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

Abstract

Changes in lying behaviour in response to extreme ambient temperatures have not been examined in dairy calves so far. In this study, lying time, and frequency of lying down were investigated in shaded (n = 8) and non-shaded (n = 8) Holstein bull calves during a 5-d period [temperature, average/max (°C); Day 1 (control, all calves shaded): 22.9/29.4, Day 2 (heat stress day): 28.3/38.8, Day 3: 26.2/33.5, Day 4: 23.7/28.7, and Day 5: 21.2/24.7]. The thermal environment around the calves was characterized by the temperature–humidity index (THI). A three-dimension accelerometer was used to record posture of the calves and lying time and lying down frequency were analysed with 4-h sampling intervals. On Day 1 no differences were found in THI between the shaded and non-shaded environments. On Days 2, 3 and 4 maximal and average THI were higher in the shaded than those recorded for the non-shaded environment. On Day5 no significant differences in THI were observed between calf environments. A similar diurnal pattern of lying time and lying down frequency was observed in both groups. Lying times were shorter during the afternoon (P = 0.003); however, no group differences were found in lying time (P = 0.551). During the daytime (between 8:00 and 20:00), the frequency of lying down was 50, 33, and 41% higher, respectively, than during the nighttime on Days 2, 3 and 4 (P < 0.001, P = 0.011, and P < 0.001). On the heat stress day, non-shaded calves changed posture 88.4 and 76.6% more often than shaded ones between 8:00 and 12:00 and 12:00 and 16:00, respectively (P < 0.001 for both intervals). Similar group differences were observed for Day 3 between 8:00 and 12:00 (71.2%) and Day 4 between 12:00 and 16:00 (76.6%), respectively (P = 0.003, and P = 0.001). On Day 5, there was no difference between groups (P = 0.732). As indicated by our results, heat stress causes changes in lying down frequency and lying time in dairy calves. Supplemental shading reduces discomfort as indicated by lying down frequency, but not by lying time.

Prenatal heat stress effects on gestation and postnatal behavior in kid goats

“…Lying and inactivity are common behaviors observed during the exposure to high ambient temperatures as a strategy to reduce heat load. In addition, feeding behavior was decreased as a mechanism to reduce heat production [38,39].…”

Heat stress in dairy calves from birth to weaning

“…Calves seek shade, change posture, move less during the hottest hours of the day and bunch to provide shade for each other (Roland et al, 2016). Frequency of changing posture is reduced in hot conditions as a sign of discomfort (Kovács et al, 2018a) similarly to cows (Allen et al, 2015). Hutch vs. pen preference or lying vs. standing provides valuable information about the heat-absorbing nature of hutch material or thermal conductive properties of the bedding.…”

Impacto del estrés por calor en terneros de tambo sobre parámetros fisiológicos y conductuales.

“…Es importante destacar que era de esperar que la proporción de animales de pie hubiera resultado superior ya que uno de los cambios de comportamiento reportados en la bibliografía ante situaciones de estrés por calor es permanecer de pie en lugar de acostarse (Broucek et al, 2009). Por otra parte, es posible señalar que debido a la mayor relación superficie / masa de los terneros en comparación con el ganado adulto, la disipación de calor de los animales jóvenes podría no ser considerablemente mayor mientras se hayan de pie (Kovács et al, 2018b). Si se consideran ambos parámetros es posible inferir que el rango de ITH considerado para el presente estudio, entre 72 y 88, no resultó suficiente para inducir a cambios compatibles con estrés sobre estas variables (Blackshaw y Blackshaw, 1994).…”