Energy Utilization by Sheep as Influenced by the Physical Form, Composition and Level of Intake of Diet

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Abstract
The efficiency of utilization of the energy of 3 diets (chopped hay; pelleted, ground hay; pelleted mixture of 55% of ground hay and 45% of corn meal) was studied in metabolism and slaughter-chemical analysis experiments with 63 sheep. The hay used in the 3 diets was prepared from the same source. Each diet was fed at 3 levels during a 196-day period. Sheep of 2 ages were used; at the beginning of the feeding period, 18 were 8 months old and 27 were 20 months old. Nine animals of each age group were killed and analyzed to obtain reference body composition and energy measurements at the beginning of the feeding period. The gain in body energy represented the following percentages of the gross energy and metabolizable energy, respectively, ingested above the maintenance level: chopped hay, 15.1 and 31.0; pelleted, ground hay, 20.8 and 43.3; and pelleted corn-ground hay, 31.3 and 56.6. Although the degree of energy absorption was about the same for the 2 forms of hay, the heat increment for body gain and wool growth was 21.7% greater for the chopped hay than for the pelleted, finely ground hay. Sheep fed ad libitum ingested 28.4% more dry matter and 63.4% more of net energy for body gain as pelleted, ground hay than as chopped hay. The greater energy retention by sheep ingesting the pelleted, ground hay than by those fed chopped hay was 78.5% attributable to the greater intake of dry matter and 21.5% attributable to the greater nutritive effect per unit of feed ingested. No difference in the proportion of energy absorbed or in the net utilization of metabolizable energy was observed between the lambs and older wethers. The lambs were 65% more efficient converters of feed weight to body weight, but the energy concentration of the body gain was 56% greater in the older sheep.