Blood mineral, hormone, and osteocalcin responses of multiparous Jersey cows to an oral dose of 25-hydroxyvitamin D3 or vitamin D3 before parturition

Twenty-seven multiparous Jersey cows were randomly assigned to receive an oral bolus containing corn starch (control, CON), corn starch plus 15 mg of 25-hydroxyvitamin D₃ (25-OH), or 15 mg of cholecalciferol (D₃) at 6 d before expected parturition. Cows were maintained in individual box stalls from 20 d before expected parturition and fed a common diet. Jugular blood samples were collected at −14, −13, −5, −4, −3, −2, −1 d before expected calving, at calving, and at 1, 3, 5, 7, 9, 11, 13, 28, 56, and 84 d postcalving. After calving, cows were housed in 1 pen in a free-stall barn and consumed a common diet. Colorimetric assays were used to analyze Ca, P, and Mg concentrations in serum. Serum concentrations of osteocalcin (OC), an indicator of bone formation, serum 25-hydroxyvitamin D₃, and parathyroid hormone (PTH) were determined in samples obtained from d −5 through d 13. The 9 control multiparous cows and 5 untreated primiparous cows were used to evaluate the effect of parity on the variables that were measured. There was no effect of parity on Ca, PTH, or 25-OH concentration. Compared with second-lactation cows and older cows (>2 lactations), first-lactation cows had greater serum OC (22.3, 32.0, and 48.3 ng/mL, respectively), indicating that younger animals were forming more bone. Blood Ca, P, and Mg decreased near the time of calving and then increased over time. Serum 25-hydroxyvitamin D₃ was greater for cows dosed with 25-OH (119.0 ng/mL) compared with those dosed with D₃ (77.5 ng/mL) or CON (69.3 ng/mL). Cows dosed with 25-OH tended to have lower serum PTH concentration, but treatments did not affect serum Ca, P, or Mg. Serum OC was greater in second-lactation cows compared with cows entering their third or fourth lactation but OC was unaffected by treatment. Although results indicated a 60% increase in serum 25-hydroxyvitamin D₃ due to a single oral dose of 25-OH before calving, the amount administered in this study apparently was not sufficient for initiation of any improvement in Ca homeostasis at parturition.     

Field trial of 2 calcium supplements on early lactation health and production in multiparous Holstein cows

Our objectives were to measure serum Ca concentrations in the first 48 h postpartum in cows supplemented with oral Ca or subcutaneous Ca and nonsupplemented cows and evaluate the effect of these treatments on the incidence of metritis, displaced abomasum, mastitis, and early lactation disease (any of the diseases milk fever, retained placenta, metritis, or displaced abomasum), removal from the herd, pregnancy to first insemination, and average daily milk yield for the first 10 wk of lactation. We conducted 2 experiments on 1 commercial herd in New York State. In experiment 1, multiparous Holstein cows (n = 30) were blocked by parity (2 and ≥3) and sequentially assigned at calving to nontreated control (CON, n = 10), subcutaneous administration of 500 mL 23% Ca gluconate at calving (SC, n = 10), or administration of an oral Ca bolus containing 43 g of calcium at calving and again 12 h later (OB, n = 10). Blood was collected before treatment and at 1, 2, 4, 8, 12, 24, and 48 h thereafter for measurement of serum total Ca concentration. In experiment 2, 1,478 multiparous Holstein cows were sequentially assigned by calving date to the same 3 treatments (CON, n = 523; SC, n = 480; OB, n = 475). In experiment 1, SC cows had greater Ca concentrations from 1 through 12 h post-treatment and OB cows had greater Ca concentrations at 1 and 24 h post-treatment compared with CON cows. We found no difference in risk of metritis, displaced abomasum, early lactation disease diagnosis, or pregnancy to first insemination among treatments. Treatment with SC or OB had no effect on average daily milk yield compared with CON cows (CON = 46.7 kg; SC = 47.1 kg; OB = 47.0 kg). Cows treated with SC or OB that had a high relative herd milk rank in the previous lactation were almost half as likely to be diagnosed with mastitis in the first 60 DIM compared with CON cows [risk ratio (RR)_SC = 0.57, RR_OB = 0.54]; however, we found no difference in risk of mastitis among treatments for cows with low relative herd milk rank. Second-parity cows fed a negative prepartum dietary cation-anion difference ration and treated with SC or OB were more likely to be removed from the herd than CON cows (RR_SC = 3.91, RR_OB = 4.72); this difference was not observed in second-parity cows fed a neutral prepartum dietary cation-anion difference ration or in parity ≥3 cows. Although Ca supplementation increased serum Ca, this effect did not greatly improve milk production or health and reproductive outcomes.     

