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Effects of Natural and Electrical Ejaculation on Predicting Fertility in the Ram

U. S. Department of Agriculture and Utah State University¹

Abstract

Electroejaculation and natural ejaculation were compared as methods for obtaining semen samples for predicting ram fertility. Rams were assigned independently of semen quality to breeding pens containing from 5 to 65 ewes. The data consisted of fertility and various semen traits. When possible, two consecutive, natural ejaculates and two electroejaculates using two different ejaculators were obtained from each ram. Natural ejaculates were obtained from 94 rams. Both natural and electrically induced ejaculates were obtained from 91 rams.

Correlations between semen quality traits and fertility were generally lower for electroejaculates than for natural ejaculates from the same rams. Four of these correlations from naturally ejaculated semen differed significantly from the corresponding correlations from electrically ejaculated semen. The multiple correlations and standard errors of estimate for the natural ejaculates and electroejaculates were 0.812 and 0.17, and 0.695 and 0.21, respectively. However, when data from all natural ejaculates (94) and electroejaculates (140) were used, multiple correlations were somewhat lower in each case (0.73 and 0.46, respectively).

Data from the second of the two consecutive natural ejaculates were slightly more accurate (but not statistically significant) in predicting ram fertility than data from the first sample (R=0.74 vs. R=0.69). The predictive value of data from the second ejaculate was also slightly superior to that from the mean of the first and second ejaculates obtained naturally. Selecting the better of the two natural ejaculates did not improve fertility prediction over that achieved by routinely selecting second ejaculates. Retesting rams that gave initial low-quality semen did not improve fertility prediction.

It is concluded that natural ejaculates are preferable to electroejaculates for predicting fertility. Electroejaculation should be limited to use as a supplement or alternate to natural ejaculation, when the natural ejaculate is either impossible or impractical to obtain. Selection of the second natural ejaculate of each ram is apparently the most efficient method of sampling a ram's semen.

¹ From the U. S. Sheep Experiment Station and Western Sheep Breeding Laboratory, Sheep and Fur Animal Research Branch, Animal Husbandry Research Division, ARS, Dubois, Idaho, in cooperation with Utah State University and University of Idaho. Published with approval of the Director of the Idaho Agricultural Experiment Station, Moscow, as Research Paper No. 596.