Effects of season and reproductive state on lipid intake and fatty acid composition of gastrointestinal tract contents in the European hare

Abstract

We investigated lipid content and fatty acid (FA) composition of gastrointestinal tract contents in free-living, herbivorous European hares (Lepus europaeus). Mean crude fat content in hare stomachs and total gastrointestinal (GI) tracts was higher than expected for typical herbivore forages and peaked in late fall when hares massively deposited body fat reserves. Changes of FA proportions in different parts of the GI-tract indicated a highly preferential absorption of polyunsaturated fatty acids (PUFA). A further reduction of PUFA content in the caecum, along with the appearance of odd-chained FAs in caecum, caecotrophes, and colon content, pointed to a biohydrogenation of PUFA in the hare's hindgut. GI-tract contents showed significant seasonal changes in their FA composition. Among PUFA, α-linolenic acid peaked in spring while linoleic acid was predominant in late summer and fall, which probably reflected changes in the plant composition of forage. However, independent of seasonal changes, GI-tracts of lactating females showed a significantly (+33%) higher content of linoleic acid, a FA that is known to increase reproductive performance in European hares. This finding suggests that lactating females actively selected dietary plants rich in linoleic acid, a PUFA that may represent a limited resource for European hares.

Fig. 1

Seasonal change of intraperitoneal fat content (w/o gonadal fat depots) in free-living European hares (both sexes) shot at bi-monthly intervals in Lower Austria. The numbers above the symbols indicate sample sizes. Means ± 95% confidence intervals

Fig. 2

Crude fat content of digesta in different fractions of the gastrointestinal tract of free-living European hares. SI small intestine, CT caecotrophes. Means ± 95% confidence intervals

Fig. 3

Mean crude fat content of digesta in the gastrointestinal tract of European hares as a function of season. Means ± 95% confidence intervals

Fig. 4

Fatty acid content in different fractions of the gastrointestinal tract of European hares. Means ± 95% confidence intervals. a Proportions of polyunsaturated (PUFA), monounsaturated (MUFA) and saturated (SFA) fatty acids. b Proportions of linoleic acid (C18:2n-6) and α-linolenic acid (C18:3n-3) within PUFA

Fig. 5

Mean fatty acid proportions in the gastrointestinal tract contents of European hares as a function of season. Means ± 95% confidence intervals. a Proportions of polyunsaturated (PUFA) monounsaturated (MUFA) and saturated (SFA) fatty acids. b Proportions of linoleic acid and α-linolenic acid within PUFA

Fig. 6

Linoleic acid and α-linolenic acid proportions in the gastrointestinal tract content of lactating and non-lactating female European hares. Means from all fractions of the gastrointestinal tract ± 95% confidence intervals