The objectives of this study were to determine the effect of decreasing dietary cation-anion difference [DCAD; (Na + K) - (Cl + S)] of the prepartum diet on aspects of mineral metabolism, energy metabolism, and performance of peripartum dairy cows. Multiparous Holstein cows (n = 89) were enrolled between 38 and 31 d before expected parturition and randomized to treatments in a completely randomized design (restricted to balance for previous 305-d mature equivalent milk production, parity, and body condition score) at 24 d before expected parturition. Treatments consisted of a low-K ration without anion supplementation [CON; n = 30, DCAD = +18.3 mEq/100 g of dry matter (DM)]; partial anion supplementation to a low-K ration (MED; n = 30, DCAD = +5.9 mEq/100 g of DM); and anion supplementation to a low-K ration to reach a targeted average urine pH between 5.5 and 6.0 (LOW; n = 29, DCAD = -7.4 mEq/100 g of DM). Cows were fed a common postpartum diet and data collected through 63 d in milk. Urine pH (CON = 8.22, MED = 7.89, and LOW = 5.96) was affected quadratically by decreasing prepartum DCAD. A linear relationship between urine pH and urine Ca:creatinine ratio was observed (r = -0.81). Plasma Ca concentrations in the postpartum period (d 0 to 14; CON = 2.16, MED = 2.19, and LOW = 2.27 mmol/L) were increased linearly with decreasing prepartum DCAD. A treatment by parity (second vs. third and greater) interaction for postpartum plasma Ca concentration suggested that older cows had the greatest response to the low DCAD diet and older cows fed LOW had decreased prevalence of hypocalcemia after calving. A quadratic effect of decreasing DCAD on prepartum DMI was observed (CON = 13.6, MED = 14.0, and LOW = 13.2 kg/d). Milk production in the first 3 wk postpartum was increased linearly with decreasing DCAD (CON = 40.8, MED = 42.4, and LOW = 43.9 kg/d) and DMI in this period also tended to linearly increase (CON = 20.2, MED = 20.9, and LOW = 21.3 kg/d). Overall, effects on intake and milk yield analyzed over wk 1 to 9 postpartum were not significant. This study demonstrates that feeding lower DCAD diets prepartum improves plasma Ca status in the immediate postpartum period and results in increased DMI and milk production in the 3 wk after parturition. Compared with no anion supplementation or lower levels of anion supplementation, greater improvements were observed with the lower DCAD feeding strategy, in which an average urine pH of 5.5 to 6.0 was targeted.

The objectives of this study were to (1) compare a test for serum measurement of total Ca (tCa), Mg, and P (VetTest Chemistry Analyzer, IDEXX Laboratories Inc., Westbrook, ME) to reference methods (spectrophotometric assays on a Beckman Coulter 640e automated clinical chemistry analyzer; Beckman Coulter, Brea, CA), (2) determine the relationship between ionized Ca (iCa) and reference method tCa in the immediate postpartum period, and (3) assess the relative value of these blood Ca indices as predictors of neutrophil oxidative burst activity. Samples were collected from multiparous Holstein cows (n = 33) over the first 5 d in milk. A total of 183 samples for objective 1 and 181 samples for objective 2 were available. Neutrophil oxidative burst activity was assessed once between 2 and 5 d in milk (n = 29). Linear regression demonstrated strong relationships between serum tCa, Mg, and P concentrations measured by the VetTest compared with the reference method. Bland Altman analysis indicated that the VetTest values were higher than the reference method by 0.22 mmol/L for tCa, 0.12 mmol/L for Mg, and 0.16 mmol/L for P. Compared with hypocalcemia categorized at ≤2.0 or ≤2.125 mmol/L with the reference method tCa, thresholds for the VetTest measured tCa of ≤2.23 mmol/L (sensitivity = 87%, specificity = 89%) or ≤2.30 mmol/L (sensitivity = 86%, specificity = 96%) could be used. The relationship between whole-blood iCa and reference method serum tCa differed by sampling time point after calving. Compared with identification of hypocalcemia with serum tCa measurements from the reference method (thresholds of ≤2.0 and 2.125 mmol/L), a whole-blood iCa threshold of ≤1.17 mmol/L resulted in the highest combined sensitivities (94 and 82%) and specificities (80 and 94%) at either threshold. Ionized Ca measurements were more consistently related to outcomes of neutrophil oxidative burst activity measured in vitro. The VetTest measurements of serum tCa reliably identified hypocalcemia when thresholds were adjusted to account for the bias of the test. The variation in the relationship between iCa and reference method tCa in the days following parturition suggest that these measures cannot be used interchangeably as indicators of Ca status. The more consistent associations between iCa and in vitro measures of neutrophil function, compared with tCa, indicated that this may be a more sensitive predictor of functional outcomes associated with postpartum Ca status.

