248
Artificial Insemination in Cattle
on the right side, holding the A.V. mouth
downwards in his right hand. As the bul
mounts the A.V. is held behind his foreleg
against the cow's flank, at an angle of 45° with
the mouth pointing towards the bull's penis
The penis is directed into the A.V. by the
operator holding the sheath with his left hand
It is better not to touch the penis itself with
the hand as this may cause the bull to retract
and dismount. As soon as the penis comes into
contact with the warm libricated inner surface
of the A.V. the bull thrusts vigorously upwards
and ejaculates. The A.V. should then be
turned with the cup downwards to allow the
semen to run into the cup. If the bull has not
been used for some time, it is best to make a
second collection in a fresh cup and to use this
semen for insemination, discarding the first
collection.
In such a case, the first sample
usually contains a large percentage of old
immotile or abnormal spermatozoa which have
been matured for a considerable time in the
epididymes. Also. if the quantity of the ejacu-
late is small, a second collection should be made
immediately after the first.
For ejaculation to occur, it is necessary that
the animal shall thrust vigorously into the
A.V. Sometimes a bull will introduce his
penis into the apparatus several times without
ejaculating, and several c.c. of a slightly
cloudy and watery secretion will accumulate in
the collecting cup. It comprises chiefly secre-
tion from the seminal vesicles and should be
discarded. It is probable that conditions in
the lumen of the A.V.—either temperature,
pressure or lubrication—are incorrect.
After collection the semen should be protect-
ed from too sudden cooling in cold weather.
It must not be exposed to strong sunlight,
which quickly destroys spermatozoa.
In the
absence of special storage conditions semen is
best used for insemination as soon as possible
after collection. and it is recommended that it
should not be kept longer than three hours.
4. THE EXAMINATION OF SEMEN
Data published by numerous workers ex-
perienced in large-scale artificial breeding work
in the U.S.S.R. and in the U.S.A. show that
great variations exist in the quantity and quality
of the semen obtained from different bulls.
There is also considerable evidence of variation
in the quantity and quality of the semen ob-
tained from the same bull at different
times.
A knowledge of such variations and
the ability to detect inferior samples is a matter
of prime importance in the successful conduct
of artificial insemination.
Consequently the
semen of every bull should be carefully exa-
mined before it is used for insemination.
The following routine of examination is
recommended as being practical under field
conditions :*
(i) Volume of the ejaculate.
(ii) Colour and density of the semen.
(iii) Motility of the spermatozoa.
(iv) Detection of extraneous matter.
The best single index of fertility or otherwise
is the motility of the sperm, when examined
immediately after collection. It is emphasized,
however, that in assessing the potential fertility
of a sample of semen all available criteria
should be taken into consideration.
Volume of the Ejaculate. This may be con-
veniently measured in the graduated glass stem
of the "Cambridge" pattern collecting cup.
The volume of the ejaculate obtained from
different bulls may vary within fairly wide
limits. The average, however, may be taken
as between 3 c.c. and 5 c.c. when the semen is
collected by the artificial vagina method. In
general, mature bulls produce a greater volume
of semen than young bulls which usually give
1½ to 2½ c.c. Often a bull will ejaculate a small
quantity only at the first thrust, but a larger
one at the second, taken immediately after-
wards.
Colour and density of the semen. These
characters can be determined by submitting the
sample to a macroscopical examination in good
daylight; the examination should not be carried
out in strong sunlight.
The normal ejaculate of the bull is an
opaque, white or yellowish-white fluid with a
milky or creamy appearance. The greater the
concentration of spermatozoa, the whiter the
fluid. Clear watery semen, sometimes of light
yellow colour,
contains few spermatozoa.
Occasionally a bull of normal fertility produces
this latter type of ejaculate and when such a
sample is obtained from any animal, it is
essential that a second collection be made: in
the fertile bull this second sample should be of
normal colour and density.
A decided yellowish or greenish colour may
indicate the presence of pus. A dark yellow or
brownish discoloration usually indicates the
* In addition to the examination outlined here, the
number of spermatozoa per unit volume of semen is of
the greatest importance in assessing fertility. This part
of the examination is best carried out in the laboratory.
For details, see Addendum.