LAUSR

Intensive dairy production systems encourage feeding of high-concentrate diets to increase milk production efficiency. However, there is limited information regarding the effect of a SARA challenge diet on chewing behavior and rumino-reticular short chain fatty acid (SCFA) concentration. The objective of this study was to evaluate chewing activity and SCFA production in the rumen and reticulum, using nine ruminally cannulated non-lactating Holstein cows. Preceding the trial, cows were transitioned from 100% forage to 65% DM concentrate over eight days. Trial day 1 began once cows reached 65% DM concentrate and monitoring during 23 days. RumiWatch halters were used to monitor chewing activity. SCFA analysis was conducted on rumen and reticulum fluid collected 4 hours after feeding using gas chromatography. Data were analyzed with SAS, with the fixed effect of days and cow as random effect. There was an increase in DM intake during the first four hours after feeding: 1.97 and 2.25 ± 0.12 kg for day 1 and 23, respectively (P < 0.05). There was no difference in rumination time (P = 0.16) with 29 ± 8.5 minutes during the first four hours of feeding. However, chewing index (P = 0.08) tended to decrease from 36.7 to 29.4 ± 4.4 minutes of chewing/kg of DM for day 1 and 23, respectively. Moreover, on day 1, propionate increased from 19.9 ± 1.02 to 20.1 ± 1.02% and from 24.04 ± 0.93 to 25.4 ± 1.02% compared to day 23 for rumen and reticulum, respectively (P < 0.05). In addition, from day 1 to day 23, the rumen and reticulum acetate/propionate ratio declined from 3.2 ± 0.15 and 3.1 ± 0.1, to 2.5 ± 0.15, respectively, and reticulum SCFA decreased from 87 to 67 µmol/g, respectively. Overall, there was no effect of the 23-day SARA challenge diet on chewing activity. However, there was a reduction of SCFA concentration in reticulum, which may be due to enhanced SCFA absorption or increased feed bolus neutralizing capacity.