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Methods to Improve Nutrient Intake in Grazing Cattle: Pasture management and Supplementation
Most of the grassland areas in Brazil are covered with tropical grasses. The majority of the milk (Stock et al, 2011) and beef (Millen et al., 2009) are produced on pasture based systems. In intensive grazing systems during the hot rainy season, stocking rates of 6 to 10 AU//ha (1 AU = 450 kg BW) can be achieved (Santos et al., 2014). Despite the high stock capacity, the average daily gain (ADG) and milk production are lower than the animals genetic potential and this is attributed to the limited energy intake. Some of the major factors imposing limitations to energy intake by the animals in tropical grazing systems are: a) low efficiency of the grazing process because of sward structure and b) rumen fill. During the last 2 decades, considerable amount of information has been published related to new management practices of tropical pastures. The adoption of the start grazing point based on the 95% light interception criterion, has successfully resulted in a more favorable sward structure which allows the animal to harvest a greater daily amount of forage in a shorter grazing period. However, even when all the available technology on tropical pasture management is applied, forage intake is still limited because of rumen fill. The quality of the tropical forage NDF (IVNDFD) is greater than for alfalfa. However the NDF content (51 to 65%) and its low cell fragility cause rumen fill and they limit energy intake. Studies related on cell fragility of tropical grasses are limited and this topic deserves more attention. Supplementing high energy concentrates for grazing cattle is at the same time, an efficient strategy to increase energy intake and to decrease the energy expended with the grazing activity. The substitution effect observed when concentrate is fed to grazing cattle is related not only to the amount of concentrate fed, but it is also related to the pasture management practices.
Keywords: grazing, nutrient intake, efficiency