Exploring gastric pH

Through our many years of developing telemetry devices not only we have learnt a thing or two about the gastrointestinal pH of cows, but of several other species as well.

As we now enter the fifteenth year of pH monitoring using rumen telemetry, we have gained a wealth of knowledge regarding digestive health. Our highlights include collection pH and temperature data for over 3,000 cows (including beef animals and bulls), advising on the monitoring of pH in other livestock, and expanding the use of our boluses to other animals. In this review we will explore what we have learnt regarding gastrointestinal pH, and the variation among different species.

Summary

  • Use of indwelling pH sensors has revolutionised our understanding of the relationship between reticulo-rumen pH and subacute ruminal acidosis (SARA) in dairy cows
  • Continual measurement of reticulo-rumen pH can also be of use to monitor the health of other ruminants, such as antelope species
  • Monitoring of pH in other non-ruminant species can also be vital to understand the implications of dietary changes on health
Rumenocentesis diagram
A simple diagram indicating the positioning of the eCow bolus in the gastrointestinal sysem

Cows

The eCow bolus was designed to measure the pH and temperature of the reticulo-rumen of dairy cows. Due to increasing production demands resulting in a ration with a higher proportion of concentrates, modern dairy cows are facing an increasing risk of subacute ruminal acidosis (SARA). It is believed that at least 30% of cows in the UK are suffering from SARA, and analysis of our data supports this [1]. Through data collected from our boluses we have been able to gain insight into the changes in reticulo-rumen pH associated with an increased SARA risk. Within the rumen the generally accepted threshold for an increased SARA risk is 5.5 pH units, but the eCow bolus deploys to reticulum and this threshold is around 0.2-0.3 pH units higher than the rumen [2]. Although the reticulum pH is constantly fluctuating we believe that an increasing amount of time spent below 5.8 pH units increases the risk of SARA.

In addition to this, using the continual pH data provided by the eCow boluses we have established a more reliable definition of SARA in terms of pH variations. It has become increasingly clear to us that several changes in pH profiles can indicate an increased risk of SARA. To address this, we believe that analysis of pH data should include not only the mean  values but also the range and daily variability, the amount of time spent below the SARA threshold, and the length of non-feeding periods [2]. A perhaps surprising finding was that the risk of SARA is not only increased by dietary changes, but also by farm routine [3]. Slight variations in farm management or practices can have a negative impact on the SARA risk, but when identified promptly using the bolus can be easily rectified [3]. Through our extensive monitoring of dairy cow pH we have found the issue of SARA to not only be more prevalent in the UK, but also to be far more complex than previously assumed.

The eCow bolus has allowed farmers to make data driven decisions regarding cow health and welfare

Antelope

In addition to monitoring reticulo-rumen pH and temperature in dairy cows the eCow bolus has also been used in Eland, a species of antelope. All species of antelope are ruminants and so have a similar digestive system structure to cows. In the wild the Eland is predominantly a browser; the majority of their diet comes from woody species with grass only eaten rarely [4]. During winter and when in captivity it can be difficult to maintain a diet which accurately reflects their natural feeding, so it is often supplemented with hay and concentrates. This can put them as risk of acidosis, and can also lead to other health and welfare issues.

'The eCow bolus has given us the opportunity to monitor the Eland from a distance, and over a prolonged period of time. Hopefully this should help us make sure we are keeping them as healthy as possible!'
Jen Quayle
Veterinarian, Knowsley Safari Park

The eCow bolus was used to monitor the reticulo-rumen pH and temperature of Eland at a UK safari park. Using data from the boluses it was possible to see that the animals winter diet was leading to low and highly fluctuating pH. Upon making changes to the diet the mean pH rose and the daily pH range decreased. In this case the eCow bolus proved a powerful diagnostic tool, as well as demonstrating that dairy cows are not the only species at risk from acidosis. Overall this highlights the potential benefit of continual monitoring the reticulo-rumen pH in other ruminants who may be at risk of acidosis, such as dairy sheep and goats [5].

Downloading data from boluses in antelope, photo courtesy of Jen Quayle

Non-ruminants

Although our boluses cannot be used to monitor the pH of non-ruminants, eCow have advised researchers on the continual monitoring of pH in poultry and swine. Currently there is no technology designed specifically for these species, so the Heidelberg capsule was used. The Heildelberg capsule has been used for over 40 years to monitor the gastric pH of humans [6], but to our knowledge has not been used in either poultry of swine before.  As in ruminants, the gastric pH of non-ruminants can also be a useful indicator as to the health of the animal and can be associated with certain disorders. 

