356 Effects of rumen fluid preservation methods on in vitro true digestibility.

Abstract In vitro true digestibility (IVTD) is a widely used method for evaluating feed quality and predicting ruminant performance using rumen fluid inoculum from cattle. However, the maintenance of cannulated animals for rumen fluid collection can present logistical and ethical challenges. Alternative inoculum sources, such as stomach-tubed rumen fluid, can induce stress in animals and may be contaminated with saliva, potentially altering microbial composition. Frozen rumen inoculum has been proposed as an alternative to fresh inoculum, though its use may result in reduced digestibility values. The incorporation of cryoprotectants may mitigate microbial viability loss, improving the efficacy of preserved inoculum for IVTD assessments. The objective of this study was to evaluate the effects of rumen fluid preservation methods on IVTD values. Rumen fluid samples were collected from two ruminally fistulated steers. Preservation methods included traditional freezing at -20°C (FZN) or freezing with liquid nitrogen (LN2), either with or without a preservative of dimethyl sulfoxide (DMSO; + or -). A fresh control (CON) was maintained from each sample. Feedstuffs evaluated were bahiagrass (BHG), bermudagrass (BMG), broiler litter (LIT), corn gluten meal (CGM), dried distillers’ grains (DDG), peanut hay (PNT), ryegrass (RG), soybean hulls (SH), tall fescue (TF), and whole cottonseed (WCS). Feedstuffs were subjected to batch culture in vitro true digestibility using the ANKOM Daisy II incubator. Both freezing technique and the use of preservative influenced IVTD values (P < 0.05) compared to the fresh control for BMG, TF, and DDG. No effects were observed for PNT or CGM. For SH and RG, IVTD values were lower in the absence of preservative (FZN- and LN-), whereas preserved samples (FZN+ and LN+) showed no differences (P > 0.05) from CON. In LIT and WCS, IVTD was lower (P < 0.05) in FZN- samples compared to CON, with other treatments showing no effect. These findings suggest that preservation methods and the use of preservatives can mitigate IVTD losses in frozen and liquid-nitrogen preserved samples, potentially improving the nutritional retention of stored feedstuffs. Further research is warranted to optimize preservation strategies for enhanced digestibility and nutrient availability.