In the agreement in principle reached Oct. 5, Canada conceded an additional 3.25 per cent of its dairy market to imports from the 11 other Pacific Rim countries signing on, most notably the U.S., New Zealand and Australia.
That amount may not seem significant, but until recently, Canada's supply-managed dairy sector offered only the stingiest of tariff-free market access to its trading partners, on specific terms — such as the cheese deal struck with the European Union in 2013.
Small levels of imports are possible while maintaining supply management, if they are managed carefully. The ultimate impact of the TPP on the dairy industry might depend on details not yet available on what kinds of products — and in what amounts — make up that 3.25 per cent.
Unique to the TPP is the prospect of fluid milk crossing the border from the U.S. The terms of the agreement made public earlier this month specify that 85 per cent of fluid milk imports must be processed in Canada before hitting store shelves.
At the initial briefing offered to journalists, TPP negotiators said Canadian health and safety regulations would apply.
"The TPP fully protects Canada's right to maintain and implement measures to ensure food safety for consumers, as well as to protect animal or plant life or health," a trade department spokesman wrote CBC News.
But further clarification recently revealed that doesn't mean dairy producers outside Canada have to follow the same rules Canadian farms do.
Most notably, it's illegal in Canada to administer bovine growth hormone (rBST) to boost milk production in dairy cattle. But there's no such restriction in the U.S.
No new certification or inspection regime appears set to screen milk destined for import into Canada. It's also unclear whether U.S. milk would be segregated at Canadian processing facilities, or simply mixed with Canadian product.
Yves Leduc from the Dairy Farmers of Canada says this "double standard" concerns farmers because it creates confusion.
"It seems incoherent to restrict the use of rBST in Canada, when products made with the hormone can still enter the Canadian market," he wrote to CBC News.
Health Canada banned bovine growth hormone because of animal welfare concerns. It found no evidence of adverse health effects in humans who consumed dairy products originating with rBST-receiving cows.
But some consumers may have concerns about the changing content of dairy products on their shelves.
In an email to CBC News, a Canadian trade department spokesman cited a survey conducted by the U.S. Department of Agriculture in 2007 that found rBST used on approximately 17 per cent of cows in the U.S.
The hormone is not used in the European Union, Australia, New Zealand and Japan, which share Canada's view of the animal health concerns.
The Dairy Farmers of Canada says that when regulators reviewed rBST in Canada, neither farmers nor consumers wanted it.
Canadian farmers use improved nutrition and veterinary monitoring to maximize milk production instead.
A familiar blue dairy cow logo already appears on some 100 per cent Canadian dairy products as a marketing initiative. Consumer education campaigns refer to Canada's "hormone-free" milk as a selling point.
While fluid milk imports haven't been crossing the border, other ingredients derived from milk already are imported: some food processors use a limited amount of things like U.S. cheese for frozen pizzas, for example.
When "modified milk ingredients" appear on a processed food label, the geographical origin is unspecified.
If the TPP is ratified and imports from the U.S. increase, the dairy industry wants more attention paid to labelling.
If the origin of milk ingredients is clearly labelled, shoppers can avoid non-Canadian dairy if that's important to them.
During the 2015 federal election, dairy farmers also lobbied candidates to propose food labelling changes that would identify the percentage of each ingredient, so consumers can compare not just what but how much each product contains.
The Dairy Farmers of Canada believes consumers are on its side.
In late July, it commissioned a national survey from Environics Research that suggests:- 85 per cent of respondents either strongly or somewhat agreed with the statement they "didn't mind paying more for Canadian dairy products because they are hormone-free."
- 78 per cent said it was "very important" that the milk products they use are Canadian, with a further 13 per cent saying it was "somewhat important."
- 87 per cent were either very or somewhat concerned about the TPP lowering Canadian food safety and quality standards.
The interactive voice recognition (IVR) telephone survey of 1,707 Canadians aged 18 and older was conducted July 24-28, 2015, and has a margin of error of 2.4 percentage points, with a 95 per cent confidence level.