Before there was use of ultrasonographic imaging, determination of the ratio of estrogens to androgens in the same individual was a technique used for differentiating the sex of monomorphic animals in captivity, with larger estrogen concentrations in the females. Due to species-specific differences in both concentration and changes throughout the year of these hormones, corroboration of the method is needed in each case. In this study, there was use of a chemo-immuno assay to quantify sex steroids in fecal samples collected from seven (five females and two males) Neotropical otters, Lontra longicaudis. The reproductive season for this species was determined to be between October and March, with increased estradiol in the females and relatively greater concentrations of testosterone in the males as compared with other seasons of the year. Results from utilization of a k-means analysis procedure indicated that the use of steroid ratios in fecal samples to differentiate otter sex is an effective technique when there are evaluations during the breeding season. The estrogen to androgen ratios during this period, however, are the inverse of what was expected, with there being larger testosterone concentrations in the female otters. The ratio of estrogens to androgens in feces of captive otters can be effectively used to determine the sex of otters in the field. We propose this method is reliable for sex determination in wild otter populations during the reproductive season.

在使用超声成像之前，确定同一个体中雌激素与雄激素的比率是一种用于区分圈养单形动物性别的技术，雌性雌激素浓度较高。由于这些激素的浓度和全年变化的物种特异性差异，在每种情况下都需要证实该方法。在这项研究中，使用化学免疫分析来量化从七只（五只雌性和两只雄性）新热带水獭Lontra longicaudis收集的粪便样本中的性类固醇. 该物种的繁殖季节确定在 10 月至 3 月之间，与一年中的其他季节相比，雌性雌二醇增加，雄性睾酮浓度相对较高。使用 k 均值分析程序的结果表明，在繁殖季节进行评估时，使用粪便样本中的类固醇比率来区分水獭性别是一种有效的技术。然而，在此期间雌激素与雄激素的比例与预期相反，雌性水獭的睾酮浓度更高。圈养水獭粪便中雌激素与雄激素的比例可以有效地用于确定野外水獭的性别。