Chemical sterilisation of Bos indicus bull calves following intratesticular injection of zinc acetate: Effects on semen quality and testicular changes

• Chemical sterilization was attempted in Bos indicus bull calves using zinc acetate.
• Treatment decreased sperm counts, testis weight and caused testicular degeneration.
• Results did not differ between two dose rates of zinc acetate administered.
• Results confirm that zinc acetate is a potential chemical sterilant in bull calves.
• Variability in responses within and between bulls requires further investigation.

The aim of this study was to determine the effects in Bos indicus bull calves of intratesticular administration of 1 mL of either saline (n = 9) or one of the two doses of zinc acetate (ZA1, 57.75 mg, n = 10 or ZA2, 71.75 mg, n = 10) on semen quality and testicular changes. Semen was collected by electroejaculation on Days 343, 524 and 783 and animals were slaughtered on Day 860. Treatment reduced median maximum number of progressively motile and morphologically normal sperm collected (P = 0.001) and the percentage of animals in which sperm were recovered (saline: 100%, 9/9; ZA1: 44.9%, 4/9 and ZA2: 40.0%, 4/10; P = 0.013). Compared to saline treated controls, treatment with ZA reduced the mean diameter of the testes after Day 34 of treatment (treatment × time, P = 0.013) and total testicular weight at slaughter (treatment: mean ± SEM; saline: 569.4 ± 59.0 g, ZA1: 249.3 ± 72.9 g, ZA2: 247.5 ± 68.1 g; P = 0.004). Histological changes in testes of bulls treated with ZA were characterized by germ cell depletion, vacuolation of Sertoli cells, interstitial fibrosis, epididymal duct atrophy with variable remnants of testicular tissue and degeneration. We conclude that intratesticular administration of two doses of ZA in B. indicus calves is able to severely impair spermatogenesis and cause varying degrees of testicular degeneration and a reduction in testicular diameter and mass. Further investigation is required to determine ways of obtaining more consistent results from treatment.