A comparison of the concentrations of energy-balance-related variables in jugular and mammary vein blood of dairy cows with different milk yield.

The aim of this study was to compare the concentrations of blood variables obtained simultaneously from the jugular and mammary veins of dairy cows. Eighty Holstein cows were divided into four equal groups: dry, low- (LY), medium- (MY) and high-yielding (HY). Blood insulin, glucose, non-esterified fatty acid (NEFA), beta-hydroxybutyrate (BHBA) and urea concentrations were measured. The jugular and mammary vein (J/M) ratio between concentrations of each variable was calculated. Differences between the groups of cows in concentrations of variables in the jugular vein were not in accordance with those obtained for the mammary vein. J/M values for insulin and glucose concentrations were above 1.0 in all groups of cows. The ratios for NEFA and BHBA concentrations were under or equal to 1.0 in dry and LY cows but above 1.0 in the MY and HY groups, indicating that in MY and HY cows those metabolites are apparently utilised by the mammary gland. J/M values for urea were above 1.0 in dry and LY cows but less than 1.0 in groups MY and HY, indicating that in the latter case urea is apparently released by the mammary gland. In conclusion, J/M for NEFA, BHBA and urea may be useful for estimation of the critical point when the mammary gland receives insufficient energy precursors for its current activity.

Effects of feeding buffering mineral mixture on subacute rumen acidosis and some production traits in dairy cows.

This trial was designed in order to evaluate the incidence of subacute rumen acidosis (SARA) during early lactation and to investigate the possibilities for its prevention by use of a buffering mineral mixture. On the beginning of the trial it was found that the pH value of rumen fluid in 4 animals was lower than normal (pH < 6.0) and that 20% of animals have had SARA. The control and the experimental group of cows were fed the same meal with exception of concentrated feed which in the experimental group contained the mineral mix with buffering activity in amount of 1%. Continuous addition of buffering mineral mixture in the amount of 1% in concentrated feed for early lactation cows successfully prevents SARA formation and leads to increased milk production, as well as increased milk fat and protein content.

Thyroid Hormones Concentrations during the Mid-Dry Period: An Early Indicator of Fatty Liver in Holstein-Friesian Dairy Cows.

Relationship between postpartal fatty liver and thyroid gland activity during the peripartal and mid dry periods was studied. Twenty one dry cows were chosen. Blood samples were obtained on days -30, -2, and +12 related to calving and analized for thyroxine (T(4)) and triiodothyronine (T(3)). A T(3)/T(4) ratio was calculated. Liver tissue samples were taken 12 d after calving and tested for the lipid content. Cows were divided into three groups: mild (<20% fat), moderate (20 to 30%), or severe fatty liver (>30%). Cows, that were affected with severe fatty liver, were hypothyroid prior to development of the condition due to lower T(4) concentrations, and had significantly lower concentration of T(3) and higher T(3)/T(4) ratios than cows with mild and moderate fatty liver. Thus, hypothyroid state during mid-dry period may be an early indicator of postpartal fatty liver and may provoke T(3)/T(4) ratio increase in this group of cows.