I had a really nice device on SSP that could do that without any waste. It is huge however.
Two placeholder where adult cow/pigs could be place. In those there is a dispenser with wheat that mate the two of them. Right after, 3 minecart are moving beside them to take the 2 adult and the child. A railcraft device detect if they are adult or not, sending the child one to a "growing" enclosure and the adult into the "ready" enclosure. Minecart are frequently sent into the "growing" one to fetch a animal and check if it has grow or not to put them in the "ready" enclosure if yes (and back in the growing if not). A timer can do the same to fetch adults and send them back to the holders to breed, or you can manually send a signal.
The problem is that animal don't stay in the minecart when you delog and SMP will make some animal glitch out of the holders... that is why animal need to be sent back to larger, safer enclosure.
Very efficient on wheat usage, but costly on time to make it and in redstone for logic gate.
In SMP, I only did railcraft feeding station and solve the wastefull wheat consuming with a very large automated wheat farm.
Redpower is good; two row of wheat with deployer that plant them and piston that realease water to harvest after 40~60minutes timer (2 large, 7 long-drop-7long-drop-7long ect... and repeat the rows as needed)
OR
Filler with buildcraft... way more simple and cost efficient, but somewhat less reliable... Obisdian pipe are 5 high from the soil(4 air space between the soil and the pipe), powered by combustion engine they cover a 9x9 area to fetch drop.. warning; put them 1 lower, and they cover 7x7 only.
I recommend first option if you like to engineer and experiment, but the second if you are ok with a simpler design that works.
Of course ccensors now can automate with more reliability, but it hurt to get into it if you never have done something like that before