My Labrador is normally ravenous like crazy, but for about a week now he's only eating half his food. He seems fit otherwise though and playful, goes for walks normally. Could it be the heat? It's over 30 degrees in July right now.
The combination of heat and eating less isn't really a big problem at first if he's otherwise lively - a lot of dogs just turn down their appetite when it's warm.
What the others didn't mention: pay attention to whether he's drinking more or if you notice behavioral changes like more panting or sluggishness - that would be a sign of heat stress rather than just loss of appetite.
Smaller portions at cooler times of day are a good idea, but if that doesn't improve in two or three weeks or he starts seeming listless, you should get it checked out.
Heat can actually play a role there - dogs usually eat less when it's over 30 degrees because they don't need as much energy and the stomach upset comes from the warmth.
As long as he seems otherwise normal, plays and drinks, I wouldn't worry too much, but keep an eye on him for another week.
If it doesn't get better or he seems lethargic, take him to the vet - could just be a tooth or mild stomach upset, but you should get that checked out.
try feeding him in smaller portions throughout the day and especially in the evening when it's cooler - that often helps more than just blaming the heat alone.
with labs it's typical that they eat less in extreme warmth, but if he's otherwise doing well and playful, i'd just watch him for a week first and if needed try some moister food types or pureed stuff, that goes down easier.
if it doesn't get better after a whole week though or he becomes lethargic, you should still go to the vet just to make sure there's nothing else going on!
I've experienced this with my own dogs too, and what the previous answers didn't mention: it's important to check whether he might just be eating too quickly or if his stomach is sensitive to the heat. Some dogs actually get a bit queasy in high temperatures - it's similar to how we feel when it's too warm and we just don't want a big meal. But I'd still rule out fever, because loss of appetite can also be a sign of infections or minor zoonoses. A quick check with a thermometer (rectal, around 38.5 degrees is normal for dogs) would give you clarity on that.
In addition to the tips about smaller portions, what I'd also recommend: pay attention to whether his drinking habits have changed. Some dogs do drink more in the heat, but not always proportionally to eating a bit less food - that's completely normal. But if he's drinking as usual and his weight doesn't drop noticeably over two or three weeks, you honestly don't need to worry. Labradors are actually pretty robust dogs. If nothing improves in two weeks though, or if he becomes lethargic, then I'd go to the vet - just to make sure there's nothing else going on.
Don't forget that dogs need to drink even when it's hot - if he's eating less, make sure he's getting enough water. That's actually more important than the amount of food itself. If he seems otherwise healthy and is playing, it's usually just the heat in most cases. Labs are generally more relaxed about eating than their reputation suggests.
That said, I wouldn't just write off the heat as the reason. A week is quite a while - check if maybe he's eating stuff while you're out (treats, leftovers) that he's not telling you about. Some dogs snack all day and then eat less at home. You should also check if his stool is normal or if it's loose. That would point more to an upset stomach rather than just heat.
If he's still eating only half as much after another week, or if he gets lethargic or seems off - then go to the vet. But as long as he's playful and his bathroom habits are normal, you can keep an eye on it for now. Smaller portions in the evening are a good idea, but don't stress about it.
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