Effects of Feed Intake and Thermal Stress on Mammary Blood Flow and Other Physiological Measurements in Lactating Dairy Cows

Abstract

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 × 3 Latin squares to evaluate effects on mammary blood flow and other physiological measurements. Daily DM intake decreased from 17.8kg in thermal comfort with ad libitum intake to 12.5kg in thermal comfort with restricted intake and to 14.8kg in thermal stress. Daily milk production decreased from 23.9kg in thermal comfort ad libitum to 22.2kg in thermal comfort restricted and 21.6kg in thermal stress. Mammary blood flows (half udder) over the entire sampling interval (18h) 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 10min before through 10min 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).