|PAYNE, JASON - University Of Georgia|
|ELLESTAD, LAURA - University Of Georgia|
Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2020
Publication Date: 3/2/2020
Citation: Payne, J.A., Proszkowiec-Wegla, M.K., Ellestad, L.L. 2020. Delayed access to feed alters gene expression associated with hormone signaling, cellular differentiation, and protein metabolism in muscle of newly hatch chicks. General and Comparative Endocrinology. https://doi.org/10.1016/j.ygcen.2020.113445.
Interpretive Summary: In the current broiler production systems, chicks are deprived of food and water for up to 72 hours due to uneven hatching, hatchery procedures such as sexing, sorting, selection and vaccination, and transportation time to destination farms. Lack of access to feed during the first 48-72 hours results in lower body and organ weight, higher feed conversion ratio (amount of feed required for 1kg of body weight gain) and mortality, delayed growth rate and gastrointestinal tract development. The best growth and development of any organism can be achieved only when the energy and nutrient needs are met. Immediately after hatch, chicks depend on lipid-rich nutrients that are stored in yolk sack to provide nutritional support. After chicks are supplied with post-hatch feed they transition to utilization of carbohydrate-rich diets. Little is known about the effects of a delayed feed access post-hatch on expression of genes related to hormonal signaling, overall body growth and differentiation of muscle tissues in broiler chickens. Therefore, the aim of the present study was to characterize the expression pattern of genes associated muscle growth during the first two weeks post-hatch in chickens that were fed or had delayed access to feed. To mimic commercial settings, newly hatched chicks were subjected to 48 hours delay in feeding or fed immediately after hatch. We have determined that delay in post-hatch feeding: 1) alters hormonal signaling in muscle, 2) interrupts muscle tissue differentiation, 3) postpones onset of growth and 4) may lead to increased protein catabolism in muscle. In summary, we have shown, that delayed access to feed post-hatch negatively impacts carbohydrate and amino acid utilization in newly hatched chicks. These processes could ultimately contribute to a reduction in proper growth and development of broiler chickens and attenuate the long-term potential of muscle accretion in meat-type chickens.
Technical Abstract: Birds rely solely on utilization of the yolk sac as a means of nutritional support throughout embryogenesis and early post-hatch, before first feeding occurs. Newly hatched broiler (meat-type) chickens are frequently not given immediate access to feed, and this can result in numerous alterations to developmental processes, including those that occur in muscle. The objective of this study was to characterize the gene expression profile of newly hatched chicks’ breast muscle with regards to hormonal regulation of growth and metabolism and development and differentiation of muscle tissue, and determine impacts of delayed access to feed on these profiles. Within 3 hours of hatch, birds were placed in battery pens and given immediate access to feed (Fed) or delayed access to feed for 48 hours (Delayed Fed). Breast muscle collected from male birds at hatch, or 4 h, 1 day (D), 2D, 4D, and 8D after hatch was used for analysis of mRNA expression by reverse transcription-quantitative PCR. Under fully fed conditions, insulin-like growth factor receptor and leptin receptor mRNA expression decreased as birds aged; however, delayed access to feed resulted in prolonged upregulation of these genes so their mRNA levels were higher in Delayed Fed birds at 2D. These expression profiles suggest that delayed feed access alters sensitivity to hormones that may regulate muscle development. Myogenin, a muscle differentiation factor, showed increasing mRNA expression in Fed birds through 2D, after which expression decreased. A similar expression pattern in Delayed Fed birds was deferred until 4D. Levels of myostatin, a negative regulator of muscle growth, increased in Fed birds starting at 2D, while levels in Delayed Fed birds began to increase at 4D. In Fed birds, levels of transcripts for two genes associated with protein catabolism, F-box protein 32 and forkhead box O3, were lower at 2D, while Delayed Fed mRNA levels did not decrease until 4D. Mechanistic target of rapamycin mRNA levels decreased from 1D through 8D in both treatments, except for a transient increase in the Delayed Fed birds between 1D and 2D. These data suggest that within breast muscle, delayed feeding alters hormonal signaling, interrupts tissue differentiation, postpones onset of growth, and may lead to increased protein catabolism. Together, these processes could ultimately contribute to a reduction in proper growth and development of birds not given feed immediately after hatch, and ultimately hinder the long-term potential of muscle accretion in meat type birds.