AbstractSix Brown Swiss and six Holstein heifers were assigned to one of two experimental rations as they reached 127 days of age, for use in an experiment involving a randomized block design. The 240-day experiment was divided into 8 periods of 30 days each. The heifers were fed individually. Both rations included the same harvested forages, principally sorghum silage or sugarcane silage, the daily allowance of which increased from 5 pounds in period 1 to 28 pounds in period 8. In ration I the forage was supplemented with 5 pounds of a conventional concentrates mixture throughout the experiment. In ration II the daily allowance of concentrates mixture was reduced from 3 pounds in period 1 to 0 in period 4, while the daily allowances of blackstrap molasses and of dehulled soybean oilmeal were increased from 2 to 0.6 pounds, respectively, in period 1 to 5 and to 1.2 pounds, respectively, in period 4, at which level they remained until the end of the experiment. Both experimental rations were expected to supply approximately the amounts of total digestible nutrients and digestible protein needed for normal growth of heifers, according to published feed analyses and published nutrient requirements. Considerable variation in growth rate was found for individual 30-day periods on both rations. During the whole experiment the heifers which consumed ration I gained significantly (P < .05) more than the heifers which consumed ration II (1.01 vs. 0.76 pounds per heifer per day). The former growth rate can be considered barely adequate, while the latter is definitely not adequate. Part of the poor growth rate in the heifers fed ration II can be ascribed to a lower total forage consumption per heifer than in the heifers fed ration I (3,304 vs. 3,045 pounds). Ration II was adversely affected by an overestimation of the digestible protein content of the soybean oilmeal in planning the rations, which was revealed by subsequent chemical analysis. Judging from other published reports, the high levels of molasses employed in ration II may have lowered the amount of net energy for growth contributed per pound of molasses, and decreased the crude-protein digestibility of the whole ration. The following feed costs were calculated under rations I and II: Average costs per heifer per day, $0.26 and $0.23; and cost per pound of live-weight gain $0.26 and $0.30, respectively. The results suggested that the use of a high level of molasses supplemented with a minimal amount of soybean oilmeal as a substitute for all other concentrate feeds in rations based on poor-quality forage for heifers under 12 months of age, is neither nutritionally satisfactory nor economically advantageous.
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