Relationship between estrous status and urinary near infrared spectral patterns in Bornean Orangutan (Pongo pygmaeus)

For promoting in situ and ex situ conservation, it is important to estimate the density distribution of fertile individuals and the female estrous status for breeding. Also, there is a need for developing an easy monitoring method to discriminate between physiological states. To date, physiological state has generally been determined by measuring hormone concentration using radioimmunoassay or enzyme immunoassay (EIA) methods. However, 　these methods have rarely been applied in situ because of the requirements for a large amount of reagent, instruments, and a radioactive isotope. These factors complicate the analysis of hormonal data not only in the wild but also in zoos because of the number of staff required for conducting measurement as well as economic reasons. Therefore, there are few zoos in which staff measure hormone concentrations on a daily basis.
This NIR region absorbs mainly bonds related to oxygen (O), carbon (C), nitrogen (N), and hydrogen (H). All biological samples contain many a lot of C-H, O-H, and N-H molecular bonds. Therefore, this technique enables the attainment of obtain the qualitative and quantitative information regarding the chemical composition of biological samples. The present study used NIR spectroscopy to examine the possibility of detection of estrus from urine.
Daily urine samples had been collected from female Bornean orangutans (Pongo pygmaeus). Transmittance spectra of samples were analyzed from 1300 to 1600 nm (NIR System 6500: Foss, Laurel, USA). Also, 100 uL urine was placed in drops on the 21 mm diameter glass microfiber filter paper (GF/B: Whatman, Maidstone, UK). The urinary filter paper was dried in an airtight container with silica gel (10% volume). From the urinary filter papers, the NIR diffused reflectance spectra were measured by using the NIR spectrometer (MPA: Bruker, Ettlingen, Germany) from 2100 to 2400 nm. The reference data, i.e., the urinary estrone-3-glucuronide (E1G) concentration which is a part of estrogen metabolite was measured by EIA method.
In the result of transmittance spectra, characteristic 12 water absorbance bands were discovered, which displayed high urine spectral variation, suggesting that hydrogen-bonded water structures increase with estrus. The variation was similar to one that we have reported in female giant panda (Ailuropoda melanoleuca) (Kinoshita et al., Scientific reports, 2013). However, the degree of variation in orangutan was smaller than that in giant panda. It was suggested that this was related to their different reproductive style, i.e., they are whether mono-estrus or poly-estrus. Estrus state in mono-estrus animal shows more dramatically-different from anestrus state than that in poly-estrus animal. It was reflected in the deference spectra in between estrus and anestrus. On the other hand, diffused reflectance spectra of urinary filter paper showed high accuracy (R2 = 0.68) in E1G partial least square regression models. From these results, it was suggested that urinary NIR spectra have a possibility of detection of their estrus status in both liquid and dried filter paper. The main component of the body is water. Further comparative researches of these two kinds of spectra will enable to understand the changes of biological liquid with the estrus.