Abstract #T214

# T214
Characteristics of dairy cows with a greater or lower risk of subacute rumen acidosis: Volatile fatty acid absorption, rumen digestion kinetics and consistency of the risk.
Xiaosheng Gao*1, Masahito Oba1, 1University of Alberta, Edmonton, AB, Canada.

The objectives of this study were to examine if lactating dairy cows with a greater or lower risk of subacute ruminal acidosis (SARA) have differences in volatile fatty acid (VFA) absorption rate, rumen digesta passage rate, and in situ rumen digestion, and determine if cows identified to have a greater risk of SARA in mid-lactation consistently have lower rumen pH in late-lactation than cows with a lower risk of SARA. Fourteen ruminally-cannulated dairy cows (DIM = 119 ± 47.2; BW = 640 ± 47.9 kg) were fed a high-grain diet consisting of 30% forage to induce SARA. Eight cows with the lowest acidosis index (area below pH 5.8 normalized for DMI; 0.10 ± 0.16 pH·min/kg) and 5 with the highest acidosis index (3.72 ± 0.19 pH·min/kg) were classified as animals with lower (LOW) and higher (HIGH) risk of SARA, respectively. All response variables were evaluated for the group effect using the PROC TTEST procedure of SAS (version 9.2, SAS Institute Inc., Cary, NC). Minimum (5.75 vs. 5.33; P < 0.01) and mean ruminal pH (6.33 vs. 5.98; P < 0.01) was higher for LOW compared with HIGH animals. However, there were no differences in VFA absorption rate, rumen digesta passage rate, and in situ runminal digestibility of starch and NDF between HIGH and LOW cows. Nine of these 14 animals (4 HIGH and 5 LOW) were fed the same high-grain diet at a later stage of lactation (DIM = 243 ± 19.6) for 21 d. Similar to the mid-lactation, minimum (5.73 vs. 5.32; P = 0.02) and mean ruminal pH (6.32 vs. 6.07; P = 0.01) was higher for LOW compared with HIGH animals. These results suggested that variable risk of SARA among lactating dairy cows fed a high grain diet cannot be attributed to the differences in VFA absorption rate, rumen digesta passage rate, and ruminal digestibility, and that stage of lactation does not affect the risk category of animals in developing SARA.

Key Words: acidosis, VFA absorption, rumen digestion kinetics