Meta-analysis of 0 to 8 h post-prandial evolution of ruminal pH

Abstract

The objective of this study was to identify relevant descriptors of ruminal pH post-prandial evolution that can replace the mean pH (considered unsatisfactory). These descriptors are to be used in the attempts to predict ruminal pH from dietary characteristics, in order to quantify the potential of a diet to induce subacute ruminal acidosis from its intrinsic characteristics. A total of 219 pH curves, reported as graphics in 48 published articles describing the post-prandial evolution of ruminal pH (first 8 h), were digitized by image analysis then summarized in 15 pH variables. Relationships among pH variables and the principal components (PCs) of pH variability were analyzed in order to identify possible alternatives to mean pH, as the average value of all pH data the curve is composed of. Two groups of pH variables were identified according to their relationship with the most important principal components. A first group, including mean pH, was closely related to PC 1 , which accounted for 78% of data variability; hence, correlations between variables of this group were generally high. Of these, threshold-related variables were distinct as their withinstudy correlations with mean pH were rather moderate (0.69 on average). This suggests they might carry supplementary information that could explain the variation in ruminal pH induced by within-study factors, e.g. diet characteristics. However, caution should be taken in their use because of their truncation at 0 h and their non-normal distribution. Variables from the second group were independent of the PC 1 , and thus of the first group of variables, whereas they were mostly related to PC 2 and PC 3 . This implies they are complementary to mean pH. Of this second group, the rate of pH decreases or the time period when pH reaches its minimum might be useful to better describe the ruminal status, from the point of view of the risk of subacute ruminal acidosis.

The use of a multivariate analysis to study between-goat variability in feeding behavior and associated rumen pH patterns

“…The improvement in ruminal pH status with increased rumination observed by Beauchemin et al (2003) might have been more due to the differences in dietary fiber content than to the differences in time spent ruminating per se. Given that similar mean rumen pH can result from very different rumen pH patterns, the present analysis confirms that mean rumen pH cannot be considered as the sole descriptor of ruminal acidosis (Dragomir et al, 2008). Further, the present analysis shows that means over long periods of time of duration of eating, ruminating or rumen pH are not sufficient to describe what really happened during the studied period.…”

Identification of Differentially Expressed Proteins in Liver in Response to Subacute Ruminal Acidosis (SARA) Induced by High-concentrate Diet

“…But the average pH over a day is sometimes considered as a poor indicator of SARA (Sauvant et al, 1999), because it does not reflect the large daily fluctuations in pH (Dijkstra et al, 1993; Dragomir et al, 2008). Several authors have pointed out the necessity of analyzing pH fluctuations (Nocek, 1997; Beauchemin et al, 2001), and the time spent under a pH threshold.…”

Approche quantitative de l’aidose chez les ruminants

“…Outre la teneur moyenne du pH, d'autres critères ont été créés à partir de ces cinétiques, comme la durée de pH en dessous d'une valeur seuil (par exemple 6,0), la chute de pH durant la période postprandiale proximale, l'aire sous la courbe d'évolution post prandiale du pH etc…. Dans une étude de synthèse quantitative de la littérature (Dragomir et al 2008), nous avons montré que tous ces critères étaient en fait étroitement corrélés entre eux. Aussi la valeur moyenne du pH est-elle la donnée la plus fréquemment utilisée.…”