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Substantial changes occur in skeletal metabolism during lactation. These dynamic changes are monitored with biochemical bone markers. The goal of the present study was to follow these changes in lactating cows and to investigate whether cows with a higher milk yield have a higher mobilization rate of calcium from bone. Hydroxyproline, deoxypyridinoline, pyridinoline, and the carboxyterminal telopeptide of type I collagen (ICTP) were chosen as markers for bone resorption, whereas osteocalcin was used as a bone formation marker. Urine and blood samples were collected from cows with a mean standard milk yield of 4900 and 6500 kg, respectively, 14 d before, and 14 d, 1 mo, 1.5 mo, and monthly after parturition. Urinary hydroxyproline, deoxypyridinoline, and pyridinoline concentrations increased with time, but no differences between the two groups were evident. Concentrations of 1,25-dihydroxy vitamin D and ICTP of the two groups showed an increase 14 d after parturition. Furthermore, using multivariate regression models with age and milk yield as covariates, ICTP concentrations were higher in the group with a higher milk yield. In contrast, osteocalcin concentrations decreased 14 d after parturition and returned to prepartum values 1 mo after parturition. The increase of ICTP concentrations in both groups indicates that bone was substantially resorbed. At the same time, probably less Ca was embedded in bone, as indicated by the decrease of the osteocalcin concentrations. In conclusion, cows showed increased bone resorption around parturition, and cows with higher milk yield mobilize calcium more actively from bone than cows with lower milk yield.

This study investigated whether hydroxyproline, deoxypyridinoline, or the carboxyterminal telopeptide of type I collagen could be used as markers to provide evidence of bone resorption during hypocalcemia of dairy cows. Serum concentrations of the amino-terminal propeptide of type III procollagen were also analyzed to study the effect of parturition on type III collagen, which is a component of soft connective tissues. Urine and blood samples were collected on d 1 to 5, on d 9, and d 14 after parturition from 18 cows with symptoms of periparturient paresis (group 1) and 19 healthy control cows without symptoms (group 2). Urine concentrations of hydroxyproline and deoxypyridinoline were measured with a colorimetric assay and an enzyme immunoassay, respectively. Serum concentrations of the amino-terminal propeptide of type III procollagen were measured using a commercially available radioimmunoassay. A radioimmunoassay was developed to analyze serum concentrations of the carboxyterminal telopeptide of bovine type I collagen. The mean corrected urinary hydroxyproline concentrations in group 1 increased from parturition to d 14; concentrations in group 1 were significantly higher for group 2 after d 5. Mean corrected deoxypyridinoline concentrations in urine increased after parturition to reach a peak at d 9, and serum concentrations of the carboxyterminal telopeptide of type I collagen peaked at d 5. However, mean concentrations of deoxypyridinoline and the carboxyterminal telopeptide of type I collagen did not differ significantly between groups. The variation in the behavior of the three markers is likely a reflection of the different phases and aspects of the bone collagen degradation. In conclusion, assays for urinary deoxypyridinoline and serum carboxyterminal telopeptide of type I collagen determinations are useful tools to follow the course of degradation of bone collagen in dairy cows.

Summary Abomasa from 912 randomly selected cows were examined; specimens were obtained at the local slaughter house on 35 days spread over one year. Abomasal lesions were assessed macroscopically and histologically. Additionally, haematological and blood chemistry (urea, aspartate aminotransferase, potassium, chloride, calcium) evaluations and the determination of rumen chloride concentration were performed. Of the 912 abomasa examined, 187 (20.5 %) had ulcerative lesions of the mucosa. Lesions were classified from 1 to 4 based on severity as described by Whitlock (1980). All ulcers were classified as type 1 (erosions and non‐perforating ulcers); thus, further division into four subtypes 1 a, 1 b, 1 c and 1 d was carried out. Fifty‐six abomasa had minimal mucosal defects which were classified as type 1 a. Deeper erosions combined with local hemorrhage, classified as type 1 b, were observed in 54 abomasa. Type 1 c were crater‐like ulcers and were seen in 61 abomasa. Sixteen abomasa had type 1 d ulcers which included two forms: ulcers with radial wrinkles converging on a central point, and ulcers with perforated folds. Types 1 a and 1 c occurred mainly in the pyloric region, and types 1 b and 1 d were observed mainly in the fundic region. Type 1 abomasal ulcus could not be diagnosed based on alterations in haematological or blood and rumen chemistry values.

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