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The primary-secondary rumen contraction and gas expulsion in sheep (Ovis Aries)
Camp. Biochem. Physiol.
Vol. 87.4, No. 4, pp. 993-1002, 1987
0300-9629/87$3.00+ 0.00 0 1987Pergamon Journals Ltd
Printed in Great Britain
THE PRIMARY-SECONDARY RUMEN CONTRACTION AND GAS EXPULSION IN SHEEP (OVIS ARIES) LAURA E. PERUZZODE NAVILLE*,HARRY W. Co~vm, JR? and ROBERTC. BACKUS Department of Animal Physiology, University of California, Davis, CA 95616, USA (Received 14 November 1986)
Abstract-l.
Sheep rumens were insuthated with nitrogen to 5, 10, 15 and 20 cm HOH pressure and sustained at each pressure for 5 min. 2. Measurements included rumen motility, reticulorumen myoelectrical activity, eructation frequency and volume, and changes in tracheal pressure. 3. Associated with elevated intrarumen pressure was a previously unreported type of rumen contraction on which gas expulsion occurred, the primary-secondary contraction. 4. Gas expulsion volume was similar on primary-secondary and secondary contractions. 5. The maximum rumen contraction rate per min was 45 for secondaries and 1-2 for primary-secondaries. 6. Irrespective of the sustained initial pressure, resting intrarumen pressure was reached within 5 min.
INTRODUCI’ION
placed in individual cages in a temperature-controlled room (20°C) with a lightdark cycle consisting of two twelve-hour periods, 6 a.m. to 6 p.m. and 6 p.m. to 6 a.m., respectively. The daily diet consisted of approximately one kg good quality hand-shredded alfalfa hay and 0.25 kg concentrate mixture (Fat Lamb Pellets, Farmers Warehouse B., Inc., P.O. Box 996, Modesto, CA 92672). Salt blocks and water were available ad libitum.
The effect of legume bloat on ruminal motility and eructation was studied by Colvin et al. (1958, 1978). Louvier et al. (1979) evaluated the effect of artificially elevated intrat-umen pressure on motility using a variety of gases. During the course of these studies,
great difficulty was encountered when it became necessary to differentiate between primary and secondary contractions when intrarumen pressure was elevated, despite the simultaneous measurement of eructation. In a preliminary report in which rumen motility and reticulorumen myoelectrical activity were studied, Colvin et al. (1982) observed a disappearance of motility and myoelectrical activity following insufflation of the reticulorumen with nitrogen to various pressures which were sustained for five minutes. Eructation was not measured. In view of the previous work, it will be the purpose of the experiments reported hereafter to study the effect of sustained elevated intrarumen pressure on rumen motility, reticulorumen myoelectrical activity, and eructation. The latter two parameters measured simultaneously greatly facilitated the differentiation of primary and secondary contractions and enabled us to describe the primary-secondary contraction, a new type of rumen contraction.
Surgical techniques To measure the volume of eructated gas, the tracheal transection technique described by Colvin er aI. (1957) as modified by Louvier (1978) and Fleming (1982). was used. Microelectrodes were implanted in the reticulum and rumen posterior ventral blind sac according to the according to the technique of Ruckebusch (1973). Three electrodes were placed at each position using Stabilohm 110 (80/20 Ni/Cr, Johnson Matthey Metals Limited, London). The electrodes were exteriorized through the wall of the left paralumbar fossa. A small fistula was established high in the dorsal sac of the rumen through the left paralumbar fossa. To keep the fistula open and to prevent the escape of rumen fluid, a Foley Catheter, Teflon coated, 22 Fr. (Cat. No. 21152-022, American Hospital Supply, 1450 Waukegan Road, McGraw Park, IL 60085) with an inflatable cuff was inserted in the fistula and inflated. A small plastic funnel was slipped over the exterior end of the catheter with the wide opening of the funnel oriented toward the body and pressed tightly against the flank. Tension was applied to the catheter and a small clip was placed on the catheter so that it rested on the tip of the funnel. This procedure served to keep the inflated cuff against the inside of the rumen wall and prevented fluid leakage.
MATERIALSAND METHODS Animals Four sheep (Oois arks) of mixed breeding, two males and two females, whose average weight was 43.8 f 2.2 kg, were
Rumen myoelectric activity The three electrodes from the posterior ventral blind sac of the rumen and the three from the reticulum were connected to two HiZ probes (Model HiPSllE, Grass Instrument Co., 101 Old Colony Road, Quincy, MA 02169). three electrodes to each probe. The.pr&es were connect& to a PS 11 Grass Instrument Amplifier and the signal relayed to a Beckman Type R Dynograph six-channel recorder (Beckman Instruments, Inc., 3900 River Road, Schiller
*In partial fulfillment for the MS. Degree, University of California, Davis, CA 95616, USA. Present address: Universidad National de Rosario, Facultad de Ciencias Veterinarias, 2170 Casilda (Sta. Fe), Republica Argentina. tTo whom correspondence should be addressed. 993
LAURA
994
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Park, IL 60176). The system was calibrated using a function generator, a TM 501 Power Module F6501 (Tektronix Inc., 2345 Stanwell Circle, Concord, CA 94520) and a 350C Attenuator (Hewlett-Packard, 1829 Embarcadero Road, Palo Alto, CA 94303). The function generator and attenuator were used to adjust the final output to a range of 0.2 to 0.5mV and a frequency of 10 Hz for calibration purposes. Intrarumen pressure changes The rumen canula was attached to a T-tube. One end of the T-tube was connected to a Statham Pressure Transducer (Model PMSTC +/- 0.5-350, Statham-Gould Instrument, Inc., 1633 Adrian Road, Burlingame, CA 94010) and the other end to a source of gas for insulIlation (Nitrogen, extra dry, Liquid Carbonics, 901 Embarcadero Street, Oakland, CA 94606). The pressure transducer was coupled to the Beckman Dynograph which in turn was connected in series to a two-channel Houston Omniscribe Recorder (Model 5231-15, Houston Instruments, One Houston Square at 8500 Rd., Austin, TX 78753). The system was calibrated with a water manometer. Changes in intrarumen pressure were recorded simultaneously on the Dynograph and Omniscribe recorders. Eructation
At the time of an experiment, the tracheal canula used to connect the ends of the transected trachea was replaced by one which assured separation of the gases associated with those of eructation from those of respiration. The anterior tracheal canula was connected to a three-way valve (R-738840, Cole-Parmer Instrument Co., 7425 North Oak Park Ave., Chicago, IL 60648) which led to a gas flowmeter (Wright Respirometer, Type PM. Mannee Medical, 3399 Mt. Diablo Blvd., Lafayette, CA 94549) used to measure the gas eructated. To detect rumen gas which might be expelled via the mouth and/or external nares, a mask was placed over the muzzle; tubing connected the mask to another three-way valve and flowmeter.
NAVILLEet al.
Tracheal Pressure Changes
To indicate pressure changes in the anterior and posterior tracheal canulas, pressure transducers (Model PM6TC +/l-350, StathamGould Instrument, Inc.) were connected to ports in the respective canulas. Changes in pressure were recorded on the Dynograph. Rumen insuflation
Extra dry nitrogen was introduced into the rumen through the rumen canula using a two stage gas regulator (Model S-350, Matheson Gas Products, 6775 Central Ave., Newark, CA 94580). Trial procedure
Each trial began with a 15min control period during which were recorded myoelectric activity of the reticulum and rumen posterior ventral blind sac, changes in intrarumen pressure, i.e. rumen motility, gas eructated through the anterior tracheal canula and mask, and changes in pressure in the anterior and posterior tracheal canulas. Immediately following the control period, the valves leading from the anterior tracheal canula and the mask were closed to prevent the escape of gas when nitrogen insufflation was begun. Insufflation to a predetermined pressure was maintained for five min. All parameters except gas expulsion were recorded during the insufflation period. After the insufflation period, the valves leading from the anterior tracheal canula and the mask were opened and gas expulsion measured along with the other parameters until the resting intrarumen pressure reached preinsufflation levels. Insufflation pressures sustained included 5, 10, 15 and 20 cm HOH. After each 2Ocm HOH trial, there was a 15 min control period during which all parameters were recorded. RESULTS A typical recording of all the parameters, except eructation, made during the control period is shown in Fig. 1A. Rumen motility is shown in Record 4
Fig. 1. Rumen motility and associated events during the: (A) pre-insufflation period; (B) 0 to 1.5 min of the post-insu!Ilation control period; and (C) the terminal 1.5 min of the post-insufhation control period. The post-insufflation control period began 10 min following the termination of insufflation to a pressure of 20 cm HOH. Legend: 1, respiration; 2, pressure changes in the anterior tracheal cannula; 3, reticular myoelectric activity; 4, intrarumen pressure; 5, posterior ventral blind sac myoelectric activity; a, respiratory activity during eructation; b, pressure in the anterior tracheal cannula during eructation; c, myoelectrical spiking in the reticulum associated with reticular contraction; d, myoelectrical spiking in the posterior ventral blind sac; p, primary (mixing) contraction; s, secondary (eructation) contraction; ps, primary-secondary contraction.
