Influence of immunocastration vaccine administration interval on serum androgen concentrations and testis activity in ram lambs

Abstract

The objective of this study was to establish whether different intervals between primary and secondary immunocastration vaccinations had similar effects on the production of C-19 steroid hormones and testis tissue functionality. Forty Dohne Merino rams (5.5 months old) were allocated to the respective treatment groups, which included no vaccination (R), and four (IC4), three (IC3) or two (IC2) weeks between the primary and secondary vaccination. Administration of the secondary vaccination to all immunocastrated lambs occurred four weeks prior to slaughter. Blood samples were collected weekly for eight weeks, and serum C-19 steroid metabolites were determined with ultra-performance convergence chromatography tandem mass spectrometry. Testes were collected at slaughter to assess size and level of tissue activity, as indicated by the cut surface CIE Lab colour measurement, seminiferous tubule circumference and seminiferous tubule epithelium thickness. Serum cortisol concentrations fluctuated but immunocastration had no influence. Serum testosterone concentrations decreased in IC4, IC3 and IC2 lambs between primary and secondary vaccinations, but consistently low testosterone concentrations (<0.5 ng/mL) were only observed a week after the secondary vaccination. Immunocastration resulted in a decrease in testis weight, seminiferous tubule circumference and tubule epithelium thickness across all vaccination treatments, which indicates impaired spermatogenesis. However, the most pronounced decrease in seminiferous tubule epithelium depth was observed in the testes of IC3 and IC2 lambs. The CIE colour a* values measured on the cut testis surface differed between vaccination intervals, indicating potential differences in the extent of interrupted activity. Therefore, the immunocastration vaccination interval of lambs is flexible, while still being successful in suppressing testosterone secretion and interrupting functioning of the testes.