Signals for identifying cows at risk of subacute ruminal acidosis in dairy veterinary practice

Abstract

SummaryControlling rumen disorders is critical to ensure successful dairy herd health management. Lactation diets of dairy cows are commonly rich in concentrates and low in physically effective fibre. Feeding of these diets increases the risk of rumen disorders with far-reaching consequences for cattle health, welfare and sustainability of dairy production. The term subacute ruminal acidosis or SARA is often used as a synonym for poor rumen health. Being subclinical, SARA lacks of clear symptoms and is therefore difficult to diagnose and to control in the practice. This review article summarises common and identifies new direct and indirect cow signals related to SARA. We have performed a scientific evaluation and interpretation of each of these cow signals by highlighting their advantages and disadvantages from the practitioner's point of view.The gold standard of SARA cow signals still remains direct measurement of ruminal pH. However, continuous pH monitoring is cost-intensive and often biased by sensor drift. Single-point ruminal pH measurements by oral stomach tubing or rumenocentesis have strong limitations. Therefore, there is a need for reliable and robust markers of SARA that are easily accessible and inexpensive. Such indirect parameters are the observation of chewing and feeding activities, as well as the monitoring of milk, faecal, urine and blood variables. Also, novel technologies that allow rapid and non-invasive measurement of the rumen mucosa thickness and ruminal motility patterns might provide advantages in SARA diagnosis. Due to several constraints of these indirect diagnostic tools, such as limited specificity and sensitivity, we strongly recommend using a combination of the signals to reliably identify cows at risk of SARA in a dairy herd. K E Y W O R D Sdairy cow, diagnosis, ruminal pH, subacute ruminal acidosis | INTRODUCTIONA common practice to meet the high nutritional requirements of dairy cows during early and mid-lactation is the inclusion of large quantities of concentrate in the diet. The inclusion of rapidly fermentable carbohydrates generates large amounts of short-chain fatty acids (SCFA) within a short time after ingestion, which can cause a decline in ruminal pH when their production surpasses the absorptive, buffering and outflow capacity of the rumen (Aschenbach, Penner, Stumpff, & Gäbel, 2011). This increase in energy-dense feeds occurs at the expense of fibre-rich forages, impairing digesta stratification and providing fewer stimuli for chewing, thus lowering salivary buffer supply, motility of rumen walls and ruminal mixing (Allen, 1997;. This cascade of events can lead to long and frequent ruminal pH depression with negative effect on rumen health, a condition commonly termed subacute ruminal acidosis (SARA) (Plaizier, Khafipour, | 381 HUMER Et al.Li, . Although there is not yet a consensus on the definition of SARA, it is generally agreed that SARA occurs when the ruminal pH is lower than 5.5-5.8 for several hours a day (Plaizier, Krause, Gozho, & McBride, 2008;Zebeli &...

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

“…For example, if the two cows fed the RAP diet would have been sampled at 1300 h (approximately 3 h after feeding the basal diet), one cow would have a pH value close to the minimum pH value of the full 24-h period (i.e., 5.3), whereas the other cow would have a pH value close to the mean pH value of the full 24-h period (i.e., 6.2) ( Figure 1). Although recommendations have been suggested as to the optimal time of sampling when using infrequent sampling techniques (review Humer et al, 2018), individual variation remains a large obstacle to properly interpret infrequently sampled data.…”

“…Ruminal pH is the outcome of the concerted acid-base regulation efforts of the rumen, including rumen microbiota, and the host (Humer et al, 2018). Microbial fermentation of feed in the rumen yields VFA and (in particular situations) lactic acid.…”

“…Many studies have addressed and classified subacute and acute acidosis based on the degree of ruminal pH depression. A wide range of thresholds to identify acidosis has been proposed, including the mean pH value, nadir pH value, time below a certain pH, and indices that weigh the time spent under the optimal ruminal pH by the magnitude of the deviation from this pH (Humer et al, 2018; et al, 2018). Given the large pH variation in time and location within the rumen, it is of little surprise that there is no scientific consensus regarding pH-related thresholds for identification of acidosis.…”

“…An overview is presented in Table 2. Detailed reviews of these symptoms in relation to ruminal pH can be found elsewhere (Humer et al, 2018;Plaizier et al, 2018;Aschenbach et al, 2019).…”

Effects of substituting kraft pulp with corn silage on dry matter intake, ruminal mat formation, rumen fermentation, and rumination activity in non‐lactating cows

“…). Therefore, when using an NFFS as the main fiber source for cows, attention must be paid to the risk of developing subacute ruminal acidosis (SARA) (Humer, Aschenbach et al., ; Krause & Oetzel, ). On the contrary, we measured the physical properties of the ruminal mat using the penetration resistance test in the rumen (Izumi, Miwa, & Ishizuka, ; Izumi & Unno, ) and found that a suitable ruminal mat was formed if grass forage was used in combination with NFFS, even if a large proportion of NFFS was given to dairy cows.…”