Decrease in pumped amount - question

Mrs.AMB07

DD gets one bottle of pumped milk a day for bottle practice and so DH can feed her. I sometimes pump while she's having that feeding, but mostly I pump after she's in bed for the night. Up until about a week ago we had needed a shield, and I'm excited to say we're finally done with that! The thing is, ever since the very day we stopped the shield my pumped amount has drastically dropped.

I still pump roughly the same time, if anything it's a little later than her last feeding, so I figured I'd given myself plenty of time to "refill". I went from 5-7 oz. one day, to 3, 2, and now today only 1.5 oz. The change came as soon as we dropped the shield. I don't think there's a supply issue since she's wetting plenty and gaining properly. She's content.

I know you can't judge your supply by the amount you pump, but since all factors are bascially the same and it's decreasing it has me wondering. I can't think of why it would have dropped so quickly. Any ideas?