The result of this study showed that in swines going through a dietary change, the superdosing of Phytase (a commonly used animal feed supplement [7]), allowed the maintenance of a healthy gastric pH. However, the same effect was not seen in poultry [7], where large variations in gastric pH were seen. This highlighted the impact that even small changes to diet can have on gastric pH, but also emphasized the  importance of continual pH monitoring technologies as a tool in animal healthcare.

An overview of the anatomy of gastrointestinal tract in several species, adapted from a figure by Furness et al., 2015.

Humans

In addition to livestock, there is a wealth of knowledge regarding the gastrointestinal pH of humans and it’s importance in health. Humans are monogastrics and so their gastrointestinal tract is different in structure to ruminants, with particular points of difference being the stomach architecture and length of the small intestine. These differences are due to humans consuming an omnivorous diet, with less fibrous plant material than ruminants. As a consequence, humans have a much lower average gastric pH of around 1.5-3.5 pH units in the stomach [8]. This provides the optimum conditions for the function of digestive enzymes [8]. After a meal this increases due to the buffering action of food, but recovers to baseline relatively quickly. However in the rest of the gastrointestinal tract the pH is much higher, at around 6-7 pH units [9]. As previously mentioned the Heidelberg capsule has been used for 40 years to continually monitor the gastric pH of humans over a short space of time, and is important in diagnosing a variety of disorders and diseases [6]. More recently a new technology, based on the Heidelberg capsule, called the SmartPill®  has been used to measure gastric acid output, and is another promising tool in the diagnosis of gastric acid secretion disorders [10]. 

Conclusions

We began our work devising a technology to continually monitor the reticulo-rumen pH of cows to improve the diagnosis of SARA. Since then our boluses have been used by both farmers, vets, and researchers to understand pH changes in dairy cows. As well as vastly improving the diagnosis of SARA, use of the boluses has also furthered our understanding of the disorder. We now understand the changes in pH that occur during SARA, and some of the management factors which can increase the risk of SARA. 

Our boluses are primarily used in dairy cattle, but they have also been deployed in beef cattle, bulls, and antelope. The use of the boluses in antelope indicated that the animals were at risk of SARA, and were used to guide a change in diet in order to mitigate this. We have also advised on the use of a pH capsule in poultry and swine, where gastrointestinal pH can also have a substantial impact on health.

Overall, our work has taught us more about the connections between gastrointestinal pH and animal health. We have found that continual monitoring of pH is a useful diagnostic tool in a variety of animals from cows to humans. In a time where an ever increasing emphasis is being placed on ensuring the  health and welfare of livestock, we believe that the application of innovative technology driven solutions is the vital to the future of the industry. 

Bibliography

[1.] Atkinson, O. (2013) A cross-sectional survey to investigate prevalence of and clinical indicators for Subacute Ruminal Acidosis (SARA) in lactating cows on UK dairy farms. British Cattle Veterinary Association.

[2.] Mottram, T. T. F. (2016) Is monitoring rumen pH a routine tool or a seasonal adjustment to new forage quality?. Proceedings of the 7th Nordic Feed Science Conference.

[3.] Mottram, T. T. F., Hamilton, J. (2014) Measuring rumen pH on farms with wireless telemetyr boluses shows the impact of farm routine. British Cattle Veterinary Association Congress.

[4.] Watson, L. H., Owen-Smith, N. (2000) Diet composition and habitat selection of eland in semi-arid shrubland. African Journal of Ecology, 38(2): 130-137.

[5.] Enemark, J. M. D. (2008) The monitoring, prevention and treatment of sub-acute ruminal acidosis (SARA): A review.  Veterinary Journal,  176(1): 32-43.

[6.] Mojaverian, P. (1996) Evaluation of gastrointestinal pH and gastric residence time via the Heidelberg radiotelemetry capsule: Pharmaceutical application. Drug Development Research, 38(2): 73-85

[7.] Dersjant-Li, Y., Awati, A., et al. (2015) Phytase in non-ruminant animal nutrition: a critical review on phytase activities in the gastrointestinal tract and influencing factors. Journal of the science of food and agriculture, 95(5): 878-896

[8.] Dressman, J. B. and Berardi, R. R., et al. (1990) Upper Gastrointestinal (GI) pH in Young, Healthy Men and Women. Pharmaceutical Research, 7(7): 756-761.

[9.] Kararli, T. T., Searle, G D. (1995) Comparison Of The Gastrointestinal Anatomy, Physiology, And Biochemistry Of Humans And Commonly Used Laboratory Animals. Biopharmaceutics & Drug Disposition, 16: 351-380.

[10.] Weinstein, D. H. et al. (2013) A new method for determining gastric acid output using a wireless pH sensing capsule. Alimentary pharmacology & therapeutics, 37(12): 1198-1209