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J. Anim Sci. 2007. 85:213-217. doi:10.2527/jas.2006-095
© 2007 American Society of Animal Science
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ANIMAL NUTRITION

Technical note: A system for continuous recording of ruminal pH in cattle1

O. AlZahal*, B. Rustomo*, N. E. Odongo*, T. F. Duffield{dagger} and B. W. McBride*,2

* Department of Animal and Poultry Science, and {dagger} Department of Population Medicine, University of Guelph, Guelph, Ontario, Canada N1G 2W1


   Abstract
Top
 Abstract
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 IMPLICATIONS
 LITERATURE CITED
 
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 animal mobility during data acquisition. A further objective 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 electrode 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 digital assistant was used to configure and download data from the data logger during the experiment. Ruminal 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 continuous system to spot samples taken from the ventral sac of the rumen, the same location as the continuous electrode. 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-roaming cattle.

Key Words: ruminal pH • continuous recording • cattle


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 IMPLICATIONS
 LITERATURE CITED
 
In vivo measurement of bovine ruminal pH was first reported by Smith (1941)Go. However, the continuous acquisition of ruminal pH data was not reported until 1968 (Johnson and Sutton, 1968Go; McArthur and Miltimore, 1968Go). Dado and Allen (1993)Go integrated continuous pH recording into a more comprehensive data acquisition system that recorded feed and water intake, chewing activity, and reticular motility. This approach provided a means to study the interaction between different cow variables (Dado and Allen, 1993Go). 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, 1993Go). Studies have used continuous recording of ruminal pH to evaluate nutritional strategies to mitigate subacute ruminal acidosis in dairy cattle (Keunen et al., 2002Go; Cottee et al., 2004Go; Rustomo et al., 2006Go) and to study the effect of feed intake variation and feeding management on acidosis and performance in beef cattle (Cooper et al., 1999Go). The severity of acidosis could be determined by the time spent below a critical rumen pH rather than mean daily pH (Keunen et al., 2002Go).

Most systems reported have relied on cables to transfer data to a central recording device, thereby prohibiting the animals’ movement during data acquisition. Therefore, the objective of this study was to develop a continuous ruminal pH data acquisition system that permits the mobility of animals during data acquisition. A further objective was to compare pH readings obtained using the continuous recording system with readings obtained at the same time using spot sampling.


   MATERIALS AND METHODS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 IMPLICATIONS
 LITERATURE CITED
 
Continuous Recording System
The continuous recording system was composed of 2 main components: an indwelling pH electrode and a portable data logger (Figure 1aGo).


Figure 1
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  		Figure 1. Components of the continuous ruminal pH recording system: (a) recording unit on the animal during exercise; (b) pH probe assembly; (c) weight connector; (d) stainless steel weight; (e) pH electrode; (f) protective tubing; (g) plastic connectors; (h) data logger; (i) logger housing; (j) belt; and (k) personal digital assistant and its cable.

 
The electrode (PHE-7352-6-PT100, Omega Engineering Inc., Stamford, CT) was heavy-duty and designed for submersible applications (Figure 1bGo). The sensor on the electrode had a sealed, double junction construction that was highly resistant to poisoning solutions and could be used in any angle orientation (Figure 1eGo). The outer body was made of strong poly-phenylene sulfide (Ryton, Chevron Philips Chemical, The Woodlands, TX), which was resistant to harsh chemicals. The probe could tolerate pressure up to 689 kPa and was provided with a temperature sensor to allow automatic temperature compensation of pH.

The front end of the probe threaded into an ultra-high-molecular weight polyethylene plastic connector (Figure 1cGo) to protect the electrode’s bulb from any stresses during vertical immersion in the rumen and to carry a 0.5-kg stainless steel weight (Figure 1dGo) that helped to keep the electrode within the ventral sac of the rumen. The lead of the electrode was protected from rumen contents by a vinyl pipe (2.5 cm o.d., 1.9 cm i.d., 59-cm long; Figure 1fGo) threaded into the end of the electrode from one end and threaded to the rubber stopper of the cannula on the other end via plastic connectors (Figure 1gGo). This assembly provided a strong and liquid-tight protection to prevent breakdown inside the rumen. Additionally, the use of rigid plastic tubing aided in maintaining the location of the probe in the rumen. The total length of the system inside the rumen was approximately 64 cm. This allowed the tip of the probe to reach the bottom of the ventral sac. However, adjustments might be necessary depending on cow size and cannula location. The electrode’s (182 cm) cable was connected to the data logger (pHTemp101, Monarch Instrument, Amherst, NH; Figure 1hGo) for data acquisition.