Rumen gas expulsion in sheep
,
1 min.
995
I
Fig. 2. (A) Rumen motility and associated events during insufflation of nitrogen to a pressure of 5 cm HOH; and (B) 1Ocm HOH. Legend: See Fig. 1.
where “p” refers to a primary (mixing) contraction
and “s” to a secondary (eructation). Record 3, c, shows the myoelectrical spiking of the reticulum associated with each primary contraction and Record 5, d, to myoelectrical activity of the posterior ventral blind sac (PVBS) related to primary and secondary contractions. Associated with each secondary contraction was a change in pressure in the anterior tracheal canula (Record 2, b) which resulted from the passage of gas from the esophagus through the anterior tracheal canula during eructation. The change in respiratory activity during eructation associated with the secondary contraction is shown in Record 1, a. When the intrarumen pressure was elevated to 5 cm HOH and sustained at this level for 5 min, a new type of rumen contraction appeared (Fig. 2A, ps). We have called these contractions “primary-secondary”. The electrical activity associated with the primarysecondary (ps) contraction began in the reticulum (Fig. 2A, Record 3, c) and from this aspect, was similar to the primary contraction (Fig. IA, Record 3, c; Record 4, p). The second phase of the ps contraction (Fig. 2A, Record 4, ps; Record 1, a; Record 2, b) involved events common to the secondary contraction, i.e. an alteration of respiration (Fig. lA, Record 1, a), pressure changes in the anterior tracheal canula (Fig. lA, Record 2, b), and gas flow through the flowmeter. During the insufllation period, the contractions were either ps or secondaries. When the intrarumen pressure was increased to 10 (Fig. 2B), 15 (Fig. 3A), and 20 (Fig. 3B) cm HOH by the insufflation of nitrogen and sustained at each pressure for 5 min, there was a dramatic increase in the frequency of secondary contractions. As resting intrarumen pressure (RIP) increased, respiration be-
came more depressed and electrical activity in the PVBS increased in frequency and amplitude. Accompanying each ps and secondary contraction during the insufflation period, eructated gas reached the anterior tracheal canula as shown by the pressure changes signalled by the attached pressure transducer (Record 2, Figs 2B, 3A, 3B). However, gas escape was prevented by the closed valves at the mask and anterior tracheal canula. When RIP was maintained at 2Ocm HOH, there was a gradual increase in the incidence of coughing (Fig. 3B, Record 4, e), an apparent attempt to increase the efficiency of gas expulsion. Immediately following the insufflation period the valves between the flowmeters and the mask and anterior tracheal canula were opened and the volume of gas expelled during eructation measured. Figs 4A, 4B, 5A and SB refer to events during the first 1.5 min of deflation following insufflation to 5, 10, 15 and 20cm HOH, respectively. All contractions were either ps or secondaries; gas expulsion accompanied each contraction. Figures 6A, 6B, 7A and 7B represent the last 1.5 min of the deflation period of the 5, 10, 15 and 20 cm HOH insul?Iation trials, respectively. Each deflation period was approximately 7 min in duration. Infrequently, primary contractions appeared during the deflation period, e.g. Figs 6B and 7A, Record 4, p. The absence of a pressure change in the anterior tracheal canula (Figs 6B and 7A, Record 2, b) and lack of respiration interruption (Figs 6B and 7A, Record 1, a) verify the primary contraction. The first 1.5 min and the last 1.5 min of the 15 min post-insufflation control period of the 2Ocm HOH trial are shown in Figs 1B and lC, respectively. There was evidence of a carry-over effect of insufflation in
LAURA E. PERUZ~O DE NAVILL.Eet a/.
996
1 min. e
4
Fig. 3. (A) Rumen motility and associated events during ins~ation of nitrogen to a pressure of 15 cm HO& and (B) 20cm HOW. Legend: See Fig. I.
the first minute as illustrated by the presence of a ps contraction (Fig. lB, Record 4, ps). By the end of the period, primary contractions replaced all ps contractions (Fig. IC, Record 4, p). The effect of RIP on the frequency of primary, ps, secondary, and total rumen contractions is shown in Fig. 8. The data used in the calculation of these
regressions came from the insufflation periods of each trial, i.e. 5, 10, 15 and 2Ocm HOH. All trials were pooled and a mean calculated for each pressure level. The means were used to calculate the regressions. A third degree polynomial best expressed the data for the secondary, ps, and total contraction frequencies. The decline in the primary contractions with in-
b
,
1
min.
I
20 P’ J-k-10 d
10
p*
‘
,
*
P’
I
’ 4--
d
Fig. 4. (A) Rumen motility and associated events 1 to 3 min following termination of rumen insufflation with nitrogen to a pressure of 5 cm HOH; and (B) 10 cm HOH. Legend: See Fig. 1.
Rnmen gas expulsion in sheep
997
2
1 min.
dd
dd
d
d
d
4
d
d
SO
Fig. 5. (A) Rumen motility and associated events I to 3 min following termination of the ins~tion nitrogen to a pressure of 15cm HOH; and (R) 20 cm HOH. Legend: See Fig. i _
creasing pressure was linear. The various regressions used to plot Fig. 8 are as follows:
contractions
Y = 0.79 - 0.028X + 0.012X2 - 0.~39~3,
Primary contractions Y=O.iS-0.01X,
primary-secondary
of
_+s,,=O.O6,
r=-0.80;
f svX= 0.09,
R2 = 0.99;
b
d
Fig. 6. (A) Rumen motility and associated events 7.5 to 9 mitt following termination of rumen in&I&ion with nitrogen to a pressure of 5 em HOH; and (El) 4.5 to 6 min following the termination of rumen in&Ration to IOctn HOH. Legend: See Fig. I.
b, I’
1 min,
-m-
20 P -0
‘
10
P’ 4
d
5_____
d
Fig. 7. (A) Rumen motility and associated events 7.5 to 9 min following termination and the insuflation of nitrogen to a pressure of 15cm HOH; and (B) 20 cm HOH. Legend: See Fig. 1.
secondary contractions
total contractions
Y = - 1.3 + 0.66X -0.021X2 + s,, = 0.14,
+ 0.00011X~,
R2 = 0.99;
+_s,,=O.ll,
60-
50 -
PRIMARY-SECONDARY
/’
/
-..-..-..-
5
0 Resting
.._..
_..
10
lntrarumen
Y = -0.68 + 0.76X - 0.022X2 + 0.000071X3,
15 Pressure
1
20
km Hz01
Fig. 8. The effect of resting intrarumen pressure on the frequency of primary, primary-secondary, secondary and total rumen contractions.
R*=0.99.
As RIP increased, there was an increase in the frequency of the secondary and ps contractions and a rapid decline in the number of primaries. The maximum frequency for ps and secondary contractions was reached when RIP was approximately 20 cm HOH. Within 5 min following the termination of insufflation, the intrarumen pressure had returned to a level which was no longer stressful to the sheep (Fig. 9). For the purpose of comparing the rate of decline in RIP from the maximum insufflation values of 5, 10, 15 and 20 cm HOH pressure, the curvilinear data for the first 5 min were forced to linearity (Fig. 10). The slope for the 5 cm HOH trials differed significantly from the slopes of the 10, 15 and 20 cm HOH trials (p c 0.001). The slope for the 1Ocm HOH trials was significantly different from the slopes for the 15 and 20 cm HOH trials (p < 0.001). The difference between the slopes for the 15 and 20 cm HOH trials was significant at the 10% level. Thus, the higher the initial insufflation pressure, the more rapid the rate of decline. The effect of insufflation pressure on the volume of gas eructated during the first 5 min of deflation is shown in Fig. 11. As would be expected, higher insufflation pressures resulted in more gas to be eructated. When the RIP exceeded 5 cm HOH, the volume of gas eructated on ps and secondary contractions was similar. By 5 min, the RIP was essentially at the pre-insufflation level irrespective of the insufflated pressure (Fig. 9).