Effects of postpartum oral calcium supplementation on milk yield,milk composition,and reproduction in multiparous Jersey and Jersey × Holstein crossbreed cows

The objective of the present study was to evaluate the effects of postpartum oral calcium supplementation on milk yield, energy-corrected milk yield, milk fat concentration, milk protein concentration, and somatic cell count linear score across the first 3 monthly tests postpartum, peak milk yield, risk of pregnancy at first service, and hazard of pregnancy by 150 d in milk on 1,129 multiparous Jersey and Jersey × Holstein crossbreed cows from 2 commercial dairies. After calving, cows were systematically assigned to control (no oral calcium supplementation; n = 567) or oral calcium supplementation at 0 and 1 d in milk (oral Ca; 50 to 60 g of calcium as boluses; n = 562). Monthly test milk yield, composition, and somatic cell count information was obtained from the Dairy Herd Improvement Association. Herd records were used for reproductive data. Statistical analysis was conducted using generalized multiple linear, Poisson, and Cox's hazard regressions. Treatment effects were evaluated considering cow-level information available at parturition (parity, breed, previous lactation milk yield, previous lactation length, dry period length, gestation length, body condition, and locomotion score at calving, calving ease, and calf sex). In addition, for a subset of cows serum calcium concentration before treatment administration was evaluated (n = 756). Overall, oral calcium supplementation did not affect the evaluated productive and reproductive variables. However, effects conditional to previous lactation length and calving locomotion score were observed. Milk yield and energy-corrected milk yield across the first 3 monthly tests were 1.8 kg/d higher for supplemented cows with a previous lactation length within the fourth quartile, compared with control cows on the same quartile. Energy-corrected milk yield tended to be 1.1 kg/d lower for supplemented cows with a previous lactation length within the first quartile, compared with control counterparts. Peak milk yield tended to be 1.6 kg higher for supplemented cows with a calving locomotion score ≥2, compared with control cows with the same locomotion score. Treatment effects were not conditional to serum calcium concentration before treatment administration. Our results suggest that postpartum oral calcium supplementation effects are conditional to cow-level factors such as previous lactation length and calving locomotion score in multiparous Jersey and Jersey × Holstein crossbreed cows.     

Strategies to gain body condition score in pasture-based dairy cows during late lactation and the far-off nonlactating period and their interaction with close-up dry matter intake

