Calves is the standard plural of calf in all its senses. Two young cows are calves, and the back portions of your lower legs are also calves. Calfs has never been a widely accepted form, and some might consider it incorrect.
Calf, incidentally, only works as a noun. The verb meaning to birth a calf is calve. The verb’s participles are calved and calving. It also has a secondary sense: to break off a mass at the edge (of an iceberg or glacier).
He would help feed chickens — 135,000 of them — and tag calves on his father’s 250-acre farm. [New York Times]
But her toned calves could still be seen as she turned around in her black high heels by Gianvito Rossi. [Daily Mail]
There are no wild cattle remaining to give us an indication of the natural weaning age of calves. [Principles of Cattle Production, Clive J.C. Phillips]
Surgical techniques to enhance buttocks’ or calves’ volume consisted of placement of silicone implants below the gluteus maximus muscle in the buttocks or over the internal gemellus muscle in the calves. [Autologous Fat Transfer: Art, Science, and Clinical Practice, ed. Melvin Shiffman]
One farmer claims to have damaged his iPhone while calving, accidentally inserting it into the rear of a cow. [Telegraph]
Long calving intervals on Irish farms result in reduced milk yield. [Irish Independent]