Milk fever (MF, parturient hypocalcaemia) is a serious metabolic disorder in periparturient dairy cows, typically resulting in recumbency. Although its clinical incidence is generally less than 10% on farms, the condition can affect more than 25% of calving cows (DeGaris and Lean, Reference DeGaris and Lean2008). The disease arises when the cow’s calcium (Ca) homeostatic mechanisms fail to adapt to the substantial Ca demand associated with colostrum production (DeGaris and Lean, Reference DeGaris and Lean2008). The risk of MF increases with parity, being particularly high in multiparous cows, especially those in their fourth or later lactation (DeGaris and Lean, Reference DeGaris and Lean2008). Moreover, MF is associated with considerable economic losses in the dairy industry, both directly and indirectly, through reduced milk production, impaired reproductive performance, increased veterinary costs and higher rates of involuntary culling (Bzuneh et al., Reference Bzuneh, Alemneh and Getabalew2020).
The maintenance of Ca homeostasis is particularly challenging in parturient dairy cows because bone Ca resorption is known to be delayed (Ramberg et al., Reference Ramberg, Mayer, Kronfeld, Phang and Berman1970, Reference Ramberg, Johnson, Fargo and Kronfeld1984), despite the high demand for Ca required for colostrum synthesis. Therefore, the activation of bone metabolism to mobilize Ca stores is essential to prevent periparturient hypocalcaemia (Wilkens et al., Reference Wilkens, Nelson, Hernandez and McArt2020). Preventive strategies, such as feeding low dietary cation–anion difference diets prepartum, aim to stimulate osteoclastic bone resorption (Wilkens et al., Reference Wilkens, Nelson, Hernandez and McArt2020). Given this critical physiological role, evaluation of bone metabolic status in parturient cows may aid in understanding and predicting the risk of hypocalcaemia.
Bone metabolic markers provide valuable insights into the dynamic processes of bone formation and resorption (Allen, Reference Allen2003). Various serum bone metabolic markers have been investigated to assess bone metabolism in periparturient dairy cows (Kim et al., Reference Kim, Yamagishi, Ueki, Miura, Saito, Sato and Furuhama2010; Hatate et al., Reference Hatate, Kawashima, Hanada, Kayano and Yamagishi2018; Starič and Hodnik, Reference Starič and Hondnik2021; Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022). These include bone-specific alkaline phosphatase (BAP), an isoenzyme of alkaline phosphatase (ALP), also known as ALP3, which serves as a biomarker for osteoblast function and bone formation, playing a critical role in bone mineralization (Allen, Reference Allen2003). Its activity in bovine circulation can be measured using methods such as spectrometry with heat inactivation or wheat germ lectin precipitation (Mohebbi et al., Reference Mohebbi, Khaghani and Mohammadnia2010), as well as agarose gel electrophoresis (Chiba et al., Reference Chiba, Hatate, Onomi, Moriyama, Goto and Yamagishi2020a, Reference Chiba, Onomi, Hatate, Moriyama, Goto and Yamagishi2020b). Cross-linked N-telopeptide of type I collagen (NTx), a product of bone collagen degradation, serves as a marker for bone resorption (Allen, Reference Allen2003). Tartrate-resistant acid phosphatase isoform 5b (TRAP5b) is another biomarker of osteoclastic bone resorption (Allen, Reference Allen2003); its circulating levels are correlated with osteoclast number (Rissanen et al., Reference Rissanen, Suominen, Peng and Halleen2008). Osteoprotegerin (OPG), a protein that regulates bone resorption, acts by inhibiting osteoclast differentiation and formation (Simonet et al., Reference Simonet, Lacey, Dunstan, Kelley, Chang, Lüthy, Nguyen, Wooden, Bennett, Boone, Shimamoto, DeRose, Elliott, Colombero, Tan, Trail, Sullivan, Davy, Bucay, Renshaw-Gegg, Hughes, Hill, Pattison, Campbell, Sander, Van, Tarpley, Derby, Lee and Boyle1997). Elevated blood OPG levels observed during pregnancy in mice and women suggest a protective role in preventing excessive maternal bone resorption (Yano et al., Reference Yano, Shibata, Mizuno, Kobayashi, Higashio, Morinaga and Tsuda2001; Naylor et al., Reference Naylor, Rogers, Fraser, Hall, Eastell and Blumsohn2003).
