237 Evaluation of Thermal Variation During Early-Stage Incubation on Broiler Chicken Pectoralis Major Muscle Satellite Cell Mitotic Activity and Heterogeneity at 28 Days Post-Hatch

Abstract

Abstract Muscle satellite cells (SC) have an essential role in post-hatch skeletal muscle growth. To evaluate the effects of thermal variation (TV) during early-stage incubation (ESI) on Pectoralis major (PM) muscle SC heterogeneity of broiler chickens reared to 28 d post-hatch a randomized complete block design experiment with a 3 × 2 factorial treatment structure was conducted. Yield Plus × Ross 708 broiler breeder eggs (n = 2,160) ranging from 54 to 59 g were allotted equally by weight into 90-egg trays (n = 4 trays per incubator). All eggs were pre-warmed at 24 °C for 8 h and incubated at 37.5 °C from embryonic day (ED) 0 to 4. From ED 4 to 11, eggs were incubated at 1 of 3 temperatures (n = 2 incubators per TV treatment); 37.5 °C (CTL), 36.4 °C (COLD), or 38.6 °C (HOT). On ED 11, all incubators were returned to the CTL (37.5 °C) set point until ED 18. On ED 18, all eggs were transferred to baskets in hatchers set to 36.7 °C. After 514 h of incubation, all chicks were removed simultaneously, vent sexed, and weighed. Chicks were randomly allotted to floor pens (6 pens per treatment per sex) blocked by location and reared on a common diet. On d 28, birds (n = 10 per TV x sex treatment) were injected with bromodeoxyuridine (BrdU) before PM sample collection. Cryosections were immunofluorescence stained to facilitate taxonomy of SC populations expressing the myogenic regulatory factors Pax7 and MyoD as well as the proliferation marker BrdU by fluorescence microscopy. Data were analyzed as a 2-way ANOVA using SAS PROC GLIMMIX with TV treatment and broiler sex as main effects. Means were separated with the PDIFF option at P ≤ 0.05. Tendencies were declared when 0.0501 ≤ P ≤ 0.10. A TV × sex interaction was observed only for the MyoD+: Pax7+ SC density (P = 0.0232); however, none of the pairwise mean comparisons were significant at P < 0.05. Though CTL male and COLD female chicks had twice the density of MyoD+:Pax7+ SC as CTL females (P = 0.0535) and HOT males (P = 0.0645), respectively. There is no clear explanation for this observation. There were no interactive or main effects on density of MyoD+, Pax7+, MyoD+:BrdU+, Pax7+:BrdU+, MyoD+:Pax7+:BrdU+ SC (P ≥ 0.1258) or nuclear density (P = 0.1017) in 28-d-old broilers. These data suggest that if TV during ESI impacts SC myogenic regulatory factor heterogeneity and mitotic activity in broilers, the effects have concluded by d 28 post-hatch in commercial broilers. Further exploration of earlier time points will be necessary to determine whether the previously observed effects of TV during ESI on growth performance and meat yield are SC-mediated post-hatch.