Thursday, May 21, 2015

Bigger Pigs, More Manure – A Follow-up

On April 23rd I posted a blog entry called “Bigger Pigs: More Manure and Impact on Facility Design.” Though they didn’t all get shared on the post (note there are like zero comments there), but I did get a few helpful emails and had several good conversations about it with different colleges.

As I discussed there were a few (lots) assumptions that went into making that estimate, but a big one was the growth curve of the pig. I pulled a growth curve out of the literature and rolled with it, thinking it would probably be ok; I mean I needed something to work with, but after looking it over, that growth curve seemed low - I mean it wasn't bad, the average daily gain was 1.8 lb/day, but as several people pointed out not only are we growing bigger pigs, but finish times are often decreasing as well. As I got to thinking about it, I wondered what does this mean for manure production?

So to answer this question I needed some growth curve data to work with. As a starting point I found a table published in National Hog Farmer showing that in 1980 a typical finish pig (at least at the research site they found a useful study from) had an average daily gain of about 1.50 lb/day, took 105 days to get to market, and had in and out weights of 49 and 206 pounds respectively. The same report said that in 2001, a typical rate of daily gain was 1.95 lb/day, the pig took 102 days to get to market, and had in and out weights of 62 and 260 respectively. As a point of references, the latest PIC wean-to-finish manual suggested the expected performance of a grow-finish pig was 2.03 lb/day going from 60 to 270 lbs (103 days), with optimized performance at 2.36 lb/day going from 60 to 270 lbs (89 days)

So where does that leave us? Well, it seemed like the best place to start was with the model I developed in the last post, but modifying it with different growth curves and seeing what happened. In this work I’ll focus on just grow-finish average manure production and look at the four new cases, i.e., 1.5 lb per day, 1.95 lb per day, 2.03 lb/day, and 2.36 lb/day and going to finish weights of 206, 260, 270, and 270 lbs and using initial weights of 49, 62, 60, and 60 respectively. Just for fun I'll compare that to the manure production I estimated from the growth curve with 1.8 lb/day with a start and finish weight of 60 and 270 lbs.

In the first case (that 1980 pig) I got an average manure production of 0.96 gallon per day, or about 100 gallons of manure being produced as I get that pig to market. In the second case (that 2001 pig) I got 1.15 gallons per day, or 117 gallons of manure produced in the time it took to get the pig to market. Finally, for the average 2015 pig I got 1.17 gallons per day, or 120 gallons of manure to get that pig to market. Finally, what about that optimized 2015 pig? I’d estimate about 1.17 gallons per day from that pig, but only 104 gallons to get it to market because of the more rapid finish time.

So, bringing it all back - what does this mean to us. To me, it still looks like bigger finish weights will lead to more manure, but improved genetics that are leading to larger daily gains and faster finish times. As a result, even though we are getting more manure on a daily basis, our total volume of manure per amount of pork produced seems to be going down.