Observations on the stomach pH in pigs following massive infections with Hyostrongylus rubidus larvae

1. COMP.

PATH.

1974.

VOL.

127

84.

OBSERVATIONS ON THE STOMACH pH IN PIGS FOLLOWING MASSIVE INFECTIONS WITH HTOSTRONGTLUS RUBIDUS LARVAE BY

*R.N.

TITCHENER, Department

I. V.

HERBERT

and A.J.

PROBERT

of A&&d
R.F.E. Department

AXFORD

of Biochemistry and Soil Science, University College of North Wales, Bangor INTRODUCTION

Previous studies in our laboratory by Castelino, Herbert and Lean (1970) have shown clinical symptoms of mild fever, listlessness, inappetence, diarrhoea and reduced weight gains in pigs following infection with massive doses (up to 500 000 larvae given as a single dose) of infective larvae of Hyostrongylus rubidus, the red stomach worm of pigs. Diarrhoea and a rise in abomasal pH is a feature of stomach worm infections in cattle and sheep with the nematode parasites Ostertagiu spp. and Trichostrongylus axei (Jarrett, 1966; Ross, Purcell, Dow and Todd, 1968 ; Ross, Purcell and Todd, 1969). Davidson, Murray and Sutherland (1967) reported gastric pH (up to 6.5) in field cases of hyostrongylosis. The object of the present investigation is to confirm these results using experimental infections of 500 000 larvae and to monitor continuously changes in gastric pH during the course of infection using radiotelemetry capsules, since wide fluctuations occur from hour to hour. As far as can be determined from the literature this study represents the first use of radiotelemetry capsules in the study of pH changes in parasitized pigs. It also confirms the use of this technique in the study of gastrointestinal pH changes in livestock. MATERIALS

AND

METHODS

Fifteen week-old conventionally reared Large White x Landrace minimal disease (M.D.) female and castrate male pigs were used. All animals were fed a commercial meal (Sow and Weaner Meal, B.O.C.M. Ltd.). Infection was per OS as a single dose of infective larvae. In the first experiment a litter of 10 pigs was divided into 2 equal groups. At 15 weeks of age group 1 was infected with 500 000 larvae whilst group 2 served as uninfected controls. Each animal received 2 feeds per day, each consisting of 635 g. of meal in 1 500 ml. of water. Three h. after the morning feed a sample of the stomach contents was obtained by stomach tube and its pH immediately determined with a portable pH meter. During the period 15 to 30 days after infection daily faecal egg counts were made using the Clayton-Lane centrifuge method with saturated magnesium sulphate (SC. 1.25) as the flotation fluid. * Present address: Department Auchincruive, Ayr.

of Nematology

and Zoology, West of Scotland Agricultural

College,

128

R. N. TITCHENER et al.

One pig was used in the second experiment. It was housed in a wooden metabolism cage and received 4 feeds per day, each consisting of 400 g. of meal in 2000 ml. of water. At 16 weeks of age the pig was infected with 500 000 larvae. Daily faecal egg counts were made during the period 15 to 20 days after infection. In this experiment continuous changes in pH were measured by radiotelemetry capsules (Rigel Research Ltd., Richmond, Surrey). Two types of capsule were used, (i) a standard capsule, inserted orally, designed to pass quickly through the gut and (ii) a prototype capsule, surgically inserted, designed to remain in the stomach. The latter, whilst remaining in the stomach, was not expected to transmit accurate pH readings for much longer than a week. Because of this it was used during the period when clinical symptoms were apparent and gastric pH might be expected to be elevated. The standard capsule was used to obtain pre-infection values for comparison since it passed through the gut and did not have to be removed before the insertion of the prototype capsule. The standard capsule, however, only monitored gastric pH for the short time when it was in the stomach. Two aerials of copper wire, each having an inductance of approximately 200 pH, were attached to the wooden cage. The signals received by the radiotelemetry pill receiver were continuously monitored with an electronic polyrecorder. At 20 days after infection the pig was killed to recover and re-calibrate the prototype radiotelemetry capsule. RESULTS

pH Values on Withdrawn Stomach Contents (Exp. 1) Stomach pH values (Table 1) fluctuated with time, a mean pH range of l-9 to 6.3 being observed in the control animals. There was also a wide variation between values recorded for each animal within each of the 2 experimental groups which is reflected in the wide 95 per cent. confidence limits. Clinical symptoms of inappetence and vomiting were observed in the period 17 to 27 days after infection, being most severe between 18 and 20 days. Eggs first appeared in the faeces 17 days after infection and a mean peak egg count of 635 e.p.g. (eggs per g.) was recorded on the 20th day. TABLE 1 STOMACH

Day after infection

pH

VALUES

-5

BASED

ON WITHDRAWAL

OF STOMACH

CONTENTS

0

4

8

11

16

18

22

25

30

Mean, controls (5 animals) *95% Confidence limits

4.1

4.2

4.8

3.9

5.3

4.5

4.5

63

1.9

3.4

3.5

3.4

3.5

3.5

3.3

396

3.7

3-l

3.0

3.0

Mean, infected (5 animals) +95% Confidence limits

3-2

4.7

5.4

5.0

4.8

4.2

6.0

5.4

4.8

3.6

3.6

3.3

3.2

3.3

3.3

2~8

3.1

3.0

3.1

3.5

Samples of gastric juice from the infected pigs during this period of severe clinical symptoms and high egg counts, on the 18th day, had a mean pH of 6 compared with a mean value of pH 4.5 in the control group. A high mean pH of 6-3 was, however, recorded from the uninfected pigs on the 22nd day, but whereas the samples from the infected pigs had a foul odour and were clear, very little food being present, the high pH samples from the control animals

OBSERVATIONS

contained large had the distinct this sample was of the parasite. where there has 1970).

ON THE STOMACH

129

pH IN PIGS

amounts of food and mucus. One sample from an infected pig colour of bile which might indicate that the high pH of 6.8 of the result of duodenal regurgitation due to the irritating effect Duodenal regurgitation has been reported to occur in pigs been severe irritation of the gastric mucosa (Reed and Kidder,

pH Values on Capsule Readings (Exp. 2) The infection became patent 16 days after infection and a peak egg count of 718 e.p.g. was reached on the 19th day. Clinical symptoms were less marked than in the first experiment. There was only a slight reduction in appetite 17 to 20 days after infection. Vomiting also occurred between the late evening and morning feeds at 18, 19 and 20 days. The vomit contained some food material, a few small strands of fibrin and large quantities of mucus. Between 17 and 20 days the difference between pre- and post-infectionpHvalues was most marked between the evening and morning feeds. Stomach pH values (Table 2) rose some time after the evening feed, but, stomach pH after infection reached a higher level (maximum 7-5) and remained high for a longer period than the v-alues obtained before infection (maximum pH 5). TABLE 2 STOMACH

Hours after feed

pH 0

VALUES

BASED

1

2

ON

RADIOTELEMETRY

3

4

CAPSULE

5

READINGS

6

7

8

9

10 -

3.5

2.5

2.5

3.0

2.5

Pre-infection Evening day 3 Morning day 2

2..5

1.3

2.5

2.0

5.0

5.0

Post-infection Evening day 17 Morning day 18

1.0

3.0

0.8

2.5

5.5

7.0

6.0

6.0

6.1

6.1

6.5

Evening day 18 Morning day 19

2.0

2-o

2.0

2-5

2-o

4.0

7.0

7-o

7.5

4.0

4.0

Evening day 19 Morning day 20

2.0

2.0

2.0

2.0

2.5

2.0

4-o

7.0

6.5

6.5

2,s

DISCUSSION

Davidson et al. (1967) reported elevated gastric pH in H. rubidus infections, levels of up to pH 6.5 being recorded. Similar values were observed in the present investigation in infected pigs on the 18th day after infection in the first experiment. It is interesting that this period coincides with the time when most marked clinical symptoms are apparent and egg laying is at its height. Raised values observed in this experiment and in those reported by Davidson et al. (1967) have to be interpreted with caution since radiotelemetry pills showed gastric pH to vary considerably from one hour to another. These hours,. furthermore, do not necessarily correspond from one pig to another as shown

130

R. N. TITCHENER

et al.

