Although glomerular filtration rate (GFR) is a most acceptable index for kidney function assessment in humans, there are methodological difficulties with its application in bovine practice. For example, the classic urinary inulin clearance corresponding to GFR is labor intensive and time consuming because it requires accurately timed blood and urine collection. Therefore, only a few studies have reported bovine GFR measurements to date. The objctive of the present study was to establish the simplified procedure to estimate GFR in cattle using the isotonic non-ionic dimeric contrast medium iodixanol as a test tracer. Iodixanol is rapidly excreted into urine without metabolic degradation, and no or a very little protein binding with very short half-life.In chapter 1, the study was designed to develop a single-blood-sample method for estimating the GFR in Holstein dairy cattle. First, iodixanol and the standard GFR tracer inulin were coadministered as a bolus intravenous injection to clinically healthy cattle at 10 mg I/kg and 30 mg/kg, respectively, followed by blood collection for multisample strategies. The GFR values estimated by iodixanol were well consistent with those by inulin. Neither effect of body weight gain, age, nor parity on the GFR estimates was noted with the protocol used. No difference was observed between the GFR values obtained from non-lactating and lactating cattle. Jacobsson’s formula for calculating the GFR in the single-blood-sample method was derived from the injected dose, sampling time, serum concentration, and estimated volume of distribution based on the data from the multisample method in clinically healthy cattle and cattle with reduced renal function. The GFR values estimated by the single-blood-sample-method were correlated with those calculated by the multisample method. These results demonstrate that the single-blood-sample method using iodixanol (Holstein equation) can apply as a screening for the GFR estimates in dairy cattle.In chapter 2, the study was carried out to clarify whether Holstein equation based on the single-blood-sample-method in Holstein dairy cattle as described in chapter 1 can apply to the GFR estimates for Japanese Black cattle (beef cattle). Iodixanol and inulin were coadministered intravenously to identical cattle at doses of 10 mg I/kg and 30 mg/kg, respectively, and the GFR was determined by the conventional multisample method. The GFR values from iodixanol were consistent with those from inulin, and no effect of body weight, age, or parity on GFR estimates was noted. Using clinically healthy cattle and those with reduced renal function, the GFR values estimated from Holstein equation were in good agreement with those by the multisample method using iodixanol. The results indicate that Holstein equation can be used for the GFR estimate of beef cattle in the same dose regimen as Holstein dairy cattle, and provides a practical and ethical alternative.In chapter 3, a newly integrated formula, which can apply to both dairy and beef cattle, was developed. Using clinically healthy dairy and beef cattle and cattle with reduced renal function, the GFR values estimated from the integrated formula were compatible with those calculated by the multisample method. The basal reference GFR values were also equal among the three procedures; namely, the integrated formula, Holstein equation, and the multisample method. The results suggest that the integrated formula based on Jacobsson’s formula using iodixanol can be used for the GFR estimates in cattle of either strain.In conclusion, the validity for the application of Jacobsson’s formula to estimate the bovine GFR was proven, and the integrated formula would be used extensively as an alternative tool in a clinically relevant situation.