The airline said traffic grew to 8.6mln customers last month from 8.2mln a year ago, sending shares up 2% to 15.5p in morning trade.
The load factor, a measure of how full its planes are, remained at 95%.
"Although this is the first time Ryanair has not increased its load factor since March 2017, and only the second time in the past four years, this is not a surprise with load factors nearing their practical maximum," Liberum said, leaving its rating at 'buy'.
Chief marketing officer, Kenny Jacobs said customers can “look forward to more low fares and an improved customer experience” in 2018 as it continues to roll out its so-called Always Getting Better programme.
Ryanair launched the AGB programme in 2014 after drawing criticism over its hard-line cabin allowance and penalties for printing out boarding passes. The company cut some of its fees, including a charge to check in at an airport desk rather than online, and relaxed its cabin allowance. It also improved its website and mobile app.
Wizz Air's traffic soars but load factor falls
Revenue passenger kilometres grew 22.9% to 3.3mln and available seat kilometres increased 24.0% to 3.7mln.
The budget airline increased its seat capacity by 24.4% to 2.3mln as it expanded its route network and fleet.
It added four new routes to and from Romania and Poland and expanded its fleet at London Luton with a new Airbus A321 aircraft.
In February, the company signed a deal, valued in excess of US$17.2bn, for 146 new Airbus aircraft for delivery between 2021 and 2026.
Shares dipped 0.9% to 3,500p.
IAG carries more passengers
The company, which also owns Aer Lingus, Iberia and Vueling, said its load factor grew 1.7 pts to 79.1%.
Revenue passenger kilometres edged up 5.8% to 17.4mln while available seat kilometres climbed 3.55 to 21.8mln.
At British Airways, revenue passenger kilometres rose 1.85 to 10.5mln, the load factor increased 1.2 pts to 78% and the available seat kilometres gained 0.25 to 13.4mln.