Effects of heating the testes and epididymides of rams by scrotal insulation on fertility and embryonic mortality in ewes inseminated with frozen semen

Fertilization rate and embryonic mortality were assessed in 636 ewes inseminated in each uterine horn with 50 x 10(6) frozen spermatozoa from four control rams and from four rams submitted to a moderate (1.4-2.2 degrees C), but repeated, intermittent (16 h/day for 21 consecutive days) increase in their subcutaneous scrotal temperature by means of scrotal insulation. Pregnancy was assessed twice in each ewe from concentration of progesterone in blood plasma at 17 days and by ultrasound at 65 days after insemination. No differences were observed in the pregnancy rate at 17 days between ewes inseminated with semen collected from control rams (56.0, 65.2, 66.7 and 60.3%) and from heated rams (60.6, 71.8, 63.6 and 48.2%) before or after 4, 15 and 21 days of heating, respectively. In contrast, the rate of embryonic mortality between 17 and 65 days after insemination was significantly higher at days 4, 15 and 21 in the heated rams (78.7, 78.6 and 93%) than in the control rams (55, 59 and 65.7%). These results indicate that an intermittent slight, but repeated, increase in the subcutaneous scrotal temperature could induce a significant increase in the embryonic mortality rate. As these changes were apparent on day 4 of heating, an effect must have occurred on sperm stored in the epididymis.