2009: Testosterone decreases to basal values within 24 hours following castration in alpacas


Testosterone decreases to basal values within 24 hours following castration in alpacas 
M. Kutzlera , T. Fiamengoa , S. Lambb 

a Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, 
Corvallis, OR, USA 

 bEndocrinology Laboratory, Animal Health Diagnostic Center, Cornell University, Ithaca, NY,  
USA 

 
The objective of this study was to compare serum testosterone concentrations ([T]) in 

adult male alpacas (Vicugna pacos) following administration of human chorionic gonadotropin 
(hCG) before and after castration. This information is of diagnostic significance for the 
determination of retained testicular tissue following castration or in the case of cryptorchidism. 
Jugular blood samples were collected from nine adult alpacas prior to intravenous administration 
of hCG (2500 IU; Chorulon®, Intervet, Millsboro, DE, USA) as well as 2, 4 and 6 post-hCG. 
Alpacas were castrated using routine surgical techniques 24 h post-hCG. Testes were removed 
from the vaginal tunica, the epididimydes were removed, and the testes were weighed. A post-
castration hCG response test was performed 24 h after castration (48 h from the previous hCG 
response test). Serum [T] was measured using a double antibody radioimmunoassay (Diagnostic 
Products Corporation, Los Angeles, CA, USA). The assay sensitivity was 0.04 ng/ml and the 
intra-assay and inter assay CVs were <10%. All of the samples were tested within one assay. The 
mean [T] at each treatment time were compared using an analysis of variance. In addition, [T] 
were compared to testicular weight using linear regression. Significance was defined as p<0.05. 
The results for individual animals are summarized in the table below. The [T] was significantly 
increased from pre-hCG values by 2 h post-hCG. The highest mean [T] occurred 6 h post hCG, 
however [T] did not differ significantly between 2, 4 and 6 h post hCG. At 24 h post-castration 
(48 h post-hCG), the [T] was below the limits of detection. There was no significant correlation 
between [T] at any time point and testicular weight. In summary, serum [T] is not correlated with 
testicular weight and falls to undetectable values within 24 h following castration in alpacas. 

Serum Testosterone Concentrations (ng/mL) 
ID Testicular 

Weight (g) 
Pre-
hCG 

2 h Post-
hCG 

4 h Post-
hCG 

6 h Post-
hCG 

48 h Post-hCG        
(24 h Post-castration) 

1 23.49 3.23 10.32 15.53 20.37 <0.04 
2 22.62 7.72 14.30 14.21 18.58 <0.04 
3 21.99 3.62 5.98 10.43 8.53 <0.04 
4 28.80 4.22 9.89 9.74 13.25 <0.04 
5 28.09 4.44 7.15 6.33 6.96 <0.04 
6 17.94 7.14 10.65 16.21 19.23 <0.04 
7 14.69 0.67 3.81 6.26 4.71 <0.04 
8 28.91 9.12 17.66 20.89 24.91 <0.04 
9 36.16 5.60 18.48 19.83 24.94 <0.04 
 24.74 5.08 10.92 13.27 15.72  

SD 6.48 2.60 5.06 5.40 7.64  
Keywords: Castration, hCG, alpaca, testes, testosterone 

 
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