Atmospheric ammonia alters lipid metabolism‐related genes in the livers of broilers (Gallus gallus)
Atmospheric ammonia has been recognised as the main aerial contaminants in the poultry houses. In many countries, the limit of ammonia exposure is 25 ppm for an 8‐h working day for staff and for the living environment of livestock. The recommended ammonia threshold in pullet and layer houses is 25 ppm (18 mg/m3) (United Egg Producers (UEP), 2016), and NOISH's guidelines for 8‐hr average and short‐term (15 min) exposure limits for workers are 25 ppm (18 mg/m3) and 35 ppm (27 mg/m3) respectively (NIOSH, 2016). According to European regulations, occupational exposure limit values are set to 20 ppm and 14 mg/m3 of ammonia for 8‐h exposure. In France, the limit is 10 ppm or 7 mg/m3 of ammonia (Nimmermark, Lund, Gustafsson, & Eduard, 2009). The limiting level of ammonia for poultry is under 20 ppm (15 mg/m3) in China. The temperature, air flow rate and air velocity around the manure affected the amount of ammonia released in poultry houses. A Swedish study of 18 randomly selected laying hen flocks in floor systems revealed that most houses exceeded 25 ppm ammonia and in some cases went up to 80 ppm (Nimmermark & Gustafsson, 2005). Zhao, Shepherd, Li, and Xin (2015) reported that daily mean ammonia concentrations exceeded 25 ppm on winter days in the aviary house. Li, Wen, Alphin, Zhu, and Zhou (2017) reported that the average ammonia concentration in the litter house was 10.44 ppm while in the netting house was 15.02 ppm when the same ventilation strategy was used. In some cases, the levels of ammonia are approximately 50 ppm and may reach 200 ppm in poorly ventilated poultry houses, particularly during winter season (Carlile, 1984). High level of ammonia can severely impact broiler growth performance (Shlomo, 2004), may augment disease risk and interfere with animal welfare (Miles, Branton, & Lott, 2004). Previous studies in our laboratory have shown that high levels of ammonia triggered chronic hepatic dysfunction, produced oxidative stress and influenced intestinal immunity and histomorphology (Wei et al., 2014; Zhang et al., 2015). In a recently published study, Yi et al. (2016) found that high concentrations (75 ppm) of ammonia altered body fat distribution of broilers. They also identified a total of 267 differentially enriched genes in breast muscle in broilers exposed to high and low concentrations of ammonia using RNA‐Seq. Most of these promising candidate genes were involved in steroid biosynthesis (gga00100) and peroxisome proliferator‐activated receptor (PPAR) signalling pathway (gga03320), which both participated in the lipid metabolism processes. These results indicated that high level of ammonia can modulate the lipid metabolism of broilers. However, the effects of lower concentration of ammonia on body fat distribution of broilers are unknown. This study was to investigate the effects of different levels of ammonia on the growth performance, body fat distribution, serum metabolites and lipid metabolism gene expression of broiler chickens.