Abstract #T224

# T224
Plane of nutrition affects muscle fiber hypertrophy and satellite cell activity in neonatal bull calves.
Jennifer S. Bradley*1, Meghan E. MacGhee1, Sarah R. McCoski1, Amanda M. Reeg1, Alan D. Ealy1, Sally E. Johnson1, 1Virginia Polytechnic Institute and State University, Blacksburg, VA.

Muscle growth in newborn calves is a product of protein accretion concomitant with addition of nuclei to the muscle fiber. The objective of the experiment was to examine the effect of diet on live animal performance, muscle fiber hypertrophy and satellite cell activity in young calves. Neonatal Holstein bull calves were fed either a high nutritional plane (HNP; 27% CP, 10% fat) or low nutritional plane (LNP; 20% CP, 20% fat) milk replacer. Daily intake of GE for the LNP group was 50% of HNP, but exceeded the NRC requirement for NEm and NEg. Groups of HNP (n = 4) and LNP (n = 4) were slaughtered at 2, 4 and 8 wk. The LM was removed for fiber morphometric evaluation and satellite cell isolations. Data were analyzed by ANOVA using PROC GLM for the main effects of diet and time and their interaction. Calves fed HNP gained more (P < 0.05) BW at 2, 4 and 8 wks than LNP with the largest difference at 8 wks (HNP = 749 g/d, LNP = 134 g/d, pooled SEM = 0.05). Fiber cross-sectional area was larger (P < 0.05) in HNP than LNP at 8 wk (1502 ± 242 μm2 vs. 356 ± 25 μm2). The numbers of Pax7 immunopositive satellite cells per fiber did not differ (P > 0.05) between the groups with time or diet. Satellite cell isolates were cultured in growth media and pulsed for 2 h with EdU, a thymidine analog, to measure proliferation rate. Isolates from HNP at 2 wks contained a greater (P < 0.05) percentage of proliferating cells during log phase growth than LNP at equal cell densities (51.7 and 35.2%, respectively, SEM = 2.1). At 4 wks, the percentage of proliferating HNP satellite cells was less (P < 0.05) than that of LNP isolates (21.5 vs. 39.1%, SEM = 1.6) and tended (P = 0.10) to remain lower at 8 wk. No differences were observed in the numbers of myofibers formed from HNP or LNP satellite cell isolates. These results demonstrate that calves fed a higher plane of nutrition gain more weight and experience greater muscle fiber hypertrophy than calves fed at a lower level. The larger HNP fiber may be attributed to greater satellite cell proliferation and their subsequent fusion into the adjacent fiber.

Key Words: muscle fiber, hypertrophy, Pax7