Understanding environmental impacts on physiology and behavior is critical to improve animal welfare and performance. Our objective was to identify correlations between environments, vaginal temperature (VT) and behaviors of grazing lactating dairy cows on pasture during summer. Lactating cows (n = 119, 29–30/farm) from 4 farms were randomly enrolled. Each farm had different milking schedules and cooling facilities in holding pens and feedlots. Pivots equipped for evaporative cooling were provided during day but not night on all farms. The VT was recorded every 5 min. Times of lying and standing were recorded every 15 min using Smarttag Leg (Nedap) for 6 consecutive days. Meteorological variables were measured on pasture, and temperature humidity index (THI) calculated. Data were averaged or summed every 30 min and only the data collected between milkings (on pasture during day and night, Table 1) were used for correlation analyses by PROC GLM procedure of SAS 9.4. At day, VT had strongest correlation with dry bulb temperature (= 36.79+0.08 × dry bulb temperature, r² = 0.254, P < 0.001), but lying time (= 28.21–0.58 × black globe temperature, r² = 0.172, P < 0.001) and standing time (= −0.88+0.58 × black globe temperature, r² = 0.185, P < 0.001) had strongest correlations with black globe temperature. At night, VT had strongest correlation (= 35.50+0.05 × THI, r² = 0.041, P < 0.001) with THI, but lying time (= 80.23–2.62 × dry bulb temperature, r² = 0.168, P < 0.001) and standing time (= −38.44+1.99 × dry bulb temperature, r² = 0.12, P < 0.001) had strongest correlations with dry bulb temperature. In conclusion, at day under pivots, VT had the strongest correlation with dry bulb temperature, but black globe temperature explained more of the variation of lying and standing times. At night, THI is a better variable to predict VT, and lying and standing times had strongest correlations with dry bulb temperature. Table 1. Mean or sum of environmental and behavioral variables every 30 min on pasture

Variable	Day	Night
Dry bulb temperature, °C	29.4	24.1
Relative humidity, %	74.0	93.9
Black globe temperature, °C	37.4	23.7
THI	80.7	74.7
VT, °C	39.3	39.5
Lying time, min	6.4	17.0
Standing time, min	20.7	9.5