The D810 is not yet supported by Lightroom. Anytime the camera makers bring out a new camera, makers of third party raw converters have to go out and buy one and profile the color rendition and such and then bring out an update to the software before the software will read the files. Some camera makers (but not Nikon) share new models with companies like Adobe to get their cameras supported or they use a file format that is non-proprietary such as dng giving you support in Lightroom from the day the camera is released, but Nikon doesn't do that and then you have to wait until the next Lightroom release unfortunately.
Thank you for the answer.
Any idea on how to get more specific info?
No, you'll have to wait until Adobe releases LR 5.6. You can also download the ACR 8.6 release candidate from Adobe beta labs and use the DNG converter included to convert the D810 nefs to dng. Those will work in LR 5.5. Adobe Photoshop Camera Raw 8.6 RC for CC and CC 2014 Release Candidate | digital camera raw file support - Adobe Labs