PS13-17. Effects of Different Supplementation Strategies on the Performance of Pasture-Finished Nellore Heifers.

Abstract The objective of this study was to evaluate the effects of different supplementation strategies on the performance and production parameters of pasture-finished Nellore heifers. Thirty-six yearling Nellore heifers (initial body weight [BW] = 327 ± 13.28 kg) were blocked by initial BW and assigned to 12 paddocks (4 paddocks/treatment; 3 animals/paddock). The experimental area consisted of 24 paddocks of Megathyrsus maximus cv. Mombaça, managed under a rotational grazing system based on pre- and post-grazing canopy heights. The experimental period lasted 90 days. The treatments were as follows: 1) an enriched mineral supplement provided at 0.3 g/kg BW daily, containing 1,000 mg of narasin per kg of mineral (Zimprova; Elanco Animal Health, São Paulo, Brazil; EMIN; n = 4); 2) a protein–energy supplement provided at 5 g/kg BW daily, containing 75 mg of narasin per kg of supplement (Zimprova; PES5; n = 4); and 3) a protein–energy supplement provided at 10 g/kg BW daily, containing 40 mg of monensin per kg of supplement (Rumensin; Elanco Animal Health; PES10; n = 4). Stocking rate was adjusted using regulator Nellore heifers under a put-and-take grazing system to maintain target canopy heights. When a paddock in the rest phase approached the pre-grazing height while the grazed paddock still contained excess herbage mass, regulator animals were added to increase grazing pressure and ensure attainment of the post-grazing target. Test animals were then moved to the next paddock in the grazing rotation. Body weight was recorded on days 0 and 90 following a 16-h of feed and water withdrawal to determine initial and final BW. Average daily gain was calculated as the difference between final and initial BW divided by the number of days. Intermediate body weight measurements were performed every 30 days without fasting to allow adjustments in the supplement allowance. Stocking rate was expressed as animal units per hectare (AU/ha; 450 kg BW). Production per area was calculated as kilograms of BW gain per hectare. As designed, initial BW did not differ among treatments (P > 0.90; Table 1). However, final body weight and average daily gain were influenced by supplementation strategy (P < 0.01), with higher values observed for PES10 vs. PES5 and EMIN, whereas PES5 and EMIN did not differ (Table 1). Production per area (kg BW/ha) differed among treatments (P < 0.01), increasing progressively from EMIN to PES5 to PES10 (Table 1). Stocking rate (AU/ha) was also affected by supplementation (P < 0.05), with greater values for PES10 vs. EMIN, whereas PES5 was intermediate and did not differ from either treatment (Table 1). Overall, increasing supplementation levels improved both animal performance and productivity per unit area, with PES10 being the most effective strategy under the conditions of this study. For image description, please refer to the figure legend and surrounding text.