Ruminal pH regulation and nutritional consequences of low pH☆
Introduction
Fermentation of feedstuffs in the reticulo-rumen (hereafter: rumen) produces volatile fatty acids (VFA) and lactic acid. These acids can accumulate and reduce ruminal pH if rumen buffering cannot keep pace with their accumulation (Plaizier et al., 2009). Low rumen pH for prolonged periods each day can negatively affect feed intake, microbial metabolism, and nutrient degradation, and low ruminal pH is related to inflammation, laminitis, diarrhea and milk fat depression (Stone, 2004, Krause and Oetzel, 2006, Enemark, 2008), although the extent of problems that occur and the precise mechanisms by which low ruminal pH increases these disorders have not been fully characterized. High yielding dairy cows fed energy dense rations rich in rapidly fermentable starch or sugars at high feed intake levels are particularly susceptible to acidosis, although goats, sheep and other ruminants are also prone to the disease (Braun et al., 1992). Subacute ruminal acidosis, which induces an elevation in rumen temperature (AlZahal et al., 2008), affects from 10% to 40% of dairy cattle in a herd, resulting in large financial losses and major concern for animal welfare reasons (Garrett et al., 1999, Kleen et al., 2009, Tajik et al., 2009).
Despite the impact of low ruminal pH on farm profitability and animal welfare, current empirical feed evaluation systems are unable to address the complex interrelationships in the rumen that result in acidosis following the ingestion of certain feeds. These systems aim to match nutrient requirements with nutrient intake at pre-defined production levels but are not suitable to predict the responses to dietary changes in terms of production level and product composition, digestion of nutrients and excretion of waste end-products to the environment, and nutrition related disorders. The change from a requirement to a response system to meet the needs of various stakeholders requires prediction of the profile of absorbed nutrients and its subsequent utilization for various purposes (Hanigan, 2005, Dijkstra et al., 2007, Kebreab et al., 2009). Mechanistic approaches to feed evaluation may address the relationships between host animal, feed and rumen micro-organisms, and demonstrate a greater capacity for describing ruminal fermentation processes that determine ruminal pH (Baldwin, 1995, Dijkstra et al., 2008). The development of these models to address prediction of ruminal pH requires concepts and data on the dynamics of nutrient degradation, microbial fermentation and acid removal from the rumen. Therefore, this contribution considers aspects of pH regulation, as well as effects of ruminal pH on rate of substrate degradation and on type of VFA formed.
Section snippets
Ruminal pH regulation
Fermentation of feed by microorganisms in the rumen produces VFA and sometimes lactic acid. Ruminal pH will drop when VFA or lactic acid accumulate in the rumen. To prevent this drop in pH related to production of acids in the rumen and acids ingested with the feed, the acids have to be removed from the rumen or buffered. Volatile fatty acids are removed from the rumen by passage in the liquid phase and by absorption through the rumen wall (Aschenbach et al., 2009). Acids accumulated in the
Ruminal pH and substrate degradation
The primary fibrolytic bacteria are intolerant to low ruminal pH, and rumen fiber digestion rapidly decreases when pH drops below critical values (Erdman, 1988, Russell and Wilson, 1996). In contrast, low pH values can facilitate the growth and activity of amylolytic bacteria (Mackie et al., 1978). High dietary levels of rapidly fermentable carbohydrates that results in high amounts of VFA produced and/or insufficient buffering of the rumen contents, both leading to low pH values, can thus
Ruminal pH and type of VFA produced
Volatile fatty acids produced through ruminal fermentation are of paramount importance, providing some 0.7 of the ruminant's energy supply (France and Dijkstra, 2005). The proportions among individual VFA are of particular interest because different VFA arise from variations in substrate intake and bacterial populations, and the individual VFA have distinct metabolic fates. In particular, propionic acid is a substrate for gluconeogenesis and is the main source of glucose in the ruminant.
Conclusion
Ruminal pH is a key determinant of the profile of nutrients available for absorption. Rate of clearance of VFA and secretion of buffers into the rumen have a major impact on ruminal pH, and more quantitative information is required on VFA absorption mechanisms. Reduction in ruminal pH is associated with decreased fiber degradation, decreased acetate to propionate ratio, and decreased CH4 formation. Quantitative understanding and description of the processes involved in pH regulation, and in the
Funding
JF and SL gratefully acknowledge receipt of collaborative grant no. SAB2010-0151 from the Spanish “Ministerio de Educación” under the program “Programa Nacional de Movilidad de Recursos Humanos del Plan Nacional de I-D+i 2008-2011 – subprograma EXTESP-EDU”. Dairy Farmers of Canada is thanked for financial support.
Conflict of interest
None.
References (111)
- et al.
Frequent allocation of rotationally grazed dairy cows changes grazing behavior and improves productivity
J. Dairy Sci.
(2008) - et al.
The effect of silage and concentrate type on intake behavior, rumen function, and milk production in dairy cows in early and late lactation
J. Dairy Sci.
(2008) - et al.
Rumen stoichiometric models and their contribution and challenges in predicting enteric methane production
Anim. Feed Sci. Technol.
(2011) Relationship between fermentation acid production in the rumen and the requirement for physically effective fiber
J. Dairy Sci.
(1997)Effects of diet on short-term regulation of feed intake by lactating dairy cattle
J. Dairy Sci.
(2000)- et al.
A mathematical approach to predicting biological values from rumen pH measurements
J. Dairy Sci.
(2007) - et al.
