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1369
Close-up diet DCAD, urine pH, and total plasma calcium at calving on a commercial Jersey herd
The objectives of this study were to (1) evaluate the daily variability of close-up dietary cation-anion difference (DCAD) and the DCAD feedbunk distribution, (2) evaluate the daily variability of urine pH, (3) determine if acidification levels were maintained as parturition approached, (4) investigate if DCAD and urine pH were associated, and (5) evaluate if peri-partum urine pH and pospartum calcium levels were related on a commercial 3,500 Jersey herd. Prior to enrollment all cows had to be fed close-up diet >10 d. Over a 40 d period feedbunk samples were collected daily for wet chemistry. Mixing uniformity was evaluated weekly by sampling 5 feedbunk locations. Midstream urine of 70 multiparous cows was collected via manual stimulation from enrollment to calving. Urinary pH was measured cow-side with a handheld meter (Horiba, Montpellier, FR). Coccygeal blood samples were collected after calving for total plasma calcium analysis (47 cows). Changes on urinary pH -10 to 0 d relative to calving (RC) was conducted with MIXED procedure of SAS with repeated measurements. The association between DCAD and urine pH was evaluated using CORR procedure of SAS. DCAD ranged from -136 to 151 mEq/kg of DM with a coefficient of variation (CV) of 216% and DCAD distribution throughout the feedbunk was highly variable (CV = 36 to 182%). The within-day variation on urine pH ranged from 3 to 19% of CV. There was a tendency for an effect of day of the week (P = 0.07) on urine pH, greatest on Monday (6.2) and lowest on Saturday (5.9). Urine pH was lower from -10 to -6 d RC (from 5.6 to 6.1) compared to -5 to 0 d RC (from 6.0 to 6.2; P = 0.08). There was a tendency for a weak association between the dietarian DCAD fed 24 h prior and the urine pH (r = 0.31; P = 0.09). Although urine pH was not associated with postpartum total plasma calcium from -10 to -4 d RC, it was from -3 to 0 d RC (P= 0.02); mostly because cows with acidic urine (pH < 5.8) had lower calcium levels. Our results indicate that in the study herd there was a wide within and across day variation in DCAD as well as urinary pH, and suggest that urine pH might not be a good indicator of postpartum plasma calcium levels.
Keywords: DCAD, urine pH, total plasma calcium