Each mower is equipped with 60in rear discharge decks.
East Ayrshire operations manager Felix Wright said: "The main reason for increasing the fleet size is that the zero-turns have considerably reduced the amount of pedestrian mowing that we have to do.
"The 997s can be used in the same areas as the walk-behinds, but we can get round the route that much more quickly.
"We generally replace mowers every three-years and to date we've been very happy with them."
Wright added that the mowers fuel efficiency was a key factor in the council's decision because they require considerably less downtime.
This has led to the council's grass-cutting cycle being reduced by one day and a significantly lower fuel bill.
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