Endocrine Responses in Relation to Compensatory Testicular Growth after Neonatal Hemicastration in Boars1

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Abstract
Mass (TM) and relative mass (organ mass/body mass; RTM) of the right testis and epididymis (EM and REM, respectively) were determined every 14 days from 10 to 122 days of age for intact boars (I) and boars hemicastrated on Day 10 (HC) in two crossbred herds (Trial 1 and Trial 2). Plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin, growth hormone (GH), and testosterone were determined in four blood samples from each pig, three collected 24 h prior to castration and one immediately prior to castration. Values for TM and RTM of HC boars were approximately double (p < 0.0001) those of I boars by 38 days of age, and these differences were maintained through Day 122. Both EM and REM were greater (p < 0.05) in HC than in I boars from Day 52 to Day 122. The TM, RTM, EM and RFM were greater (p < 0.05) in Trial 1 than in Trial 2 for both I and HC boars from Day 80 to Day 122, indicating an earlier onset of pubertal testicular growth in the Trial-1 boars. Plasma GH concentration was greater (p < 0.05) in HC than in I boars from Day 16 to Day 38. A transient increase in plasma FSH (p < 0.05) was observed from Day 24 to Day 38. After Day 38, there was no difference (p > 0.05) in FSH or GH between HC and I boars, or between trials. Plasma LH, prolactin, and testosterone concentrations were also similar in HC and I boars. Trial-2 boars exhibited higher plasma LH concentrations (p < 0.05) than Trial-1 boars throughout the study and lower testosterone concentration (p < 0.05) from Day 24 to Day 80. Plasma prolactin was also less (p < 0.05) from Day 80 to Day 122 in Trial-2 than in Trial-1 boars. Thus, neonatal hemicastration of boars resulted in rapid compensatory testicular hypertrophy. Elevated blood plasma concentration of GH and a transient increase in FSH were seen during the time of compensatory hypertrophy, whereas plasma testosterone, LH, and prolactin were unaffected by hemiorchidectomy.