Rising costs and a ban on certain pork exports to China led Smithfield Farms (SFD.NYSE) to post a 63% drop in first-quarter profits just weeks after a Chinese firm proposed to buy it out for US$4.7 billion, Reuters reported. Smithfield said it has already started to curb its use of ractopamine, an additive used for producing leaner meat, after China and Russia banned the substance. Exports resumed in March, but profit fell to US$29.7 million in the quarter ending April 28, down from US$79.5 million a year earlier. China’s largest meat processor Shuanghui International proposed to buy Smithfield in May.