Rumen gas expulsion in sheep -18 S
N I
0 _i E
16
999
5 cm H,O r/.5.07- .95X*.06X2-2.39X',*sr ' .16), A'=.99
-10
cm H,O fY* 10.0-2.66X+.30X2 -9,63X',ts,, * .32), R".QQ . \ -..-15cmH,O(Y.14.0-4.52X*.51X2.02X'+ *.92),R2'.96 \-.-20
cm H,O (Y.16.7-6.53X+.74X2 - .03X',%, 1.30),R's.97 5000-
i
14
\
4000-
? E In A 3000r g '5 ?I ?zooow t 0
A ./
IOOO-
time
(mm)
Fig. 9. Effect of the level of resting intrarumen pressure (cm HOH) following the ins&Ration of nitrogen on the rate of return of intrarumen pressure to pre-insufflation levels.
E
1 0
I
5
Resting
The volume of gas expelled (ml) through the mask and trachea on ps and secondary contractions from all trials, i.e. 5, 10, 15 and 20 cm HOH, inclusive, for
each parameter for all sheep was pooled and means and SE’s calculated, as follows: mask ps 117 -+ 33.1, -
5 cm Hz0 (v- 4.91- .61X.+sy, s .061), I = -.96 10 cm H,O (v* Q.Ql- 1.57X,'+ . 1.37), r . -.97
-..-
15 cm H,O (Y‘13.26-2.45X.tsl, . 1.79), r . -.94
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20 cm H,O @.16.44- 3.24X,=sy, . 2.96), I = -.92
PRIMARY-SECONDARY
IO
I5
lntrarumen Pressure (cm
20 H20)
Fig. 11. The effect of resting intrarumen pressure on the volume of gas expelled during the first 5 min of deflation for primary-secondary and secondary rumen contractions. The total gas expelled is also shown.
trachea ps 1885 + 239; mask secondary 74 _+24, trachea secondary 2023 _+315. Neither the difference between the means for the volume of gas expelled into the mask during ps and secondary contractions nor the difference between the means for the volume of gas expelled from the trachea was statistically significant. Thus, the volume of gas which escaped from the mouth into the mask during ps and secondary contractions was less than 10% of the total gas expelled on each type of contraction. DISCUSSION
I
,
0
I
2
3
4
J
5
Time (mm)
Fig. 10. Effect of the level of resting intrarumen pressure following the insufaation of nitrogen on the deflation rate during the first 5 mm of deflation. The curvilinear data from Fig. 9 for the first 5 rain of deflation were forced to linearity.
Contractions of the reticulorumen have only two purposes, the mixing and propulsion of ingesta and the movement of gas to the cardiac orifice for expulsion. The mixing contraction is referred to as the primary and the eructation contraction, the secondary. During normal resting rumen motility there is no difficulty in differentiating the primary from the secondary contractions (Fig. IA, Record 4). However, during elevated intrarumen pressure (Fig. 3B, Record 4) deciding which is a primary contraction and which a secondary, is difficult. The use of the transected tracheal technique for measuring the volume of eructated gas (Colvin et al., 1957) made it considerably easier to identify secondary contractions since eructation, under normal conditions, occurs on every secondary contraction (Colvin et al., 1958; Ruckebusch and Tomov, 1973). On the other hand, it has been reported that eructation occurred frequently on primary contractions (Akester and Titchen, 1969; Reid and Cornwall,
1000
LAURA E. PERLJZZO DE NAVILLEet al.
1959; Stevens and Sellers, 1959) or in the absence of rumen contractile activity (Akester and Titchen, 1969; Reid, 1960; Reid and Cornwall, 1959). More recently, during rumen insufflation studies in sheep (Louvier et al., 1980), frequent gas expulsion was observed on “special primary contractions”. It was apparent that more definitive methods were essential to ascertain the incidence of eructation and on which contraction, or absence thereof, the event occurs. Ruckebusch and Tomov (1973) have shown that primary contractions are preceded by electrical activity in the reticulum and secondary contractions by electrical activity in the posterior ventral blind sac. Therefore, electrodes were implanted at these sites in the sheep used in these experiments (Fig. 1, Records 3 and 5). Since it has been shown that eructated gas is inhaled into the trachea during an inspiratory effort (Colvin et al., 1957; Dougherty and Cook, 1962), respiratory events associated with eructation were demonstrated in our experiments by connecting a pressure transducer to the posterior tracheal canula (Fig. 1, Record 1, a). To indicate that gas expulsion was being attempted during rumen insufflation with the anterior tracheal canula blocked, a pressure transducer was connected to the canula proximal to the site of the anterior tracheal valve (Fig. 1, Record 2, b). Using the above procedures simultaneously, there was no difficulty in identifying primary and secondary contractions under normal conditions (Fig. 1). Every primary contraction was preceded by reticular electrical activity (Fig. 1, Record 3, c) and followed by PVBS electrical activity (Fig. 1, Record 5, d). The secondary contractions (Fig. 1, Record 4, s) were: (a) preceded by PVBS electrical activity (Fig. 1, Record 5, d), (b) associated with pressure changes in the anterior tracheal canula as eructated gas passed through (Fig. 1, Record 2, b), and (c) related to the interruption of respiration (Fig. 1, Record 1, a). These same criteria were also used successfully to identify primary and secondary contractions during elevated intrarumen pressure (Fig. 3B, Record 4). When resting intrarumen pressure was elevated to only 5 cm HOH by the insufflation of nitrogen, rumen gas expulsion began to occur on what appeared to be regular primary contractions when deflation was permitted (Fig. 4A, Record 4, ps). Reticular electrical activity (Fig. 4A, Record 3, c) indicated that they were indeed primary contractions. Gas expulsion was substantiated by pressure changes in the anterior tracheal canula (Fig. 4A, Record 2, b) and an interruption of respiration (Fig. 4A, Record la); furthermore, the volume of gas expelled was measured with the flowmeter. Thus, the measurement of gas expulsion on primary contractions would appear to support previous reports (Akester and Titchen, 1969; Reid and Cornwall, 1959; Stevens and Sellers, 1959). This raises the question, “Are these primary contractions on which gas expulsion had occurred following rumen insuffIation in fact ‘regular’ primary contractions?’ The complex nature of the eructation reflex is well documented and involves the close coordination of
reticulorumen musculature (Colvin et al., 1958; Weiss, 1953; Wester, 1926), muscles of the cardiac orifice and esophagus (Dougherty and Habel, 1955; Dougherty and Meredith, 1955) and the abdominal wall (Cole et al., 1942; Reid, 1960). On the other hand, Wester (1926) observed that the cardiac orifice is pulled slightly open during the primary contraction and it is not difficult to hypothesize that if the resting intrarumen pressure is sufficiently elevated, gas could escape on a primary contraction and be expelled into the environment directly via the mouth and external nares because the reflex activity of the glottis and inspiratory muscles associated with normal eructation would be absent. Because of the events in the anterior tracheal canula (Fig. 4A, Record 2, b), the inhibition of normal respiratory activity (Fig. 4A, Record 1, a), and the large amount of gas expelled, all events associated with the reflex act of eructation, the primary contractions associated with gas expulsion in these experiments cannot be viewed as “regular” primary contractions. In other words, part of these contractions was primary and part secondary. How then does one explain these special “primary-secondary” contractions? According to Ruckebusch and Tomov (1973), the electrical activity of the reticulorumen during during a primary contraction proceeds as follows: reticulum, dorsal sac, posterior dorsal blind sac, ventral sac, and posterior ventral blind sac. Electrical activity of the secondary contraction occurs as follows: posterior ventral blind sac, posterior dorsal blind sac, dorsal sac, ventral sac, and posterior ventral blind sac. Observing the primary-secondary (ps) contraction closely (Fig. 4A, Record 4, ps) it can be seen that the relaxation phase or descending segment of this contraction is not smooth. Rather, the relaxation begins but then is interrupted, at which time, the pressure elevates sharply again followed by a smooth decline to the resting pressure level, a biphasic contraction. In every case, on these ps contractions, gas expulsion occurred at the peak of the pressure re-elevation. It is postulated that the electrical activity of these ps contractions occurs as follows; reticulum, dorsal sac, posterior dorsal blind sac (the primary component), then posterior dorsal blind sac again, dorsal sac (eructation), ventral sac and posterior ventral blind sac. The electrical activity in the reticulum (primary component) followed by the pressure activities shown in the anterior tracheal canula, and the interruption of respiration (secondary component) shown in Fig. 4A, associated with the ps contraction, supports such a postulate. It would now appear that the eructations observed on primary contractions by other workers (Akester and Titchen, 1969; Reid and Cornwall, 1959; Stevens and Sellers, 1959) are in fact eructations associated with these ps contractions. Because we recorded simultaneously rumen myopressure, pressure electrical activity, intrarumen changes in the anterior and posterior trachea, and eructation frequency and volume, it was possible to clearly differentiate the various types of rumen contractions (Fig. 3A). As intrarumen pressure increased (Fig. 8), the primary contractions were converted t( ps contractions and were associated with gas expul
