236 Assessment of Early-Stage Thermal Manipulation on Broiler Chicken Muscle Satellite Cell Populations at Transfer and Hatch

Abstract Multi-stage hatching egg incubators are challenging to manage but still common throughout the US broiler industry. It is difficult to satisfy all embryonic temperature requirements in systems where late-stage embryos must be kept from overheating while ensuring early-stage embryos are not at sub-optimal temperatures. Our previous work showed improvements in performance and meat yield when incubation temperature was increased to 38.6 °C from embryonic day (ED) 4 to 11 as opposed to lowering it to 36.4 °C compared with a 37.5 °C control. The objective of this work was to assess the effect of thermal variation (TV) during early-stage incubation (ESI) on muscle satellite cell (SC) heterogeneity in broiler chicks at transfer and hatch to explore the mechanism responsible for increased meat yield in our previous study. Broiler breeder eggs (n = 2,160) were incubated at 37.5 °C from embryonic day (ED) 0 to 3. On ED 4, COLD incubator set points decreased to 36.4 °C, HOT incubator set points increased to 38.6 °C, and control 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), pectoralis major (PM) and biceps femoris (BF) muscle samples were collected from 6 chicks per treatment. Samples were immunofluorescence stained to facilitate taxonomy of SC populations expressing the myogenic regulatory factors and SC markers, MyoD, MRF4, and Myf5, by fluorescence microscopy. Data were analyzed as a 1-way ANOVA with the GLIMMIX procedure of SAS. Means were separated at P ≤ 0.05 with the PDIFF option. Tendencies were declared when 0.0501 ≤ P ≤ 0.10. Chicks from COLD incubators had the greatest density of MyoD+:Myf5+ SC in their BF (P = 0.0261) and tended to have a greater density of MyoD+:MRF4+ SC in their PM muscle (P = 0.0562) compared with chicks from HOT incubators. On ED 21, chicks from HOT incubators had the greatest density of MyoD+:MRF4+:Myf5+ SC in their PM muscle (P = 0.0406). Temperature gradients as small as 1.1 °C during ESI altered BF SC populations in chicks at transfer and PM SC populations at both transfer and hatch. Overall, these results indicate that TV during ESI can influence SC population kinetics in both PM and BF muscles of modern, fast-growing, high-yielding broiler chicks at ED 18 and 21. Further investigation is needed to understand the longer-term effects on SC populations and the cell signaling