Abstract

PORDOMINGO, Anibal J. et al. Uso de monensina y virginiamicina en el engorde a corral de vaquillonas basado en maíz entero. RIA. Rev. investig. agropecu. [online]. 2022, vol.48, n.1, pp.71-77.  Epub Apr 06, 2022. ISSN 1669-2314.

This experiment studied the effects of the combination of monensin (Mo) and virginiamycin (Vi) included in a whole corn-based diet for feedlot finished Angus heifers. A group of 192 330.38 kg Angus heifers were allocated to 48 pens, in groups of 4. A factorial arrangement of 3 diets (DT) x 2 finishing degrees (FD) were imposed randomly on the 48 pens. Factor DT was comprised of 3 diets: NA (Base diet without Mo and Vi), Mo (Base diet + Mo; 30 mg a.i./kg MS), and MoVi (Base diet + Mo + Vi, 30 and 25 mg a.i./kg MS, respectively). Factor FD included: FD1 (harvest at 6 to 7 mm of back fat thickness -BFT-, and 440 to 450 kg live weight -LW-), and FD2 (harvest at 8 to 9 mm of back fat thickness -BFT-, and 470 to 480 kg live weight -LW-). Animals from FD1 reached the harvest point after 82 days of feeding, and animals from FD2 at 92 days. The diet was based on whole corn, chopped millet hay and a protein concentrate including a vitamin and mineral premix. Ultrasound determinations for BFT were performed every 15 days, starting on day 60 of study. Individual body weights (BW) were recorded on days o, 32,82 and 96. Average daily gain (ADG) was calculated for each partial period and the duration of each FD. In addition, animals were ultrasounded for BFT and REA on day 0. Daily dry matter intake was determined continuously for the average animal for each pen. The absolute average (DMI) and DMI relative to BW (DMIBW) for the period of each FD were registered for analysis and further calculations. Global feed efficiency (FE = ADG/DMI) was calculated for each FD. Upon harvest, carcass weight (CW), carcass yield (CY) were recorded for each animal. Seventy-two hours later, BFT and REA were determined on the Longissimus thorasis section at the 10th rib level of each left ½ carcass. No DT effects were detected (P≥0,93) on partial or global BW. In FD1, MoVi had greater (P< 0.05) ADG than SA for the 32-to-82-day period. In FD2, no DT effects (P>0,16) on ADG were detected. In both FD, DMI and DMIBW were greater (P<0,01) for NA, compared with MoVi, and Mo was intermediate. For FD1 and FD2, respectively, FE of MoVi resulted 20 and 17% greater (P<0,01) than FE of SA, and 9 and 7% greater (P< 0,05) than FE of Mo. No DT effects were detected (P>0,05) in CY, CW, REA and BFT in either FD1 or FD2. Adding Vi+Mo in whole corn-based finishing diet improved FE of feedlot heifers. Such improvement did not affect main carcass parameters.

Keywords : monensin; virginiamycin; heifers; feedlot fattening.

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