Short Communication: Feeding behaviors are not correlated with area-under-the-curve for reticulorumen pH below 5.8 and 5.6 in finishing steers

Abstract

Persistent low rumen pH (<5.8-5.6) is the most researched sign of Subacute Ruminal Acidosis (SARA), a disorder in cattle caused by consumption of a high-concentrate diet. Animals may ruminate less and eat forages to slow acid accumulation, but there are no other easily detectable signs of SARA. The objective was to evaluate whether feeding behavior is correlated to daily time spent below reticulorumen pH 5.8 and 5.6. We predicted that the severity of daily fluctuation in pH below 5.8 would be negatively correlated to daily intake, the number of visits to the feed bin, and time spent eating, as decreases in these variables are indicative of sickness behavior. These aspects of feeding behavior are moderately, positively correlated to each other (r≥0.3), thus do not represent 3 independent tests of our hypothesis, but rather, create an overall picture of feeding behavior. Eighteen steers were fed a high-concentrate finishing ration ad-libitum, with delivery twice daily into automated feed bins that measured feeding behavior. Wireless boluses measured reticulorumen pH in 10-min intervals continuously for 11.5±0.9 d (mean±SD). The mean daily pH was 6.1±0.2, the mean daily maximum pH was 6.7±0.1, and the mean daily minimum pH was 5.5±0.2 (mean±SD). The area-under-the-curve (AUC) for pH below 5.8 and 5.6 for each 24-h day was calculated for each animal (AUC: 75.2±15.5 and 30.3±7.4 pH x min/24 h, respectively, mean±SE). Repeated-measures correlation analyses investigated the relationship between AUC and each of the behavioral variables. There was no correlation between time spent eating (74.0±>3.0 min/24 h, mean±SE) or visits to the feed (27.0±2.4 no./24 h) and AUC (r=-0.072; p=0.34). A weak negative correlation existed between the DMI (10.0±0.2 kg/24 h) and AUC < pH 5.6 (r=-0.164; p=0.03), but not for AUC < pH 5.8 (r=-0.122, p=0.10). The same analyses were conducted for daily AUC and the feeding behaviors on the following day to capture a delayed behavioral response, but no associations were detected (p≥0.12). The feeding behaviors measured alone were not adequate to describe the severity of reticulorumen pH depression in finishing cattle. Individual variation in tolerance to low pH, adequate time to adapt to the finishing ration, and/or selection pressures for weight gain may have contributed to the lack of a defined sickness response to SARA.