ST. LOUIS — Unfavorable product mix, higher trade spending and overall declines in the ready-to-eat cereal category contributed to a 59% decline in earnings at Post Holdings, Inc. during the second quarter.

For the quarter ended March 31, the company had earnings of $4.3 million, equal to 13c per share on the common stock, which compared with $10.5 million, or 31c per share, during the same quarter of the previous year. Sales for the quarter were $248.2 million, down 1% from $250.5 million during the same quarter of the previous year.

The company said selling, general and administrative expenses decreased during the quarter but interest expense increased compared with the same quarter of the previous year.

For the six months ended March 31, the company saw earnings decline 49% to $11.9 million, equal to 36c per share, which compared with earnings of $23.3 million, or 68c per share, during the same period of the previous year. Sales for the six months were $485.1 million, up 3% from $469.8 million during the same period of the previous year. Sales were up on higher volumes and a decrease in average net selling prices. Increases in volume have been the result of growth in the Great Grains, Grape Nuts and Good Morenings brands.