RESUMEN
Dos preparaciones enzimáticas comerciales: Fibrozyme (F) y Promote (P) se aplicaron en forma independiente a muestras de rastrojo de maíz (RM) a dosis de 1.5 g·kg-1 y 0.2 g kg-1 de materia seca (MS), respectivamente, a 24 h ó 0 h, antes de iniciar la incubación in vitro en un fluido ruminal modificado. Además, se añadieron juntos o independientes a las muestras, dos aditivos químicos: urea (U) o hidróxido de calcio (cal apagada, C), 48 h antes de la incubación in vitro a dosis de 0.75 o 1.5%. Las combinaciones de enzimas y aditivos arrojaron 16 tratamientos (F o P solos, F+C o U, P+C o U, F+C+U o P+C+U a 24 o 0 h; T1-T16) y un testigo sin enzimas ni aditivos (T0). Mediante un diseño bloques al azar generalizado (2 corridas y 4 repeticiones por corrida) y utilizando un modelo logístico no lineal se evaluaron volumen máximo de gas (Vmax), tasa fraccional (S) y fase lag (FL); además se evaluaron a 24 h las producciones de CO2, CH4, CO2:CH4; además se midieron la materia seca desaparecida (MSD), fibra detergente neutro residual (FDNr), digestibilidad in vitro (DV) de la MS, AGVt, masa microbiana (MM) y adherencia microbiana (AM). A 24, 48, 60 y 72 h se evaluaron la degradación de la materia orgánica (DMO) y la DMO fraccional (DMO/t); a 24 y 48 h se estimaron energía metabolizable (EM) y energía neta de lactancia (ENL). Mediante un diseño completamente al azar con 4 repeticiones por tratamiento se evaluaron AGVt, AA, AP, AB, AA:AP y nitrógeno amoniacal (N-NH3) a 24 h. Por lo general los tratamientos con aplicación enzimática a 0 h (T9-T16) superaron a T0 y al resto de los tratamientos en S, AP, MSD, FDNr, DV, AP, DMO (a 48, 60 y 72 h), DMT/t (en todos los tiempos), EM (a 48 h) y ENL (a 48 h) (P<0.05). En N-NH3 los tratamientos que incluyeron U superaron a T0 (P<0.05). En el resto de las variables no hubo diferencias entre tratamientos y T0. En la etapa in situ se evaluaron las mismas combinaciones entre preparados enzimáticos y aditivos químicos pero únicamente se aplicaron las enzimas a 0 h y se incluyeron dos testigos, el primero: muestras de rastrojo de maíz molido + solución melaza:agua (T0) y el segundo: rastrojo de maíz solo (T00). Se midió digestibilidad a 24, 48, 72 y 96 h en arreglo factorial (10x4) y los tratamientos fueron confundidos dentro de enzimas. Se evaluaron digestibilidad in situ de MS (DIS) y FDNr. En la etapa in vivo sólo se evaluaron los tratamientos F (T1), P (T2), F+C (T3), P+C (T4), F+C+U (T5), P+C+U (T6) y un testigo [(dieta base+56% de RM+melaza:agua (T0)]. Se utilizaron 42 borregos (21 machos 19 kg y 21 hembras, 17 kg en un diseño bloque generalizado (sexo) con 3 repeticiones por sexo y seis repeticiones
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por tratamiento. En DIS los tratamientos F+C y F+C+U así como P+C (a 48 h) y P+C+U (a 48 y 72 h) superaron a T0 y T00 (P<0.05), pero no hubo diferencias en FDNr. En la etapa in vivo, los siguientes tratamientos reportaron valores superiores a T0: T1, T2 y T6 en ganancia de peso; T1, T4, T5 y T6 en conversión alimenticia; T1, T2, T3, T5 y T6 en porcentaje de AA; T1, T2 y T3 en porcentaje de AP y concentración de AGVt; y, T3, T5 y T6 en digestibilidad por cenizas insolubles (P<0.05). En el resto de la variables: consumo de alimento, pH, porcentaje de AB, proporción AA:AP, concentración de N-NH3, tasa de desaparición de FDN, FDA y lignina no hubo diferencias entre tratamientos y T0. Los tratamientos que mejores resultados reportaron en las tres etapas experimentales fueron: F+C, P y P+C+U seguidos por F y P+C; con aplicación enzimática a 0 h en todos los casos. Se concluye que Fibrozyme ó Promote, solos o combinados con cal o urea, tienen efectos positivos sobre la degradación del rastrojo de maíz in vitro e in situ, y pueden mejorar el comportamiento productivo en ovinos.
