Patterns of periparturient rumination and activity time in multiparous Holstein cows with and without dyscalcemia in early lactation.

Dyscalcemia, defined as reduced blood Ca at 4 DIM, is associated with reduced milk production and reproduction and an increased risk of negative health events. Cowside testing of blood Ca to diagnose dyscalcemia is difficult, and alternative methods to identify dyscalcemia are needed. Our objectives were to explore differences in periparturient rumination and activity time between cows with and without dyscalcemia and use activity and rumination variables to identify dyscalcemia. We performed a retrospective cohort analysis on data collected from multiparous Holstein cows (n = 182) from 2 herds in New York. Cows were affixed with ear or neck loggers to record daily activity (arbitrary units [AU]/d, defined by manufacturer) and rumination (min/d) times. Daily activity and rumination times were collected from 14 d before calving until 14 DIM. No cows received supplemental calcium or experienced clinical hypocalcemia during the study period. A blood sample was collected at 4 DIM and analyzed for total calcium concentration, and cows were subsequently classified as dyscalcemic if total calcium was ≤2.2 mmol/L (n = 57) or eucalcemic if total calcium was >2.2 mmol/L (n = 125). Linear mixed models were used to analyze differences in pre- and postpartum activity and rumination times between the calcemic groups. Logistic regression models were used to identify the probability of dyscalcemia from activity and rumination time variables from 0 to 4 DIM. Prepartum activity time was similar between eucalcemic and dyscalcemic cows (402.0 ± 10.4 AU/d and 395.1 ± 14.5 AU/d, respectively). Postpartum eucalcemic cows had greater activity time than dyscalcemic cows (436.1 ± 10.7 vs. 407.8 ± 14.7 AU/d, respectively). Prepartum rumination time was similar between eucalcemic and dyscalcemic cows (512.6 ± 9.8 min/d vs. 504.2 ± 14 min/d, respectively). Postpartum eucalcemic cows had greater rumination time than dyscalcemic cows (512.3 ± 10.5 min/d vs. 480.5 ± 15 min/d, respectively). Logistic regression models yielded AUC values ranging from 0.71 to 0.79, sensitivities of 17.5% to 40.3%, specificities of 91.2% to 94.4%, accuracy of 70.3% to 77.0%, positive predictive values of 59.0 to 76.0%, and negative predictive values of 72.0% to 78.0%. Our findings suggest that differences exist in postpartum activity and rumination times between cows that experience dyscalcemia and those that remain eucalcemic. Utilizing activity and rumination time data in the immediate postpartum period shows utility in identifying cows with dyscalcemia, which could aid in management decisions that ameliorate the associated negative outcomes; however, further work is needed to optimize their capabilities.

Effects of timing of oral calcium administration on milk production in high-producing early-lactation Holstein cows.

Supplementation of oral Ca via blanket administration of an oral Ca bolus at 0 and 24 h after calving has shown limited success in increasing production and minimizing adverse health events. Recent evidence that reductions in blood Ca at 4 d in milk (DIM) are more closely associated with negative outcomes than hypocalcemia at 0 to 24 h postpartum might explain this lack of Ca bolus efficacy. Therefore, our primary objective was to explore the effect of delayed oral Ca bolus supplementation on milk production, with secondary objectives of exploring the effects on disease incidence and postpartum blood Ca dynamics. We conducted a randomized controlled trial on multiparous Holstein cows (n = 998) from 4 herds in New York. At calving, cows were randomly assigned to 1 of 3 treatment groups: (1) control, no supplemental Ca at or around parturition (CON; n = 343); (2) conventional bolus, an oral Ca bolus containing 43 g of Ca at calving and 24 h later (BOL-C; n = 330); or (3) delayed bolus, an oral Ca bolus containing 43 g of Ca at 48 and 72 h after calving (BOL-D; n = 325). We created generalized linear mixed models to analyze differences in milk yield for the first 10 wk of lactation and serum total Ca (tCa) at 1 and 4 DIM between treatment groups; multivariable Poisson regression models were used to analyze adverse event outcomes (metritis, displaced abomasum, herd removal, or a combination of one or more of the 3) in the first 30 DIM. Milk yield increased by week and was not affected by treatment. However, a treatment by parity group interaction for milk yield showed that BOL-D cows in the third parity produced more milk than third-parity BOL-C or CON cows (BOL-D = 52.0 kg/d, 95% confidence interval [50.6, 53.4] kg/d, BOL-C = 47.9 [46.3, 49.5] kg/d, CON = 49.8 [48.2, 51.2] kg/d). The incidence of adverse health events was similar between treatments (BOL-D = 3.7%, BOL-C = 3.7%, CON = 3.6%). Serum tCa was lower at 1 than 4 DIM, and we detected no difference in tCa between treatment groups. Our findings suggest that delaying oral Ca bolus supplementation has limited influence on blood Ca concentrations but may be beneficial to cohorts of cows as a targeted prophylactic supplement to support milk production.

