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Hormones and bile acids to determine prehistoric grazing habits

A study by the UPV/EHU-University of the Basque Country reveals that Neolithic shepherds also separated pregnant ewes and suckling lambs from the rest of the flock

  • Research

First publication date: 20/04/2022

Asier Vallejo
Asier Vallejo. Photo: Nuria González. UPV/EHU.

The UPV/EHU's METABOLOMIPs research group has used bile acids and hormones from deposits in the El Mirador cave in Atapuerca, used as a sheepfold in prehistoric times, as biomarkers to determine Neolithic grazing habits. They found that the proposed method is appropriate for understanding how flocks were managed at that time. They found that pregnant ewes and suckling lambs were separated from the flock even back then.

Agriculture and grazing practices emerged and became widespread during the Neolithic period, with farming societies developing as a result. Caves and rock shelters began to be used as livestock pens. A common grazing practice throughout the Mediterranean, from the Neolithic to the Bronze Age, was to burn the dung that had accumulated in the caves and rock shelters of the flocks in order to clean these places, remove parasites and so on. This continual burning produced an accumulation of various layers of organic and mineral sediments called fumiers.

The bile acids left behind in the unburnt layers of the fumiers enable researchers to find out which species were sheltering in a particular fold, because the composition of bile acids varies from one species to another. Right now, the UPV/EHU’s METABOLOMIPs research group has begun to search for hormonal biomarkers to better understand how prehistoric shepherds managed their flocks. “The hormone ratios vary according to whether the ewes are pregnant, lactating or in any other situation,” explained Asier Vallejo, a UPV/EHU PhD-holder.

Archaeologists' hypotheses confirmed

"In the archaeological work in the El Mirador cave, located on the Sierra de Atapuerca (Burgos, Spain), many animal bone remains had been found, and it was assumed that the flocks used to be divided, because in one part of the cave there is a larger quantity of lamb bones," explained the lead author of the study. So members of this group from the UPV/EHU's Department of Analytical Chemistry began to look for hormonal biomarkers "to see if the hormonal activity was in fact higher in that part. And it was," he added.

The analytical method used for this is not particularly novel, but "the idea was. This is the first time that hormonal biomarkers have been studied to predetermine how flocks were managed 6,000-7,000 years ago," said Dr Vallejo. Bile acid analysis gives an idea of the number of animals in the flock: "The higher the amount of bile acid, the more animals there would have been. We use this to normalise the progesterone concentration in the manure. If the flock is large, the progesterone level will also be high; however, if the flock is small and the progesterone level is high, that means that the ewes located in that part of the cave were gestating and lactating". Therefore "we cross-checked the hypotheses of the archaeological studies with our own, and they were found to coincide. So their hypotheses were confirmed," he said.

He is currently conducting a similar study in an area of Sicily. The group wants to further the search for more precise biomarkers that make it possible, firstly, to easily recognise the type of animals that lived in the prehistoric shelters, since "the animals were often intermingled and in some cases it is not easy to differentiate between the biomarkers", and secondly, to determine their hormonal status more easily.

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