This research aimed to establish reference values of thyroid-stimulating hormone (TSH) and free thyroxine (T4) in small ruminants under seven months old, by analyzing the influence of gender on determined values. Blood samples were collected from 48 fasting sheep (25 males and 23 females under 7 months old), and TSH and free T4 levels were determined using enzyme immunoassay. Average, minimum, maximum, and standard deviation values for TSH (μUI/ml) in young females were: 0.34 0.0 0.57 0.15, respectively. In young males, they were: 0.09 0.0 0.57 0.15, respectively. The F-test p-value was 0.147 (p ≥ 0.05), which indicates that there is no statistically significant difference with a reliability of 95% for TSH in young sheep with regard to gender. Average, minimum, maximum, and standard deviation values for free T4 (ng/dL) in young females were: of 0.44 0.13 0.73 0.21, respectively. In young males, the values were: 0.66 0.31 1.17 0.24, respectively. The F-test p-value was 0.04 (p < 0.05), which shows a significant difference with a reliability of 95% for free T4 values in young sheep. The study concludes that sex causes variation in the secretion of free T4 in young small ruminants.