Hello, my name is***** and I have over 20 years of experience as a veterinarian. I understand that you are concerned about your pup Goliath possibly being constipated.
Are you sure that he is constipated (hard, dry small pebbled or large, hard to pass stools)?
Dogs with diarrhea will strain repeatedly as they feel like the have to go because of the irritation but they may only produce a little very soft or liquid stool.
If he has diarrhea rather than constipation then I can give you some suggestions to help with diarrhea.
I would not feed him any food for 24 hours. This should help stop gut spasms and restore normal gut motility. Small amounts of water or ice cubes given frequently are fine as he needs fluid. You can give him pedialyte to replace electrolytes too, but Gatorade is much too high in sugar which can make his colon irritation worse.
Today even with the fast for diarrhea you can start Kao-pectate at 1ml per pound or 1 tablespoon per 15 pounds of body weight every 6 to 8 hours. This is quite safe and will coat his irritated gi tract as well as absorbing bacterial toxins. You can use it for several days until his stools look normal. You can find kao-pectate at the drug store.
If he has a tense painful abdomen, continues to have diarrhea with no improvement after being on kao pectate for 24 hours, becomes very lethargic, begins vomiting or runs a fever greater than 103.5F then he really must be seen by a veterinarian as soon as possible.
After his food fast start a bland diet of 1/3 boiled, lean hamburger (or boiled, white, skinless chicken), all fats and juices drained off the meat mixed with 2/3 boiled, plain white rice. Feed several small meals a day. You might wish to add 1-2 tablespoons of canned pumpkin to each meal if you see mucous in his stools as fiber helps soothe an irritated colon.
Once he feels better (no diarrhea for 48 hours) start mixing in his regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert him back.
However if Goliath is indeed constipated, having difficulty passing firm, dry, very small or large stools, I can give you some recommendations as well.
If he is still eating and drinking normally and not vomiting there are a few things we can do to help him.
One is to increase fiber by adding canned pumpkin (not pie filling, just pumpkin) to each meal. One tablespoon to each meal for a small (poodle or shih tzu sized dog) to 2 tablespoons to start.
These are just guidelines, you can adjust the amount based on his ease passing stool as well as whether his stool is too soft.
If you have Miralax you can use that instead of the pumpkin. Sprinkle 1/8 th 1/4 of a teaspoon on his meals. If you use Miralax make sure to increase his fluid intake as it works by drawing fluids into the intestines and can lead to dehydration if his fluid intake isn't increased enough.
Increasing the amount of fluids in his diet in general will help as well. You can add low salt chicken or beef broth to his food. The more fluids he takes in the better so if he likes to lick ice cubes give him those as well.
Slow walks can also sometimes help to get the intestinal tract moving properly.
If he is vomiting or no longer eating we are probably beyond home therapy. He needs to see his veterinarian. But you can use the above tips for preventative measures in the future. And if he seems to have chronic troubles with constipation pumpkin or Miralax can be used long term if needed.
For either diarrhea or constipation you might also wish to add a probiotic to get his gut bacteria back to normal. Fortiflora, Proviable, or Benebac are very good ones.
Please let me know if you have any further questions.