We often forget that the efficiency by which animals convert feed to products like body weight, eggs or milk (often called feed conversion rate or FCR) is but an index, and not always related to true profitability. It is true that under similar conditions, an improved FCR is deemed preferable. After all, if animals need less feed for the same unit of productivity, that unit has a reduced input cost. But this is not always the whole picture.
Here’s a situation that proves that the devil often hides in details. A broiler farm wanted to maximize the FCR (for reasons of no importance to this discussion) and asked me to design a series of diets with increased energy density (based on recommendations from their genetic supplier). It is well-known that birds will adjust feed intake based on the energy content of the feed; that is, they will eat less when the feed contains more energy to maintain a fixed energy intake, and vice versa. Of course, there are limits and objections to this notion, but again, this takes us further deep into nutrition matters that derail us from our focus: FCR.
So, I designed the requested diets, but I also prepared a number of similar sets with graduated levels of energy. To keep matters simple, I present below only a generalized summary based on the set of diets that was actually used:
Energy Cost per kg feed Expected FCR Cost per kg gain
Kcal ME/kg % of actual diet % of actual diet % of actual diet
3,100 100 100 100
3,150 102 98 100
3,200 111 97 107
3,250 120 95 114
3,300 130 94 121
Based on the above example, it was still profitable to go from 3,100 (current diet) to 3,150 kcal/kg feed because the increased cost of the new feed would be covered by the expected improvement in FCR. Any level above this step would still improve feed efficiency, but cost of gain was becoming now unprofitable.
In this particular case, it was not expensive, energy-rich ingredients that made high-energy diets cost prohibitive. Here, we had to use increased amounts of feed-grade amino acids to maintain the ideal protein profile in balance to energy while keeping a reduced total protein concentration in an antibiotic-free program. Obviously, in this case, soybean meal was less expensive to use than feed-grade amino acids, but we had to limit its use to prevent protein from exceeding strict limits. Aside from formulation issues, this example serves to illustrate the point that FCR is not always the best measure of profitability.