"Sperm Accumulation" in a Stallion
By Patrick M. McCue, DVM, Ph.D.,
Diplomate American College of Theriogenologists
History
A 15 year old American Quarter Horse stallion presented to the clinic for a breeding soundness evaluation (BSE)
at the beginning of the breeding season. The referring veterinarian had collected semen the previous week and
reported a high concentration of spermatozoa and all were dead. The stallion had been used for pasture breeding
the previous year. The owner indicated that the seasonal pregnancy rate last year was good. However, he had
observed that mares bred early in the season did not become pregnant; they did become pregnant on later
cycles.
Physical Examination
The stallion was noted to be in good body condition and had an excellent disposition. Examination of his external
genitalia revealed no significant abnormalities of his epididymides, spermatic cords, prepuce or penis. Both testes
were fully descended into the scrotum and approximately equal in size and consistency.
Initial Semen Collection and Analysis
The stallion exhibited normal breeding behavior at the time of semen collection. His libido was excellent and he
mounted the breeding phantom uneventfully. The stallion was collected twice, one hour apart. Semen analysis
consisted of measurements of semen volume, sperm concentration, sperm motility, and sperm morphology.
Volume was measured in a graduated cylinder; concentration of spermatozoa was determined using a calibrated
spectrophotometer (ARS Densimeter); total and progressive sperm motility was evaluated by a computer assisted
semen analysis (CASA) system; and sperm morphology was determined under a microscope after eosin-nigrosin
staining.
Results of the two semen collections are presented in Table 1. The sperm concentration was greater than 400
million sperm per ml and the total number of sperm was over 30 billion in each of the two ejaculates. However,
there were no live spermatozoa noted in either ejaculate. Less than 30 % of sperm were morphologically normal,
with the most common abnormality being detached heads (approximately 40 %) (Fig. 1).
Table 1. Semen parameters for two ejaculates collected one hour apart.
Equine Reproduction Case Files
|
July 2013
|
Issue No. 2
|
Parameter
|
Collection # 1
|
Collection # 2
|
Gel-free Volume (mls)
|
64
|
80
|
Sperm Concentration (million/ml)
|
482
|
414
|
Total and Progressive Motility (%)
|
0/0 %
|
0/0 %
|
Morphology (% normal sperm)
|
20.5 %
|
28 %
|
Total # sperm in ejaculate (billions)
|
30.85
|
33.12
|
Parameter
|
#3
|
#4
|
#5
|
#6
|
#7
|
#8
|
#9
|
#10
|
#11
|
Volume (mls)
|
69
|
43
|
48
|
85
|
48
|
59
|
40
|
29
|
35
|
Concentration
(millions/ml)
|
308
|
527
|
316
|
162
|
223
|
158
|
205
|
52
|
193
|
Motility (%)
|
4/2
|
25/21
|
27/17
|
23/17
|
32/26
|
62/57
|
61/50
|
49/39
|
62/55
|
Morphology (%)
|
29.5
|
32
|
29.5
|
37.5
|
30.1
|
36.5
|
38
|
28.5
|
34
|
Total # Sperm
(billions)
|
21.25
|
22.66
|
15.17
|
13.77
|
10.7
|
9.32
|
8.20
|
1.51
|
6.76
|
1st Collection http://www.youtube.com/v/COYqilvAywc
3rd Collection http://www.youtube.com/v/IsSf3szcKv8
4th Collection http://www.youtube.com/v/oif_QExGdek
Final Collection http://www.youtube.com/v/jrCrC5mzxt8
Figure 1. Photograph of spermatozoa in the first ejaculate from the clinical case. Note the abundance of
detached heads (black arrow).
The stallion was collected multiple times over the subsequent three days. Semen parameters from those
collections are presented in Table 2. Sperm concentration eventually stabilized at around 160 to 200 million
sperm per ml and the total motility also stabilized at approximately 60% by the 8th collection. The stabilization
of the semen parameters indicate that most of the dead spermatozoa had been removed or ‘cleaned out’ by the
8th collection and we had reached ‘daily sperm output’.
Table 2. Semen parameters for subsequent ejaculates from the clinical case.
The relationship between the increase in sperm motility and the decrease in the total number of sperm in the ejaculates is shown in the two graphs below (Figure 2). Sperm numbers were very high in the first collections, but declined to more normal levels by the 8th to 11th collection. No motile sperm were noted in the first two ejaculates and sperm motility eventually plateaued by the 8th collection as the accumulated dead sperm were removed from the epididymides.
Take home message(s):
1. This stallion was determined to be a ‘sperm accumulator stallion’. Affected stallions accumulate large numbers
of spermatozoa in their epididymides, which are the highly coiled tubular sperm storage structures located just
caudal to the testes.
2. In the normal series of events, spermatozoa are made in the testes, a process which takes approximately 57
days. Spermatozoa leave the testes and travel through the head and body of the epididymis and finally enter
the tail of the epididymis where they are stored. The process of epididymal transport takes approximately 7 to
10 days. In the normal male, a combination of fluid flow and smooth muscle contractions of the epididymis/vas
deferens slowly and constantly move sperm along the tubular tract out of the epididymis and they are eventually
passed into the urethra and voided during urination.
3. However, sperm from some stallions do not move out of the epididymal tail and accumulate in that structure in
very large numbers. The accumulated sperm eventually die and start to break down, leading to poor motility and
high percentage of detached heads during initial semen collection and evaluation.
4. ‘Sperm accumulation’ would also account for the low percentage of mares that became pregnant early in the
previous breeding season for this stallion. It is possible that his ejaculates contained primarily dead and
morphologically abnormal sperm early in the year. Once he was naturally ‘cleaned out’ by way of multiple, albeit
infertile, live cover ejaculations his subsequent fertility was good and eventually lead to an acceptable seasonal
pregnancy rate.
5. This year, it is anticipated that the stallion should do well in the same pasture breeding program now that he
is ‘cleaned out’ and ejaculating a population of normal motile spermatozoa.
~~~~~
The goal of this report is to provide veterinarians and horse owners with an educational opportunity based on an
actual clinical case presented to the Equine Reproduction Laboratory at Colorado State University. Publication of
the report is sponsored by Animal Reproduction Systems, Chino, CA.
For more information on equipment and supplies available at ARS, please visit our website at www.arssales.com
or call us at (800) 300-5143
Equipment described in this case report available at Animal Reproduction Systems includes:
Please visit www.arssales.com/equine for additional information.
For more information call us at 1-800-300-5143 or visit our web site at www.arssales.com.
Comments/questions/suggestions - e-mail them to sales@arssales.com
To unsubscribe from this list simply reply to this message or send an E-mail to: