Libido, or sexual desire, is an important trait in bovine males that can be measured through serving capacity tests. These tests observe the number of mounts and services a bull completes with females in a 30 minute period. Bulls that achieve 2 or more services are considered high capacity. High capacity bulls increase pounds of calf weaned. A bull's libido is affected by age, scrotal circumference, breed, social factors, and nutrition. Proper selection ensures bulls can adequately service females.

1. Libido in Bovine Males
Allen Livingston IV
ANSC 481
June 16, 2005

2. Objectives
• To show the importance of Libido in
Bovine males
– Breeding Soundness Exams – what can they tell
us about bulls
– How is libido measured?
– What factors affect libido?

3. Breeding Soundness Exams
• BSE’s are administered by a veterinarian, usually
30 to 60 days before the breeding season
• Examinations include a physical exam, internal
and external exam of the reproductive tract, and
semen evaluation for sperm motility and normality
• Libido is not included in a BSE

4. Libido
• Libido or sexual desire, is a measurable
behavioral trait, it can only be calculated by
visual observation
• This can be accomplished by:
– Watching bulls in a mating pasture
– Serving capacity test

5. Serving Capacity Tests
• Brahman influenced bulls
– Estrus females penned with bulls at a female-
to-male ratio of 1.5:1 or 2:1
– No more than eight females are penned with up
to five bulls at one time
• British and Continental bulls
– Stanchioned females, in estrus or not, penned
with bulls at a female-to-male ratio of 1:1

6. Scoring System
• The number of mounts and services are
recorded in a 30-minute period determine
scores
• Brahman influenced bulls that achieve two
or more services in the 30-minute period are
considered high serving capacity
• Bulls completing only one or no services
are considered low serving capacity

7. Scoring System cont.
• British and Continental bulls that achieve
more than three services in a 20 to 30-
minute period are considered high serving
capacity
• Bulls that achieve two or three services are
considered moderate
• And bulls that achieve one or no services
are classed as low

8. Scoring System
• High serving capacity bulls are more desirable
• Research conducted by Hawkins et al. (1998)
show that high serving capacity bulls increased
pounds of calf weaned per cow by an additional
60 to 98 pounds compared to low serving capacity
bulls
• Serving capacity is heritable, selection for this trait
can increase reproductive performance

9. Age of the bull
• If a bull has not reached puberty, libido will
be low
• Bulls usually reach puberty at 12-14 months
of age
• Age of puberty can vary by breeds
– Brahman breeds usually reach puberty at 14-15
months of age when scrotal circumference
reaches 26 cm or greater

10. Scrotal Circumference
• Scrotal circumference also determines
puberty in bulls
– Circumference should at least be 26 cm in all
bulls
– However most producers wait to breed with
bulls that have a scrotal circumference of 32 cm
• Scrotal shape is also important when
determining puberty in bulls

11. Scrotal Shape
Dr. Glenn Coulter (1994)

12. Breeds
• Libido can be seen in differences between
breeds
• Dairy bulls are reputedly more sexually
active than beef breeds
• Bos indicus bulls often display lower levels
of libido than Bos taurus bulls
– This is due to a perception that they tend to be
selective and shy breeders

13. Breeds
• There is no definitive answer why Bos
indicus bulls tend to score lower in serving
capacity tests
• Bos indicus bulls are no longer tested with
stanchioned females, instead they are put in
a pen test

14. Breeds
• Cross-bred bulls generally exhibit higher
libido in pen-tests than their parental pure
breeds
– This indicates that heterosis also influences
libido
• Even though different breeds may have
either high or low libido, bulls should still
be selected that can adequately service
estrus females

15. Social Effects
• Dominant bulls can interfere with younger
bulls and prevent them from servicing
females
• Bull-to-female ratios (BFR’s) are usually
1:30
• BFR’s can be increased up to 1:50
– Overuse of a bull can cause temporary
infertility

16. Social Effects
• Bulls are attracted to females by:
– Vocalizations from females
– Pheromones from vulva secretions
– Homosexual activity by females
• These social factors act as signals to a bull
and also increase their libido

17. Nutrition
• Over weight bulls may lack vigor and
prevent a bull from being able to breed up
to his potential
– Bulls can develop feet and leg problems from
being obese, which can lower libido and semen
quality
• Ideally, bulls should have enough fat cover
at the start of breeding so their ribs appear
smooth across the animal’s side

18. Testosterone
• Testosterone does not affect libido
• Testosterone is important for reproductive
health
– Without this steroid, reproductive problems can
occur
• Studies have been conducted, with little or
no correlation between testosterone and
libido

19. Conclusion
• Because bulls contribute to half of the
expected calf crop, selection of top quality
bulls is extremely important
• In order for any bull to be effective, libido
must be high enough to service females
adequately