Ruminal temperature may aid in the detection of subacute ruminal acidosis
J. Dairy Sci.
(2008) - et al.
Modeling of the rumen water kinetics and effects on rumen pH changes
J. Dairy Sci.
(1988) - et al.
Survival of Escherichia coli O157:H7 in feces from corn- and barley-fed steers
FEMS Microbiol. Lett.
(2005) - et al.
Estimation of the stoichiometry of volatile fatty acid production in the rumen of lactating cows
J. Theor. Biol.
(2006)
Modelling the implications of feeding strategy on rumen fermentation and functioning of the rumen wall
Anim. Feed Sci. Technol.
A model of enteric fermentation in dairy cows to estimate methane emission for the Dutch National Inventory Report using the IPCC Tier 3 approach
Anim. Feed Sci. Technol.
Effects of urea and starch on rumen fermentation, nutrient passage to the duodenum, and performance of cows
J. Dairy Sci.
Eating and resting salivation in early lactating dairy cows
J. Dairy Sci.
Simulation of nutrient digestion, absorption and outflow in the rumen: model description
J. Nutr.
Production and absorption of volatile fatty acids in the rumen
Livest. Prod. Sci.
Application of the gas production technique to feed evaluation systems for ruminants
Anim. Feed Sci. Technol.
Predicting the profile of nutrients available for absorption: from nutrient requirement to animal response and environmental impact
Animal
Comparison of energy evaluation systems and a mechanistic model for milk production by dairy cattle offered fresh grass-based diets
Anim. Feed Sci. Technol.
Dietary buffering requirements of the lactating dairy cow: a review
J. Dairy Sci.
The monitoring, prevention and treatment of sub-acute ruminal acidosis (SARA): a review
Vet. J.
Diagnostic methods for the detection of subacute ruminal acidosis in dairy cows
J. Dairy Sci.
Effect of abomasal pectin infusion on digestion and nitrogen balance in lactating dairy cows
J. Dairy Sci.
Influence of feed ion content on buffering capacity of ruminant feedstuffs in vitro
J. Dairy Sci.
Influence of carbohydrate source and buffer on rumen fermentation characteristics, milk yield, and milk composition in early lactating Holstein cows
J. Dairy Sci.
Short communication: effect of subacute ruminal acidosis on in situ fiber digestion in lactating dairy cows
J. Dairy Sci.
Understanding and preventing subacute ruminal acidosis in dairy herds: a review
Anim. Feed Sci. Technol.
Effect of concentrate level and feeding management on chewing activities, saliva production, and ruminal pH of lactating dairy cows
J. Dairy Sci.
Evaluation of models to predict the stoichiometry of volatile fatty acid profiles in rumen fluid of lactating Holstein cows
J. Dairy Sci.
Initial pH as a determinant of cellulose digestion rate by mixed ruminal microorganisms in vitro
J. Dairy Sci.
Carbohydrate quantitative digestion and absorption in ruminants: from feed starch and fibre to nutrients available for tissues
Animal
pH dynamics and bacterial community composition in the rumen of lactating dairy cows
J. Dairy Sci.
The dietary forage to concentrate ratio does not affect the rate of volatile fatty acid absorption but alters the expression of genes regulating energy metabolism in rumen tissue
J. Dairy Sci.
Influence of time of feeding a protein meal on ruminal fermentation and forestomach digestion in dairy cows
J. Dairy Sci.
The importance of pH in the regulation of ruminal acetate to propionate ratio and methane production in vitro
J. Dairy Sci.
Why are ruminal cellulolytic bacteria unable to digest cellulose at low pH?
J. Dairy Sci.
Production of volatile fatty acids in the rumen and cecum–colon of steers as affected by forage: concentrate and forage physical form
J. Dairy Sci.
Digestion and passage kinetics of forage fiber in dairy cows as affected by fiber-free concentrate in the diet
J. Dairy Sci.
Nutritional approaches to minimize subacute ruminal acidosis and laminitis in dairy cattle
J. Dairy Sci.
Effect of pH and energy spilling on bacterial protein synthesis by carbohydrate-limited cultures of mixed rumen bacteria
J. Dairy Sci.
Formation and utilization of end products of lignocellulose degradation in ruminants
Anim. Feed Sci. Technol.
Effects of feeding perennial ryegrass with an elevated concentration of water soluble carbohydrates on intake, rumen function and performance of dairy cows
Anim. Feed Sci. Technol.
The influence of nutrient balance on milk yield and composition
Ammonia and urea transport across the rumen epithelium: a review
Anim. Health Res. Rev.
Effect of daily movement of dairy cattle to fresh grass in morning or afternoon on intake, grazing behaviour, rumen fermentation and milk production
J. Agric. Sci. (Camb.)
Bicarbonate-dependent and bicarbonate-independent mechanisms contribute to nondiffusive apical uptake of acetate in the ruminal epithelium of sheep
Am. J. Physiol. Gastrointest. Liver Physiol.
The effect of absorption on the acidity of rumen contents
J. Physiol.
Modeling Ruminant Digestion and Metabolism
Dietary mitigation of enteric methane from cattle
CAB Rev.: Perspect. Agric. Vet. Sci. Nutr. Nat. Resour.
Cited by (239)
Effect of short-term abomasal corn starch infusions on postruminal fermentation and blood measures
2023, Journal of Dairy Science
- ☆
This paper is part of the special issue entitled: Rumen Health: A 360̊ Analysis, Guest Edited by A. Van Vuuren, S. Calsamiglia and Editor for Animal Feed Science and Technology, P. Udén.