The flow of ruminal undegradable protein (RUP) to the small intestine can be increased if ruminal degradation of dietary protein is reduced. The objective of this study was to evaluate the effect of extrusion on ruminal degradability of dry matter (DM) and crude protein (CP) from dehulled lupin (Lupinus albus L.) (DL) and rapeseed (Brassica napus L.) meal (RM). Unextruded soybean (Glicine max L.) meal (SBM) was used as a control. The DL was extruded at 130 ºC with 20% moisture and RM was extruded at 120 ºC with 20% moisture. Ruminal degradability was evaluated in situ by incubating feed samples for 2, 4, 8, 12, 24, and 48 h of fermentation in the rumen using three rumen-fistulated dairy cows. Values of CP soluble fraction ("a") in SBM, DL, extruded dehulled lupin (EDL), RM, and extruded rapeseed meal (ERM) was lower in the extruded feeds (P < 0.05). The slowly degradable fraction ("b") of SBM, DL, EDL, RM, and ERM was 858, 593, 622, 451, and 457 g kg-1 , respectively, and was increased by extrusion (P < 0.05). Extrusion reduced the effective degradability (ED) of CP in lupin from 807 to 788 g kg-1 ; kp = 0.05 h-1 while ED was reduced from 868 to 789 g kg-1 ; kp = 0.05 h-1 in ERM. This resulted in an increase in RUP of 8.95% in EDL (P < 0.05); the increase was 37.35% (P < 0.05) in ERM. It may be concluded that extrusion in the presence of moisture reduced the degradability of CP, particularly in the case of ERM.

El objetivo de este trabajo fue caracterizar rebaños lecheros que presentaban muestras de leche positivas a la prueba de alcohol sin estar ácidas, y compararlos con predios negativos a esta prueba, considerándose el efecto de la estacionalidad. Se estudiaron cuatro rebaños (tres positivos a la prueba de alcohol y uno negativo). En dos años, se muestreó leche durante tres meses en lactancias de invierno (época 1) y tres meses en lactancias de verano (época 2). En la dieta, se realizó análisis proximal relativo a EM, Ca, P, Mg y K. En leche, se determinó proteína, lactosa, Ca, P, Mg, K, pH, prueba de alcohol, acidez titulable y actividad proteásica. En casos negativos a la prueba de alcohol, se observó alta correlación entre proteína cruda láctea, proteína cruda en alimento, fósforo lácteo y lactosa. Los predios positivos a la prueba de alcohol se correlacionaron fuertemente con la menor concentración de materia seca y el alto contenido de fibra cruda, además presentaron menor concentración de proteína láctea. Ello indicaría que existió un efecto del manejo alimentario sobre la inestabilidad de la leche. Las lactancias desarrolladas durante la sequía estival sufren de un stress alimenticio, por lo cual podrían presentar inestabilidad láctea.

Microbial protein synthesis is essential to meet protein requirements in ruminants. The aim of this investigation was to evaluate the effect of incorporating extruded corn (Zea mays L.) into the ration of young steers fed with grass silage on microbial protein synthesis (MPS). Twenty young steers in metabolic cages were used for supplying food. The treatments consisted of combinations of extruded corn (EC) and ground corn (GC) EC-10 (10% EC-30% GC); EC-25 (25% EC-15% GC) and EC-40 (40% EC-0% GC). These foods constituted 40% of the ration (DM-based) and the remaining 60% was grass silage. The MPS was calculated through the excretion of purine derivatives (PD) in the urine, using total collection of urine . The microbial protein absorption and flow of duodenal N also increased with a higher portion of extruded corn (EC-40, P < 0.05). The differences between treatments can be explained by the effect of corn extruding. This allows more energy available for ruminal bacteria and improved synchrony between energy and protein.

Enzymatic in vitro digestibility has been studied as a method to predict energy values of forages for ruminants, although results have been affected by type of forage and methodological details of the technique. This work was performed to evaluate the effects of cellulase concentration (0.75, 1.0 and 6.25 g L -1 ), incubation time (24 or 48 h) and type of final washing of the residue (water or acetone) on the in vitro digestibility of the dry matter (DMD), organic matter ( repens). Regression equations among cellulase results andin vitro values obtained with rumen fluid were also developed. Higher enzyme concentration, longer incubation time and final washing with acetone, resulted in a significant (P < 0.05) increase in DMD, OMD and D value. A strong interaction (P < 0.001) among forage type, maturity stage and incubation time was observed. Interactions between stage and enzyme concentration were also apparent (P < 0.05) for D value, DMD and OMD. Type of pasture and maturity affected the performance of the enzymatic method to predict in vitro digestibility obtained with rumen fluid. Therefore, different prediction equations should be developed for any combination of the above mentioned factors. Adjusting this methodology with in vivo data is encouraged to improve prediction of digestibility values.

In pasture-based dairy herds where silage is a widely adopted supplement, optimized feeding requires reliable estimations of nutritional quality of this conserved forage. Metabolizable energy, an important nutritional fraction, can be predicted from digestibility-related traits, such as the digestible organic matter contained in the dry matter (D-value). The aim of the present study was to evaluate the prediction of D-value and dry matter digestibility (DMD) of grass silages made from four different pastures and maturity stages, using the pepsin-cellulase method. Fungal cellulase was used, applying different enzyme concentrations, incubation times and types of final wash. The silages were prepared from permanent pasture (Dactylis glomerata L., Lolium perenne L., Bromus catharticus Vahl var. catharticus, Trifolium repens L. and Holcus lanatus L.), rotation pasture (Lolium multiflorum Lam. cv. Tama), oats (Avena sativa L.), and mixed pasture (L. perenne-T. repens). These were harvested at three different physiological stages (vegetative, ear emergence and dough grain). The treatment using an incubation time of 24 h, a cellulase concentration of 6.25 g L-1 and final wash with water (Treatment 3) presented the best prediction capacity of the in vivo D-value (R 2 = 0.78) and in vivo DMD (R 2 = 0.71). In vivo D-value prediction improved (R 2 = 0.8) when a chemical determination (crude fibre, gross energy, neutral detergent fibre, total ash or acid detergent fibre) was included in addition (multiple regression) to D-value obtained with cellulases (Treatment 3). Results of DMD obtained with cellulases show good precision, but underestimate in vivo values, and are closer to those obtained with ruminal fluid. Suitable equations could be used to improve accuracy.

El nabo forrajero (Brassica rapa L.) es utilizado durante el verano como cultivo suplementario en vacas a pastoreo. El objetivo de este estudio fue evaluar el efecto de la suplementación estival con dos niveles de oferta de nabo forrajero en la producción de leche, y la respuesta metabólica de energía y proteína en vacas lecheras a pastoreo. Se emplearon 16 vacas Frisón Negro Chileno distribuidas aleatoriamente en dos tratamientos: dieta A (2,6 kg DM vaca-1) y dieta B (5,1 kg DM vaca-1). La producción de leche del grupo con la dieta A no presentó diferencia significativa con el grupo que recibió la dieta B. La proteína y grasa láctea fue similar entre los grupos (p > 0,05). Los dos niveles de suplementación con nabo mantuvieron un adecuado balance energético y de proteínas, reflejado en concentraciones plasmáticas de βHB, proteína total, albúmina y urea que fluctuaron dentro de los intervalos de referencia. Bajo las condiciones del ensayo la respuesta productiva fue igual en ambos tratamientos, no afectando la composición láctea y manteniendo un balance energético normal. Se observó una hipofosfatemia en el tratamiento con la dieta B.