• arterie arciformi renali
• asini
• cavalli
• donkeys
• Doppler
• ecografia
• horses
• indice di resistività
• renal arcuate arteries
• resistivity index
• ultrasonography

Introduction. The renal resistive index (RI) is the ratio of the difference between maximum and minimum (end diastolic) flow velocity derived from the Doppler spectrum of intra-renal (segmental/interlobar) arteries. The Doppler RI was evaluated as a useful parameter for quantifying the alterations in renal blood flow that may occur with renal disease. To our knowledge, only one report is available about the values of renal RI in not sedated horses. Aim. The aims of this study were to assess the RI by Doppler ultrasonography in horses and donkeys in order to establish a normal reference range and to analyze the differences related to age and breed.
Material and methods. Thirty-three conscious healthy horses and nine donkeys were included. Arcuate arteries were scanned by pulsed Doppler ultrasonography. The peak-systolic and end-diastolic velocities of arcuate arteries were measured for calculating the RI. Data were evaluated for normality by the Kruskal-Wallis test. Data were expressed as median and standard error. The left vs right RI from the whole study population has been compared using the MannWithney test. Data have been then divided in two subgroups based on age (young/adult vs old) and based on breed (Standardbred vs other). The Mann Whitney test has been applied in order to evaluate possible differences between the subgroups. Finally, the Spearman test and the linear regression have been performed in order to correlate the RI of the left and right kidney with the weight and BCS of the animals included. The statistical analysis has been performed by a commercial software (GraphPad Prism, La Jolla, USA). Results have been considered significant for P<0,05. Results. A statistically significant difference has been found between the left vs right RI values for horses (left 0.51± 0.01 vs. right 0.58±0.01) but not for donkeys. There were no differences between left vs right RI for the age and breed subgroups. No correlation has been found between weight and RI for both kidneys, while a negative correlation has been found between BCS vs right kidney RI in horses. No correlation was found for RI of the left kidney and BCS.
Discussion and conclusions. The Doppler ultrasonography of the equids kidney was slightly difficult to perform in some subjects. Results concerning the left vs right RI were in line with literature about horses, but not with studies in small animals which found no differences between left and right RI. It was not possible to compare data concerning donkeys because to the authors’ knowledge, this is the first study on donkeys. Correlation between kidneys RI vs weight, but not vs BCS has been evaluated in small animals. Our results are in line with literature. In conclusion, despite the needed of some experience in performing the Doppler ultrasonography of the renal arcuate arteries, the use of this technique could be considered feasible in equids. The renal RI might be useful for the investigation of kidney blood flow alterations. Further studies are needed to better understand Doppler kidney ultrasonography in donkeys.