Impact of feed restriction, sexual class and age on the growth, blood metabolites and endocrine responses of hair lambs in a tropical climate

treatments consisted of two sexual classes (15 intact males and 15 castrated males, 13.0 ± 1.49 kg initial BW and two months old), different levels of quantitative feed restriction (FR) (ad libitum, 300 and 600 g/kg) and various ages (14, 19 and 23 weeks). Lamb age influenced the blood leptin (P < 0.001), chloride, calcium, phosphorus and magnesium (P < 0.05) concentrations. The blood insulin and glucose concentrations (P < 0.001) were positively influenced by diet and age. The increased feed restriction resulted in a higher concentration of blood β-hydroxybutyrate (β-HB) (P < 0.001). The blood urea nitrogen (BUN) concentration was influenced by diet (P < 0.001), age (P < 0.001) and the interaction of sexual class and age (P < 0.01), with the highest concentrations in the oldest and castrated lambs. A positive correlation was observed between insulin and thyroxine in animals fed ad libitum (P < 0.05). The thyroxin is present in low concentrations in the hair lambs raised in a tropical climate. Hair lambs exhibited significant changes in their growth, blood metabolites and endocrine responses, which enabled them to adapt to the feed conditions.