The association between diet estrogenicity in exotic felids and poor spermatozoa quality in tigers (<i>Panthera tigris</i>)

A high incidence of morphologically abnormal spermatozoa has been observed in felid species including snow leopard (SL), Sumatran tiger (ST), and cheetah (CH). In managed settings, these species consume diets different than their wild counterparts, which can contain soy products with detectable levels of phytoestrogens. Previous work has demonstrated that estrogenic diets can interfere with endocrine function and may be associated with reproductive failure. We evaluated the relationship between diet and poor spermatozoa quality in felids by quantifying the estrogenicity of commercial felid diets that were collected from facilities at the time of semen analysis on individual tigers consuming that diet. In vitro estrogen receptor activity was characterized for estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) of each species by treating with purified estrogens, phytoestrogens, and diet extracts. Phytoestrogens activated all receptors, which were more sensitive to coumestrol and genistein than daidzein or equol at lower concentrations. ST ERβ was the most sensitive to coumestrol and genistein (P < 0.05). Of the seven diets tested, three resulted in significant activation of ERβ, two of which contained soy products. The highest levels of activation from each diet occurred on ST ERβ (P < 0.05). Significant correlations were found between three tiger spermatozoa defects and diet estrogenicity: bent midpiece (R2 = 0.2794, P = 0.0079), bent midpiece with cytoplasmic droplet (R2 = 0.1776, P = 0.040), and bent tail (R2 = 0.280, P = 0.0078). The potential for dietary estrogenic compounds to contribute to decreased sperm quality may provide novel insight into one reason why morphological abnormalities persist in captive exotic felid spermatozoa.