by the wide 95 per cent. confidence limits in the first experiment. In pigs the validity of methods based on samples taken from the stomach by intubation or fistula to determine gastric pH appear questionable and further studies using radiotelemetry pills, which provide a continuous record of gastric pH, are required in pigs with hyostrongylosis to provide further information. The presence and nature of the food in the stomach influences the pH of the gastric fluid (Baskerville and Ross, 1970). In the first experiment samples with large quantities of food contained considerable amounts of mucus and it appears likely that the presence of food in the stomach affects mucus secretion within it. It was observed in this investigation that values between pH 6 and 7 were recorded in gastric samples containing large amounts of mucus. In the second experiment post mortem examination revealed the presence of large quantities of mucus. In view of the large amounts of mucus vomited, infection with H. rubidus would appear to result in increased mucus production which might to some extent explain the elevated gastric pH levels, a maximum of pH 7.5 being recorded in this experiment. Infection with H. rubidus produces a loss of differentiation of the cells of the gastric glands and reduction in the number of parietal cells in particular (Davidson et al., 1967). I n such circumstances an elevated stomach pH would be expected since parasitaemia with Ostertagia s@ and Trichostroqylus axei, which results in a loss of parietal cells and hyperplasia of undifferentiated epithelium, is associated with a rise in abomasal pH to neutrality or just above (Jarrett, 1966; Ross et al., 1968, 1969). In the infected animal (Exp. 2) there is no in ability to produce an acid pH, but perhaps there is a quantitative deficiency so that the pH is not maintained sufficiently low for such a period to permit effective digestion. Raised abomasal pH in 0. ostertagi and T. axei infections is associated with a period of severe diarrhoea. Vomiting rather than diarrhoea was a feature of the digestive upset following infection with H. rubidus and this may have biochemical implications as Neilsen (1968) considered diarrhoea to be a major factor in gastrointestinal protein loss. The standard radiotelemetry capsule passes easily through the human gut and has been used to investigate pH throughout its length (Meldrum, Watson, Riddle, Bown and Sladen 1972). The capsule did not, however, pass easily through the gut of the pig and it was 10 days before it appeared in the faeces. It was also necessary to feed pig meal which had been soaked in a large volume of water, otherwise the meal absorbs moisture in the stomach and the capsule ceases to function due to the drying out of its porous reference end. No complications followed surgical insertion of the prototype radiotelemetry capsule into the stomach of the pig in the second experiment, neither did the capsule seem to cause the pig any distress. The pH glass electrode of the prototype was not affected by the mucus and fibrin produced in response to infection with H. rubidus. SUMMARY

Clinical symptoms of inappetence and vomiting were observed in minimal disease (M.D.) growing pigs infected with 500 000 infective larvae of Hyostroqylus rubidus.

OBSERVATIONS

ON THE

STOMACH

pH

IN

PIGS

131

Elevated gastric pH values, a mean of pH 6 compared with a mean control value of pH 4.5 in one experiment and a maximum pH value of 7.5, compared with a maximum preinfection value of 5 in a second experiment, were observed in the infected pigs when clinical signs were evident. Radiotelemetry capsules which were successfully used to monitor gastric pH in pigs, provide a continuous record of gastric pH and in this respect are superior to the methods currently used to measure gastric pH since wide variations from hour to hour are normally seen and the pH recorded therefore depends on the time at which samples are withdrawn. ACKNOWLEDGMENTS

We are indebted to Dr B. W. Watson and his staff at St Bartholomew’s Hospital, London for their technical assistance with the radiotelemetry capsules. The authors would also like to thank the Agricultural Research Council for financial assistance. R. N. Titchener, would like to thank the Sir William Roberts Trust (U.C.N.W.) for financial support whilst carrying out this study. REFERENCES

and field Baskerville, A., and Ross, J. G. (1970). Ob servations on experimental infections of pigs with Hyostrongylus rubidus. British Veterinary Journal, 126,538-542. Castelino,. J. B., Herbert, I. V., and Lean, I. J. (1970). The live-weight gain of growing pigs experimentally infected with massive doses of Hyostronpylus rubidus (Nematoda) larvae. British Veterinary Journal, 126, 579-582. Davidson, J. B., Murray, M., and Sutherland, I. H. (1967). Observations on the clinical pathology of natural strongyle infestations in the pig, and their control, with special reference to Hyostronsylus rubidus. Proceedings of the 3rd International Conference of the World Association for the Advancement of Veterinary Parasitology, 9-23, Elwert N.G.; Marburg/Lahn. Jarrett, W. F. H. (1966). The Pathology of Parasitic Diseases, pp. 33-40, Fourth Symposium of the British Society for Parasitology, Blackwell. Oxford. Meldrum, S. J., Watson, B. W., Riddle, H. C., Bown, R. L., and Sladen, G. E. (1972). pH profile of gut as measured by radiotelemetry capsule. British Medical Journal, 2, 104-106. Nielsen, K. (1968). Isotopes and Radiation in Parasitology, p. 125, International Atomic Energy Agency, Vienna. Reed, J. H., and Kidder, D. E. (1970). A post-mortem survey of the relationships

between bile staining and ulceration of the oesophageal portion of pig’s stomach. Research in Veterinar?, Science, 11, 438-440. Ross, J. G., Purcell, D. A., Dow, C., and Todd, J. R. (1968). Experimental infections of calves with Trichostrongylus axei : Observations on lethal infections. Research in Veterinary Science, 9, 3 14-3 18. Ross, J. G., Purcell, D. A., and Todd, J. R. (1969). E x p erimental infections of lambs with Trichostrongylus axei: Investigation using abomasal cannulae. Research in Veterinary Science, 10, 133-I 41. [Receivedfor publication, June 25th, 19731