Histological Comparison of Testicular Needle Biopsy and En Bloc Samples in Abattoir Calves

SIMPLE SUMMARY: The histological examination of testicular tissue offers a suitable diagnostic method for investigating possible testicular causes of reduced fertility. A diagnostic measure of testicular health or function that does not impair fertility is needed. One possibility could be a needle biopsy of the testis. The testicular biopsy provides the attending veterinarian with a useful tool for plastic evidence of testicular infertility causes. Since the representativeness of this method in equine medicine was questioned, and has not been sufficiently answered in young bull calves so far, this study was carried out on male calves that were sent for slaughter. The aim of this study was to evaluate the significance of needle biopsy compared to en bloc resection. No differences between the individual locations of the tissue samples could be found. The results of the needle biopsy differ significantly from those of the tissue samples in almost all locations. This suggests that needle biopsy does not provide the same histological information as the tissue samples to determine the fertility status of the testes of bull calves. ABSTRACT: The aim of this study was to test whether a single testicular needle biopsy could provide histological results comparable to en bloc resection histology and whether one biopsy was sufficient to reflect the histology of an entire pair of testicles. Two methods of sample collection were tested on 32 bull calves aged five to eight months to compare histological parameters of needle biopsy with those of en bloc resection samples. One testicular needle biopsy of the right and three en bloc samples of both testicles were collected and compared for the number of tubular cross sections, tubules with elongated spermatids (ES), outer/inner diameter of tubules, thickness of tubular wall, and number of Sertoli cells (SC). Additionally, animal data were considered. No significant differences were found between the left and right testis or among the individual locations of en bloc samples. However, histologically significant differences (Bonferroni-adjusted significance level: p < 0.05/6 = 0.0083) were found between the needle biopsy and en bloc resection regarding the tubular cross sections per visual field (p < 0.05), the outer (p = 0.01) and inner diameter and the thickness of the tubular wall (both p < 0.01). In the SOX9 immunohistochemical staining, no significant differences (p > 0.05) could be observed for SC numbers between needle biopsy and en bloc samples. In conclusion, results of testicular needle biopsy do not have the same validity as the en bloc resection histology. Furthermore, one biopsy is insufficient to reflect the histology of the entire testicular pair.