Forty-five multiparous Holstein cows and 15 springing Holstein heifers were used in a randomized block design trial to determine the effect of length of feeding a negative dietary anion-cation difference (DCAD) diet prepartum on serum and urine metabolites, dry matter (DM) intake, and milk yield and composition. After training to eat through Calan doors (American Calan Inc., Northwood, NH), cows within parity were assigned randomly to 1 of 3 treatments and fed a negative-DCAD diet for 3 (3 W), 4 (4 W), or 6 wk (6 W) before predicted calving. Actual days cows were fed negative-DCAD diets was 19.2 ± 4.1, 27.9 ± 3.1, and 41.5 ± 4.1d for 3 W, 4 W, and 6 W, respectively. Before the trial, all cows were fed a high-forage, low-energy diet. During the trial, cows were fed a diet formulated for late gestation (14.6% CP, 42.3% NDF, 20.5% starch, 7.1% ash, and 0.97% Ca) supplemented with Animate (Prince Agri Products Inc., Quincy, IL), with a resulting DCAD (Na + K - Cl - S) of -21.02 mEq/100g of DM. After calving, cows were fed a diet formulated for early lactation (18.0% CP, 36.4% NDF, 24.2% starch, 8.1% ash, and 0.94% Ca) for the following 6 wk with a DCAD of 20.55 mEq/100g of DM. Urine pH was not different among treatments before calving and averaged 6.36. No differences were observed in prepartum DM intake, which averaged 11.4, 11.5, and 11.7 kg/d for 3 W, 4 W, and 6 W, respectively. Prepartum serum total protein, albumin, and Ca concentrations, and anion gap were within normal limits but decreased linearly with increasing time cows were fed a negative-DCAD diet. No differences were observed in serum metabolite concentrations on the day of calving. Postpartum, serum total protein and globulin concentrations increased linearly with increasing length of time the negative-DCAD diet was fed. No differences were observed in postpartum DM intake, milk yield, or concentration of fat or protein among treatments: 19.1 kg/d, 40.6 kg/d, 4.30%, and 2.80%; 19.6 kg/d, 41.5 kg/d, 4.50%, and 2.90%; and 18.6 kg/d, 41.0 kg/d, 4.30%, and 2.73% for 3 W, 4 W, and 6 W, respectively. Results of this trial indicate that no differences existed in health or milk production or components in cows fed a negative-DCAD diet for up to 6 wk prepartum compared with those fed a negative-DCAD diet for 3 or 4 wk prepartum.

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The objective of this experiment was to determine the effects of dietary vitamin D source on serum calcium (Ca), urinary Ca excretion and milk production when fed in combination with a prepartum acidogenic negative DCAD diet. Non-lactating, pregnant multiparous cows (n=15), balanced for breed (Holstein n = 9 and Jersey n = 6) and previous mature equivalent milk production, were assigned to 1 of 3 treatments (5 cows/treatment), consisting of a control (PCH; positive DCAD, 8.9 mEq/100g DM) and two negative DCAD diets (-15.4 mEq/100g DM), one with vitamin D3 (Cholecalciferol; NCH), and one with 25-hydroxyvitamin D3 (calcidiol; NCA; DSM Nutritional Products). The treatments were formulated to provide 1.95 mg/d of vitamin D and were fed 28 d prior to expected calving date. Delivery of vitamin D sources was accomplished by manufacture of a pellet and 2 kg of these pellets were individually fed simultaneously each day along with 2 kg of ground corn daily at 0800. Negative DCAD treatments were formulated to provide 0.46 kg/d of Animate (Phibro Animal Health) and, if needed, additional Animate was top-dressed at each feeding to achieve a urine pH between 5.5 – 6.0 based on the previous day’s urine pH. Close-up cows had ad libitum access to chopped bermudagrass (Cynodon dactylon L.) hay and hay intake was measured using SmartFeed Pro systems (C-Lock Inc.; Rapid City, SD). Prepartum urine and serum samples were collected weekly and serum was collected 36, 48, and 72 h post-calving. Prepartum DMI as a percent of body weight was not (P = 0.66) affected by treatments. Cows fed NCH and NCA had greater (P = 0.02) prepartum serum Ca than PCH and tended to have greater urinary Ca excretions (P = 0.10). Average postpartum serum Ca (mg/dL) was greater (P = 0.05) for cows fed NCH (8.8) compared with PCH (7.8), whereas NCA (8.4) was numerically intermediate and not (P > 0.05) different from either of the other treatments. Postpartum DMI was not affected by treatment (P = 0.39). Daily MY (kg/d) was greatest (P < 0.01) for NCA (37.5) compared with the other treatments and NCH (34.1) was intermediate and greater than PCH (29.9). These results suggest that an acidogenic prepartum diet in combination with vitamin D was effective in maintaining peripartum serum Ca and the 25-hydroxy form of vitamin D improved MY compared with NCH in early lactation.