Influence of storage time and temperature on in vitro digestion of neutral detergent fibre at 48 h, and comparison to 48 h in sacco neutral detergent fibre digestion

The effect of within-day delays of 0.5, 2.5, 4.5 and 6.5 h between collection of rumen fluid from a cow and initiation of in vitro fermentation, as well as storage of rumen fluid for 48 h at either −24°C or 6, 22 and 39°C, on in vitro digestion of neutral detergent fibre (NDF) at 48 h was determined. In addition, the 48 h in vitro digestion of NDF, determined with a minimum time delay (i.e., 0.5 h) between collection from the cow and initiation of incubation, was compared to NDF digestion determined in sacco at 48 h. Rumen inoculum from a single cow was utilized in a thrice replicated incubation with whole crop alfalfa, corn, cereal and sudangrass forages of a lower and higher quality. The same cow was used as the host for the in sacco bags. The in vitro procedure used a bulk procedure with 5.0 cm × 5.5 cm multi-weave polyethylene polyester polymer bags that retained particles of 25 mm and larger. The in sacco procedure used the same bags retained in a large mesh bag. A within-day time delay of up to 6.5 h between collection of rumen fluid from the cow and initiation of in vitro fermentation had no impact on measured 48 h in vitro digestion of NDF. In contrast, no temperature dependent storage procedure maintained 48 h in vitro digestion of NDF at levels determined with no 48 h storage, although high quality alfalfa was least affected by any storage procedure. The 48 h in vitro digestion of NDF, determined using the minimum time delay between collection from the cow and initiation of the incubation, was higher than values obtained in sacco. Results show that this bulk in vitro procedure resulted in higher 48 h digestion of NDF than those determined with a similar in sacco procedure, thereby suggesting that laboratories located some distance from the donor animal can utilize in vitro procedures to accurately estimate 48 h digestion of NDF. However, storage of rumen fluid for 48 h, by any temperature dependent procedure examined, in order to facilitate fewer trips to the donor animal, or trips of substantially longer duration, will underestimate 48 h digestion of NDF to an extent that depends upon the forage incubated.