report made by Dauzier20 that fertilizing capacity
of buck (and ram) semen decreased with an
increase in storage time. But it was thought that
a longer duration of extended semen might show
a significant difference.
An astonishing observation made was that there
was no difference (p = 0.106) in preservation of
sperm cell motility when D2 at 3 hours p.e. was
compared with D3 at 2 hours p.e. We suggested
therefore that D3 might be useful for preserving
WAD buck semen (non-refrigerated) but may be
for less than 3 hours after semen extension.
The mean motility score of sperm cells at zero
hour (i.e. immediate assessment post- extension)
in D2 was 73% in the 5 trials (data not shown).
This was higher than the pre-freezing motility
score of 49% recorded by Melo and Nunes12 for
buck semen extended in coconut milk - citrate
extender. This suggests that 20% coconut milk
plus 80% sodium citrate buffer (i.e. D2) might
be appropriate for extension of WAD buck
semen intended for storage at freezing
temperature; because the higher the pre-freezing
motility, the higher would be the post-thawing
sperm cell motility.
The 0.6 ml extended semen in D2 contained
161.5 million motile sperm cells, which may be
sufficient for artificial insemination in does as
Pagot21 and Zemjanis22 observed that 100
million sperm cells were compatible with A.I. In
addition, estimation of the above motile sperm
cells gave 13.5 million and 53.8 million in 0.05
ml and 0.20 ml respectively. This 0.6 ml
extended semen and the motile sperm cell
concentration contained in it might make a good
insemination dose for does by intra-cervical
route. The reason is, according to Roberts23,
workers in this field recommended 50 to 150
million motile spermatozoa in a volume of 0.05
to 0.20 ml extended semen for intra-cervical
insemination, but that higher volume and
numbers of spermatozoa, on the order of 10
times greater, were needed for intravaginal
insemination to obtain good fertility in goat and
sheep.
The ratio of semen to extender (1:6) used in this
work, according to the observations, appeared
suitable for sperm cell survival at 2 hours postextension.
Tewari et al24 reported that a ratio
slightly higher than 1:5 could still be used,
though John25 observed that buck semen
viability declined with higher dilution ratio and
ageing.
One factor, among others, that might be
responsible for the observed drastic decline of
the sperm cells motility was the non-addition of
antibiotics to the extenders. This probably
allowed quick depletion of sugar by the
competing microbes. This probably affected trial
5 (Table 4a and 4b) in which after 1 hour of
semen extension at room temperature, the
motility score sharply dropped to zero value for
all the extenders. In support of addition of
antibiotics, Foote and Bratton26 reported that
yolk-citrate-antibiotic medium enhanced and
extended the usefulness of semen. A similar
study with inclusion of antibiotics is hence
recommended.
It is also remarkable to report that slightly
alkaline pH (7.6) of D2 made a significant
difference in supporting WAD buck sperm cell
motility compared to virtually neutral pH values
7.1 and 7.0 of D3 and D4 respectively. The pH
value 7.6 (alkaline) of D2 was contrary to
slightly acidic pH values of buck semen reported
by Oyeyemi et al3. However, it was surprising
that acidic extender D6 with pH similar to
bucks’ semen reported by Oyeyemi et al3 did not
give any appreciable support to motility of
extended sperm cells. The same reason of high
viscosity of this extender might be responsible
for this observation.
Worthy of note, as well, is the observation that,
though a mean motility score of 52.6% of fresh
extended WAD buck semen in coconut milk at 2
hours storage period might be compatible with
fertility, it remains to be proven whether it
would give good reproductive performance (i.e.
fertility, fecundity and prolificacy) in goats
artificially inseminated. Therefore, the
reproductive performance of WAD buck semen
extended in 20% coconut milk plus 80% citrate
buffer needs to be investigated.
This study has shown that D2 has the most
suitable proportions of coconut milk and citrate
buffer (20% coconut milk plus 80% citrate
buffer) to support WAD buck semen motility