Beef cattle responses to pre-grazing sward height and low level of energy supplementation on tropical pastures. (15th May 2020)

• Record Type: Journal Article
• Authors: Dórea, João R R; Gouvêa, Vinícius N; Agostinho Neto, Luiz Roberto D; Da Silva, Sila C; Brink, Geoffrey E; Pires, Alexandre V; Santos, Flávio A P
• Is Part Of: Journal of animal science. Volume 98:Number 6(2020)
• Publication Date: 2020-05-15
• Subjects: corn -- grazing management -- supplementation -- tropical pastures; Livestock -- Periodicals; Livestock; Electronic journals; Periodicals; 636.005
• DOI: 10.1093/jas/skaa163
• Languages: English
• ISSNs: 0021-8812

Abstract

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 × 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.