Markets reporter Christopher Adams looks at last year's winners and losers on the stockmarket.

Buoyed by profit upgrades and bullish investor appetite for infant formula firms, A2 Milk soared in 2015 to become the S&P/NZX 50's best-performing stock by a wide margin.

The alternative dairy company's stock price delivered a 220.7 per cent gain for the year, well ahead of the second best performer on the index, NZ Refining, which posted a 69.7 per cent gain.

A2 shares, which closed as low as 46c in February, hit an intraday record of $2.49 on Wednesday, before coming off the boil to close down 9.7 per cent at $1.86 yesterday.

The company upgraded profit guidance for the second time since November on December 18, flagging a "significant uplift" in infant formula sales.

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Operating earnings before interest, tax, depreciation and amortisation (ebitda) in the range of $33 million to $37 million is now expected for the 2016 financial year.

That's a big increase on the previous guidance of $22 million.

The company, which fended off a takeover approach by Freedom Foods and US-listed Dean Foods earlier in 2015, has been riding a wave of Australasian investor enthusiasm for businesses in its sector.

Major rallies were seen in other infant formula stocks, including ASX-listed Bellamy's Australia, which delivered an annual gain of over 700 per cent.

Australian supermarkets have been struggling to meet demand as baby milk has been cleared from their shelves for re-sale online in China.

Last month A2 said its infant formula was selling out despite increased supplies, highlighting the appeal of its brand in Australia and China.

"If you start looking through what A2's doing, it is easy for people to get excited about growth in [the] Chinese infant formula space, pushing into the UK and US markets with whole milk products or milk-based products," Shane Solly, portfolio manager at Harbour Asset Management, told BusinessDesk.

A2 sources its milk from cows selected to produce A2 beta-casein protein, which is claimed to provide health benefits over the more common A1 variety including lower risk of heart disease.

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Meanwhile, NZ Refining, which gained 69.68 per cent last year, has been a beneficiary of the oil price slump, which has reduced its import costs. In August it reported a $65.2 million half-year profit, compared with a $7 million loss in the same period a year earlier.

Speciality chemicals maker Nuplex Industries was in third place, with a 59.4 per cent gain.

In November the company gave guidance for full-year operating ebitda in the range of $140 million to $155 million, which would be an up to 22 per cent gain on the previous year. Retirement village operator Summerset was in fourth place with a 47.3 per cent gain, just ahead of Chorus, which rallied by 47 per cent.

Chorus had a bumper end to 2015. Its shares spiked to a record last month after the Commerce Commission increased the price the network operator can charge the likes of Spark and Vodafone for access to its copper lines.

Z Energy also had a great run in 2015 - rising 46 per cent - largely thanks to the acquisition bid the firm launched for Caltex operator Chevron NZ in June.

The deal still requires regulatory approval, but will provide Z with a 49 per cent share of the local fuel market if it goes ahead.

Seventh-ranked Fisher & Paykel Healthcare had a solid run, with the stock rising 42.4 per cent on the back of strong financial results.

The medical device maker's shares closed up 1.1 per cent at a record $8.90 yesterday, taking the firm's market capitalisation across the $5 billion mark.

"F&P Healthcare is a major beneficiary of a weaker New Zealand dollar, with currency hedges beginning to roll off," said Mark Lister, head of private wealth research at Craigs Investment Partners.

Shares in Auckland Airport, which is benefiting from a tourism boom, also ended the year at a record, closing up 0.2 per cent at $5.75 last night, taking the annual gain to 35.9 per cent.

Accounting software developer Xero managed to scrape into the leader board, in 10th place with a 22.6 per cent annual rise.

As a whole, the NZX 50 - which closed at a record high of 6324.3 yesterday - rose 13.6 per cent in 2015, down from an 18 per cent gain in the previous year.

And now for the worst ...

Healthcare software developer Orion Health floated on the sharemarket with much fanfare in November 2014, but proved to be a big disappointment for investors last year.

Its shares, issued in the initial public offering at $5.70 a piece, were the worst performer on the NZX 50 in 2015, slumping by 44.8 per cent to close at $3.20 yesterday.

The stock plunged in January 2015 when the firm - which didn't provide financial forecasts in its IPO prospectus - reported disappointing fourth quarter revenue figures. They took another hit in June when the company revealed a delay to an expected contract signing.

Many market players believe Orion's shares were priced too steeply in the IPO, which raised $120 million in new capital. "Great company - very badly priced float," one fund manager said last month.

Outdoor equipment retailer Kathmandu also had a tough year, with a 27.8 per cent share price fall, making it the second worst NZX 50 performer.

The company's bottom-line has been suffering from aggressive discounting required to shift excess stock, as well as subdued consumer sentiment across the Tasman.

Kathmandu, which recently fended off a takeover bid from Briscoe Group, reported a 52 per cent drop in full-year net profit to $20.4 million in September.

Sky TV, with a 24 per cent negative return, has fallen out of favour with many investors as it grapples with rising costs and online competition from streaming services such as Netflix.

Its shares took a hammering in October after the firm revealed annual profit would fall by up to 11 per cent.

Shares in Contact Energy, which fell 19 per cent in 2015, slumped last month after the power firm failed to meet market forecasts amid tough competition and higher than expected costs related to bad debt.

Contact's former cornerstone investor, Australia's Origin Energy, sold its 53.1 per cent stake in the company through a $1.8 billion block trade in August.

Big box retailer The Warehouse Group, whose shares fell 14.4 per cent, had another challenging year as the firm tried to convince investors it's on the right track with a turnaround strategy that's involved millions spent on refurbishing stores and acquisitions.

In March the company blamed a disappointing half-year result, which included a 19 per cent fall in adjusted profit to $37.2 million, on a lacklustre performance by its Red Sheds and Noel Leeming stores.

Trading improved in the second-half, and in September the retailer reported full-year adjusted profit of $57.1 million, down from $60.7 million a year earlier.

• The S&P NZX 50 gross index reflects share price movements and any dividends paid. Individual returns listed for companies show share price movements only.