Technical note: A system for continuous recording of ruminal pH in cattle 1 O. AlZahal,* B. Rustomo,* N. E. Odongo,* T. F. Duffield,† and B. W. McBride* 2 *Department of Animal and Poultry Science, †Department of Population Medicine, University of Guelph, Guelph, Ontario, Canada N1G 2W1 ABSTRACT: Continuous recording of ruminal pH in cannulated cattle has been practiced to study rumen metabolism. However, most systems reported did not permit animal mobility during pH recording. Therefore, the objective of this study was to develop a continuous rumen pH data acquisition system that permitted ani- mal mobility during data acquisition. A further objec- tive was to compare the pH readings obtained using the continuous recording system to readings obtained at the same time using spot sampling. The continuous recording system was composed of a heavy-duty elec- trode and a data logger. The electrode was attached to a 0.5-kg weight to help maintain the electrode in the ventral sac of the rumen. The electrode was connected via a 0.5-m cable to a lightweight data logger that was mounted on the animal’s back using a belt wrapped around the girth. The data logger was battery powered and could hold over 13,000 pH data values. A personal Key words: ruminal pH, continuous recording, cattle ©2007 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2007. 85:213–217 doi:10.2527/jas.2006-095 INTRODUCTION In vivo measurement of bovine ruminal pH was first reported by Smith (1941). However, the continuous acquisition of ruminal pH data was not reported until 1968 (Johnson and Sutton, 1968; McArthur and Milti- more, 1968). Dado and Allen (1993) integrated contin- uous pH recording into a more comprehensive data acquisition system that recorded feed and water in- take, chewing activity, and reticular motility. This ap- proach provided a means to study the interaction be- 1 The authors would like to thank the research technicians, Univer- sity of Guelph, for the care of the animal; the staff of the Physics Machine shop, University of Guelph, for their technical assistance; and the Ontario Ministry of Agriculture, Food and Rural Affairs and the Natural Sciences and Engineering Research Council of Canada (BWM) for their continued support. 2 Corresponding author: bmcbride@uoguelph.ca Received February 16, 2006. Accepted August 23, 2006. 213 digital assistant was used to configure and download data from the data logger during the experiment. Rumi- nal pH was continuously recorded (every 10 s) using a dry Holstein cow fed alfalfa hay ad libitum in a 3-d experiment to compare the performance of the continu- ous system to spot samples taken from the ventral sac of the rumen, the same location as the continuous elec- trode. The spot samples were collected 3 times per d for 3 d. At every sampling time, 3 replicate samples were collected, pH was determined immediately using a handheld pH meter, and readings were averaged (n = 3) and compared with the average of the 3 pH readings recorded using the continuous system at the same time. The pH recorded by spot sampling (6.63 ± 0.04) was greater (P = 0.009) than that of the continuous system (6.56 ± 0.03), with a correlation of r = 0.88 (P = 0.002). The continuous recording system has the potential to facilitate measurement of ruminal pH in free-roam- ing cattle. tween different cow variables (Dado and Allen, 1993). Furthermore, continuous recording of ruminal pH can detect rapid fluctuations in variables that are often more difficult to acquire with spot sampling (Dado and Allen, 1993). Studies have used continuous recording of ruminal pH to evaluate nutritional strategies to mitigate subacute ruminal acidosis in dairy cattle (Keunen et al., 2002; Cottee et al., 2004; Rustomo et al., 2006) and to study the effect of feed intake varia- tion and feeding management on acidosis and perfor- mance in beef cattle (Cooper et al., 1999). The severity of acidosis could be determined by the time spent below a critical rumen pH rather than mean daily pH (Keu- nen et al., 2002). Most systems reported have relied on cables to transfer data to a central recording device, thereby prohibiting the animals’ movement during data acqui- sition. Therefore, the objective of this study was to develop a continuous ruminal pH data acquisition sys- tem that permits the mobility of animals during data acquisition. A further objective was to compare pH