Page 555 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

530 CHAPTER 2

VetBooks.ir 2.139 A 2.140

B
C
Proximal droplet

D

2.141

Figs. 2.139–2.141 Abnormal equine sperm.
(2.139) A = small head (abnormal) with asymmetric
Distal droplet tail position at attachment to head (normal);
B = distal droplet; C = bent midpiece; D = coiled tail.
(2.140) Proximal droplet. (2.141) Distal droplet.

pH chromatin structure assay is used to assess the
The pH of the semen should be measured to deter- denaturability of sperm chromatin. This test is rec-
mine if it is free from urine or purulent material and ommended in cases where a stallion presents with
that a complete ejaculation has occurred. The opti- low fertility (or high early embryonic death rates
mal pH for stallion semen is between 7.2 and 7.7. in bred mares), but all normal tests within the BSE
are within normal limits. Sperm suffering chroma-
Sperm longevity tin damage may appear normal and may in fact be
Sperm longevity should be assessed for all stallions capable of fertilisation. Sperm membrane integrity
whose semen is being chilled and transported. The can be evaluated using the hypo-osmotic swelling
semen sample is extended to a concentration of test or fluorescent probes such as the Fertilight Kit
25–50 million/ml in several different extenders that (Molecular Probes, Eugene, USA). Sperm viability/
may vary in the sugar, buffers and antibiotics used. membrane integrity can also be assessed with the
One sample from each extender is stored at room Nucleocounter SP-100 cytometry machine or with
temperature and another is stored in the transport fluorescent stains. Acrosomal integrity can also
container. Alternatively, the chilled samples can be be assessed using specialised fluorescein staining.
stored in the refrigerator by placing the plastic tube Fluorescent staining requires specialised micro-
containing the sample into a beaker of 35°C (95°F) scopic equipment, including flow cytometry, and
water to allow slow cooling. The motility of the is therefore generally only available in academic
extended semen in the various extenders is examined or specialised settings. Scanning electron micros-
at various times: examination intervals suggested copy can be used to investigate subtle structural
might include 12, 24, 36, 48 and 72 hours post collec- abnormalities.
tion. The results of this evaluation suggest whether
a particular stallion’s semen is likely to ship well over CHROMOSOMAL ANALYSIS
prolonged periods of time.
The normal chromosomal complement in the stal-
Advanced tests lion is 64XY. Chromosomal analysis may be required
Advanced tests can be performed that evalu- to investigate unexplained infertility in a young stal-
ate other aspects of sperm function. The sperm lion or to confirm the presence of a chromosomal