The Newcastle document states that, so long as food hygiene is maintained, there is no limit on the amount of milk that can be included in a ration but that too much in a finishing ration is likely to lead to grading issues. (Ie., make them too fat!

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It says that 4.5kgs whole milk can replace 1kg concentrate. However, the protein and lysine would need augmenting - beans or peas would be one way to give this.
On the write-up for skimmed milk, it says to not feed more than 4.5L (1 gallon) per head per day and to use a 'balancer ration' that is lower in protein than the normal ration. In a sow's ration, 3L skimmed milk can replace 0.4kgs feed.
Whey can be used to a max of 10L per day for finishing pigs, at a rate of 15L whey per kg replaced compound feed. Whey from cheesemaking is usually salty, so plenty of water must be available.