I soap at 120 degreesF for my lard soaps, but that's only because I have other fats mixed in with the lard that need a higher melting temp to stay liquid throughout the soaping session. My lye temperature for these particular lard batches is at about 110-115 degreesF. I've never had a piggy smell or overheating at these temps- all has always gone well and smoothly for me, and I make a lot of lard batches.
If it was just 100% lard that I was using, I would only heat the lard on low until just melted, which is way lower than 140 degreesF. Also- I would let my lye cool down to about 100 to 100 degreesF before mixing in with the 100% lard. Here is a chart of the melting points of each particular kind of lard:
Melting point backfat: 30–40 °C (86–104 °F)
leaf fat: 43–48 °C (110–118 °F)
mixed fat: 36–45 °C (97–113 °F)
Smoke point 121-218 °C (250–425 °F)
It sounds like your lard may have gotten overheated. Heating it to 140 and then adding freshly mixed lye solution to it would bring the temp up even higher than 140, seeing as how fresh lye solution is very hot. Not to mention the added heat on top of that that comes from the normal chemical reaction that happens when lye and oils are mixed.
At this point, I wouldn't throw your soap out just yet. Let it sit and cure for awhile before making that decision. You'd be amazed what a good cure can do for some seemingly botched batches.
If after 4 to 6 weeks of curing it still
smells like a barnyard, I would toss it if it were me. I wouldn't even try to rebatch it at that point for it may make it worse seeing as how you have to subject the soap to even further heat to melt it down. It's never easy to throw out a batch, believe me I know
, especially 10 lbs. worth, but sometimes you just have to cut your losses and start afresh.
Next time, I would make a much smaller batch, say 2 lbs worth, to see how it goes before making a larger batch. It's much easier to throw away 2 lbs if it comes to that than 10 lbs.
I feel your pain!