ABSTRACT
Two commercial enzyme preparations: Fibrozyme (F) and Promote (P) were independently added to corn stubble samples at 1.5 g·kg-1 and 0.2 g kg-1 of dry matter (DM), respectively, at 24 h or 0 h before in vitro incubation in a modified ruminal fluid. Also, two chemical additives: urea (U) or calcium hydroxide (mineral lime, C) were added together or separately to the samples, 48 h before in vitro incubation at levels of 0.75 or 1.5%. The combination of enzyme preparations and chemical additives resulted in 16 treatments (F or P alone, F+C or U, P+C or U, F+C+U or P+C+U at 24 h or 0 h; T1-T16) and a control without enzymes or additives (T0). Maximum gas volume (Vmax), fractional rate (S) and lag phase (FL) were evaluated through a generalized randomized blocks design (2 runs and 4 replicates per run) using a nonlinear logistic model; in addition, CO2, CH4 and CO2:CH4 were evaluated at 24 h; also, dry matter disappearance (MSD), residual neutral detergent fiber (FDNr), in vitro digestibility (DV) of MS, total volatile fatty acids (AGVt), microbial mass (MM) and microbial adherence (AM) were measured. Organic matter degradation (DMO) and fractional DMO (DMO/t) were evaluated at 24, 48, 60 and 72 h; metabolizable energy (EM) and net energy of lactation (ENL) were estimated at 24 and 48 h. AGVt, acetic acid (AA), propionic acid (AP), butyric acid (AB), AA:AP ratio and ammonia nitrogen (N-NH3) were evaluated at 24 h using a completely randomized design and 4 replicates per treatment. In general, treatments with enzyme preparation added at 0 h (T9-T16) were better than the control and the rest of the treatments in S, AP, MSD, FDNr, DV, AP, DMO (at 48, 60 and 72 h), DMT/t (at all times), EM (at 48 h) and ENL (at 48 h) (P<0.05). In N-NH3, treatments with U were better than T0 (P<0.05). For the rest of the variables, there were no differences between treatments and T0. In the in situ phase of the study, the same combinations between enzyme preparations and chemical additives were evaluated, but enzyme preparations were added only at 0 h, and two controls were included: the first contained ground corn stubble + molasses:water solution (T0), and the second one consisted of corn stubble alone (T00). Digestibility was measured at 24, 48, 72 and 96 h in a factorial array (10x4) and the treatments were confounded within enzyme preparations. In situ digestibility of dry matter (DIS) and FDNr were evaluated. In the in vivo phase, the only treatments evaluated were F (T1), P (T2), F+C (T3), P+C (T4), F+C+U (T5), P+C+U (T6) and a control [(basal diet+56% of RM+molasses:water (T0)]. Forty two sheep [21 males (19 kg) and 21 females (17 kg)] were utilized in a generalized
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block (sex) design with 3 replicates per sex and 6 replicates per treatment. Regarding DIS, treatments F+C and F+C+U as well as P+C (at 48 h) and P+C+U (at 48 and 72 h) were better than T0 and T00 (P<0.05), but there were no differences in FDNr. In the in vivo phase, the following treatments reported values better than T0: T1, T2 and T6 in weight gain; T1, T4, T5 and T6 in feed conversion; T1, T2, T3, T5 and T6 en AA level; T1, T2 and T3 in AP and AGVt levels; and T3, T5 and T6 in digestibility by insoluble ash (P<0.05). For the rest of the variables: feed intake, pH, AB level, AA:AP ratio, N-NH3 level, FDN, FDA and lignin disappearance rates, there were no differences between treatments and T0. The treatments which reported the best results in all three experimental phases were: F+C, P and P+C+U followed by F and P+C with enzyme preparation added at 0 h. It is concluded that Fibrozyme or Promote, alone or combined with mineral lime or urea, have positive effects on the in vitro and in situ degradation of corn stubble, and can improve the productive behavior in ovine cattle.
