Effects of scrotal heating in the ram on semen characteristics, fecundity, and embryonic mortality

Abstract

In three experiments the testes of rams were heated to 40.5¦C for either 1.5 hr or 2 hr, or to 39.5¦C for 4 hr; the effect on the number of spermatozoa in the ejaculate and the proportion of these that were dead or tailless was examined over the subsequent 60 days. The fecundity of the rams was tested over the same period and compared with that of the unheated rams, a total of 396 ewes being used. Spermatozoa present in the epididymis at the time of heating appeared to be unaffected, but there was considerable damage to spermatozoa developing in the testes. This was manifested by increased proportions of dead and of tailless spermatozoa between days 14 and 50 (day 0 = day of heating). In rams whose testes were heated to 40.5¦C there was also a marked depression in the number of spermatozoa per ejaculate between days 34 and 47, and their fecundity was low between days 14 and 34 and was zero between days 34 and 47. Embryonic losses were estimated by comparing the number of eggs fertilized (in ewes 2 days post coitum) with the number of embryos present in ewes examined 37-42 days post coitum. In only one of the three experiments was there a significantly increased loss of embryos in ewes mated to heat-treated rams. It is concluded that, in ewes mated to heat-treated rams, embryonic losses are of minor importance compared with losses due to non-fertilization.