Vaginal temperature of lactating cows during heat waves or normal summer day and effect of additional daily cooling treatments as heat load mitigation strategy

The vaginal temperature (VT) of lactating Holstein cows was monitored in not heat wave (NHW) and in heat wave (HW) summer days. Temperature humidity index (THI) was monitored and assigned to four classes of heat load (HL): THI < 68 null; 68 < THI < 74 low; 74 < THI < 80 moderate; and THI > 80 high. Five daily treatments consisting of continuous forced ventilation and sprayed water (1′ on follow by 5′ off) were assumed as control cooling protocol (CC) and compared with two experimental cooling protocols (EC) applied in the feed bunk and based on the CC plus two additional cooling treatments which lasted a total of 90′ (EC90) or 150′ (EC150) in the day. Sixty lactating cows were enrolled in two summer trials carried out in NHW or HW. In each trial, 10 cows were cooled by CC, 10 by EC90 and 10 by EC150. Twenty additional cows were monitored in a fall trail to have reference value of THI and VT under thermoneutral conditions (TN). Each trial lasted 72 h, and measurements of VT were carried out by intra-vaginal data loggers. The 33