Ruminant Utilization of Silage in Relation to Hay, Pellets, and Hay Plus Grain. I. Composition, Digestion, Nitrogen Balance, Intake, and Growth

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Abstract
Two 4 x 4 Latin square experiments were conducted using fistulated Holstein heifers. Experiment 1 compared silage, hay, pelleted hay, and hay plus grain. Experiment 2 compared direct-cut silage and hay harvested from the same source. The silage of Experiment 1 contained more acid detergent fiber than the hay. In Experiment 2, the silage was more highly lignified than the hay and contained more total N relative to calories. The silage N was more soluble. Compared to the hay, the silage of Experiment 1 resulted in a lower digestion of dry matter, organic matter, neutral detergent fiber and N. In Experiment 2, the ad libitum feeding of silage resulted in less N retained when expressed as g/day, percent of that fed, or percent of that digested than the feeding of hay. In a companion growth trial conducted on the forages of Experiment 2, the silage-fed animals had a lower energy intake, lower gain and required more energy above maintenance per unit gain. The amount of N retained per unit weight gain indicated that the lower utilization of N on the silage ration was first caused by the lower energy relative to N.