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Dormant Season Grazing: Effect of Supplementation Strategies on Heifer Resource Utilization and Vegetation Use

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Heifer development is essential to the productivity and longevity of a cow/calf operation and typically results in additional feed costs to ensure heifers reach a target prebreeding weight that supports ideal reproductive performance ( Patterson et al., 1992; Roberts et al., 2009; Mulliniks et al., 2013a ). However, high feed costs have caused producers to explore low-input management strategies that minimize costs associated with providing harvested feeds ( Adams et al., 1996 ). Late-season forage corresponding to fall weaned heifers is typically low in quality, potentially putting animals in a state of negative energy balance ( Mulliniks et al., 2013b ). Protein supplementation while grazing dormant range can enhance heifer growth and improve pubertal status at breeding and reproductive performance ( Stalker et al., 2006; Martin et al., 2007 ). Thus, developing heifers on poor-quality forages may require considerable supplementation of nutrients in order to achieve target bodyweight and reproductive efficiency ( Galyean and Goetsch, 1993; Bowman et al., 2004; Mulliniks et al., 2013a ).

One of the primary goals of a forage-based livestock production system is to obtain optimal animal productivity while effectively using the forage resource base. Thus, the spatial component of herbivory is a central aspect of domestic livestock ecosystems ( Coughenour, 1991 ). Topography, thermal environments, and forage resources (e.g., standing crop and nutritional quality) interact to determine space use ( Jamieson and Hodgson, 1979; Adams et al., 1986; Beaver and Olson, 1997 ). Providing a supplement alters the nutrient status of animals, which can have strong influences on grazing behavior ( Allison, 1985; Adams et al., 1986 ). Supplementation changes grazing distribution on rangelands ( Ares, 1953; Bailey et al., 2001 ) and daily grazing activities ( Adams, 1985 ), altering the distribution of vegetation use based on supplement form, delivery method, and location ( Bailey and Welling, 2007; Bailey and Jensen, 2008 ). Therefore, it is...