Effect of oral calcium administration on the cure and reproductive performance of Holstein cows diagnosed with puerperal metritis

A randomized field trial assessing the timing of postpartum calcium bolus administration on milk yield of multiparous Holstein cows

Recent studies have shown that cows with subclinical hypocalcemia (SCH) at 4 d in milk (DIM), regardless of their blood Ca concentration before that time point, suffer from an increased early-lactation disease risk and reduced milk yield, whereas cows experiencing a transient reduction in blood Ca that regain normocalcemia by 4 DIM are at a reduced risk of disease and have greater milk yields. With a goal of improving outcomes for dyscalcemic cows with SCH at 4 DIM, our primary objective was to assess the effect of a herd-level oral Ca bolus strategy that delayed supplementation to 24 and 48 h postpartum on productive performance of multiparous Holstein cows. Our secondary objectives were to assess the effects of delayed Ca bolus supplementation on blood Ca concentration, disease incidence within 30 DIM, and pregnancy risk to first service. At calving, multiparous cows on a single commercial dairy farm in Iran were randomly assigned to 1 of 3 treatment groups: (1) control, no Ca bolus administration (CON; n = 95); (2) traditional bolus, one Ca bolus administered immediately following calving and a second Ca bolus administered 24 h after calving (TRD, n = 102); or (3) experimental bolus, one Ca bolus administered 24 h after calving with a second Ca bolus administered 48 h after calving (EXP, n = 99). Blood samples were collected at 0, 24, 48, 72, and 96 h, and 7 d after parturition, with sampling occurring before bolus administration for the TRD (0 and 24 h) and EXP (24 and 48 h) groups. A general linear mixed model was created to analyze the change milk yield over the first 4 monthly tests and serum Ca concentrations over 7 DIM. Given the lack of disease events diagnosed within 30 DIM, no statistical analysis was conducted for this outcome. The effect of treatment group on risk of pregnancy to first service was assessed using Poisson regression. The incidence of dyscalcemia within CON cows was 72%. We found no difference in mean monthly milk yield among treatment groups across the first 4 tests, with an average monthly production of 51.8 ± 8.8 kg/d for CON cows, 52.5 ± 8.7 kg/d for TRD cows, and 51.8 ± 8.7 kg/d for EXP cows. Mean blood Ca concentration also did not differ across 7 DIM among treatment groups and was 2.04 mmol/L [95% confidence interval (CI) = 2.00 to 2.07 mmol/L] for CON cows, 2.06 mmol/L (95% CI = 2.03 to 2.09 mmol/L) for TRD cows, and 2.09 mmol/L (95% CI = 2.05 to 2.12 mmol/L) for EXP cows. The risk of pregnancy to first service was numerically greater for CON than TRD and EXP cows but not statistically different; however, our study was underpowered for this outcome. Under the conditions of our study, our findings suggest that delaying oral Ca bolus supplementation to 24 and 48 h postpartum has no effect on milk production across the first 4 monthly tests.

Ursache, Verbreitung und evidenzbasierte Therapie sowie Prävention der peripartalen Hypokalzämie

Die peripartale Hypokalzämie ist eine weit verbreitete Stoffwechselstörung, dessen klinische Form etwa 7 % der Milchkühe und dessen subklinische Form fast jede 2. multipare Kuh betrifft. Obwohl sich hinsichtlich Diagnostik und Therapie in den letzten 30 Jahren kaum etwas verändert hat, herrscht bei Landwirten und Tierärzten Unklarheit über die Prävalenz und den Risikozeitraum dieser Stoffwechselstörung. Darüber hinaus gibt es sehr unterschiedliche Angaben darüber, wieviel Kalzium einer Kuh mit klinischer Hypokalzämie substituiert werden sollte. Ziel dieses Übersichtsartikels ist es, die Entstehung und Verbreitung von Hypokalzämie evidenzbasiert darzustellen. Des Weiteren werden die Ergebnisse älterer und neuer Studien zusammengefast, mit dem Ziel eine möglichst genaue Empfehlung zur Behandlung von klinischer Hypokalzämie zu geben. Da in einer 2017 durchgeführten Studie gezeigt wurde, dass der überwiegende Teil deutscher Milchviehbetriebe keine Prophylaxe gegen Hypokalzämie betreibt, werden in dem letzten Teil dieser Arbeit die verschiedenen Prophylaxekonzepte, unter Berücksichtigung der aktuellen Literatur, dargestellt.