In pasture-based systems, cows are generally thinner at the end of lactation than cows fed total mixed rations and, as a result, over-feeding of metabolizable energy (ME) during the far-off nonlactating period is a standard management policy to achieve optimum calving body condition score (BCS). An alternative would be to manage cows to gain BCS through late lactation, such that cows ended lactation close to optimum calving BCS and maintenance of BCS through to calving. We sought to quantify the effect of moderate or excessive ME intakes during the far-off nonlactating period in cows that had been managed to gain or maintain BCS through late lactation and whether the far-off management strategy interacted with close-up level of feeding. Effects on milk production and circulating indicators of energy balance and metabolic health in early lactation were evaluated. A herd of 150 cows was randomly assigned to 1 of 2 feeding levels in late lactation to achieve a low and high BCS at the time of dry-off (approximately 4.25 and 5.0 on a 10-point scale). Following dry-off, both herds were managed to achieve a BCS of 5.0 one month before calving; this involved controlled feeding (i.e., maintenance) and over-feeding of ME during the far-off dry period. Within each far-off feeding-level treatment, cows were offered 65, 90, or 120% of their pre-calving ME requirements for 3 wk pre-calving in a 2 × 3 factorial arrangement (i.e., 25 cows/treatment). Body weight and BCS were measured weekly before and after calving, and milk production was measured weekly until wk 7 postcalving. Blood samples were collected weekly for 4 wk pre-calving and 5 wk postcalving, and on d 0, 1, 2, 3, and 4 relative to calving, and analyzed for indicators of energy balance (e.g., blood fatty acids, β-hydroxybutyrate), calcium status, and inflammatory state. No interaction was observed between far-off and close-up feeding levels. Over-feeding of ME to low BCS cows during the far-off nonlactating period reduced blood fatty acid and β-hydroxybutyrate concentrations in early lactation, and increased blood albumin to globulin ratio compared with cows that were dried off close to recommended calving BCS and control-fed during the far-off dry period. Cows consuming 65% of their ME requirements during the close-up period had lower fatty acids and β-hydroxybutyrate in early lactation, but produced less milk, particularly during the first 21 d of lactation, had more than 3-fold greater concentration of haptoglobin immediately postcalving, and had a lower blood cholesterol concentration and albumin to globulin ratio, when compared with cows offered 90 or 120% of their ME requirements. Collectively, these measurements indicate that a severe restriction (<70% of ME requirements) during the close-up nonlactating period increases the risk of disease in early lactation and reduces milk production. In summary, far-off over-feeding of ME to cows that needed to gain BCS did not influence peripartum metabolic health in grazing dairy cows, but restricting cows below 70% ME requirements during the close-up transition period resulted in a blood profile indicative of greater inflammation.     

Epidemiology of subclinical hypocalcemia in early-lactation Holstein dairy cows: The temporal associations of plasma calcium concentration in the first 4 days in milk with disease and milk production

The objectives of this study were to characterize the epidemiology of subclinical hypocalcemia (SCH) in Holstein dairy cows by assessing the temporal associations of plasma Ca concentrations in the first 4 d in milk (DIM) with the risk of cows being diagnosed with metritis or displaced abomasum (or both), and milk production across the first 15 wk of lactation. A prospective cohort study was conducted in 2 dairy herds in New York State, in which cows had a blood sample collected daily for the first 4 DIM. A total of 396 Holstein cows (137 primiparous and 259 multiparous) were enrolled. Multivariable Poisson regression models were built to evaluate the associations of plasma Ca concentration at each of the 4 d following parturition with the risk of primiparous cows being diagnosed with metritis and multiparous cows being diagnosed with metritis, displaced abomasum, or both. Similarly, generalized linear mixed models were built to evaluate the associations of plasma Ca concentration with milk production across the first 15 wk of lactation. Plasma Ca concentration was assessed on a continuous scale in all models; dichotomization and SCH classification only occurred in the final models if the Ca concentration variable was meaningful by creating an optimized threshold based on receiver operating characteristic curve analysis. Plasma Ca concentration assessed at 1 DIM was not associated with the risk of metritis in primiparous cows, but an association was observed at 2, 3, and 4 DIM (critical thresholds were plasma Ca concentration ≤2.15, 2.10, and 2.15 mmol/L, respectively). Plasma Ca concentration was associated with the risk of metritis or displaced abomasum diagnosis (or both) for 2nd parity animals at 2 DIM (threshold ≤1.97 mmol/L), and at 4 DIM for 3rd and greater lactations (threshold ≤2.20 mmol/L). Reduced plasma Ca concentration was associated with higher milk production when assessed at 1 DIM in primiparous and multiparous cows, and lower milk production when assessed at 4 DIM in multiparous cows only. For primiparous cows, plasma Ca concentration was not associated with lower milk production at any of the DIM assessed. In conclusion, assessments of SCH at the individual cow level must take into account the DIM of Ca concentration measurement and parity of the cow, as the epidemiology of the disorder was demonstrated to be highly dependent on these variables. This study advances the knowledge of the epidemiology of SCH and better establishes thresholds for optimizing SCH diagnosis.     

