30 Prenatally Stressed Brahman Bull Calves had Increased Pro-Inflammatory Cytokines and Transportation-Induced Mitochondrial Impairments

Abstract

Abstract Prenatal transportation stress has been reported to alter behavior and adrenal glucocorticoid secretion in calves; however, the impact on mitochondrial and inflammatory responses to an industry-relevant stressor have not been explored. Sixteen Brahman bull calves were used to test the hypothesis that calves previously stressed by transportation in utero (PNS; n = 8; mean ± SD, 654 ± 71 kg, 11.7 ± 0.4 months) would have impaired mitochondrial capacity and greater plasma concentrations of two pro-inflammatory cytokines [interleukin (IL)-6 and tumor necrosis factor (TNF)-a] following a 3-hr transportation stressor compared with calves that experienced no prenatal stress (CON; n = 8; 645 ± 90 kg, 11.8 ± 0.5 months). Longissimus thoracis muscle samples were collected from calves, pre-transportation, and 6- and 24-hour post-transportation and were analyzed for citrate synthase activity (CS) as a marker of mitochondrial volume density and for mitochondrial oxidative phosphorylation (P) and electron transport (E) capacities via high resolution respirometry. Plasma was collected pre-transportation and post-transportation at hour 0, 1, 6, 24, and 48 for analysis of cytokine concentrations using custom MesoScale Discovery U-Plex kits. Data were analyzed using PROC MIXED with repeated measure (time) in SAS v9.4 with time, treatment, and time × treatment as fixed effects. Integrative (relative to tissue wet weight) E with complex II only (ECII), intrinsic (relative to CS) ECII, the contribution of P with complex I (PCI) to total E (flux control ratio, FCRPCI), and FCR ECII decreased from pre- to 6 hour post-transport (P ≤ 0.04) and remained suppressed at 24 hour post-transport (P ≤ 0.02) in all animals regardless of prenatal treatment. Integrative PCI was also decreased 24-hour post-transportation compared with pre-transport (P = 0.02). Intrinsic ECII tended to be greater in CON than PNS bulls overall (P = 0.07). Intrinsic Leak, integrative Leak, and FCR Leak tended to be impacted by the interaction of treatment and time (P ≤ 0.10) whereby all 3 measures were greater in PNS than CON bulls at 6-hour post-transport (P ≤ 0.02) but were similar between treatments at 24-hour post-transport. Both plasma IL-6 and TNF-a were greater in PNS than CON bulls overall (P ≤ 0.008) but neither cytokine was affected by postnatal transport. Bull calves subjected to prenatal transportation stress had sustained increased plasma pro-inflammatory cytokine concentrations and an increase in mitochondrial leak with a decrease in complex II supported electron transfer following a single postnatal transportation stressor. Importantly, the postnatal stressor utilized in this study did not affect plasma cytokines. A more stressful postnatal stimulus may provide a clearer assessment of potential impacts of prenatal stress on the progeny’s physiological responses to stress.