PSVIII-23 - Mycotoxin exposure on fetal skeletal muscle fiber hypertrophy and miRNA transcriptome

The objective of this study was to evaluate the miRNA transcriptome and muscle fiber characteristics of lambs from ewes consuming endophyte-infected tall fescue (E+) seed during two stages of gestation at two animal ages. Pregnant Suffolk ewes (yr 1 n = 36; yr 2 n = 60) were randomly assigned to one of two gestational treatments: E+ seed (1.77 mg/hd/d of ergovaline/ergovalinine) during mid- (gd 35 - 85; MID) or late-gestation (gd 86 – 133/parturition; LATE). Longissimus muscle samples (n = 3/E+ treatment/time) were collected from fetuses on gd 133 (FETAL; expt. 1) or from wethers after finishing to market weight (MKT; expt. 2) from ewes from MID and LATE E+ treatments. Data were analyzed as a 2 x 2 factorial with E+ treatment (MID or LATE), time (FETAL or MKT), and the two-way interaction in the model. Exposure to E+ fescue seed during LATE gestation reduced (P = 0.03) cross-sectional area of Type II muscle fibers at MKT but not at FETAL. Cross-sectional area of Type II muscle fibers were larger (P < 0.05) at MKT than FETAL. Animal age influenced miRNA expression with 120 miRNA differentially expressed. miRNA-22-3p and -29a were down regulated (P < 0.001; > -5 log fold change) with animal age; whereas miR-3958-3p, -410-3p, -299-5p and -487b-3p (P < 0.0001; > 3 log fold change) were up-regulated. Exposure to E+ during MID or LATE gestation did not alter miRNA expression. Muscle fiber hypertrophy increased from FETAL to MKT age altered the expression of miRNA in longissimus muscle.