Effects of dietary supplementation with cysteamine on growth performance, rumen microflora, and endogenous hormones levels in Hu lambs

Cysteamine (CS) is known for its ability to elevate the concentration of growth hormone and thereby promote animal growth. This study was conducted to determine the effects of CS on growth performance, apparent nutrient digestibility, ruminal fermentation and bacterial community, endogenous hormone concentration and the expression of their receptors of Hu lambs during the whole feeding period. Thirty-six healthy male Hu lambs with similar age (75 ± 10 d) and initial body weights (20.3 ± 0.3 kg) were selected and randomly divided into 2 groups, including a CON group and a CS group. The CON group was fed with the basal diet, and the CS group was fed 20 mg/kg BW cysteamine added to the basic diet. The results showed that the addition of CS to the diet had no effects (P > 0.05) on growth performance, slaughter performance, apparent nutrient digestibility, rumen fermentation characteristics, rumen bacterial diversity, growth hormone axis and related hormone receptors of lambs. Furthermore, dietary CS supplementation increased (P ＜ 0.05) hypophysis luteinising hormone concentrations and tended to increase hypophysis growth hormone (P = 0.09) and induced serum testosterone concentrations (P = 0.06). Analysis of rumen bacterial diversity revealed no differences in ACE and Chao1, but the Simpson and Shannon indices were lower in the CS group (P < 0.01), indicating reduced bacterial diversity. Community composition was dominated by Bacteroidetes and Firmicutes, with CS supplementation decreasing the relative abundance of Ruminococcaceae_UCG_014 and Rikenellaceae_RC9_gut_group. Our study demonstrates that supplementation of 20 mg/kg body weight cysteamine did not affect the growth performance, rumen fermentation and nutrient apparent digestibility of Hu lambs under house feeding conditions, but exerts effects on the secretion of reproductive hormones within the hypothalamic-pituitary-gonadal axis.