The effect of shade on vaginal temperature of cows housed outside under subtropical summer conditions

Abstract Text:

It is generally agreed that lactating dairy cows with access to shade have lower body temperatures than those without shade. The aim of this study was to determine the effect of shade on vaginal temperature (T_VAG) of cows housed outside in a sub-tropical environment. Holstein Friesian cows (n = 40) were paired based on milk yield and live-weight. Each pair was then allocated to either a shade (S) or a no shade (NS) treatment. Pairs were then randomly allocated to a T_VAG group (5 pairs/ group). Data were collected on one group per week, over 8 weeks (2 reps/ group). A temperature logger was attached to a CIDR and inserted into the vagina for 5 d, logging every 10 min. Weather was monitored via an automated weather station (200 m from cows) and temperature humidity index (THI = 0.8 x ambient temperature + relative humidity x (ambient temperature – 14.3) + 46.3) was calculated using these data. Cows were milked twice daily at 0500 and 1500 h. Fans and sprinklers were used for 15 min before afternoon milking. Cows were placed within treatment from 0700 to 1445 h daily; fed a mixed ration twice daily, and turned out to improved pasture overnight. Averages for T_VAG and THI were obtained for each h over each 5 d period. Three data periods were examined: day (D), night (N), and evening (E); T_VAG_D and THI_D (0900 to 1500 h); T_VAG_N and THI_N (2200 to 0600 h); and T_VAG_E and THI_E (1700 to 2100 h. Pearsons correlations were performed on T_VAG against THI for each period. Overall, relationships were found between T_VAG_N and THI_N (r = -0.256; P = 0.041); T_VAG_D and THI_D (r = 0.34; P=0.006); and T_VAG_D-N and THI_D-N (r = 0.61; P < 0.000) on the whole herd. Moderate correlations were determined for T_VAG_D-N and THI_D-N for S (r = 0.516; P=0.003) and NS (r = 0.769; P < 0.000) cows. Shaded cows were better able to regulate T_VAG up to a THI of 76, after which T_VAG increased, whereas NS showed a positive, linear increase in T_VAG with increasing THI. It appears that S cows were better able to regulate body temperature than NS when THI_D-N was smaller than seven THI units. Above this point, the rate of increase in T_VAG against THI was greater in both treatments. 

Keywords: vaginal temperature; shade; dairy cows