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– 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

• 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• Testosterone levels • 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

0

0.2

0.4

0.6

0.8

1

1.2

8Wks

24Wks

40Wks

56Wks

72Wks

Control

S.C.

I.M.

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– Not significantly different (P>0.05)

• Only slight swelling at site• 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

Semen Characteristics

200mg 400mg

Live, Normal Sperm (%)

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

• Measurements and Tests

• Hormone assays

• Semen collection & behavior

• Semen evaluation

• Testes examination

• Testicular histology

• Site examination

Results

• 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

Stallion Time Before

Min:sec

Week 13

A 8:08 9:19

B 2:57 11:59

C 1:08 6:50

D 3:05 7:58

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