Effect of Temperature – Humidity Index (THI) on Resting Pattern of Dairy Cows in Different Agro-Ecological Areas of Sri Lanka

The ability to spend more time in lying down is extremely important on dairy cattle welfare. Lying behavior provide impending data on how cows interact with their environment. To assess how well the lying behavior of dairy cows in tie-stalls were varied with the THI, we assessed a total of 170 Holstein-Friesian and Jersey crosses lactating cows belongs to four agro-ecological zones which differ from environmental temperature and sea level height (UP-Up Country, MC-Mid Country, CT-Coconut Triangular and WP-Western Province). Lying behavior was recorded using electronic data loggers (HOBO Pendant G Acceleration Data Loggers), which attached to the cow’s hind leg, below the hock after validating for recording positions at 30 sec intervals for 5 consecutive 24-h periods. Variation of temperature and Relative Humidity (RH) inside the cattle shed was recorded throughout the experimental period using HOBO^® temperature loggers (HOBO U23 Pro v2 Temperature/RH Data Loggers) in five minutes’ interval of time. Recorded data were converted into a readable mode using SAS 9.4 version and then further statistical analyzes were continued using SPSS 23.0 version. Greater resting behaviors were attained by dairy cows in UP and MC areas with longer lying times (11.74 h/d, 11.26 h/d respectively) and lying duration (78.0 min, 84.95 min respectively) compared to WP and CT (lying times - 9.00 h/d, 9.26 h/d respectively and lying duration 48.32 min, 64.34 min, respectively). Significantly higher frequency of lying bouts were perceived in WP (13.22), and others remain comparable (UP = 11.87, MC = 9.82, CT = 9.67). All cows in four agro-ecological areas, prefer to lie on their left side. However, majority (78%) were in thermal stress condition (Discomfort – 72 < THI < 75, Alert – 75 < THI < 79, Danger – 79 < THI < 84, Emergency –THI > 84) and elevated THI had significantly (p < 0.05) reduced total lying time (p = −0.492), lying duration (ρ = −0.341), total lying time at right side (ρ = −0.213), total lying time at left side (ρ = −0.429), right side lying duration (ρ = −0.353), and left side lying duration (ρ = −0.341). Thus, we can conclude, heat stress condition due to climatic changes could diminish the welfare of cows and their sustainability.