Meta-analysis and meta-regression of core body temperature in taurine and zebuine cattle under different environmental conditions

Abstract

Heat stress affects livestock productivity and is often determined by an increase in the core body temperature (CBT). To evaluate the latter, both vaginal and rectal temperatures can be used. The aims of this study were (1) to perform a meta-analysis in order to evaluate the impact of heat stress in comparison to thermoneutral conditions on CBT in Bos taurus and Bos taurus indicus cattle, and (2) to evaluate the effects of genetic group, sex, productive purpose, climate zone, and temperature-humidity index (THI class) heat stress on the vaginal and rectal temperatures of cattle. Eighty-nine studies were included in this meta-analysis. Systematic review and meta-analysis were performed following the PRISMA guidelines. The standardized mean difference (SMD) in CBT between the heat stress (HS) and thermoneutral (TN) environments was used as a measure of effect size, considering a 95% confidence interval (CI). Cochran's Q test and I² statistic indicated high variability among studies; thus, a random effects model was used. Subgroup and meta-regression analysis were performed to investigate the source of heterogeneity. Genetic group, sex, productive purpose, climate zone, and THI class were included as covariates. The SMD in CBT between the HS and TN environments was 7.45 °C (95%CI: 5.89;9.02 °C, P = 0.0001), indicating a physiological response to the heat stress condition. The SMD in CBT was 3.92 °C higher in Bos taurus than Bos taurus indicus animals (P < 0.05). Animals in climate zone D (warm temperate zone) showed a lower SMD in CBT than those in climate zone B (arid zone) (SMD = 4.04 ºC vs 12.38 ºC). The THI class affected the SMD in CBT (P < 0.05). The genetic group, climate zone, THI class and interaction between genetic group and climate zone explained 29.89% of the heterogeneity observed among studies. In conclusion, heat stress exposure affects the vaginal and rectal temperatures of cattle. The CBT measured by rectal and vaginal temperatures can be used to detect heat stress-induced changes in CBT. Bos taurus and Bos taurus indicus animals seem to respond differently to heat stress in terms of CBT.