Beyond serum, attention has also been directed towards the composition of colostrum, the initial mammary secretion postpartum, which is essential for the health of newborn calves (Stelwagen et al., Reference Stelwagen, Carpenter, Haigh, Hodgkinson and Wheeler2009). Colostrum contains bone metabolic markers. For instance, OPG activity has been identified in human colostrum, suggesting a role in neonatal bone formation and immune system development (Vidal et al., Reference Vidal, Van Den Broek, Lorget and Donnet-Hughes2004; Rafeey et al., Reference Rafeey, Ghorbanihaghjo, Masoumi, Alizadeh and Farid2013). In cattle, our previous studies have revealed the presence of bone metabolic markers such as TRAP5b, BAP, NTx and OPG in colostrum (Hatate et al., Reference Hatate, Kayano, Kawashima, Hanada, Bicalho and Yamagishi2019); they have shown that circulating levels of these markers increase in newborn calves after colostrum intake (Hatate et al., Reference Hatate, Shinya, Matsuo-Sato, Sasaki, Devkota, Takahashi, Hirata and Yamagishi2016, Reference Hatate, Kayano, Kawashima, Hanada, Bicalho and Yamagishi2019). Additionally, NTx concentrations in breast milk from postpartum women have been shown to fluctuate depending on maternal health status, including factors such as delivery method and thyroid function (Bouroutzoglou et al., Reference Bouroutzoglou, Malamitsi-Puchner, Boutsikou, Marmarinos, Baka, Boutsikou, Hassiakos, Gourgiotis and Briana2014). These findings suggest that bone metabolic markers in colostrum not only contribute to neonatal physiological functions but may also reflect maternal health and metabolic status during the periparturient period.
We therefore hypothesized that bone metabolic markers present in colostrum reflect the metabolic status of the dam during the periparturient period, particularly regarding MF incidence. This research communication aimed to measure the concentrations of major bone metabolic markers (BAP, TRAP5b, NTx and OPG) in colostrum and serum samples collected from dairy cows on the day of calving, to clarify their association with parity and the occurrence of MF.
Materials and methods
Animals
This study used samples that were already collected on the day of parturition for a previous study (Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022). Therefore, this research is a descriptive study whose sample size is based on the number of available samples from that prior collection. That study was conducted at the University Farm of Obihiro University of Agriculture and Veterinary Medicine (OUAV), Obihiro, Japan, between December 2018 and July 2019. For the present analysis, colostral and serum samples collected on the day of calving from these cows were used. Clinical information, including age and cumulative milk yield during the first day postpartum, was recorded. Cows had ad libitum access to water and hay; they were fed a total mixed ration containing maize and grass silage, a concentrated mix (containing ingredients such as corn, corn gluten feed, corn distillers by-products, grain soluble, bran, rapeseed and soy-bean cake), vitamins and minerals prior to parturition. The composition of the prepartum diet has been previously reported (Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022) and included Ca at 0.9% dry matter (DM), phosphorus at 0.4% DM, magnesium at 0.2% DM and a dietary cation–anion difference of 9.3 mEq/100 g DM.
Cows were categorized into three parity groups: primiparous (first parity [P1], n = 18), second parity (P2, n = 11) and multiparous (third to sixth parity [P3], n = 16). Within the multiparous group, 6 cows developed MF within a few hours after calving (MF cows), whereas 10 cows showed no clinical signs of MF (non-MF cows). A tentative clinical diagnosis of MF was made based on the clinical history and presence of clinical signs characteristic of MF, as reported previously (Sasaki et al., Reference Sasaki, Sasaki, Sato, Devkota, Furuhama and Yamagishi2013). Briefly, before treatment initiation, each animal was checked for the presence of any of eight characteristic clinical signs of MF: astasia, anorexia, cold extremities, flaccid tail, tachycardia (>80 beats/min), tachypnoea (>36 breaths/min), decreased rectal temperature (<38.0°C) and coma. Other problems were identified by careful physical examination and information from the staff of the University Farm. The response to Ca treatment and serum Ca concentration measured later were also the basis for the diagnosis of MF. All MF cows recovered after intravenous administration of 500 ml of a 40% calcium borogluconate solution (Ca treatment). The experimental procedures were approved by the OUAV Laboratory Animal Care and Use Committee (Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022).
Sample collection and processing
Colostrum samples (50 ml) were obtained from the first milking (0.4–12 h after calving), by farm staff using a milking machine as part of routine calf-feeding procedures. Within 1 h of collection, colostrum samples were centrifuged at 1,500 × g for 30 min at 4°C, and the supernatant was stored at −60°C until analysis.
