The Effect of Seasonal Thermal Stress on Lipid Mobilisation, Antioxidant Status and Reproductive Performance in Dairy Cows.

Heat stress is a major factor contributing to low fertility of dairy cows with a great economic impact in dairy industry. Heat-stressed dairy cows usually have reduced nutrient intake, resulting in a higher degree of negative energy balance (NEB). The aim of this study was to investigate the seasonal thermal effect on lipid metabolism, antioxidant activity and reproductive performance in dairy cows. Thirty-two healthy dairy heifers were included in the study. According to the ambient temperature, animals were divided into two groups: winter (N = 14) and summer season (N = 18). Metabolic parameters, paraoxonase-1 (PON1) activity and total antioxidant status (TAS) were monitored at the time of insemination (basal values) and from 1 week before until 8 weeks after calving. Number of services per conception and calving-to-conception (CC) interval were calculated from the farm recording data. Serum triglyceride, non-esterified fatty acids (NEFA) and beta-hydroxybutyrate (BHB) concentrations were significantly increased after calving in summer compared to winter, indicating higher degree of NEB in cows during summer. PON1 activity was significantly decreased after calving in both summer and winter group. TAS concentration was significantly lower in summer than that in winter. A significantly higher number of services were needed for conception in summer compared to winter, and CC interval was significantly longer in summer than that in winter as well. Additionally, reproductive performance significantly correlated with the severity of NEB, suggesting that lipid mobilization and lower antioxidant status contributed to poor reproduction ability in dairy cows during hot months.

Lipid mobilisation and oxidative stress as metabolic adaptation processes in dairy heifers during transition period.

The objective of this study was to evaluate metabolic disorders and oxidative stress in dairy heifers during the transition period. Possible relationships between lipid mobilisation indicators and oxidative stress markers were investigated as well. Nineteen dairy heifers were included in the study. Blood samples were collected at the time of estrus synchronisation in heifers, at insemination, three weeks after insemination, one week before calving, at calving and 1, 2, 4 and 8 weeks postpartum. Common metabolic parameters, beta-hydroxybutyrate (BHB), free fatty acids (FFA), paraoxonase-1 (PON1) activity and total antioxidative status (TAS) were analysed. Around insemination, no significant difference was observed in the majority of tested parameters (P>0.05). However, the transition period markedly affected the concentration of triglycerides, total cholesterol, HDL-C, BHB, FFA, TAS and PON1activity. Positive correlations between PON1 activity and total cholesterol, HDL-C and triglycerides were noted but inverse correlations with FFA, BHB and bilirubin were found indicating that PON1 activity changed with lipid metabolism and was influenced by negative energy balance. These findings suggest that lipid mobilisation and oxidative stress are part of a complex metabolic adaptation to low energy balance which reaches equilibrium later in advanced lactation.

[Biologic variation in electrolytes and essential microelements in the blood of neonates and their mothers]. / Bioloska varijacija elektrolita i esencijalnih mikroelemenata u serumu zdrave novorodencadi i njihovih majki.

Serum concentration and biological variability (CVB%) of total calcium (Ca) magnesium (Mg), iron (Fe), zinc (Zn) and copper (Cu) were determined in 22 sera of maternal and umbilical cord blood in normal pregnancies. The concentrations of Ca (2.48 +/- 0.13 vs 2.27 +/- 0.13 mmol/l), Mg (0.84 +/- 0.06 vs 0.80 +/- 0.07 mmol/l), Fe (24.1 +/- 6.62 vs 10.7 +/- 4.94 mumol/l) and Zn (14.1 +/- 1.78 vs 9.1 +/- 2.21 mumol/l) in the cord sera were significantly higher than in maternal sera (p < 0.01), whereas maternal copper concentrations (36.6 +/- 4.82 vs 9.2 +/- 2.21 mumol/l), were significantly higher than in cord sera (p < 0.01). Biological variability of Ca (5.37 vs 4.84%), Mg (8.39 vs 6.69%), Fe (46.1 vs 27.3%) and Zn (24.1 vs 12.3%) values was higher in the maternal sera than the respective values in the cord sera, while the biological variability of copper in the cord sera was significantly higher than the respective value in the maternal sera (26.7 vs 12.8%). These results are in agreement with those previously reported and suggest that fetal homeostasis of Ca, Mg, Fe and Zn is at least partly independent of maternal factors.