I find this the most useless. If it costs 1$/day i may as well send them straight to the butcher for sparks. They directly give 20~65$ in pure no strings attached profit immediately. 10 decades would mean that you make a loss just from feeding them at all. Food is scarce in rome D: You can do your part by providing the butcher with more meat immediately rather than wasting it on your pigs. Too bad fiends aren't edible. They reproduce so fast I much rather feed the pig to them and slaughter fiends for sparks.
You're right, now that I "fixed" the rounding error that was making pig feed free, the costs have become too high for it to be profitable. I've increased the calories/spark to accelerate the growth so that growing to Chubby is usually profitable with average nature or below. Growing all the way to Corpulent is not profitable under the new system; at best it is break-even. Therefore, if your assistant is ordered to slaughter pigs automatically, she will now do it at Chubby instead of at Corpulent.
Feeding the pig leftovers during Voluptuous to Chubby and Chubby to Corpulent growth phases is equivalent to reducing nature or metabolism by two levels, meaning that if you disable the leftovers rule on your slave and you have a farmhand, a B+ nature/average metabolism pig grows like an F- nature/average metabolism pig or a B+ nature/weak metabolism pig. Leftovers don't have any benefit for the timings if the slave is already F- nature and weak metabolism. That's the limit for how quick they'll grow.
In total, instead of 105 days from Bony to Corpulent at B+ nature/average metabolism, it's now 23 days. 6 days from Voluptuous to Chubby, 11 days from Chubby to Corpulent.
In total, instead of 54 days from Bony to Corpulent at F- nature/average metabolism, it's now 20 days. 5 days Voluptuous to Chubby, 9 days from Chubby to Corpulent.
A Mature, Healthy, Voluptuous slave is worth 45 - 60$ depending on chest size. Increase physique to Chubby and they're worth 48 - 68$. Corpulent and they're worth 51 - 76$.
A Mature, Enduring, Voluptuous slave is worth 47 - 62$ depending on chest size. Increase physique to Chubby and they're worth 52 - 72$. Corpulent and they're worth 55 - 80$.
So going from Voluptuous to Corpulent increases the value by at least 3$ per level of physique (flat-chested, only healthy) and at most 8-10$ per level (stacked, enduring). Clearly, stacked chests and endurance are the key to profitability. Endurance affects value more for young-virgin than for mature; a healthy young-virgin is worth less than a healthy mature. Enduring young-virgin is the same value as mature at Chubby and Corpulent physique.
Obviously if you already have a pig you don't have room for two, so for pigs you would optimally select enduring mature or young-virgin slaves with average or lower nature and a stacked chest, and dispose of the rest in other ways. But if you're ever without a pig, it's probably still worthwhile to toss a less-than-optimal slave into the barn, as long as you keep an eye on them or have your farmhand on the job.
Using the pig slot to hold "extra" slaves for training is now less of a good idea as it will significantly impact their endurance and physique in a short time period. It is a quick and inexpensive option for getting "Feeble" slaves up to Weakened, though, if you want to do that in parallel with training another slave. If you're not training another slave, it's still faster (though not cheaper) to put a Feeble slave on nutritionist/calculated diet with supplements and rest.