Circulating parathyroid hormone and serotonin in multiparous cows with differing postparturient serum calcium concentrations.

Many multiparous dairy cows experience subclinical hypocalcemia (SCH) in the immediate postpartum period as they adapt to the demands of lactation. Furthermore, differing dynamics of SCH in the days following parturition are associated with varied health and production outcomes, with cows experiencing transient SCH producing more milk and facing fewer negative health events than cows with delayed or persistent SCH. Our objectives were to describe differences in mediators of calcium (Ca) homeostasis between cows experiencing differing Ca dynamics postpartum. A prospective cohort of 89 multiparous Holstein cows from 2 herds in New York were classified into 1 of 4 SCH groups based on mean serum total Ca (tCa) at 1 and 4 d in milk (DIM): normocalcemic (NC; [tCa] >1.89 mmol/L at 1 DIM and >2.25 mmol/L at 4 DIM, n = 30); transient SCH (tSCH; [tCa] ≤1.89 mmol/L at 1 DIM and >2.25 mmol/L at 4 DIM, n = 12); delayed SCH (dSCH; [tCa] >1.89 mmol/L at 1 DIM and ≤2.25 mmol/L at 4 DIM, n = 23); and persistent SCH (pSCH; [tCa] ≤1.89 mmol at 1 DIM and ≤2.25 mmol/L at 4 DIM, n = 24). Blood samples were collected at -5, -1, 1 through 5, 7, and 10 DIM and analyzed for tCa, parathyroid hormone (PTH), and serotonin. Repeated measures ANOVA models were used to analyze differences between SCH groups and changes over time for tCa, PTH, and serotonin. During the prepartum period, tCa was greater in the NC, tSCH, and dSCH cows as compared with the pSCH cows and there was marginal evidence for a difference in PTH between SCH groups. Postpartum tCa varied over time between SCH groups. Mean postpartum (95% confidence interval) tCa for respective SCH groups were NC = 2.32 (2.28, 2.35) mmol/L; tSCH = 2.20 (2.14, 2.25) mmol/L; dSCH = 2.17 (2.13, 2.21) mmol/L; and pSCH = 2.03 (1.99, 2.07) mmol/L. Mean concentrations of PTH in the postpartum period were NC = 70.1 (66.2, 74.4) pmol/L; tSCH = 72.1 (66.1, 79.2); dSCH = 75.8 (70.8, 81.5) pmol/L; and pSCH = 77.7 (72.4, 83.9) pmol/L. Serotonin was similar between SCH groups pre- and postpartum and followed a cyclical pattern from 1 to 10 DIM. Our results agreed with our hypothesis that differences in postpartum PTH might exist between cows experiencing different dynamics of SCH in the early lactation period; however, further studies are needed to confirm this difference. If true, this would suggest that Ca homeostasis may be disrupted in cows with dSCH and pSCH. Gaining a better understanding of these modulatory differences may aid in the prevention, management, and treatment of SCH.

Patterns of Fourier-transform infrared estimated milk constituents in early lactation Holstein cows on a single New York State dairy.

