Does hog size impact manure production?

Daniel Andersen, aka Dr. Manure, addresses a multi-part question about the proper facility design and size to adequately handle the manure produced in a swine operation in a late-April blog. Andersen is an assistant professor in the Iowa State University Agricultural and Biosystems Engineering Department.

He had received the question “why are more swine farmers hauling in spring and fall, why is this occurring, and what is a good number to use for sizing your manure storage?”

He explained that though the answer seemed easy on the surface, but he went onto answer a follow-up question posed, asking how all of this is impacted by feeding hogs to a higher finished weight, say 285 to 315 pounds.

Obviously bigger hogs require more space to grow efficiently, but what do larger hogs mean for manure? Andersen looks mostly at deep pits, but says his discussion points also work for other storage systems.

He starts out by looking at four discussion points.

  1. A recent survey of swine producers around the Midwestern U.S. 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 to 40% in DDGS increases fecal output by 5 to 10%.
  3. Switching from nipple or cup waters reduces water consumption and potentially excess water reaching the manure storage, probably by roughly 5 to 10%.
  4. Pig finish weights have tended to be increasing with 280 to 300 pound finish weights becoming more common.

Andersen writes that he refers to his “old go-to references” of the ASABE Manure Production and Characteristics standard, Midwest Plan Services (specifically the Livestock Waste Facilities Handbook), or an Extension publication from your local land grant university, but he asks if these numbers still apply with bigger pigs.

He and some colleagues recently had a project where they collected manure samples from swine manure deep-pits at around 60 farms for a little over a year. As part of this study every month they measured the depth of manure in the storage pit, which allowed us to calculate manure accumulation rates. The operations had a variety of diets being fed, hogs at various growth stages, a variety of growth units, and they had some different types of watering systems.

They found that on average manure was accumulating at a rate of 1.3 gallons of manure per pig per day (including any wash water used on the site). This was only a little above the ASABE manure production standard rate which suggests about 1.2 gallons per pig per day, so it seems reasonable. However, they saw lots of variation between barns, though they average 1.3 gallons per pig per day, the standard deviation was 0.4 gallons per pig per day. This means there is a lot of variation between barns, and in particular barns have a 25% chance of making more than 1.5 gallons per pig per day.

Larger pigs impact on manure production

But, how will bigger pigs impact manure production? You’d think there would be lots of data floating around about how manure production changes with pig size, but it turns out that’s not typically how we collect the data. It’s normally collected as amount of manure produced over a finishing cycle. So to get an estimate of manure production Andersen used a couple of techniques. The first was looking back at some old manure production standards used to provide an estimate of manure production per 1,000 pounds of animal mass. Using this information we can estimate the manure production rate for lots of different pig sizes. For the second approach, he contacted Brian Kerr, an animal scientist from USDA ARS, who had used some feeding trial data and the MWPS data and prorated it so that manure production didn’t increase quite as quickly in larger pigs as he thought the constant method over-predicted excretion from lager pigs. So these two methods are shown in Figure 1. We expect actual manure production to fall somewhere between those two lines.

Figure 1: Swine manure production as a function of body weight.

The truth is that estimating actual manure amounts gets a little more complicated – do you double stock during the wean phase? When we start selling from a 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.

Click here to read this and other Manure Scoop blogs by Daniel Andersen.

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