Body Protein Stores and Isotopic Indicators of N Balance in Female Reindeer (Rangifer tarandus) during Winter

Abstract

We studied bred and unbred female reindeer (Rangifer tarandus tarandus) during 12 wk of winter when ambient temperatures were low and nitrogen (N) demand for fetal growth is highest in pregnant females. Animals were fed a complete pelleted diet ad lib. that contained 2.54% N in dry matter that was 80% +/- 2% (X +/- SD) digestible. Female reindeer lost 64% +/- 14% of body fat but gained 34% +/- 11% of lean mass from 10 wk prepartum to parturition. These changes were equivalent to average balances of -14.14 +/- 2.35 MJ d(-1) and 10 +/- 3 g N d(-1). Blood cells, serum, and urine declined in (15)N/(14)N in late winter as body protein was gained from the diet. Blood cells of newborn calves were more enriched in (15)N and (13)C than that of their mothers, indicating the deposition of fetal protein from maternal stores. To quantify pathways of N flow in reindeer, N balance was measured by confining animals to cages for 10 d at 4 wk from parturition. N balance was inversely related to (15)N/(14)N in urea-N but not related to (15)N/(14)N of blood cells, creatinine, and feces. The proportion of urea-N derived from body protein increased above 0.46 as N balance fell below -200 mg N kg(-0.75) d(-1). Proportions of urea-N from body protein were -0.01 +/- 0.21 in pregnant females before and after caging and were consistent with average body protein gain in winter. Storage of protein allows reindeer and caribou to tolerate diets that are low in N without impairing fetal development.

Using ultrasound measurements of rump fat to assess nutritional condition of woodland caribou in northern British Columbia, Canada

“…Monitoring changes in body protein, however, is challenging because of the relatively small changes that occur throughout the year (approx 9.5-11.2% of body mass for breeding female caribou, Chan McLeod et al, 1999). Recent use of nitrogen isotopes in snow urine to assess nitrogen balance in late winter (Parker et al, 2005;Barboza & Parker, 2006) is promising, but this technique requires validation in wild populations of caribou.…”

“…We were unable to make direct comparisons of our measurements of rump fat with those of Arctic populations because back fat of barren-ground animals mostly was measured manually and at different locations on animal carcasses. Ultrasonography with standardized protocols is now being used to determine thickness of rump fat in both live barren-ground and woodland caribou for captive (Parker et al, 2005;Barboza & Parker, 2006) and wild (E. Jones, unpublished data from British Columbia; M. Oakley, unpublished data from Yukon; this study) populations.…”

Standardized monitoring of Rangifer health during International Polar Year

“…Transverse cuts through both the heart and the gastrocnemius muscle, and sometimes additional muscles, were done to examine for cysts of Taenia spp. Feces, muscle, fur, and urine were also collected for protein/nitrogen balance studies (Barboza & Parker, 2006). is sampling level allowed for more detailed quantitative analyses of a broader range of pathogens.…”

Modeling energy and protein reserves in support of gestation and lactation: glucose as a limiting metabolite in caribou and reindeer

“…Given that reindeer express a greater dependency on body reserves than do caribou in late gestation and early lactation (Barboza & Parker, 2006), the question as to whether caribou and reindeer respond with similarly evolved responses to the use of body reserves relative to resource availability remains to be studied. We assumed the relative Krebs, 1964 use of reserves for the same resource availability would be the same for both subspecies.…”

“…During gestation this exercise controls fetal growth, and during lactation it controls milk production and calf growth. As validation we rely on seasonal changes in body composition of female caribou (R. t. granti) of the Porcupine caribou herd (PCH) (Gerhart et al, 1996) and experimental data derived from caribou and reindeer (R. t. tarandus) fed a known diet and intake during late gestation (Barboza & Parker, 2006;2008).…”