Cows undergo immense physiological stress to produce milk during early lactation. Monitoring early lactation milk through Fourier-transform infrared (FTIR) spectroscopy might offer an understanding of which cows transition successfully. Daily patterns of milk constituents in early lactation have yet to be reported continuously, and the study objective was to initially describe these patterns for cows of varying parity groups from 3 through 10 d postpartum, piloted on a single dairy. We enrolled 1,024 Holstein cows from a commercial dairy farm in Cayuga County, New York, in an observational study, with a total of 306 parity 1 cows, 274 parity 2 cows, and 444 parity ≥3 cows. Cows were sampled once daily, Monday through Friday, via proportional milk samplers, and milk was stored at 4°C until analysis using FTIR. Estimated constituents included anhydrous lactose, true protein, and fat (g/100 g of milk); relative % (rel%) of total fatty acids (FA) and concentration (g/100 g of milk) of de novo, mixed, and preformed FA; individual fatty acids C16:0, C18:0, and C18:1 cis-9 (g/100 g of milk); milk urea nitrogen (MUN; mg/100 g of milk); and milk acetone (mACE), milk ß-hydroxybutyrate (mBHB), and milk-predicted blood nonesterified fatty acids (mpbNEFA) (all expressed in mmol/L). Differences between parity groups were assessed using repeated-measures ANOVA. Milk yield per milking differed over time between 3 and 10 DIM and averaged 8.7, 13.3, and 13.3 kg for parity 1, 2, and ≥3 cows, respectively. Parity differences were found for % anhydrous lactose, % fat, and preformed FA (g/100 g of milk). Parity differed across DIM for % true protein, de novo FA (rel% and g/100 g of milk), mixed FA (rel% and g/100 g of milk), preformed FA rel%, C16:0, C18:0, C18:1 cis-9, MUN, mACE, mBHB, and mpbNEFA. Parity 1 cows had less true protein and greater fat percentages than parity 2 and ≥3 cows (% true protein: 3.52, 3.76, 3.81; % fat: 5.55, 4.69, 4.95, for parity 1, 2, ≥3, respectively). De novo and mixed FA rel% were reduced and preformed FA rel% were increased in primiparous compared with parity 2 and ≥3 cows. The increase in preformed FA rel% in primiparous cows agreed with milk markers of energy deficit, such that mpbNEFA, mBHB, and mACE were greatest in parity 1 cows followed by parity ≥3 cows, with parity 2 cows having the lowest concentrations. When measuring milk constituents with FTIR, these results suggest it is critical to account for parity for the majority of estimated milk constituents. We acknowledge the limitation that this study was conducted on a single farm; however, if FTIR technology is to be used as a method of identifying cows maladapted to lactation, understanding variations in early lactation milk constituents is a crucial first step in the practical adoption of this technology.

Calcium dynamics and associated temporal patterns of milk constituents in early-lactation multiparous Holsteins.

At the onset of lactation, calcium (Ca) homeostasis is challenged. For the transitioning dairy cow, inadequate responses to this challenge may result in subclinical hypocalcemia at some point in the postpartum period. It has been proposed that dynamics of blood Ca and the timing of subclinical hypocalcemia allow cows to be classified into 4 Ca dynamic groups by assessing serum total Ca concentrations (tCa) at 1 and 4 days in milk (DIM). These differing dynamics are associated with different risks of adverse health events and suboptimal production. Our prospective cohort study aimed to characterize the temporal patterns of milk constituents in cows with differing Ca dynamics to investigate the potential of Fourier-transform infrared spectroscopic (FTIR) analysis of milk as a diagnostic tool for identifying cows with unfavorable Ca dynamics. We sampled the blood of 343 multiparous Holsteins on a single dairy in Cayuga County, New York, at 1 and 4 DIM and classified these cows into Ca dynamic groups using threshold concentrations of tCa (1 DIM: tCa <1.98 mmol/L; 4 DIM: tCa <2.22 mmol/L) derived from receiver operating characteristic curve analysis based on epidemiologically relevant health and production outcomes. We also collected proportional milk samples from each of these cows from 3 to 10 DIM for FTIR analysis of milk constituents. Through this analysis we estimated the milk constituent levels of anhydrous lactose (g/100 g of milk and g/milking), true protein (g/100 g of milk and g/milking), fat (g/100 g of milk and g/milking), milk urea nitrogen (mg/100 g of milk), fatty acid (FA) groups including de novo, mixed origin, and preformed FA measured in grams/100 g of milk, by relative percentage, and grams/milking, as well as energy-related metabolites including ketone bodies and milk-predicted blood nonesterified FA. Individual milk constituents were compared among groups at each time point and over the entire sample period using linear regression models. Overall, we found differences among the constituent profiles of Ca dynamic groups at approximately every time point and over the entire sample period. The 2 at-risk groups of cows did not differ from each other at more than one time point for any constituent, however prominent differences existed between the milk of normocalcemic cows and the milk of the other Ca dynamic groups with respect to FA. Over the entire sample period, lactose and protein yield (g/milking) were lower in the milk of at-risk cows than in the milk of the other Ca dynamic groups. In addition, milk yield per milking followed patterns consistent with previous Ca dynamic group research. Though our use of a single farm does limit the general applicability of these findings, our conclusions provide evidence that FTIR may be a useful method for discriminating between cows with different Ca dynamics at time points that may be relevant in the optimization of management or development of clinical intervention strategies.

