Radiosonde for Measuring Bovine Intraruminal Reticular Pressures

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JOURNAL

RADIOSONDE

OF D A I R Y S C I E N C E

FOR MEASURING BOVINE RETICULAR PRESSURES

Radio telemetry transmitters for measuring intraruminal pressures have been described by Wallace (3), Rahm (2), and Dracy (1). All of these units were frequency-modulated transmitters. Their lack of reliability resulting from long term drift is undesirable. I n addition, the repeatability of recordings is extremely difficult because of the need for two heterodyning stages in the receiver. A more sophisticated AM/F1V[ pressure transmitting unit has been designed and tested. This transmitter consists of three major components. The first is a potentiometric transducer which converts a change in pressure to a change in resistance. This resistor determines the frequency of an audio frequency oscillator. The audio frequency amplitude modulates a radio frequency in the range from 180 to 400 ke per second, in a manner similar to a broadcast radio station. The outside dimensions of the unit are one and one-eighth inches in diameter and eight inches in length. This is large enough to encase the mechanism, yet small enough to pass down the esophagus of a large cow so that it can be implanted into the rumen without surgery. The unit is not harmful to the esophageal lining and thus no ill effects have been encountered while placing the unit into the rumen. The unit is sufficiently heavy so that it sinks to the bottom of the rumen and gravitates with the aid of ruminal contractions into the reticuh m . I n this location it remains stationary and thus transmits the uniform pressures of the combined rumen and reticulum. The transmitter has the ability to send a signal approximately 20 ft. Thus, when the animal is in a pen with a three-dimensional loop antenna, accurate signals can be received and transferred via coaxial cable to the receiver and on to the a p p r o p r i a t e instruments. However, when testing the system the animal was kept in a stanchion. During these recordings a ferrite stick antenna was mounted on a belt placed around the animal's body; the signal was carried directly into the receiver. This antenna in no way inhibited the cow from

INTRARUMINAL

normal activity in a conventional stabling facility. Figure I depicts a block diagram of the physical arrangement of the additional equipment essential for recording rumen contractions. There are many brand names of equipment that can be used, but those available in this laboratory are as follows: The receiver is a W R 3000 Hallicrafters Receiver, capable of receiving signals between 180 and 400 kc. The transmitter fabricated transmits at 340 kc per second. The frequency meter is a Hewlett Packard 500 B. This is used to change the audio frequency to an electrical potential. The amplifier recorder in this system is a Model 964 Sanborn recorder. The amplifier is a DC amplifier, the same as the one used for recording ECG potentials. The oscilloscope and the frequency counter are both auxiliary facilities for determining the strength and stability of the signal received. A square wave pattern on the oscilloscope shows evidence of a stable signal. When more than one line is visible or when the line is wavy, this is evidence of outside interference. The frequency counter likewise counts the audio frequencies at the receiver output, thus enabling the operator to know when outside interference is sufficiently great to give incorrect readings. The sending unit was initially calibrated in a water-tight chamber, using a column of mercury as a standard. Figure 2 is the calibration curve obtained. This is used to obtain pressure data from frequency readings taken when the transmitter is in a cow's rumen. When recording analog data, it is possible to calibrate the recorder directly in terms of pressure. When this unit is calibrated, atmospheric pressure must be taken into consideration, because the

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Fro. 1. Block diagram of the receiving, recording, and auxilialT equipment.

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FIG. 2. Calibration curve of the audio frequency vs. pressure for an atmospheric pressure 30.35 in. of Rg.

TECHNICAL NOTES

base pressure in the rumen is equal to atmospheric pressure. F o r example, if the zero point is calculated at 30.1 in. of H g pressure and the atmospheric pressure drops to 29.1 in. of H g pressure, this must be compensated f o r in the recording. The data plotted in F i g u r e 2 were taken at the barometric pressure of 30.35 in. of tIg. The sending unit is slightly temperaturedependent. To minimize this effect the unit was calibrated at 40 C. This was previously found to be the mean t e m p e r a t u r e in the rumen of a normal cow. W h e n the recordings were being made the p a p e r was run at 0.5 mm p e r second. A representative tracing is shown in F i g u r e 3. I n this tracing, the baseline is atmospheric pressure and each m a j o r division is 11 mm I-Ig pressure. This figure shows the ruminal reticular con-

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of the rumen activity during rumination. The pressure and time scales are identical to those in F i g u r e 3. This unit has been tested repeatedly both in vivo and in vitro. F o r any constant pressure applied to the sending unit, the audio frequency remains constant with time, thus indicating no long-term drift. The calibration curve is repeatable and is the same for increasing pressure or decreasing pressure. Results of the in vivo tests are shown in F i g u r e s 3 and 4. A. E. DRACY D a i r y Science D e p a r t m e n t AND A. J . KURTElqBACH D e p a r t m e n t of Electrical Engineering South D a k o t a State University Brookings

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~m. 3. Record of rumina] reticular contractions while eating. Chart speed: 0.5 ram/see. Pressure scale: 22 mm Hg/cm. (5 r a m = 1 ~ a j o r division.) tractions during the normal eating cycle. Note that when the r u m i n a n t stomach contracts there are two sequential contractions. The first is of lesser m a ~ d t u d e than the second, but both are of similar duration. Furthermore, long-term recordings exhibit a highly u n i f o r m rate of contractions. The magnitude of the contractions during eating varies. The maxinmm pressure created by the ruminal muscle within the cow is a p p r o x i m a t e l y 70 mm of Hg. Another tracing, shown in F i g u r e 4, is typical : ...... V:~LLJ:;',"~',I~II~I:IrlI~!~

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REFERElqCES (1) DRACY, A. ]~., AND [ESSLEI~ W. O. 1964. Some Ruminal Reticular Pressures Recorded by Radio Telemetry. J. Dairy Sci., 47; 1428. (2) RAHI~[, ]~. L. 1961. The Design and Construetion of a Radio Telemetry Unit for the Study of Ruminal Pressures. M.S. thesis, South Dakota State College, December. (3) WALLACE, V., DRACY, A. E., AN]) OINES, R. K. 1959. A Radiosonde for Measuring Ruminal Pressure. Proc. South Dakota Aead. Sci., 38 : 146.

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:PIG. 4. Record of rumina] activity during rumination. Chart speed: 0.5 ram/see. Pressure scale : 22 mm ttg/em. (5 mm ----1 major division.)