ST. LOUIS — Net income at Post Holdings Inc. in the first quarter ended Dec. 31, 2011, totaled $12.8 million, equal to 37c per share on the common stock, down 45% from $23.4 million, or 68c per share, in the same period a year ago. This was the company’s first earnings report since it was spun off in February from Ralcorp Holdings.

Net sales during the quarter ended Dec. 31 were $219.3 million, down 2% from $223.7 million in the same period a year ago. The sales decline primarily reflected a 3% decline in overall volumes, which partially was offset by higher net selling prices.

“Volumes were down across most of the Post brand portfolio, driven by lower trade spending compared to the trade spending levels a year ago with the exception of Great Grains, which experienced a 13% volume increase supported by a national advertising campaign to re-launch the brand,” Post said in a March 8 filing with the Securities and Exchange Commission.

The company said volumes for its Honey Bunches of Oats and Pebbles brands each declined 4% during the first quarter.