Extended negative dietary cation-anion difference feeding does not negatively affect postpartum performance of multiparous dairy cows

Low postpartum blood calcium remains one of the largest constraints to postpartum feed intake, milk yield, and energy balance in transitioning dairy cows. Supplemental dietary anions decrease the dietary cation-anion difference (DCAD) and reduce the risk for postpartum hypocalcemia. Prepartum management strategies aiming to minimize social stress and diet changes have resulted in a need to explore the effects of extended exposure to a negative DCAD (>21 d) diet. Holstein and Holstein-cross dairy cows (n = 60) were assigned to 1 of 3 treatments 42 d before expected calving to evaluate effects of supplying anions for 21 or 42 d during the dry period on energy status, postpartum production, and Ca homeostasis. Treatments included (1) a control diet (CON; DCAD = 12 mEq/100 g of DM), (2) a 21-d negative DCAD diet (21-ND; DCAD = 12 and −16 mEq/100 g of DM), and (3) a 42-d negative DCAD diet (42-ND; DCAD = −16 mEq/100 g of DM). Cows fed CON were fed positive DCAD prepartum for 42 d. Cows fed 21-ND received the positive DCAD (12 mEq/100 g of DM) diet for the first 21 d of the dry period and the anionic diet (−16 mEq/100 g of DM) from d 22 until calving. Cows fed 42-ND received the anionic diet for the entire dry period. Control and anionic diets were formulated by using 2 isonitrogenous protein mixes: (1) 97.5% soybean meal and (2) 52.8% BioChlor (Church & Dwight Co. Inc.), 45.8% soybean meal. Supplementing anions induced a mild metabolic acidosis, reducing urine pH for 21-ND and 42-ND compared with CON. Prepartum DMI was not different among treatments. Postpartum DMI was higher for 21-ND compared with CON (20.8 vs. 18.1 ± 1.1 kg/d), and 42-ND had similar DMI compared with 21-ND. During the first 56 d of lactation 21-ND had greater average milk production compared with CON (44.8 vs. 39.2 ± 2.1 kg/d). Average milk production by 42-ND was similar to 21-ND. Postpartum total blood Ca concentration was greater for 42-ND. Cows fed anionic diets prepartum tended to have lower lipid accumulation in the liver after calving compared with CON. These data suggest low-DCAD diets fed for 21 or 42 d during the dry period can have positive effects on postpartum DMI, Ca homeostasis, and milk production.     

Association of subclinical hypocalcemia dynamics with dry matter intake,milk yield,and blood minerals during the periparturient period

Subclinical hypocalcemia (SCH) affects many high-producing dairy cows in the postpartum period. Recent work has shown that cows experiencing prolonged or delayed SCH are at increased risk for disease and produce less milk than cows experiencing a transient reduction in or normal concentrations of plasma Ca following parturition. Our objective was to determine the association between different postpartum SCH dynamics with pre- and postpartum dry matter intake (DMI), milk yield, and blood mineral concentrations. Data were retrospectively collected from multiparous Holstein cows (n = 78), and cows were classified into 1 of 4 SCH groups based on mean blood total Ca (tCa) concentrations at 1 and 4 d in milk (DIM): normocalcemic (NC; [tCa] >1.95 mmol/L at 1 DIM and >2.2 mmol/L at 4 DIM, n = 28); transient SCH (tSCH; [tCa] ≤1.95 mmol/L at 1 DIM and >2.2 mmol/L at 4 DIM, n = 27); delayed SCH (dSCH; [tCa] >1.95 mmol/L at 1 DIM and ≤2.2 mmol/L at 4 DIM, n = 6); and persistent SCH (pSCH; [tCa] ≤1.95 mmol at 1 DIM and ≤2.2 mmol/L at 4 DIM, n = 17). Linear mixed models were created to analyze the change in pre- and postpartum DMI, milk yield, and blood mineral concentrations over time as well as differences between SCH groups. Prepartum intake was similar between groups, but the NC and tSCH cows consumed more feed than the pSCH or dSCH cows during the first 3 wk of lactation. The tSCH cows produced more milk than the other 3 groups during the first 6 wk of lactation. Postpartum blood tCa and Mg were different between SCH groups and were highest in the NC cows and lowest in the pSCH cows. Our results suggest that the high level of DMI consumed by the NC and tSCH cows in the postpartum period supported an appropriate homeostatic response to the increased Ca demands of lactation, allowing for higher milk yield compared with their counterparts experiencing delayed or prolonged episodes of SCH.     

