As-Fed to Dry Matter

This is the most consequential multiplication in livestock feeding, and the one most often skipped. Feed is bought, hauled, stored and weighed AS FED, with whatever water it happens to contain. Feed is analysed, formulated and fed on a DRY MATTER basis, water excluded. Every feed test, every ration and every intake figure is on the dry basis; every scale ticket is on the wet one.

The gap is enormous for wet feeds and trivial for dry ones, which is exactly why it catches people. Grain at 88% dry matter is close enough that ignoring the difference costs 12% — annoying, survivable. Maize silage at 32% dry matter is more than two-thirds water, and a ration that treats 20 kg of silage as 20 kg of feed has over-stated the actual feed by a factor of three. Wet brewers grains at 22% are worse again.

The conversion runs both ways and both directions get used daily. Going down, an as-fed weight times the dry matter percentage gives the dry matter delivered: 30 kg of silage at 35% is 10.5 kg of dry matter. Going up is the one the mixer operator needs — a ration calling for 12 kg of dry matter from that silage requires $12/0.35 = 34.3$ kg on the scale.

Two practical cautions. Dry matter is not a fixed property of a feed: silage dry matter drifts across a pit face, hay picks up moisture in a humid week, and a rained-on windrow bears no resemblance to the book value. Measure it — a kitchen microwave and a scale will get within a couple of points, and a laboratory will do better. And when comparing two feeds on price or on analysis, put both on the same basis first; a 20% protein figure means very different things as-fed and dry, and salespeople are not always careful about which one they quote.