Alternatives to
castration in horses
Why castrate?
• Aggressive behavior
– Sex-related aggression
– Dominance Related aggression
• No distractions at shows
– Will perform, with mares, in classes
• Easier to manage
– 5 ft vs. 7 ft fencing
– Limited areas; can pasture with mares
What are some
alternatives?
Progestin therapy
GnRH vaccination
Progestins
• Progestins inhibit Leutenizing Hormone
production
• Results
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–
–
–
–
Reduced Leydig cell activity
Reduced testosterone levels in blood plasma
Reduced ejaculate volume
Reduced libido
Reduced sperm production
*Stephen J. Roberts (VT) & Bonnie V. Beaver (TX)
Gonadotropin releasing
hormone
Objective: To investigate the effect of GnRH
on testicular function
The studies: The First
Study
• Six yearling colts were divided into three
groups 1) control 2) subcutaneous & 3)
intramuscular vaccination
– They were fed to ensure adequate growth
throughout study
– Vaccinated against tetanus
The first study
•
•
•
•
Injections
2 cc of mineral oil based GnRH vaccine
The control group: never injected
The Subcutaneous group: emulsion on the
side of neck
• Intramuscular group: injection in the neck
The first study
• Measurements and Tests
• *Jugular vein blood assayed before study for testosterone
level and GnRH antibodies
• *Scrotal diameters and body weights were measured prior
to study
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•
•
•
•
•
•
•
Body weights and Blood assays
Scrotal diameters and testicular lengths
Blood samples
Antibody Assays
Semen Collection and Examination
Daily sperm production
Testis Histology
Morphometric Analysis
The Results
• No weight differences 1.2
• Testosterone levels
1
• The treated colt’s
– Testes failed to grow
during first 32 weeks
– Irregular groups of
Leydig cells
– Reduced volume of
semineferous tubules
– Reducd Leydig cell
volume
*No “P” values given
Control
S.C.
I.M.
0.8
0.6
0.4
0.2
0
8
24 40 56 72
Wks Wks Wks Wks Wks
The Second Study
• Twelve 2-year-old colts divided into two
groups: 1) 200 mg dose 2) 400 mg dose of
water based GnRH vaccine
– They were run in paddocks and fed to maintain
condition
– Vaccinated against strangles and tetanus
The Second Study
• Injections: given Intramuscularly
• *Water based vaccine vs
• *Mineral Oil based vaccine
• Lesions
• Soreness
• Scarring
The Second Study
• Measurements and Tests
• Testosterone concentrations and semen quality
assessed before trial
• Body Weights
• Testicular widths and lengths
• Blood samples
• Testosterone concentrations
• Antibody assays
• Semen examination
• Libido
Results
• Vaccination Dose on body
weight and testicular
dimensions
Semen
– Not significantly different Characteristics
200mg 400mg
(P>0.05)
• Only slight swelling at site Live, Normal
Sperm (%)
• Vaccination dose on
semen characteristics
– Significantly different in
percentage of live, normal
sperm (P<0.05)
• No significant effects on
antibody titres or
testosterone levels
– (P>0.05)
• Displayed gelding-like
behavior
38.7
52.1
Sperm
Concentration
(106/mL)
319.4
294.0
Total # of Sperm
(106)
4729
3893
The Third Study
• Four standardbred stallions: 3 treated and 1
control
• Vaccinated with water soluble GnRH
vaccine
– Kept in paddocks during day & stalls at night
*September to January
The Third Study
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•
•
•
•
•
•
Measurements and Tests
Hormone assays
Semen collection & behavior
Semen evaluation
Testes examination
Testicular histology
Site examination
Results
Stallion Time
Week 13
Before
Min:sec
A
8:08
9:19
B
2:57
11:59
C
1:08
6:50
D
3:05
7:58
• Testosterone levels
decreased, but varied
by individual
• Libido decreased
• # of mounts increased
• Time in collection
room increased
• Interest in tease mare
decreased
No “P” values were given
Conclusion
• Immunocastration IS an alternative to
castration
• Needs more research
• May become the norm in the race and show
horse industries
• DEFINITELY WORTH LOOKING INTO