1001
Rumen gas expulsion in sheep
sion via the normal route for eructated gas, i.e. aspiration into the trachea (Colvin et al., 1957; Dougherty and Cook, 1962). When RIP reached approximately IOcm HOH, ordinary primary contractions as such had disappeared. Whereas, others have shown the increase in rumen contraction frequency with increasing intrarumen pressure (Colvin et al., 1959 and 1978; Louvier et al., 1979; Weiss, 19X3), the maximum contraction frequency has only been alluded to (Colvin and Horn, 1983). Our experiments indicated a maximum secondary contraction frequency when the intrarumen pressure reached approximately 20 cm HOH. For the ps contractions, the maximum rate occurred when the intrarumen pressure was approximately 15 cm HOH (Fig. 8). The maximum frequency for secondary contractions was betwen 4-5/min and for ps, approximately Z/min. Presumably, refractory periods in the motility center and/or rumen musculature made a further increase in motility improbable. From Figs 9 and 10, it is clear that by 5min following the cessation of insufflation, the intrarumen pressure was similar for all experiments. However, the higher the initial insufflation pressure, the more rapid the rate of deflation. It is reasonable to expect the cardiac orifice to be open a finite period of time during the eructation reflex. Thus, with the cardiac orifice open, the higher the intrarumen pressure, the greater the pressure gradient, and the greater the volume of eructated gas; therefore, a more rapid rate of pressure decline. In addition, it must be recognized that elevated RIP was associated with large volumes of gas expelled on ps contractions (Fig. 11). This finding, coupled with the more rapid rate of secondary contractions associated with elevated RIP (Fig. 8) can explain the more rapid rate of deflation associated with elevated RIP. The effect of RIP on the volume of gas expelled is shown in Fig. 11. In the long term, secondary contractions were more important than ps contractions in the reduction of intrarumen pressure because there were more of them (Fig. 8). However, gas expulsion on ps contractions was important during the initial reduction of elevated intrarumen pressure (Figs 8, 9, 10) since equal volumes of gas were shown to be expelled on ps and secondary contractions during the first 5 min of deflation. Apparently, the efficiency of eructation on ps contractions was enhanced by the sustained intrarumen pressure associated with the biphasic nature of this contraction (Fig. 4). The second phase of the biphasic contraction occurred while the intrarumen pressure was already elevated; thus, the summation effect could allow the escape of more gas during eructation. Possibly, the rapid recovery from acute legume bloat in ruminants following the intraruminal administration of an anti-frothing agent (Colvin et al., 1959) is a function of eructation during ps contractions. Reid and Cornwall (1959) and Sellers and Stevens (1966) have reported eructations on mixing (primary) and eructation (secondary) contractions. The former also alluded to eructation in the absence of rumen contractions and increasing eructations on primary contractions by insufflating 8-10 1 gas/min into the rumen of cows. Neither of these reports mentioned quantitative measurements of gas expulsion. In view C.B.P. *,,,A-‘
of our findings, the eructations these workers observed during primary contractions were probably eructations during ps contractions. Contrary to the reports of Reid and Cornwall (1959) and Akester and Titchen (1969), we have not recorded gas expulsion without a concomitant rumen contraction, even when RIP was elevated. In their eructation measurements, Dougherty and Cook (1962) reported that in one cow, 13.6% of expelled gas escaped via the mask and in another cow, 30.5% by-passed the trachea and escaped via the mask. In our work, the volume of gas escaping from the mouth and mask following insufflation was measured during primary, primary-secondary, and secondary contractions; the volume was found to be slight, i.e. less than lo%, and followed no particular pattern, an almost incidental event. In two of our four sheep, no gas was recorded from the mask until RIP reached 15 cm HOH. Our work indicates that three rather than two types of rumen contractions exist in sheep: primary, primary-secondary (ps), and secondary. The ps contractions appear when RIP is elevated and become increasingly important for gas expulsion as RIP increases. SUMMARY
Rumen motility and eructation trials were conducted on four sheep. To evaluate motility, a canula was placed in the dorsal sac of the fistulated rumen and myoelectrodes were implanted in the reticulum and posterior ventral blind sac (PVBS). To study the events associated with eructation, the trachea was transected and cannulated. A transducer was installed in the anterior tracheal canula to determine pressure changes. Respiration was evaluated by placing a pressure transducer in the posterior tracheal canula. Flowmeters attached to the anterior tracheal canula and the muzzle mask measured the volume of eructated gas. The rumen was insufflated with nitrogen to pressures of 5, 10, 15 and 2Ocm HOH; each level was sustained for 5 minutes. When the resting intrarumen pressure (RIP) was normal, primary contractions of the rumen were preceded by reticular myoelectric activity and ended with myoelectric activity in the PVBS. Secondary contractions were preceded by myoelectric activity in the PVBS and followed by a pressure change in the anterior tracheal canula; also, there was an interruption of normal respiration and a flow of gas through the anterior tracheal flowmeter. When RIP was elevated by insufflating nitrogen, the frequency of primary and secondary contractions increased, with the secondary contractions increasing at a more rapid rate than the primaries. Gas expulsion occurred in association with primary contractions when RIP reached 5 cm HOH. The primary contractions became biphasic in appearance with gas expulsion at the peak of the second phase. Associated with gas expulsion on the primary contraction was a pressure change in the anterior tracheal canula, an interruption of respiration, and a flow of gas through the flowmeter; these events were the same as those associated with a secondary contraction. The first phase of the primary contraction began with myo-
LAURA
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E. PERUZZODE NAVILLE et al.
electric activity in the reticulum. As the result of these events, when gas expulsion occurred on a primary contraction, the contraction was referred to as a “primary-secondary” contraction. Irrespective of the initial insuiation pressure, RIP became normal within 5 minutes of the beginning of deflation. The higher the initial RIP, the more rapid the return of pressure to normal. The more the rapid decline in RIP was a function of an increased number of secondary contractions and a high volume of gas expulsion on primary-secondary contractions. During the first 5 minutes of deflation, equal volumes of gas were expelled on primary-secondary and secondary contractions. Less than 10% of the total gas eructated was via the mouth. The evidence presented indicates the existence in sheep of three rather than two types of rumen contractions; primary, secondary, and primarysecondary. Gas expulsion occurred on both the secondary and primary-secondary contractions.
REFERENCES
Akester A. R. and Titchen D. A. (1969) Radiographic studies of the reticula-rumen in the sheep. J. Anar. 104, 137-151. Cole H. H., Mead S. W. and Kleiber M. (1942) Bloat in Cattle. Calif. Agric. Exp. Sra. Bull. 662. Colvin H. W. Jr, Boda J. M. and Wegner T. (1959) Studies on the experimental production and prevention of bloat in cattle. III. The effect of vegetable oil and animal fat on acute legume bloat. J. Dairy Sci. 42, 333-345. Colvin H. W. Jr, Bueno L. and Ruckebusch Y. (1982) Elevated intrarumen pressure and rumen myoelectric activity in sheep. J. Dniry Sci. 65 (Suppl. l), 193. Colvin H. W. Jr, Cupps P. T. and Cole H. H. (1958) Dietary influences on eructation and related ruminal phenomena in cattle. J. Dairy Sci. 41, 1565-1579. Colvin H. W. Jr, Digesti R. D. and Louvier J. A. (1978) Effect of succulent and nonsucculent diets on rumen motility and pressure before, during, and after eating. J. Dairy Sci. 61, 1414-1421.
Colvin H. W. Jr and Horn G. W. (1983) The significance of ruminal motility in the etiology of bloat. Okla. State Univ. MP-115, pp. 165-195. Colvin H. W. Jr, Wheat J. D., Rhode E. A. and Boda J. M. (1957) Technique for measuring eructated gas in cattle. J. Dairy Sci. 40, 492-502.
