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Accurate measurement of herbage intake rate is critical to advance knowledge of the ecology of grazing ruminants. This experiment tested the integration of behavioral and acoustic measurements of chewing and biting to estimate herbage dry matter intake (DMI) in dairy cows offered micro-swards of contrasting plant structure. Micro-swards constructed with plastic pots were offered to three lactating Holstein cows (608±24.9 kg of BW) in individual grazing sessions (n=48). Treatments were a factorial combination of two forage species (alfalfa and fescue) and two plant heights (tall=25±3.8 cm and short=12±1.9 cm) and were offered on a gradient of increasing herbage mass (10 to 30 pots) and number of bites (~10 to 40 bites). During each grazing session, sounds of biting and chewing were recorded with a wireless microphone placed on the cows? foreheads and a digital video camera to allow synchronized audio and video recordings. Dry matter intake rate was higher in tall alfalfa than in the other three treatments (32±1.6 v. 19±1.2 g/min). A high proportion of jaw movements in every grazing session (23 to 36%) were compound jaw movements (chew-bites) that appeared to be a key component of chewing and biting efficiency and of the ability of cows to regulate intake rate. Dry matter intake was accurately predicted based on easily observable behavioral and acoustic variables. Chewing sound energy measured as energy flux density (EFD) was linearly related to DMI, with 74% of EFD variation explained by DMI. Total chewing EFD, number of chew-bites and plant height (tall v. short) were the most important predictors of DMI. The best model explained 91% of the variation in DMI with a coefficient of variation of 17%. Ingestive sounds integrate valuable information to remotely monitor feeding behavior and predict DMI in grazing cows. Fil: Galli, Julio Ricardo. Universidad Nacional de Rosario; Argentina Fil: Cangiano, Carlos Alberto. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina Fil: Pece, M. A.. Universidad Nacional de Rosario; Argentina Fil: Larripa, M. J.. Universidad Nacional de Rosario; Argentina Fil: Milone, Diego Humberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigación en Señales, Sistemas e Inteligencia Computacional. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas. Instituto de Investigación en Señales, Sistemas e Inteligencia Computacional; Argentina Fil: Utsumi, S. A.. Michigan State University; Estados Unidos Fil: Laca, E. A.. University of California at Davis; Estados Unidos

The effect of different levels of daily allowance and supplementation on intake, milk production and composition and per hectare productivity was studied. Pasture consisted of an association of alfalfa (Medicago sativa), tall fescue (Festuca arundinacea) and prairie grass (Bromus wildenowii) and high moisture corn was used as supplement. 32 cows were allocated to four levels of pasture allowance (NA) and two levels of energy supplementation (SE). Pasture intake and individual and per hectare production were affected by NA, but SE had no signifi cant effect. No interactions were detected between any of the variables. Milk composition were not affected by NA, whereas only non fat solids were affected by SE. Liveweight change and condition score did not show differences among treatments. Urea level in both, plasma and milk, was not affected by NA, whereas the level of urea in plasma showed a trend to be different and the level of urea in milk was signifi cantly different for SE. Critical levels of pasture allowance which directly affect the productivity per hectare, need to be reached in order to perform a signifi cant increase of individual production. Milk fat and protein concentration did not appear to be responsive variables to different levels of supplementation and allowance, whereas the little variation in urea levels, as a response to a greater level of supplementation, did not make this a valuable tool to improve the milk protein constituents. Se estudio el efecto que distintos niveles de asignacion diaria y suplementacion producen sobre el consumo, la produccion y composicion de la leche y la productividad por hectarea. La pastura utilizada fue una asociacion de alfalfa (Medicago sativa), festuca (Festuca arundinacea) y cebadilla criolla (Bromus wildenowii) y el suplemento fue grano de maiz humedo. Se utilizaron 32 vacas y se establecieron cuatro niveles de asignacion de pastura (NA) y dos niveles de suplementacion energetica (SE). El consumo de pastura y la produccion individual y por hectarea fueron afectados por NA y no por SE. Al igual que para el resto de las variables, no se detectaron interacciones entre NA y SE. La composicion de la leche no fue afectada por NA, mientras que SE solo tuvo efecto sobre los solidos no grasos. La evolucion del peso vivo y del estado corporal no mostraron diferencias entre tratamientos. Los niveles de urea en plasma y leche no difi rieron signifi cativamente para NA, no ocurriendo lo mismo para SE, donde el nivel de urea en plasma tendio a diferir y el nivel de urea en leche difi rio signifi cativamente. Se concluyo que para conseguir aumentos signifi cativos en la produccion individual es necesario ofrecer niveles de asignacion que afectan negativamente la produccion por hectarea. La concentracion de grasa y proteina de la leche no parecieron ser variables sensibles a distintos niveles de suplementacion y asignacion, mientras que la escasa variacion en los niveles de urea, debida al mayor nivel de suplementacion, relativizo el valor de esta herramienta para mejorar la composicion de la proteina lactea.