Subacute Ruminal Acidosis in Dairy Herds - University of Wisconsin ...

Preconvention Seminar 7A: Dairy Herd Problem Investigation Strategies:Lameness, Cow Comfort, and Ruminal AcidosisRuminal pH varies considerably during the course of a day, and is particularly driven by theamount of fermentable carbohydrate in each meal. Shifts of 0.5 to 1.0 pH units within a 24-hourperiod are common. This represents a 5- to 10-fold change in hydrogen ion concentration in therumen (pH is a log base 10 transformation of hydrogen ion concentration). A typical pattern ofruminal pH variation during the day is presented in Figure 3.7.006.756.50Meal #1 Meal #2Ruminal pH6.256.005.755.505.255.006:30AM8:30AM10:30AM12:30PM2:30PM4:30PM6:30PMTime of Day8:30PM10:30PM12:30AM2:30AM4:30AM6:30AMFigure 3. Changes in ruminal pH after feeding; early lactation cow fed TMR twice daily.(Oetzel, unpublished data, 1997).Feeding TMR more frequently (e.g., six times daily) will not necessarily solve the problemof post-feeding ruminal pH variation. In fact, more frequent feeding will increase dry matterintake and can lower ruminal pH more than less frequent feeding (Figure 4).The enormous changes in ruminal pH after eating make it very difficult to evaluate ruminalpH, even in research settings. Continuous acquisition of ruminal pH data by indwellingelectrode provides the most information possible about post-feeding variations in ruminal pH.Intake depression. Because ruminal acid production from fermentation of carbohydratesvaries so much from meal to meal, ruminants possess highly developed systems to maintainruminal pH within a physiological range of about 5.5 to 7.0. As ruminal pH begins to dropfollowing a meal, the ruminant’s first response is to stop eating. Low ruminal pH may also beassociated with increased osmolality of the ruminal contents, which in turn inhibits feed intake(Carter and Grovum, 1990). Inflammation of the ruminal epithelium (rumenitis) could also playa role in depressing feed intake following ruminal acidosis.University of Wisconsin, School of Veterinary Medicine, 2015 Linden Drive, Madison, WI 5370692