Subclinical hypocalcemia,plasma biochemical parameters,lipid metabolism,postpartum disease,and fertility in postparturient dairy cows

A study was conducted to evaluate the potential association between Ca status at calving and postpartum energy balance, liver lipid infiltration, disease occurrence, milk yield and quality parameters, and fertility in Holstein cows. One hundred cows were assigned to 1 of 2 groups based on whole-blood ionized Ca concentration ([iCa]) on the day of calving [d 0; hypocalcemic [iCa] <1.0 mmol/L (n = 51); normocalcemic [iCa] ≥1.0 mmol/L (n = 49)]. Cows were blocked based on calving date and parity. Blood samples were collected approximately 14 d from expected calving date (d −14), the day of calving (d 0), and on d 3, 7, 14, 21, and 35 postpartum for measurement of plasma nonesterified fatty acid, iCa, total Ca, glucose, and total and direct bilirubin concentrations, and plasma aspartate aminotransferase and gamma glutamyl transferase activities. Liver biopsies were obtained from a subset of cows on d 0, 7, and 35 for quantification of lipid content. Milk samples were collected on d 3, 7, 14, 21, and 35 postpartum for measurement of somatic cell count and percentages of protein, fat, and solids-not-fat. Data for peak test-day milk yield, services per conception, and days open were obtained from Dairy Herd Improvement Association herd records. Disease occurrence was determined based on herd treatment records. Hypocalcemic cows had significantly higher nonesterified fatty acids on d 0. Hypocalcemic cows also had significantly more lipid in hepatocytes on d 7 and 35 postpartum. However, no statistically significant differences were observed between groups for plasma aspartate aminotransferase and gamma glutamyl transferase activities or total and direct bilirubin concentrations. Milk protein percentage was lower in hypocalcemic cows on d 21 and 35. However other milk quality variables (somatic cell count, milk fat percentage, and solids-not-fat) and milk yield variables (peak test-day milk yield and 305-d mature-equivalent 4% fat-corrected milk yield) did not differ between groups. No differences were observed between groups in the occurrence of clinical mastitis, ketosis, displaced abomasum, dystocia, retained placenta, metritis, or fertility measures (percentage cycling at 50–60 d postpartum, services per conception, or days open). These data suggest that early lactation fatty acid metabolism differs between cows with subclinical hypocalcemia and their normocalcemic counterparts.     

Effect of oral calcium bolus supplementation on early-lactation health and milk yield in commercial dairy herds

The objective of this study was to evaluate the effect of supplementation with oral Ca boluses after calving on early-lactation health and milk yield. Cows in their second lactation or greater (n = 927) from 2 large dairies in Wisconsin were enrolled during the summer of 2010. Both herds were fed supplemental anions during the prefresh period and less than 1% of fresh cows were treated for clinical milk fever. Cows were scored before calving for lameness and body condition, and then randomly assigned to either a control group or an oral Ca bolus-supplemented group. Control cows received no oral Ca boluses around calving. Cows in the oral Ca bolus group received 2 oral Ca boluses (Bovikalc, Boehringer Ingelheim, St. Joseph, MO), one bolus 0 to 2 h after calving and the second 8 to 35 h after calving. The oral Ca bolus administration schedule allowed fresh cows to be restrained in headlocks only once daily. Whole-blood samples were collected immediately before the second oral Ca bolus was given and were analyzed for ionized Ca (Ca²⁺) concentration. Early-lactation health events were recorded and summed for each cow. Only 6 cases (0.6% of calvings) of clinical milk fever occurred during the trial, and only 14% of cows tested were hypocalcemic (Ca²⁺ less than 1.0 mmol/L) at 8 to 35 h after calving. Mean Ca²⁺ concentrations were not different between the control and oral Ca bolus-supplemented groups. Blood samples from the cows given oral Ca boluses were collected an average of 20.6 h after administration of the first bolus. Subpopulations of cows with significant responses to oral Ca bolus supplementation were identified based on significant interactions between oral Ca bolus supplementation and covariates in mixed multiple regression models. Lame cows supplemented with oral Ca boluses averaged 0.34 fewer health events in the first 30 d in milk compared with lame cows that were not supplemented with oral Ca boluses. Cows with a higher previous lactation mature-equivalent milk production (greater than 105% of herd rank) and supplemented with oral Ca boluses produced 2.9 kg more milk at their first test after calving compared with cows with higher previous lactation milk yields that were not supplemented. Results of this study indicate that lame cows and higher producing cows responded favorably to supplementation with oral Ca boluses. Supplementing targeted subpopulations of cows with oral Ca boluses was beneficial even for dairies with a very low incidence of hypocalcemia.     

