Influence of main chemical constituents on in vitro fermentation using frozen rumen fluid: preliminary results

The study of the nutritional value of feed is an essential prerequisite for nutritionists and livestock operators. The assessment of nutritive value of feed is determined by chemical components, as well as their rate and extent of digestion. The description of digestive and metabolic processes can be done by using in vitro models that simulate the in vivo digestion processes with different levels of complexity. Compared to in vivo experiments, in vitro methods have the advantage not only of being less expensive and less time-consuming, but they allow one to maintain experimental conditions more precisely and reproducible than do in vivo trials. Gas production (GP) test has become a valuable tool in the evaluation and selection of feeds for ruminants, since it provides information on the fermentability, digestibility and nutritional value of feeds. These techniques require rumen microbial inoculum taken directly from fistulated animals that is a practice subjected to criticism not only from the cost demanding and difficulty of keeping such rumen-fistulated animals, but the ethical issues poses questions on the compliance of animal welfare leading to seek to other alternatives. Ruminal fluid (RF) taken from slaughtered animals as microbial inoculum is an alternative source. Another mitigating question is the feasibility usage of frozen RF for GP test. Storing microbial fluid while maintaining its microbial activity is an approach that enable the standardization of in vitro studies, giving ample time to determine useful parameters and to work on a large number of substrates. The aim of this preliminary study conducted on Ankom system is to test the frozen RF on in vitro fermentation of different substrates along with the assessment of proximate parameters and polyphenolic content. Six substrates (maize, bran, sorghum, animated oats, soft bread and hard bread), present locally in the Maltese Islands, were selected. The data for cumulative GP (as mL of gas produced per g dry matter) were processed by the three parameters Gompertz sigmoidal function. The GP results showed the R2 higher than 0.96 for all the substrates (maize = 0.98; bran = 0.98; animated = 0. 98; sorghum = 1; soft bread = 0.97; hard bread = 0.96). Animated oats showed the lowest fermentation kinetics (65.48 mL/g) according to its Crude protein, Neutral Detergent Fiber and Acid Detergent Fiber content, while hard bread the highest one (192.59 mL/g), followed by maize, sorghum, soft bread and bran respectively 184.8, 180.64, 178.04, and 130.6 mL/g. The antioxidant activity may be partially related to the polyphenol content: bran and animated oats showed highest values, respectively 26 and 24 mg/100g, while soft and hard bread the lowest one respectively 9.8 and 11 mg/100g. The results highlight that the frozen ruminal fluid seems potentially valid to replace the fresh one, showing rate of fermentation for all the substrates according to their chemical composition.