Thinking about animal production and sustainability

Last week I had the opportunity to give some freshman agricultural engineering students a tour of a beef feedlot near Ames. I enjoy doing this as I often get lots of interesting questions and discussion about animal production. There is great variety in the student’s agricultural backgrounds. Some grew up on animal farms while others have never seen an animal production facility before; this adds a degree of difficulty to discussing the topic, as you have to keep both audiences interested and engaged.

This means it’s important to cover the basics, i.e., what are we trying to accomplish at these farms, what are potential issues we might have, and what are the basic principles behind what we are doing. We are providing the animals with food, water, and protection to keep them healthy, happy, and growing quickly to make a product… meat, eggs, milk, or fiber. This makes sense as a first cut approach to thinking about the farm and discussing about design for animal needs, but to me the real excitement is a discussion on nutrient cycling at animal farms, specifically talking about the manure.

Nutrients are constantly cycling on farms and how we manage these cycles controls how effective we are at achieving our production goals while limiting environmental impact (of course mother nature plays a pretty big role in the nutrient cycling as well). At animal production facilities our goal is to take nutrients (in the form of animal feed ingredients) and change them into a more valuable form, specifically we are trying to convert them into tasty proteins. What we really want is to get as many of those nutrients as possible incorporated into our animals and then to sell them, unfortunately, only about 10-30% of the nitrogen and phosphorus we feed to animals ends up in the end products (meat, milk, or eggs). The remaining portion of these nutrients is excreted in manure.

Because of these relatively low protein conversion efficiencies (10-30%) many scientific arguments suggest that we need to eat less meat to promote sustainability. However, what many of these arguments fail to consider is that recycling of animal manure in integrated farms (farms with both crop and animal production) keeps a substantial share of the N, P, and K excreted by the animals circulating within agro-ecosystems, and in doings, means those proteins can still be used. This means our actual protein conversion efficiency can be substantially higher than those calculated just by calculating what percent of the nitrogen fed to an animal ends up in its body.

For example if I was to make a guess for swine farms in Iowa, I’d say about 20% of the N we feed ends up in the pig, 15% ends up lost as ammonia volatilization during manure storage, and the remaining 65% gets land applied to serve as a crop fertilizer for next year’s crop. This means that we are really looking at a protein conversion efficiency a lot closer to 85% that the 10-30% we might originally suggest. Of course, it gets a little more complicated as the crop will use not all of the nitrogen we apply to our field; some will be lost during the growing season. As a first guess I’d say about 20% of the applied N will be lost (though it depends on the production practices, crop rotation, soil and weather conditions during the growing season, as well as numerous other factors), but even including this in the calculation we still would estimate a conversion efficiency of around 75%.

Getting our students to start think about these issues, understanding the challanges facing production agricultural, and giving them an opportunity to get their hands a little dirty are crucial steps in continuing to move agriculture forward and getting the next generation of Agvocates ready to raise to the challenges ahead.