Abstract #W145

# W145
Forced air versus microwave oven sample drying does not affect rumen starch digestibility, estimated by in situ rumen technique, for total mixed ration, corn silage, or high-moisture corn grain.
J. Goeser*1,2, C. Goldberg1, E. Opgenorth1, D. Sawyer1, 1Rock River Laboratory Inc, Watertown, WI, 2University of Wisconsin, Madison, Madison, WI.

Laboratory drying technique has been thought to impact rumen starch digestibility however little published data exist to support the discussion. The objective here was to determine if commercial laboratory drying techniques impact rumen starch digestibility measures. Commercial dairy total mixed ration (TMR, n = 5), corn silage (CS, n = 5) and high moisture corn (HMC, n = 5) samples were assessed. Samples were split and treated using different drying techniques; undried (UN), forced air (FA) and microwave (MW) oven. For each FA and MW, 2 additional intensities were applied. With FA and MW, low and medium intensities were defined as 52°C (FAL) and 105°C (FAM) or power setting equal to 3 (MWL) and 6 (MWM) in a 1500W oven, respectively. Approximately 200 g of subsample was dried by each technique until weight loss upon further drying was less than 1 g. Mean minutes to dry were 1200, 380, 24 and 16 for FAL, FAM, MWL and MWM. Dried CS and TMR samples were ground to 6 mm and HMSC and UN samples were not ground before being weighed, 3 g, into Ankom R510 bags, and incubated for 3, 7 and 16 h, in triplicate in 3 ruminally cannulated lactating dairy cows consuming a 60% forage, corn silage based diet. Residue bags were rinsed in a laundry machine, dried at 50°C for 24 h and weighed to determine DM disappearance. Residues were composited and starch (% of DM) assessed. Starch digestibility at 3, 7 and 16 h (SD3, SD7, and SD16; % of starch) were determined as starch lost during incubation. Starch, SD3, SD7 and SD16 (dependent variables) were related to feed, oven type, and drying intensity. Farm was considered a random effect. All parameters were fit to model using backward elimination using SAS JMP Pro v11. Effects were considered trends at P < 0.10 and significant at P < 0.05. Starch, SD3, SD7 and SD16 were not affected by drying technique but each was related to feed type (P < 0.05). Drying technique tended to affect SD3 (P = 0.09), with MW numerically less than FA or UN. These observations and results suggest that forced air versus microwave oven drying does not impact rumen starch digestibility measures for commercial dairy feeds.

Key Words: starch digestion, corn silage, drying technique