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.

Effect of hyperketonemia on the diurnal patterns of energy-related blood metabolites in early-lactation dairy cows.

Most dairy cows experience a period of energy deficit in early lactation, resulting in increased plasma concentrations of nonesterified fatty acids (NEFA) and ß-hydroxybutyrate (BHB). Our objectives were to determine (1) the diurnal variation in plasma BHB and NEFA, (2) the correlation between plasma NEFA and BHB when accounting for diurnal changes, and (3) the effect of hyperketonemia (HYK) on the diurnal pattern of blood metabolites. Jugular catheters were placed in 28 multiparous Holstein cows between 3 and 9 days in milk, and blood samples were collected every 2 h for 96 h. Cows were retrospectively classified as HYK positive (HYK; n = 13) if they had plasma BHB concentrations ≥1.2 mmol/L for ≥3 study days, or HYK negative (non-HYK; n = 15) if they had plasma BHB concentrations ≥1.2 mmol/L for ≤2 study days. Generalized linear mixed models were used to analyze concentrations of analytes over time and differences in metabolites between HYK groups. The correlation between total plasma NEFA and BHB was analyzed by calculating the area under the curve for plasma NEFA and BHB for all cows. Plasma NEFA reached a peak approximately 2 h before morning feed delivery, falling to a nadir in the late evening. Plasma BHB was at a nadir at the time of morning feed delivery, peaking 4 h later. We observed a strong positive correlation between daily plasma NEFA and BHB. Additionally, HYK cows had greater concentrations of plasma NEFA and BHB than non-HYK cows. The HYK cows also experienced a greater magnitude of change in BHB throughout the day than the non-HYK cows. Our results suggest that the time relative to feeding should be considered when analyzing plasma metabolites, as classification of energy status may change throughout a day.

Postpartum supplementation with fermented ammoniated condensed whey altered nutrient partitioning to support hepatic metabolism.

Our previously published paper demonstrated that fermented ammoniated condensed whey (FACW) supplementation improved feed efficiency and metabolic profile in postpartum dairy cows. The objective of this study was to further explore the effects of FACW supplementation on liver triglyceride content, hepatic gene expression and protein abundance, and plasma biomarkers related to liver function, inflammation, and damage. Individually fed multiparous Holstein cows were blocked by calving date and randomly assigned to postpartum (1 to 45 d in milk, DIM) isonitrogenous treatments: control diet (n = 20) or diet supplemented with FACW (2.9% dry matter of diet as GlucoBoost; Fermented Nutrition, Luxemburg, WI, replacing soybean meal; n = 19). Liver biopsies were performed at 14 and 28 DIM for analysis of mRNA expression, protein abundance, and liver triglyceride content. There was marginal evidence for a reduction in liver triglyceride content at 14 DIM in FACW-supplemented cows compared with the control group. Cows supplemented with FACW had greater mRNA expression of glucose-6-phosphatase at 14 DIM relative to control. Supplementation with FACW increased mRNA expression of pyruvate carboxylase (PC), but did not alter cytosolic phosphoenolpyruvate carboxykinase (PCK1), resulting in a 2.4-fold greater PC:PCK1 ratio for FACW-supplemented cows compared with control. There was no evidence for a FACW effect on mRNA expression of propionyl-CoA carboxylase nor on mRNA expression or protein abundance of lactate dehydrogenase A or B. Cows supplemented with FACW had lower plasma urea nitrogen compared with control. Plasma l-lactate was greater for FACW-supplemented cows compared with control at 2 h before feeding time at 21 DIM. There was no evidence for altered expression of IL1B or IL10, or blood biomarkers related to liver function and damage. Greater glucose-6-phosphatase and PC gene expression, together with greater blood glucose and similar milk lactose output, suggests that FACW increased the supply of glucose precursors, resulting in greater gluconeogenesis between 3 and 14 DIM. Greater hepatic PC:PCK1 ratio, together with previously reported decreased plasma ß-hydroxybutyrate and the marginal evidence for lower liver triglyceride content at 14 DIM, suggests greater hepatic capacity for complete oxidation of fatty acids in FACW-supplemented cows compared with control. Overall, improvements in metabolite profile and feed efficiency observed with postpartum supplementation of FACW may be attributed to increased gluconeogenic and anaplerotic precursors, most likely propionate, due to modulated rumen fermentation.

