Inhibition of testicular development by suppressing neonatal LH rise in male domestic pigs

The neonatal increase in circulating luteinizing hormone (LH) is crucial for testicular development. In male pigs, blood LH levels start to increase approximately 1 week after birth and return to basal level by 5-6 weeks of age. This study tested the hypothesis that neonatal treatment with a combination of estrogens and androgens suppresses LH secretion and thereby inhibits testicular development. On Day 1 after birth, piglets received a slow-release implant containing estradiol (E₂, 8-40 mg) and trenbolone acetate (TBA, 40-200 mg) or remained intact. At 4 weeks of age, mean serum LH concentrations were ∼ 7 ng/mL in untreated males, whereas pigs with implants had serum LH concentrations < 1 ng/mL. Despite this reduction, LH was still detected in the pituitary glands of treated pigs. Interestingly, neonatal castration also lowered circulating LH, highlighting the importance of testis physiology in the early establishment of the reproductive axis. The higher dose (20 mg E2 + 100 mg TBA) inhibited testis function more effectively, as evidenced by lower circulating testosterone concentrations compared to intact pigs. Furthermore, E2 + TBA treatment had a lasting impact on testicular growth, resulting in smaller testes at 26 weeks of age and the presence of immature Leydig cells. Overall, neonatal E2 + TBA treatment suppressed the postnatal LH rise and testicular growth until market age, offering a potential non-surgical alternative to castration in male pigs.