TESTICULAR SHAPE AND ITS RELATIONSHIP TO SPERM PRODUCTION IN MATURE HOLSTEIN BULLS

This study was conducted to determine the relationship between testicu lar shape, scrotal circumference (SC) and sperm production. Twenty-sev en mature Holstein bulls were evaluated subjectively and objectively f or testicular shape as indicated by testicular length and width, then placed in 1 of 3 groups. Group 1 contained 17 bulls with a normal ovoi d testicular shape and a length to width ratio of 1.61:1 +/- 0.01 (SEM ). Group 2 was composed of 4 bulls with a long, slender testicular sha pe and a length to width ratio of 1.95:1 +/- 0.06 (SEM). Group 3 was c omprised of 6 bulls with spheroid-shaped testicles and a length to wid th ratio of 1.3:1 +/- 0.03 (SEM). All the groups were statistically di fferent for length to width ratios (P < 0.05). Length measurements fro m cranial to caudal pole of the testis proper were also different betw een groups (P < 0.05). Width or testicular diameter was different betw een Group 2 and Group 3 at P < 0.05; however, there was no difference between Group 1 and Group 2 or between Group 1 and Group 3. Predicted volumes and weights of testicles were not significantly different betw een groups. Scrotal circumference measurements were significantly diff erent between groups (P < 0.05). Group 1 had an average SC of 43.07 +/ - 0.36 cm (SEM), Group 2 of 39.33 +/- 1.18 cm (SEM) and Group 3 of 46. 22 +/- 0.69 cm (SEM). Sperm production for a twice daily, 2-day-per-we ek collection schedule revealed a statistically significant difference for sperm output. A total of 2742 ejaculates was evaluated. A total o f 1818 ejaculates was evaluated in Group 1, 440 ejaculates in Group 2 and 484 ejaculates in Group 3. The mean spermatozoal harvest per day f or Group I bulls was 13.62 +/- 0.09 x 10(9) (SEM). Group 2 bulls with the longer-shaped testicles produced 14.82 +/- 0.18 x 10(9) (SEM) sper matozoa per day, and Group 3 bulls, with the more rounded testicle sha re and the significantly larger SC produced 11.72 +/- 0.64 x 10(9) (SE M) sperm cells per day. All 3 groups were statistically different at t he P = 0.05 level. The results suggest that prediction of sperm produc tion may be dependent on factors other than SC, testicular volume, or weight. Testicular shape may influence sperm output in mature Holstein bulls.