Ecological Archives E094-165-A2

Joëlle Taillon, Perry S. Barboza, Steeve D. Côté. 2013. Nitrogen allocation to offspring and milk production in a capital breeder. Ecology 94:1815–1827.

Appendix B. Details on the enrichment of 15N in maternal tissues, from blood clot to serum protein to muscle, of migratory caribou females (Rangifer tarandus) from the Rivière-George (RG) and Rivière-aux-Feuilles (RAF) herds, northern Quebec and Labrador, Canada.

At calving, we noted an enrichment of 15N from blood clot to muscle, which is consistent with the faster turnover of blood compared to muscle and the incorporation of lighter dietary δ15N into blood clot during gestation (Podlesak et al. 2005, Barboza and Parker 2006, Karasov and Martinez del Rio 2007). The positive relationship between muscle δ15N and blood clot δ15N indicates that the two tissues have a similar fractional turnover of N. This is supported by previous work on captive Rangifer where females fed on a low N winter diet presented an increase in blood clot δ15N when N intakes declined below the requirement for maintenance (Parker et al. 2005, Barboza and Parker 2008). Our results, therefore, support N recycling from muscle to blood clot in late gestation for both wild migratory caribou herds. Conversely, the poor relationship between muscle δ15N and serum proteins δ15N suggests that the two pools of N have different turnovers. Most proteins in serum are produced by the liver from recycled body N as well as absorbed dietary N for redistribution to muscles and organs including the uterus and mammary gland. Serum proteins δ15N may therefore reflect a labile pool of N that is transferred from body stores to proteins in fetal tissue or milk (Lobley et al. 2000, Lapierre et al. 2006). The maternal source of N may therefore shift among metabolic pools during reproduction. However, maternal muscle δ15N is the largest N pool and the least variable isotopic endpoint for estimates of allocation. In this study, blood clot δ15N and serum proteins δ15N confirmed the estimates of muscle δ15N as the main maternal endpoint and improved our understanding of N allocation from body reserves compared with dietary sources.


Literature cited

Barboza, P. S., and K. L. Parker. 2006. Body protein stores and isotopic indicators of N balance in female reindeer (Rangifer tarandus) during winter. Physiological and Biochemical Zoology 79:628–644.

Barboza, P. S., and K. L. Parker. 2008. Allocating protein to reproduction in arctic reindeer and caribou. Physiological and Biochemical Zoology 81:835–855.

Karasov, W. H., and C. Martinez del Rio. 2007. Physiological ecology: how animal process energy, nutrients and toxins. Princeton University Press, Princeton, New Jersey, USA.

Lapierre, H., D. Pacheco, R. Berthiaume, D. R. Ouellet, and C. G. Schwab. 2006. What is the true supply of amino acids for a dairy cow? Journal of Dairy Science 89:E1–E14.

Lobley, G. E., G. D. Milano, and J. G. van der Walt. 2000. The liver: integrator of nitrogen metabolism. Pages 149–167 in P. B. Cronjé, editor. Ruminant physiology: digestion, metabolism, growth and reproduction. CAB International, Wallingford, UK.

Parker, K. L., P. S. Barboza, and T. R. Stephenson. 2005. Protein conservation in female caribou (Rangifer tarandus): effects of decreasing diet quality during winter. Journal of Mammalogy 86:610–622.

Podlesak, D. W., S. R. McWilliams, and K. A. Hatch. 2005. Stable isotopes in breath, blood, feces and feathers can indicate intra-individual changes in the diet of migratory songbirds. Oecologia 142:501–510.

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