Breed-dependent metabolic and growth responses to saturated and unsaturated fat supplements in fat-tailed and thin-tailed lambs

Abstract This study was conducted to investigate the breed-specific effects of different dietary energy sources on performance, expression of energy metabolism-related genes, and metabolic parameters in fat tailed and thin tailed sheep. A 2 × 3 factorial arrangement (two breeds × three dietary treatments) was used. Thirty-six fat tailed (Taleshi breed) and 36 thin tailed lambs (zel breed) were assigned to three dietary treatments for 116 days ( n = 12 for each Breed*diet comparison): a control diet (no fat supplement), a diet containing 4% stearic acid-rich saturated fatty acid (SFA), and a diet containing 4% protected unsaturated fatty acids (US FAS ). A significant breed × diet interaction was found for average daily gain (ADG) ( P < 0.05 ). Fat-tailed lambs fed the SFA diet had the highest ADG (115.71 g/day), which was significantly greater ( P < 0.05) than thin-tailed lambs on the same diet (108.57 g/day) and fat-tailed lambs on USFA (107.14 g/day). Dry matter intake (DMI) was not significantly affected by breed × diet interaction. Gene expression analysis showed that protected USFA significantly upregulated ( P < 0.05) LPL and FAS genes in the tail fat of fat-tailed lambs. In thin-tailed lambs, protected USFA significantly increased ( P < 0.05) subcutaneous adipose tissue expression of GLUT4, TNF-α, and IGF-1 genes. Moreover, LPL and FAS were also upregulated in thin-tailed lambs fed protected USFA. A significant breed × energy source interaction was observed for ruminal butyric acid concentration and the acetate: propionate ratio ( P < 0.05). Metabolically, fat-tailed lambs demonstrated greater insulin sensitivity, particularly when fed SFA and protected USFA, as evidenced by a significantly lower area under the curve (AUC) in the insulin tolerance test ( P < 0.05), whereas thin-tailed lambs exhibited higher insulin resistance. Plasma glucose, triglycerides, and cholesterol were significantly influenced by breed × fat source interaction ( P < 0.05), with thin-tailed lambs on the SFA diet showing the highest values. Rumen parameters, including pH and protozoal count, were significantly affected by fat source ( P < 0.05) but not by breed. In conclusion, metabolic and performance responses to dietary energy sources are highly breed-dependent. Fat-tailed sheep are more efficient at utilizing SFA for growth, while protected USFA significantly modulates key metabolic genes in thin-tailed sheep. These findings highlight the importance of tailoring dietary energy strategies to the animal’s genetic background.