Atmospheric Ammonia Affects Myofiber Development and Lipid Metabolism in Growing Pig Muscle

Ammonia, an aerial pollutant in animal facilities, affects animal health. Recent studies showed that aerial ammonia negatively impacts meat quality but the mechanism remains unknown. To understand how ammonia drives its adverse effects on pig meat quality, 18 crossbred gilts were exposed to 0, 10 or 25 mg/m³ ammonia for 25 days. Ammonia exposure increased fat content in the Longissimus dorsi muscle, and meat color got lighter after 25 mg/m³ ammonia exposure. Analysis of MyHC isoforms showed an increased MyHC IIx but decreased MyHC I after ammonia exposure. Besides, muscular glutamine decreased significantly as aerial ammonia increased. Although hyperammonemia was reported to upregulate MSTN and inhibit downstream mTOR pathway, no changes have been found in the mRNA expression level of MSTN and protein expression level of mTOR signal pathway after ammonia exposure. RNA-Seq showed that 10 mg/m³ ammonia exposure altered genes related to myofiber development (MyoD1, MyoG), whereas 25 mg/m³ ammonia affected genes associated with fatty acid synthesis and β-oxidation (SCD, FADS1, FASN, ACADL). Collectively, our findings showed aerial ammonia exposure appears to regulate myofiber development and lipid metabolism in the skeletal muscle, which results in the negative impacts on meat quality in pigs.