Sperm Production and Sperm Morphology of Swedish Warmblood Stallions

The present study investigated daily sperm output and sperm morphology of fresh semen in eight Swedish Warmblood stallions aged 5–8 years. They were used for artificial insemination, and their fertility during the breeding season of semen collection exceeded 60% per cycle. One ejaculate of semen was collected daily for 10 consecutive days from each stallion. The gel-free volume was measured, and the sperm concentration was assessed with a Bürker chamber. The volume of gel-free fraction was multiplied by the sperm concentration to give the total number of spermatozoa (TSN). Sperm morphology was examined in ejaculates collected on days 2, 5 and 10. An aliquot from each ejaculate was fixed in 1 ml formol–saline immediately after collection and examined under a phase-contrast microscope (magnification 1000×) to assess morphological abnormalities. Furthermore smears were prepared and stained according to Williams (carbolfuchsin–eosin) for a more detailed examination of the sperm heads under a light microscope (magnification 1000×). Analysis of variance was applied to data. Total spermatozoa number decreased progressively during the first 8 days of collection, and daily sperm output (DSO) was calculated as mean TSN of collections on days 8–10, being 6.4 × 10⁹ spermatozoa. The overall percentages of morphologically normal spermatozoa in ejaculates collected on days 2, 5 and 10 were above 70%, being significantly lower in ejaculate 2 (68.6%) compared with ejaculates 5 and 10 (72.9% respectively 75.3%).