This is my take on it.
Greenfeed is output positive (2 items in for 3 items out)
Premium greenfeed is output negative (4 items in for 3 items out)
It's just easier to use regular greenfeed.
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i always feed my animals premium feed for best returns.
I tend to them only once per 24 hours about 8 hours before reset so their mood is is always maxed for leavings. Essentially, when I log on I feed them with premium food and collect leavings right after. There is no need to feed them twice a day to keep their mood up. The garden lets you produce more than enough veggies so it is not harder to feed them with the best food.
I feed them every other day with the tier 2 food and still get 2 items more often than not.
Thinking about feeding them less
Let's keep it simple.
Feed each animal 1 premium greenfeed per day. I do it at around 8-10pm EST. By the time I pick up leavings (which are supposedly snapshotted around 4am EST), they are still gleeful but maybe only 2/3 full. Just 1 per day. Nothing else. By the time I feed them at 8pm, they tend to be chipper still and the premium tops them off to gleeful.
Let's talk cropland by which we feed these 20 animals (which is a little less simple).
1 feed per day for 20 animals, equates to 40 feed per two days. A crop cycle is 2 days. To make the math divide in evenly, let's talk every 6 days. 6 days = 3 crop cycles. 6 days = 120 feed going to the animals. 120 feed is 40 synths. 40 synths requires 160 yield from your crop land. Every plot yields 5 crops per 2 days. To get 160 yield over 6 days, you need to allocate 10 2/3rd plots just to feeding your animals. Make it 11 to keep it simple.
If you give up 11 crop plots to feed your animals 1 premium greenfeed daily, it leaves you with 9 plots for the workshop. Spread out those 9 plots however you want. 1 of each type of remaining seed for the other 9 spots. Or whatever you want. I honestly find that the the cropland items aren't highly valued in the workshop. It is more common that the animal leavings and granary items have the most value, even factoring in popularity and demand.