Dougherty R. W. and Cook H. M. (1962) Routes of eructated gas expulsion in cattle. A quantitative study. Am. J. Vet. Res. 23, 997-1000. Dougherty R. W. and Habel R. E. (1955) The cranial esophageal sphincter. Its action and its relation to eructation in sheep as determined by cinefluorography. Cornell Vet. 45, 459464. Dougherty R. W. and Meredith C. D. (1955) Cinefluorographic studies of the ruminant stomach and of eructation. Amer. J. Vet. Res. 16, 96100. Flemina P. (1982) Effects on rumen motilitv and eructation in sheep fed diets differing in physical form. MS. Thesis. Univ. of Calif., Davis. Louvier J. A. (1978) Effect of rumen insufflation on ruminal motility. M.S. Thesis, Univ. of Calif., Davis. Louvier J. A., Colvin H. W. Jr and Fleming P. (1980) Unpublished data. Louvier J. A., Colvin H. W. Jr, lshizaki G., Iwamoto G. A. and Parker H. R. (1979) Effect of rumen insufflation on ruminal contraction rate in sheep. J. Animal Sci. 48, I.
I
934-940.
Reid C. S. W. (1960) Eructation and rumen movements in sheep. J. Physiol. 153, 394OP. Reid C. S. W. and Cornwall J. B. (1959) The mechanical activity of the reticula-rumen of cattle. Proc. N.Z. Sot. Animal Prod. 19, 23-35.
Ruckebusch Y. (1973) L’electromyographie globale des muscles lisses a partir d’electrodes chroniques intraparietales souples. Rev. Med. Vet 124, 1407-1434. Ruckebusch Y. and Tomov T. (1973) The sequential contractions of the rumen associated with eructation in sheep. J. Physiol. 235, 447458. Sellers A. F. and Stevens C. E. (1966) Motor functions of the ruminant forestomach. Physiol. Rev. 46, 634-661. Stevens C. E. and Sellers A. F. (1959) Studies of the reflex control of the ruminant stomach with special reference to the eructation reflex. Amer. J. Vet. Res. 20, 461482. Weiss K. E. (1953) Physiological studies on eructation in ruminants. Ondersteioort .f Vet. Res. 26, 251-283. Wester J. (1926) Die Physiologie und Pathologic &r Vormagen beim Rinde. R. Schoetz, Berlin.
Vol. 87.4, No. 4, pp. 993-1002, 1987
0300-9629/87$3.00+ 0.00 0 1987Pergamon Journals Ltd
Printed in Great Britain
THE PRIMARY-SECONDARY RUMEN CONTRACTION AND GAS EXPULSION IN SHEEP (OVIS ARIES) LAURA E. PERUZZODE NAVILLE*,HARRY W. Co~vm, JR? and ROBERTC. BACKUS Department of Animal Physiology, University of California, Davis, CA 95616, USA (Received 14 November 1986)
Abstract-l.
Sheep rumens were insuthated with nitrogen to 5, 10, 15 and 20 cm HOH pressure and sustained at each pressure for 5 min. 2. Measurements included rumen motility, reticulorumen myoelectrical activity, eructation frequency and volume, and changes in tracheal pressure. 3. Associated with elevated intrarumen pressure was a previously unreported type of rumen contraction on which gas expulsion occurred, the primary-secondary contraction. 4. Gas expulsion volume was similar on primary-secondary and secondary contractions. 5. The maximum rumen contraction rate per min was 45 for secondaries and 1-2 for primary-secondaries. 6. Irrespective of the sustained initial pressure, resting intrarumen pressure was reached within 5 min.
INTRODUCI’ION
placed in individual cages in a temperature-controlled room (20°C) with a lightdark cycle consisting of two twelve-hour periods, 6 a.m. to 6 p.m. and 6 p.m. to 6 a.m., respectively. The daily diet consisted of approximately one kg good quality hand-shredded alfalfa hay and 0.25 kg concentrate mixture (Fat Lamb Pellets, Farmers Warehouse B., Inc., P.O. Box 996, Modesto, CA 92672). Salt blocks and water were available ad libitum.
The effect of legume bloat on ruminal motility and eructation was studied by Colvin et al. (1958, 1978). Louvier et al. (1979) evaluated the effect of artificially elevated intrat-umen pressure on motility using a variety of gases. During the course of these studies,
great difficulty was encountered when it became necessary to differentiate between primary and secondary contractions when intrarumen pressure was elevated, despite the simultaneous measurement of eructation. In a preliminary report in which rumen motility and reticulorumen myoelectrical activity were studied, Colvin et al. (1982) observed a disappearance of motility and myoelectrical activity following insufflation of the reticulorumen with nitrogen to various pressures which were sustained for five minutes. Eructation was not measured. In view of the previous work, it will be the purpose of the experiments reported hereafter to study the effect of sustained elevated intrarumen pressure on rumen motility, reticulorumen myoelectrical activity, and eructation. The latter two parameters measured simultaneously greatly facilitated the differentiation of primary and secondary contractions and enabled us to describe the primary-secondary contraction, a new type of rumen contraction.
Surgical techniques To measure the volume of eructated gas, the tracheal transection technique described by Colvin er aI. (1957) as modified by Louvier (1978) and Fleming (1982). was used. Microelectrodes were implanted in the reticulum and rumen posterior ventral blind sac according to the according to the technique of Ruckebusch (1973). Three electrodes were placed at each position using Stabilohm 110 (80/20 Ni/Cr, Johnson Matthey Metals Limited, London). The electrodes were exteriorized through the wall of the left paralumbar fossa. A small fistula was established high in the dorsal sac of the rumen through the left paralumbar fossa. To keep the fistula open and to prevent the escape of rumen fluid, a Foley Catheter, Teflon coated, 22 Fr. (Cat. No. 21152-022, American Hospital Supply, 1450 Waukegan Road, McGraw Park, IL 60085) with an inflatable cuff was inserted in the fistula and inflated. A small plastic funnel was slipped over the exterior end of the catheter with the wide opening of the funnel oriented toward the body and pressed tightly against the flank. Tension was applied to the catheter and a small clip was placed on the catheter so that it rested on the tip of the funnel. This procedure served to keep the inflated cuff against the inside of the rumen wall and prevented fluid leakage.
MATERIALSAND METHODS Animals Four sheep (Oois arks) of mixed breeding, two males and two females, whose average weight was 43.8 f 2.2 kg, were
Rumen myoelectric activity The three electrodes from the posterior ventral blind sac of the rumen and the three from the reticulum were connected to two HiZ probes (Model HiPSllE, Grass Instrument Co., 101 Old Colony Road, Quincy, MA 02169). three electrodes to each probe. The.pr&es were connect& to a PS 11 Grass Instrument Amplifier and the signal relayed to a Beckman Type R Dynograph six-channel recorder (Beckman Instruments, Inc., 3900 River Road, Schiller
*In partial fulfillment for the MS. Degree, University of California, Davis, CA 95616, USA. Present address: Universidad National de Rosario, Facultad de Ciencias Veterinarias, 2170 Casilda (Sta. Fe), Republica Argentina. tTo whom correspondence should be addressed. 993
LAURA
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PERUZZO DE
Park, IL 60176). The system was calibrated using a function generator, a TM 501 Power Module F6501 (Tektronix Inc., 2345 Stanwell Circle, Concord, CA 94520) and a 350C Attenuator (Hewlett-Packard, 1829 Embarcadero Road, Palo Alto, CA 94303). The function generator and attenuator were used to adjust the final output to a range of 0.2 to 0.5mV and a frequency of 10 Hz for calibration purposes. Intrarumen pressure changes The rumen canula was attached to a T-tube. One end of the T-tube was connected to a Statham Pressure Transducer (Model PMSTC +/- 0.5-350, Statham-Gould Instrument, Inc., 1633 Adrian Road, Burlingame, CA 94010) and the other end to a source of gas for insulIlation (Nitrogen, extra dry, Liquid Carbonics, 901 Embarcadero Street, Oakland, CA 94606). The pressure transducer was coupled to the Beckman Dynograph which in turn was connected in series to a two-channel Houston Omniscribe Recorder (Model 5231-15, Houston Instruments, One Houston Square at 8500 Rd., Austin, TX 78753). The system was calibrated with a water manometer. Changes in intrarumen pressure were recorded simultaneously on the Dynograph and Omniscribe recorders. Eructation
At the time of an experiment, the tracheal canula used to connect the ends of the transected trachea was replaced by one which assured separation of the gases associated with those of eructation from those of respiration. The anterior tracheal canula was connected to a three-way valve (R-738840, Cole-Parmer Instrument Co., 7425 North Oak Park Ave., Chicago, IL 60648) which led to a gas flowmeter (Wright Respirometer, Type PM. Mannee Medical, 3399 Mt. Diablo Blvd., Lafayette, CA 94549) used to measure the gas eructated. To detect rumen gas which might be expelled via the mouth and/or external nares, a mask was placed over the muzzle; tubing connected the mask to another three-way valve and flowmeter.
