If he is eating and pooing ok, then it might be that he is burning the weight of with either play, or staying warm.
My 2 b's, the male is able to keep himself in shape, my girl, tends to be like me and can drink water and gain weight! laugh.
Hopefully, if you just add a bit more food to your thin boy, he might bulk up a bit more.
Thanks for the reply! :o
Duke is just over 2 years. As of today, he weighed 21.5. His brother from the same litter weighed 26 pounds. They eat together and we watch them, so it's not that his brother is taking his food.We are learning the hard way about bad breeders. I am going to get my paperwork from the breeder out and write them a nice letter. Our other B Raj has had persistent skin rashes and other problems. Both boys had demodetic mange. I feel like so many of these problems are a result of bad breeding. Reflecting back on it now, the person we bought them from was like a mini-puppy mill. She bred B's, boxers, pugs, and I think one or 2 others.
I would have to agree with you about where you got your boys… but lucky for them that you have given them a great forever home... and yes... someone that breds that many different breeds is certainly on a short list of a mini puppymill at least IMO.... Doubt that you will get any satisfaction from the breeder....
Again, I would not think that he has IPSID without the other symptoms... how big is he? Does seem that he is underweight.. but again depends on size and body build... anyway you can post some pictures?
Here's a pic of Duke a few months back-
Here's one from New Year's-
He's basically in the same position. The one from New Year's really shows his ribs.
Here's one to compare our 2 B's. You can see that there's not nearly as much meat on Duke as Raj.
And just an extra one because they look so cute in their jackets!
The weight loss could be exactly what Sharron said, Duke may have a higher metabolism and as he gets thinner then burns more calories to stay warm so he get even thinner. Some of my dogs keep weight easily while others have to eat significantly more just to maintain weight. Feed the boys separately and try to slowly increase the amount that Duke is eating. Maybe adding some wet food to one of his meals to help boost calories.
With Raj's skin problems, have you had his thyroid checked? Skin and coat problems can often be symptoms of a thyroid problem.
Gosh they are cute! I love their coats in the last picture!
Thank you to all of you for all your advice and insight! It really helps!
I was thinking about seeing if they make like a dog weight gainer. Maybe that in addition to the blood tests will help and give some answers.
Thank you again!
PS- This site is addicting! I think I might become a regular poster!
PS- This site is addicting! I think I might become a regular poster!
I agree but tell my boyfriend that it's a "healthy addiction" 
They have some supplements but I have one who runs thin and the best thing I found for keeping her weight up was a high quality, high calorie food. She does really well on puppy food, Wellness Puppy, mixed with some Merrick's canned food. She just burns a lot of calories so needs the extra fat that is in the puppy food.
Very cute boys… and yes, I can see the difference between the two pictures of him... He looks to be about 2lbs under weight and hopfully the blood panel will shed some light on what the problem might be... and it could be as easy as he is just burning more calories then Raj. For sure feed them separate. What are you feeding?
UPDATE-
Duke's blood tests all came back normal. Looks like he might just be a higher energy dog than his brother, thus he needs a higher calorie diet. We're going to probably pick up some other food this weekend. I've been looking at Blue Buffalo. In addition to this, I'm trying all sorts of veggies on both of them. Thus far Duke love carrots, so it's a nice additive to his diet.
Thanks to everyone for all your help and advice!! 
rocky stopped eating a lot after we got mia..made me really nervous..
i just switched to blue buffalo yesterday and i caught him snacking earlier today
maybe hes just tired of his old food? i think thats what it was with rocky.
UPDATE-
Duke's blood tests all came back normal. Looks like he might just be a higher energy dog than his brother, thus he needs a higher calorie diet. We're going to probably pick up some other food this weekend. I've been looking at Blue Buffalo. In addition to this, I'm trying all sorts of veggies on both of them. Thus far Duke love carrots, so it's a nice additive to his diet.Thanks to everyone for all your help and advice!!
That is great, did they do a full thyroid panel? To do a full panel it needs to be sent out, as the part that is done with a regular blood panel is not the complete test. Low Thyroid is very common to Basenjis and can cause a bunch of different symtoms….
rocky stopped eating a lot after we got mia..made me really nervous..
i just switched to blue buffalo yesterday and i caught him snacking earlier today
maybe hes just tired of his old food? i think thats what it was with rocky.
I would bet with Rocky it was the pup, not the food….;)
