Abstract
In ruminant field of digestive research, the appeal to methods of less invasive studies and reproducing the in vivo conditions is essential. The objective of the present study was to determine whether the conditions created with the proposed in vitro batch culture was an accurate reproduction of the physico-chemical and fermentative ruminal conditions observed in vivo. Two experiments were conducted to compare ruminal reducing power measured in vitro, i.e. in batch cultures or, in vivo i.e. in live animals: dairy cows at maintenance (Experiment 1) and lactating dairy cows (Experiment 2). In Experiment 1, at the beginning of incubation period, in vitro redox potential (Eh), pH and Clark’s exponent (rH) values were significantly higher than in vivo (+42 mV, +0.25 and +1.9, respectively) whereas volatile fatty acids (VFA) contents were 2.6 fold lower on average. At the end of incubation, Eh, rH values and VFA contents were similar between both methods whereas pH still remained different. In Experiment 2, at the beginning and at the end of incubation period, in vitro Eh, pH and rH values differed significantly than in vivo. As a result, the in vitro method did not provide a tool to evaluate accurately the level of the reducing status of ruminal milieu compared with in vivo measurement. Nonetheless, it provided strong reducing conditions after 8 h of incubation with levels of rH relatively closed to those observed in vivo. In vitro batch culture could be a good alternative to in vivo trials for a screening approach from an ethic and economic point of view in ruminant field of research.
Highlights
Redox potential (Eh) is a physico-chemical measurement used to characterize an oxidizing or reducing milieu
Julien et al [9] observed a relation between level of dry matter intake (DMI) and ruminal Eh which could vary from −210 to −165 mV, for a low (8 kg of DMI) and high (21 kg) level of DMI respectively
There are very few references regarding measurement of ruminal Eh in vitro: values reached from −211 to −233 mV in an experiment conducted by Farghali and Iben [13] using rumen simulating fermenter technique (Rusitec) [14]
Summary
Redox potential (Eh) is a physico-chemical measurement used to characterize an oxidizing or reducing milieu. Baldwin and Emery [5] previously suggested a clear cut relationship between the metabolic rate of rumen microorganisms and ruminal Eh. As a matter of fact, ruminal Eh is a mixed potential because of the strong fermentative activity involving numerous oxido-reducing couples. As a matter of fact, ruminal Eh is a mixed potential because of the strong fermentative activity involving numerous oxido-reducing couples It reflects a weighted average of the potentials contributed by each of the redox couples as later mentioned by DeLaune and Reddy [2] in soil. To give a better appreciation of absolute reducing power in the milieu, Clark’s Exponent (rH) is likely to be interesting to calculate because of integrating both pH and Eh values in Nernst’s equation [15]
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