U.S. manufacturing growth slowed sharply in January as factories cut production and new orders plunged by the most in 33 years, an industry report showed Monday. The Institute for Supply Management (ISM) said its index of manufacturing activity fell to 51.3 last month from 56.4 in December. The January activity level was the lowest since May 2013 and was well below economist forecasts of 56. In the ISM survey, any reading above 50 indicates expansion in the manufacturing sector, while a reading below 50 reflects contraction. The January reading marked a second consecutive month of slowing growth from November's recent peak reading of 57, which had been the highest since April 2011, suggesting the economy may be losing some of the momentum it had seen in the second half of 2013. According to the ISM report, new orders fell to 51.2 from 64.4 in December. The 13.2-point drop was the biggest monthly decline in the component since December 1980, when the U.S. economy was in recession. Indicators of employment, production, and inventory growth also declined in January. At 52.3, the employment reading was the weakest since June and significantly below December's 18-month high of 55.8.