A Randomized Clinical Trial Evaluating the Effect of an Oral Calcium Bolus Supplementation Strategy in Postpartum Jersey Cows on Mastitis, Culling, Milk Production, and Reproductive Performance

Simple Summary

The time around parturition is a challenging period in the lactation cycle of high-yielding dairy cows as it is characterized by several endocrine, metabolic, and physiological changes. Among those challenges, calcium demands are rapidly increased to support colostrogenesis and lactogenesis during a time of reduced dry matter intake; invariably, some cows may suffer from clinical and subclinical hypocalcemia. Oral calcium supplementation is a common preventative strategy adopted in the postpartum of high-yielding dairy cows to minimize the negative impact of suboptimal blood calcium concentration during this period. Despite a great number of studies evaluating the effects of oral calcium supplementation in postpartum Holstein cows, very limited information is available for the Jersey breed. This study aimed to evaluate the effect of an oral Ca supplementation strategy in the first 24 h after parturition on health and production outcomes in multiparous Jersey cows. Overall, treatment did not improve milk production or reproductive performance compared to control cows. Additionally, treatment had no effect on early lactation culling. A tendency for a minor impact on the odds of mastitis was evident though it depended on the parity of the cows.

Abstract

The objectives of this study were to evaluate the effects of a postpartum oral calcium supplementation strategy in multiparous Jersey cows on (1) the odds of clinical mastitis in the first 60 days in milk (DIM); (2) the odds of culling up to 60 DIM; (3) the risk of pregnancy in the first 150 DIM; (4) milk production in the first 15 weeks of lactation. A randomized clinical trial was performed in a dairy herd located in west Texas, United States. A total of 809 cows were used in the final analyses. Overall, postpartum oral calcium supplementation did not influence milk production, reproductive performance, or culling. Among second parity cows, oral calcium supplementation tended to decrease the odds of clinical mastitis in the first 60 DIM compared to controls; however, no differences were observed for cows in parities three and greater. To date, data evaluating the effect of postpartum oral calcium supplementation in multiparous Jersey cows are limited. In our study, oral calcium supplementation tended to reduce clinical mastitis in second parity cows. No positive benefits based on the reduction of culling, and improvement of milk production and reproductive performance were evident for the herd included in this study.

Association of low serum calcium concentration after calving with productive and reproductive performance in multiparous Jersey cows

Consequences of postpartum low blood calcium (Ca) concentration are still under study and literature describing this condition in Jersey cows is scarce. A prospective cohort study was conducted to evaluate the association of low serum Ca concentration shortly after calving with milk and energy-corrected milk yields, somatic cell count linear score, and pregnancy to first service and within 150 d in milk in multiparous Jersey cows from 2 commercial herds. Blood samples for serum Ca determination were collected on average at 3 h 10 min postpartum from 352 multiparous Jersey cows. Productive data up to the 10th monthly test were obtained from the Dairy Herd Improvement Association and reproductive data were obtained from herd records. Multiple linear, log-binomial, and Cox's proportional hazards regressions were used to evaluate the association of low serum Ca concentration with productive and reproductive outcomes. Serum Ca concentration ≤2.18 mmol/L was associated with 1.43 and 1.85 kg/d more milk and energy-corrected milk. However, lower serum Ca concentrations were associated with a 0.28-unit-higher somatic cell count linear score per monthly test (Ca ≤2.00 mmol/L), and decreased pregnancy risk at first service (risk ratio = 0.64; Ca ≤1.94 mmol/L) and hazard of pregnancy within 150 d in milk (hazard ratio = 0.40; Ca ≤1.90 mmol/L). The present study is based on a convenience sample of multiparous Jersey cows from 2 commercial herds; further research including more herds and additional blood Ca determinations is needed to describe postpartum blood Ca dynamics and its association with productive and reproductive outcomes for the Jersey breed.

Effect of oral calcium administration on metabolic status and uterine health of dairy cows with reduced postpartum rumination and eating time

Background

Hypocalcemia has detrimental effects on health and performance of dairy cows. As hypocalcemic cows show reduced feed intake, we hypothesized that cows with reduced combined rumination and eating time (CRET) may benefit from Ca supplementation. The objective was to evaluate the effect of postpartum oral Ca administration on metabolic status (Calcium [Ca], fatty acids [FA], and β-Hydroxybutyrate [BHB] serum concentrations) and incidence of puerperal metritis (PM) in dairy cows with reduced postpartum CRET. Cows in an organic-certified dairy, diagnosed with reduced CRET (< 489 min/d; n = 88) during the first day postpartum were assigned into 1 of 2 treatments: i) Calcium administration (CA; n = 45) that received 1 Ca oral capsule (Bovikalc bolus, Boehringer Ingelheim, St. Joseph, MO) containing CaCl2 and CaSO4 (43 g of Ca) once per day, for 3 consecutive days, starting at d 1 postpartum; and ii) Control (CON; n = 43) that did not receive oral Ca. A convenience group consisting of cows with CRET ≥489 min/d was used for comparison and did not receive oral Ca (NOR; n = 96).

