EFFECTS OF THE DEGREE OF SELECTIVE FEEDING ALLOWED ON FORAGE VOLUNTARY INTAKE AND DIGESTIBILITY ASSAY RESULTS USING SHEEP

Abstract

Red clover (Trifolium pratense L.), first- and second-cut alfalfa (Medicago sativa L.), timothy (Phleum pratense L.) hays, and oat (Avena sativa L.) straw were assayed for digestible dry matter (DDM) and dry matter intake (DMI) using sheep with various opportunities for feed selection provided by varying weighbacks between 0 and 30%. Digestible energy intakes (DEI) were also calculated. There was a slight increase in DMI values as the opportunity for selection increased, due to slightly lower DMI at low levels of weighback and higher DMI as weighback approached 30%. There were no changes in DMI due to the opportunity for selection when weighbacks varied only from 5 to 25%. Except for an apparent curvilinear relationship for the first-cut alfalfa, the change in DDM as the opportunity for selection increased was similar to that of DMI. However, the maximum changes in DDM that could be attributed to the opportunity for selection would be barely detectable in normal digestion trials. Changes in DEI attributable to the opportunity for selection were caused primarily by DMI rather than digestibility. DEI showed a slight increase as weighback increased, due to lower values at low levels of weighback and, in some cases, higher values at higher levels of weighback. There were no changes in DEI values that could be attributed to the opportunity for selection when weighbacks varied only from 5 to 25%. The data indicate that, for forage evaluation purposes, DMI and DDM can be assayed with confidence at levels of weighback between 5 and 20%.