My 5-month old daughter started taking bottles of expressed breast milk about 1 month ago, since her mother needed to go back to work. Up until 5 days ago, she takes about ~24 oz per 24 hours (3 feedings of 5-6 oz during the day, and 1-2 feedings of 4-5 oz during the night).
Starting about 5 days ago, she would only take about 2-3 oz per feeding (turns her head away or refuses to suck on the nipple after that), with the last feeding of the day (~7pm) being especially bad (only take 1-2 oz from bottle, and her mother then breast feeds her after that, which she does take). The night feeding is ok, once for 5 oz.
As a result, her total intake now is only about 15-16 oz per 24 hours.
She doesn't really cry out of hunger, and does not show any other signs of distress (smiles, no cries for no reason, reasonably energetic) during the day or night.
What can be the cause? Should we be concerned?