Relationships among testicular size, daily production and output of spermatozoa, and extragonadal spermatozoal reserves of the dog.

Two experiments established the relationships among total scrotal width (TSW), daily spermatozoal production (DSP), daily spermatozoal output (DSO) and extragonadal spermatozoal reserves (EGR) of dogs ejaculated daily. In Experiment 1, 11 dogs (14 to 36 kg) were ejaculated daily for two 10-day periods and in Experiment 2, seven dogs (15 to 47 kg) were ejaculated daily for two 20-day periods. Approximately six daily ejaculations were required for stabilizing DSO. After the second period of daily ejaculations, dogs were castrated or killed and the testes were weighed and DSP and EGR were determined. In Experiments 1 and 2, DSP averaged 11.7 +/- 0.5 and 16.7 +/- 1.4 X 10(6) per gram of testicular parenchyma, respectively, or 369 and 594 X 10(6) per dog. DSP per gram of testicular parenchyma was not significantly correlated with parenchymal weight for the same testis in either experiment (r = 0.04 and 0.26). Mean (+/- SEM) EGR of dogs in Experiment 1 were 4024 +/- 368 X 10(6) and 4791 +/- 767 X 10(6) in Experiment 2. Approximately 63% of the EGR were contained in the caput and corpus epididymidis, 36% in the cauda epididymidis and 1% in the ductus deferens. DSO averaged 79 and 82% of DSP for the 2 groups of dogs. Based on combined data for all 18 dogs, TSW was correlated with testicular weight (r = 0.95; P less than 0.01), DSP (r = 0.82; P less than 0.01) and DSO (r = 0.75; P less than 0.01). Thus, measurement of TSW is a useful predictor of a dog's ability to produce and ejaculate spermatozoa.