The results of our DachsLife 2015 survey showed that the odds of a neutered Dachshund suffering IVDD over the age of 3 is nearly double (1.8x) that of an entire Dachshund. Neutering under the age of 12 months has higher odds of IVDD than neutering over the age of 1. (Note: "neutering" includes castration of males and spaying of females) When we analysed our survey, we excluded dogs aged up to 3 as these are much less likely to have IVDD and including them would distort the real risks of IVDD.
This does not mean there is a cause and effect relationship between neutering and IVDD, but it has some parallels with a study of Golden Retrievers that showed neutered animals were more likely to suffer from Hip Dysplasia. Although the mechanism for this is not clear, it is easy to hypothesise about the effects of early neutering on bone and muscle development when an animal is not fully mature. This is discussed in the 2018 paper which analysed the data further.
There is a body of evidence emerging that neutering (and early neutering in particular) has more disadvantages than advantages.
Be very cautious of making a decision to spay or neuter your Dachshund, particularly before the age of 12 months.
There are lots of useful links to research into the pros and cons of spaying/neutering on the "You did what with your wiener" website.