This was 5.3 pence ahead of the same auction last year and around 0.4 pence behind last month's auction returns.
Commenting on Thursday's figures, United's Group Chief Executive David Dobbin told Farming Life that while this auction result was over 5 pence per litre ahead of last year, a year-on-year increase of 30%, the dip against last month reflects the recent weakening of international and EU dairy markets as a result of increasing milk supply.
He added: "The EU Farm Ministers' decision to increase EU milk quotas by a further 2% is unwelcome and can only make the situation worse. The decision to increase quota comes just after the Irish Dairy Board's decision to slash their on account price for skimmed powder by 250 Euros per tonne.
"However we are pleased that the auction remained over 5 pence ahead of last year's level, an increase that is absolutely essential for our farmers and one which will be totally swallowed up by higher bills for feed, fertiliser, fuel and other inputs."
"This was our largest milk auction of the year. We sold 54 million litres for delivery in the peak supply months of April, May and June.
"We now have about two thirds of our May milk sold at prices between 22.5 and 23 pence per litre, giving reasonable certainty that the price we pay farmers for their spring milk will be above 20p for the first time in 10 years.
"The EU allocation of 2% extra quota for 2008/09 comes on top of an increase of 0.5% previously agreed for the UK and 10 other member states as part of the 2003 CAP reform agreement.
"The total increase for the EU is 3.9 billion litres - equivalent to double the annual milk output of Northern Ireland."
"Such a large increase in one year will definitely impact on the market. Farmers need look no further than GB where milk supply has been falling and farm milk prices have remained firm.
"We do not want to see a rising supply in a weakening market.
"Milk supply is surging in the US, France, Ireland and Germany. Thankfully dry weather has curtailed the end of season supply in New Zealand and this has helped counterbalance increasing supply elsewhere. The weakness in sterling exchange against the Euro is also helping offset falling commodity prices."
In the auction a total of 57 million litres of milk were sold. Of this, 54 million litres were sold on 3-month contracts for delivery in April, May and June at an average price of 22.60 pence per litre. The other 3 million litres were sold on one month contracts for delivery in April an average price of 22.83 pence. The overall auction average was 22.61 pence per litre, compared to an average of 22.99 pence in last month's auction and 17.30 pence in the auction in March last year.
The Ulster Farmers' Union says dairy farmers will be disappointed with the outcome of this week's auction.
UFU Dairy Policy Chairman Jackson Wright told Farming Life that producers traditionally saw the March milk auction as a time when prices began to move upwards.
He added: "However this month's milk auction was marginally down on February prices. Auction prices continue to be much higher than last year but so are production costs and that is the big topic with producers at present. The cost of feed, fertiliser and fuel continues to rise and strong milk prices are essential for profitability".
Mr Wright said there would be disappointment that March milk prices were not higher: "The Euro is at an all time high against Sterling and this should be boosting returns. Retail prices for milk remain strong and we heard recently at the Northern Ireland dairy conference that Australian milk production continues to be limited by low rainfall.
"Meanwhile global demand for dairy products is growing at 2% per year. These should all be contributing to better milk prices and producers will continue to urge processors to deliver the best possible returns so that producers are able to offset the soaring production costs."
Farmers for Action co-ordinator William Taylor also expressed his disappointment at the outcome of Thursday's auction.
"The European Milk Board is currently quoting a cost of production figure for milk of 30.45 pence per litre," he told Farming Life.
"This week's auction price is some 23 per cent below this level. As a result, significant numbers of local farmers will now find themselves in a loss making situation."
He added: "In contrast retail milk prices are strengthening, while New Zealand and Australia are still coping with the impact of the ongoing drought.
"Local dairy processers are failing their farmer suppliers at the present time. There is significant scope for them to get a better price from the retailers and to have this reflected in the returns generated by milk producers.