# Study on the Development and Formation Specifics of Longissimus Dorsi Muscles in Ziwuling Black Goats

## TL;DR

This study examines how muscle development in Ziwuling black goats changes with age and how it affects meat quality.

## Contribution

The study identifies age-related changes in muscle structure and gene expression that influence meat quality in Ziwuling black goats.

## Key findings

- 6-month-old goats have higher myofiber density and more fast-twitch myofibers compared to 12-month-olds.
- Transcriptome analysis revealed 387 differentially expressed genes linked to muscle growth and metabolism pathways.
- 12-month-old goats show myofiber hypertrophy and increased slow-twitch fibers, suggesting optimal meat quality at this age.

## Abstract

This study aimed to clarify the relationship between muscle development and meat quality in Ziwuling black goats. We used the longissimus dorsi muscle of 6-month-old and 12-month-old goats as samples, and analyzed muscle structure, myofiber type transformation, and molecular regulation via HE staining, fast–slow myofiber immunofluorescence double staining, and transcriptome sequencing. Results showed that compared with 12-month-old goats, 6-month-old goats had higher myofiber density, smaller myofiber diameter, and more fast-twitch myofibers (Type II); in contrast, 12-month-old goats exhibited myofiber hypertrophy (larger diameter) and an increase in slow-twitch myofibers (Type I). Transcriptome sequencing identified 387 differentially expressed genes (DEGs: 156 upregulated, 231 downregulated). GO analysis indicated DEGs were involved in processes such as skeletal muscle growth and cAMP biosynthesis, while KEGG analysis showed DEGs were enriched in arginine–proline metabolism (related to muscle maturation) and AMPK/MAPK signaling pathways (AMPK regulates fatty acid metabolism genes like ACACB/CPT1A). Additionally, WGCNA clustered genes into nine modules, with key modules (e.g., MEblue, MEgreen) correlating with myofiber density, diameter, and MAPK/AMPK pathways. In conclusion, we recommend focusing on protein nutrition at 6 months (to promote myofiber proliferation) and regulating energy intake at 12 months (to improve meat quality); 12 months of age is determined as the optimal slaughter age for Ziwuling black goats.

To clarify the relationship between muscle development and meat quality in Ziwuling black goats, this study used the longissimus dorsi muscle of 6-month-old and 12-month-old goats as samples. With HE staining, fast–slow myofiber immunofluorescence double staining, and transcriptome sequencing, this study analyzed muscle structure, myofiber type transformation, and molecular regulation. Results showed that 6-month-olds had higher myofiber density and smaller diameter; 12-month-olds showed myofiber hypertrophy (larger diameter); immunofluorescence revealed more fast-twitch myofibers (Type II) at 6 months and increased slow-twitch ones (Type I) at 12 months. Transcriptome sequencing identified 387 differentially expressed genes (DEGs: 156 upregulated, 231 downregulated). GO analysis indicated that DEGs are involved in skeletal muscle growth, cAMP biosynthesis, etc.; KEGG analysis showed enrichment in arginine–proline metabolism and AMPK/MAPK signaling pathways (AMPK regulates fatty acid metabolism genes like ACACB/CPT1A; arginine–proline metabolism relates to muscle maturation). WGCNA clustered genes into nine modules (MEblue correlated with myofiber density/MAPK; MEgreen correlated negatively with diameter but positively with density, involving PPARGC1A/AMPK). In conclusion, protein nutrition at 6 months (promote myofiber proliferation) and regulating energy intake at 12 months (improve meat quality) are recommended, and 12 months is the optimal slaughter age.