What would cause a cow's production to halve overnight?

[U-Turn]

We've got a new cow...a first-timer Jersey who came to us about 3 weeks ago. She's been giving us about 2.5 gallons/day (milking twice/day) since she came. Now today, all of a sudden, she's giving less than 1.5 gallons. Nothing seems to be wrong otherwise...she looks just fine and no sign of mastitis or anything. Our first thought is that another yearling may be stealing milk (not her calf, but from a different cow). But, is there anything else that could make milk production plummet like that overnight? I don't want to assume a milk thief and overlook something important.

[DaleK]

All kinds of things. Is she eating the same? Drinking normally? Is it a hot spell there? Manure look normal? Maybe she's in heat? Etc. etc.

[Valmai]

I immeadiately thought of a change in the weather as well.

[copperhead46]

I'd look to her being in "heat" that will cause a drop in production, too.
P.J.

[U-Turn]

It must've been that she was in heat. When I told dh last night that was one of the possibilities, he said that she was...and she's back to normal this morning! Thanks for the help! Our other cow didn't do that, so I didn't know it was a possibility...learn something new every day!