We kept driving innovation and strengthening our diverse portfolio of 13 blockbusters and more than 300 product lines across eight species and seven major product categories.
For the full year, we generated 9% operational growth in revenue primarily based on new products in our companion animal business, the continued strength of our key dermatology portfolio and growth in China.
And as part of our long-term value proposition, we once again grew revenues faster than the anticipated growth for 2020, and faster than the historical industry rates of 4% to 6%.
For the full year, we delivered operational growth of 10% in adjusted net income while adapting our operations in the pandemic and continuing investments in our pipeline and new product launches.
We are guiding operational growth of 9% to 11% in revenue for full year 2021.
Our investment plans and focus on growth for 2021 include, continuing the successful launch of Simparica Trio in the U.S. and other markets as well as the ongoing adoption of other new parasiticides, Revolution Plus and ProHeart 12, driving growth in dermatology through increased use of direct-to-consumer advertising and disease awareness campaigns in the U.S. and globally.
Our focus remains on growing this market and increasing customer loyalty through our innovative treatments, which we expect to help us top $1 billion in annual sales for the first time.
We had another exceptional year with revenue of $6.7 billion and adjusted net income of $1.8 billion, both exceeding the high end of our November full-year guidance range.
Full year revenue grew 9% operationally and 7% on a reported basis with adjusted net income increasing 10% operationally and 5% on a reported basis.
Going deeper into the numbers, price contributed 2% to full year operational revenue growth with volume contributing 7%.
Volume growth consisted of 3% from new products, 3% from key dermatology products and 1% from acquisitions, with other in-line products flat for the year.
We again saw broad-based revenue growth with the U.S. growing 11% and International growing 7% operationally.
The innovation we brought to the market and the diversity of our portfolio was key to our strong performance, as companion animal grew 17% while livestock was flat on a year-over-year basis.
Performance in companion animal was led by our parasiticide portfolio, bolstered by the launch of Simparica Trio which generated revenue of $170 million.
This added approximately $150 million of incremental revenue and exceeded our expectations set prior to the pandemic.
Sales of Simparica also grew double-digits for the year with operational revenue growth of 16%.
Our key dermatology portfolio demonstrated continued strength in 2020 growing 23% operationally, generating revenue of $925 million and increasing more than $170 million versus prior year.
Operational growth and adjusted net income of 10% were driven mainly by strong revenue growth and operating margin expansion.
Now, moving on to our Q4 financial results where we posted another strong quarter with revenue of $1.8 billion representing an increase of 9% operationally and 8% reported.
Adjusted net income of $438 million is an increase of 3% operationally and flat on a reported basis.
Operational revenue grew 9% with 2% from price and 7% from volume.
Volume growth of 7% consisted of 4% from new products, 3% from key dermatology products, 1% from acquisitions and a decline of 1% from other in-line products.
Companion animal products led the way in terms of species growth, growing 25% operationally, while livestock declined 5% operationally in the quarter.
Companion animal parasiticides grew 52% in the quarter, gaining market share in the U.S. of more than 7% within the flea, tick and heartworm segment, versus the same period in the prior year.
This includes the continued adoption of Simparica Trio which generated sales of $60 million in Q4.
Our key dermatology products, Apoquel and Cytopoint again had significant global growth in the quarter with $257 million of revenue, representing 27% operational growth versus an extremely difficult comparative period in which key derm grew 29% for the fourth quarter of last year.
This was the primary driver of the 5% operational decline in livestock for the fourth quarter.
Now moving on to revenue growth by segment for the quarter, U.S. revenue grew 11% with companion animal products growing 30% and livestock sales declining by 15%.
For companion animal, the positive trends at the vet clinic continued in Q4 with patient visits up 2% and revenue per visit increasing by 13%.
Simparica Trio performed well again in the quarter with sales of $56 million.
Key dermatology sales were $176 million for the quarter, growing 32% with significant growth for Apoquel and Cytopoint.
Companion animal diagnostic sales increased 22% in the quarter as a result of reference lab expansion and growth in point-of-care instruments and consumables.
U.S. livestock declined 15% in the quarter driven primarily by cattle, which had a portion of Q4 sales pulled into the third quarter as a result of the earlier movement from pasture to feedlot.
Revenue in our International segment grew 7% operationally in the quarter.
Companion animal revenue grew 17% operationally and livestock revenue grew 2% operationally.
Companion animal diagnostics grew 16% in the quarter, led by an increase in point-of-care consumable usage.
Swine revenue grew 14% operationally, posting a third consecutive quarter of double-digit growth.
Swine sales in China grew in excess of 100% for the second straight quarter.
China total products grew 45% operationally in the quarter and 34% operationally for 2020.
Brazil was also a significant contributor to international growth in the quarter, growing 18% operationally.
Adjusted gross margin of 67.7%, fell 80 basis points on a reported basis compared to the prior year resulting from other manufacturing costs, inventory charges, recent acquisitions and elevated freight expense.
Adjusted operating expenses increased 10% operationally, resulting from increased advertising and promotion expense for Simparica Trio and Apoquel, partially offset by T&E savings.
The adjusted effective tax rate for the quarter was 13.5%, a decrease of 70 basis points, driven by the impact of net discrete tax benefits, partially offset by the jurisdictional mix of earnings.
And finally, adjusted net income and adjusted diluted earnings per share for the quarter grew 3% operationally.
In December, we announced 25% annual dividend increase, continuing our commitment to grow our dividend at or faster than the growth in adjusted net income.
In addition, we resumed our share repurchase program in January with $1.4 billion of remaining capacity under the current authorization.
For 2021, we are projecting revenue between $7.400 billion and $7.550 billion representing 9% to 11% operational growth.
We are expecting foreign exchange favorability in 2021 of approximately 200 basis points.
Beginning with dermatology, our guidance does not assume a meaningful competitive entrant in 2021 and with continued investment behind the franchise, we believe revenue will exceed $1 billion for the full year.
For the remainder of the P&L, adjusted cost of sales as a percentage of revenue is expected to be approximately 30% which is relatively consistent with our cost of sales in 2020.
Adjusted SG&A expenses for the year are expected to be between $1.775 billion and $1.85 billion with the increase from 2020 focused on supporting primary drivers of revenue growth, including recent and future product launches, key brands and recent acquisitions and reference lab expansion in diagnostics.
Adjusted R&D expense for 2021 is expected to be between $500 million and $520 million as we remain committed to investing in pipeline opportunities for new therapies and lifecycle innovation.
Adjusted interest and other income deductions is expected to be approximately $260 million with the increase over 2020 driven by increased interest expense as well as lower interest income.
Our adjusted effective tax rate for 2021 is expected to be approximately 20%.
Adjusted net income is expected to be in a range of $2.08 billion to $2.13 billion, representing operational growth of 9% to 12%.
Finally, we expect adjusted diluted earnings per share to be in the range of $4.36 to $4.46, and reported diluted earnings per share to be in the range of $4.02 to $4.14.
To summarize, 2020 was another exceptional year in which we delivered 9% operational revenue growth and 10% operational growth in adjusted net income.

Summary:
Now, moving on to our Q4 financial results where we posted another strong quarter with revenue of $1.8 billion representing an increase of 9% operationally and 8% reported.
Finally, we expect adjusted diluted earnings per share to be in the range of $4.36 to $4.46, and reported diluted earnings per share to be in the range of $4.02 to $4.14.