Review: Rumen sensors: data and interpretation for key rumen metabolic processes

Abstract

Rumen sensors provide specific information to help understand rumen functioning in relation to health disorders and to assist in decision-making for farm management. This review focuses on the use of rumen sensors to measure ruminal pH and discusses variation in pH in both time and location, pH-associated disorders and data analysis methods to summarize and interpret rumen pH data. Discussion on the use of rumen sensors to measure redox potential as an indication of the fermentation processes is also included. Acids may accumulate and reduce ruminal pH if acid removal from the rumen and rumen buffering cannot keep pace with their production. The complexity of the factors involved, combined with the interactions between the rumen and the host that ultimately determine ruminal pH, results in large variation among animals in their pH response to dietary or other changes. Although ruminal pH and pH dynamics only partially explain the typical symptoms of acidosis, it remains a main indicator and may assist to optimize rumen function. Rumen pH sensors allow continuous monitoring of pH and of diurnal variation in pH in individual animals. Substantial drift of non-retrievable rumen pH sensors, and the difficulty to calibrate these sensors, limits their application. Significant within-day variation in ruminal pH is frequently observed, and large distinct differences in pH between locations in the rumen occur. The magnitude of pH differences between locations appears to be diet dependent. Universal application of fixed conversion factors to correct for absolute pH differences between locations should be avoided. Rumen sensors provide high-resolution kinetics of pH and a vast amount of data. Commonly reported pH characteristics include mean and minimum pH, but these do not properly reflect severity of pH depression. The area under the pH × time curve integrates both duration and extent of pH depression. The use of this characteristic, as well as summarizing parameters obtained from fitting equations to cumulative pH data, is recommended to identify pH variation in relation to acidosis. Some rumen sensors can also measure the redox potential. This measurement helps to understand rumen functioning, as the redox potential of rumen fluid directly reflects the microbial intracellular redox balance status and impacts fermentative activity of rumen microorganisms. Taken together, proper assessment and interpretation of data generated by rumen sensors requires consideration of their limitations under various conditions.

Between-herd variation in resilience and relations to herd performance

“…Not only intake of large amounts of rapidly fermentable carbohydrates, but also grazing can increase the probability of an inverted fat-protein ratio (Elgersma et al, 2004;Couvreur et al, 2006). Yet, grazing does not necessarily deprive health (Dijkstra et al, 2020). Grazing is also likely to lead to a higher LnVar than TMR due to variations in grass quality, which may explain the positive association between LnVar and the proportion of cows with a rumen acidosis indication.…”

Dose–Response Effects of 3-Nitrooxypropanol Combined with Low- and High-Concentrate Feed Proportions in the Dairy Cow Ration on Fermentation Parameters in a Rumen Simulation Technique

“…End-products of microbial fermentation, i.e., VFA, act as electron acceptors, which maintain the strongly reductive rumen milieu and can, therefore, directly be linked to microbial activity [34]. Correspondingly, the Eh in the fluid, reflecting the redox homeostasis and electron transfer, is hypothesised to be a control of enzymatic processes in rumen microorganisms [34,35]. However, Eh positively correlated to total VFA (r = 0.563; N = 24; p = 0.004) in the present investigation, which contrasts findings of an inverse relationship [36].…”

Pressure measurement in the reticulum to detect different behaviors of healthy cows

“…The future perspective is that behavior detection based on measurement of only the A-wave in the reticulum is feasible and would therefore be relevant for wireless sensor techniques. Wireless ruminal sensors are available in commercial dairy farms and particularly in animal research [24][25][26]. Most orally applied sensors migrate towards the reticulum and can measure temperature or pH in the reticulum continuously [26].…”

“…Wireless ruminal sensors are available in commercial dairy farms and particularly in animal research [24][25][26]. Most orally applied sensors migrate towards the reticulum and can measure temperature or pH in the reticulum continuously [26]. Measuring rumen motility by threeaxis acceleration data using a sensor bolus has also been explored [9].…”