Comparative Pasture Management on Canadian Cattle Ranches With and Without Adaptive Multipaddock Grazing

Abstract

Significant interest exists in the potential for specialized grazing systems, including adaptive multipaddock (AMP) grazing, to enhance grassland health and function. However, specific pasture management practices associated with AMP grazing at the ranch level remain poorly understood in comparison with more regionally representative management systems. As part of a larger study examining grazing effects on soil carbon, greenhouse gases, and other ecosystem attributes, here we report on differences in disturbance history and grazing management practices on a sample of AMP operators and their neighboring (n-AMP) ranches at 32 paired sites across the prairie provinces of western Canada. Most ranches studied (77.5%) relied on pastures composed of introduced (seeded) forage. On average, the AMP ranches surveyed were larger in size, supported greater animal numbers, and were more likely to use seeded forages comprising diverse mixes. Relative to n-AMP ranches, AMP ranches used 18.6-fold higher average stock densities in smaller paddocks (22.3 vs. 120.7 ha) while grazing over a grazing season that was 76 d longer, although computed stocking rates remained similar (P ≥ 0.10). AMP operators specifically used much shorter grazing periods (2.8 d) during the early growing season (i.e., before August 1) that were followed by a prolonged rest period (69 d) and could be used to compute a rest-to-grazing ratio for the first half of the grazing season for all ranches. This ratio, along with cattle stock density computed at the pasture scale, exhibited the greatest potential to differentiate the two groups of ranchers. Finally, both groups, and in particular ranchers within the AMP group, demonstrated high variability in management practices among individual operators, highlighting the importance of using specific management metrics rather than generalized descriptors of “grazing system type” to interpret their influence.

Introduction

Grasslands occur across nearly 40% of the Earth's terrestrial surface and are an important source of ecosystem goods and services (EG&S) including forage and livestock production, as well as soil carbon storage (Sanderson et al. 2020). Grasslands and their associated EG&S remain at risk of decline, including from conversion to agricultural crops and industrial uses (Allred et al. 2015). However, the effects of grazing on EG&S, including specialized grazing systems, remain less clear. Grazing systems involve complex disturbance regimes that simultaneously alter numerous management parameters, such as the timing of grazing initiation and cessation, livestock numbers and stock densities, as well as the frequency and duration of individual grazing periods (Hunt et al. 2014; Roche et al. 2017).

Given the inherent complexity of grazing strategies available, varying perspectives exist on whether, when, and how variation in grazing alters grassland function. For example, several studies conclude that the benefits of rotational grazing for maintaining grassland production and range condition may not be as large and consistent as previously thought, with the majority of studies reporting no difference between areas subject to rotational and continuous grazing (Holechek et al. 1999; Briske et al. 2008; Hawkins 2017). In contrast, McDonald et al. (2019) concluded that strategic rest appeared capable of enhancing ground cover and animal production per unit area relative to continuous grazing, with no changes to plant biomass, richness and diversity, or individual animal weight gain (McDonald et al. 2019). In their review of past studies examining rotational grazing, Teague et al. (2013) noted that past research had often failed to properly test rotational grazing due to the inability of controlled deductive studies to replicate the spatial scale, as well as the adaptive framework that involves flexible grazing over time, within which livestock production typically occurs. Moreover, studies evaluating grazing systems often confound stock density and stocking rate and employ limited sampling regimes in space and time at scales outside of those where grazing management decisions are made, further reducing their ability to evaluate the merits of alternative grazing practices (Teague et al. 2013). In general, while the unique knowledge and experience of ranchers is critical in shaping management behavior over time, individual rancher behavior, as manifest through management actions, has seldom been quantified or tested (Wilmer et al. 2018), although efforts are under way in this capacity as exemplified by a recent study implementing collaborative adaptive management directly involving ranchers (Derner et al. 2021).

