Effect of glutamate and/or testosterone administration on appetitive and consummatory sexual behaviors in pubertal rams and their influence on the reproductive performance of nulliparous anovulatory ewes

Abstract

We tested whether glutamate and/or testosterone administration to pubertal Dorper rams would increase their apptetitive sexual behavior (ASB) and consummatory sexual behavior (CSB). We then evaluated their ability to induce the sexual response of nulliparous-anestrous ewes during early spring (26° N). Dorper rams (n = 20, 11 months old) were distributed in four groups homogeneous regarding live weight ([LW], 55 ± 0.09 kg), body condition score (3.2 ± 0.1 units), and scrotal circumference (30 ± 0.3 cm) and received the following treatments of: 1) intramuscular glutamate (GG); 7 mg kg−1 LW of glutamate (every 3 days × 28 days; iv), 2) testosterone treated (GT); 1 ml of saline (every 3 days × 15 days; iv) + 25 mg of testosterone (every 3 days × 15 days; im), 3) glutamate + testosterone (GGT); 7 mg kg−1 LW of glutamate (every 3 days × 28 days; iv) + 25 mg testosterone (every 3 days × 15 days; im), and 4) GC; 1 mL of saline (every 3 days × 28 days; iv). Thereafter, nulliparous-anestrus Dorper ewes (n = 80; LW 42.2 ± 2.3 kg, body condition score 3 ± 0.09 units) were exposed to these treated males. On male-to-female contact, a sexual behavioral test (2 hours × 2 days) was conducted to evaluate the ASB and CSB frequencies. Afterward, the female reproductive performance (interval to estrus, estrus response, ovulation response, ovulation rate, and pregnancy rate) was quantified. Although the GGT-males had the best ASB and ASB+CSB (P < 0.05), the GT-males had the best CSB (P < 0.05). The estrus response, ovulation response, and ovulation rate did not differ (P < 0.05) among groups, yet, interval to estrus and pregnancy rate favored (P < 0.05) to the ewes-GGT rams. Our results revealed that the ASB and CSB of young Dorper rams were improved by frequent GGT administration. Moreover, the shortest onset to estrus and the largest pregnancy rate were observed in those ewes exposed to the GGT-treated pubertal rams. Such results are encouraging from a comparative sexual behavior standpoint, while may hold potential translational applications.