Abstract #T136

# T136
Evaluation of two pH strips on urine from multiparous Holstein cows fed a partially acidified diet prepartum.
L. K. Fehlberg*1, F. C. Cardoso1, 1University of Illinois, Urbana, IL.

Feeding a partially acidified diet prepartum (negative DCAD) can induce metabolic acidosis, thereby decreasing urine pH. The objective of this study was to determine the efficacy of 2 methods to measure urine pH and the effect of urine pH on prepartum dry matter intake (DMI) and milk yield of the first week postpartum. Thirty multiparous, multiparous Holstein cows were provided a DCAD diet (DCAD = −118 mEq/kg) beginning at 28 d relative to predicted calving (DRC) until calving. Urine pH was collected by manual massage at 5 time points (TP1, TP2, TP3, TP4 and TP5). Time point 1 was −30 DRC (±4.2; n = 23) before cows consuming the DCAD diet, TP2 was −23 DRC (±3.9; n = 30), TP3 was −16 DRC (±4.0; n = 30), TP4 was −9 DRC (±3.9; n = 30), and TP5 was −4 DRC (±3.0; n = 24). Cows were blocked (n = 5) by calving month. Urine pH was measured using Fisher pH sticks (pHF; Thermo Fischer Scientific, Waltham, MA), pHion balance test strip (pHI; pHion Balance, Scottsdale, AZ), or a portable pH meter (pHP; Accumet AP115, Thermo Fisher Scientific, Waltham, MA). Cows were categorized as HIGH (urine pH greater than the median) or LOW (urine pH lower than median) for each TP. Individual DMI and milk yield were obtained daily. Cows were milked 2×/d. Statistical analyses were performed using the MIXED and REG procedures of SAS (SAS Institute Inc., Cary, NC). Milk yield and DMI were not different between cows in LOW or HIGH using the pHP at any time point (P > 0.10). Dry matter intake tended (P = 0.06) to be greater in cows classified as HIGH (15.12 kg) compared with LOW (12.79 kg) at TP 1 when pHF and pHI were utilized but not pHP. Milk yield and DMI in cows were not different at TP 2, 3, 4, and 5 when urine was measured using pHF and pHI (P > 0.10). When all TP were pooled (n = 156), the pHP and pHF were positively correlated (P < 0.01; R2 = 0.95; pHP = 0.88pHF+0.94). There was also a positive correlation between pHP and pHI (P < 0.01; R2 = 0.94; pHP = 0.88pHI+0.98). In conclusion, pHF and pHI seems to be accurate methods of urine pH measurement. Additionally, the DCAD diet did not affect milk yield or DMI.

Key Words: dietary cation-anion difference, pH, urine