In the first quarter, we grew our top line revenue at 21% operationally, our best quarter ever, with 25% operational growth internationally and 19% growth in the U.S. China and Brazil led our international performance with 75% and 48% operational growth respectively, exhibiting their strength in both companion animal and livestock product sales.
In total, our containment animal portfolio grew 34% operationally based on the strength of our parasiticides and dermatology products, while our livestock portfolio grew 8% operationally with solid growth in cattle, swine and fish products.
It is exceeding expectations and has been well received by customers, with a 90% plus penetration rate in our largest U.S. corporate accounts.
After several successful innovations in the last few years, these products made up 16% of our total sales in the first quarter and includes such brands as Simparica, Simparica Trio, Revolution, Stronghold and ProHeart.
In the containment animal space, we've also continued to be pleased with our diagnostics portfolio, which grew 47% operationally in the first quarter.
Looking ahead, we are raising guidance for operational growth and full year revenue to the range of 10.5% to 12%.
We've built a comprehensive and rigorous approach through our Driven to Care program, and our goals include support for 10 of the 17 United Nations Sustainable Development Goals.
In 2014, our companion animal business was 34% of our total revenue.
Last year, it had grown to 55% based on the strength of our innovation and investment in growth, and we see that continuing to expand.
In the first quarter, we generated revenue of $1.9 billion, growing 22% on a reported basis and 21% operationally.
Adjusted net income of $603 million with an increase of 33% on a reported basis and 34% operationally.
Operational revenue grew 21%, resulting entirely from volume increases with price flat for the quarter.
Volume growth of 21% includes 13% from other in line products, 5% from new products, and 3% from key dermatology products.
Companion animal products led the way in terms of species growth, growing 34% operationally, with livestock growing 8% operationally in the quarter.
Following blockbuster sales in year one, Simparica Trio began 2021 with strong first quarter performance, posting revenue of $90 million, growing sequentially each quarter since launch.
U.S. market share within the flea, tick and heartworm segment is now at an all-time high of 31%, representing an increase of more than 9% for the first quarter versus the same period in the prior year.
Global sales of our key dermatology portfolio were $245 million in the quarter, growing 24% operationally.
We remain confident that key dermatology sales will exceed $1 billion this year.
Our diagnostics portfolio grew 47% in Q1, led by increases in consumable and instrument revenue.
Our swine portfolio grew 19% operationally as large producers continued rebuilding herds as they recover from African swine fever and created significant demand for our products.
U.S. revenue grew 19%, with companion animal products growing 32% and livestock sales declining by 4%.
While severe weather caused a slight decline in vet clinic traffic for the quarter, revenue per visit was up more than 10%.
Our small animal parasiticide portfolio was the largest contributor to companion animal growth, growing 74% in the quarter.
Simparica Trio continues to perform well in the U.S. with sales of $83 million.
The Simparica franchise generated sales of $112 million in the quarter and is now the number 2 brand in the U.S. flea, tick and heartworm segment.
Companion animal diagnostic sales increased 62% in the quarter as the continued recovery at the vet clinic and a favorable prior year comparative period led to significant growth in point-of-care consumable revenue.
Key dermatology sales were $157 million for the quarter, growing 16% with significant growth for Apoquel and Cytopoint.
U.S. livestock declined 4% in the quarter, driven primarily by poultry as producers switching to lower-cost alternatives unfavorably impacted our business.
Cattle grew 6% in the quarter as promotional programs and the timing of generic entrants drove growth across the product portfolio.
Revenue in our international segment grew 25% operationally in the quarter, with companion animal revenue growing 37% operationally and livestock revenue growing 17% operationally.
Companion animal diagnostics grew 18% in the quarter, led by a 24% increase in point-of-care consumable revenue and a second consecutive quarter of double-digit increase in instrument placement revenue.
Swine revenue grew 29% operationally led by growth in China of 128%, marking the third consecutive quarter with swine growth in excess of 100%.
Cattle grew 11% operationally in the quarter as a result of marketing campaigns, key account penetration, and favorable export market conditions in Brazil and several other emerging markets.
Our fish portfolio delivered another strong quarter, growing 39% operationally driven by strong performance in Chile, the timing of seasonal vaccination protocols, and the 2020 acquisition of Fish Vet Group.
China total sales grew 75% operationally, which in addition to the significant growth in swine, delivered 59% operational growth in companion animal.
Brazil grew 48% operationally in the quarter as sales of Simparica, the leading oral parasiticide in the Brazilian market, drove a 73% operational increase in companion animal.
Adjusted gross margin of 71% increased 70 basis points on a reported basis compared to the prior year as a result of favorable product mix, partially offset by foreign exchange and other costs, including freight.
Adjusted operating expenses increased 8% operationally, resulting from increased compensation-related costs and advertising and promotion expense for Simparica Trio.
The adjusted effective tax rate for the quarter was 19%, an increase of 230 basis points driven by a reduction in favorable discrete items compared to the prior year's comparable quarter, partially offset by the favorable impact of the jurisdictional mix of earnings.
Adjusted net income and adjusted diluted earnings per share grew 34% operationally for the quarter, primarily driven by revenue growth.
We resumed our share repurchase program in the first quarter, repurchasing approximately $180 million worth of shares.
For revenue, we are raising and narrowing our guidance range, with projected revenue now between $7.5 billion and $7.625 billion and operational revenue growth between 10.5% and 12% for the full year versus the 9% to 11% in our February guidance.
Adjusted net income is now expected to be in the range of $2.12 billion to $2.16 billion, representing operational growth of 12% to 14% compared to our prior guidance of 9% to 12%.
Adjusted diluted earnings per share is now expected to be in the range of $4.42 to $4.51, and reported diluted earnings per share to be in the range of $4.08 to $4.19.

Summary:
In the first quarter, we generated revenue of $1.9 billion, growing 22% on a reported basis and 21% operationally.
For revenue, we are raising and narrowing our guidance range, with projected revenue now between $7.5 billion and $7.625 billion and operational revenue growth between 10.5% and 12% for the full year versus the 9% to 11% in our February guidance.
Adjusted diluted earnings per share is now expected to be in the range of $4.42 to $4.51, and reported diluted earnings per share to be in the range of $4.08 to $4.19.