Dietary cysteamine addition remarkably improved the growth performance and increased carcass protein deposition via inhibiting proteolysis-related genes in feedlot lambs

Abstract

Cysteamine (CS), a metabolic product of coenzyme A in mammals, has been increasingly employed in China as a potential growth promoter in cattle and lamb feedlotting. This study was conducted to investigate the potential effects of CS on apparent nutrient digestibility, rumen methane fermentation, N metabolism, and slaughter performance. The experiment involved 48 male Dorper-Hu hybrid lambs with an initial live body weight of 33.32 ± 0.94 kg. These lambs were assigned to four dietary CS addition treatment groups with diets consisting of foxtail millet silage, corn straw, corn grain, soybean meal rapeseed meal, and different concentrations of CS (0, 20, 40, and 60 mg/kg body weight). The results showed that increasing dietary CS concentrations led to a linear increase in dry matter intake and average daily weight gain, as well as a quadratic increase in the apparent digestibility of dry matter, organic matter and crude protein (P < 0.05). Furthermore, increasing dietary CS concentrations linearly increased free fatty acids, growth hormone and insulin-like growth factor-I, while linearly decreased somatostatin levels (P < 0.01). In addition, increasing dietary CS concentrations linearly increased propionate but decreased acetate and methane prediction by 7.9–15.2% (P < 0.05). Based on the N balance measurement, increasing dietary CS concentrations quadratically increased daily N intake by 12.3% and daily N retention by 8.1–34.8% via reducing N loss efficiency in urine by 13.5% and in feces by 14.8% (P < 0.01). Dietary CS addition linearly increased the meat-to-bone ratio by 8.0–23.1% and lean yield by 6.4–22.2%; however, it decreased back tissue thickness (GR) by 8.7–11.3% and the fat-to-net meat yield ratio by 2.2–13.0% (P < 0.05). Furthermore, increasing dietary CS concentrations linearly increased the mRNA relative expression of insulin-like growth factors - I and protein kinase B (P < 0.05), while linearly decreased the relative mRNA expression of forkhead box protein o4, muscle ring finger 1, and muscle atrophy F-Box (P < 0.05). Cysteamine increased weight gain (+22.1%) via increasing feed intake and inhibiting somatostatin levels, and 40 mg/kg BW was determined to be the optimal dose for feeding. Furthermore, CS increased carcass protein deposition and decreased GR by inhibiting proteolysis, which improved carcass performance.