Disease & heat resistance

Genetic differences in thermoregulatory ability between sheep reared in a hot humid environment

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Abstract

Heat stress can compromise health and productivity of sheep. There is genetic variation in thermal tolerance, but differences among breed groups remain poorly defined. In this study, we compared several lines of sheep for ability to maintain vaginal temperature during heat stress conditions. Experiments were conducted in Northern Florida during June-September 2025 on ewes on pasture. Vaginal temperature was measured at 10 min intervals for 3 days using an iButton temperature recording device (±0.0625°C accuracy) attached to a blank CIDR intravaginal device for goats and sheep. Data was analyzed using GLIMMIX. Four experiments were conducted involving different sheep breeds and crosses. For Experiment 1, vaginal temperatures were recorded for ewes that were purebred Katahdin (KT; n=12), purebred Florida Native (FN; n=32) or an admixture of the two breeds that ranged from 25-75% of one breed (n=9). Average daily maximum temperature-humidity index (THImax) was 87. Vaginal temperature was higher (P=0.027) for KT than the other two groups, which were similar to each other (P=0.781). Average vaginal temperature was 39.45 ± 0.26°C for KT, 38.68 ± 0.16°C for FN and 38.78 ± 0.30°C for crosses. Experiment 2 (average THImax=88) compared admixtures of FN crossbred ewes where the cross was with Finn (n=10), Lacaune (n=5) or St. Augustine (STA; n=8).Finn crosses had higher (P=0.024) vaginal temperatures (39.58 ± 0.10°C) than Lacaune (39.17 ±0.15°C) or STA (39.31 ± 0.12°C), which were not different from each other (P=0.475). Differences between breeds were least when vaginal temperatures peaked at ~1800 to 2000 H (breed x time, P< 0.0001). Experiment 3 (average THImax=87) compared admixtures of FN with either KT (n=8) or STA (n=9). Vaginal temperatures were lower (P=0.045) for KT than STA (39.08 ± 0.07°C vs 39.30 ± 0.07°C). There was a breed x time interaction (P=0.007) with breed differences least at ~1500 to 1700 H when vaginal temperatures peaked. Experiment 4 (average THImax=89) compared purebred Dorper (n=10) and Awassi (n=9). Vaginal temperatures were not affected by the main effect of breed (P=0.985) but there was a breed x time interaction (P< 0.0001), because vaginal temperatures were lower for Dorper from ~2200 H to ~1000 H but not at other times. For example, vaginal temperature at 0600 H was 39.00 ± 0.11°C for Dorper vs 39.39 ± 0.11°C for Awassi whereas vaginal temperature at 1900 H was 40.08 ± 0.11°C for Dorper vs 39.94 ± 0.12°C for Awassi. Results demonstrate that heat stress can cause hyperthermia even in breeds of sheep that were developed in hot climates and that the ability to regulate body temperature varies among genetic groups. Further research is being conducted to uncover genetic architecture underlying breed differences in regulating vaginal temperature.

Keywords: 2026

How to Cite:

Cuellar, C., Bright, C., Zayas, G., Sproull, A., Obeso, S., Mateescu, R., Diehl, B. & Hansen, P., (2026) “Genetic differences in thermoregulatory ability between sheep reared in a hot humid environment”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285201. doi: https://doi.org/10.31274/wcgalp.23638

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