Available phosphorus levels modulate growth performance, serum indices, metabolome, rumen fermentation, and microorganism in Hu lambs

Phosphorus (Pi) is an essential nutrient, which plays an important role in maintaining normal physiological function. Pi deficiency could reduce growth performance and affect health. The aim of this study was to investigate growth performance, serum indices, metabolism and rumen parameters, and microbiota of Hu lambs. For this purpose, a total of 36 healthy 2-month-old Hu lambs were randomly allocated to three groups: low Pi (LP): 1 g/kg; medium Pi (MP): 2 g/kg; high Pi (HP): 3 g/kg. The results indicated that the dry matter intake and average daily gain of Hu sheep increased in HP compared with MP and LP (P < 0.05). In terms of serum indices, there were higher serum concentrations of albumin, alkaline phosphatase, calcium, magnesium, and Pi in HP compared to LP, while blood urea nitrogen was higher in MP than in LP and HP (P < 0.05). At the same time, it has a higher salivary Pi concentration in HP compared to LP (P < 0.05). In addition, serum metabolome was changed, which led to the up-regulating three key pathways in amino acid metabolism in HP (P < 0.05). The concentrations of iso-butyrate and valerate in HP were lower than LP (P < 0.05). The microbial protein of MP was higher than that of HP, and HP was higher than that of LP (P < 0.05). Firmicutes were significantly higher in MP and HP, while Actinobacteriota were more abundant in LP (P < 0.05). Feeding different available phosphorus levels resulted in the changes of growth efficiency that may be associated with differential metabolites and rumen microbiota in Hu lambs. Therefore, the appropriate Pi content should be specifically considered to improve growth performance.