can I breed these two?

Francismilker, your vet maybe a very good vet, but he's no geneticist. Too many people think genetics is like mixing paint (I've actually been asked by people who were truly puzzled why their puppies weren't gray, as one parent was black and the other white) nor like shuffling 2 decks of cards (my hair, his nose, my ears...pick a feature..go fish) but far more complicated.

In cattle (though not in every animal) it is very well proven that the bull goes a long way towards determining the size of the calf. While a Jersey/Charolais will likely be at least a little smaller then a pure Charolais there is not even the slightest hope of it "taking after the mother's side" and being as small as your average Jersey calf - or even a big Jersey calf, as that vet would have you believe.
It is a simple and well-proven fact that a cow bred to a bull known to throw big calves will have a big calf, sometimes big enough to kill her. You should ask that vet to think about that next time he's called out to pull a calf or do a C-section to save the cow!!!

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A ship in the harbor may be safe, but that's not what ships are built for

I think I detect a little animosity here Otter! As I understand it, the decision has already been made to not use the Charolais bull. I was trying to shed some after thought on it. It never hurts to look at both sides of the coin.

On the flip side, can you explain to me how my accidentally bred jersey heifer last week had a 31 lb. calf out of a MS bull? I bought him 1-1/2 years ago as a two day old bottle calf that weighed 89lbs. My personal opinion is that the mother being jersey played a pretty good part in it.
BTW, this heifer was only five months old at breeding. She was not even expected to be bred. She was my son's show project and was fed a pretty good feed mix to keep her in good condition. She was well into her last trimester before pregnancy was detected. This high protein/high fat feed should have also contributed to a larger birthweight calf.

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Francismilker

"The effectual fervent prayer of a righteous man availeth much" James 5:16

Why not use AI you can use the bull of choice a lot easier. If you can find her in heat the Neighbor, vet or the technition can breed her with no expence or danger of the bull . There is program to breed at a certain time that the vet should be able to help with.A bull is a big resposeablity and can be dangerous or just take the cow to the bull down the road

Sorry Francismilker, no animosity!! Just a little peeved that a vet who should know better would say something like that. I've seen an obstetrical saw used and it's not pretty.

I'm glad everything worked out well with your son's heifer. I can't explain it except there's an exception to every rule and I'm glad for you, your son and the heifer that you lucked out.

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A ship in the harbor may be safe, but that's not what ships are built for