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Evaluation of reticuloruminal pH measurements from individual cattle: Sampling strategies for the assessment of herd status
- Jonsson, Nicholas N., Kleen, Joachim L., Wallace, R. John, Andonovic, Ivan, Michie, Craig, Farish, Marianne, Mitchell, Malcolm, Duthie, Carol-Anne, Jensen, Dan B., Denwood, Matthew J.
- The veterinary journal 2019 v.243 pp. 26-32
- beef, carbohydrates, dairy cattle, data collection, diet, fermentation, herds, milking, pH, probability, ruminal acidosis
- The application of pH observations to clinical practice in dairy cattle is based on criteria derived primarily from single time-point observations more than 20 years ago. The aims of this study were to evaluate these criteria using data collected using continuous recording methods; to make recommendations that might improve their interpretation; and to determine the relationship between the number of devices deployed in a herd and the accuracy of the resulting estimate of the herd-mean reticuloruminal pH. The study made use of 815,475 observations of reticuloruminal pH values obtained from 75 cattle in three herds (one beef and two twice-daily milking herds) to assess sampling strategies for the diagnosis of sub-acute rumen acidosis (SARA), and to evaluate the ability of different numbers of bolus devices to accurately estimate the true herd-mean reticuloruminal pH value at any time.The traditional criteria for SARA provide low diagnostic utility, the probability of detection of animals with pH values below specified thresholds being affected by a strong effect of time of day and herd. The analysis suggests that regardless of time of feeding, sampling should be carried out in the late afternoon or evening to obtain a reasonable probability of detection of animals with pH values below the threshold level. The among-cow variation varied strongly between herds, but for a typical herd, if using reticuloruminal pH boluses to detect a predisposition to fermentation disorders while feeding a diet that is high in rapidly fermentable carbohydrates, it is recommended to use a minimum of nine boluses.