The objective was to (1) identify relationships between prefresh diet sorting, as measured by herd urine pH coefficient of variation (pHCV), and management and TMR factors related to the initially fed (0 h) and 6 h post-feeding (6 h) rations, and (2) determine whether pre-fresh sorting factors are associated with herd level prevalence of hyperketonemia (herdBHB), defined as the percentage of fresh cows with BHB ≥1.2 mmol/L. Data were collected from commercial dairy herds (n = 23) fed pre-fresh rations supplemented with anions in a cross-sectional study design. Pre-fresh TMR particle size was analyzed at 0 h and 6 h, urine pH was measured on ~15 multiparous prefresh cows at 6 h postfeeding, and whole blood BHB concentrations (Nova Vet, Nova Biomedical, Waltham, MA) were measured on ~15 multiparous fresh cows. In SAS v. 9.4, univariable relationships were explored for each predictor with the outcomes phCV and herdBHB using PROC REG. Variables associated with pHCV (P < 0.20) were offered to a multivariable regression model. A backward selection method was used and variables remained if P < 0.10. The final model (P < 0.001) had 3 remaining variables for predicting pHCV; average herd urine pH (avepH), ash (%DM) at 0 h (Ash0h) and percent of DM at 0h (DM0h). The parameter estimates are presented in Table 1. The model resulted in an adjusted R² = 0.69. For interpretation purposes, a 1-unit increase in avepH, Ash0h, and DM0h results in the pHCV to increase by 4.73, 1.44, and decrease by 0.44, respectively. No relationship existed between herdBHB and pHCV (R² = 0.06), avepH (R² = 0.01), or the percentage of TMR on the top sieve of the Penn State Particle Separator at 0h (R² = 0.00). This study provides insight on factors that may influence ration sortability, as reflected in the variation of the herd urine pH. The avepH was the most influential variable on pHCV and we did not find any biologically plausible prepartum variables to influence fresh cow health, as determined by herdBHB. Table 1.

Variable	Parameter estimate	SE	P-value
Intercept	−12.02	7.65	0.13
avepH	4.73	0.99	<0.001
DM0h	−0.44	0.10	0.007
Ash0h	1.44	0.47	<0.001