Nutritional Selection

[Phage]

Ok, as a result of evolution animals tend to get the nutrients they need in their diets. However, what happens if they are low on a certain vitamin or mineral? How do they react?

Through discussion, we have come up with a few different possible results:

1. The animal has no idea what is wrong, and wanders around in the regular pattern until it dies. (I reject this, as evolution would tend to find some way of fixing this, even if it was to eat random stuff in the hope something would work)

2. The animal experiences some sort of compulsion to eat certain foods based on what is lacked. (e.g. the body lacks iron, the animal wants to eat foods that are high in iron)

3. A more extreme version of #2, where the animal actually craves a certain nutrient even to the point of recognizing it in the natural form. (e.g. when low on iron, the animal will actually gnaw on iron ore, rusting metal, etc…)

Which if any of these is accurate? Can the body sense and interpret the lack of a certain nutrient similarly to the sense of hunger and thirst? There are two opinions in the discussion now:

1. The body cannot recognize the lack of a certain nutrient, either cognitively or in the form of a preference for certain things.

2. The body can recognize the lack of a certain nutrient, not cognitively but will cause a preference for either certain foods or a certain taste indicative of a contained nutrient.

Is there any evidence of animals eating nutrients, specifically iron as an example, in their base forms? Please differentiate between things such as salt licks, as animals will partake even if they have healthy levels of salt already.

I leave it to the excellent minds present to settle this matter.

[Duckster]

Animals have a more well defined appetite for sodium chloride than any other compound in nature except water. Ruminants have such a strong appetite for sodium that the exact location of salt source is permanently imprinted into their memory which they can then return to when they become deficient. Bell showed that when steers were trained to receive their sodium in response to pressing a panel, maximum effort to receive the sodium occurred at eight days and after, on a sodium deficient diet. Cattle also have a keen sense of smell for sodium. Sodium deficient steers were offered a cafeteria of 12 buckets of water with only one containing moderate levels of sodium salts. Steers would quickly choose the water containing sodium salts without having to taste the water sources.

Source: http://www.saltinstitute.org/25.html

Animal lick sites are considered an essential component of the landscape. Although lick sites are probably discovered initially by chance, ungulates, such as sheep (Ovis sp.), goats (Oreamnos sp.), moose (Alces sp.) and deer (Odocoileus sp.), may subsequently visit mineral or “salt” licks and mineral springs to ingest the earth and muck, drink the water, or lick the rock to obtain mineral elements, presumably not in sufficient supply in their food. Jones and Hanson (1985) noted that animals in temperate regions invariably seek out salt licks during late spring and early summer. Lick sites are usually surrounded by an extensive network of trails.

Source: http://www.nrc.ca/aic-journals/cjss_96/nov/S96-044.pdf (Research report)

My post may not directly answer your questions, however, I hope it spurs some experts in this area to offer the information you seek.

[Blake]

OK, I can tell you that animals can sense when they are nutrient deficient and take steps to eat foods to remedy the deficiency. That much is easy.

Most animals will utilise natural or synthetic salt licks. While you’re right tha this is used when salt levels are already acceptable or even excessive, the desire becomes far stronger when salt levels fall ( as Duckster has already pointed out.

In parts of Africa elephants have hollowed out large sections of a cliff face and either create dor deepened a cave through there efforts at salt mining.

Cattle suffering from phosphorous deficiency become scavengers and chew on the bones of dead cattle to obtain the mineral. This is a major cause of botulism in cattle. The behaviour is almost never seen in cattle not suffering the deficiency.

Grazers will preferentially seek out those areas of grass with the highest mineral levels even in a huge area of seemingly identical grass.

The other part of your question is going to be impossible to answer. How can we tell what is going through an animal’s mind? If a steer chews on a dead relative we know that it’s trying to cure a phosphorous deficiency. What we can’t tell is whether this is simply a compulsion to eat bones triggered by the lack of the mineral, or if the animal recognises that the bones contain the mineral in question.

Consider it like this. Your body craves fat and salt. It’s a hangover from our days as savannah apes on the verge of starvation. Salt was always rare and fat is a very concentrated energy supply… Hormonal changes, particularly shortening day length and decreasing temperatures, increases appetite, and appears to increase our appetite for fats particularly. But we don’t necessarily know that we are seeking out fat, we have a greater desire for rich soups and pizzas on rainy winter evenings. If the foods tasted the same and contained no fat (a dream I know) we’d still crave them.

In comparison someone addicted to nicotine knows that it is nicotine they crave and they seek it out. If cigarettes aren’t available most will chew tobacco or apply a patch to get their fix. Conversely if a tobacco substitute with no nicotine were available the person would not bother with it. The person isn’t just going through a craving triggered behaviour, they are going through any behaviour to get a specific substance.

Which of these is applicable to animals is hard to know. It appears it may be both depending on the substance. Cattle will take salt from any source (natural licks, drum licks, blocks, salt water etc), but in order to get them to take phosphorus supplement it normally needs to be added to feed or salt. It seems that they have an craving for specific foods (bones)r triggered by phosphorus deficiency but they are completely unable to recognise high phosphorous levels in supplements.

BTW, asking for examples of “evidence of animals eating nutrients, specifically iron as an example, in their base forms” is a poor choice Mammals, and I assume all other vertebrates, can’t absorb iron ingested in its base form. The oxidation states are all wrong for absorption. A camel could eat 50 pounds of rusty nails and still remain horribly anaemic.