Originally Answered: Is "because he likes it" a good reason to feed a dog something?
"Because he likes it" CAN be a decent reason as long as the food isn't terrible and there are no alternatives. However, in this case, I actually flinched reading what the poor dog eats.
Dachshunds are already painfully prone to spinal problems. The less strain on their backs, the better, and ANY extra weight puts huge stress on the vertebrae. Dachshunds have the tendency to become lazy and obese without the help of disgustingly fatty foods. Even a little extra weight might seem like no big deal, but think about how small those dogs are.
Scale them up, and think about it. If a dachshund was the size of a golden retriever, one extra pound of fat would be like seven pounds. Two pounds is like fourteen pounds of fat. Three pounds like twenty-one, and so on -- and that's when your puppy is full-grown at about ten pounds.
If he's like seven pounds now, one extra pound is like TEN extra pounds.
If it makes more sense, scale him up to being a person. If he were 140 pounds (a little less than my Mastiff puppy), one extra pound would be equivalent to twenty extra pounds! If he's two pounds overweight, that's like if he were forty pounds overweight.
As he's only a growing puppy, it's imperative that he receive proper nutrition. THIS is the time he needs it.
Let's look at Beggin' Strips. The first FOUR ingredients -- which make up the vast majority of the food -- are WHEAT, CORN GLUTEN, more wheat, and more corn. Guess what? Those are some of the biggest culprits for dog allergies, and they do nothing positive nutritionally. Bacon doesn't even factor in until the TENTH ingredient. It makes up very little of the treat. How can your dad expect him to glean ANY nutrients out of this stuff? It is pure junk food. It's like feeding your four-year-old nothing but Twinkies and Big Macs.
Then there's Pup-Peroni. Admittedly, yes, this is a better choice than Beggin' Strips.. as a TREAT. The first ingredient is beef. The second ingredient.. meat by-products. Great. That can mean anything from roadkill to the nastiest, most disgusting bits of the animal. After soy grits (isn't soy another major dog allergen?), SUGAR. Sugar in large quantities isn't healthy for ANYONE.
For crying out loud, these products even specify on the package that they are intended ONLY as TREATS. Can't your dad read?
Fatty foods can be special occasion things. Sure, he can have a SMIDGEN of spaghetti, RARELY. That will not hurt him.
Dogs REQUIRE protein. They are CARNIVORES.
Check out this article of the protein a dog (or puppy) requires:
Here are some more articles on puppy nutrition. Feel more than free to share them with your dad.
Hopefully, there are a few foods your dad NEVER feeds. Most important? Chocolate, grapes and onions. As many as six grapes can potentially prove fatal, and onions are toxic as well. (Tiny amounts won't hurt -- for instance, a dash of onion powder in a food.)
Here's a chart that very clearly shows how much chocolate (and what kinds) can harm your dog:
Pencils and pens can easily prove fatal. If he swallows a shard of wood or plastic, it is VERY easy for the sharp object to perforate his internal organs. Hi, guess what else? That ends in about a 70% mortality rate. SEVENTY. If he gets a shard of pencil puncturing his gastrointestinal tract, he only has a THIRTY PERCENT CHANCE OF SURVIVAL, give or take a bit. Does that hit your dad hard enough?
I hope he doesn't think his dog is a special case, either. This can happen to ANYONE'S dog. Heck, it happened to my NEIGHBOR's dog, a standard dachshund. It's pretty simple: dog swallows something sharp, the something sharp stabs through organs, dog dies.
He's a little guy, too, so he would only have to swallow something small for an obstruction to be caused. Less deadly than a perforation. Still deadly.
So, let's see. Yeah, he can feed his dog whatever he wants, as long as he expects his malnourished, obese puppy to die young and miserably, potentially murdered by, say, a pencil.
Oh, now here are some articles about the negative effects of poor nutrition.
(Hey, look, the last one even targets Dachshunds specifically. Maybe because of how devastating poor nutrition can be to them, huh. Here are more for Dachshunds:)
Ooh, this one seems REALLY helpful:
Assess how overweight your puppy might be now. Here is a scale to use according to his appearance. Scores of 4 or 5 are ideal.
1 – Ribs, lower back vertebrae, pelvic bones, and all bony prominences evident from a distance. No discernable body fat. Obvious loss of muscle mass.
2 – Ribs, lower back vertebrae, and pelvic bones easily visible. No fatty areas felt. Some evidence of other bony prominence. Minimal loss of muscle mass.
3 – Ribs easily felt and may be visible with no fatty areas felt. Tops of lower back vertebrae visible. Pelvic bones becoming prominent. Obvious waist and abdominal tuck.
4 – IDEAL: Ribs easily felt with minimal fat covering (i.e. they feel slightly padded – think of feeling a hand knuckle through a thin cloth glove). Waist easily noted when viewed from above. Abdominal tuck evident.
5 – IDEAL: Ribs easily felt without excess fat covering. Waist observed behind ribs when viewed from above. Abdoment tucked up when viewed from side.
6 – Ribs felt with slight excess fat covering (i.e. they feel padded – think of feeling a hand knuckle through a thick glove). Waist is discernible viewed from above but is not prominent. Abdominal tuck apparent.
7 – Ribs difficult to feel because there’s a heavy fat covering (i.e. think of feeling a hand knuckle through snowmobile gloves). Noticeable fat deposits over lower back area and base of tail. Waist absent or barely visible. Abdominal tuck may still be evident.
8 – Ribs can’t be felt due to heavy fat covering or can be felt if using significant pressure. Heavy fat deposits over lower back area and base of tail. Waist absent. No abdominal tuck. Obvious abdominal distension may be present (i.e. a visible beer gut).
9 – Massive fat deposits over chest, spine and base of tail areas. Waist and abdominal tuck completely absent. Fat deposits on neck and limbs. Obvious abdominal distension.
Good luck, for the sake of the poor dog.
EDIT: Whoops, forgot to answer something. NO, dogs cannot tell what they should or shouldn't eat. There are exceptions when a dog might be wary of something that smells suspicious. But those are exceptions. That's why TEN THOUSAND dogs die every year from ingesting antifreeze. It tastes sweet and is completely lethal, but all they know is that it tastes good.