Coccygeal blood samples (9 ml) were collected from non-MF cows within 5 min after the first milking and from MF cows immediately before Ca treatment. Blood samples were allowed to coagulate for 30 min at 37°C using a water bath, then centrifuged. Serum was stored at −60°C until analysis, as previously described (Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022).
Biochemical analysis
The concentrations of several biochemical markers were measured in serum and colostrum samples. These included Ca, OPG, TRAP5b, NTx, colostral BAP and serum ALP3. Serum Ca concentrations were measured using an Arsenazo-III reagent kit (Ca-II Seiken; Denka Seiken, Tokyo, Japan), whereas colostral Ca concentrations were measured using a Chlorophosphonazo-III reagent kit (Metalloassay Calcium Measurement LS; Metallogenics, Chiba, Japan). Concentrations of OPG, TRAP5b and NTx were measured in both colostral supernatant and serum samples in accordance with previously described protocols (Hatate et al., Reference Hatate, Kawashima, Kayano, Hanada and Yamagishi2020; Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022). Colostral BAP concentrations were determined using a commercial ALP assay kit (LabAssay ALP Kit; Wako Pure Chemical Industries, Osaka, Japan), as previously described (Hatate et al., Reference Hatate, Kayano, Kawashima, Hanada, Bicalho and Yamagishi2019). The samples assayed using ELISA, spectrometry and fluorometry methods were all measured in duplicate. The intra- and interassay coefficients of variation were 4.5% and 6.0% for Ca measured by the Arsenazo-III reagent kit, 5.1% and 6.9% for Ca measured by the Chlorophosphonazo-III reagent kit, 11.3% and 9.7% for the OPG ELISA kit, 5.6% and 7.8% for the TRAP5b fluorometry method, 6.2% and 5.0% for the NTx ELISA kit, and 7.9% and 10.0% for the BAP spectrometry method, respectively. Serum ALP3 concentrations were analysed using an agarose gel electrophoresis system, as we previously reported (Onomi et al., Reference Onomi, Hatate and Yamagishi2019).
Statistical analysis
Data were expressed as medians with minimum and maximum values. Differences in colostral and serum biochemical parameters, as well as clinical information (age, parity and cumulative milk yield during the first day postpartum), among the parity groups (P1, P2 and P3) were analysed using the Kruskal–Wallis test, followed by Dunn’s post hoc test. Comparisons between MF and non-MF cows were performed using the Mann–Whitney U test. Associations between colostral bone biomarkers and other parameters were evaluated using Spearman’s rank correlation test. Spearman correlation coefficients (rs) were interpreted as strong (rs = 1.0–0.81), good (rs = 0.80–0.61), moderate (rs = 0.60–0.41), fair (rs = 0.40–0.21), or poor (rs < 0.20) (Brennan and Silman, Reference Brennan and Silman1992). All statistical analyses were conducted using JASP software (version 0.19.3; https://jasp-stats.org/). P-values < 0.05 were considered statistically significant.
Results
Table 1 summarizes the age, serum and colostral biochemical data of the 45 parturient cows, categorized by parity group (P1, P2 and P3), and by MF status within the P3 group. Median ages were 1.9 years for P1, 3.0 years for P2 and 4.8 years for P3. Milk yield during the first day postpartum was higher in P2 (median 12.7 kg) and P3 (median 12.1 kg) than in P1 (median 8.1 kg; P < 0.01–0.001).
Clinical characteristics and serum and colostral biochemical data of 45 parturient dairy cows across three parity groups (P1: 1st parity; P2: 2nd parity; P3: 3rd–6th parity) and of 16 multiparous cows (P3 group) in the 3rd–6th parity
ALP3, bone isoenzyme of alkaline phosphatase measured by an agarose gel electrophoresis method; BAP, bone-specific alkaline phosphatase measured by heat-inactivation techniques; Ca, calcium; NTx, cross-linked N-telopeptide of type I collagen; OPG, osteoprotegerin; TRAP5b, tartrate-resistant acid phosphatase isoform 5b.
Significant differences or trends were observed between values marked with the same letters, numbers, or symbols following Kruskal–Wallis test with Dunn’s post-hoc test for comparisons between P1, P2 and P3 groups:
# 0.05 < P < 0.1; a,b P < 0.05; A,B P < 0.01; 1,2,3 P < 0.001.
Significant differences or trends in values between the MF and non-MF groups within Group 3 cattle, as determined by the Mann–Whitney U test:
$ 0.05 < P < 0.1; *P < 0.05; ***P < 0.001.