Numerous studies have reported on the effects of grazing and/or defoliation on the provisioning of EG&S, including forage production (e.g., DeBruijn and Bork 2006) and soil conditions (e.g., Pyle et al. 2019), though most studies manipulate single variables such as the intensity, frequency, or timing of defoliation. At its core, select management actions, including stocking rates during the grazing season, are well known to influence grassland properties and ecosystem function (Holechek 1988). What is less understood under various rotational grazing systems is how variation in the timing of initial grazing, frequency of grazing and intermittent rest periods, and the relationship between alternating grazing and rest periods during the growing season varies among cattle producers, as well as how this might influence agroecological outcomes. Using a meta-analysis of global data, McDonald et al. (2019) reported that increases in the duration of rest period relative to grazing time led to measurable benefits on grasslands, including plant biomass, ground cover, and animal weight gain.

Many management-intensive grazing systems have their origins in rational grazing (Voisin 1961) and time-controlled (a.k.a. planned) grazing—an essential element of holistic management (Savory and Butterfield 1999). There are many related terms describing this concept, including adaptive multipaddock (AMP) grazing, a term described by Teague et al. (2011). AMP involves the use of rotational grazing patterns that are highly flexible in time and space to accommodate changing plant growth, foraging conditions, and animal needs. Operators place a relatively large number of animals at high stock density in a given pasture for short periods of time (Society for Range Management 1998) and usually at increased stocking rates (Teague et al. 2011). In theory, these systems balance the periodic removal of plant biomass with the need to facilitate prompt forage regrowth, thereby maintaining plant vigor and associated productivity. As a result, any assessment of these systems, including AMP grazing, is predicated on the notion that ranchers using AMP grazing can be differentiated from neighboring cattle ranches with respect to one or more of the aforementioned grazing management practices. For purposes of this study, AMP grazing is defined using the framework of Teague et al. (2011) to be grazing that “involved multiple paddocks per herd, high animal densities, very short periods of grazing, long recovery periods and higher stocking rates than were traditionally considered sustainable.”

Similar to other regions of the world, native temperate grasslands in western Canada have markedly declined to less than a third of their original area (Gauthier and Wiken 2003), though the extent of loss varies from 57% in the Mixedgrass Prairie of Alberta (Adams et al. 2013) to > 85% in the highly fragmented Parkland (Kupsch et al. 2013). In the Parkland subregion, croplands together with planted pastures containing introduced forages now represent most of the agricultural land base, which together provide much of the feed stock for the Canadian beef industry (McCartney 1993). Given the significant footprint of cattle production in western Canada, particularly grazing-based operations (Alemu et al. 2015), a high level of interest exists in understanding how variation in ongoing land-use activities such as grazing alters grassland sustainability, including on lands never cultivated and those once seeded but now managed as permanent grassland. This knowledge gap extends to understanding whether and how specialized rotational systems, including AMP grazing, can alter key grassland functions such as ecosystem carbon storage and greenhouse gas fluxes.

Rotational grazing has become more common in recent decades, and the majority of cattle producers (83%) in the prairie provinces of Canada now practice rotational rather than continuous grazing (Chorney and Josephson 2000; Pyle et al. 2018). What remains unclear is the extent to which variation in nuanced grazing practices among these cattle ranches regulates grassland responses, such as the length of grazing or subsequent rest periods (Heitschmidt and Taylor 1991). Advocates of AMP (and holistic) grazing highlight the need for high stock densities (i.e., animals per unit land area) for short periods at the optimal time during the growing season to maximize benefits (Savory and Butterfield 1999; Teague et al. 2011, 2013), a response that can vary with environmental conditions (Hawkins 2017).

In 2016 we initiated a comprehensive study to compare agronomic and environmental outcomes on a set of ranches situated across the prairie provinces of western Canada with the support of the Agricultural Greenhouse Gases Program of Agriculture and Agri-Food Canada. One aspect of this work compared metrics of grazing practices between beef cattle ranches employing AMP grazing with neighboring ranches, where the latter can be regarded as regionally representative management for the cattle industry. Here, we report on the specific differences in grazing practices and historical disturbance regimes taking place between and within these two groups of beef producers. Specific objectives were to 1) quantify differences in management practices between self-identified AMP ranchers and their neighboring (n-AMP) ranches and 2) identify management metrics that might show differences in agroecological attributes among these cattle ranches in western Canada.