NAVILLEet al.
Tracheal Pressure Changes
To indicate pressure changes in the anterior and posterior tracheal canulas, pressure transducers (Model PM6TC +/l-350, StathamGould Instrument, Inc.) were connected to ports in the respective canulas. Changes in pressure were recorded on the Dynograph. Rumen insuflation
Extra dry nitrogen was introduced into the rumen through the rumen canula using a two stage gas regulator (Model S-350, Matheson Gas Products, 6775 Central Ave., Newark, CA 94580). Trial procedure
Each trial began with a 15min control period during which were recorded myoelectric activity of the reticulum and rumen posterior ventral blind sac, changes in intrarumen pressure, i.e. rumen motility, gas eructated through the anterior tracheal canula and mask, and changes in pressure in the anterior and posterior tracheal canulas. Immediately following the control period, the valves leading from the anterior tracheal canula and the mask were closed to prevent the escape of gas when nitrogen insufflation was begun. Insufflation to a predetermined pressure was maintained for five min. All parameters except gas expulsion were recorded during the insufflation period. After the insufflation period, the valves leading from the anterior tracheal canula and the mask were opened and gas expulsion measured along with the other parameters until the resting intrarumen pressure reached preinsufflation levels. Insufflation pressures sustained included 5, 10, 15 and 20 cm HOH. After each 2Ocm HOH trial, there was a 15 min control period during which all parameters were recorded. RESULTS A typical recording of all the parameters, except eructation, made during the control period is shown in Fig. 1A. Rumen motility is shown in Record 4
Fig. 1. Rumen motility and associated events during the: (A) pre-insufflation period; (B) 0 to 1.5 min of the post-insu!Ilation control period; and (C) the terminal 1.5 min of the post-insufhation control period. The post-insufflation control period began 10 min following the termination of insufflation to a pressure of 20 cm HOH. Legend: 1, respiration; 2, pressure changes in the anterior tracheal cannula; 3, reticular myoelectric activity; 4, intrarumen pressure; 5, posterior ventral blind sac myoelectric activity; a, respiratory activity during eructation; b, pressure in the anterior tracheal cannula during eructation; c, myoelectrical spiking in the reticulum associated with reticular contraction; d, myoelectrical spiking in the posterior ventral blind sac; p, primary (mixing) contraction; s, secondary (eructation) contraction; ps, primary-secondary contraction.
Rumen gas expulsion in sheep
,
1 min.
995
I
Fig. 2. (A) Rumen motility and associated events during insufflation of nitrogen to a pressure of 5 cm HOH; and (B) 1Ocm HOH. Legend: See Fig. 1.
where “p” refers to a primary (mixing) contraction
and “s” to a secondary (eructation). Record 3, c, shows the myoelectrical spiking of the reticulum associated with each primary contraction and Record 5, d, to myoelectrical activity of the posterior ventral blind sac (PVBS) related to primary and secondary contractions. Associated with each secondary contraction was a change in pressure in the anterior tracheal canula (Record 2, b) which resulted from the passage of gas from the esophagus through the anterior tracheal canula during eructation. The change in respiratory activity during eructation associated with the secondary contraction is shown in Record 1, a. When the intrarumen pressure was elevated to 5 cm HOH and sustained at this level for 5 min, a new type of rumen contraction appeared (Fig. 2A, ps). We have called these contractions “primary-secondary”. The electrical activity associated with the primarysecondary (ps) contraction began in the reticulum (Fig. 2A, Record 3, c) and from this aspect, was similar to the primary contraction (Fig. IA, Record 3, c; Record 4, p). The second phase of the ps contraction (Fig. 2A, Record 4, ps; Record 1, a; Record 2, b) involved events common to the secondary contraction, i.e. an alteration of respiration (Fig. lA, Record 1, a), pressure changes in the anterior tracheal canula (Fig. lA, Record 2, b), and gas flow through the flowmeter. During the insufllation period, the contractions were either ps or secondaries. When the intrarumen pressure was increased to 10 (Fig. 2B), 15 (Fig. 3A), and 20 (Fig. 3B) cm HOH by the insufflation of nitrogen and sustained at each pressure for 5 min, there was a dramatic increase in the frequency of secondary contractions. As resting intrarumen pressure (RIP) increased, respiration be-
came more depressed and electrical activity in the PVBS increased in frequency and amplitude. Accompanying each ps and secondary contraction during the insufflation period, eructated gas reached the anterior tracheal canula as shown by the pressure changes signalled by the attached pressure transducer (Record 2, Figs 2B, 3A, 3B). However, gas escape was prevented by the closed valves at the mask and anterior tracheal canula. When RIP was maintained at 2Ocm HOH, there was a gradual increase in the incidence of coughing (Fig. 3B, Record 4, e), an apparent attempt to increase the efficiency of gas expulsion. Immediately following the insufflation period the valves between the flowmeters and the mask and anterior tracheal canula were opened and the volume of gas expelled during eructation measured. Figs 4A, 4B, 5A and SB refer to events during the first 1.5 min of deflation following insufflation to 5, 10, 15 and 20cm HOH, respectively. All contractions were either ps or secondaries; gas expulsion accompanied each contraction. Figures 6A, 6B, 7A and 7B represent the last 1.5 min of the deflation period of the 5, 10, 15 and 20 cm HOH insul?Iation trials, respectively. Each deflation period was approximately 7 min in duration. Infrequently, primary contractions appeared during the deflation period, e.g. Figs 6B and 7A, Record 4, p. The absence of a pressure change in the anterior tracheal canula (Figs 6B and 7A, Record 2, b) and lack of respiration interruption (Figs 6B and 7A, Record 1, a) verify the primary contraction. The first 1.5 min and the last 1.5 min of the 15 min post-insufflation control period of the 2Ocm HOH trial are shown in Figs 1B and lC, respectively. There was evidence of a carry-over effect of insufflation in
LAURA E. PERUZ~O DE NAVILL.Eet a/.
996
1 min. e
4
Fig. 3. (A) Rumen motility and associated events during ins~ation of nitrogen to a pressure of 15 cm HO& and (B) 20cm HOW. Legend: See Fig. I.
the first minute as illustrated by the presence of a ps contraction (Fig. lB, Record 4, ps). By the end of the period, primary contractions replaced all ps contractions (Fig. IC, Record 4, p). The effect of RIP on the frequency of primary, ps, secondary, and total rumen contractions is shown in Fig. 8. The data used in the calculation of these
regressions came from the insufflation periods of each trial, i.e. 5, 10, 15 and 2Ocm HOH. All trials were pooled and a mean calculated for each pressure level. The means were used to calculate the regressions. A third degree polynomial best expressed the data for the secondary, ps, and total contraction frequencies. The decline in the primary contractions with in-
b
,
1
min.
I
20 P’ J-k-10 d
10
p*
‘
,
*
P’
I
’ 4--
d
Fig. 4. (A) Rumen motility and associated events 1 to 3 min following termination of rumen insufflation with nitrogen to a pressure of 5 cm HOH; and (B) 10 cm HOH. Legend: See Fig. 1.
Rnmen gas expulsion in sheep
997
2
1 min.
dd
dd
d
d
d
4
d
d
SO
Fig. 5. (A) Rumen motility and associated events I to 3 min following termination of the ins~tion nitrogen to a pressure of 15cm HOH; and (R) 20 cm HOH. Legend: See Fig. i _
creasing pressure was linear. The various regressions used to plot Fig. 8 are as follows:
contractions
Y = 0.79 - 0.028X + 0.012X2 - 0.~39~3,
Primary contractions Y=O.iS-0.01X,
primary-secondary
of
_+s,,=O.O6,
r=-0.80;
f svX= 0.09,
R2 = 0.99;
b
d
Fig. 6. (A) Rumen motility and associated events 7.5 to 9 mitt following termination of rumen in&I&ion with nitrogen to a pressure of 5 em HOH; and (El) 4.5 to 6 min following the termination of rumen in&Ration to IOctn HOH. Legend: See Fig. I.
b, I’
1 min,
-m-
20 P -0
‘
10
P’ 4
d
5_____
d
Fig. 7. (A) Rumen motility and associated events 7.5 to 9 min following termination and the insuflation of nitrogen to a pressure of 15cm HOH; and (B) 20 cm HOH. Legend: See Fig. 1.
secondary contractions
total contractions
Y = - 1.3 + 0.66X -0.021X2 + s,, = 0.14,
+ 0.00011X~,
R2 = 0.99;
+_s,,=O.ll,
60-
50 -
PRIMARY-SECONDARY
/’
/
-..-..-..-
5
0 Resting
.._..
