A process-based deterministic model was used to model the flow of pigs through the U.S. swine industry by animal age-gender subclass for both the U.S. breeding and market hog herds. The model was designed to estimate feed, water, energy, land and crop nutrient resources required to support the population. Furthermore, estimates were made of manure and global warming gases (carbon-equivalents, CO2e) produced annually. Each population flow was based on the yearlong flow of pigs through each age-gender subclass from December 1 to November 30 of the following year as published by USDA. Then, we estimated the dynamics of the population using known/published biological parameters representative typical of production practices of the era.
Results from the population flow model yielded the number of average animal-days in a year for each age-gender subclass in the population. Knowing the number of animal-days made it possible to estimate resource requirements such as feed and water. From this point, it was a natural progression to determine crop requirements using annual crop yield and input data from inputs such as pesticides, energy and irrigation. Emission factors were obtained for each process, including but not necessarily limited to, swine life functions, cropping, feed processing, feed transportation and manure storage
The U.S. swine industry produces pigs far more efficiently today (2009) than in 1959. The number of hogs marketed has increased 29% (87.6 million in 1959 to 112.6 million in 2009 after removing market hogs imported directly to harvest) from a breeding herd that is 39% smaller. The efficiency gain is even more impressive when measured against the total dressed carcass weight harvested. Dressed carcass yield leaving the farm has nearly doubled in 50 years from 12.1 billion pounds to 22.8 billion pounds. This increase in productivity has resulted in an increase of 2,231 pounds (2.5x) of carcass harvested annually per sow-year. Today, it takes only five hogs (breeding and market) to produce the same amount of pork that required eight hogs in 1959.
Increased crop yields have resulted in a 59% decrease in the total amount of land required resulting in a 78% decrease in the amount of land required per 1,000 pounds of dressed carcass produced. This gain in efficiency, while primarily due to improved crop yields, is also a result of by-product feed use (eg. dried distiller’s grain solubles (DDGS) and soybean meal (SBM)). Dietary changes based on improved feed milling and ration formulation have most likely played a role as well.
Much like feed utilization, total water demand for animal consumption has increased only 11% from 32.7 million gallons in 1959 to 36.2 million gallons in 2009. This has resulted in water consumption dropping from 2.7 gallons per pound of dressed carcass to 1.6 gallons, a 41% improvement. Most likely this improvement is due to a reduction in the size of the breeding herd and animals going to harvest at a much younger age today than in 1959.
The U.S. swine industry has managed to stabilize its overall resource demand over the past 50 years. This feat is remarkable because pork production, as measured by pounds of dressed carcass leaving the farm gate, has nearly doubled in that same period. What the swine industry has been able to accomplish very successfully over the past 50 years is to significantly reduce its environmental impact and natural resource use nearly 50% across the board per 1,000 pounds of dressed carcass produced.