Effect of Temperature Humidity Index (THI) on resting pattern of dairy cows in different regions of Sri Lanka

The ability to spend time resting is extremely important for dairy cattle welfare. Through this study, lying behaviour of dairy cows in to Up-Country (UP), Mid-Country (MC), Coconut-Triangle (CT) and Western-Province (WP) of Sri Lanka was studied to get an insight into their resting pattern. Resting pattern was assessed in 170 Holstein-Friesian/ Jersey crossed, tie-stalled lactating cows (UP = 49, MC = 49, CT = 48 and WP = 24) using electronic data loggers. Appropriate resting behaviours were attained in UP and MC regions, with longer lying time (11.7, 11.3 h/day) and lying bout durations (78.0, 84.9 min) respectively, where lower THI ranges were observed compared to other regions. WP and CT resulted with lower lying times (9.00, 9.26 h/day) and lying bout durations (48.3, 64.3 min) respectively with higher THI. There is a slight variation of the environmental temperature of each region with the time period of experiment. Cows in all regions prefer to lie on their left side (UP-6.1, MC-6.1, CT-4.4, WP-4.7 h/d) and with significant differences (P<0.05) between MC-WP, MC-CT, UP-CT and UP-WP. A negative significant (P<0.05) correlation was observed between THI and lying behaviours. There were significant effects of time (hour) and time × region interaction (P<0.05) on the lying down pattern. More lying down was observed in late night and early morning with a peak rest around the hours of 21:00-05:00. Overall, according to the results of the current study, the existing environmental conditions of four regions affected the resting pattern of dairy cows and, identification of possible mechanisms to modify the environment to enhance cow comfort is vital.