Buy-and-hold investing is the key to what makes many of the best investors great in the first place. If you had purchased shares of Amazon.com or Netflix a decade ago -- and held on through today -- then you'd be sitting on a significant chunk of change. While hindsight is 20/20, it's important to acknowledge that buy-and-hold investing only works when you buy great companies, not just those with grandiose promises and slick investor presentations.

One way to uncover investment opportunities that fit the bill is to find trends with long-term sustainability, then find the best companies exploiting those trends. As the second decade of the 21st century comes to a close, two trends with staying power are the emerging dominance of American energy and the under-the-radar need for animal health products. That leads investors to Antero Midstream GP (NYSE:AMGP) and Zoetis (NYSE:ZTS), which, as it turns out, are two great stocks you can probably buy and hold forever.

A pipeline through the forest.

Image source: Getty Images.

Northeast natural gas production could double by 2021

The United States is on pace to become a net exporter of energy by 2022 -- a remarkable turnaround given the last 50-plus years of energy trade imbalances. In fact, the trend will erase a massive trade deficit in energy products that peaked at $321 billion in 2011. While crude oil dominates the headlines in discussions of the topic, other energy products -- such as natural gas liquids (NGLs) and liquefied natural gas (LNG) -- should also be on the radar of individual investors in the long run.

Antero Midstream GP is all over the opportunity. Even better, investors soon will have a simpler way to own a piece of the business and collect a healthy dividend payment. In mid-October it was announced that Antero Midstream GP would acquire Antero Midstream Partners, then convert from a master limited partnership to a corporation. That simplifies the operating structure of the high-growth business and allows income investors to own shares in retirement accounts. Those shares will sport a 4.4% dividend yield, which is expected to grow 27% per year through 2021. 

That above-average dividend growth is supported by above-average growth potential of the underlying business, which supports the operations of natural gas-heavy parent Antero Resources. It's been a sweet gig in recent years. Antero Midstream Partners has grown adjusted EBITDA at a compound annual growth rate (CAGR) of 82% since 2014 just by trying to keep up with the parent's expanding footprint in the gas-rich Marcellus and Utica shales. It should get even sweeter.

While the Marcellus and Utica regions account for 41% of the country's total tight gas production today, they're expected to double output by 2021. The new Antero Midstream will follow that trend by doubling its dividend payout. Remarkably, the company expects to deliver on that goal while self-funding $2.7 billion in growth investments and lowering its leverage ratio to half of the peer average by 2022. Long story short: This business operates at the confluence of superb location, excellent management, and industry-leading investment opportunities -- and that should deliver solid long-term returns for individual investors. 

Cows eating.

Image source: Getty Images.

Animal health is big business -- and pretty profitable

It's easy to overlook Zoetis, but that may be a mistake. Since Pfizer spun off the business in 2013, the stock has absolutely smoked the S&P 500, with a total return (stock performance plus dividends) of 199%, compared to 112% for the index. The company's success has come from quietly delivering on an important yet forgotten niche: medical products for animals. After all, humans aren't the only ones that get sick or need vaccines -- and a $43 billion market cap proves there's a huge market for animal health products.

Zoetis built its industry-leading position by developing, manufacturing, and marketing medicines for animals including livestock, horses, cats, and dogs. It generated $2.8 billion in revenue and $854 million in income before taxes in the first half of 2018, representing year-over-year growth of 11% and 25%, respectively. It ended July with the $2 billion acquisition of veterinary diagnostic developer Abaxis, which serves a corner of the animal health industry that's growing at an annual clip of 10%. And it expects 2018 to be a great year for the business overall.

Management's latest full-year 2018 guidance calls for revenue of $5.75 billion, diluted EPS of $2.81, and adjusted diluted EPS of $3.05 -- all handsome improvements from last year. Looking even further over the horizon provides a peek of what may be ahead for the business. Earlier this year, Zoetis announced a collaboration agreement with Regeneron Pharmaceuticals to develop biologic drugs for animal health applications. Considering there are significantly fewer regulatory hurdles to jump through for veterinary biotech medicine development, the partnership could yield an impressive return on investment for the industry leaders and individual investors alike. 

A businessman with his feet on his desk.

Image source: Getty Images.

Go long and prosper

Buy-and-hold investing is powered by compound interest, which can't work its magic when investors trade in and out of stocks, or don't put their hard-earned money into great companies. It can be difficult to find stocks capable of beating the S&P 500 over the long haul, but finding sustainable long-term trends can simplify the process. Investors that identify American energy production growth or the recession-proof animal health market as powerful investing themes will inevitably stumble across Antero Midstream and Zoetis, respectively. As it turns out, both are great stocks you can buy and hold forever.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Maxx Chatsko has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends AMZN and NFLX. The Motley Fool has a disclosure policy.