Results

At day 1 postpartum cows with reduced CRET had lower Ca serum concentrations (CA = 2.08 mmol/L; CON = 2.06 mmol/L) compared with NOR cows (2.17 mmol/L). Calcium concentrations at d 3, 5, and 12 postpartum were not different among the three groups. Serum FA concentrations at d 1, 3 and 5 postpartum were higher in both CA and CON cows compared with NOR. At d 12, only CA cows had higher FA concentrations than NOR cows. Serum BHB concentrations at d 3 were highest in CA, with no difference between CON and NOR. At d 5, BHB concentrations were higher in CA, followed by CON, and NOR. No effect was observed for Ca administration on incidence of PM and reproductive performance. CON cows had lower survival at 30 DIM (86.5%) than NOR cows (97.9%).

Conclusions

The use of remote sensor technology identified cows with reduced rumination and eating time that had lower postpartum serum concentrations of calcium and altered metabolic status. However, oral calcium administration to cows with reduced CRET did not affect incidence of metabolic disorders nor reproductive health and subsequent pregnancy. Although survival at 30 days postpartum was lower for non-Ca supplemented cows, the identification of effective interventions in cows with reduced CRET requires further consideration.

Effects of Premating Calcium and Phosphorus Supplementation on Reproduction Efficiency of Grazing Yak Heifers

Simple Summary

This study was realized to explore the effects of calcium chloride (CaCl) and monocalcium phosphate (MCP) supplementation on the reproductive efficiency of grazing yak heifers. The body weight, serum markers of bone metabolism, and conception and calving rate of grazing yaks in control group and supplementary feeding groups were compared. The results revealed that supplementation with MCP but not CaCl could significantly improve the reproductive performance, possibly due to the improvement in body weight and bone phosphorus storage providing better estrous physiological conditions for grazing yak heifers. The findings of this study may be helpful and instructional to improve the reproductive efficiency of yaks on the Qinghai Tibet Plateau.

Abstract

Reproductive efficiency is the main factor limiting yak production on the Tibet Plateau. The purpose of this study was to investigate the effect of supplementation with calcium chloride (CaCl) and monocalcium phosphate (MCP) for 30 days before breeding on body weight (BW) change, serum bone metabolism biomarkers, conception rate, and calving rate of grazing yaks. Ninety 3 year old yak heifers (153.05 ± 6.56 kg BW) were assigned to three treatments (n = 30 per treatment): grazing without supplementation (CONT), grazing plus calcium chloride supplementation (CaCl), and grazing plus monocalcium phosphate supplementation (MCP). Compared with the CONT group, supplementation with CaCl increased the serum concentrations of osteocalcin and decreased the alkaline phosphatase (ALP) levels (p < 0.05); supplementation with MCP increased the average daily gain (ADG), serum concentrations of phosphorus (P) and osteocalcin, conception rate, and calving rate (p < 0.05), whereas it decreased the serum concentrations of hydroxyproline, ALP, and calcitonin (p < 0.05). Both CaCl and MCP supplementation had no effect on serum calcium (Ca) concentration. The ADG, conception rate, and calving rate were higher in the MCP group than in the CaCl group (p < 0.05), while the serum concentrations of hydroxyproline and calcitonin were lower (p < 0.05). It could be concluded that premating supplementation with MCP increased the body weight gain and subsequent conception and calving rate of grazing yaks. Supplementation with MCP had a positive effect on body condition and bone metabolism, thus providing a better estrous condition for grazing yak heifers, which could contribute to enhancing reproduction efficiency.

