Physiological responses of Holstein calves to hot weather conditions
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ORIGINAL PAPER
Physiological responses of Holstein calves to hot weather conditions Heather Young 1 & Briah Parchment 1 & Adriana Lopez Ayala 1 & Amber Adams Progar 1 Received: 15 July 2019 / Revised: 24 June 2020 / Accepted: 11 August 2020 # ISB 2020
Abstract The objectives of the study described were to (1) compare environmental temperature-humidity index (THI) with the THI measured within two different calf housing systems and (2) determine how THI affects Holstein heifer calf body temperatures, serum cortisol concentrations, and serum thyroxine concentrations. At 24 to 48 h of age, calves were assigned to one of two individual housing treatments: (1) stalls in a three-sided barn (n = 8) or 2) hutches placed outside (n = 8). Calves were observed until 42 days of age during the summer months. Ambient temperature and relative humidity within housing systems were recorded hourly. Calf body temperatures were measured hourly using devices attached to the underside of each calf’s tail. Blood samples were collected at 7, 21, and 42 days of age via jugular venipuncture. Blood serum was analyzed for cortisol and thyroxine concentrations using enzyme-linked immunosorbent assays (ELISAs). Overall average THI was higher in hutches than in stalls (P < 0.0001). Calves housed in hutches had higher body temperatures (39 ± 0.18 °C vs 38 ± 0.15 °C, P = 0.005). No differences occurred in serum cortisol concentrations (P = 0.89) but at 21 days of age, calves housed in hutches had higher serum thyroxine concentrations (16.55 ± 0.51 μg/dl vs 13.91 ± 0.54 μg/dl, P = 0.0006) than calves housed in stalls. Although both housing systems in this study were located on the same dairy, calves housed in hutches were exposed to higher THI values, had higher body temperatures, and at 21 days of age had higher serum thyroxine concentrations than calves housed in stalls inside a three-sided barn. Keywords Cortisol . Dairy calf . Heat stress . Thyroxine
Introduction The temperature-humidity index (THI) is a common tool for measuring the severity of heat stress dairy cows experience. Ambient temperature and relative humidity are used to calculate THI, where a THI of 68 is considered as the upper critical THI of a cow’s thermoneutral zone, and a THI ≥ 68 is considered a heat stress environment for dairy cows (Collier et al. 2009). Because mature dairy cows can thermoregulate better than young dairy calves, the thermoneutral zone for dairy calves is expected to be narrower and higher (Bateman et al. 2012). Although an upper critical THI for calves has not been established, the upper critical temperature is 26 °C for newborn calves and 23 °C for 1-month-old calves (Wathes et al. 1983). Under hot weather conditions, dairy calves exhibit physiological and behavioral responses to heat stress. For * Amber Adams Progar [email protected] 1
Department of Animal Sciences, Washington State University, P.O. Box 646310, Pullman, WA 99164, USA
example, calves exposed to ambient temperatures higher than 44.3 °C have higher respiration rates, heart rat
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