[Productive performance of dairy primiparous cows fed protected fat] | Comportamiento productivo de vacas primiparas holstein suplementadas con grasa protegida

English. The energy requirements for growth and milk production of dairy primiparous cows exceed the energy intake of conventional diets high in concentrate; therefore, we evaluated the effect of increasing the energy content of the diet using protected fat, on growth and productivity of Holstein heifers. Two treatments were compared: control diet, and control diet plus protected fat, in a completely randomized block design. Thirty heifers, with an average age of 2.6 years and body weight of 540 kg, were fed ad libitum a ratio of 50:50, green-chopped alfalfa: concentrate. Protected fat was included as 5 % of the daily concentrate intake. Heifers were distributed into three blocks of ten animals each, according to calving date. The analyzed variables were: individual milk production and composition, voluntary intake, body weight change, body condition, reproductive efficiency, and net energy balance. There were no differences between diets for any of the variables evaluated (p0.10), which suggests that probably energy was partitioned to cover the requirements for maintenance and growth, and the additional energy supplied by the protected fat was not expressed as an increase in milk production

Spanish; Castilian. El requerimiento de energia para crecimiento y produccion de leche de vacas primiparas excede al consumo de energia de dietas convencionales altas en concentrados, por lo que se evaluo el efecto de incrementar el aporte de energia, como grasa protegida, en la productividad de vaquillas Holstein de primer parto. Hubo dos tratamientos: dieta testigo y dieta testigo mas grasa protegida, en un diseno en bloques al azar. Se utilizaron 30 vaquillas de 2.6 anos de edad promedio, 540 kg de peso promedio, y alimentadas con una proporcion 50:50 de alfalfa verde picada: concentrado comercial, adicionandose la grasa protegida en el concentrado a razon de 5 % del consumo diario del mismo. Las vaquillas se dividieron en tres bloques, segun la fecha de parto, de 10 animales por bloque. Las variables analizadas fueron: produccion de leche y su contenido de grasa y proteina, consumo voluntario promedio de forraje y concentrado por corral, cambio de peso y de condicion corporal, eficiencia reproductiva y balance de energia neta. No hubo diferencias (p0.10) entre dietas para ninguna de las variables evaluadas, por lo que se infiere que la energia probablemente se utilizo para cubrir las necesidades de mantenimiento y crecimiento sin que la energia adicional pudiera expresarse como una mayor produccion de leche