” (8). In this study, goats were ate a shrub called blackbrush, both old season growth and current season growth. The current season growth has much lower levels of condensed tannins than old season growth. The animals did not differentiate between the two until they ate more current season growth than old in a meal, enough to acquire an aversion. Yet, taste and odor were still important factors to that acquired aversion. Read the full summary of the study here https://pubmed.ncbi.nlm.nih.gov/24242115/.
Animals do not “instinctively” recognize nutrients, but sodium is dissolved and absorbed so quickly it does appear instinctual. In early studies on nutritional wisdom, sodium was mixed in every mineral that was offered cafeteria-style. Proponents of nutritional wisdom and cafeteria-style mineral programs note this as a flaw and argue that it made it impossible for the animal to “associate feedback from the mineral with its flavor.” – “On Pasture: Can Animals Figure Out What Minerals They Need”.
To date, there are no studies proving ruminants can recognize minerals other than calcium, sodium, and phosphorus. Phosphorus deficiency often results in pica, or a depraved appetite that results in eating odd things like wood, bones, rocks, and even feces. There’s several interesting studies on mineral deficient animals in the sources, including a study in which phosphorus-deficient steers were eating rabbits and one in which calcium-deficient sheep would lick up the urine and feces of the animals in the adjacent pen that were in the non-deficient control group.
In an interesting case I found online, a goat owner fed her animals a popular mineral mix that was very low in zinc and very high in copper (a zinc antagonist) for several years. Animals began dying and were necropsied. Copper toxicity was ruled as the cause of death. What was interesting was that her goats were attempting to eat raw meat that was being fed to her livestock guardian dogs. It was hypothesized the animals were doing so because they were starved for zinc and raw beef is an excellent source of that mineral. To date, I have found no formal study on animals being able to select to correct for zinc deficiency, but that fascinating anecdotal evidence certainly points that direction and is worthy of further study.
Many goat owners believe that perhaps too often in the case of goats, palpability and curiosity trump need – I’ve personally experienced goats developing a taste for toxic plants, including hemlock – goats that were healthy and well-fed with an abundance of other forage and hay available but simply liked the taste of the dangerous plant. The aforementioned research suggests that might be the case sometimes, perhaps especially in the case of concentrates or tasty treats. Dr. Holliday notes – “I realize mainstream nutritionists tend to downplay or totally reject the idea that animals can self-regulate their nutritional needs. I admit that this ability may not apply to all situations and to every type of feed. Some feed items (grains and concentrates) may be so tasty that most animals would overeat if fed free choice.”
Nutritional wisdom is a fascinating, complex subject worth studying more, but at the moment the evidence points out that the nutritional wisdom of ruminants is limited.
By Kenda Shatswell
- Provenza FD, Lynch JJ, Burritt EA, Scott CB. How goats learn to distinguish between novel foods that differ in postingestive consequences. J Chem Ecol. 1994 Mar;20(3):609-24.