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Crude Protein Content of Forage Consumed by Steers Grazing Nitrogen-Fertilized Bermuda Grass and Orchard Grass-Ladino Clover Pastures

University of Tennessee, Knoxville 37916

Abstract

Crude protein (CP) content of forages actually consumed by grazing beef cattle was determined. The treatments were Midland Bermuda grass pastures not fertilized (Mid-0); Midland Bermuda grass fertilized with 112 (Mid-112), 224 (Mid-224) or 448 (Mid-448) kg N•ha^-1•yr^-1; common Bermuda grass fertilized with 112 (CB-112) kg N•ha^-1•yr^-1, and orchard grass-ladino clover (OG) pastures not fertilized with N during three grazing seasons. Yearling Angus steers were used in a modifed put-and-take grazing system. Forage intake was determined by the, cage-and-strip method and CP content of consumed forages was calculated from forage dry matter intake and CP content of the cage and the strip samples. Day within grazing season accounted for 21 to 47% of the variation in CP content of consumed forages. The high CP forages (Mid-448 and OG) were less affected by day within grazing season than were low CP forages (CB-112 and Mid-0). In all treatments except in Mid-112, CP content of consumed forage decreased from the beginning of May to the end of August (20 to 17, 19 to 8, 17 to 11, 17 to 19, 19 to 13 and 30 to 17% for OG, CB-112, Mid-0, Mid-112, Mid-224 and Mid-448, respectively). Seasonal means for die same treatments were 19.0, 13.4, 11.4, 14.4, 14.5 and 21.1% CP, respectively. Crude protein content of consumed forages was adequate for 200 to 300 kg grazing steers gaining .5 kg/d, except for CB-112 forage near the end of August. If CP content of available rather than consumed forages had been considered for CP adequacy in the present study, several treatments would have appeared to be CP deficient for a considerable portion of the grazing season.

¹ Dept. of Anim. Sci.

² Dept. of Plant and Soil Sci.

³ Present address: NU-Labs Div., Pioneer Hi-bred Int., Inc., Johnston, IA 50131.