Influence of Megasphaera elsdenii and starch exposure on transdifferentiation of mesenchymal stem cells in early-weaned, lightweight beef steers

The objective of this study was to evaluate the effect of supplementing aggressive energy diets with Megasphaera elsdenii NCIMB 41125 (M. elsdenii culture; Lactipro NXT; MS Biotec Inc., Wamego, KS) on satellite cell differentiation. Approximately 4 month old, crossbred Simmental ×Angus steers (N = 36) were blocked into 2 body weight groups and randomly assigned to 1 of 3 diet treatments: 1) Control (CTRL) - fed exclusively a 35% roughage diet; 2) Aggressive (NO-LAC) - fed a blend of a 10% roughage and 35% roughage diets; 3) M. elsdenii culture (LAC), fed AGR and drenched with 20 mL of M. elsdenii NCIMB 41125, 1 x 1010 CFU/mL on d 1. Steers [N = 36 (6/pen × 2 weight blocks × 3 treatments)] assigned to the same weight block and treatment were fed in the same pen for 274 d. Muscle biopsies were collected throughout the feeding period and just prior to harvest to measure satellite cell differentiation and fiber typing. Carcass traits were obtained at slaughter, and shear force was measured on steaks from the longissimus muscle. For satellite cell imaging, myonuclei, myogenic factor 5 (MYF5), paired box protein 7 (PAX7) and dual positive (Dual+) of MYF5 and PAX7 were evaluated. For fiber typing, overall mean cross-sectional area (CSA), mean myosin heavy chain (MHC) Type I CSA, mean MHC Type IIA CSA and mean MHC Type IIX CSA were obtained. Data were analyzed as a one-way ANOVA with block included as a random effect. Animal was also included as random effect to account for repeated measure when day, treatment and day x treatment were included in analyses for histology. Feeding strategies was contrasted as a secondary evaluation where diet was the fixed effect, regardless of probiotic treatment and weight block considered a random effect. Significant differences were established at alpha value of P = 0.05 and tendencies at P = 0.10. Differences (P < 0.05) were observed on performance parameters intermittently during the feeding trial for AGR versus CTRL. Harvest performance revealed that the NO-LAC steers tended to have greater ( P = 0.09) amounts of marbling than that of LAC and CTRL steers. Proximate fat analysis confirmed marbling scores by showing that NO-LAC steers tended to have greater (P = 0.10) percent fat than LAC and CTRL steers. No treatment difference (P > 0.05) was observed for slice and Warner-Bratzler shear force. Consistent numerical increases in numbers of myonuclei, MYF5, PAX7 and Dual+ for CTRL were observed for the first 112 days on feed, after which AGR fed steers increased in those same factors. AGR fed steers had a numerically greater cross-sectional area for all muscle fiber types (MHC Type I, IIA, IIX). This study shows data from satellite cell imaging and fiber typing information expected, but not well studied on light weight beef calves entering directly into the feedlot setting on a high concentrate diet.

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