Association between serum calcium dynamics around parturition and common postpartum diseases in dairy cows

The objective of this study was to compare periparturient serum Ca dynamics (CaDyn) in cows with and without diseases in early lactation. The study enrolled 1,949 cows from a commercial dairy farm in northern Germany. Blood samples were drawn 7 d before expected calving date and on d 0, 1, 3, and 7 after calving and analyzed for serum Ca concentration. Cows were monitored for clinical hypocalcemia (CH), ketosis, left displaced abomasum (LDA), retained placenta, acute puerperal metritis (APM), mastitis, and pneumonia. To evaluate the association between CaDyn and diseases during the transition period, repeated measures ANOVA with first-order autoregressive covariance were performed. Serum CaDyn of healthy cows (i.e., without any of the aforementioned diseases) was compared with CaDyn of cows with one of the aforementioned diseases (CH, ketosis, APM, mastitis, LDA, and pneumonia), and cows with multiple diseases (CH+, ketosis+, APM+, mastitis+, LDA+, and pneumonia+). Separate models were built for primiparous and multiparous cows. For primiparous cows, we evaluated the association between CaDyn and ketosis (healthy cows vs. cows with ketosis vs. cows with ketosis+) and CaDyn and APM (healthy cows vs. cows with APM vs. cows with APM+). The same models were built for multiparous cows. Three additional models were built for multiparous cows to evaluate the association between CaDyn and CH (healthy cows vs. cows with CH vs. cows with CH+), mastitis (healthy cows vs. cows with mastitis vs. cows with mastitis+), or LDA (healthy cows vs. cows with LDA vs. cows with LDA+). In primiparous cows, serum Ca concentrations of cows with ketosis, APM, and APM+ were significantly reduced on d 3 and 7 after calving, compared with healthy cows. Serum Ca concentrations of primiparous cows with ketosis+ were reduced on d 3, but not on d 7 after calving. Multiparous cows with CH had significantly reduced serum Ca concentrations on d 0, 1, and 3 compared with healthy cows. On d 3 and 7, serum Ca concentration of CH+ cows was significantly reduced compared with healthy multiparous cows. Multiparous cows with ketosis and ketosis+ had significantly reduced serum Ca concentrations on d 1 and 3 compared with healthy cows. Cows with APM+ had significantly increased serum Ca concentrations on d 0 and reduced serum Ca concentrations on d 3, compared with healthy cows. Whereas multiparous cows with mastitis had a reduced serum Ca concentration on d 1, mastitis+ cows had a reduced serum Ca concentration on d 1 and 3, compared with healthy multiparous cows. Overall, multiparous cows with LDA+ had reduced serum Ca concentrations. Especially a delayed onset of hypocalcemia (d 3 and 7) was indicative for the development of disease in primiparous cows. In multiparous cows, reduced serum Ca concentrations on d 1 and 3 were associated with occurrence of diseases. Future studies should evaluate whether reduced serum Ca concentrations are a cause or concomitant circumstance of diseases in early lactation.

Common and specific mineral and metabolic features in dairy cows with clinical metritis, hypocalcaemia or ketosis

The objectives were to evaluate differences in serum concentration of metabolites, macro minerals and hepatic enzymes at pre and postpartum time-points in dairy cows diagnosed with clinical metritis, hypocalcaemia or ketosis postpartum. A total of 144 Holstein cows from 11 commercial dairy herds in Alberta, (Western Canada) were enrolled in this study. Cows with clinical metritis had lower serum concentrations of glutamate dehydrogenase (GLDH) at pre and postpartum and lower total Ca, albumin, urea, and cholesterol at postpartum when compared to control cows. Cows with hypocalcaemia had greater serum concentrations of Na, Cl, and calculated osmolarity (CalOsmo) at prepartum and lower concentration of total serum Ca, glucose, cholesterol, gamma-glutamyl transpeptidase (GGT), GLDH, total protein and albumin at postpartum. Prepartum serum concentrations of non-esterified fatty acids (NEFA), beta hydroxybutyrate (BHB), Cl, albumin/globulin ratio (A/G), Na, K and sum of Na and K were greater in ketotic cows when compared with control cows. Cows with ketosis had also greater postpartum serum concentrations of NEFA, BHB, GGT and aspartate transaminase (AST) when compared with control cows. Prepartum serum Na and Cl concentrations and CalOsmo were greater in cows diagnosed with hypocalcaemia or ketosis when compared with control cows. Furthermore, postpartum serum concentrations of total Ca, cholesterol, albumin and GLDH were significantly affected by hypocalcaemia or clinical metritis and concentrations of GGT by hypocalcaemia or ketosis. Finally, postpartum serum concentrations of haptoglobin increased in all disease groups when compared with control cows. These results suggest common metabolic features for clinical metritis, hypocalcaemia and ketosis in dairy cows in addition to the specific ones.

