Reproductive parameters of miniature stallions

Breeding soundness evaluation (BSE) of stallions is a routine component of stud farm practice. Guidelines for assessing satisfactory breeding potentia l have been developed using data derived from stallions of full-size breeds . In view of the increasing popularity of miniature stallions, knowledge of normal semen parameters of these stallions is important. Therefore, testic ular measurements and semen parameters from 216 sexually rested miniature s tallions were obtained. Semen was collected twice, 1.5 to 3 h apart, using an artificial vagina. Values were averaged over the 2 collections because o f the sexual inexperience of the stallions. The smaller stallions (Group A, 72 to 86 cm; Group B, 87 to 96 cm) had smaller testicles (P<0.05), and Gro up A stallions had the lowest ejaculate volume (P<0.05) compared with Group C (97 to 10(4) cm) stallions. Thus, although there was no difference in th e concentration of spermatozoa per milliliter between groups of stallions, Group A stallions had fewer total spermatozoa in their ejaculate than Group C stallions (4.31 +/- 0.47 x 10(9) vs. 5.41 +/- 0.30 x 10(9), P<0.05). Mor eover, miniature stallions had smaller testicles and fewer total spermatozo a in their ejaculate than is commonly accepted as normal in full-size stall ions. Average total scrotal width of miniature stallions was found to be 7. 13, 7.38 and 7.95 cm for Groups A, B and C, respectively. The average total number of spermatozoa in the ejaculates of miniature stallions in this stu dy was 4.94 +/- 0.22 x 10(9) cells, with 1.75 +/- 0.09 x 10(9) total normal , motile spermatozoa. When only stallions <96.5 cm in height were considere d (conforming to requirements of the American Miniature Horse Association R egistry), the average total number of spermatozoa in the ejaculates was 4.5 9 +/- 0.30 x 10(9) cells, with 1.70 +/- 0.11 x 10(9) total normal, motile s permatozoa. Based on these findings, different criteria should be used to e valuate the potential breeding soundness of miniature stallions than are co mmonly applied to full-size stallions. (C) 1999 by Elsevier Science Inc.