Turning to Slide seven. Period end loans in our core loan portfolio were $20.7 billion down 3% for the quarter, as we continue to see borrowers reduce leverage as expected in early 2021. Line utilization in the overall portfolio has dropped from 68% pre-COVID, the 62% at the end of the first quarter of this year, with the largest declines occurring in the energy, healthcare, and general C&I portfolios were cumulative line utilization is down from 65% pre-COVID to 58% today.
As the economy continues to reopen, we feel confident that line utilizations will normalize and our positive outlook for loan growth will materialize later this year.
Over the long-term, we've always grown our loans at two times to three times the normal rate of GDP growth. And we believe our competitive position will continue to serve us well, once macro-economic factor stabilize.
Looking at the energy portfolio, balances contracted 7.7% for the quarter.
While commodity prices have continued to improve and stabilize, sourcing new deal sufficient to offset pay downs in the current environment remains a challenge, as existing borrowers continue to reduce leverage. Despite these factors, we remain optimistic for lending and energy related revenue opportunities, as we continue to support our customers in this space. This industry vertical provides a great example of how we manage the Bank to the long-term economic outcomes, as opposed to short-term optics.
During the first quarter, we recognized a $14 million gain on energy property sales from an equity interest, we received as part of a workout in this most recent downturn.
We have consistently indicated a willingness to own foreclosed assets.
One of the short-term impact of this was higher non-performing levels, we held the assets until such time, the market had improved and that's we're in a position to provide a full economic recovery on this loan. Healthcare balances were largely unchanged this quarter, as a pocket of growth in senior housing loans was offset by a decrease in hospital system loans.
Looking forward, we remain confident in our healthcare portfolio of long-term growth and credit outlook and expect it to return to its status, as a growth leader for us, as health and economic conditions migrate into a more normal state later this year. PPP loan balances increased to $166 million or nearly 10% and represent 8% of total loans. We originated $544 million of new PPP loans this quarter, maintaining our strategy of focusing on our existing client base, to ensure timely support of our existing client needs. Growth from new originations this quarter was partially offset by pay downs of the first round of loans, forgiveness activity from previous rounds of PPP were slower in the first quarter than our expectations. The net interest revenue impact was about $10 million less than we anticipated. This should just move into future periods when the forgiveness occurs.
Looking ahead, we remain optimistic in our outlook for loan growth in the latter half of this year, once these unprecedented levels of liquidity normalize. The speed of vaccine distributions and the resulting broader economic recovery today leads us to believe confidence and resulting capital investment will return to the US economy later this year.
Turning to Slide eight, you can see that credit quality continues to be a clear differentiator for BOKF. We saw meaningful credit quality improvement across the broader loan portfolio with below expectation charge-offs and criticized asset levels this quarter. This coupled with the near-term stability in commodity prices and dramatically improving economic metrics, lead us to release $25 million in reserves this quarter. Net charge-offs were down from $16.7 million or 31 basis points annualized, net of PPP loans in the fourth quarter to $14.5 million or 28 basis points annualized net of PPP loans this quarter. Net charge-offs totaled 31 basis points, net of PPP loans over the last four quarters, at the lower end of our historic loss range. The combined allowance for loan losses totaled $385 million or 1.86% of outstanding loans at quarter end, excluding PPP loans. The combined allowance for credit losses attributed to energy was 3.29% of outstanding energy loans on March 31st. Non-accruing loans decreased significantly, down $19 million from last quarter, primarily due to a reduction in non-accruing energy loans. Potential problem loans totaled $422 million at quarter end, down significantly from $478 million under on December 31st. Almost all potential problem loan classes were down compared to the prior quarter, led by potential problem energy and general business loans.
Looking ahead, from a credit perspective, there is still a degree of uncertainty in the current environment.
So it remains difficult to predict. That said, based on what we know today and assuming our economic forecast is in-line as we advance, we believe 2021 net charge-offs will remain consistent with our experience over the last 12 months. We'll continue to set our reserve with the appropriate level, as we always have.
We are generally positive about the credit outlook for the remainder of the year, allowing us to continue to release this quarter. Once we have more clarity around the spread of COVID-19, case count reductions, vaccine distribution and a broad resumption of regular economic activity in 2021, we could potentially see additional opportunity for reserve release this year.
Turning to Slide nine.
You can see the brokerage and trading fee revenues are down this quarter. When looking at fee income and net interest income generated from our brokerage and trading business comprehensively, the business is down about $15 million linked quarter. This is largely due to some reversion from record volumes in the third and fourth quarters and compressing margins in the mortgage industry that impacted trading margins by about 70 basis points compared to the last quarter.
In addition, customer hedging revenue decreased $2.1 million, primarily due to a modest decrease in energy customer hedging activities from the record fourth quarter. Investment banking revenue decreased $2.1 million, mainly due to timing of loan syndication activity.
While the net interest revenue and trading revenue related to our enhanced mortgage trading desk experienced a slowdown from the record levels in 2020, as expected it is still a major contributor to the overall success of the Company and it's still up over 15% from the same quarter a year-ago. Mortgage banking revenue decreased roughly $2.2 million linked quarter, but remained strong despite a national lack of housing inventory and rising interest rates.
While margins have been relative to historic levels in the summer of 2020, they remain roughly 45% above where they were in March of 2020. Total production volume this quarter remained consistent with prior quarters and looking ahead, inventory constraints could continue to build a case for these elevated production levels to be sustainable, as it will take a while, before inventory has materially improved. Other revenue increased $2.1 million this quarter, due to higher revenue from repossessed oil and gas properties.
Although not included on Slide nine. I'll also note that net economic changes in the fair value of mortgage servicing rights and related economic hedges are positive $4.7 million during the quarter. I'll now turn the call over to Steven to highlight our NIM dynamics, and the important balance sheet items for the quarter. Steven?