73 Impact of storage conditions on the viability of microbial inoculum for estimating in vitro digestibility in the horse

Abstract

This study evaluated the effect of storage conditions of equine fecal material on the viability of derived microbial inoculum used for in vitro equine digestibility trials. Fecal material collected via rectal palpation from 3 mature quarter horse geldings was stored at 4 storage temperatures: 39°C for 15 min (control), 22°C for 6h, 3°C for 6h, and −18°C for 24h. Utilizing pooled microbial inoculum from stored fecal material, the in vitro digestion of 6 forage samples (NDF range 41 to 62%) consisting of 3 alfalfa and 3 mixed grass sample were digested in the Ankom Daisy II Incubator to evaluate interactions between storage condition of microbial inoculum and chemical composition of digested forage samples. After determination of dry matter digestibility (DMD), an Ankom2000 Fiber Analyzer was used to measure neutral detergent fiber digestibility (NDFD) and acid detergent fiber digestibility (ADFD). A mixed linear model was used to analyze differences in DMD, NDFD, and ADFD, with forage and treatment as class statements with date included as a random effect. No significant interaction of forage x treatment was observed ( P = 0.81 for DMD). Further analysis with a mixed linear model was used to evaluate the effect of forage quality parameters crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) as covariates for DMD, NDFD, and ADFD results. Significant differences were observed for DMD ( P < 0.0001 ), NDFD ( P < 0.01 ), and ADFD ( P < 0.001 ) between 39°C and 3°C, 39°C and −18°C, 22°C and 3°C, and 22°C and −18°C. No differences ( P > 0.05 ) were observed in DMD, NDFD, or ADFD between 39°C and 22°C or 3°C and −18°C. Covariance analysis found no difference ( P > 0.05 ) in slope between any of the 4 storage condition levels when CP, NDF, and ADF were modeled as covariates for DMD, NDFD, and ADFD. Results support that fecal material stored for up to 6 h in 22°C temperature conditions provide a viable alternative to fresh fecal material for the formation of microbial inoculum. When used to harvest inoculum for use in the Daisy II incubator fecal material that had been previously chilled or frozen did not result in DMD, NDFD or ADFD values of forage samples that were as high as when inoculum from the other 2 storage treatments were used. Further research is needed to determine the reason for the decline in DMD, NDFD, and ADFD when utilizing inoculum from chilled and frozen fecal samples.