Association of immediate postpartum plasma calcium concentration with early-lactation clinical diseases,culling, reproduction,and milk production in Holstein cows

The objective of this study was to evaluate the association of postpartum plasma Ca concentration with early-lactation disease outcomes, culling within 60 d in milk, pregnancy to first service, and milk production. A total of 1,453 cows from 5 commercial dairy farms in New York State were enrolled in a prospective cohort study from February to November 2015. Blood samples were collected within 12 h of parturition, and plasma was submitted to a diagnostic laboratory for total Ca measurement. Early-lactation disease, reproductive performance, and milk production from Dairy Herd Improvement Association (DHIA) test-day data were compiled from each farm's management software. Multivariable Poisson regression models were built to evaluate the association of plasma Ca with the risks of retained placenta (RP), metritis, displaced abomasum (DA), clinical mastitis, culling within 60 d in milk, and pregnancy to first service. Repeated-measures ANOVA were used to evaluate the association of Ca at parturition with milk production across the first 9 DHIA tests. Herd was considered a random effect in all models. Primiparous cows were modeled separately from multiparous cows if differential responses were observed. Calcium was not associated with the risk of RP, metritis, clinical mastitis, or pregnancy to first service in primiparous or multiparous cows. For multiparous cows only, higher Ca concentration tended to be associated with increased culling within the first 60 d in milk. Multiparous cows with Ca ≤1.85 mmol/L had an increased risk of being diagnosed with a DA compared with cows with Ca >1.85 mmol/L. For the milk production models, Ca was not associated with the amount of milk produced within the first 9 DHIA tests in primiparous cows; however, multiparous cows with Ca ≤1.95 mmol/L produced, on average, 1.1 kg more milk per day across the 9 DHIA tests than their multiparous counterparts with Ca >1.95 mmol/L. Our results indicate that plasma Ca concentration measured within 12 h of parturition is a poor predictor of early-lactation health outcomes. Reduced Ca concentration in the immediate postpartum period was associated with higher milk production in multiparous cows. From these results, we caution that studies attempting to categorize subclinical hypocalcemia based on a single sample in the immediate postpartum period could misclassify the disorder.     

Intravenous calcium infusion in a calving protocol disrupts calcium homeostasis compared with an oral calcium supplement

Hypocalcemia is a common postpartum condition in dairy cows, which negatively affects health and production. Intravenous Ca infusions are commonly included in calving protocols to prevent or mitigate the effect of hypocalcemia in multiparous cows. Thus, we sought to contrast the effect of intravenous Ca infusion against voluntary oral Ca intake on Ca metabolism. Serum total Ca (tCa) and whole-blood ionized Ca (iCa) were monitored in 24 multiparous Holstein cows after parturition. Precalving diets were formulated with a positive dietary cation-anion difference of 172 mEq/kg of DM and contained 4.1 g of Ca/kg of DM. At parturition, cows were blocked by calving sequence and calcemic status as either normocalcemic (cutoff threshold of iCa ≥1.10 mmol/L) or hypocalcemic (cutoff threshold of iCa <1.10 mmol/L). Cows in each block were randomly assigned to 1 of 2 treatments: either an oral source of Ca (Ca-Oral; n = 12) or an intravenous source of Ca (Ca-IV; n = 12). Cows in the Ca-Oral group were offered a 20-L commercial Ca suspension (48 g of Ca) for voluntary consumption. The supplement contained Ca carbonate, Ca formate, Ca propionate, and other minerals and vitamins (Farm-O-San Reviva, Trouw Nutrition, Amersfoort, the Netherlands). Cows in the Ca-IV group received a 450-mL intravenous Ca solution (13 g of Ca) that contained 298 mg/mL of Ca gluconate, 33 mg/mL of magnesium chloride, and 82 mg/mL of boric acid (AmosCAL, Kommer-Biopharm BV, Heiloo, the Netherlands). Both treatments were initiated within 25 ± 10 min after calving. The oral Ca suspension was offered to cows in a 25-L bucket and was available for 10 min. All cows in the Ca-Oral group voluntarily consumed the entire 20 L of the Ca suspension within 5 min. Blood samples for Ca analyses were collected at 0 (before treatment initiation), 1, 3, 10, and 18 h relative to treatment, and at 0700 and 1900 h for the next 2 consecutive days, to represent the 24-, 36-, 48-, and 60-h sampling time points. In Ca-IV cows, both iCa and tCa concentrations peaked at 1 h (1.54 mmol/L for iCa and 2.85 mmol/L for tCa) and declined to a nadir at 24 h following treatment initiation (0.94 mmol/L for iCa and 1.74 mmol/L for tCa). Although whole-blood iCa and serum tCa were higher at 1 and 3 h in Ca-IV cows, concentrations of iCa were greater for Ca-Oral cows at 18, 24, and 36 h and for tCa at 24 and 36 h. Our data indicate that intravenous Ca infusion immediately induced a state of hypercalcemia followed by lower whole-blood iCa and serum tCa concentrations 24 h later compared with oral Ca.     

