Objectives of the experiment were to determine the length of exposure to an acidogenic diet that would elicit changes in acid-base balance, mineral digestion, and response to parathyroid hormone (PTH)-induced changes in blood Ca and vitamin D 3 in prepartum dairy cows. Nonlactating parous Holstein cows (n = 20) at 242 d of gestation were blocked by lactation (1 or >1) and pretreatment dry matter (DM) intake and, within block, they were randomly assigned to a diet with a dietary cation-anion difference (DCAD) of +200 mEq/kg of DM (DCAD +200) or an acidogenic diet with −150 mEq/kg of DM (DCAD −150). Water and DM intake were measured and blood was sampled daily. Urine was sampled every 3 h for 36 h, and then daily. During PTH challenges on d 3, 8, and 13, cows received i.v. PTH 1-34 fragment at 0.05 µg/kg of body weight every 20 min for 9 h to mimic the pulsatile release of endogenous PTH. Blood was sampled at 0 h, and hourly thereafter until 10 h, and at 12, 18, 24, 36, and 48 h relative to each challenge. Acid-base measures and concentrations of ionized Ca (iCa) in whole blood, and total Ca, Mg, P, and vitamin D metabolites in plasma were evaluated. On d 2 and 7, Ca, Mg, and P balances were evaluated. Cows fed DCAD −150 had smaller blood pH (7.431 vs. 7.389) and HCO 3 − (27.4 vs. 22.8 mM) compared with DCAD +200, and metabolic acidosis in DCAD −150 was observed 24 h after dietary treatments started. Concentrations of iCa begin to increase 24 h after feeding the acidogenic diet, and it was greater in DCAD −150 compared with DCAD +200 by 3 d in the experiment (1.23 vs. 1.26 mM). During the PTH challenges, cows fed DCAD −150 had greater concentration of iCa and area under the curve for iCa than those fed DCAD +200 (48.2 vs. 50.7 mmol/L × hour), and there was no interaction between treatment and challenge day. Concentration of 1,25-dihydroxyvitamin D 3 in plasma did not differ during the PTH challenge, but change in 1,25-dihydroxyvitamin D 3 relative to h 0 of the challenge was smaller in cows fed DCAD −150 than cows fed DCAD +200 (44.1 vs. 32.9 pg/mL). Urinary loss of Ca was greater in cows fed DCAD −150 compared with DCAD +200 (1.8 vs. 10.8 g/d); however, because digestibility of Ca increased in cows fed DCAD −150 (19.7 vs. 36.6%), the amount of Ca retained did not differ between treatments. Diet-induced metabolic acidosis was observed by 24 h after dietary treatment started, resulting in increases in concentration of iCa in blood observed between 1 and 3 d. Collectively, present results indicate that tissue responsiveness to PTH and changes in blood concentrations of iCa and digestibility of Ca are elicited within 3 d of exposure to an acidogenic diet. The increased apparent digestibility of Ca compensated for the increased urinary loss of Ca resulting in similar Ca retention.

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One objective was to evaluate the association of dry matter intake as a percentage of body weight (DMI%BW) and energy balance (EB) prepartum and postpartum, and energy-corrected milk (ECM) postpatum with digestive disorders postpartum. For this, ANOVA was used, and DMI%BW, EB, and ECM were the outcome variables, and left displaced abomasum (LDA), indigestion, and other digestive disorders (ODDZ) were the explanatory variables. The main objective was to evaluate prepartum DMI%BW and EB as predictors of digestive disorders. For this, logistic regression was used, and LDA, indigestion, and ODDZ were the outcome variables and DMI%BW and EB were the explanatory variables. Data from 689 cows from 11 experiments were compiled. Left displaced abomasum was not associated with prepartum DMI%BW or EB. Postpartum data were normalized to the day of the event (day 0). Cows that developed LDA had lesser postpartum DMI%BW on days −24, −23, −12, −7 to 0 and from days 1 to 8, 10 to 12, and 14 and 16, lesser postpartum EB from days −7 to −5, −3 to 0, and 12, and lesser postpartum energy-corrected milk on days −19, −2, −1, 0, 7, 9, 10, 15, and 17 relative to diagnosis than cows without LDA. Cows that developed indigestion had lesser prepartum DMI%BW and EB than cows without indigestion, and lesser postpartum DMI%BW on days −24, −1, 0, 1, and 2, and greater DMI%BW on day 26, lesser ECM on days −24, −2, −1, 0, 1, and 2 relative to diagnosis. Postpartum EB was not associated with indigestion postpartum. Cows that developed ODDZ had lesser prepartum DMI%BW on day −8 and from days −5 to −2, lesser prepartum EB on day −8 and from days −5 to −2, and lesser postpartum DMI%BW than cows without ODDZ. Each 0.1 percentage point decrease in the average DMI%BW and each Mcal decrease in the average EB in the last 3 days prepartum increased the odds of having indigestion by 9% each. Cutoffs for DMI%BW and EB during the last 3 days prepartum to predict indigestion were established and were ≤1.3%/day and ≤0.68 Mcal/day, respectively. In summary, measures of prepartum DMI%BW and EB were associated with indigestion and ODDZ postpartum and were predictors of indigestion postpartum, although the effect sizes were small.

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