Incidence and risk factors for reproductive disorders in organic certified dairies

The objective was to determine the lactational incidence risks of reproductive disorders (RD) including dystocia (DYS), retained fetal membranes (RFM), puerperal metritis (PM), clinical endometritis (CE), pyometra (PYO), late pregnancy loss (LPL), and culling due to reproductive reasons (CRR) in large organic certified dairies with predominant use of Holstein genetics. In addition, potential risk factors for RD, including parity category, milk yield in the previous lactation, season of dry-off, access to grazing at dry-off, length of the dry period (DPL), length of the close-up period (CUPL), calculated gestation length (CGL), season of calving, access to grazing at calving, concurrent health conditions, and total number of artificial inseminations were analyzed. A retrospective study was performed using information from 8 organic certified herds located in northern Colorado and west Texas, ranging from 900 to 6,000 milking cows. Cow information consisted of finalized lactations starting with calvings occurring between January 1, 2016, and December 31, 2018. Data were analyzed using time-to-event analyses and multivariable logistic regression. Clinical endometritis had the greatest lactational incidence risk (incidence risk = 10.1%; 95% CI = 9.8-10.3%), followed by DYS (8.8%; 8.5-9.1%), PM (4.9%; 4.7-5.1%), PYO (4.0%; 3.8-4.1%), LPL (3.6%; 3.4-3.7%), and RFM (2.0%; 1.8-2.1%). The incidence risk of CRR was 7.5% (7.3-8.7%), representing 29.1% (28.4-30.0%) of all culling reasons. Median time from calving to diagnosis of PM, CE, PYO, and LPL were 6, 23, 111, and 228 d, respectively. Median time for CRR was 391 d. The main risk factors for RD were DPL, CGL, and CUPL. Season of dry-off was a risk factor for RFM, PM, CE, LPL, and PYO. Short DPL (<30 d) was associated with increased odds (95% CI) of RFM [2.1 (1.6-2.7)], PM [1.4 (1.2-1.7)], and LPL [2.5 (1.5-4.2)]. Shortened CGL (<270 d) increased the odds of DYS [1.5 (1.3-1.8)], RFM [3.2 (2.4-4.1)], and PM [2.4 (1.7-3.3)], whereas extended CGL (>285 d) increased the odds of DYS [1.5 (1.4-1.7)], PM [1.5 (1.2-2.0)], CE [1.5 (1.1-2.0)], and CRR [1.2 (1.10-1.4)]. Shortened CUPL was associated with increased odds of all the RD. Cows spending less than 7 d in the close-up groups had greater odds of DYS [1.4 (1.1-1.8)], RFM [2.1 (1.8-2.4)], PM [1.9 (1.6-2.1)], PYO [1.5 (1.2-1.8)], LPL [2 (1.7-2.3)], and CRR [1.4 (1.04-1.8)] compared with cows spending more than 14 d in the close-up group. Season of calving was associated with the odds of PM [summer = 1.13 (1.01-1.2)], PYO [summer = 1.7 (1.1-2.5)], and LPL ([fall = 0.8 (0.6-0.96)] compared with winter calving. Other risk factors affecting RD were parity number, total number of artificial inseminations, and concurrent health conditions. Overall, lactational incidence risks of reproductive diseases were comparable with those reported in conventional herds. The identified risk factors for RD open opportunities for interventions, especially focused in precalving management, estimation of due dates, and closer monitoring of pregnancies from natural services in large organic certified dairy herds.

Serum calcium dynamics within the first 3 days in milk and the associated risk of acute puerperal metritis

