Evaluation of macromineral meters to detect cation- anion difference concentration and uniformity in a total mixed ration

Our objectives were to evaluate prediction of macromineral concentrations in a TMR by various meters compared with laboratory macromineral analyses, to determine whether these meters could estimate DCAD in the TMR for close-up and lactating-cow pens, and to determine whether meters could estimate uniformity of TMR. Meters used were Cl (Oakton SaltTestr, Oakton Instruments, Vernon Hills, IL), K (Laqua Twin K Meter, Horiba Scientific, Kyoto, Japan), S (Hanna Instruments Smithfield, RI), and Ca and Mg (Hanna Instruments Ca/Mg Photometer, Smithfield, RI). The TMR samples were collected from close-up and lactating-cow pens in 10 dairies. Ten subsamples of TMR were collected per pen at the time of feeding and sent to Analab (Agri-King Inc., Fulton, IL) for analysis, and another 10 were used to measure mineral concentrations with the meters. Mineral concentrations analyzed by the laboratory were regressed on meter mineral concentrations. Prediction of Cl and K concentrations in TMR were best (R2 = 0.53 and R2 = 0.66, respectively). The combination of K and Cl meter concentrations was able to predict TMR DCAD (R2 = 0.72). The Cl meter was also able to predict TMR coefficient of variation (R2 = 0.57) to evaluate TMR uniformity. Chloride and K meters can aid in identifying the source of TMR DCAD failure and can predict overall TMR uniformity delivered by the mixer wagon.