_..
10
lntrarumen
Y = -0.68 + 0.76X - 0.022X2 + 0.000071X3,
15 Pressure
1
20
km Hz01
Fig. 8. The effect of resting intrarumen pressure on the frequency of primary, primary-secondary, secondary and total rumen contractions.
R*=0.99.
As RIP increased, there was an increase in the frequency of the secondary and ps contractions and a rapid decline in the number of primaries. The maximum frequency for ps and secondary contractions was reached when RIP was approximately 20 cm HOH. Within 5 min following the termination of insufflation, the intrarumen pressure had returned to a level which was no longer stressful to the sheep (Fig. 9). For the purpose of comparing the rate of decline in RIP from the maximum insufflation values of 5, 10, 15 and 20 cm HOH pressure, the curvilinear data for the first 5 min were forced to linearity (Fig. 10). The slope for the 5 cm HOH trials differed significantly from the slopes of the 10, 15 and 20 cm HOH trials (p c 0.001). The slope for the 1Ocm HOH trials was significantly different from the slopes for the 15 and 20 cm HOH trials (p < 0.001). The difference between the slopes for the 15 and 20 cm HOH trials was significant at the 10% level. Thus, the higher the initial insufflation pressure, the more rapid the rate of decline. The effect of insufflation pressure on the volume of gas eructated during the first 5 min of deflation is shown in Fig. 11. As would be expected, higher insufflation pressures resulted in more gas to be eructated. When the RIP exceeded 5 cm HOH, the volume of gas eructated on ps and secondary contractions was similar. By 5 min, the RIP was essentially at the pre-insufflation level irrespective of the insufflated pressure (Fig. 9).
Rumen gas expulsion in sheep -18 S
N I
0 _i E
16
999
5 cm H,O r/.5.07- .95X*.06X2-2.39X',*sr ' .16), A'=.99
-10
cm H,O fY* 10.0-2.66X+.30X2 -9,63X',ts,, * .32), R".QQ . \ -..-15cmH,O(Y.14.0-4.52X*.51X2.02X'+ *.92),R2'.96 \-.-20
cm H,O (Y.16.7-6.53X+.74X2 - .03X',%, 1.30),R's.97 5000-
i
14
\
4000-
? E In A 3000r g '5 ?I ?zooow t 0
A ./
IOOO-
time
(mm)
Fig. 9. Effect of the level of resting intrarumen pressure (cm HOH) following the ins&Ration of nitrogen on the rate of return of intrarumen pressure to pre-insufflation levels.
E
1 0
I
5
Resting
The volume of gas expelled (ml) through the mask and trachea on ps and secondary contractions from all trials, i.e. 5, 10, 15 and 20 cm HOH, inclusive, for
each parameter for all sheep was pooled and means and SE’s calculated, as follows: mask ps 117 -+ 33.1, -
5 cm Hz0 (v- 4.91- .61X.+sy, s .061), I = -.96 10 cm H,O (v* Q.Ql- 1.57X,'+ . 1.37), r . -.97
-..-
15 cm H,O (Y‘13.26-2.45X.tsl, . 1.79), r . -.94
-.-
20 cm H,O @.16.44- 3.24X,=sy, . 2.96), I = -.92
PRIMARY-SECONDARY
IO
I5
lntrarumen Pressure (cm
20 H20)
Fig. 11. The effect of resting intrarumen pressure on the volume of gas expelled during the first 5 min of deflation for primary-secondary and secondary rumen contractions. The total gas expelled is also shown.
trachea ps 1885 + 239; mask secondary 74 _+24, trachea secondary 2023 _+315. Neither the difference between the means for the volume of gas expelled into the mask during ps and secondary contractions nor the difference between the means for the volume of gas expelled from the trachea was statistically significant. Thus, the volume of gas which escaped from the mouth into the mask during ps and secondary contractions was less than 10% of the total gas expelled on each type of contraction. DISCUSSION
I
,
0
I
2
3
4
J
5
Time (mm)
Fig. 10. Effect of the level of resting intrarumen pressure following the insufaation of nitrogen on the deflation rate during the first 5 mm of deflation. The curvilinear data from Fig. 9 for the first 5 rain of deflation were forced to linearity.
Contractions of the reticulorumen have only two purposes, the mixing and propulsion of ingesta and the movement of gas to the cardiac orifice for expulsion. The mixing contraction is referred to as the primary and the eructation contraction, the secondary. During normal resting rumen motility there is no difficulty in differentiating the primary from the secondary contractions (Fig. IA, Record 4). However, during elevated intrarumen pressure (Fig. 3B, Record 4) deciding which is a primary contraction and which a secondary, is difficult. The use of the transected tracheal technique for measuring the volume of eructated gas (Colvin et al., 1957) made it considerably easier to identify secondary contractions since eructation, under normal conditions, occurs on every secondary contraction (Colvin et al., 1958; Ruckebusch and Tomov, 1973). On the other hand, it has been reported that eructation occurred frequently on primary contractions (Akester and Titchen, 1969; Reid and Cornwall,
1000
LAURA E. PERLJZZO DE NAVILLEet al.
1959; Stevens and Sellers, 1959) or in the absence of rumen contractile activity (Akester and Titchen, 1969; Reid, 1960; Reid and Cornwall, 1959). More recently, during rumen insufflation studies in sheep (Louvier et al., 1980), frequent gas expulsion was observed on “special primary contractions”. It was apparent that more definitive methods were essential to ascertain the incidence of eructation and on which contraction, or absence thereof, the event occurs. Ruckebusch and Tomov (1973) have shown that primary contractions are preceded by electrical activity in the reticulum and secondary contractions by electrical activity in the posterior ventral blind sac. Therefore, electrodes were implanted at these sites in the sheep used in these experiments (Fig. 1, Records 3 and 5). Since it has been shown that eructated gas is inhaled into the trachea during an inspiratory effort (Colvin et al., 1957; Dougherty and Cook, 1962), respiratory events associated with eructation were demonstrated in our experiments by connecting a pressure transducer to the posterior tracheal canula (Fig. 1, Record 1, a). To indicate that gas expulsion was being attempted during rumen insufflation with the anterior tracheal canula blocked, a pressure transducer was connected to the canula proximal to the site of the anterior tracheal valve (Fig. 1, Record 2, b). Using the above procedures simultaneously, there was no difficulty in identifying primary and secondary contractions under normal conditions (Fig. 1). Every primary contraction was preceded by reticular electrical activity (Fig. 1, Record 3, c) and followed by PVBS electrical activity (Fig. 1, Record 5, d). The secondary contractions (Fig. 1, Record 4, s) were: (a) preceded by PVBS electrical activity (Fig. 1, Record 5, d), (b) associated with pressure changes in the anterior tracheal canula as eructated gas passed through (Fig. 1, Record 2, b), and (c) related to the interruption of respiration (Fig. 1, Record 1, a). These same criteria were also used successfully to identify primary and secondary contractions during elevated intrarumen pressure (Fig. 3B, Record 4). When resting intrarumen pressure was elevated to only 5 cm HOH by the insufflation of nitrogen, rumen gas expulsion began to occur on what appeared to be regular primary contractions when deflation was permitted (Fig. 4A, Record 4, ps). Reticular electrical activity (Fig. 4A, Record 3, c) indicated that they were indeed primary contractions. Gas expulsion was substantiated by pressure changes in the anterior tracheal canula (Fig. 4A, Record 2, b) and an interruption of respiration (Fig. 4A, Record la); furthermore, the volume of gas expelled was measured with the flowmeter. Thus, the measurement of gas expulsion on primary contractions would appear to support previous reports (Akester and Titchen, 1969; Reid and Cornwall, 1959; Stevens and Sellers, 1959). This raises the question, “Are these primary contractions on which gas expulsion had occurred following rumen insuffIation in fact ‘regular’ primary contractions?’ The complex nature of the eructation reflex is well documented and involves the close coordination of
reticulorumen musculature (Colvin et al., 1958; Weiss, 1953; Wester, 1926), muscles of the cardiac orifice and esophagus (Dougherty and Habel, 1955; Dougherty and Meredith, 1955) and the abdominal wall (Cole et al., 1942; Reid, 1960). On the other hand, Wester (1926) observed that the cardiac orifice is pulled slightly open during the primary contraction and it is not difficult to hypothesize that if the resting intrarumen pressure is sufficiently elevated, gas could escape on a primary contraction and be expelled into the environment directly via the mouth and external nares because the reflex activity of the glottis and inspiratory muscles associated with normal eructation would be absent. Because of the events in the anterior tracheal canula (Fig. 4A, Record 2, b), the inhibition of normal respiratory activity (Fig. 4A, Record 1, a), and the large amount of gas expelled, all events associated with the reflex act of eructation, the primary contractions associated with gas expulsion in these experiments cannot be viewed as “regular” primary contractions. In other words, part of these contractions was primary and part secondary. How then does one explain these special “primary-secondary” contractions? According to Ruckebusch and Tomov (1973), the electrical activity of the reticulorumen during during a primary contraction proceeds as follows: reticulum, dorsal sac, posterior dorsal blind sac, ventral sac, and posterior ventral