What brand of food are you feeding? Cheap grocery store brands are sometimes little more than junk food. A high energy breed like a BC requires a premium food and enough of it to supply the calories he burns in his daily activities. There's going to be a BIG difference between the amount of food required to maintain 50 lbs on a BC and the amount required to maintain 50 lbs on a couch-potato breed.

Did you adopt this boy through a BC breed rescue? If so, ask them for food recommendations or contact a BC breeder and ask them.

Laurie

Why do you consider 50 lbs his ideal weight? Border collies' max weight is usually 42-45 lbs. One would hope that he's just getting in better shape from the exercise he's getting, but if you're concerned then a trip to the vet is in order. As Laurie said, the brand of food could be the problem.

Weight loss despite good appetite is can be a sign of cancer in dogs. Hyperthyroidism is extremely rare in dogs and is also caused by cancer. He'd be young for cancer if he's truly 5 years old, but in my experience the shelters grossly underestimate age. Aleks lost 5 pounds but still looked beautiful before he started vomiting and became anorexic due to stomach cancer. The weight loss was my only clue that something was wrong at first.
Usually dogs with malabsorption syndromes have loose stool, but not always. That's a possibility- you may be feeding correctly but his body can't absorb the nutrients. A routine CBC and chem screen may provide some clues as to what is going on. But many times a specific diagnosis requires additional diagnostics.
A really simple cause for his weight loss could be intestinal parasites. I've rarely seen a shelter dog without some sort of GI parasite. A fecal exam could show that very easily.
Weight loss despite good appetite, assuming a properly proportioned quality diet, is always something that should be investigated because always a sign of disease.

I had Max on Iams initially. The Rescue people suggested switching foods, so I followed their advice and put him on Chicken Soup. This hasn't worked so I just placed an order Saturday for Flint River Ranch Salmon and Potato. I have had his stool checked and came out fine. Stool looks good, I am planning on Monday to make an appt with our vet. He is larger boned than most BC's. I had him at the ranch with other rescue's working with sheep and they all said he is way too skinny, he also is quite a bit taller than then the others, that's why I figure probably around 50 would be a good weight for him. They agreed with that also(I mean those who saw him.) So I am getting pretty concerned for our boy. I just wondered if any body has ever seen or know of bc's having this problem.
Hope this clarifies things a little better. Thanks all

If the stool test wasn't recent, you may want to do that again to screen for all potential parasites. Also, you don't say where you're located, but TBDs are no longer just diseases of the south. Don't test just for Lyme and RMSF, make sure they test for Babesia and Erhlichia as well. These will cause weight loss.

PS: I am so excited that your BC has actual sheep work to do!!!!

Thank you Cynthia, I am not sure what all those things are, but I wrote them down and will mention these to the vet.

We are in the Kansas city area in missouri.
We actually went out on Saturday to the farm. Some of the people from the rescue decided to start a sheep herding club. We took our boy out there to play and they tried him on the sheep. He did really well. I was impressed. I think some training he will be pretty good at it. They didn't think he had the sheep instinct in him, but he surprised them. Aaand while we were were there, we took home a couple of pups to foster. LOL
Cappi

My Rottweiler lost 40 lbs and I swear I didn't even know it. This is not a dog tied up in the back yard, she slept on the bed. The vet tested her for everything. I even requested a lead poisoning test because I live in an old house. We tested for every kind a parasite and disease.

I asked if we find out do you think it will be anything she can survive, she said probably not. When I took the male in for yearly shots he too had lost a lot of weight.

The only change was I got a new fence that included the entire backyard instead of half the backyard. That was it. They were running around so much more and I didn't increase their food because I didn't know. I didn't even know they were losing because they both lost at the same rate and were over 100 lbs.

If my vet hadn't known me she surely would have suspected neglect but she knew those dogs were my kids. So I doubled up their food until they put weight back on.

So the cheap easy test feed him more and more and see if he gains.

cappi, Iams is a great food. One of the best because the main ingredient is rice. Eat rice and you are hungry an hour later.

Look at the ingredients of the brands, talk to your vet and figure out what your dog needs for his health. Don't worry about some "Ideal weight" that people say.

If the dog is healthy and happy that is what counts.

If Max checks out at the vet, I'd just assume he's a naturally skinny guy that needs to eat alot. Maybe if you supplemented his kibble with some really high quality canned food that would stabilize his weight. Or see if you can find a kibble designed for very active dogs.

OT...I used to live in Leavenworth, KS, eons ago. I envy you, that is beautiful country out there.

My daughters border collie lost a lot of weight down to 12 KG 4 vets and $2000 later hes still loosing weight. the dog has a good appetite, she eats dogfood,special food, raw meat and still she looses weight, what can we do?
Could someone p[lease help?

get the vet to give him some vitamin b12 shots border collies tend to be prone to malabsorption, if thats the problem he will probably need one shot a month