The effect of harvesting time (morning vs. afternoon) on the chemical composition and nutritional value of sun-drying alfalfa, clover and barley forages

Introduction[1] Forages are grown mainly for feeding livestock, especially in dairy cows, because adequate roughage is needed in diets to provide good rumen function. However, as more roughage is fed, the energy density of the diet is reduced. So, the production of high quality forage is very important for dairy producers. High quality forage has direct effects on animal production efficiency, including weight gain, milk production, and reproductive success. Producing and conserving of high quality forage is a challenge because several factors can be affected forage quality including plant species, soil fertility, maturity at harvest, and harvesting (mowing, field curing, baling or chopping) and storage methods and other factors (weeds, insects and diseases). Fiber and energy contents are the most important in forage quality measures. As the fiber level increases, the energy content generally decreases. Therefore, improving forage quality can be achieved by managing forage carbohydrate content. Carbohydrates are the primary source for ruminants and contribute 60 to 70% of the net energy used for milk production and are classified as structural and non-structural. As usual, structural carbohydrates defined as neutral detergent fiber (cellulose, hemicellulose, lignin and portion of the pectin) and non-structural carbohydrates consist of the sugars, starches and pectin. Non-structural carbohydrates are a highly digestible energy source and together with degraded protein, are needed by the rumen for microbial growth and digestion. Plants accumulate sugars during the day via photosynthesis, but incur a net loss at night via dark respiration. This diurnal cycling reflects the concentration of total nonstructural carbohydrates in forages. The aim of this study was to evaluate the effect of morning versus afternoon cutting time on chemical composition, gas production parameters and digestibility of sun-drying alfalfa, clover and barley forages. Materials and Methods About 5-7 cm above the soil stage, alfalfa, clover and barley were harvested in two times, at 06:00 AM and 18:00 PM. Whole Alfalfa and clover plants were harvested at the first bud stage of development and whole barley plant at the medium dough stage of maturity used. Their nutritive value was evaluated through the determination of chemical compositions and in vitro gas production techniques. Samples were tested in an in vitro gas production method (96 h incubation) and batch rumen culture system (24 h