ST. LOUIS — Merger and acquisition costs, Post separation costs and costs related to plant closings contributed to an 8% decline in earnings for Ralcorp Holdings, Inc. during the first quarter.

For the first quarter ended Dec. 31, 2011, the company had earnings of $65.3 million, equal to $1.18 per share on the common stock, which compared with income of $71.3 million, or $1.30 per share, during the same quarter of the previous year. Sales for the quarter were $1,380.9 million, up 18% from $1,173.3 million.

The results include the operations of the North American private-brand refrigerated dough business of Sara Lee Corp. and the operations of the Post cereal business. The refrigerated dough acquisition helped boost sales, but during the quarter Ralcorp also faced $2.7 million in costs related to the separation of the Post cereal business. In addition, the company had about $5.6 million in expenses related to acquisitions.

The Branded Cereal Products segment posted operating profit of $34.9 million, down 30% from $49.7 million during the same quarter of the previous year. Sales for the quarter were $214.4 million, down 3% from $221.6 million during the same quarter of the previous year.

Operating income within the Frozen Bakery Products segment was $33.9 million, up 47% from $23 million during the same quarter of the previous year. The segment had sales of $308 million, up 59% from $193.7 million during the same quarter of the previous year.