Donaldson Co. Inc. will close its muffler plant in Grinnell, Iowa, by the end of next year because of technology changes that made the traditional “off-road” mufflers nearly obsolete, the company said Wednesday.

About 75 workers will be affected by the closing.

Employees learned about the plant closing from managers Wednesday morning. Employment at the 62-year-old factory had dwindled from 200 eight years ago to 75 today.

The plant, which makes mufflers for large tractors, combines, construction and other “off-road” vehicles, will see its work relocated to Donaldson’s muffler and emissions controls factory in Alabama.

Grinnell employees, however, are not expected to make the move, the company said. Donaldson and the United Auto Workers union are negotiating a severance package for those losing jobs.

Bill Cook, CEO of Bloomington-based Donaldson, said in a statement that closing the Grinnell plant was necessary because stricter fuel laws are gradually making stand-alone mufflers obsolete.

“Demand for our muffler products has fallen steeply as our customers moved from [noise control] mufflers to emission control systems,” Cook said. “The need to align our global manufacturing capacity to remain cost-competitive is the overriding reason for our plan to close the Grinnell facility.”

Donaldson Assistant Treasurer Rich Sheffer said in an interview that the government’s newer diesel-fuel requirements led the industry to create more advanced “emission control systems” that not only squelch sound but also remove diesel particulate, measure exhaust gases and temperatures and employ sensors.

While Donaldson controlled 50 percent of the ag and construction vehicle muffler market, it controls less than 20 percent of the emissions controls market, Sheffer said.

Donaldson’s Alabama plant makes both product lines and will take on Grinnell’s remaining work. Grinnell now mostly provides traditional mufflers to the aftermarket sector, which outfits older trucks with new parts.

Donaldson last closed a factory around 2000, when it shut its 125-employee plant in Oelwein, Iowa, during an industry slowdown. The company still has a plant in Cresco, Iowa, which was not affected then and will not be affected now, Sheffer said. The Grinnell building and land will most likely be sold, he said.

Donaldson, which last opened a new factory in Pennsylvania in 2002 and expanded one in Indiana in 2009, has 140 global locations and 12,800 employees, including about 1,300 in Minnesota.