Postpartum supplementation of fermented ammoniated condensed whey improved feed efficiency and plasma metabolite profile.

Postpartum dietary supplementation of gluconeogenic precursors may improve the plasma metabolite profile of dairy cows, reducing metabolic disorders and improving lactation performance. The objective of this trial was to examine the effects of supplementation with fermented ammoniated condensed whey (FACW) postpartum on lactation performance and on profile of plasma metabolites and hormones in transition dairy cows. Individually fed multiparous Holstein cows were blocked by calving date and randomly assigned to control (2.9% dry matter of diet as soybean meal; n = 20) or FACW (2.9% dry matter of diet as liquid GlucoBoost, Fermented Nutrition, Luxemburg, WI; n = 19) dietary treatments. Treatments were offered from 1 to 45 d in milk (DIM). Cows were milked twice a day. Dry matter intake and milk yield were recorded daily and averaged weekly. Individual milk samples from 2 consecutive milkings were obtained once a week for component analysis. Rumen fluid was collected (n = 3 cows/treatment) at 4 time points per day at 7 and 21 DIM. Blood samples were collected within 1 h before feeding time for metabolite analysis and hyperketonemia diagnosis. Supplementation of FACW improved feed efficiency relative to control; this effect may be partially explained by a marginally significant reduction in dry matter intake from wk 3 to 7 for FACW-supplemented cows with no detected FACW-driven changes in milk yield, milk protein yield, and milk energy output compared with control. Also, there was no evidence for differences in intake of net energy for lactation, efficiency of energy use, energy balance, or body weight or body condition score change from calving to 45 DIM between treatments. Supplementation of FACW shifted rumen measures toward greater molar proportions of propionate and butyrate, and lesser molar proportions of acetate and valerate. Cows supplemented with FACW had greater plasma glucose concentrations in the period from 3 to 7 DIM and greater plasma insulin concentrations compared with control. Plasma nonesterified fatty acid and ß-hydroxybutyrate concentrations were decreased in cows supplemented with FACW compared with control cows in the period from 3 to 7 DIM. These findings indicate that FACW may have improved the plasma metabolite profile immediately postpartum in dairy cows. Additionally, supplementation of FACW resulted in improved feed efficiency as accessed by measures of milk output relative to feed intake.

Does knowledge of blood calcium concentration at 2 days postpartum affect decisions of calcium supplementation?

