Julia T. da Silva

This study aimed to evaluate the effect of bromoform (CHBr₃) dose on in vitro rumen fermentation and on CHBr₃ and dibromomethane (CH₂Br₂) concentrations in solution and the gas cap. In vitro treatments consisted of CHBr₃ (DOSE: 0, 1, 10, 100, 1000, 10,000 µg of CHBr₃), with five replicates per DOSE at each time-point (TIME: 0, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 12, 24, 48, and 72 h). The 10,000 µg CHBr₃ DOSE inhibited fermentation completely and was removed from the dataset. The acetate:propionate ratio, nitrogen, and methane (CH₄) produced per gram of DMD decreased as DOSE increased (p = 0.01). As the DOSE increased, CH₄ decreased, and H₂ increased in a dose-dependent manner (p < 0.01). The CHBr₃ concentration dropped below the detection limit within 3 h of incubation. Dibromomethane concentrations for DOSE 1000 and 100 µg of CHBr₃ increased in solution and gas cap beginning at 0.25 h and 1 h post incubation and plateaued by hour 3 and 5, respectively (p < 0.01). The addition of CHBr₃ alters the molar proportion of volatile fatty acids, decreases CH₄, and increases H₂ production, and it is dehalogenated to CH₂Br₂ within 3 h of incubation in an in vitro system.

Heat stress (HS) induced by global warming is a real welfare, productivity, and economic burden of cattle production. However, some cattle breeds have superior physiological adaptive traits to others, yet the underlying molecular mechanisms are not fully defined. The present study aimed, therefore, to determine the expression profile of stress-related molecular signatures in the blood of thermosensitive Angus (Bos taurus) and thermotolerant Brahman (Bos indicus) cattle breeds managed without (CON) or with growth-promoting technology (TRT) during the summer (April–October, 2023) season in Colorado, US. Body weight (BW) was significantly increased from April to October, and the amplitude was greater for the Angus compared to the Brahman breed. The TRT system slightly increased BW, mainly in the Angus breed. Molecular analyses showed that all tested genes were expressed in beef cattle blood. When comparing production systems, the expression of HSP1A1 was significantly upregulated, and HSP90 was downregulated in CON compared to TRT cattle. The expression of IL6, CCL20, and OCLN was induced by the CON system only in the Angus and not in the Brahman breed. At the breed level, Angus cattle exhibited greater expression of IL10, CCL20, and CLDN1 compared to their Brahman counterparts. There was a significant period by production system as well as period by breed interactions. The expression of HSP1A1 increased in both breeds during October. The expression of IL10, CXCL14, CXCR2, and CLDN1 was affected by the production systems in a period-dependent manner. However, the expression of IL6, CXCL14, CCL5, and CXCR2 was upregulated in Angus cattle in a period-sensitive manner. In summary, HSPs, (chemo)cytokines, and tight junction proteins are expressed in the whole blood of beef cattle, and their expression is regulated in a breed-, period-, and/or production system-dependent manner. This could open new vistas for future research to identify molecular signatures for non-invasive stress monitoring and/or marker-assisted genetic selection for robustness and resilience to HS.