Timothy hay with a low dietary cation-anion difference improves calcium homeostasis in periparturient Holstein cows

The current study was undertaken to evaluate the effects of feeding timothy (Phleum pratense L.) hay differing in dietary cation-anion difference (DCAD) on the capability of cows to maintain calcium homeostasis around parturition. We hypothesized that feeding low-DCAD timothy hay during the prepartum period would induce a mild metabolic acidosis prepartum and improve calcium homeostasis postpartum with no effect on dry matter intake. Forty-one dry pregnant Holstein cows entering their second lactation or greater were used in a randomized complete block design. Timothy hay was obtained from an established timothy stand under a pivot irrigation system. Low-DCAD timothy hay was produced by fertilizing the area between the second and third pivot towers at a rate of 224 kg of CaCl₂/ha, and control timothy hay (high DCAD) was grown on the area between the fourth and fifth pivot towers of the same field. The chloride concentration was 1.07 and 0.15% on a dry matter (DM) basis, and the DCAD was 1.2 and 21.6 mEq/100 g of DM for the low- and high-DCAD timothy hay, respectively. Experimental diets, containing timothy hay at 63% of dietary DM, were fed ad libitum starting 30 d before the expected calving date. The DCAD values were 1.6 vs. 14.5 mEq/100 g of DM for the low- and high-DCAD timothy-based diets, respectively. At the beginning of the study, urine pH and blood bicarbonate concentration averaged 8.22 ± 0.06 and 28.5 ± 0.3 mM, respectively. The low-DCAD timothy diet decreased urine pH compared with the high-DCAD timothy diet on d 21 (7.75 vs. 8.31), d 14 (7.69 vs. 8.22), and d 7 (7.50 vs. 8.19) before calving, and it also decreased the prepartum blood bicarbonate concentration by 2 mM. In addition, cows fed the low-DCAD timothy diet had greater blood ionized calcium concentration prepartum (1.22 vs. 1.19 mM), greater blood ionized calcium concentration at 0 and 8 h after calving, and similar prepartum dry matter intake. These results indicate that timothy hay differing in DCAD affects the acid-base balance of periparturient dairy cows, and that low-DCAD timothy hay improves calcium homeostasis postpartum with no negative effect on dry matter intake.     

Effects of prepartum dietary cation-anion difference on aspects of peripartum mineral and energy metabolism and performance of multiparous Holstein cows

The objectives of this study were to determine the effect of decreasing dietary cation-anion difference [DCAD; (Na⁺ + K⁺) ? (Cl^? + S^2?)] 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 effect of source of supplemental dietary calcium and magnesium in the peripartum period,and level of dietary magnesium postpartum,on mineral status,performance, and energy metabolites in multiparous Holstein cows

