1. A recent survey of swine producers around the Midwestern US (lots of Iowa farms) conducted by the University of Minnesota suggested that about 50% of our farmers were applying once per year and 50% were hauling twice per year.
2. Increasing fiber in the diet (an example being DDGS) increases fecal output from the pig. An inclusion rate of 30-40% in DDGS increase fecal output by 5-10% .
3. Switching from nipple or cup waters reduces water consumption and potentially excess water reaching the manure storage, probably by roughly 5-10%.
4. Pig finish weights have tended to be increasing with 280 to 300 lb finish weights becoming more common.
So where does this leave us? So for a grow-finish operation finishing at 285 lbs my average manure production number is right around 1.1 gallons per head per day, at 300 lbs it is right around 1.15 gallons per head per day. At this time I still use 1.2 gallons per head per day. For a wean finish operation I'd bring that number down to about 1.0 gallons per head per day. The truth is estimating actual manure amounts gets a little more complicated - do you double stock during the wean phase? When we start selling from barn how quickly is it empty? Is there down time between turns? Beyond that it seems like bigger pigs should lead to a bit more manure, but water and feeder systems and barn washing techniques probably still have as big of impact on manure amount variability that it is hard to see the impact of bigger pigs.