Feed Intake, Growth, and Feed Conversion: What Does it All Mean?

Feed intake and growth are two key traits for the bottom line of a commercial grow-finish or farrow-to-finish producer. However, the metric commonly used to measure herd performance is the ratio of these two traits or feed efficiency, measured as feed intake over weight gain, writes Nick Boddicker, Ph.D.
calendar icon 9 September 2016
clock icon 5 minute read

By definition, changes in feed efficiency are due to changes in one or both of these component traits. Because intake and growth are associated with each other, a change in one of the traits will result in a change in the other, on average. For example, Stalder (2013) looked at average daily gain and feed conversion by year from 2007 to 2012 using data submitted to a national database system. The analysis included data from 50 different companies representing over 1700 farms. Between 2007 and 2012, average daily gain changed from 1.71 pounds to 1.81 pounds, an improvement of 6%, and feed conversion decreased from 2.75 to 2.68, an improvement of 2.5%. What wasn’t discussed
in the article is the change in feed intake, which increased by 3%. All 3 traits changed;
however, there is a good chance that only 2 of them were actually selected on at the level
of the genetic sources of these farms (growth and feed conversion).

FIGURE 1. Average daily feed intake, average daily gain, and feed:gain during the grow-finish phase
with a constant feed conversion ratio for all scenarios. Lines of the same color for ADFI and ADG are
part of the same scenario:
Red = decreasing average daily feed intake by 0.1 lbs per year; Green = holding average daily feed intake constant; Purple = Increasing average daily feed intake by 0.1 lbs per year

There are different strategies to improve feed efficiency through genetic selection. Figure 1 demonstrates the relationships behind average daily feed intake, average daily gain, and feed conversion ratio during the grow-finish phase using 3 different feed intake scenarios: selection for reduced feed intake, selection for no change in feed intake, and selection for increased growth while allowing intake to increase with growth. For all scenarios the feed conversion ratio is the same across years with the same trend of -0.1 per year (starting value of 3 in year 1 and ending value of 2.5 in year 6) and the starting value for average daily feed intake was the same at 5 lbs per day. When selecting for reduced feed intake over time (red line) by -0.1 lbs per year, growth still has a positive change, but only at 0.03 lbs per year. In the 6-year span, average daily gain increased only by 0.13 lbs. When restricting change in feed intake to zero (green line), average daily gain increased by 0.6
lbs per year, resulting in a cumulative improvement of 0.33 lbs. When feed intake was allowed to increase by 0.1 lbs per year (purple line), growth increased by 0.1 lbs per year, resulting in a cumulative increase of 0.53 lbs. Through these examples, it is clear that feed intake drives growth.

Another way to look at this is by change as a percentage. For the scenarios of increasing or decreasing feed intake, the change in in feed intake across the 5 years is 10%. When feed intake decreased by 10% in 5 years, growth increased by 7.8%. When feed intake increased by 10% in 5 years, growth increased by 31.7%. Here in lies the problem with the feed conversion ratio; when the ratio and the improvement of the ratio over time is the same and feed intake is increased or decreased by the same magnitude over that same time frame, the effect on growth is not the same.

The first 2 scenarios focus on minimizing feed costs, but this clearly has an affect on growth. The last scenario focuses on increasing profitability and this is the foundation of Genesus, maximizing profitability for our customers. By increasing growth and allowing feed intake to increase as well
while maintaining competitive feed efficiency, the producers will have increased pounds of carcass in a fixed time operation or increased turns through the barn in a fixed weight operation.

Outside of growth, there may be additional benefits to allowing feed intake to increase with growth rate. Although anecdotal, animals that naturally have higher intake (voluntary intake) appear to withstand environmental challenges better than those that have lower intakes. It is well documented that animals under stressors (heat, disease, etc.) have reduced intake and growth. When appetite is reduced due to stressors in animals that have lower voluntary intake, the result could mean higher mortality rates. Conversely, animals that have an appetite due to naturally higher intakes even when immunologically challenged may have less mortality because they are still consuming to support
maintenance energy requirements to stay alive. They will also receive any medications that are fed through the feed or water. Less mortality in the finishing phase has great monetary value. Stalder calculated that a 2% reduction in mortality during grow-finish for a 1000 head finishing barn is worth $3,240 per turnover (270 pound finishing weight and $60/cwt).

Genesus records individual intake on our Duroc sires using electronic feed intake equipment to fully understand the intricate relationship between growth and intake, and to select sires that have superior profitability by balancing growth and efficiency.

Through this, the Genesus commercial animal is feed efficient, fast growing, has good voluntary feed intake, and has low mortality rates, altogether maximizing profitability for our customers.


Johnson. (2012). Fueling the immune response: what’s the cost? Chapter 10 in Feed Efficiency in Swine. Wageningen Academic Publishers. Edited by John F. Patience.

Stalder, K. (2013) Pork Industry Productivity Analysis. Pork.org

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