Methods for the indirect estimation of testes weight and sperm numbers in Merino and Romney rams

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Abstract
There were large variations among 67 Merino and 25 Romney rams in testes weight, number of sperm in the testes, number of sperm per g testis, and number of sperm in the epididymides. Correlations among these variables are presented. In Merino rams the in situ measurement of scrotal volume combined with age gave good estimates of testes weight (r = 0.91), number of sperm in the testes (r = 0.77), and number of sperm in the epididymides (r = 0.82). In Romney rams, scrotal volume, scrotal circumference, mean in situ diameter, and length of the testis and the Σ length × diameter2 of the testes (testes volume) were compared as indirect methods of estimating testicular measurements. Except for testis length, which had lower relationships, all the in situ measurements had similar correlations with the testes weight (r = 0.92–0.94), number of sperm in the testes (r = 0.74–0.78), and number of sperm in the epididymides (r = 0.61–0.67). Scrotal volume had the advantage of high coefficients of variation (36% for Merino and 29% for Romney rams) and a high between-operator correlation (r = 0.96) and within-operator repeatability (0.97).