How to divide the most scientific pig compound feed feeding stage?

With the development of large-scale pig breeding, the division of pig feeding stage has a trend of refinement. But at the present stage, the fattening pig feeding stage stipulated by law is 15-30kg, 30-60kg and 60kg-out. Seen in Pig raising magazine two days ago, the fattening stage of Landrace and Landrace is expected to be 25-50kg and 50-100kg. At present, the actual situation in Northeast China is that the body weight of piglets is 8-9kg when they are weaned, and when they are fed to 12-13kg, they start to fattening, and when they are raised to 40kg or so, they start to change the formula of medium pig feed, some feed directly to the pen, and some change pig feed at 70kg. In short, there is no unified standard (the stage division of the national standard of pollution-free pig feeding-2004 is rarely used), so what more scientific division standards can be used for reference? -our company is 0-weaned for 7 days:-20kg / m / m / 60kg / m / m. Birth-- one week after weaning-- 42 days old-- 60 days old-- 90 days-- 120 days-- 150 days-- Thank you for your attention! The division is based on weight and age. As far as large-scale pig farms are concerned, the latter is more important-weight should be the standard of division. -- is it really difficult to tell the difference between weight and days? How do you get it for the record?-- according to the breeding situation-- I think it is still divided by weight, specific to what weight stage or each pig farm according to its own actual situation. -- personally, the division by time is more reasonable, convenient for management, and suitable for intensification-- the scale of breeding is getting larger and larger, and it may be more reasonable to divide it by time. This issue has been debated for a long time. Intensive farming is more reasonable in terms of time division. But what about small-scale farming? -- is it really difficult to tell the difference between weight and days? How do you get it when you put it on record?