Sustainability of dormant season grazing: Does protein supplementation impact beef cattle performance, soil organic matter, vegetation, and residual cover for wildlife?

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Commodities

• Additional Plants: native plants
• Animals: bovine

Practices

• Animal Production: grazing management, mineral supplements, range improvement, stockpiled forages, winter forage
• Education and Training: extension, mentoring
• Natural Resources/Environment: biodiversity, habitat enhancement, wildlife
• Production Systems: agroecosystems, holistic management
• Soil Management: organic matter

Economic efficiency of cattle production is threatened by high feed and input costs (Meyer and Gunn 2015).  To improve profitability and transition to reduced reliance on transported harvested feeds, many cow-calf producers have adopted management strategies involving dormant season grazing (Adams et al. 1996).  The primary goal in a forage-based livestock production system is to obtain optimal animal performance while effectively utilizing the forage resource base.  Dormant range forage is deficient in nutrients and may result in decreased performance (Krysl and Hess 1993, Bowman et al. 1995, Mulliniks et al. 2013).  Providing protein supplements to grazing beef cattle during times of low forage quality can improve animal performance and provide increased economic returns (Lusby et al. 1967, Bowman et al. 1995, DelCurto et al. 2000, Bodine et al. 2001).  However, supplementation strategies assume that all animals consume a targeted quantity of supplement, which ignores variation of supplement intake by individual animals (Bowman and Sowell 1997).  Deviation from the targeted consumption of supplement can have strong effects on animal nutirent status (Bowman and Sowell 1997).  Effectiveness of supplementation programs on grazing cattle performance have been inconsistent (DelCurto et al., 1990). This inconsistency may be due to variation in supplement intake by individual cows, often influenced by social dominance associated with age class within the herd (Wagnon, 1965; Friend and Polan, 1974).

Winter grazing typically exposes cattle to periods of severe cold which increases energy expenditure to maintain homeothermy (Webster, 1970, 1971). In addition, at cold temperatures wind induces a higher metabolic rate and heat production (Webster, 1970; Christopherson et al., 1979). Thus, winter conditions can have considerable economic impact on the energetic efficiency of cattle production on rangelands (Webster, 1970). Potential changes in energetic requirements to maintain homeothermy could alter supplement intake during winter months.

The spatial component of herbivory is a central aspect of domestic livestock ecosystems, but has remained difficult to interpret (Coughenour 1991).  Topography, thermal environments and forage resources, such as standing crop and nutritional quality, interact to determine space use (Malechek and Smith 1976, Jamieson and Hodgson 1979, Adams et al. 1986, Beaver and Olson 1997).  Livestock age, experience, body weight and condition can also directly influence grazing behavior, distribution patterns and forage resource use (Holmes et al. 1961, Allden 1968, Langlands 1968, Allison 1985, Dunn et al. 1988, Walburger et al. 2009).  Furthermore, supplementation alters the nutrient status of grazing livestock, which can have strong influences on grazing behavior (Allison 1985, Adams et al. 1986).  The act of supplementation alone can change grazing distribution on rangelands (Ares 1953) and daily grazing activities (Adams 1985), altering the distribution of vegetation use based on location of supplements.  Thus, it is likely that grazing behavior may vary with protein supplement intake and/or cow age, body weight and condition in dormant-season grazing systems.

