Feeding cattle to a target gain
ration formulationdry matter intakefeed conversion ratiocost of gainPearson square
Building a ration to a target gain: dry matter intake, blending two feeds, the energy supplied, and what a kilo of gain costs in feed.
Dry Matter Intake from Body Weight
Daily dry matter intake estimated as a percentage of body weight — the first figure in any ration, and the one that sets how much of everything else the animal can physically consume.
As-Fed to Dry Matter
Converts a weight of feed between the as-fed basis it is handled in and the dry matter basis every ration and feed test is written on. The conversion behind the most expensive mistake in feeding.
Blending Two Feeds to a Protein Target
The share of the higher-protein ingredient needed when blending two feeds to hit a target analysis — the Pearson square, written as the algebra it always was.
Total Digestible Nutrients Supplied
The digestible energy a feed delivers, as the mass of total digestible nutrients in it. TDN is quoted as a percentage of the DRY MATTER, so the feed weight has to be on a dry matter basis before this multiplication means anything.
Average Daily Gain
Liveweight gained per day across a weighing period — the measurement that turns two scale readings and a calendar into a growth rate, and the basis of every projection to a target weight.
Feed Conversion Ratio
Feed consumed per unit of liveweight gained — the headline efficiency figure for any growing animal, and the one that decides whether a feeding period paid for itself.
Feed Cost per Unit of Gain
What a kilogram of liveweight cost in feed — the feed bill divided by the weight it produced. The figure that decides whether to sell an animal now or feed it further.
How they fit together
A ration is built forwards and judged backwards, and this set runs in both directions. Dry matter intake starts it, because an animal's appetite is the hard ceiling on everything else — you cannot feed more energy than it will eat. As a share of body weight it is roughly 2.5% for a growing steer and up to 3.5 to 4% for a high-producing dairy cow, and it moves with the ration itself: a wet, bulky forage fills the rumen before it meets the requirement, which is why intake and diet quality cannot be chosen independently.
As-fed to dry matter is the conversion that makes the rest possible and the one that wrecks rations when it is skipped. Every feed in the yard is bought, weighed and fed as-fed; every requirement and every book value is stated on a dry matter basis. Silage at 32% DM means two-thirds of what goes in the mixer is water. Feed 20 kg of that silage against a 20 kg dry matter requirement and the animal is on a third of its ration, which is exactly how cattle lose condition on a diet that looked generous in the bucket. Do this conversion before anything is blended. Blending two feeds to a protein target is Pearson's square in equation form, and its one limitation is honest and worth stating: it solves for one nutrient at a time. Balance for protein with it and you have said nothing yet about energy, and the two often pull opposite ways. Total digestible nutrients supplied is that energy check.
Then the animals answer back. Average daily gain is what the scale says, and it is the only unarguable number in the set — weigh at the same time of day, off the same fill, or a full rumen will flatter you by 20 kg. Feed conversion ratio is feed per unit of gain, so lower is better, and the one thing to nail down before quoting it is whether it is on a dry matter or an as-fed basis, since the two differ by a factor of two or three and are quoted interchangeably in conversation. Feed cost per unit of gain is the number the operation is actually run on, and the reason to end here rather than at FCR: the cheapest ration per tonne is frequently not the cheapest gain, because a poorer feed drags out the days on feed and every one of those days carries yardage, interest and overhead that this formula does not see. Compare rations on cost of gain, then check the calendar.