Delaying oral Ca supplementation might benefit cows with low blood Ca concentrations at 4 d in milk (DIM), a time when reduced blood total Ca (tCa) is associated with negative health and production outcomes. To implement a targeted approach to manage subclinical hypocalcemia (SCH) at the herd level, it is important to identify which cows benefit from supplemental Ca. Therefore, our objective was to determine if SCH diagnosis at 2 DIM could inform decisions of oral Ca supplementation at 2 and 3 DIM based on milk yield and 4 DIM blood Ca concentration. Data were analyzed from a previously conducted randomized controlled trial on multiparous cows (n = 518) from 4 farms in New York State. Cows were randomly assigned to 1 of 2 treatment groups at calving: (1) control (CON; no Ca supplementation, n = 259) or (2) bolus (BOL; 43 g of oral Ca administered at 2 and 3 DIM postcalving, n = 259). For each parity group (2, 3, 4+), we used generalized linear mixed models to identify serum tCa concentrations at 2 DIM that maximized the difference in milk yield to diagnose SCH. Cows were classified as normocalcemic (NC; parity 2 tCa >1.9 mmol/L, parity 3 tCa >1.87 mmol/L, n = 327; parity ≥4 had no defining threshold) or SCH (parity 2 tCa ≤1.9 mmol/L, parity 3 tCa ≤1.87 mmol/L, n = 58; parity ≥4 had no defining threshold). Parity 2 and 3 cows were further classified into 1 of 4 SCH-treatment groups (SCHTRT) based on 2 DIM SCH status and random treatment allocation: (1) NC-CON, n = 165, (2) SCH-CON, n = 28, (3) NC-BOL, n = 162, or (4) SCH-BOL, n = 30. Generalized linear mixed models were used to analyze the difference in milk yield for the first 10 wk of lactation and tCa at 4 DIM between SCHTRT groups with separate analyses performed for parities 2 and 3. Mean milk yield differed between SCHTRT groups for both parities. For parity 2, SCH-CON and SCH-BOL cows produced more milk than NC-CON and NC-BOL cows with SCH-CON producing 50.9 (95% confidence interval [CI] = 48.4, 53.4) kg/d, SCH-BOL 51.7 (49.1, 54.2) kg/d, NC-CON 47.5 (46.3, 48.7) kg/d, and NC-BOL 47.2 (45.8, 48.5) kg/d of milk. Milk yield was also different between SCHTRT groups for parity 3 with SCH-BOL cows producing more milk than NC-CON and NC-BOL cows. In parity 3, SCH-BOL cows produced 56.3 (95% CI = 53.1, 59.3) kg/d, SCH-CON 51.7 (48.6, 54.7) kg/d, NC-BOL 50.6 (49.0, 52.2) kg/d, and NC-CON 48.7 (46.9, 50.5) kg/d of milk. For both parities, SCH-CON and SCH-BOL cows had lower tCa at 2 DIM than NC-CON and NC-BOL cows. At 4 DIM, tCa concentrations were similar for all SCHTRT groups respective to parity. Our results suggest that although delayed Ca bolus administration does not improve blood Ca concentration when compared with controls, it does support increased milk production in parity 3 cows regardless of Ca status at 2 DIM. Thus, knowledge of blood Ca at 2 DIM should not affect decisions of Ca supplementation in this parity of cows.

Effect of postpartum calcium supplementation on serum calcium and parathyroid hormone concentrations in multiparous Holstein cows.

Although postpartum Ca supplementation strategies are often employed to prevent subclinical hypocalcemia in dairy cows, these strategies have produced a mix of beneficial, neutral, and detrimental results when assessing milk yield and subsequent disease outcomes. Because the mechanisms underlying these differing results are unknown, our objectives were to determine how common postpartum Ca supplementation strategies affect blood Ca concentrations and parathyroid hormone (PTH). We conducted a randomized controlled trial with 74 multiparous dairy cows on a commercial dairy in central New York. Cows were assigned to 1 of 4 supplementation groups immediately after calving: (1) control (CON; no Ca supplementation, n = 15); (2) conventional oral Ca supplementation (BOL-C; 43 g of oral Ca bolus administered immediately after calving and 24 h later, n = 17); (3) delayed oral Ca supplementation (BOL-D; 43 g of oral Ca bolus administered 48 and 72 h after calving, n = 15); or (4) subcutaneous infusion (SQ; 500 mL of 23% Ca borogluconate infused subcutaneously once immediately after calving, n = 15). Blood samples were collected immediately after calving (0 h) and at 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96, 120, and 168 h postpartum for a total of 15 blood samples per cow. Cows were excluded if administered Ca, via any route, by farm employees or if they died or were sold within 96 h following parturition, which left 62 cows for analysis. Linear mixed models, accounting for repeated measures, were created to analyze changes in serum total Ca (tCa) and PTH over the first 168 h after parturition and assess differences between supplementation groups. Serum tCa and PTH concentrations were not different at the time of calving among supplementation groups. There was a supplementation group by hour postcalving interaction for mean tCa concentration in which SQ cows had reduced tCa concentrations from 32 to 64 h compared with CON cows, 32 to 96 h compared with BOL-C cows, and 40 to 64 h compared with BOL-D cows. Mean PTH concentration did not differ among supplementation groups across 168 h after enrollment and was 158.1 pmol/L (95% confidence interval [CI] = 148.2 to 168.0) for CON cows, 164.0 pmol/L (95% CI = 154.9 to 173.1) for BOL-C cows, 158.7 pmol/L (95% CI = 149.2 to 168.1) for BOL-D cows, and 153.2 pmol/L (95% CI = 143.6 to 162.8) for SQ cows. Our findings suggest that although serum tCa does not differ between cows that receive conventional or delayed oral Ca bolus supplementation at calving and cows that receive no supplemental Ca, subcutaneous infusion of Ca at calving reduces serum tCa for a substantial period between 32 and 64 h postsupplementation. However, as PTH concentrations did not differ among groups across 168 h postpartum, the mechanism by which tCa is reduced remains unclear.

