Understanding the environmental stress on thermoregulation actions of native goats using broken-line regression

Abstract

This study's objective was to evaluate the thermoregulation aspects of native goats through broken-line regression to understand the triggering of physiological responses in the homeothermy process. Data were collected from ten healthy dams of the Canindé breed once a week at hourly intervals (24h) for eight consecutive weeks. Air temperature (AT; °C), relative humidity (RH; %) were measured and temperature-humidity index (THI) calculated. The thermoregulation parameters evaluated were: respiratory rate (RR; breaths.min-1), rectal temperature (RT; °C) and sweating rate (SR; g.m-2.h-1). All variables were subjected to analysis of variance with repeated measures over time. The hour was considered a fixed effect (00:00h, 01:00h, …, 23:00h), and the animal was a random effect. Multiple regression analyses were also examined using General Linear Models and Variance Inflation Factors were calculated. Broken line non-linear regressions for RR, RT and SR were examined using independent variables. The highest average for AT and RH were 35.9°C (13:00h) and 92.4% (04:00h), respectively. The lowest average of TA and RH were 22.1°C (05:00h) and 28.0% (12:00h), respectively. The highest average THI was 102.1 (13:00h), and the lowest 78.0 (05:00h). The environmental thresholds at which RR, RT and SR began to increase for AT were between 17-21°C and RH were > 17% (RR), ≥ 21 (RT) and > 23% (SR). For THI the limits were 108.4 for RR, 78.0 for RT and 100.1 for SR. Using THI, the thermoregulatory parameters are activated in the following order: SR, RR and RT. Estimates can serve as a basis to implement heat stress mitigation and improve animal welfare strategies for native goats.