Measurement of BSP clearence T ½ is useful in evaluating liver excretory function in adult cattle
6. In the present study, clearence of BSP was prolonged from 1 st wk before calving to 1st wk post partum cows at 1st wk compared to that in animals at other time-point. The increase in half-time and retention of BSP and decrease in fractional clearence before calving suggested that LBF changes were occuring in the liver during peripartum period. Reid and collins
7 reported that the ultrastructural changes in postpaturient cows particularly the decrease in the volume of rough endoplasmic reticulum and mitochondrial damage, have functional consequences and could account for alterations in the pattern of BSP excretion and in blood chemistry in periparturient cows. In the study, the marked infiltration during periparturient period was similar to results of this study and a previous study performed by Collins et al
2. Furthermore, the serum and liver TG accumulation levels were higher in the study. According to Sevinc et al
13, the accumulation of fat in liver cells and development of fatty liver are caused by reduced synthesis of VLDL (very low density lipoprotein).
The results of this study were in agreement with previous studies indicating that activities of liver enzymes are sensitive indicators of liver damage in cattle 14,15. Changes in blood concentrations of GLU, TB, TP and AST enzyme activity may all reflect alterations in liver function associated with fat accumulation 15. The AST activity was high 8 of 12 (66%) in cows around parturition in this study, while the highest level was observed on day calving and at 1st wk after parturition. The enzyme is not, however, exclusively a liver enzyme, can come from muscle, as well as from liver, so it is not liver-specific 4. It is possible that the rise in AST activity in plasma around parturition was attri-butable to liver and muscle damage as evidenced by increase in CK aktivities at this time as well as observed in our study. The SDH and GGT values were high in only 4 (30%) of 12 cattle in periparturient period. SDH is a liver specific enzyme in the cattle, but it is not an extremely sensitive test because of serum half-life time is very short. GGT is a fairly sensitive and specific indicator of cholestasis or liver damage 7.
Our results showed that, as parturition approached, the serum glucose concentration decreased exponently, probably reflecting the increasing demands of the fetus and the mammary gland for glucose. Back out of the parturition (at wk 1 prior to calving and on day calving), plasma glucose concentration increased sharply. Herdt 9 claims that this condition is associated with possibly reflecting hormonal changes at calving that promote gluconeogenesis and glycogenolysis. The result of the study is similar to the previous studies 16-18 which declared during the 1 st wk of lactation, plasma glucose concentration decreased 25%, but by the 2nd wk in action, started to increase exponentially. The same authors claim that the increase may reflect the recovery of feed intake and improving energy status of the cow and higher than those observed in previous studies.
The low urea concentration in cows after calving in this study could be a reflection of the reduced anabolism of proteins due to fatty infiltration 7. Slightly higher serum bilirubin concentration in the study was determined especially within 2 wk after parturition. Although serum bilirubin level is neither a specific nor a sensitive test for hepatic disease 14, high concentration of bilirubin may compete with BSP for excretion, but there was not an appereant correlation between results of BSP clearence test and bilirubin concentrations in the present study.
As regards to all of the data, subclinical liver damage occurs well at 1 wk before calving and reached peak at 1 wk after parturition, then slowly fallens back to normal. None of the results of the common tests for liver damage or function were clinically usefull when used alone for detection hepatic disease 2,14, the BSP clearence test associated with the other variables studied in the trial give us important data about liver damage in cattle within periparturient period. Despite therapy is not completely effective in the period, early diagnosing may make prevent possible.