The association of subclinical hypocalcemia at 4 days in milk with reproductive outcomes in multiparous Holstein cows.

Delayed or persistent episodes of subclinical hypocalcemia (SCH) have been associated with reduced milk production and feed intake and they put cows at risk for additional disease development. However, little is known about the effect of delayed or persistent SCH on reproductive outcomes. The objectives of our study were to describe the association between SCH status at 4 d in milk (DIM) with the odds of pregnancy to first service and time to pregnancy through 150 DIM. Data were collected from multiparous Holstein cows (n = 697) from 4 farms in New York State that did not receive supplemental Ca during the first 5 DIM. Cows were classified into 1 of 2 SCH groups based on blood total Ca (tCa) at 4 DIM: normocalcemic (NC; n = 515) if tCa >2.2 mmol/L at 4 DIM or SCH (n = 182) if tCa ≤2.2 mmol/L at 4 DIM. We created a multivariable logistic regression model to assess the association between SCH group and pregnancy to first service and a time-to-event analysis to evaluate the effect of SCH group on the hazard of pregnancy by 150 DIM. Cows that were SCH at 4 DIM had lower odds of pregnancy to first service [odds ratio = 0.75, 95% confidence interval (CI) = 0.61 to 0.93, incidence = 18.1%] compared with their NC counterparts (incidence = 27.4%). Similarly, SCH cows tended to have a lower hazard of pregnancy by 150 DIM (hazard ratio = 0.82, 95% CI = 0.67 to 1.01, incidence = 65.4%) than NC cows (incidence = 70.7%). Our results indicate that delayed or prolonged reductions in blood Ca in the early postpartum period, resulting in SCH at 4 DIM, were associated with reduced reproductive outcomes in multiparous cows. Our findings, in conjunction with previous reports of the negative associations of delayed or persistent SCH on health and production, suggest that reductions in blood Ca beyond the first day of lactation might be indicative of maladaptation to lactation, and the ramifications can persist beyond the immediate postpartum period.

Diurnal variation of milk fatty acids in early-lactation Holstein cows with and without hyperketonemia.

Estimates of milk constituents by Fourier-transform mid-infrared (FTIR) analysis have been shown to be a useful tool in monitoring energy deficit in early-lactation dairy cows. Our objectives were to describe the diurnal variation in milk fatty acids (FAs) and estimate the association of hyperketonemia with concentrations and diurnal patterns of FTIR estimates of milk FA. Blood samples were collected via jugular catheters bihourly for 5 d from multiparous Holstein cows (n = 28) enrolled between 3 and 9 days in milk. Milk samples were collected thrice daily at 0600, 1400, and 2200 h for d 2, 3, and 4 of the study period. Cows were retrospectively classified as hyperketonemic (HYK; n = 13) or non-HYK (n = 15) based on blood beta-hydroxybutyrate (bBHB) concentrations analyzed during the study period. Cows were classified as HYK if bBHB was ≥ 1.2 mmol/l for ≥ 50% (22/44) of bihourly timepoints; cows were classified as non-HYK if bBHB was ≥ 1.2 mmol/l for < 50% of bihourly timepoints. The HYK cows had bBHB ≥ 1.2 mmol/l for 31.4 ± 6.8 timepoints while the non-HYK cows had bBHB ≥ 1.2 mmol/l for 8.0 ± 3.9 timepoints. We used generalized linear mixed models to analyze concentrations of milk FA over time and differences between HYK groups. The relative percentage of de novo, mixed, and preformed FAs all followed diurnal patterns, however only the yield of preformed FA diurnally cycled, reaching a nadir at 0600 h and peaking at 1400 h. The yield per milking of preformed FA was also greater in the HYK cows than in the non-HYK cows. Oleic acid in milk followed a similar diurnal pattern to the yield of preformed FA, likely driving the cyclical nature of preformed FA. Finally, stearic acid was greater in HYK cows. Our results suggest that FTIR estimates of milk FA offer the potential to provide insight on the energy status of early-lactation cows, and when interested in understanding the absolute concentrations and yields of milk FA, diurnal variation should be considered.