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Did ancient horses hibernate?

stock-eyeResearch into the diet of mankind’s Stone Age ancestors reveals that horses were well adapted to cold winters. It even suggests that horses may at one time have been hibernators.

Studies into the diet of stone age man have examined the essential fatty acid content of frozen animals such as mammoths, bison and horses, that might have formed part of the diet of our ancestors many years ago.

Humans, and presumably their ancestors, have certain nutritional requirements that have to be met from food. One requirement is for essential fatty acids such as linoleic acid and alpha-linolenic acid.

Researchers have been looking at the fatty acid profile of adipose tissue of animals found in the permafrost of Siberia. Lead researcher was José L Guil-Guerrero of the Chemistry of Biomolecules and Food Processing Research group at the University of Almeria Spain.

The latest issue of Equine Science Update reports that six specimens were included in the study: two mammoths (one a baby calf, the other a young female, that died about 40,000 years ago); two bison from about 9000 years ago; and two adult horses that died about 4500 years ago.

The researchers used gas-liquid chromatography-mass spectrometry (GLC-MS) and GLC-flame ionization detector (GLC-FID) to determine the current fatty acid content of the specimens.

Then, using information on how fats change when frozen for long periods, they were able to deduce the likely fatty acid profile of the animals at the time of death.

Several factors influence the fatty acid profile of such animals. First is the composition of the vegetation on which the animals had been feeding.

A detailed analysis of the stomach contents of the mammoth calf revealed plants known to be good sources of polyunsaturated fatty acids such as alpha-linolenic acid.

The animal’s digestive physiology is also important. Single stomach animals, such as mammoths and horses, are better able to assimilate fatty acids from the food they eat than are ruminants such as bison.

The researchers concluded that the fat of single-stomached mammals, like mammoths and horses, that were often eaten by stone age hunters contained suitable amounts of omega-3 and omega-6 fatty acids, possibly in quantities sufficient to meet today’s recommended daily intake for good health.

They added that the results also suggest that mammoths and horses at that time were hibernators. They found high proportions of both linoleic acid and alpha-linolenic acid in the reconstructed fatty acid profiles of both frozen horses examined. Such a profile is ideally suited to animals that hibernate.

These polyunsaturated fatty acids are important because they influence the metabolic rate and the length of hibernation bouts in hibernating mammals. Animals without linoleic acid in their diet tend to have higher metabolic rates and shorter bouts of hibernation.

Shorter bouts of hibernation means that the animal arouses from hibernation more frequently, using more of its energy stores. This could adversely affect its chance of survival.

The researchers point to similarities with the present day Yakutian horses,which are well adapted to living in cold conditions. They have an unusually thick layer of fat under the skin and in the abdomen. During the winter, although they move a little, they stay mainly in the sleeping position with little feeding or other activity.

The researchers conclude: “The results of this study indicate that the monogastric animals analysed, i.e. the woolly mammoth and the horse, might have had a hibernating or semi-hibernating behaviour, while their subcutaneous fat could have been consumed by Stone Age hunters to fulfil the daily needs in essential fatty acids.”

Guil-Guerrero JL, Tikhonov A, Rodríuez-Garcí I, Protopopov A, Grigoriev S, et al. (2014) The Fat from Frozen Mammals Reveals Sources of Essential Fatty Acids Suitable for Palaeolithic and Neolithic Humans. PLoS ONE 9(1): e84480.
doi:10.1371/journal.pone.0084480

Florant GL, Lipid Metabolism in Hibernators: The Importance of Essential Fatty Acids
Amer. Zool. (1998) 38 (2): 331-340
doi:10.1093/icb/38.2.331

Equine Science Update

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