Abstract
Oxygen isotopes (δ18O) in animal and human tissues are expected to be good recorders of geographical origin and migration histories. However, seasonal variation of δ18O may diminish the origin information in the tissues. Here the seasonality of δ18O in tail hair was investigated in a domestic suckler cow (Bos taurus) that underwent different ambient conditions, physiological states, keeping and feeding during five years. A detailed mechanistic model was built to explain this variation. The measured δ18O in hair significantly related (p < 0.05) to the δ18O in meteoric water in a regression analysis. Modelling suggested that this relation was only partly derived from the direct influence of feed moisture. Ambient conditions (temperature, moisture) also affected the animal itself (drinking water demand, transcutaneous vapor etc.). The clear temporal variation thus resulted from complex interactions with multiple influences. The twofold influence of ambient conditions via the feed and via the animal itself is advantageous for tracing the geographic origin because δ18O is then less influenced by variations in moisture uptake; however, it is unfavorable for indicating the production system, e.g. to distinguish between milk produced from fresh grass or from silage. The model is versatile but needs testing under a wider range of conditions.
Highlights
The potential use of the 18/16O isotope ratio values (δ18O) in animal tissues such as nail, hair, bone and feather to track geographic origin, climate and migration has been recognized during recent decades[1, 2]
These models did not link ambient conditions and body water together, and they did not consider the influence of ambient conditions on the amount of O input fluxes
For the reasons given above, we extended the Kohn model as follows: (1) Drinking water intake was estimated directly based on water demand and water provision in the feed
Summary
The potential use of the 18/16O isotope ratio values (δ18O) in animal tissues such as nail, hair, bone and feather to track geographic origin, climate and migration has been recognized during recent decades[1, 2]. Kohn[2] developed a general model to describe the relationships between δ18O of body water and the δ18O input fluxes (air O uptake, air water vapor into the lungs, chemically bound O in feed, feed moisture and drinking water) and output fluxes (CO2 production, fecal water, respiratory water, sweat water, transcutaneous water vapor, urea and urine) based on the isotopic balance and amount balance of O and the influence of ambient conditions This model was used to analyze the sensitivity of climatic variation and species-specific differences in physiology on δ18O of body water and tissue O of different genera. Only the general principle of creating an animal’s mass balance for water and O were taken from the original Kohn model while the details had to be modified
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