Janko Mrkun

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.

Superoxide Dismutase: A Predicting Factor for Boar Semen Characteristics for Short-Term Preservation

Superoxide dismutase (SOD), total antioxidant capacity (TAC), and thiobarbituric acid reactive substances (TBARS) in seminal plasma were evaluated on the basis of receiver operating characteristics (ROC) analysis as predictors for distinguishing satisfactory from unsatisfactory boar semen samples after storage. SOD on day 0 correlated significantly with progressive motility (r = −0.686; P < 0.05) and viability (r = −0.513; P < 0.05) after storage; TBARS correlated only with motility (r = −0.480; P < 0.05). Semen samples that, after 3 days of storage, fulfilled all criteria for semen characteristics (viability > 85%, motility > 70%, progressive motility > 25%, and normal morphology > 50%) had significantly lower SOD levels on the day 0 than those with at least one criterion not fulfilled (P < 0.05) following storage. SOD levels of less than 1.05 U/mL predicted with 87.5% accuracy that fresh semen will suit the requirements for satisfactory semen characteristics after storage, while semen with SOD levels higher than 1.05 U/mL will not fulfill with 100% accuracy at least one semen characteristic after storage. These results support the proposal that SOD in fresh boar semen can be used as a predictor of semen quality after storage.

VALUE OF SEMEN PARAMETERS, WITH SPECIAL REFERENCE TO TNF-α, IN PREDICTING THE QUALITY OF BOAR SEMEN AFTER SHORT-TERM STORAGE

The aim of this study was to address the question whether changes in boar semen quality after short-term storage could be predicted on the basis of standard semen parameters and TNF-α level determined on the day of semen collection under commercial conditions. Progressive motility showed the highest positive correlation with morphology on day 0 of collection, and progressive motility on day 3 (P < 0.05) showed a negative correlation with acrosome abnormalities (P < 0.05). According to the area under receiver operating characteristics (ROC) curves (AUCs), progressive motility could also be used in predicting semen quality after 3 days of storage (AUC > 0.5; P < 0.05). TNF-α in seminal plasma is the only parameter measured on day 0 to show a significant correlation with the percentage of viable spermatozoa after 3 days of semen storage (r = 0.495, P < 0.05). ROC analysis shows that TNF-α level is helpful in discriminating viability outcome after semen storage (AUC = 0.94, P < 0.001). We can predict with 92.35% certainty that fresh semen samples with more than 150 pg/ml of TNF-α in the seminal plasma will retain more than 85% of viable spermatozoa after 3 days of storage. Thus, TNF-α can contribute to predicting the quality of short-term stored semen.

Impact of negative energy balance on production and fertility in Slovenian brown-breed dairy cows.

The aim of this study was to investigate the production andreproduction ability of Slovenian brown-breed dairy cows according totheir exposure to negative energy balance (NEB). Body condition score(BCS), concentrations of metabolites such as non esterified fatty acids(NEFA), beta hydroxy butyrate (BHB), cholesterol and urea weremeasured on day 14 postpartum and progesterone profile wasdetermined for each animal. The postpartum period was closelymonitored from day 14 to conception by ultrasound examination in 10day intervals. Reproductive parameters were followed up, also. CowsweredividedintwogroupsaccordingtoNEFAandBHBconcentrationswith a threshold of 0.5 and 1.4 mmol/L, respectively. Cows withelevated NEFA and BHB levels (Group 2) in comparison to Group 1expressed a higher decrease in BCS 30 days postpartum (0.64 vs 0.33point; P<0.01), more abnormal progesteron patterns (P<0.001) andhad a significantly longer interval to first progesteron rise (49.54 vs33.82 days; P<0.05). Milk protein concentrations 30 days postpartumwere significantly lower in Group 2 comparing to Group 1 (3.08 % vs3.36 %, P<0.001) and protein ratio (FPR) 30 days postpartum wassignificantly higher in Group 2 (1.37 vs 1.21; P<0.05) comparing toGroup 1. Measurement of NEFA and BHB concentrations, bodycondition scoring and milk data recording are found to be good criteriafortherecognitionofNEBindairycowsintheearlypostpartumperiod.Key words: dairy cows, negative energy balance, body conditionscore, reproduction

Improvement of liquid stored boar semen quality by removing low molecular weight proteins and supplementation with α-tocopherol

Seminal plasma contains low-molecular weight components that can exert a harmful effect on sperm function. We have evaluated the effects of removing low-molecular weight components from seminal plasma and adding α-tocopherol on boar semen quality after 72h of liquid storage. Semen was evaluated on the basis of motility, morphology, acrosome integrity, plasma membrane modifications, mitochondrial activity, DNA fragmentation and lipid peroxidation. Thiobarbituric acid reactive substances (TBARS), 8-isoprostane, and antioxidant status (total antioxidant capacity (TAC) and superoxide dismutase activity (SOD)) were measured in seminal plasma. Removal of low-molecular weight components from seminal plasma, together with the addition of α-tocopherol, kept the lipid peroxidation and mitochondrial activity and DNA fragmentation at the same level as in native semen samples. Dialysing semen and adding 200μM of α-tocopherol led to higher progressive motility, a higher proportion of morphologically normal spermatozoa and a significantly lower level of acrosomal reacted spermatozoa compared to non-dialyzed semen samples after 72h of storage. In conclusion, liquid stored boar semen was better preserved, and oxidative stress in the semen was reduced when semen was dialyzed and α-tocopherol was added prior to storage.

Dynamics of metabolic and oxidative stress parameters in dairy heifers during transition period

Dairy cows in early postpartum period experience a rapid increase in milk yield, whereas animal feed consumption ability rises slowly and can not follow increased needs for nutrients (Eicher, 2004). Therefore dairy cows enter a period of negative energy balance (NEB) and metabolic stress. NEB is associated with the change in body condition score (BCS) and the rise of some metabolites such as non-esterified fatty acids (NEFA) and beta- hydroxybutyrate (BHB) (Lassen and Fettman, 2004). Intensified energy metabolism during periparturient period is accompanied by enlarged rates of reactive oxygen species (ROS) production and may results in oxidative stress. Calving causes significant, but temporary, changes in the antioxidant system of cows’ blood (Gaal et al., 2006). Total antioxidant status (TAS) is a single measure that may effectively describe the dynamic equilibrium between pro-oxidants and antioxidant in plasma compartment (Ghiselli et al., 2000). Paroxonase-1 (PON1) is recognized as an important part of the mammalian natural anti-oxidative system (Mackness et al., 1991; Turk et al., 2008).

Comparison of IGF-1 (insulin like growth factor-1) levels in bovine serum sampled three times during the day using validated equine IGF-1 ELISA.

Cows in negative energy balance exhibit reduced fertility, mediated by metabolic signals that influence the reproductive system. Measurement of IGF-1 contributes to the diagnosis of negative energy balance. The aim of this study was to investigate possible variations in IGF-1 levels in samples taken at different times of the day. Equine IGF-1 ELISA was used for measuring IGF-1 in bovine samples. Statistical analysis was applied to the results. Using scatter diagrams fitted with Deming regression lines, we established that paired measurements on samples obtained at different times were close to the line of equality. 90% of the absolute differences were less than the reproducibility coefficient, confirming that the level of agreement between the IGF-1 levels at different times of the day was satisfactory. IGF-1 levels in bovine samples were independent of the time of day at which samples were taken.