The most common cause for a dog to walk backwards is pain in the rectal area. In most cases the anal glands are the problem. Often a dog will drag their behind on the ground or carpet and their anus area has a bad odor and can be swollen. You will want to check to see if your dog's anus is swollen. This may cause a dog to also lick the area.
The anal glands are 2 sacs on either side of the anus at about the 4' o'clock and 8 o'clock positions. If your dog has been licking their anus and/or dragging it, it could also indicate that they are full. This problem can usually be resolved by emptying out the glands. To empty them or express them, you will want to cover the area with a tissue and press your finger on the dog's anal glands with an upward motion. A foul smelling liquid should come out. If nothing comes out and your dog appears to be in pain, you should take him to the Vet. Your vet can do this easily, as he is experienced at it.
Excellent site on anal glands
If your dog has eaten rawhides, bones or ingested non food items, it might be a problem with the object moving through his bowels causing discomfort or even severe constipation might cause a dog to walk backward. If an object has been ingested, it might cause a blockage in which case your vet will need to be consulted. Usually with a blockage you see vomiting and a loss of appetite along with an inability to defecate. If you are sure that no foreign object, rawhide or other similar item has been ingested and you haven't noticed a bowel movement then you might try adding a teaspoon of mineral oil to his food to help move things along or use a glycerine suppository. You don't want to use this too much. You might also try taking his temperature as that often starts things moving along as well.
Tramadol is usually prescribed at a dosage of 1-2 mg per pound every 8-12 hours. The range is up to 5mg per pound every 8 hours but the dosage should be kept at the lowest effective dosage. Read more on this here:
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