Official match statistics show Wales missed six tackles in the 80 minutes. That may not sound like much but the 91 per cent success rate that translates to, is unsatisfactory for the demanding second row.
"I am not sure what is going wrong in the defence," he said. "It is not the standard that we require, and it is very disappointing. It is not through want of trying - nobody goes out there on purpose to miss tackles."
He continued: "We have the systems in place, but they are not working because of missed tackles. We are missing one-on-one tackles at the moment. We had a lot of possession and territory, and that is what makes it all the more frustrating. We have under-performed in this championship. There is no doubt about that with the players we have got. Italy is a big game for us now - we have to pull our fingers out and lick our wounds."
And Shane Williams says there will be no let-up in Wales' search for a solution to shore up their leaking defence.
Ireland's three-try blast at Croke Park means Wales have conceded 10 touchdowns in this season's Six Nations Championship - eight more than when they were crowned 2008 Grand Slam champions.
"Teams are causing us problems, although we are working hard at finding a fix," said the Wales wing.
"Our defence was bad, we made mistakes in key areas and left a few holes which Ireland utilised. Our lack of concentration at times cost us.
"We did not get in the right areas often enough, and you often get punished at international level when you make a mistake."
Italian coach Nick Mallet also blasted his team's defensive performance as he watched France claim a 46-20 victory on Sunday.
He said: "It was the worst match we played for a year. We are pretty disappointed and our defence was very poor," he said. A lot of players played their worst games today and when you do that against France they will score a lot of tries. They were made to look a lot better by our missed tackles but some of our players were well off their best."