If you Google "MegaChon" you won't find much, in fact it will auto correct to MegaCon (comic book and sci-fi conventions) but we promise this is a real thing. For proof, we've asked a few owners to share photos of their beloved MegaChons.
So what exactly is a MegaChon? It's simply a Cavachon who is significantly larger than expected and larger than both parents. They aren't fat, they're just big. Some are long. Some are tall, Some are both. When I had my first MegaChon (Oattie, who is currently 12 years old and 25 pounds), I thought he was rare! How did a dog bred from an 11 pound Bichon and a 14 pound Cavalier hit 25 pounds in 18 months? Over the years, thanks to the many Cavachon and related dog forums, Oattie and I have learned we are not alone and in fact there are many MegaChons roaming the earth and even those who were originally hoping for a smaller dog end up loving this overgrown couch potatoes (although many of us wear of explaining that they aren't a small labradoodle).
When Oattie was born, he was not the largest puppy in the litter. The others ended up around 14-15 pounds. At that time, we didn't have doggy genetics but today we do and so this phenomenon can actually be explained. Before getting in to the genetics, there is one obvious (and somewhat dubious) explanation for some MegaChons. If you did not see the parents, it's simply possible that the breeder is breeding a Bichon and Cavalier that don't meet their breed standards (i.e. they are larger than what's considered normal per the AKC). Breeders may specifically do this in hopes of larger litters as larger females are often able to successfully carry more pups. If you truly want a smaller dog (perhaps for travel purposes), make sure you ask to see both parents and get their adult weight and size as well of photos with them compared to objects in the home (it's sometimes hard to determine size without seeing it relative to another object).
Now, assuming you know your dog's parents were standard (or even small) for their size then you can rest easy knowing that your MegaChon is simply a gentic phenomenon much like the 6'2" son I have (I'm 5'3"). Dog size is a complex trait and despite the best guess of even the most experienced breeder, variations do occur. Approximately 85% of dog size is genetic but the remainder is environmental (nutrition, etc.) or unexplained according to Embark DNA panels. In the case of the MegaChon, I've provided a couple of screenshots to demonstrate how this can occur.
Screenshot #1 - Layla. Layla is one of our female Bichons weighing in at just under 10 pounds (exactly what Embark predicted her adult weight would be). This puts her well within breed standards BUT you can see from the screenshot below that she carries some alleles for larger size traits.
Screenshot #2 - Bentley. Bentley is one of our male Cavaliers who weighs just over 15 pounds despite an Embark prediction that he will weigh 21 pounds. Standard weight for Cavaliers is 13-18 pounds so he's within range but smaller for a male. We chose Bentley for this comparison b/c his genetics differ from Layla although both are average or small.
As a breeder, logic might have us assume that a Bichon weighing in at 10 pounds being bred to a Cavalier weighing in at 15 pounds will produce puppies somewhere between 10-15 pounds. The breeder might also make educated guesses within the litter about future size based on birth weight, sex and whether they carry more Cavalier or Bichon genes in appearance. Prior litters are also helpful in these educated guesses. Many times, the breeder will be right. However, looking at these screenshots we can now understand that our lovable MegaChons are nothing more than a combination of genetics where a puppy ends up with all the "larger" or "intermediate" genes from both parents and suddenly outgrows them both. In our hypothetical one puppy could carry for Larger, Larger, Intermediate, Intermediate and Larger from two relatively small parents. Combine this with environmental factors and you can have an unexpected Magachon.
Those of us with MegaChons would not change them for the world; however, if you specifically want to avoid a MegaChon (perhaps for purposes of in-cabin air travel) or you specifically want to find a MegaChon (they are a great alternative to larger Doodle breeds), Embark's DNA panel can help eliminate or increase your chances by having your prospective puppy screened before purchase. While their size predictor isn't 100% accurate, it's truly the best guess at how much your adult dog will weigh!
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