Evaluación de dietas basadas en grano entero, sin fibra larga, para engorde de bovinos a corral

espanolLa provision de fibra es frecuentemente una limitante operativa y economica en dietas de feedlot. El presente trabajo evalua el potencial de dietas sin fibra larga, basadas en grano entero de maiz. Se utilizaron 48 novillitos y 48 novillos Angus, (155 ± 9,7 y 269 ± 10,8 kg de peso vivo) bloqueados por categoria, estratificados por peso en 4 estratos homogeneos, y asignados de a 4 por corral. Sobre los corrales se impusieron, durante 89 dias, 3 tratamientos consistentes en 3 dietas que incluyeron: T1 = grano de maiz entero +harina de girasol + heno de alfalfa, T2 = grano de maiz entero + harina de girasol y T3 = grano de maiz entero + grano de avena entero + harina de girasol. El tratamiento1 sirvio de dieta control. Se determino el aumento diario de peso vivo (ADPV), el consumo de materia seca (CMS) y la eficiencia de conversion (ECMS) en cuatro periodos consecutivos. Se estimo la produccion de heces, la composicion quimica de la dieta y de las heces (PB, FDA, FDN, lignina y almidon) y la fraccion de grano visible recuperado de las heces (GrHe), en tres periodos semanales. Los datos se sometieron a analisis de varianza con un modelo totalmente aleatorizado, con un arreglo factorial de tratamientos (categoria x dieta) y medidas repetidas en el tiempo. No se detectaron interacciones (P>0,12) entre tratamientos, categoria y periodo, ni diferencias (P> 0,05) entre tratamientos para ADPV (1,339 ± 0,023 kg), CMS (8,58 ± 0,107 kg dia-1), y ECMS (P>0,12; 5,46 ± 0,03). Los novillos aumentaron de peso a un ritmo superior (P0,10) entre categorias y tratamientos. Por su parte, la fraccion de GrHe fue mayor en novillos (P EnglishAddition of fiber to Argentinean feedlot diets imposes frequently an economic constraint because of hay baling and grinding costs as well as equipment required. The present work evaluated performance of feedlot diets without a long-fiber source, based on whole corn grain. Forty eight calves and 48 steers (155 ± 9.7 y 269 ± 10.8 kg live weight, respectively) were blocked by sex, stratified by weight in 4 homogeneous groups and assigned in groups of 4 to each feeding pen. Three diet treatments were imposed on pens during 89-day study period: T1 = whole shelled corn grain + sunflower meal + alfalfa hay, T2 = whole shelled corn + sunflower meal, and T3 = whole shelled corn + whole oats + sunflower meal. Treatment 1 served as control. Average daily weight gain (ADG), dry matter intake (DMI) and feed efficiency (FE) were determined for 4 consecutive periods. Fecal production, diet and feces chemical composition (CP, ADF, NDF, lignin and starch), and proportion of visible grain eliminated in feces (FeGr), were determined in three weekly periods over the study. Data were submitted to ANOVA using GLM under a completely randomized design with repeated measurements and a factorial arrangement of treatments (animal category x diet). Neither interaction was detected (P> 0.12) among diet, animal category and period, nor differences were found (P> 0.05) among treatments for ADG (1.339 ± 0.023 kg), DMI (8.58 ± 0.107 kg day-1) and FE (P> 0.12; 5.46 ± 0.03). Steers gained weight faster that calves (P0.10) between categories and among diets. The FeGr fraction was greater (P Seven to 9% of grain consumed by calves and 9 to 9.5% of grain consumed by steers escaped in feces as visible forms. Starch use efficiency followed a similar pattern to grain. Results suggested that use of whole shelled corn grain or whole corn plus oats grain, complemented with sunflower meal would be a solution for counteracting effective-fiber deficiency of hay-free feedlot diets.