Preliminary study on the effect of castration and testosterone replacement on testosterone level in the New Zealand male rabbit

To study the effect of castration and testosterone replacement on the testosterone level of the New Zealand rabbit, 16 apparently healthy adult male rabbits were used. The animals were divided into four groups with each group having four rabbits. The first group served as the control group. The rabbits in the second group were unilaterally castrated, while those in the third group were bilaterally castrated. The rabbits in the fourth group were bilaterally castrated and then had testosterone replacement. The normal value of plasma testosterone in the male New Zealand rabbit was 7.17 ± 0.72 nmol/L. There was a sharp significant (p<0.05) drop in the level of testosterone one week after unilateral castration and by 2nd week, it returned to the pre-castration value. The plasma level of testosterone also dropped significantly (p<0.05) after one week of castration in the bilaterally castrated and bilaterally castrated with testosterone replacement groups, and by 2nd week in the latter group (bilaterally castrated with testosterone replacement), the plasma level had risen to a slightly higher value than pre-castration value. In the bilaterally castrated group, the plasma level of testosterone also rose but was lower than the pre-castration value. The study shows that the unilateral castration does not permanently alter the plasma testosterone level as does the bilateral castration.