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Total Digestible Nutrient Content of Consumed Forage and Total Digestible Nutrient Consumption by Yearling Beef Steers Grazing Nitrogen-Fertilized Bermudagrass and Orchardgrass-Ladino Clover Pastures

University of Tennessee, Knoxville 37916

Abstract

Midland bermudagrass pastures not fertilized with N (MID-1) or fertilized with either 112 (MID-2), 224 (MID-3) or 448 (MID-4) kg N/ha/year, were compared to common bermudagrass fertilized with 112 kg N/ha/year (CB) and to orchardgrass-ladino clover pastures (OG) without N fertilization. Forage consumption was determined by the cage-and-strip method and yearling Angus steers were used in a modified put-and-take grazing system. Estimated total digestible nutrient (ETDN) content was calculated from Tilley-Terry digestible dry matter.

OG contained more (P<.05) ETDN in the consumed forage (61.7%) than the mean of all bermudagrasses (51.2%). No significant differences were noted in the percentages of ETDN in consumed forage among the bermudagrass treatments. The % ETDN in consumed forage decreased (P<.05) during the season in all treatments (62.3 to 45.8; 59.8 to 42.3; 61.6 to 43.6; 65.8 to 49.9; 57.2 to 48.6; and 67.6 to 57.8% for MID-1, MID-2, MID-3, MID-4, CB and OG, respectively). Elapsed days of grazing accounted for about 50% of the variation in ETDN percentage of consumed forage in MID-3 and OG, for about 40% in MID-1 and MID-2 and for less than 30% for MID-4 and CB.

Comparing bermudagrasses in general, ETDN consumption of MID-2 was highest throughout the grazing season, consumption of MID-1 and MID-3 intermediate, and that of MID-4 was the lowest. Regarding time within the growing season, ETDN consumption of OG and CB per unit of metabolic weight was highest toward the middle of the growing season, but with the Midland forages it tended to be highest at the start of the growing season. The percentage ETDN in consumed forage was significantly correlated with ADG of animals grazing fertilized Midland and OG forages.

¹ Department of Animal Science.

² Present address: Nu-Labs Division, Pioneer Hi-Bred International, Inc., Johnston, IA 50131.

³ Department of Plant and Soil Science.

⁴ Ames Plantation, Grand Junction, TN 38039.