Roenicke opted to give Mat Gamel a day off and replaced him with Travis Ishikawa.
"I don't know if the shoulder is bothering [Gamel] other than I know it's still sore," Roenicke said. "I don't know if it affects his swing. He says he's fine, which I'm sure he is. Probably if he would have been swinging great the last couple of days he'd be back in there. It's just my observation that maybe a day would help him."
Gamel, who has a sore shoulder from a home-plate collision on Monday, was hitless in eight at-bats in the first two games in St. Louis and committed a costly error in Saturday's 7-3 loss.
The left-handed Ishikawa, who made his fourth start of the season at first base, performed well in two games earlier in the week while filling in for Gamel.
He went 1-for-4 with a two-run home run in the 9-6 win over the Astros on Tuesday, then went 1-for-3 with a solo home run in a 7-5 loss on Wednesday.
"The last time I started him against a lefty like I'm doing today, he had a nice game," Roenicke said of Wednesday's start against Houston's J.A. Happ. "It's not ideal. It would be ideal if he was right-handed. But in his two starts he's had two nice games. We know he's going to play good defense. He's a nice guy to be able to put in there."