Steroid hormones, boar taint compounds, and reproductive organs in pigs according to the delay between immunocastration and slaughter

Abstract

The producer of vaccine against GnRH recommends that immunocastrated pigs are to be slaughtered within 4 to 6 weeks after the second vaccination (V2). The objective of the study was to examine the effect of shorter or longer delay on steroid hormones, boar taint compounds, and morphologic and histologic traits of reproductive organs. Forty male pigs (individually housed and fed a commercial diet) were assigned within litter to four treatment groups, 10 pigs were left entire (EM27) and the others were vaccinated against GnRH (Improvac, Pfizer Animal Health) at the age of 12 and 19 weeks. Pigs were slaughtered at 21 (IC21), 24 (IC24), and 27 (IC27 and EM27) weeks of age. Two EM27 pigs died during the experiment, one IC21 pig was excluded because of illness, one IC27 pig was a nonresponder, and two pigs (IC24 and IC27) were hermaphrodites. To assess the effect on steroid hormones, blood was taken at 12, 15, 19, 21, and 24 weeks of age. Subcutaneous fat and reproductive organs were sampled after slaughter for determination of androstenone, skatole, morphologic, and histologic measurements. Immmunocastration interrupted the rise of estrogen and caused a substantial fall of testosterone in IC21, IC24, and IC27 pigs. As a result, androstenone and skatole levels were successfully reduced regardless of the time elapsed from V2. The weight of the reproductive organs was also drastically reduced, the shrinkage being proportional to the length of the interval between V2 and slaughter and was the most evident for vesicular glands, followed by bulbourethral glands, and testes. Corresponding changes were observed also on a histologic level with a progressive decrease in the size and number of Leydig cells, a diminishing immunoreactivity of 3β-hydroxysteroid dehydrogenase/Δ-5-4 isomerase, and luteinizing hormone receptor, along with a shrinkage of tubuli seminiferi, atrophy of seminiferous epithelium, and a loss of germ cells, indicating a disruption in testicular spermatogenetic function. Regression of the glandular tissue with a decreasing amount of secreta was also observed for bulbourethral and vesicular glands. The investigated physiologic, morphologic, and histologic traits were progressive with the increasing delay to slaughter (clearly seen already 2 weeks after V2), though no signs of functional or morphological restoration was observed within 8 weeks after V2.