Automated head chamber systems (AHCS) are increasingly deployed to measure enteric emissions in vivo. However, guidance for AHCS-derived emissions data analyses pertains to confined settings, such as feedlots, with less instruction for grazing systems. Accordingly, our first objective in this experiment was to determine the utility of two data preprocessing approaches for grazing-based analyses. Using Pearson’s correlation, we compared “simple arithmetic” and “time-bin” averaging to arrive at a single estimate of daily gas flux. For our second objective, we evaluated test period length averaging at 1, 3, 7, and 14 d intervals to determine daily pasture-based emissions estimates under two experimental conditions: herd access to a single AHCS unit vs. two AHCS units. Unlike findings from the confinement-based literature, where slight improvements have been observed, time-bin averaging, compared to simple arithmetic averaging, did not improve gas flux estimation from grazing for CH₄ (p ≥ 0.46) or CO₂ (p ≥ 0.60). Irrespective of experimental condition, i.e., herd access to a single AHCS unit vs. two AHCS units, assessment of variability of diurnal emissions patterns revealed CH₄ flux on pasture had at least half as much variability for the same individuals acclimated in confinement. Using a 7-day test period length interval, aggregating gas flux data at 7 d at a time was adequate for capturing diurnal emissions variation in grazing steers, as no improvement was observed in the percentage of individuals with five of six time bins measured for a 14-day test period length interval. This analysis should provide insights into future research to standardize AHCS data preprocessing across experiments and research groups.

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.

Three experiments were conducted to evaluate the effects of narasin inclusion on the growth performance of grazing beef cattle under similar forage availability and quality. All three experiments were arranged in a randomized complete block design according to the initial BW. Exp 1: 200 Nellore calves (initial BW = 177 ± 15 kg) were randomly allocated in three treatments for 84 d during the rainy season: (1) CONT: mineral supplement; (2) 1400 N: 1400 mg of narasin/kg of supplement; and (3) 2100 N: 2100 mg of narasin/kg of supplement. Narasin inclusion increased (p ≤ 0.01) ADG by 0.077 kg/d and final BW by 6.7 kg, with no differences (p ≥ 0.50) between narasin doses. Exp 2: 240 Nellore calves (initial BW = 195 ± 19 kg) were allocated to CONT or N1400 for 112 d during the rainy season. Narasin inclusion increased (p ≤ 0.01) ADG by 0.082 kg/d and final BW by 9.1 kg. Exp 3: 150 Nellore yearlings (initial BW = 332 ± 22 kg) were allocated for 112 d during the dry season: (1) PROT: protein supplement and (2) PROT250: inclusion of 250 mg of narasin/kg of supplement. Narasin inclusion increased (p ≤ 0.04) ADG by 0.048 kg and final BW by 5.3 kg. For all experiments, narasin inclusion did not impact (p ≥ 0.25) supplement intake. Hence, inclusion of narasin in mineral and protein supplements consistently enhances growth performance of grazing beef cattle across different seasons and production stages, without impacting supplement intake, providing an effective nutritional strategy to enhance productivity on tropical pastures.

Three experiments were conducted to evaluate the effects of narasin inclusion on the growth performance of grazing beef cattle under the same availability and quality forage conditions. All three experiments were arranged in a randomized complete block design according to the initial BW of each experiment. Exp 1: Two hundred Nellore calves were allocated in three treatments: 1) CONT: mineral supplement; 2) 1400N: inclusion of 1400 mg of narasin/kg of supplement; and 3) 2100N: inclusion of 2100 mg of narasin/kg of supplement. Narasin inclusion increased (P ≤ 0.01) ADG and final BW, with no effect (P ≥ 0.50) between doses of narasin supplementation. Exp 2: Two hundred and forty Nellore calves were allocated into two treatments: CONT and N1400. The inclusion of narasin increased (P ≤ 0.01) cattle ADG and final BW. Exp 3: One hundred and fifty Nellore yearlings were allocated in two treatments: 1) PROT: protein supplement, and 2) PROT250: inclusion of 250 mg of narasin/kg of supplement. The inclusion of narasin in the protein supplement increased (P ≤ 0.04) cattle ADG and final BW. In conclusion, the inclusion of narasin in mineral and protein supplements increased the growth performance of cattle on tropical pastures without changing supplement intake.