Variability of mammary blood flow in lactating Holstein-Friesian cows during the first twelve weeks of lactation

The goals of the present study were to measure mammary blood flow volume (BFV) during the first 12 wk of lactation in dairy cows by using color Doppler sonography and to determine what affects the mammary blood flow. Forty cows were examined via color Doppler sonography on d 1, 7, 14, 28, 56, and 84 after parturition (d 0). The total BFV (BFVtotal) to the 4 mammary glands was calculated by measuring time-averaged maximum velocities (TAMV) and cross-sectional areas (A) of the left and right pudendoepigastric trunks via transrectal color Doppler sonography. Because there were no significant differences in A, TAMV, and BFV between the right and left pudendoepigastric trunks, the means of A and TAMV, and the BFVtotal of both trunks were used for calculations. The intraindividual and interindividual variability of repeated BFV measures quantified by intraclass correlation coefficients were 96 and 98%, respectively. The BFVtotal ranged from 19.9 to 27.9 L/min, with a mean of 22.3 4.9 L/min. Interindividual differences in BFV values were attributable to variations in A and TAMV. The interindividual variability of the BFVtotal, which was determined using the coefficients of variation of the BFVtotal on individual days, ranged from 16 to 28%. All the cows had similar changes in the BFVtotal during the study. Changes in BFVtotal were not correlated with changes in the mean of A, but there was a good correlation between changes in BFVtotal and in the mean of TAMV (r = 0.94). The BFVtotal was highest on d 1 of lactation, decreased 28% by d 7, and remained at this level until d 28. By d 56, the BFVtotal had increased by 15% compared with d 14 and by 10% compared with d 28. The BFVtotal on d 84 was significantly different from all other days except d 56. There were moderate correlations between daily milk yield and BFV on individual days (0.24 < r < 0.35). In conclusion, Doppler sonography is a reliable method for determining blood flow in the pudendoepigastric trunk of cows. There is great variability in mammary blood flow among cows and in BFV