Evaluation of Laboratory Methods for Determining Quality of Corn and Sorghum Silages: III. Biological and Chemical Methods for Predicting Animal Intake1

Abstract

AbstractThe intake of forage plants by ruminant animals is a crucial determinant of forage quality. Laboratory assays have sometimes provided reasonable estimates of the intake potential of grasses and legumes. Laboratory procedures have not been adequately tested for their ability to predict intake of silages of corn (Zea mays L.) and sorghum (Sorghum bicolor [L.)] Moench, S. sudanense [Piper] Stapf., or their hybrids). Our objectives were to determine whether various biological and chemical tests proposed for measuring forage quality are applicable to prediction of intake of corn and sorghum silages, and to determine whether digestibility and intake of these silages are associated.In vivo digestibility of 49 silages was measured by using lambs in conventional 30 to 35‐day stall trials. We measured voluntary intake by using other lambs in feeding trials that extended 41 days or more.Dry matter intake (g/Wkg0.75) by lambs was correlated (r = 0.66) with in vivo digestible dry matter of sorghum silages. The correlation between intake and digestibility was much lower (r = 0.40) for corn silages.The biological laboratory assays were not as well correlated with intake of sorghum silages as were several chemical assays. However, a biological assay (in vitro true digestible dry matter) was best associated with intake of corn silages (r = 0.64) of all assays.Of the chemical assays, Fonnesbeck and Harris cell walls, acid detergent fiber, crude fiber, and calculated cellulose accounted for 24% or more of the variation in intake of corn silages and 60% or more of the variation in intake of sorghum silages. Crude protein was highly correlated (r = 0.81) with intake of sorghum silages, but it was not correlated with intake of corn silages.We present simple regression equations for prediction of intake of sorghum silages from the five laboratory assays that accounted for 60% or more of the intake variation.