Rumen fluid from donor cows fed different additives can affect the <i>in vitro</i> fermentation parameters

This study assessed the impact of rumen ‘fluid not adapted’ (FNA) and of rumen ‘fluid adapted’ (FA) to three additives on in vitro kinetics of gas production and end products of fermentation. The experiment was performed according to a Latin Square Design of 4 cows and 4 experimental periods. The dry cows received a total mixed ration designed for lactating cows without (control) or with 1 g/d of one of three additives (allyl-sulphide, cinnamaldehyde, limonene) that were selected for their known effects on rumen fermentation. The collected rumen fluids (FNA and FA, respectively) were used as inoculum of 4 consecutive in vitro incubations (1 for each experimental period) adding or not adding 30 mg of one of the three pure compounds. The incubations were performed using a commercial equipment to evaluate the kinetics of gas production and collect the end products of fermentation. The results indicated that FA did not influence any fermentation parameters compared to FNA. However, when allyl-sulphide was added in vitro, the effects of this compound tended to be more pronounced with FA than with FNA. This experiment highlights that the three tested pure additives, which show activity on in vitro fermentations, can alter the in vitro activity of rumen fluid collected from cows fed with these compounds. Therefore, the administration of pure additives directly to the cows can influence the rumen microbial activity and the response of in vitro experiments.