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<p>The Uruguayan livestock system, particularly in the northern region, is predominantly pastoral and highly dependent on climatic conditions, making it vulnerable to increasing droughts, high temperatures, and reduced rainfall. The objective of this study was to evaluate breed-level thermoregulatory responses under field heat stress using rectal temperature (RT), respiratory rate (RR), and surface temperatures across three THI<sub>hadj</sub> strata. Physiological responses were assessed in one-year-old castrated male calves from five beef breeds: Angus (<i>n</i> = 5), Hereford (<i>n</i> = 5), Brangus (<i>n</i> = 10), Braford (<i>n</i> = 10), and Tulianguy (<i>n</i> = 16). Measurements were collected on three occasions (28 December 2023; 23 January 2024; 7 February 2024), yielding three repeated observations per animal for each physiological trait. All statistical analyses were performed in R software (version 4.4.1) using the packages lme4, lmerTest, and emmeans. Repeated measures mixed models were fitted with breed, THI<sub>hadj</sub> category, and their interaction as fixed effects, and animal as a random effect. Model assumptions were verified prior to analysis: residual normality (Shapiro–Wilk test and Q–Q plots), homogeneity of variances (Levene’s test), and sphericity (Mauchly’s test), with Greenhouse–Geisser corrections applied when sphericity was violated. Results showed significant increases in all physiological variables with rising THI<sub>hadj</sub>. Angus and Hereford (<i>Bos taurus</i>) exhibited the highest RT and RR at THI<sub>hadj</sub> = 10, indicating greater heat-stress susceptibility. In contrast, Brangus and Braford (composite breeds with <i>Bos indicus</i> influence) and Tulianguy (a <i>Bos taurus</i> composite derived from heat-adapted African taurine ancestry combined with Limousin and Angus) displayed more stable physiological responses, demonstrating enhanced thermal resilience. These findings highlight the importance of selecting heat-tolerant biotypes to sustain productivity, animal welfare, and system resilience in increasingly hot and variable environments. Additionally, the study provides novel field-based comparative data for Tulianguy and other composite breeds, addressing a significant knowledge gap in heat-stress adaptation research.</p>

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Assessment of adaptive and physiological trait expression in one-year-old male calves from Braford, Brangus, Tulianguy, Hereford, and Angus breeds in northern Uruguay

  • 期刊论文

  • 发表日期：

    2026年1月27日

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  • Paula Alicia Batista Taborda

摘要

The Uruguayan livestock system, particularly in the northern region, is predominantly pastoral and highly dependent on climatic conditions, making it vulnerable to increasing droughts, high temperatures, and reduced rainfall. The objective of this study was to evaluate breed-level thermoregulatory responses under field heat stress using rectal temperature (RT), respiratory rate (RR), and surface temperatures across three THIhadj strata. Physiological responses were assessed in one-year-old castrated male calves from five beef breeds: Angus (n = 5), Hereford (n = 5), Brangus (n = 10), Braford (n = 10), and Tulianguy (n = 16). Measurements were collected on three occasions (28 December 2023; 23 January 2024; 7 February 2024), yielding three repeated observations per animal for each physiological trait. All statistical analyses were performed in R software (version 4.4.1) using the packages lme4, lmerTest, and emmeans. Repeated measures mixed models were fitted with breed, THIhadj category, and their interaction as fixed effects, and animal as a random effect. Model assumptions were verified prior to analysis: residual normality (Shapiro–Wilk test and Q–Q plots), homogeneity of variances (Levene’s test), and sphericity (Mauchly’s test), with Greenhouse–Geisser corrections applied when sphericity was violated. Results showed significant increases in all physiological variables with rising THIhadj. Angus and Hereford (Bos taurus) exhibited the highest RT and RR at THIhadj = 10, indicating greater heat-stress susceptibility. In contrast, Brangus and Braford (composite breeds with Bos indicus influence) and Tulianguy (a Bos taurus composite derived from heat-adapted African taurine ancestry combined with Limousin and Angus) displayed more stable physiological responses, demonstrating enhanced thermal resilience. These findings highlight the importance of selecting heat-tolerant biotypes to sustain productivity, animal welfare, and system resilience in increasingly hot and variable environments. Additionally, the study provides novel field-based comparative data for Tulianguy and other composite breeds, addressing a significant knowledge gap in heat-stress adaptation research.