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Feed Efficiency

David P. Price is a consulting nutritionist specializing in feedlot and range cattle

Last time we talked about bull-test feedlots. The point of these facilities has been to provide data on the gaining ability of breeding stock. But while gain has been the Holy Grail of cattle promotion, I think we all know feed efficiency is more important.

Feeds and Feeding 101. The reason gain has been given so much emphasis is it assumes what we were taught in school is correct; the cattle that gain the most will also be the most efficient. Unfortunately, that is not always true. The only consistent truism is that the cattle that gain the most are usually the cattle that eat the most. Quite often, cattle that eat less gain less, but have comparable conversions.

The Standard. For over 50 years conversion or feed for gain was the standard measure of efficiency. That is, if cattle ate 24 pounds and gained 3.0 pounds per day the F/G or conversion was 8:1 (24 lbs. / 3 = 8). As a teenage kid growing up in the ’60s, 8:1 was considered the standard. When Rumensin came on the scene in the late ’70s, 7.5:1 became pretty much a benchmark. These figures were nominally “as fed,” or 90 per cent dry. If steam-flaked, high-moisture grain or silage were in the ration; to be more precise we had to use dry matter values. In that case, 6.8:1 was (and is) considered a good overall value. These figures were traditionally “pay to pay” (purchase weight of the cattle compared to actual sale weight to the packer; including pencil shrink).

Feedlots that wanted to make their conversion look better would use off-truck weights at the feedlot (including purchase shrink) and gross sale weights (excluding pencil shrink). Some would take the deads out to make an even prettier picture.

Academic Measurements. In the 1990s the academic community began using a “new” measure. Instead of feed for gain, it was now gain for feed. This made the calculation more complicated, but really didn’t advance the knowledge of efficiency.

More recently Texas A&M University (and the University of Alberta in Canada) has begun promoting what is known as “Residual Feed Index” or RFI. This doesn’t replace feed for gain (conversion), but attempts to explain variation between cattle. RFI is a measure of the difference between predicted consumption and gain. An animal with a lower RFI will be more efficient. Basically this is an animal that eats less than predicted but has acceptable gain. Reportedly these animals release less methane and have more efficient metabolisms.

Personally, I do not understand how some cattle (particularly within breeds) can have variation in methane production, as this is a function of the rumen micro-organisms. (Rumensin and other ionophores reduce the populations of bacteria that generate methane, which is how they improve efficiency.)

Metabolism, on the other hand is easy to understand. For example, we have long known Holsteins have a higher maintenance requirement than beef breeds. They gain more than most breeds, but they are not necessarily more efficient. Where 2.8 to 3.2 pounds per day would be a benchmark gain for most feedlot steers fed for 150 days; Holstein steers will often push 3.5 pounds. But they will eat significantly more feed to do it.

Still, their conversion is usually relatively good. Indeed, going back to Ruminant Nutrition 101, when we see high consumption, we usually don’t worry. Gains and conversions will normally be acceptable. What we didn’t learn is how to evaluate low consumptions. There are cattle that will only eat 2.0–2.2 per cent of their body weight (versus 3.3 per cent for Holsteins). Some will gain as little as 1.8 to 2.0 pounds and be inefficient. Others will gain 2.4–2.5 pounds per day and convert as well as higher-gaining cattle. This is always perplexing, but it happens every day.

The problem is we have tried to make cattle gain a mathematical equation. Virtually all our software programs use the Net Energy System, which assumes maintenance energy is a constant. It isn’t. It varies with the animal. In other words, we were taught (and most software assumes), that a given amount of feed; say 10 pounds, is required to maintain the animal. The more the animal eats over 10 pounds, the more it will gain. A steer that eats 25 pounds will gain more than one that eats 22 pounds. Unfortunately, it doesn’t work that way. The steer that eats 22 pounds might gain the same. Another steer that eats only 20 pounds might gain only slightly less than the one eating 25 pounds, and be more efficient.

The Future. Most of us will accept that there can be differences between breeds (for efficiency). But according to Texas A&M, there can be low and high RFI indexes within breeds. This is a key point of learning. What this is telling us is that we are way behind our competition. The broiler and swine industries have long bred for efficiency and has made enormous gains. We have selected only for gain. We have bred our cattle to be bigger, but not necessarily more efficient. Because of ionophores, trenbolone implants and beta agonists, feedlot cattle are more efficient than they were when the industry began. But we really haven’t used genetics to improve efficiency. It’s time to get started.

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