Serum Ca concentrations also significantly differed among parity groups (P < 0.001); the median value was highest in P1 (8.1 mg/dl, followed by P2 (7.2 mg/dl), and it was lowest in P3 (6.4 mg/dl). Serum ALP3 concentrations showed significant differences among parity groups (P < 0.001); P1 cows had the highest median level (180.8 U/l), followed by P2 (139.0 U/l) and P3 (77.5 U/l). Similarly, serum TRAP5b concentrations were significantly higher in P1 cows (median 2.0 U/l) than in P2 (1.6 U/l) and P3 (1.3 U/l) (P < 0.05–0.001). Colostral BAP concentrations also significantly differed, such that P2 cows had a higher median concentration (642.7 U/l) relative to P3 cows (202.5 U/l; P < 0.01).
Within the P3 group, MF cows were significantly older than non-MF cows (median 5.5 years vs. 4.6 years; P < 0.05), although there were no significant differences in parity or milk yield between the two subgroups. As expected, serum Ca concentrations were significantly lower in MF cows (median 4.3 mg/dl) than in non-MF cows (median 7.2 mg/dl; P < 0.001). Colostral OPG concentrations tended to be higher in MF cows than in non-MF cows (median 6.1 ng/dl vs. 3.9 ng/dl), although this difference only approached statistical significance (trend P = 0.088).
Spearman’s rank correlation analysis was conducted to examine associations between colostral bone biomarkers and other parameters (Table 2). Among all 45 cows, colostral NTx showed moderate positive correlations with colostral OPG (rs = 0.548, P < 0.001) and serum NTx (rs = 0.424, P < 0.01). Colostral TRAP5b showed fair correlations with age (rs = 0.325, P < 0.05), and a fair negative correlation with serum Ca (rs = − 0.381, P < 0.05). Colostral OPG demonstrated moderate positive correlations with both serum NTx (rs = 0.402, P < 0.01) and serum OPG (rs = 0.490, P < 0.01).
Spearman's rank correlation coefficients (rs) for associations between colostral and serum bone biomarkers in 45 parturient cows (P1–P3: 1st–6th parity) and in 16 multiparous cows (P3 group: 3rd–6th parity)
ALP3, bone isoenzyme of alkaline phosphatase measured by an agarose gel electrophoresis method; BAP, bone-specific alkaline phosphatase measured by heat-inactivation techniques; Ca, calcium; NTx, cross-linked N-telopeptide of type I collagen; OPG, osteoprotegerin; TRAP5b, tartrate-resistant acid phosphatase isoform 5b. Correlation coefficients in bold text were statistically significant. ns: not significant.
* P < 0.05,. **P < 0.01,.***P < 0.001.
Within the P3 group, colostral NTx showed good and moderate positive correlations with colostral OPG (rs = 0.649, P < 0.01) and serum NTx (rs = 0.567, P < 0.05), respectively. Colostral TRAP5b demonstrated moderate positive correlations with age (rs = 0.561, P < 0.05), as well as a moderate negative correlation with colostral BAP (rs = − 0.561, P < 0.05). Colostral OPG showed good and moderate positive correlations with serum NTx (rs = 0.610, P < 0.05) and serum OPG (rs = 0.562, P < 0.05), respectively.
Discussion
Consistent with the known physiological changes in bone metabolism associated with ageing, we observed significant differences in several serum bone metabolic markers across parity groups (Table 1). Serum concentrations of ALP3 and TRAP5b, markers of bone formation and resorption, respectively (Allen, Reference Allen2003), were highest in primiparous cows and declined with increasing parity. This finding aligns with previous reports indicating higher bone turnover rates in younger animals (Yamagishi et al., Reference Yamagishi, Takehana, Kim, Miura, Hirata, Devkota, Sato and Furuhama2009; Chiba et al., Reference Chiba, Onomi, Hatate, Moriyama, Goto and Yamagishi2020b; Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022). Furthermore, colostral concentrations of BAP also showed parity-related differences or trends; for example, multiparous cows tended to have lower BAP concentrations compared with second-parity cows. While we have previously reported on the concentrations of bone metabolic markers in bovine colostrum (Hatate et al., Reference Hatate, Kayano, Kawashima, Hanada, Bicalho and Yamagishi2019), to our knowledge, the present study is the first to measure these markers in colostrum across cows with varying parities. These results suggest that colostral secretion of bone formation markers is influenced not only by systemic bone metabolism but also by physiological changes associated with parity.
