In most cases, a Pug will become constipated due to one of these common reasons:
#1 Inadequate water intake.
If a dog is not drinking enough, this can cause stools to harden, which leads to constipation. In general, canines need 1 ounce of water for each 1 pound of body weight. This requirement may increase for active dogs and may also increase in the summertime.
#2 Notable decrease in exercise.
Exercise helps keep bowel movements regular by quickly moving food along to the large intestines. If there is a sudden decline in physical activity, this process takes longer, resulting in more water being absorbed from the food, leading to dry and hard-to-pass stools.
#3 Change in diet.
This can lead to temporary issues including upset stomach, runny stools,
diarrhea, or constipation. If a Pug's main meal is quickly switched to a new brand or recipe, this can cause problems even if the new diet is a better option. Ingestion of certain food including cheese and red meats can also make stools sluggish.
#4 Stress.
An acute episode of extreme stress can throw off a dog's bathroom schedule. This includes a sudden addition to the family, moving to a new home, or a drastic change in routine that results in more time spent home alone.
#5 Holding in bowel movements.
This can happen if a dog does not want to soil inside the house. It’s also common if a dog is in a new place like a boarding kennel or when traveling.
There are other less common but possible reasons including:
Engorged anal glands.
If the anal glands are swollen and engorged, these can partically block the anal opening, making it more difficult to push out stools.
Internal blockage.
This is a very serious condition where a non-food object or hard-to-digest matter causes partial or full blockage. In addition to straining to push out stools, other signs include
drooling, panicked behavior, loss of appetite, vomiting, and/or dry heaving. This is considered an emergency and requires immediate veterinary care.
Enlarged prostate gland.
Relevant for male Pugs, this can develop due to age-related hormone changes but can also be due to bacterial infection or even cancer. Other signs aside from constipation include trouble urinating, blood in the urine and/or the stools (will appear bright red), and/or stools shaped like thin strips (often equated to ribbon).
Other causes.
While rare, an array of other conditions can cause constipation including trauma to the pelvic area, rectal tumors, and certain neurological disorders. For seniors, in particular, arthritic pain in the hips or back can lead to trouble with finding a comfortable stance to push out stools. This hesitation can cause stools back up.