Effects of Phytosterol Licking Blocks on Growth Performance, Serum Biochemical Parameters and Rumen Fermentation in Tibetan Sheep

Phytosterols are plant-derived natural compounds which resemble in structure with cholesterol. It has been demonstrated that phytosterols significantly affect growth regulation and antioxidant capacity in poultry and pigs; however, their role in ruminants remains unclear. This study aimed to investigate the effects of phytosterol lick blocks on growth performance, serum biochemical and rumen fermentation parameters in Tibetan sheep. Fifteen 5-month-old Tibetan sheep (29.16 ± 1.51 kg) were randomly assigned to three treatments: the control (supplemented with no lick blocks, CON), supplemented with basal lick blocks (BLB), or supplemented with phytosterol lick blocks (PLB); The experiment lasted for 64 days including a 14-day adaptation period. Average daily gain (p = 0.011) of Tibetan sheep in the PLB was higher than that in the CON and BLB, while the feed conversion ratio (p = 0.011) was lower. The digestibility of crude protein in the PLB and BLB was higher than that in the CON (p = 0.029). In addition, the PLB had higher total protein levels (p = 0.026) and lower malondialdehyde content (p = 0.037) in serum than other treatments. The activity of glutathione peroxidase (p = 0.040) and superoxide dismutase (p = 0.024) in the PLB was higher than in the CON, but similar to that in the BLB. In terms of rumen fermentation parameters, Tibetan sheep in the PLB had higher microbial crude protein (p = 0.005) and propionate levels (p = 0.015) and had a lower acetate to propionate ratio (p < 0.001). The principal coordinate analysis based on Bray-Curtis distance showed significant separation between the microbial communities of the treatments (p = 0.008), but the alpha diversity did not change among the three treatments. The LEfSe analysis indicated that more bacterial genera were enriched in the PLB than that in the CON and BLB. In summary, the antioxidant capacity of phytosterols has been demonstrated in Tibetan sheep. It may increase the abundance of certain specific bacterial genera to enhance nutrient digestibility, leading to accelerate growth, without altering alpha diversity.