Age effects and the influence of varying proportions of terrestrial and marine dietary protein on the stable nitrogen-isotope compositions of pig bone collagen and soft tissues from a controlled feeding experiment

Emily C Webb,Alan Stewart,Bevis Miller,John Tarlton,Richard P Evershed

doi:10.1080/20548923.2015.1133121

Emily C Webb, Alan Stewart + Show 3 more

Open Access

https://doi.org/10.1080/20548923.2015.1133121

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Abstract

In this study, femoral collagen, rib collagen, femoral muscle, loin muscle and liver samples from sows, piglets and pigs raised in a controlled feeding study are analysed for their nitrogen-isotope compositions. The objectives of this research are to investigate the relationship between tissue and dietary δ15N values across age categories under controlled feeding and housing conditions, and to assess tissue 15N-enrichment relative to diet when pigs of different ages are consuming terrestrial, marine, or mixed terrestrial-marine dietary protein. There is a strong linear relationship between all tissue δ15N values and the amount of marine protein consumed, but the δ15N values do not become consistently elevated for all individuals consuming the same diet until at least 25% of the dietary protein source is marine-derived. Adolescent pigs also had consistently lower δ15N values than either piglets or sows consuming the same diet for collagen and muscle, which is most likely caused by the differences in growth rate among the age categories. Further, for some tissues and animals, a linear relationship between the amount of marine protein consumed and the Δ15NTissue – Whole Diet offset was also observed. We suggest that this variability results from both age-associated growth rates and differential incorporation of amino acids from terrestrial and marine dietary protein into rapidly growing tissue.

Highlights

Stable nitrogen-isotope analysis (d15N) is widely used in archaeology and ecology to investigate diet and food web relationships in both modern and extinct contexts
We evaluate the sensitivity of d15N values to incremental changes in marine protein consumption, the impact of growth rate on tissue isotopic compositions, and identify potential differences in trophic offset associated with the type of dietary protein consumed
Metabolism has an important impact on tissue d15N values, and the isotopic composition of tissues formed during periods of perturbed nitrogen balance are often aberrantly 15N–enriched or – depleted relative to expected tissue nitrogen-isotope compositions based on dietary intake

Summary

Introduction

Stable nitrogen-isotope analysis (d15N) is widely used in archaeology and ecology to investigate diet and food web relationships in both modern and extinct contexts. Injury repair, infection, or inadequate diet can push the body into a state of positive or negative nitrogen balance, which alters the relationship between the isotopic compositions of newly forming tissues and diet (i.e., the D15N offset; Hobson et al 1993; Schoeller 1999) This outcome has been exploited to investigate numerous pathological conditions and perturbations in physiological or metabolic states in both archaeological and modern clinical contexts (Fuller et al 2004, 2005; Katzenberg and Lovell 1999; Mekota et al 2006, 2009; Petzke et al 2006; Olsen et al 2014; Williams et al 2011). The research presented here elucidates the relationships among trophic level offsets, growth rate, and the nature of dietary protein source, which act simultaneously to mediate tissue nitrogenisotope compositions

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