blind sac. Electrical activity of the secondary contraction occurs as follows: posterior ventral blind sac, posterior dorsal blind sac, dorsal sac, ventral sac, and posterior ventral blind sac. Observing the primary-secondary (ps) contraction closely (Fig. 4A, Record 4, ps) it can be seen that the relaxation phase or descending segment of this contraction is not smooth. Rather, the relaxation begins but then is interrupted, at which time, the pressure elevates sharply again followed by a smooth decline to the resting pressure level, a biphasic contraction. In every case, on these ps contractions, gas expulsion occurred at the peak of the pressure re-elevation. It is postulated that the electrical activity of these ps contractions occurs as follows; reticulum, dorsal sac, posterior dorsal blind sac (the primary component), then posterior dorsal blind sac again, dorsal sac (eructation), ventral sac and posterior ventral blind sac. The electrical activity in the reticulum (primary component) followed by the pressure activities shown in the anterior tracheal canula, and the interruption of respiration (secondary component) shown in Fig. 4A, associated with the ps contraction, supports such a postulate. It would now appear that the eructations observed on primary contractions by other workers (Akester and Titchen, 1969; Reid and Cornwall, 1959; Stevens and Sellers, 1959) are in fact eructations associated with these ps contractions. Because we recorded simultaneously rumen myopressure, pressure electrical activity, intrarumen changes in the anterior and posterior trachea, and eructation frequency and volume, it was possible to clearly differentiate the various types of rumen contractions (Fig. 3A). As intrarumen pressure increased (Fig. 8), the primary contractions were converted t( ps contractions and were associated with gas expul
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Rumen gas expulsion in sheep
sion via the normal route for eructated gas, i.e. aspiration into the trachea (Colvin et al., 1957; Dougherty and Cook, 1962). When RIP reached approximately IOcm HOH, ordinary primary contractions as such had disappeared. Whereas, others have shown the increase in rumen contraction frequency with increasing intrarumen pressure (Colvin et al., 1959 and 1978; Louvier et al., 1979; Weiss, 19X3), the maximum contraction frequency has only been alluded to (Colvin and Horn, 1983). Our experiments indicated a maximum secondary contraction frequency when the intrarumen pressure reached approximately 20 cm HOH. For the ps contractions, the maximum rate occurred when the intrarumen pressure was approximately 15 cm HOH (Fig. 8). The maximum frequency for secondary contractions was betwen 4-5/min and for ps, approximately Z/min. Presumably, refractory periods in the motility center and/or rumen musculature made a further increase in motility improbable. From Figs 9 and 10, it is clear that by 5min following the cessation of insufflation, the intrarumen pressure was similar for all experiments. However, the higher the initial insufflation pressure, the more rapid the rate of deflation. It is reasonable to expect the cardiac orifice to be open a finite period of time during the eructation reflex. Thus, with the cardiac orifice open, the higher the intrarumen pressure, the greater the pressure gradient, and the greater the volume of eructated gas; therefore, a more rapid rate of pressure decline. In addition, it must be recognized that elevated RIP was associated with large volumes of gas expelled on ps contractions (Fig. 11). This finding, coupled with the more rapid rate of secondary contractions associated with elevated RIP (Fig. 8) can explain the more rapid rate of deflation associated with elevated RIP. The effect of RIP on the volume of gas expelled is shown in Fig. 11. In the long term, secondary contractions were more important than ps contractions in the reduction of intrarumen pressure because there were more of them (Fig. 8). However, gas expulsion on ps contractions was important during the initial reduction of elevated intrarumen pressure (Figs 8, 9, 10) since equal volumes of gas were shown to be expelled on ps and secondary contractions during the first 5 min of deflation. Apparently, the efficiency of eructation on ps contractions was enhanced by the sustained intrarumen pressure associated with the biphasic nature of this contraction (Fig. 4). The second phase of the biphasic contraction occurred while the intrarumen pressure was already elevated; thus, the summation effect could allow the escape of more gas during eructation. Possibly, the rapid recovery from acute legume bloat in ruminants following the intraruminal administration of an anti-frothing agent (Colvin et al., 1959) is a function of eructation during ps contractions. Reid and Cornwall (1959) and Sellers and Stevens (1966) have reported eructations on mixing (primary) and eructation (secondary) contractions. The former also alluded to eructation in the absence of rumen contractions and increasing eructations on primary contractions by insufflating 8-10 1 gas/min into the rumen of cows. Neither of these reports mentioned quantitative measurements of gas expulsion. In view C.B.P. *,,,A-‘
of our findings, the eructations these workers observed during primary contractions were probably eructations during ps contractions. Contrary to the reports of Reid and Cornwall (1959) and Akester and Titchen (1969), we have not recorded gas expulsion without a concomitant rumen contraction, even when RIP was elevated. In their eructation measurements, Dougherty and Cook (1962) reported that in one cow, 13.6% of expelled gas escaped via the mask and in another cow, 30.5% by-passed the trachea and escaped via the mask. In our work, the volume of gas escaping from the mouth and mask following insufflation was measured during primary, primary-secondary, and secondary contractions; the volume was found to be slight, i.e. less than lo%, and followed no particular pattern, an almost incidental event. In two of our four sheep, no gas was recorded from the mask until RIP reached 15 cm HOH. Our work indicates that three rather than two types of rumen contractions exist in sheep: primary, primary-secondary (ps), and secondary. The ps contractions appear when RIP is elevated and become increasingly important for gas expulsion as RIP increases. SUMMARY
Rumen motility and eructation trials were conducted on four sheep. To evaluate motility, a canula was placed in the dorsal sac of the fistulated rumen and myoelectrodes were implanted in the reticulum and posterior ventral blind sac (PVBS). To study the events associated with eructation, the trachea was transected and cannulated. A transducer was installed in the anterior tracheal canula to determine pressure changes. Respiration was evaluated by placing a pressure transducer in the posterior tracheal canula. Flowmeters attached to the anterior tracheal canula and the muzzle mask measured the volume of eructated gas. The rumen was insufflated with nitrogen to pressures of 5, 10, 15 and 2Ocm HOH; each level was sustained for 5 minutes. When the resting intrarumen pressure (RIP) was normal, primary contractions of the rumen were preceded by reticular myoelectric activity and ended with myoelectric activity in the PVBS. Secondary contractions were preceded by myoelectric activity in the PVBS and followed by a pressure change in the anterior tracheal canula; also, there was an interruption of normal respiration and a flow of gas through the anterior tracheal flowmeter. When RIP was elevated by insufflating nitrogen, the frequency of primary and secondary contractions increased, with the secondary contractions increasing at a more rapid rate than the primaries. Gas expulsion occurred in association with primary contractions when RIP reached 5 cm HOH. The primary contractions became biphasic in appearance with gas expulsion at the peak of the second phase. Associated with gas expulsion on the primary contraction was a pressure change in the anterior tracheal canula, an interruption of respiration, and a flow of gas through the flowmeter; these events were the same as those associated with a secondary contraction. The first phase of the primary contraction began with myo-
LAURA
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E. PERUZZODE NAVILLE et al.
electric activity in the reticulum. As the result of these events, when gas expulsion occurred on a primary contraction, the contraction was referred to as a “primary-secondary” contraction. Irrespective of the initial insuiation pressure, RIP became normal within 5 minutes of the beginning of deflation. The higher the initial RIP, the more rapid the return of pressure to normal. The more the rapid decline in RIP was a function of an increased number of secondary contractions and a high volume of gas expulsion on primary-secondary contractions. During the first 5 minutes of deflation, equal volumes of gas were expelled on primary-secondary and secondary contractions. Less than 10% of the total gas eructated was via the mouth. The evidence presented indicates the existence in sheep of three rather than two types of rumen contractions; primary, secondary, and primarysecondary. Gas expulsion occurred on both the secondary and primary-secondary contractions.
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