Determination of endogenous fat loss and true total tract digestibility of fat in mink (Neovison vison).

The objective of this study was to determine the endogenous fat loss (EFL) and to calculate true total tract digestibility (TTTD) of fat in mink (Neovison vison) using soybean oil-based diets with different fat levels. In the digestibility assay, four diets with 6.30%, 13.9%, 22.0% and 34.0% fat in dry matter were used. Sixteen adult male mink were distributed in a complete randomised design. The apparent total tract digestibility (ATTD) of dietary fat was 90.8%, 95.9%, 96.9% and 97.8%, respectively. The apparent total digestible fat was linearly related to dietary fat intake (r2 = 0.99). The EFL was estimated from the slope of the regression equation and was determined to be 5.09 g/kg DM intake. The TTTD of soybean oil was determined to be 99.3%. Therefore, TTTD values will have negligible impact in feed formulation as they are close to ATTD values with the dietary fat levels normally used for mink.

Scale-dependent analysis of an otter-crustacean system in Argentinean Patagonia.

The Southern river otter or 'huillin', Lontra provocax, is an endangered species endemic of the Andean Patagonian region of Argentina and Chile. It feeds almost exclusively on the genera of macro-crustacea: Aegla and Sammastacus. The aim of this study was to analyse the role of food availability on the huillin's distribution using a scale-dependent analysis of crustacean and otter distributions. We compared the distributions of otters and macro-crustaceans along a north-south regional gradient, between river basins of northern Patagonia, in an altitudinal gradient within a river basin, and between habitat types within a lake. We investigated the distribution of otters by sign surveys along lake shores, river banks and marine coasts, and of crustaceans using surveys in the water, undigested remains in mink (Mustela vison) scats, presence of external skeletons at the waterside and through interviews with local people. Our results show that there were heterogeneities in the distributions of macro-crustaceans at four scales and these were generally reflected in the distributions of freshwater otters. We conclude that the main factor limiting the distributions of L. provocax in freshwater environments is the availability of macro-crustaceans. This paper shows how scale-dependent type analyses of population distribution serves as a method for identifying key environmental factors for species for which the use of long-term demographies is unfeasible.