Sheep Feed Calculator

Sheep rations are budgeted as dry matter intake expressed as a share of body weight, and each production stage carries its own percentage: 2.0 percent for a dry maintenance ewe, 2.5 percent at flushing before breeding, 2.8 percent in late gestation with a single lamb, 3.2 percent carrying twins, 3.5 percent in early lactation, and 4.0 percent for growing lambs. Crude protein climbs the same ladder, from about 8 percent of the diet at maintenance to 13 percent for twin-bearing ewes and 14 to 16 percent for lactation and growth. Energy is expressed as total digestible nutrients, and metabolizable energy is approximated here as TDN in kg multiplied by 3.6155 Mcal, which is the standard digestible energy value of roughly 4.4 Mcal per kg of TDN reduced by the usual 82 percent conversion to ME. As-fed weights exceed dry matter weights because feeds carry water, so hay is treated as 90 percent dry matter, grain 88 percent, and supplement 92 percent. Three hazards dominate practical feeding. Twin-bearing ewes underfed in the final six weeks develop pregnancy toxemia, which is why the late gestation twins figure is the highest non-lactating requirement in the table. Sheep are uniquely intolerant of copper and must never be given cattle or goat mineral. And the grain share should change by no more than about 10 percent of the ration per week, since abrupt increases cause ruminal acidosis. Calcium to phosphorus should stay near 2 to 1.

The energy accounting behind sheep rations descends from nineteenth century German agricultural chemistry. Emil von Wolff published feeding standards in the 1860s that tabulated digestible protein, fat, and carbohydrate requirements for farm animals, giving Europe its first quantitative ration tables. Oskar Kellner extended this around 1905 with the starch equivalent system, which rated feeds by their measured ability to deposit body fat rather than by chemical composition alone. American work then put the system on a calorimetric footing. Henry Prentiss Armsby, at the Pennsylvania State College agricultural experiment station, built a respiration calorimeter large enough to hold cattle in the early 1900s and used it to develop net energy values, separating the energy lost in feces, urine, methane, and heat increment from the energy actually available for maintenance and production. Total digestible nutrients emerged from the same tradition as a simpler practical proxy and remains in use for sheep despite a known bias that overvalues forages relative to concentrates. In the United States these strands were consolidated by the National Research Council, whose Nutrient Requirements of Sheep reached its sixth revised edition in 1985 and was replaced in 2007 by Nutrient Requirements of Small Ruminants, the source of the stage-specific values used here.