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Journal of Dairy Science Vol. 73 No. 2 325-332
© 1990 by American Dairy Science Association ®
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Effects of Feed Intake and Thermal Stress on Mammary Blood Flow and Other Physiological Measurements in Lactating Dairy Cows

D. S. Lough 1, D. L. Beede 1, and C. J. Wilcox 1

1 Dairy Science Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611-0701

Six midlactation Holstein cows were exposed to treatments of thermal comfort environments with ad libitum or restricted (70% of ad libitum) DM intake and a thermal stress environment with ad libitum intake in two balanced 3 x 3 Latin squares to evaluate effects on mammary blood flow and other physiological measurements. Daily DM intake decreased from 17.8 kg in thermal comfort with ad libitum intake to 12.5 kg in thermal comfort with restricted intake and to 14.8 kg in thermal stress. Daily milk production decreased from 23.9 kg in thermal comfort ad libitum to 22.2 kg in thermal comfort restricted and 21.6 kg in thermal stress. Mammary blood flows (half udder) over the entire sampling interval (18 h) were 5.1, 4.3, and 4.5 L/min for treatments: thermal comfort, ad libitum intake; thermal comfort, restricted intake; and thermal stress, ad libitum intake. Mammary blood flows did not differ significantly among between treatments. Relationship of half udder blood flow (L/min) to previous day's DM intake (kg/d) was described by the linear equation: L/min = .49 + (.27 kg/d); r2 = .46; and the quadratic equation: L/min = 6.04 – (.54 kg/d) + (.03 [kg/d]2); r2 = .55. Mammary blood flows 10 min before through 10 min after milking machine attachment were greater for cows at thermal comfort and ad libitum intake than for cows at thermal comfort and restricted intake or thermal stress and ad libitum intake (5.5, 4.8, and 4.8 L/min).

Key Words: thermal stress • feed intake • mammary blood flow

Submitted on February 27, 1989
Accepted on September 7, 1989




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Copyright © 1990 by the American Dairy Science Association ®.