Q. My dachshund recently started Straining to defecate. His stools are very hard and are light colored. He is eating and drinking normal. No vomiting.
DR. MASSIMO ORIOLES, DVM, MRCVS
A. Different causes could be the reason for the constipation.
Dry diet, or excessive fiber in the diet, or inadequate water intake could be the most common and ''easy''ones to identify (I would recommend to change diet to a wet one in this case or add some liquid paraffin to the diet). Other common ones are anal gland impaction and infections, which may cause pain on defecation.
Prostatic enlargement and inflammation of the prostate could be another possibility.
Foreign bodies might be a cause, even though less likely from what you are describing)
If he is not showing any other sign as you said I have the feeling that may be only dietary related.
After you tried to change his diet, I would recommend to take him to your veterinarian to have him checked (rectal palpation to assess prostate size, abdominal palpation to assess any discomfort).