UC Davis

Some of the most common failures of dietary cation-anion difference (DCAD) TMR to prevent hypocalcemia, are a lack or dilution of acidifying minerals or inadequate mixing of the TMR. Currently, urine pH is used to monitor metabolic acidification in cows 3 wk prior to parturition. However, urine is difficult to collect and does not indicate why the close up TMR failed to acidify the cows. Mineral meters that measure solubilized mineral from the TMR could be used to approximate the amount of mineral in the TMR. The objectives of this study were to 1) evaluate how well meters predicted macromineral concentration in a TMR compared to laboratory macromineral analyses; 2) determine if the meters could estimate DCAD in TMR for close up and lactating cows; and 3) to determine if the meters could measure TMR uniformity. 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) Ca and Mg (Hanna Instruments Ca/Mg Photometer , Smithfield, RI). The TMR samples were collected from close up and lactating cow pens at 10 commercial 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. Time length of soaking each TMR subsample for each mineral was pre-determined by identifying the time of plateau of mineral concentration (Cl for 90 min, Ca for 150 min, K for 180 min and Mg for 210 min). Data were analyzed using PROC REG in SAS (SAS Institute v. 9.4, 2021), regressing lab mineral concentration on meter mineral concentration with pen as a covariate. Prediction of Cl and K concentrations in the TMR on a DM basis were best (R2 = 0.69 and R2 = 0.78, respectively). The combination of both K and Cl meter concentrations were able to predict DCAD in the TMR in mEq (R2 = 0.88), and the Cl meter was also able to predict TMR coefficient of variation (CV) (R2 = 0.89) to evaluate TMR uniformity. All regressions had slopes not different from 1, y-intercepts not different from 0, and normally distributed residual errors. Therefore, Cl and K meters can be used to predict the macromineral concentration, DCAD of TMR, and Cl or K meters can be used to predict overall TMR uniformity of a feed drop.