| dc.description.abstract | Thermal variation (TV) occur in both multi-stage and single-stage incubators under commercial settings, and slight variation from optimal during late-stages of incubation (LSI), while embryonic muscle fibers and satellite cells (SC) are being established, result in detrimental effects on body weight (BW), body weight gain (BWG), feed conversion ratio (FCR) and carcass characteristics. Additional reductions in average Pectoralis major (PM; breast) weight and responses in breast meat yield highlight the economic importance of optimal incubation temperatures. Therefore, to better understand the cellular and molecular mechanisms behind these post-hatch responses in muscle growth, an experiment was conducted applying TV during LSI (embryonic day (ED) 11 to 18). In which growth performance, PM muscle growth characteristics and SC activity were assessed over time post-hatch. Yield Plus × Ross 708 broiler breeder eggs (n = 2,160) were incubated at 37.5 °C from ED 0 to 11. On ED 11 COLD incubator setpoints were decreased to 36.4 °C, CTRL incubators remained 37.5 °C, and HOT incubator setpoints were increased to 38.6 °C (n = 2 incubators per treatment). At transfer (ED 18), all incubators were set to 36.7 °C until hatch. Chicks were pulled simultaneously from hatchers by treatment and were allotted to floor pens with 45 birds per pen (n = 2 pens per TV treatment). On d 7, 14, 21, and 28, Bird BW was recorded and the whole left PM and muscle sample tissue from the right PM muscle were collected and stored for cryohistological and immunofluorescence analysis. Data were analyzed as a 1-way (TV) or 2-way (TV × sex) ANOVA with the GLIMMIX procedure of SAS (v9.4). Means were separated with the PDIFF option at P ≤ 0.05. Tendencies were declared when 0.0501 ≤ P ≤ 0.10. No interaction between TV treatment and sex were observed, therefore only results for TV treatment as a main effect are reported. Birds from COLD incubators were the lightest compared to the HOT group on d 7 (P = 0.015) and tended to be lighter than the CTL on d 14 (P = 0.069). Similarly, both COLD and CTL birds gained the least weight at 7 d of age compared to the HOT treatment (P < 0.001) and tended to gain the least weight compared to CTL birds on d 14 (P = 0.075). PM muscle weight was reduced by COLD temperatures during LSI at 7 d post-hatch compared to HOT temperatures (P = 0.022). On d 21 COLD birds continued to have the smallest PM muscle weight compared to CTL and HOT groups (P = 0.033). When looking at PM growth characteristics, the average PM muscle fiber cross sectional area (CSA) of COLD birds tended to be smaller than those from the HOT group (P = 0.056). Similarly, both COLD and CTL birds had smaller fibers compared to HOT birds at d 21 post-hatch (P = 0.027). As expected, inversely proportional to these results, birds incubated under hypothermic conditions had higher fiber densities compared to HOT birds at 14 (P = 0.0049) and 21 (P = 0.0044) d of age. These changes in average PM fiber CSA also reflected in fiber size distribution, with HOT birds having lower proportion of small fibers on d 7 (P = 0.010) and higher proportion of big fibers on d 21 (P = 0.047). No differences amongst TV treatments were observed on total nuclei, MRF+ SC, mitotically active MRF- cells, total MRF+ mitotically-active, total MRF+ SC, and total mitotically active cell population densities at any sampling point (d 7, 14, 21, and 28). Higher densities of mitotically active SC expressing Pax7 (Pax7+:BrdU+) were observed in PM muscle tissue from HOT birds at 28 d of age, both on a per mm2 (P = 0.038) and a per 1000 fibers (P = 0.036), while the rest of mitotically-active MRF+ SC categories remained similar amongst TV treatment over time. TV during LSI result in changes on post-hatch PM muscle growth characteristics. However, these results present no evidence for these changes to be SC-mediated. | en_US |
