Physiological parameters for thermal stress in dairy cattle

Abstract

-The objective of this study was to investigate changes in physiological parameters of dairy cows and understand which physiological parameters show greater reliability for verification of heat stress. Blood samples were collected for analysis and included hematocrit (Ht), erythrocyte count (ERY), and hemoglobin count (HEMO). In addition, physiological variables, including rectal temperature (RT), heart rate (HR), respiratory rate (RR), and panting score (PS) were recorded in 38 lactating cows. These varied according to genetic group (½, ¾, and pure bred Holstein (HO)). Analysis of variance considering the effects of genetic group, days, and their interaction as well as linear and quadratic effect of the black globe humidity index (BGHI) was performed, as well as broken-line regression. These values were higher in pure HO than in ¾ and ½ groups. The average BGHI during the morning was 74, when 70, 43, and 13% of pure HO, ¾, and ½, respectively, presented RR above reference value. The RR was the best indicator of heat stress and its critical value was 116 breaths/min for ½, 140 for ¾, and 168 breaths/min for pure HO cows. In the HO group, physiological variables increased linearly with BGHI, without presenting inflection in the regression. The inflection point occurred at a higher BGHI for the ½ group compared with the other groups. Hematocrit and HEMO were different among genetic groups and did not vary with BGHI, showing that stress was not sufficient to alter these hematological parameters. The ½ HO group was capable of maintaining normal physiological parameters for at least 3 BGHI units above that of HO and 1 to 3 units higher than ¾ HO for RR and RT, respectively. Respiratory rate is the physiological parameter that best predicts heat stress in dairy cattle, and the 1/2 Holstein group is the best adapted to heat stress.

Impact of the Egyptian summer season on oxidative stress biomarkers and some physiological parameters in crossbred cows and Egyptian buffaloes

“…HS significantly affected respiratory rate (breaths/min) when compared to normal values (76.8 and 77.8 vs. 40-50) for cow and buffalo, respectively, as presented by Das et al [26]. According to Dalcin et al, respiratory rate can be a relevant physiological indicator for HS [27]. [18].…”

“…[18]. Respiratory rate is an indicator of HS in the hot environment [27]. The normal respiratory rate is approximately 10-30 breaths/min [7].…”

Influence of Temperature Humidity Index and Dietary Energy on Certain Stress Marker Profile of Murrah Buffalo Heifers

“…The significantly (P<0.05) higher RR, PR and RT indicates that the animals are under stress and was higher during summer season. Among the physiological parameters respiratory rate is the best predictor of heat stress in dairy cattle (Dalcin et al, 2016). The increase in respiration rate with the increasing temperature may be due to the more demand of oxygen by the tissues in stressful…”

Relationship between thermal comfort indices and internal temperature of grazing lactating Holstein × Gyr cows in western Amazonia

“…Regarding the differences in the internal temperature between the genetic groups, Dalcin et al (2016) also found differences between the rectal temperature of ¾ Holstein × ¼ Gyr and ½ Holstein × ½ Gyr cows (39.39 ºC vs. 39.01 ºC, respectively). The ½ Holstein crossbred cows are more thermotolerant than ¾ Holstein cows under conditions of heat stress (Costa et al 2015).…”

“…The ½ Holstein crossbred cows are more thermotolerant than ¾ Holstein cows under conditions of heat stress (Costa et al 2015). The inability of the ¾ Holstein × ¼ Gyr cows to dissipate body heat as efficiently as the ½ Holstein × ½ Gyr cows could be explained by the fact that Zebu breeds can regulate their body temperature better than the European breeds, in response to heat stress (Dalcin et al 2016). It is well established that Bos indicus and Bos taurus regulate body temperature, including rumen temperature, differently (Lees et al 2018).…”