Pub group JD Wetherspoon said a slowdown in business in October and higher costs would hit its operating margins, knocking its shares on Wednesday morning.Wetherspoon said like-for-like sales increased 6.3% in the 13 weeks to 26 October and total sales rose 11.3%.Sales were good through August and September, but like-for-like growth decreased in October.The operating margin in the period was 7.7%, compared with 8.3% in the same period last year. In October, the pub group increased pay for hourly paid staff by 5%, utility costs increased about 4% and there were several cost increases from suppliers.Wetherspoon said in a trading update: "As a result of the slowdown in sales growth in October, combined with the cost increases referred to above, the company is currently anticipating an operating margin in the range of 7.2-7.8% for the current financial year."The company is aiming for a satisfactory outcome for the current financial year."Shares dropped 52p or 6.25% to 780p at 08:58 in London.