Macronutritional composition of Swedish moose rumen samples collected 2014/15

At northern latitudes, large spatial and temporal variation in the
nutritional composition of available foods poses challenges to wild
herbivores trying to satisfy their nutrient requirements. Studies
conducted in mostly captive settings have shown that animals from a
variety of taxonomic groups deal with this challenge by adjusting the
amounts and proportions of available food combinations to achieve a target
nutrient balance. In this study, we used proportions-based nutritional
geometry to analyse the nutritional composition of rumen samples collected
in winter from 481 moose (Alces alces) in southern Sweden and examine
whether free-ranging moose show comparable patterns of nutrient balancing.
Our main hypothesis was that wild moose actively regulate their rumen
nutrient composition to offset ecologically imposed variation in the
nutritional composition of available foods. To test this, we assessed the
macronutritional composition (protein, carbohydrates, and lipids) of rumen
contents and commonly eaten foods, including supplementary feed, across
populations with contrasting winter diets, spanning an area of
approximately 10 000 km2. Our results suggest that moose balanced the
macronutrient composition of their rumen, with the rumen contents having
consistently similar proportional relationship between protein and
non-structural carbohydrates, despite differences in available (and eaten)
foods. Furthermore, we found that rumen macronutrient balance was tightly
related to ingested levels of dietary fiber (cellulose and hemicellulose),
such that the greater the fiber content, the less protein was present in
the rumen compared to non-structural carbohydrates. Our results also
suggest that moose benefit from access to a greater variety of trees,
shrubs, herbs and grasses, which provides them with a larger nutritional
space to manoeuvre within. Our findings provide novel theoretical insights
into a model species for ungulate nutritional ecology, while also
generating data of direct relevance to wildlife and forest management,
such as silvicultural or supplementary feeding practices.