OPG is a soluble decoy receptor of the receptor activator of nuclear factor-kappa B (RANK) ligand (RANKL) (Simonet et al., Reference Simonet, Lacey, Dunstan, Kelley, Chang, Lüthy, Nguyen, Wooden, Bennett, Boone, Shimamoto, DeRose, Elliott, Colombero, Tan, Trail, Sullivan, Davy, Bucay, Renshaw-Gegg, Hughes, Hill, Pattison, Campbell, Sander, Van, Tarpley, Derby, Lee and Boyle1997). Coupling of RANKL and RANK on the immature osteoclasts induces osteoclastic cell differentiation (Boyle et al., Reference Boyle, Simonet and Lacey2003). OPG thus plays a protective role in bone resorption by blocking the interaction of RANK and RANKL (Theill et al., Reference Theill, Boyle and Penninger2002). We observed a trend towards higher colostral OPG concentrations in the MF cows within this high-risk group. Given that OPG is a well-established inhibitor of osteoclast differentiation and bone resorption (Simonet et al., Reference Simonet, Lacey, Dunstan, Kelley, Chang, Lüthy, Nguyen, Wooden, Bennett, Boone, Shimamoto, DeRose, Elliott, Colombero, Tan, Trail, Sullivan, Davy, Bucay, Renshaw-Gegg, Hughes, Hill, Pattison, Campbell, Sander, Van, Tarpley, Derby, Lee and Boyle1997; Yano et al., Reference Yano, Shibata, Mizuno, Kobayashi, Higashio, Morinaga and Tsuda2001), its elevated levels in colostrum from MF cows are intriguing. While human studies have reported milk OPG levels up to 1000-fold higher than maternal serum, indicating substantial local production by mammary epithelial cells (Vidal et al., Reference Vidal, Van Den Broek, Lorget and Donnet-Hughes2004) the present and our previous studies have found colostral OPG concentrations to be comparable to circulating levels in dairy cows (Hatate et al., Reference Hatate, Kawashima, Hanada, Kayano and Yamagishi2018, Reference Hatate, Kayano, Kawashima, Hanada, Bicalho and Yamagishi2019, Reference Hatate, Kawashima, Kayano, Hanada and Yamagishi2020). This suggests that in cows, unlike humans, colostral OPG may not be exclusively or predominantly derived from local concentration but may also reflect systemic diffusion. This observation could imply that enhanced OPG secretion, whether originating from the mammary gland or as a systemic reflection, paradoxically exacerbates hypocalcaemia by inhibiting the necessary mobilization of Ca from bone. Alternatively, it may represent a compensatory mechanism aimed at limiting further bone resorption that becomes insufficient under conditions of acute Ca demand. The moderate positive correlation between colostral and serum OPG observed in multiparous cows (Table 2) supports the hypothesis that colostral OPG partially reflects the systemic bone metabolic status of the dam. These findings highlight the potential of colostral OPG as a valuable marker for understanding and assessing the bone metabolic status in high-parity cows.
Interestingly, the RANKL signalling pathway is essential not only for bone resorption but also for the development of the lactating mammary gland in mice, thereby facilitating calcium transfer from the maternal skeleton (Fata et al., Reference Fata, Kong, Li, Sasaki, Irie-Sasaki, Moorehead, Elliott, Scully, Voura, Lacey, Boyle, Khokha and Penninger2000). In humans, it has been also reported that serum RANKL and OPG may affect breast volume change during pregnancy by increasing and decreasing, respectively (Wunderle et al., Reference Wunderle, Ruebner, Häberle, Schwenke, Hack, Bayer, Koch, Schwitulla, Schulz-Wendtland, Kozieradzki, Lux, Beckmann, Jud, Penninger, Schneider and Fasching2020). The mammary gland of dairy cows increases in size by the rise in parities, consequently increasing milk production. Although the present study did not show the difference of milk yield during one day post calving between MF and non-MF cows in the P3 group, the involvement of the OPG and RANKL pathway on mammary development may be a subject for further study.