The objective of this study was to determine the effects of feeding different supplemental sources of Ca and Mg in the peripartum period, and different dietary levels of Mg postpartum, on plasma mineral status, performance, and aspects of energy metabolism in transition dairy cows. Multiparous Holstein cows (n = 41) were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments starting at 28 d before expected parturition. Main effects were source assignments (CS = common sources of supplemental Ca and Mg, or MA = a blend of common and commercial mineral sources with supplemental minerals primarily from a commercial Ca-Mg dolomite source; MIN-AD, Papillon Agricultural Company Inc., Easton, MD) beginning at 21 d before due date; cows were further randomized within source treatments to 1 of 2 levels of Mg supplementation (LM = formulated postpartum diet Mg at 0.30% of dry matter (DM), or HM = formulated postpartum diet Mg at 0.45% of DM) beginning within 1 d after parturition. Final treatment groups included the following: common source, low Mg (CS-LM, n = 11); common source, high Mg (CS-HM, n = 11); MIN-AD, low Mg (MA-LM, n = 10); and MIN-AD, high Mg (MA-HM, n = 9). Treatment diets were fed and data collected through 42 d in milk. Postpartum plasma Mg concentrations tended to be higher for cows fed HM and cows fed CS, but no effects were observed on peripartum plasma Ca concentrations. Peripartum plasma P concentrations were higher for cows fed MA. Dry matter intake (DMI) in the prepartum period was higher for cows fed MA (CS = 15.9 vs. MA = 16.8 kg/d) and postpartum DMI was higher in some groups depending on week. Plasma nonesterified fatty acid concentrations were lower for cows fed MA during both the prepartum and postpartum periods. A source by level interaction was observed for postpartum plasma β-hydroxybutyrate (BHB) concentrations such that cows fed CS-LM had numerically higher BHB and cows fed MA-LM had numerically lower BHB (geometric means; CS-LM = 7.9, CS-HM = 6.9, MA-LM = 6.3, and MA-HM = 7.3 mg/dL) than cows fed the other 2 treatments. Higher milk fat yield, milk fat content, and fat- and energy-corrected yield during wk 1 for cows fed MA resulted in source by week interactions for these outcomes. This study demonstrated that varying supplemental Ca and Mg sources and feeding rates had minimal effect on plasma Ca status despite differences in plasma Mg and P concentrations. Effects on DMI and plasma energy metabolites suggest an opportunity for strategic use of mineral sources in the transition period to promote metabolic health.     

Risk factors associated with postpartum subclinical hypocalcemia in dairy cows

Our study objectives were to evaluate the association of prepartum plasma Mg concentrations with subclinical hypocalcemia (SCH) classification at parturition and to evaluate the association of other cow-level risk factors with SCH classification at calving or at 2 d in milk (DIM). A total of 301 animals from 2 dairy herds located in New York were enrolled in a cohort study. Blood samples were collected at approximately 1 wk before the expected calving date, within 4 h of calving, and at 2 DIM. Prepartum samples had plasma macromineral concentrations (Ca, K, Mg, P), albumin, and β-hydroxybutyrate analyzed. Samples collected at calving were analyzed for Ca only, and samples from 2 DIM had macromineral and albumin concentrations determined. Postpartum SCH was defined as Ca concentrations ≤2.1 mmol/L. The prevalence of SCH at calving was 2, 40, and 66% for first, second, and third or greater parities, respectively. Only 4% of cows could be classified with prepartum subclinical hypomagnesemia (Mg concentrations <0.8 mmol/L), which did not provide enough power to appropriately determine the association of plasma Mg with postpartum Ca concentrations and its effect on SCH classification. Multiparous cows with Ca concentrations ≤2.4 mmol/L in the prepartum period and third or greater parity cows had a higher risk of being categorized as SCH at calving [relative risk (RR) = 1.4 and 1.7, respectively]. The risk of SCH at 2 DIM was associated with the interaction of Ca status at calving and lameness score. Nonlame cows with Ca concentrations ≤2.1 mmol/L (RR = 3.2) and normocalcemic lame cows at parturition (RR = 3.4) were more likely to be SCH at 2 DIM compared with nonlame normocalcemic cows. In conclusion, we identified a prepartum Ca cut-point for identification of cows that are more likely to be classified as SCH at calving. Different risk factors were associated with SCH depending on the timing of diagnosis relative to parturition.