The data logger weighed 120 g and could hold up to 13,107 measurements per channel (pH and temperature). The source of power was a 9-V lithium battery. The battery’s life is affected by the operating temperature (1 yr at 25°C) and times of data download and is not greatly affected by the frequency of recording. To facilitate data downloading without opening the box, the data logger was housed in a plastic waterproof box (Figure 1iGo) with an external input port. The box was mounted on the animal’s back using an adjustable belt fastened around the animal’s girth (Figure 1jGo).

The data logger could be configured (e.g., started, delay-started, stopped, or reset) and the data downloaded using a personal digital assistant (Palm Inc., Sunnyvale, CA; Figure 1kGo) equipped with Monarch PDA Software (version 1.0, Monarch Instrument, Amherst, NH). The estimated downloading time was approximately 1 min per 1,440 recordings, and the data were transferred to a desktop computer equipped with Data Recorder Software (version 2.0, Monarch Instrument) that could be used to calibrate the electrodes, synchronize the data from different loggers, display graphs, perform analysis (i.e., mean, SD, minimum, and maximum), or transfer data to other programs.

The software’s Calibration Wizard option was used to calibrate the pH and temperature simultaneously. Standard buffer solutions of pH 4.00 and 7.00 (Fisher Scientific, Fairlawn, NJ) were used for pH calibration. Temperature calibration was performed by using room temperature as the low-temperature calibration point (approximately 20°C), whereas factory calibration values were unchanged for the high-temperature calibration point (100°C).

The calibration of each electrode was performed individually by connecting each electrode to the computer and using the real-time recording option. Ruminal pH readings at each calibration point were allowed to equilibrate for approximately 5 min before recording. Calibration parameters were then recorded and stored in the loggers. At the end of each calibration, the electrodes were tested against standard buffers and temperature. A calibration was repeated if a difference greater than 0.03 pH unit or 0.2°C was detected. Calibrations were performed daily to eliminate pH drift.

Animal and Validation
The animal used in this experiment was cared for and handled in accordance with the Canadian Council on Animal Care Regulations, and the University of Guelph Animal Care Committee approved its use.

A nonlactating, rumen-fistulated, Holstein dairy cow, weighing 740 kg, housed in a tie-stall facility and offered alfalfa hay (DM basis; 12.5% CP, 60% NDF, 18% nonfiber carbohydrates) daily at 0800 and 1500 was used in the study. The cow was fitted with a continuous recording system, and ruminal pH was measured every 10 s for 3 d. Rumen fluid samples were obtained by aspiration through a 0.2-mm tube located near the electrode to ensure that spot samples were collected from the same location as the continuous recording electrode. Spot samples were collected 3 times per d for 3 d at 0900, 1300, and 1600. At every sampling time, three 50-mL vials were collected, and the pH was determined immediately using a handheld pH meter (pH 310, Oakton Instruments, Vernon Hills, IL). The pH values from the continuous system corresponding to each spot sample were obtained. Spot sampling pH readings were averaged (n = 3) to determine the pH for that sampling time and compared with the average (n = 3) of the continuous recording system. The location of the pH electrode in the rumen was checked each morning.

The pH, which is the –log of the hydrogen ion concentration ([H+]), has been used since the 1920s to represent the acidity of body fluids. A change in 1 unit of pH (i.e., from 6 to 5) indicates a 10-fold increase in [H+]. However, the [H+] data are not normally distributed; therefore, a log transformation is required to perform ANOVA.

Paired t-test using PROC MEANS (SAS Inst. Inc., Cary, NC) was used to test the significance of the differences between spot sampling and continuous recording. Correlation between continuous recording and spot sampling was performed using PROC CORR of SAS. Effects were considered significant at P < 0.05.


