Abstract
The standard procedure for assessing the breeding potential of a stallion includes the parameter total number of spermatozoa classified as morphologically normal. This study investigated sperm morphology of fresh semen in randomly chosen Estonian (E, n = 8) and Tori (T, n = 7) breed stallions with proven fertility. Two ejaculates were examined from each stallion. An aliquot from each ejaculate was fixed in 1 mL formol-saline immediately after collection and examined with phase-contrast microscope at a magnification 1000× for all types of morphological abnormalities. Furthermore smears were prepared and stained according to Williams (carbolfuchsin-eosin) for a more detailed examination of the sperm heads with light microscope at a magnification 1000×. Analysis of variance was applied to the data, and results are presented as LSmeans (± SE). One T stallion that had a disturbance in the spermatogenesis and one 22-year-old E stallion were not included in the analyses. The T stallions had on average 57.5 ± 4.1% and the E-stallions 74.4 ± 3.8% morphologically normal spermatozoa (p = 0.012). In 4 of 7 T stallions and 7 of 8 E stallions both ejaculates had >50% morphologically normal spermatozoa. There was a significant difference between breeds in mean percentage of proximal droplets (17.3 ± 2.7% and 2.9 ± 2.5% for T and E stallions, respectively; p = 0.003).
Highlights
One criterion used to assess the breeding potential of a stallion is the total number of spermatozoa classified as morphologically normal (Kenney et al 1983)
Differences in least squares means show that for E stallions, this abnormality decreased with time whereas for T stallions this abnormality increased with time
Differences in least squares means show that for E stallions, percentage of abnormal tails decreased with time by 4.7% units, whereas for T stallions it increased with time by 1% unit
Summary
One criterion used to assess the breeding potential of a stallion is the total number of spermatozoa classified as morphologically normal (Kenney et al 1983). Several investigators found a considerable inter-stallion (Pattie & Dowsett 1982, Rousset et al 1987, Love et al 2000) and intra-stallion (Rousset et al 1987, Jasko et al 1991, Love et al 2000) variation in semen quality. Available computer-assisted methods can only evaluate the sperm head, not count morphological abnormalities of mid-pieces, tails and acrosomes. The aim of the present study was to investigate the sperm morphology in fresh semen of Tori and Estonian breed stallions
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