Effects of Foliar Application of Nano-molybdenum Fertilizer on Copper Metabolism of Grazing Chinese Merino Sheep (Junken Type) on Natural Grasslands Under Copper and Cadmium Stress

In recent decades, the groundwater contaminated by mineral development and metal smelting has seriously polluted natural grasslands, resulting in heavy metal residues in soils and forages exceeding the standard, especially copper (Cu) and cadmium (Cd). After animals intake contaminated forages, heavy metals may accumulate in animal tissues and threaten human health through the food chain. Previous studies found that molybdenum (Mo) fertilizer from ammonium molybdate or potassium molybdate could alleviate the decrease of antioxidant capacity caused by heavy metal poisoning, but the application of nano-Mo fertilizer in sheep is still lacking. To investigate the effects of nano-Mo fertilizer on Cu metabolism of grazing Chinese Merino sheep (Junken Type) on natural pastures under Cu and Cd stress, fertilizing experiment was carried out in the Bayanbulak Grassland in the northwest of Xinjiang Uygur Autonomous Region, China. A total of 24 hm² fenced grassland contaminated by heavy metals was randomly divided into four groups (3 replications/group and 2 hm²/replication). The experimental groups were applied 0 g Mo, 100 g Mo, 200 g Mo, and 300 g Mo per hectare for the control group, group I, group II, and group III, respectively, through foliar spraying fertilization. A total of 72 Chinese Merino sheep (1 year old, 43.8 ± 2.3 kg) grazing on polluted natural grasslands, with 18 sheep per group, were randomly assigned to the experimental pastures for 30 days. The results showed that the Mo content in soil in group II and group III nwas higher than that in the control group (P < 0.05); the Cd content in soil in group II and group III was lower than that in the control group (P < 0.05), and the Cu content in soil in fertilized pastures was lower than that in the control group (P < 0.05). The Mo content in herbage in fertilized pastures was higher than that in the control group (P < 0.05), and the content of Cu in herbage in fertilized pastures was lower than that in the control group (P < 0.05). The contents of iron (Fe) and Mo in blood and liver of grazing animals from fertilized pastures were higher than that in the control group (P < 0.05). The Cd content in blood of grazing animals in group II and group III was lower than that in the control group (P < 0.05). The Cu content in blood and liver of grazing animals in fertilized pastures was lower than that in the control group (P < 0.05). The content of selenium (Se) in blood of grazing animals in group II and group III was higher than that in the control group (P < 0.05). The levels of blood including hemoglobin (Hb), erythrocyte count (RBC), and packed cell volume (PCV) in group II and group III were higher than that in the control group (P < 0.05). The white blood cell (RBC) count in group II and group III was lower than that in the control group (P < 0.05). The activities of serum superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and ceruloplasmin (Cp) in group II and group III were higher than that in the control group (P < 0.05). The content of malondialdehyde (MDA) in group II and group III was lower than that in the control group (P < 0.05). In conclusion, the application of nano-Mo fertilizer on Cu- and Cd-contaminated grasslands changed the contents of mineral elements in soil, forage, and blood of grazing sheep, improved the antioxidant capacity, affected the Cu metabolism of grazing Chinese Merino sheep caused by Cu and Cd pollutions, and alleviated the toxic damage of heavy metal pollutions.