   RESULTS AND DISCUSSION
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
IMPLICATIONS
 LITERATURE CITED
 
The box holding the data logger mounted on the animal’s back stayed in place throughout the trial, and the animal showed no signs of discomfort as a result of the box or the belt. The electrode maintained its location in the ventral sac of the rumen throughout the trial. The mean pH for spot sampling was 6.63 ± 0.04 (n = 9), and the mean pH of continuous recording was 6.56 ± 0.03 (n = 9). The difference between the 2 methods was 0.07 ± 0.02 (P = 0.009). Correlation between continuous recording and spot sampling was high (r = 0.88, P = 0.002; Figure 2Go). Johnson and Sutton (1968)Go, McArthur and Miltimore (1968)Go, and Dado and Allen (1993)Go also have reported that in vitro pH measurements were greater than in vivo pH measurement by 0.2, 0.10, and 0.11 pH units; respectively. The difference in pH might be caused by the loss of CO2 (Smith, 1941Go) or other volatile compounds during collection of spot samples. Figure 3Go shows an example of a 24-h pH and temperature traces as displayed by the continuous recording system.


Figure 2
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  		Figure 2. The relationship between ruminal pH obtained using continuous recording and spot sampling. The dashed line represents unity. Spot sampling pH (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).

 

Figure 3
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  		Figure 3. An example of a 24-h pH (top trace) and temperature (bottom trace) traces as displayed by the software during d 1 of the experiment.

 
The advantage of using independent ruminal pH continuous recording unit (electrode and data logger combination) for each cow without relying on long cables was that it permitted mobility of cows during data acquisition; hence, cows could have access to exercise and milking without interruption. It also could minimize the loss of data as a result of central power malfunction. The continuous recording system combined with an appropriate feed intake recording system would enable researchers to measure and record ruminal pH under different management settings.


   IMPLICATIONS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 IMPLICATIONS
LITERATURE CITED
 
The continuous recording system described herein provides a reliable means to measure ruminal pH in cattle. It also has the potential to extend the use of continuous ruminal pH recording of cattle in free-roaming settings.


   Footnotes
 
1 The authors would like to thank the research technicians, University 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. Back

2 Corresponding author: bmcbride{at}uoguelph.ca

Received for publication February 16, 2006. Accepted for publication August 23, 2006.


   LITERATURE CITED
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 IMPLICATIONS
 LITERATURE CITED
 


Cooper, R. J., T. J. Klopfenstein, R. A. Stock, C. T. Milton, D. W. Herold, and J. C. Parrott. 1999. Effects of imposed feed intake variation on acidosis and performance of finishing steers. J. Anim. Sci. 77:1093–1099.[Abstract/Free Full Text]

Cottee, G., I. Kyriazakis, T. M. Widowski, M. I. Lindinger, J. P. Cant, T. F. Duffield, V. R. Osborne, and B. W. McBride. 2004. The effects of subacute ruminal acidosis on sodium bicarbonate-supplemented water intake for lactating cows. J. Dairy Sci. 87:2248–2253.[Abstract/Free Full Text]

Dado, R. G., and M. S. Allen. 1993. Continuous computer acquisition of feed and water intakes, chewing, reticular motility, and ruminal pH of cattle. J. Dairy Sci. 76:1589–1600.[Abstract]

Johnson, V. W., and J. D. Sutton. 1968. The continuous recording of the pH in the bovine rumen. Br. J. Nutr. 22:303–307.[Medline]

Keunen, J. E., J. C. Plaizier, L. Kyriazakis, T. F. Duffield, T. M. Widowski, M. I. Lindinger, and B. W. McBride. 2002. Effects of a subacute ruminal acidosis model on the diet selection of dairy cows. J. Dairy Sci. 12:3304–3313.

McArthur, J. M., and J. E. Miltimore. 1968. Continuous recording of the in vivo rumen pH in fistulated cattle. Can. J. Anim. Sci. 48:237–240.

Rustomo, B., O. AlZahal, J. P. Cant, M. Z. Fan, T. F. Duffield, N. E. Odongo, and B. W. McBride. 2006. Acidogenic value of feeds. II. Effects of rumen acid load from feeds on dry matter intake, ruminal pH, fiber degradability and milk production in the lactating dairy cow. Can. J. Anim. Sci. 86:119–126.

Smith, V. R. 1941. In vivo studies of hydrogen ion concentrations in the rumen of the dairy cow. J. Dairy Sci. 24:659–665.[Abstract/Free Full Text]


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