Clinical Examination of Farm Animals - CYF MEDICAL DISTRIBUTION

CHAPTER 11
posed time of examination of the bull. A mature cow
is usually a better teaser animal for a bull than a
young inexperienced heifer. If the bull or the cow’s
behaviour suggests that she is not in standing oestrus
she should be examined to determine if the changes
associated with oestrus are present. A mature ripening
ovarian follicle is normally palpable on rectal
examination, and a quantity of clear mucus (the bulling
string) is usually found in the vagina.
The teaser cow should be restrained in service
stocks or allowed to be free in a large box with a high
roof where the bull can be readily and closely observed.
If attempts are to be made to collect semen,
restraint of the cow is advisable but may put the bull
off in some cases.
(2) Assessment of libido
The bull is observed as he approaches the cow in
oestrus. Normal bulls should show an immediate
sexual interest. Libido may be quantified by libido
score or reaction time.
Libido score
Scores are given in Table 11.1.
Reaction time
This is the time from time of introduction of the bull
to the teaser cow to the first attempt at mounting.
This should be less than 10 minutes for the bull to
Table 11.1 Libido score for bulls
Score
Behaviour
0 Bull shows no sexual interest in presence of cow in oestrus
1 Passing interest only, sniffs perineum, no attempt to mount
2 Interest in cow shown on more than one occasion
3 Active pursuit of cow with persistent sexual interest, no mounting
4 Single mount/mounting attempt but no service
5 Two mounts/mounting attempts but no service
6 More than two mounts/mounting attempts but no service
7 Single service, no further sexual interest
8 Single service with continued sexual interest including mounting
9 Two services, no further sexual interest
10 Two services followed by persistent sexual interest including
mounting
have an adequate libido. It is less than 0.5 minute in
an animal with an excellent libido and 10 to 30 minutes
for an animal with a weak libido.
(3) Observation and assessment of
service behaviour
Normal mating behaviour is the result of the stimulation
and completion of a number of reflexes. Mating
in the bull is normally completed in less than 15
seconds, and observation must therefore be made
quickly and carefully. In a bull with good libido
several matings can be observed in a short period of
time.
Normal mating in the bull – sequence of events
(1) Sexual excitation The bull makes contact with the
cow, smells and touches her with his muzzle and
tongue. He may rest his head on the cow’s gluteal
and sacral regions. The bull licks her perineum,
udder and flanks. The cow may pass urine at this
point. The bull may taste the urine, champ his
jaws, lift his head and show flehmen (retraction
of lips and elevation of muzzle). Reflex penile
erection commences. The penis protrudes freely
from the prepuce and erection may be partial or
complete. Small quantities of clear seminal fluid
may be passed. In normal adult bulls at least
10 cm of the erect penis protrudes from the prepuce.
When the penis is fully erect, up to 40 cm
of the penis protrudes. Full penile erection
may not be seen in some animals until the bull
mounts the cow.
(2) Mounting Taking his weight on his hind limbs,
the bull rears up to place his sternum on the cow’s
lumbosacral region. The penis should be fully
erect at this stage. The bull clasps the cow with
his forelegs, each leg being anterior to the cow’s
tuber coxae. Correct positioning by the bull is
important, and failure to mount effectively may
inhibit completion of coitus.
(3) Intromission Once mounted the bull makes seeking
movements with his penis until he finds
the vulval entrance and makes contact with the
vaginal mucosa.
(4) Thrusting and ejaculation Once within the vagina
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