Table 2.
Male contraceptive agents in veterinary medicine.
| No. | Veterinary Male Contraceptives | Mechanism of Contraception | Hormone Status Alteration | Contraceptive Efficacy | Main Disadvantage |
|---|---|---|---|---|---|
| 1 | Gonadectomy/castration—surgical and with mechanical castrators | Permanent, bilateral removal of the testicles [62,77] | Yes | Proven 100% effective in all species [62] | Irreversible contraception with disruption to the hormone cascade [62] |
| 2 | Vasectomy | Occlusive contraception by bilaterally ligating the vas deferens | - | Proven 100% effective with appropriate washout period [63] | Irreversible contraception [63] |
| 3 | Epididymectomy | Occlusive contraception by bilaterally ligating the epididymis | - | Proven nearly 100% effective [63] with appropriate washout period | Irreversible contraception [63] |
| 4 | Vasocystotomy | Surgical redirection of the vas deferens, resulting in retrograde ejaculation into the urinary bladder [65] | - | Yet to be proven beyond pilot studies | Surgical risk and requirement of skilled personnel |
| 5 | Chemical castration with glycerol, calcium chloride, DMSO, formalin | Damages testicular parenchyma, which reduces spermatogenesis and testosterone production [67] | Yes | Can theoretically be used in any species [67]. Contraceptive efficacy varies by chemical. | Testicular necrosis and fibrosis with associated pain |
| 6 | GnRH agonists: deslorelin, leuprolide | Downregulation of receptor’s sensitivity to endogenous GnRH | Yes | Proven effective in many companion animals [58]. Contraceptive efficacy depends on the formulation. | Off-label use in most species due to limited formulations |
| 7 | Progestins like altrenogest | Progestin-based altered hormone cascade [69] | Yes | Proven effective in dogs [69], stallions [70], but contraceptive efficacy varies by formulation | Numerous side effects due to increased progesterone levels |
| 8 | Immunocontraception—GnRH vaccines | Causes an immune response to the GnRH molecule, thereby reducing endogenous production of GnRH | Yes | Proven effective in multiple domestic and wild species [71,72,73,74]. Contraceptive efficacy varies by species and vaccine formulation. | Not an ideal contraceptive in all species based on population dynamics [75,76] |
| 9 | Gene silencing | Prevents expression of critical genes by inhibiting their transcription ** | - | Yet to be proven beyond theoretical possibility | Very high degree of precision required for formulation |
| 10 | Testis-specific serine kinase (TSSK) protein targeting | Potential target since it is essential for sperm maturation and conserved among species | - | Yet to be proven beyond theoretical possibility | No proven evidence of efficacy |
| 11 | Reversible sperm inhibition—RISUG | Occlusive contraception temporarily blocks the release of sperm. Reversed with DMSO. | - | Yet to be proven beyond pilot studies | Yet to be proven effective in fertility trials |
| 12 | Triptonide | Altered spermatogenesis resulting in morphologically abnormal sperm—not fully understood ** | - | Proven effective in mice and monkeys with 100% penetrance [13] | Only available as an oral formulation requiring daily dosing |
** Mechanism of action not yet fully understood despite an apparent reduction in male fertility.