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An evaluation of a calf-side betahydroxybutyrate test in dairy calves fed a high plane of nutrition and weaned at six versus eight weeks of age
Recent research suggests that circulating betahydroxybutyrate (BHBA) levels may be a meaningful indicator of grain intake and rumen development in pre-ruminant calves. As such, BHBA levels may be a surrogate measure of rumen function to assure minimal weaning stress during the transition from liquid to solid feed. The Precision Xtra test for BHBA in whole blood has been validated in lactating dairy cows. The objective of this study was to validate the Precision Xtra test against a gold standard laboratory method in calves at weaning, and to determine preliminary associations between circulating BHBA levels and amount of solid feed intake in dairy calves fed higher planes of nutrition and weaned at 6 versus 8 wk of age. A total of 20 Holstein female calves were randomly assigned at birth to be weaned at 6 wk (n = 10) or 8 wk (n = 10). Milk replacer (mixed at 150 g/L) was offered at 1.2 kg/calf/d in two meals until a 1-wk step down, where meals were reduced by 50% 1 wk before weaning. Measurements included daily starter, chopped straw and water intake, as well as weekly blood BHBA, until 70 d of life. Whole blood BHBA was determined by the Precision Xtra test at calf-side. In addition, serum was separated from a clotted sample, frozen and stored until laboratory analysis was performed. Data were plotted and Spearman correlation coefficients between the Precision Xtra and laboratory BHBA levels were determined. Using an arbitrary level of BHBA to indicate meaningful rumen function, the sensitivity and specificity of the Precision Xtra test were calculated. Finally, the correlation between BHBA levels and solid feed intake was determined. The correlation coefficient between Precision Xtra and laboratory BHBA was high (r = 0.95; P < 0.05). Using a cut-off level of ≥ 250 µmol/L BHBA on the laboratory test, the sensitivity and specificity of the Precision Xtra test were 91% and 93%, respectively. These test characteristics were even higher, when the assessment was restricted to calves weaned at 8 wk (100% and 94%, respectively). The correlation between BHBA results and solid feed intake was also high (r = 0.90; P< 0.05). These results indicate that the Precision Xtra whole blood BHBA test conducted at calf-side is a highly accurate test, and shows some promise for use in the decision-making process of determining appropriate weaning age.
Keywords: Calves, weaning, betahydroxybutyrate