The objectives of this study were to evaluate postpartum serum calcium dynamics for different parity groups of dairy cows and to assess whether serum calcium concentration on d 0, 1, and 3 postpartum was associated with the risk of developing acute puerperal metritis (APM). The study took place on a commercial dairy farm in northern Germany and included 4,043 Holstein dairy cows. Calving difficulties, such as dystocia, twins, or stillbirth, were recorded. Blood samples were obtained on d 0, 1, and 3 after calving for analysis of serum calcium concentration. Animals were examined daily for clinical symptoms of retained placenta, APM, mastitis, and displaced abomasum until 10 d in milk. To determine serum calcium dynamics postpartum, we performed repeated-measures ANOVA with first-order autoregressive covariance. A logistic regression model was used to evaluate the association of serum calcium concentration with the risk of developing metritis. Serum calcium concentration was affected by time relative to calving, parity, and APM. Increasing parity negatively affected serum calcium concentration on d 0 and 1. Serum calcium concentration reached its lowest level on d 1 and 3 in multiparous and primiparous cows, respectively. The concentration increased from d 1 to 3 in multiparous cows and decreased from d 0 to 3 in primiparous cows. The association of APM and serum calcium dynamics varied by parity. On d 3, serum calcium concentration was significantly lower in animals with subsequent APM than in those without APM. The overall incidence of APM was 12.0% (primiparous cows, 20.4%; multiparous cows, 8.6%). An association existed between serum calcium concentration on d 3 after calving and APM. Primiparous cows had an odds ratio of 0.12 for serum calcium concentration on d 3, indicating that a primiparous cow with serum calcium concentration of 2.5 mmol/L had a 88% lower chance of developing APM compared with a cow with a concentration of 1.5 mmol/L. Multiparous cows had an odds ratio of 0.34 for serum calcium concentration on d 3, indicating that a multiparous cow with serum calcium concentration of 2.5 mmol/L had a 66% lower chance of developing APM compared with a cow with a concentration of 1.5 mmol/L. Primiparous cows with low serum calcium concentration had the highest predicted probability of developing APM. Our results reveal a dynamic in serum calcium concentration in the first 3 d in milk. Consequently, the day of sampling and the observed risk period for hypocalcemia are important when conducting epidemiological studies to evaluate associations between hypocalcemia and clinical diseases.

Association of postpartum hypocalcemia with early-lactation milk yield, reproductive performance, and culling in dairy cows

Periparturient hypocalcemia is frequently observed and considered as a gateway disease that is associated with various health issues. The objective of this study was to evaluate the association of hypocalcemia with early-lactation milk yield, reproductive performance, and culling across a large number of different managerial systems. A prospective cohort study was conducted based on a convenience sample of 125 dairy herds from 8 federal states of Germany between February 2015 and August 2016. A blood sample was drawn from 1,709 animals within 48 h after parturition and analyzed for serum calcium concentration. After discarding cows (n = 283) with missing data, a total of 1,426 cows were considered for final analyses. The median time from calving to sampling was 14.0 h (interquartile range = 5.0-24.9 h). For each herd, a record of the herd management software was requested 150 d after the last cow was sampled. Serum calcium concentration of each cow was associated with early-lactation milk yield (Dairy Herd Improvement Association equivalent test 1 to 3), reproductive performance [days in milk (DIM) at first artificial insemination (AI), pregnancy at first AI, time to pregnancy within 150 DIM], and culling (until 60 DIM) data. Generalized linear mixed models were used to analyze continuous or categorical data. Shared frailty models were used for time to event data. Five different thresholds were used to define hypocalcemia. Thresholds ranged from 1.8 to 2.2 mmol/L using 0.1-mmol/L increments. Clinical hypocalcemia was defined as serum calcium concentration <2.0 mmol/L in combination with clinical signs (e.g., recumbency). The effect of hypocalcemia on milk yield was conditional on parity. In primiparous cows a serum calcium concentration <2.0 mmol/L (6.4% of cows were below this threshold) had no effect on milk production, whereas there was a tendency for multiparous cows with a serum calcium concentration <2.1 mmol/L (63.2% of cows were below this threshold) to produce 0.80 kg/d more milk compared with multiparous cows at or above the threshold. Multiparous cows suffering from clinical hypocalcemia produced 2.19 kg/d less milk compared with normocalcemic cows in early lactation. Calcium status was not associated with days to first insemination. Cows with a serum calcium concentration <1.9 mmol/L (34.6% of cows below this threshold) had decreased odds (odds ratio = 0.56) of pregnancy at first AI. A serum calcium concentration <1.8 mmol/L (24.1% of cows below this threshold) had a significant effect on time to pregnancy. Compared with animals with a serum calcium concentration ≥1.8 mmol/L, the hazard of becoming pregnant within 150 DIM was reduced when cows had a serum calcium concentration <1.8 mmol/L (hazard ratio = 0.68). Cows with a serum calcium concentration <2.0 mmol/L (44.3% of cows were below this threshold) had a 1.69 times greater hazard of being culled within the first 60 DIM compared with normocalcemic animals. The present study shows that the association of hypocalcemia with milk yield was conditional on parity and serum calcium concentration measured once within 48 h after calving. Considering reproductive performance and culling in early lactation, a negative effect of postpartum hypocalcemia was demonstrated.