SERUM ANDROGEN AND GONADOTROPIN PROFILES OVER THE FIRST YEAR OF LIFE IN RAM LAMBS AND THE EFFECT OF SEASON OF BIRTH

Abstract

Testosterone (T), dihydrotestosterone (DHT), androstenedione (D), androsterone (A), 5α-androstane-3α, 17β-diol (3α-diol), 5α-androstane-3β, 17β-diol (3β-diol), LH and FSH were measured in serum from rams over the first year of life. March-born rams had higher mean serum LH levels than July-born rams, but mean serum FSH levels were higher in July-born rams. In March- and July-born rams, gonadotropin levels rose at 40–60 d of age and then declined. In all rams, serum concentrations of androstenedione (D) and the 5α-reduced androgens fell into a similar range, but were present at lower concentrations than T. In March-born rams, only serum levels of T, D and DHT changed significantly with time, rising to a peak at 200–240 d of age and then declining. Only serum levels of T rose significantly with time in July-born rams, but not to the extent seen in March-born rams. Over the first year of life mean levels of DHT, 3α-diol and A were higher in July-born rams than March-born rams, while levels of 3β-diol were higher in March-born rams. Mean levels of D did not differ between the groups. Key words: Ram lamb, androgens, LH, FSH