Background: Soybean isoflavones are structurally similar to mammalian estrogens and therefore may act as estrogen agonists or antagonists. However, it has not been determined if they have any negative effects on reproductive parameters in male livestock. Therefore, the objective of this study was to evaluate the effects of soybean isoflavones on male reproduction using Chinese mini-pig boars as a model. Fifty Xiang boars were randomly divided into five groups and fed diets containing 0, 125, 250, or 500 ppm soybean isoflavones or 0.5 ppm diethylstilbestrol for 60 days.
Results: Dietary supplementation with 250 ppm of soy isoflavones markedly increased the testis index (P < 0.05), fructose content (P < 0.05), and α-glycosidase content in testicular tissue (P < 0.01), as well as increased the number of viable germ cells (P < 0.01) and the level of Bcl-2 protein (P < 0.01). However, 500 ppm of soybean isoflavones significantly reduced both testis and epididymis indexes (P < 0.05) and lactate dehydrogenase levels (P < 0.01), as well as reduced serum LH and testosterone levels (P < 0.05). High levels of soybean isoflavones also increased malondialdehyde levels (P < 0.05), as well as increased the numbers of early and late apoptotic germ cells (P < 0.01) and the level of Bax proteins (P < 0.05) in the testis.
Conclusions: The results of this study indicate that consumption of soy isoflavones at dietary levels up to 250 ppm did not adversely affect reproductive parameters in Chinese mini-pig boars whereas higher levels of soy isoflavones may adversely affect male reproduction.