| dc.description.abstract | Although it has been known for some time that the use of multi-stage (MS) incubators results in broiler chicken embryos being exposed to sub-optimal incubation temperatures, they are still quite common in the commercial poultry industry. The impact of sub-optimal incubation temperatures, especially cold conditions, during early-stage incubation (ESI; embryonic day (ED) 4 to 11) while muscle fiber and satellite cell (SC) populations are being established are not well understood. Therefore, an experiment was conducted to determine the impact of hypothermic (COLD; 36.4 °C), standard (CTRL; 37.5 °C), and hyperthermic (HOT; 38.6 °C) incubation temperatures from ED 4 to 11 on muscle fiber hyperplasia and SC heterogeneity from 2 functionally different muscles, Pectoralis major (PM) and Biceps femoris (BF), on ED 18 and at hatch. Ross 708 × Yield Plus broiler breeder eggs (n = 2,160) were incubated at 37.5 °C from ED 0 to 3. On ED 4, COLD incubator setpoints were decreased to 36.4 °C, HOT incubator setpoints were increased to 38.6 °C, and CTRL incubators remained 37.5 °C (n = 2 incubators per treatment). On ED 11, all incubators were set to 37.5 °C until ED 18 when eggs were transferred to hatchers. At transfer (ED 18) and hatch (ED 21), PM and BF muscle samples were collected from 6 chicks per treatment. Samples from both muscles from each bird were immunofluorescence stained with two different primary antibody strategies to facilitate taxonomy of SC populations expressing the myogenic regulatory factors and SC markers, Myf5, MRF4, and MyoD or Myf5, Pax7, MyoD by fluorescence microscopy for strategy 1 and 2 respectively. Data were analyzed as a 1-way ANOVA with the GLIMMIX procedure of SAS. A complete pairwise mean comparison was performed using the PDIFF option and means were considered significantly different when P ≤ 0.05. The thermal variation (TV) treatments applied during ESI did not impact (P > 0.05) SC expression of Pax7(+), Myf5(+), MyoD(+),
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Pax7(+):Myf5(+), Pax7(+):MyoD(+), Myf5(+):MyoD(+), or Pax7(+):Myf5(+):MyoD(+) in the BF muscle of chicks on ED 18 or ED 21 nor in the PM muscle on ED 18. On ED 21, chicks from the HOT incubators had a higher number of MRF(-) external nuclei (P = 0.0431) in the PM muscle than chicks from the CTRL treatment. Although the Type 3 fixed-effects ANOVA P-value was not significant (P > 0.05), the pairwise means comparisons revealed that in the PM muscle, chicks from the HOT treatment had a higher number of total external nuclei (P = 0.0247) and Pax7(+) SC (P =0.0400) compared with CTRL chicks on ED 21. On ED 18, chicks from the COLD incubators had the highest number of Myf5(+):MyoD(+) SC (P = 0.0255) in the BF muscle. No differences were detected in SC expression of Myf5(+), MyoD(+), MRF4(+), Myf5(+):MyoD(+), Myf5(+):MRF4(+), MyoD(+):MRF4(+), or Myf5(+):MyoD(+):MRF4(+) or number of myonuclei in the PM muscle on ED18 or in the BF muscle at hatch (P > 0.05). Chicks from the HOT and CTRL incubators had a higher number of Myf5(+):MyoD(+):MRF4(+)in the PM muscle than the chicks from the COLD incubators at hatch SC (P = 0.0060). The pairwise mean comparison revealed that the chicks from the HOT incubators had more myonuclei per fiber than chicks from the CTRL treatment at hatch (P = 0.0392). The CTRL chicks had the highest number of muscle fibers per mm2 in the PM muscle at hatch indicating that CTRL chicks also had the smallest muscle fiber cross-sectional area (CSA; P = 0.0151). This data shows that myogenesis of 2 functionally different, economically important muscles of broiler chicken embryos is altered by TV during ESI and highlights the importance of proper incubation management. Further work is needed to better understand the mechanisms responsible for the observed changes in muscle fiber morphometrics and SC heterogeneity and how these changes may impact post-hatch muscle growth potential. | en_US |
