Beef cattle responses to pre-grazing sward height and low level of energy supplementation on tropical pastures

Author(s)

Dorea, Joao R. R. ^{[1, 2]} ; Gouvea, Vinicius N. ^{[1, 3]} ; Agostinho Neto, Luiz Roberto D. ^[1] ; Da Silva, Sila C. ^[1] ; Brink, Geoffrey E. ^[4] ; Pires, V, Alexandre ; Santos, Flavio A. P. ^[5]

Affiliation

^[1] Univ Sao Paulo, Luiz De Queiroz Coll Agr, Dept Anim Sci, BR-13418900 Piracicaba, SP - Brazil

^[2] Univ Wisconsin, Dept Anim & Dairy Sci, Madison, WI 53706 - USA

^[3] New Mexico State Univ, Clayton Livestock Res Ctr, Dept Anim & Range Sci, Clayton, NM 88415 - USA

^[4] US Dairy Forage Res Ctr, Madison, WI 53706 - USA

^[5] Pires, Alexandre, V, Univ Sao Paulo, Luiz de Queiroz Coll Agr, Dept Anim Sci, BR-13418900 Piracicaba, SP - Brazil

• Document type: Journal article
• Source: JOURNAL OF ANIMAL SCIENCE; v. 98, n. 6 JUN 2020.
• Web of Science Citations: 0

Abstract

The objective of this study was to investigate the effects of energy supplementation and pre-grazing sward height on grazing behavior, nutrient intake, digestion, and metabolism of cattle in tropical pastures managed as a rotational grazing system. Eight rumen-cannulated Nellore steers (24 mo of age; 300 +/- 6.0 kg body weight {[}BW]) were used in a replicated 4 x 4 Latin square design. Treatments consisted of two levels of energy supplementation (0% {[}none] or 0.3% of BW of ground corn on an as-fed basis) and two pre-grazing sward heights (25 cm {[}defined by 95% light interception (LI)] or 35 cm {[}defined by >= 97.5% LI]) constituting four treatments. Steers grazed Marandu Palisadegrass {[}Brachiaria brizantha Stapf. cv. Marandu] and post-grazing sward height was 15 cm for all treatments. Forage dry matter intake (DMI) was increased (P = 0.01) when sward height was 25 cm (1.86% vs. 1.32% BW) and decreased (P = 0.04) when 0.3% BW supplement was fed (1.79% vs. 1.38% BW). Total and digestible DMI were not affected by energy supplementation (P = 0.57) but were increased when sward height was 25 cm (P = 0.01). Steers grazing the 25-cm sward height treatment spent less time grazing and more time resting, took fewer steps between feeding stations, and had a greater bite rate compared with 35-cm height treatment (P < 0.05). Energy supplementation reduced grazing time (P = 0.02) but did not affect any other grazing behavior parameter (P = 0.11). Energy supplementation increased (P < 0.01) diet dry matter digestibility but had no effect on crude protein and neutral detergent fiber digestibilities (P = 0.13). Compared with 35-cm pre-grazing sward height, steers at 25 cm presented lower rumen pH (6.39 vs. 6.52) and greater rumen ammonia nitrogen (11.22 vs. 9.77 mg/dL) and N retention (49.7% vs. 20.8%, P < 0.05). The pre-grazing sward height of 25 cm improved harvesting efficiency and energy intake by cattle, while feeding 0.3% of BW energy supplement did not increase the energy intake of cattle on tropical pasture under rotational grazing. (AU)

• FAPESP's process: 11/13369-7 - Energy supplementation for beef steers grazing tropical grass (Brachiaria brizantha, cv Marandu) managed under rotational system with different initial sward heights
• Grantee: João Ricardo Rebouças Dórea
• Support Opportunities: Scholarships in Brazil - Doctorate