Effects of letrozole supplementation on growth performance, plasma hormones, and plasma metabolites in weaned female lambs of Turpan black sheep

This study investigates how adding letrozole (LE) to the diet affects the growth, blood hormones and metabolites, rumen fermentation, and gut microbes of weaned female Turpan Black sheep. The results could help guide strategies to enhance female growth and open new avenues for research. The study selected 60 weaned female lambs of the Turpan Black sheep breed, aged 2 months, with an average body weight of (19.93 ± 0.46) kg and in good health, which were randomly divided into the Con group (baseline diet), the 0.1 LE group (baseline diet + 0.10 mg/kg BW −1 ), and the 0.2 LE group (baseline diet + 0.20 mg/kg BW −1 ), with 20 lambs in each group. The pre-feeding period lasted 5 days, and the main feeding period lasted 75 days. The results showed that 0.2 LE group significantly improved total weight gain, body length and chest girth ( P < 0.05), and markedly increased plasma GH and IGF-1 concentrations ( P < 0.01). On days 15 and 75, plasma LE concentration in the 0.2 LE group was extremely higher than that in the 0.1 LE group ( P < 0.01). Metabolomic analysis indicated that differential metabolites in the 0.1 LE group were mainly enriched in bile acid metabolism, with significant upregulation of estrone, taurocholic acid and fumaric acid ( P < 0.05); while the 0.2 LE group presented altered cholesterol metabolism, accompanied by increased creatine and letrozole levels but decreased estrone and fumaric acid ( P < 0.05). After 75 days of feeding, ruminal LE concentration in the 0.2 LE group was significantly higher than that in the 0.1 LE group ( P < 0.05). All LE supplementation groups had higher rumen volatile fatty acid contents than the control group ( P < 0.05), and the acetate-propionate ratio was higher in the 0.1 LE group relative to the 0.2 LE group ( P < 0.05). LE treatment increased Firmicutes and decreased Bacteroidetes abundance. Within Firmicutes , the families Lachnospiraceae and Eubacteriaceae were higher in relative abundance. The LEfSe analysis showed that Butyrivibrio fibrisolvens was significantly enriched in the 0.1 LE group ( P < 0.05), while Oribacterium was significantly enriched in the 0.2 LE group ( P < 0.05). In conclusion, LE supplementation increased ruminal Lachnospiraceae and Erysipelotrichaceae , elevated butyrate, propionate and other VFAs. These products together with LE modulated bile acid/cholesterol metabolism and plasma hormones, supporting lamb growth. The optimal dose was 0.20 mg/kg BW −1 .