Although dormant forage tends to be more tolerant of grazing pressure (Holechek et al. 2004, Petersen et al. 2014), dormant season grazing has been shown to have detrimental effects on vegetation production and residual cover when improperly managed (Willms et al. 1986, Bullock et al. 1994, Holechek et al. 2004, Petersen et al. 2014).  Removal of vegetation and litter cover through grazing, reduces soil organic matter, which can be detrimental to agroecosystem efficiency and soil productivity (Greene et al. 1994, Wander 2004).  Additionally, vegetation composition and structural heterogeneity are key habitat characteristics that influence wildlife species diversity and ecosystem function (Christensen 1997, Wiens 1997, Bailey et al. 1998, Fuhlendorf and Engle 2001, Fuhlendorf et al. 2009).  Habitat structural heterogeneity serves as a precursor to biological diversity at most levels of ecological organization and has been proposed as the foundation of conservation and ecosystem management (Christensen 1997, Wiens 1997, Fuhlendorf and Engle 2001).  Western rangelands are inherently heterogeneous as vegetation composition and structure vary with topographic and edaphic features (Patten and Ellis 1995, Fuhlendorf and Smeins 1998, Fuhlendorf et al. 2006).  However, protein supplementation can been used as a tool to alter grazing distribution to promote uniform utilization across the landscape (Bailey and Welling 1999).  Livestock grazing management promoting uniform utilization can result in the homogenization of rangeland landscapes and an overall decline of ecosystem structure, function and biodiversity, which can have a profound effect on grassland wildlife habitat selection and demography (Dennis et al. 1998, Fuhlendorf and Engle 2001, Anderson 2006, Derner et al. 2009, Fuhlendorf et al. 2009, Hovick et al. 2015, López‐González et al. 2015).  Thus, maintaining heterogeneity of vegetation composition and structure in rangelands is beneficial to wildlife habitat and ecological biodiversity (Fuhlendorf et al. 2006).  However, little is known about the effects of crude protein supplementation on grazing behavior and its potential impacts on vegetation and rangeland sustainability (Schauer et al. 2005).

Information relating supplement intake cow age, body weight and condition to individual supplement intake, grazing distribution and behavior is lacking.  Thus, the intent of this study was to evaluate (1) examine the effects of cow age and environmental conditions on individual supplement intake and cattle behavior, (2) the influence of supplement intake, age, body weight and condition on grazing activity and resource utilization by cattle, and (3) the influence of dormant season use on soil organic matter, residual vegetation cover, structure and heterogeneity.  We expected dormant season grazing by supplemented livestock to have multi-faceted effects on agroecosystems in northern mixed grass prairies.  System-level impacts are likely mediated by the provision of supplement, as well as, uncontrolled environmental conditions. 

We expect dormant season grazing by supplemented livestock to have multi-faceted effects on agroecosystems in northern mixed grass prairies.  Because supplementation affects the grazing behavior of cattle, system-level impacts are likely mediated by the provision of supplement as well as uncontrolled environmental conditions.  Our specific objectives are to evaluate how supplementation during the dormant grazing season and animal age influences:

1. Supplement intake and behavior. Winter grazing typically exposes cattle to periods of severe cold which increases energy expenditure to maintain homeothermy (Webster, 1970, 1971). Inconsistent results from supplementation may be due to variation in supplement intake by individual cows, often influenced by social dominance associated with age class within the herd (Wagnon, 1965; Friend and Polan, 1974). Therefore, we expect that both cow age and winter environmental conditions affect daily supplement intake, as well as, the variation in supplement intake. Data was collected the winter grazing season of 2016 through 2017.
2. Cattle grazing behavior and performance. Altering an animal’s nutritional environment with the addition of supplement has a high potential to affect grazing distribution and behavior (Murden and Risenhoover 1993), as well as, weight gain and body condition. Therefore, we expect that supplementation will have effects on distribution of pasture use, time spent grazing and distance traveled with corresponding effects on weight and body condition.  Data was collected the winter grazing season of 2016 through 2017.
3. Vegetation use, production, and structure, and soil organic matter. Range condition is influenced by grazing behavior (Belsky and Blumenthal 1997); thus, we expect that differences in grazing behavior will have differential effects on vegetative and structural composition of rangelands. Data was collected summer of 2016 through 2017.

Our intentions are to further the understanding of dormant season grazing and supplementation effects on grazing behavior and rangeland condition, with the ultimate goal of facilitating the adoption of management strategies developed for long-term sustainability of agroecosystems.