Biological markers of bone resorption, such as sRANKL and NTx, have been identified in human breast milk, with their concentrations reflecting maternal physiological states like exclusive lactation or metabolic conditions (Bouroutzoglou et al., Reference Bouroutzoglou, Malamitsi-Puchner, Boutsikou, Marmarinos, Baka, Boutsikou, Hassiakos, Gourgiotis and Briana2014). To our knowledge, information on the excretion of bone metabolic markers into colostrum is very limited. We speculate that the permeability of the blood-milk barrier (BMB) is key to this process. This is because the BMB becomes leaky during colostrum formation before parturition in cows (Wellnitz and Bruckmaier, Reference Wellnitz and Bruckmaier2020). In cows immediately prior to parturition, tight junctions between mammary epithelial cells become permeable, allowing blood components, such as albumin and immunoglobulins, to diffuse into colostrum, resulting in high concentrations of important immune and growth factors. This common mechanism could explain the presence of multiple systemic bone markers in colostrum.
In the present study, the correlation analysis elucidated further interrelationships among the measured parameters (Table 2). NTx is, in general, a bone metabolic marker of bone collagen degradation in blood and urine (Allen, Reference Allen2003). The positive moderate correlation between colostral and serum NTx suggests that colostral NTx is primarily derived from systemic diffusion across the BMB. However, the correlation was not perfect, indicating that systemic concentration is not the sole determinant of the colostral concentration. The limited correlation may be explained by the high individual variability in the BMB permeability immediately post-calving, or that NTx undergoes partial degradation or is influenced by variable dilution or concentration dynamics as it traverses the mammary tissue. Colostral NTx and colostral OPG were positively correlated in both the overall population (moderate correlation) and within multiparous cows (good correlation), suggesting that these markers are co-secreted into colostrum or regulated by similar physiological factors. Additionally, the negative correlation between colostral BAP and colostral TRAP5b in multiparous cows may reflect an inverse relationship between markers of bone formation and resorption within mammary secretions in this group. Our previous study in calves (Hatate et al., Reference Hatate, Kayano, Kawashima, Hanada, Bicalho and Yamagishi2019) suggested that colostral OPG absorption might not significantly impact circulating levels in the neonate compared to other bone markers. This might suggest that the presence of these factors in colostrum implies a significant local regulation in the dam.
Several limitations should be considered when interpreting the results of this study. The sample size, particularly the number of MF cases, was relatively small, which may have limited the statistical power to detect significant differences or correlations for some markers. Additionally, data were collected at a single time point on the day of calving. Longitudinal sampling before and after parturition would provide a more comprehensive understanding of the dynamic changes in bone metabolic markers during the periparturient period. This study was conducted on a single farm, which may limit the generalizability of the findings to other management systems or dairy cow populations. Future studies with larger sample sizes and serial sampling at multiple time points around parturition are warranted to confirm these findings and elucidate the temporal dynamics of bone metabolic marker concentrations. Further research is also needed to clarify the biological roles of bone metabolic markers in bovine colostrum, particularly their potential involvement in both maternal Ca homeostasis and neonatal bone development and immune function.
Since colostrum is known to accumulate in the mammary gland a few days before calving (Megahed et al., Reference Megahed, Hiew, El Badawy and Constable2018), measuring colostral OPG concentrations prepartum may offer a practical approach for assessing the preparturient bone metabolic status of multiparous dairy cows susceptible to MF. Conversely, it has been reported that the MF cows had lower circulating ALP3 concentrations during the 3-week prepartum period (Starič and Hodnik, Reference Starič and Hondnik2021; Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022), suggesting that osteoblastic activity was probably decreased in those cows (Yamagishi and Kawashima, Reference Yamagishi and Kawashima2022). Therefore, further investigation of the specific mechanisms by which colostral OPG and serum ALP3 before parturition are associated with MF incidence could inform the development of novel prediction and preventive strategies for this important metabolic disorder.
Conclusions
This study demonstrated that the concentrations of bone metabolic markers in both serum and colostrum of dairy cows are influenced by parity. In particular, colostral OPG concentration in parturient cows with three or more parities showed potential as a useful indicator for reflecting the bone metabolic status of cows with and without MF. These findings suggest that evaluations of colostral bone metabolic markers can contribute to an enhanced understanding of periparturient hypocalcaemia and support improved management and prevention strategies in dairy herds.
Acknowledgements
The authors thank Dr. K. Hatate, Ms. R. Onomi and all staffs of the University Farm and Veterinary Medical Center of OUAV for their support. Funding for this study was provided, in part, by a JSPS Grants-in-Aid for Scientific Research (18K05988).
