The effect of season on in vitro degradability and fermentability of feeds in red deers’ (Cervus elaphus L.) rumen fluid

Transition from summer to winter changes red deer digestive tract physiology and digestive processes. The objective of the trial was to determine the effects of season on in vitro apparent ( iv ADMD) and true dry matter ( iv TDMD) digestibility, in vitro gas production parameters and short-chain fatty acid synthesis (SCFA) in red deer hinds of eleven substrates naturally occurring in Slovenia (chestnut fruits, acorns of common and sessile oak, two fresh grasses) and those frequently used in supplemental red deer feeding (two grass hays and two grass silages, apple pomace and sugar beet roots). There were no differences in iv ADMD, iv TDMD, determined by incubation of feeds in buffered rumen fluid, as there were no differences in majority of gas production parameters between autumn and winter season. Only the parameter “C” (specific gas production rate) was frequently higher ( p  < 0.05) in winter season than in autumn season. The amounts of SCFA were similar between two seasons. However, the proportion of acetic acid tended to be higher in winter, while the proportions of propionic and butyric acid tended to be higher in autumn than in winter especially in high fibre feeds. On contrary, in high starch feeds such as oak acorns and chestnut fruits, the proportion of propionic acid was higher ( p  < 0.05) in winter, while of butyric acid in autumn ( p  < 0.05). Despite the fact that the number of used substrates (n = 11) and animal rumen fluid donors (n = 6) were small, these results indicate a shift in rumen microbial metabolism between autumn and winter season.