Assessment of heat stress in 7-week old dairy calves with non-invasive physiological parameters in different thermal environments

Abstract

We estimated thermal stress in 7-week old Holstein bull calves during a warm episode in summer to study acute physiological responses of calves to heat stress. Data were collected over a 5-day period: day 1 (control), day 2 (heat stress), and a 3-day post-stress period in shaded (n = 8) and unshaded (n = 8) thermal environments. On the control day, both groups were shaded. Thermal environment was characterized by relative humidity, ambient temperature, and the temperature–humidity index (THI). Physiological variables included respiratory rate, rectal temperature, ear skin temperature and heart rate. Correlations between animal-based and meteorological indices were calculated, and ambient temperature correlated slightly better with physiological measures than THI. Rectal temperature was the only animal-based parameter that showed stronger correlations with the thermal indices when calculated for the shaded than for the unshaded environment [r = 0.42 vs. r = 0.47, P = 0.032 (ambient temperature), r = –0.39 vs. r = –0.45, P = 0.012 P = 0.015 (relative humidity), r = 0.41 vs. r = 0.46, P = 0.022 (THI)]. No differences were found between groups during the control day for any of the physiological parameters. During days 2 and 3, average and maximal values of respiratory and heart rates were higher in unshaded calves than in shaded ones. Maximal respiratory rates were in average by 25.9, 17.8 and 10.1 breaths/min lower in shaded calves than in unshaded calves for days 2, 3 and 4, respectively (P < 0.001, P < 0.001 and P = 0.024). Maximal heart rate was 127.4 ± 8.5 vs. 99.2 ± 6.3 beats/min on the heat stress day (P < 0.001), and 121.0 ± 6.9 vs. 103.4 ± 7.7 beats/min on day 3 (P = 0.006) in unshaded and shaded calves, respectively. Maximal body temperatures were higher measured either in the rectum or on the ear skin in unshaded calves than in shaded ones (with 0.5 and 1.6°C, P = 0.040 and P = 0.018, respectively), but only on the heat stress day. Based on our results, shading of young calves may be adequate for alleviating acute heat stress in continental regions. Ambient temperature is appropriate to estimate acute heat stress in dairy calves.

Lying down frequency as a discomfort index in heat stressed Holstein bull calves

“…Reduced heat load in the S hutch environment compared to the NS one was reflected by daily averages of THI as well on the heat stress day (78.1 ± 0.1 vs. 71.3 ± 0.1; P = 0.011). Similar reductions were found in ambient temperature 8 , 9 and THI 10 in shaded commercial calf hutches during short-term warm episodes in summer. Like on Day 2, maximal (82.3 ± 0.1 vs. 74.5 ± 0.1; P = 0.002) and average THI (74.7 ± 0.1 vs. 68.3 ± 0.1; P = 0.011) were higher in the NS than the S environment for Day 3 ( P = 0.003 and P = 0.014).…”

Heat Stress Impacts Immune Status in Cows Across the Life Cycle

“…Two studies in the southeastern region of U.S. provided supplemental shade (80% shade cloth above the hutch) to calves housed in polyethylene hutches reporting reductions in interior temperature of the hutch, compared with hutches under direct sunlight, which translated into reductions in respiration rates (150) and better feed-to-gain ratio (151). Average elevation in respiration rates and heart rates of 20 beats/min and rectal and skin temperatures of 0.5 and 1.6 • C have been observed when comparing un-shaded 7 days old bull calves with those provided with shade during a 3 days heat event (152).…”

Heat stress in dairy calves from birth to weaning

“…Studies on adaptive responses of calves in neutral/shaded vs. hot/noncooled thermal environments have reported an approx. 50% increase in average respiratory rates as a sign of increased evaporative cooling efforts [from 47 to 53 (de Lima et al ., 2013), from 50–78 to 73–105 (Peña et al ., 2016) or from 30–50 to 70–140 (Kovács et al ., 2018b)]. Heavier breathing is induced by an increase in ambient and consequently, body surface temperature.…”

“…Most sources consider 38.5–39.1(39.5)°C as the range of healthy body temperature in calves (Rosenberg, 1979; Piccione et al ., 2003). Consistently, studies on calves exposed to high ambient temperatures report on maximal body temperatures of 39.7°C (de Lima et al ., 2013), 40.1°C (Peña et al ., 2016), 40.4°C (Kovács et al ., 2018b), and 39.8°C (Hill et al ., 2016).…”