A feed-to-product ratio becomes an energy efficiency only when the energy density of both feed and product is known, and checking the caloric guide’s seven ratios against standard food energies shows that the meat rows hold but the egg, rabbit and milk rows do not. Eggs at 2.5:1 on grain give about 16% instead of the stated 20-25%, goat’s milk at 4:1 about 5% and cow’s milk at 6:1 about 3%, unless the animal’s feed is much more watery than grain.
Part of Caloric Budget for a Community
Feed-to-meat ratios are the pounds of feed an animal eats per pound of meat, milk or eggs it yields, convertible to energy efficiency by comparing the calories in each.
The Table Needs Two More Numbers To Mean Anything
The caloric guide gives, for each animal, a feed:product ratio and a stated energy efficiency. Efficiency is the product’s energy divided by the feed’s energy, so it equals:
efficiency = (kcal per lb of product) ÷ (ratio × kcal per lb of feed)
The guide does not say what the feed is or what the product weighs (live weight, carcass or edible meat). This page takes the feed as corn grain at the guide’s 1,650 kcal per lb and tests whether each row then reproduces.
Worked Example: Does Each Row Reproduce?
First, what product energy each row would need, using the guide’s own ratio and stated efficiency: implied kcal per lb = efficiency × ratio × 1,650.
| Row | Ratio | Stated efficiency | Product kcal/lb the row implies |
|---|---|---|---|
| Chickens (eggs) | 2.5 | 20-25% | 825-1,031 |
| Chickens (meat) | 3 | 15-20% | 743-990 |
| Goats (dairy) | 4 | 15-20% | 990-1,320 |
| Pigs | 5 | 10-15% | 825-1,238 |
| Cattle (dairy) | 6 | 12-18% | 1,188-1,782 |
| Cattle (beef) | 8 | 5-10% | 660-1,320 |
| Rabbits | 3.5 | 15-20% | 866-1,155 |
Now compare with typical food energies. The values below are recalled from standard food-composition tables and are approximate: egg about 143 kcal per 100 g (649 per lb); chicken meat with skin about 215 (975 per lb); goat’s milk about 69 (313 per lb); fatty pork about 240 (1,090 per lb); cow’s milk about 61 (277 per lb); beef at 15-20% fat about 215-250 (975-1,135 per lb); rabbit about 136 (617 per lb). One pound is 454 g.
- Chicken meat: 975 lies inside 743-990. The row reproduces.
- Pork: 1,090 lies inside 825-1,238. It reproduces, for a fatty cut.
- Beef: 975-1,135 lies inside 660-1,320. It reproduces, for a fatty cut.
- Eggs: 649 is below 825-1,031. Efficiency = 649 ÷ (2.5 × 1,650) = 15.7%, about 16%, below the stated 20-25%.
- Rabbit: 617 is below 866-1,155. Efficiency = 617 ÷ (3.5 × 1,650) = 10.7%, below the stated 15-20%.
- Goat’s milk: 313 ÷ (4 × 1,650) = 4.7%, against a stated 15-20%.
- Cow’s milk: 277 ÷ (6 × 1,650) = 2.8%, against a stated 12-18%.
Why The Milk Rows Fail On Grain But May Hold On Forage
Turn the dairy rows around. For efficiency e and ratio r, the feed would need to carry 313 ÷ (4 × e) kcal per lb for goats, which is 391-522 kcal per lb at 20-15%, and 277 ÷ (6 × e) for cows, which is 256-385 kcal per lb at 18-12%. Those are the energy densities of a watery feed, about the range of potatoes (350 kcal per lb in the guide) and well below grain. Fresh pasture is mostly water (recalled: typically a fifth of its weight is dry matter), so the dairy rows are plausible for animals on pasture and implausible for animals on corn. The table mixes feeds without saying so.
What The Ratios Do Not Say
The guide does not say whether “meat” in a ratio means live weight gain, carcass or edible meat. A carcass is only part of a live animal, so the same animal has a higher efficiency by one definition than by another. When you compare animals, use one definition and say which.
Method: Use The Table Safely
Step 1: Decide the feed and its kcal per lb for your own flock or herd. Step 2: Decide the product (edible meat, milk, eggs) and weigh or look up its kcal per lb. Step 3: Record the pounds of feed per pound of product over a season. Step 4: Compute efficiency with the formula and use your number, not the table’s.
Common Mistakes
- Comparing mass ratios across products. A pound of milk and a pound of pork hold very different energy.
- Using grain ratios for pasture animals. The feed’s energy per pound is what changes.
- Ignoring what the animal does besides food. Manure, draft and dairy fat and protein are separate benefits.
What’s Next
- Learn next: Pasture vs Grain-Fed Calculations — the land cost of each feed
- Combine with: Dairy and Egg Calorie Efficiency — the dairy and egg rows on a farm scale