Evaluation of portal blood flow using transcutaneous and intraoperative Doppler ultrasonography in dairy cows with fatty liver

The objective of the study was to investigate portal blood flow (PBF) in dairy cows with fatty liver by means of Doppler ultrasonography. Eighty lactating German Holstein cows less than 100 d in milk were used (mean ± standard error of the mean; body weight: 583±9kg, age: 5±0.2 yr, withers height: 145.4±0.5cm, milk yield: 9±0.6kg). All cows had left abomasal displacement and underwent omentopexy via right flank laparotomy. The size of the liver and the thickness over the portal vein were determined ultrasonographically. Doppler ultrasonographic examinations of PBF were carried out transcutaneously and intraoperatively directly via liver surface. The PBF velocities [peak maximum (vₘₐₓ), peak minimum (vₘᵢₙ), and mean maximum (vₘₑₐₙ) velocity] were recorded. Venous pulsatility index (VPI) was calculated. Because transcutaneous Doppler ultrasonography revealed images of very poor quality in 58 of the 80 cows, only data obtained intraoperatively were presented. Liver biopsies were used for hepatic triacylglycerol (TAG) determination and histological examination. Based on histopathologic and ultrasonographic examinations, none of the cows suffered from hepatic disorders other than hepatic lipidosis. Hepatic TAG content ranged from 5 to 292mg/g of liver fresh weight (FW). Cows were allocated to 1 of 4 groups according to their hepatic TAG content (very severe: TAG >150mg/g of FW, n=27; severe: >100–150mg/g of FW, n=18; moderate: ≥50–100mg/g of FW, n=19; mild: <50mg/g of FW, n=16). The VPI decreased with increasing TAG content (r=−0.55). The VPI did not differ between cows with severe and very severe fatty liver but it differed between cows of these 2 groups and cows with mild and moderate fatty liver. Velocities of PBF (vₘₑₐₙ, vₘᵢₙ, vₘₐₓ) correlated negatively with hepatic TAG content (r=−0.26 to −0.37). Mean PBF velocity of the cows with very severe fatty liver differed from cows with severe, moderate, and mild fatty liver. Variables of PBF were inversely related to hepatic size and thickness (r=−0.06 to −0.35). In conclusion, the lower VPI and PBF velocities in cows with fatty liver and the negative correlations with the degree of hepatosteatosis may be explained by a reduction of vascular compliance in the liver because of fatty infiltration. These changes, which are believed to result from parenchymal swelling, were particularly pronounced when hepatic TAG content exceeded 150mg/g FW.