Semen after Vasectomy

  My husband and I are considering a vasectomy.  Most things you read say the man's sexual function and semen remain unchanged following vasectomy, however we have come across two references that say a vasectomized man's semen gets progressively thicker over the years until it is the consistency of toothpaste.  Is this so and why would that be?  I don't think we would want to do it in that case.  Thank you.
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Dear Marjorie
Thanks for your questions.
First of all I don