Because the role of bone turnover during early to peak lactation in dairy cows is unclear, plasma levels of osteoclast- or collagen-specific bone resorption and osteoblast-specific bone formation markers from postpartum week 3 (W+3) to W+7 were compared with prepartum W-3 levels in multiparous (n=15) and primiparous (n=13) Holstein cows. The multiparous group showed a consistently low level of osteoclast-specific bone resorption markers, while collagen-specific resorption and osteoblast-specific formation markers decreased at postpartum W+7 and from W+5, respectively. In the primiparous group, the plasma levels of all three markers decreased from postpartum W+3. These results suggest that the calcium demand during the transition from early to peak lactation in dairy cows is less affected by bone turnover.
To evaluate diurnal variation of plasma bone markers, blood samples were collected from five calves at 2-hr intervals throughout a 24-hr period. Tartrate-resistant acid phosphatase isoform 5b (TRAP5b), carboxy-terminal collagen crosslinks of type-I collagen (CTX), hydroxyproline, bone specific alkaline phosphatase (BALP) and osteocalcin were measured. Cosinor analysis showed a significant rhythm in all bone markers. The acrophase of each bone marker appeared from the early to late morning. The percentage ratio of the amplitude to mesor and the within-subject variability for CTx and osteocalcin were significantly larger than those for TRAP5b and BALP. This marked diurnal variation in five bone markers suggested that the time of blood sampling should be fixed when studying bone marker concentrations in bovine plasma.
The antioxidant effect of N, N-dimethylglycine (DMG) on in vitro-produced (IVP) bovine embryos was examined. After in vitro fertilization, presumptive zygotes were cultured with or without 0.1 μM DMG under different oxygen tensions. The percentage of embryos developing to the blastocyst stage was lowest under a 20% oxygen concentration without DMG, and it was significantly increased (P < 0.05) by applying a 5% oxygen concentration. Under the 20% oxygen concentration, supplementation of the medium with DMG significantly improved blastocyst development, which was nearly equal to that achieved under 5% oxygen without DMG. Furthermore, a tendentious increase (P = 0.06) in blastocyst cell numbers was observed when DMG was applied. In the second experiment, addition of H2O2 (0.5 mM) to the culture medium significantly (P < 0.01) reduced the percentage of embryos developing to the blastocyst stage. However, DMG supplementation prevented this reduction. In conclusion, DMG enhanced the invitro development of IVP bovine embryos by acting as an antioxidant.
The responses of 64 Holstein cows with milk fever to first treatment with 500 ml of either of 2 intravenous calcium (Ca) solutions, one containing Ca alone (group A, n = 32) or 1 containing Ca, phosphate and magnesium (group B, n = 32), were evaluated by selected clinical signs and serum biochemical data. Based on the cow's ability to stand, treatment response was categorized into "immediate response" (stood after single treatment), "delayed response" (stood after repeated treatments) and "non-response" (slaughtered despite repeated treatments). No significant differences among the response categories were found between the two groups, suggesting that the solution containing Ca borogluconate alone was sufficient for the first treatment of milk fever.
