Beef cattle production on Montana farms accounted for $1.78 billion of gross income and 42% of Montana’s total agricultural sales in 2012 (USDA-NASS, 2016). Montana cattle operations are primarily cow-calf production systems that rely heavily on forages to supply nutrients for both cows and calves (Galyean and Goetsch 1993). 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). Dormant range forage is deficient in nutrients and may result in decreased animal performance (Krysl and Hess 1993, Bowman et al. 1995, Mulliniks et al. 2013). Providing supplements to grazing beef cattle during times of low forage quality may improve animal performance and provide increased economic returns (DelCurto et al. 2000). In addition, supplementation could alter livestock grazing distribution and vegetation utilization across the landscape (Fuhlendorf and Engle 2001). 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 reduces soil organic matter and exposes soil to direct raindrop impact, allowing for potential increases in erosion and runoff (Greene et al. 1994). Additionally, homogeneity of vegetation structure across the landscape has been implicated in habitat degradation for many avian species (Fuhlendorf and Engle 2001). Thus, maintaining heterogeneity of vegetation structure in rangelands is beneficial to wildlife habitat and ecological biodiversity (Fuhlendorf et al. 2006). However, little is known about the effects of supplementation on winter grazing behavior and its potential impact on vegetation, soil, and rangeland sustainability (Judkins et al. 1985, Krysl and Hess 1993, Schauer et al. 2005). Information relating supplementation strategies to individual grazing behavior and vegetation use on dormant forage is lacking. Thus, the intent of the proposed research is to examine the comprehensive agroecosystem responses of dormant season grazing, with and without supplementation, on cattle performance, soil organic matter, vegetation use, and residual cover of rangelands. Our goal is to provide insight to stakeholders concerning the ecological impacts of dormant season grazing on mixed grass rangelands, and ultimately facilitate the adoption of management strategies developed for long-term sustainability of agroecosystems in Montana.
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:
- 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.
- 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.
- 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.
The use of animals in this study was approved by the Institutional Animal Care and Use Committee of Montana State University.
This study was conducted at the Thackeray Ranch (48° 21′ N 109° 30′ W), part of the Montana Agricultural Experiment Station located 21 km south of Havre, MT. Climate is characterized as semi-arid steppe with an average annual precipitation of 410 mm. Vegetation is dominated by Kentucky bluegrass (Poa pratensis L.), bluebunch wheatgrass (Pseudoregnaria spicata [Pursh] A. Love), and rough fescue (Festuca scabrella Torr.).
A commercial herd of bred cows (Angus, Angus x Simmental) ranging in age from 1- to 12-yr-old, were classified into one of six age groups (1 year old, 2 &3 year-olds, 4&5 year-olds, 6&7 year-olds, and 8&9 year-olds, 10 and older) and grazed on a 329 ha rangeland pasture (~1.2 ha AUM-1) during 2 years (272 cows in the 1st year, and 302 cows in the 2nd year). The winter grazing season occurred from December 1, 2016 to January 12, 2017, and November 1, 2017 to December 31, 2017. All cattle had free-choice access to a 30% CP self-fed canola meal-based (35% as-fed basis) pelleted supplement with 25% salt to limit intake (Table 1). The target daily intake was 0.91 kg/cow. All cows in the research trial were weighed and body condition scored pre- and post-grazing to track individual animal performance.
We expect 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. Wide-spread adoption of dormant season grazing will depend upon long-term economic benefits which should consider not only annual differences in average inputs and returns but also individual-level heterogeneity in grazing behavior and long term effects on range condition. Our specific objectives are to evaluate how protein supplementation during the dormant grazing season influence:
- Supplement intake and behavior
- Cattle grazing activity and resource utilization.
- Forage use, range condition and floristic quality.
Objective 1 evaluates the effects of age on average daily individual supplement intake, number of visits, visit length, intake rate, and CV of supplement intake. Each individual animal was equipped with an electronic ID tag (Allflex USA, Inc., Dallas-Ft. Worth, TX) attached to the exterior of the left ear for the measurement of individual supplement intake, number of visits, visit length, and intake rate using a SmartFeed Pro self-feeder system (C-Lock Inc., Rapid City, SD) which provided a total of 8 feeding stations. Each cow was considered an experimental unit. Supplement intake variables were analyzed using ANOVA with a mixed model including age class, year, and the interaction of age class and year as fixed effects, and individual cow x age class as the random effect (R Core Team, 2017). Least square means were separated using the LSD method when P < 0.05.
An Onset (Bourne, MA, USA) HOBO U30-NRC Weather Station was placed near the supplement feeders and programmed to collect air temperature, relative humidity, and wind speed and direction data every 15 min for the entirety of the grazing period. Models were developed representing hypotheses examining the influence of environmental conditions and age on daily supplement intake. The variables considered as candidates for modeling included average daily temperature, average daily wind speed, age class, and year. Cow was used as a random effect. Akaike’s Information Criterion adjusted for small sample sizes (AICc) was then used to evaluate support for competing models (Burnham and Anderson, 2002). All data was analyzed using generalized linear mixed models in R (R Core Team, 2017).
Objective 2 is focused on evaluating cow age and protein supplementation on winter cattle grazing activity and resource utilization. Grazing activity was monitored with Lotek GPS collars (3300LR; Lotek Engineering, Newmarket, Ontario, Canada) containing head position sensors that record daily space use as well as timing and location of grazing activities (Turner et al. 2000, Ungar et al. 2005, Brosh et al. 2010). Cattle were classified into one of six age groups (1-year-old, 2 & 3-year-olds, 4 & 5-year-olds, 6 & 7-year-olds, and 8 & 9-year-olds, and ≥ 10-year-old) and randomly selected for GPS collars (5 collars/age class, 30 collars total). GPS data are used to evaluate the effects of age and supplementation strategy on animal activity and locomotion (Ungar et al. 2005, Brosh et al. 2010, Valente et al. 2013). Each collar was configured to record GPS positions 15-minute intervals and head position and vertical/horizontal movements at 5-minute intervals. Each collar stores the percentage of time the head position sensor registers in the down position (grazing activity) for each sampling period. Horizontal and vertical locomotion distances during each 15-minute interval will be computed using ArcMap software from layers containing the GPS and topographic data (Brosh et al. 2010, Valente et al. 2013).
Objective 3 is focused on evaluating cow age and protein supplementation on winter grazing forage utilization, visual obstruction (VOR; an index of biomass), residual vegetation composition and species, ground cover and soil organic matter. We randomly established 75 30-m transects within a 329-ha pasture. We measured vegetation composition, production, canopy cover, VOR and soil organic matter at six 0.1 m2 plots located every five meters along each transect. In total, we sampled 450 plots along 75 transects. Canopy cover at each plot was estimated using the Daubenmire method (Daubenmire 1959) and VOR was measured in four cardinal directions using a 1-meter Robel pole (Robel et al. 1970) at a distance of 4 meters and an observation height of 1 m. Vegetation composition and production are estimated using the dry weight rank method and clipping each plot (Mannetje 1963, Dowhower et al. 2001). Clipped samples were placed in a forced air oven at 60°C for 48 hours and then weighed. Soil organic matter is measured by taking soil core samples at a depth of 10 cm at each plot, drying and using the loss by ignition procedure (Ball 1964). All measurements were taken pre- and post-grazing prior to spring green up to model how supplementation affects the distribution of vegetation use, plant community structure residual cover and soil organic matter across the pastures. Pre-grazing vegetation samples from each transect were composited by transect and ground to pass a 1-mm screen in a Wiley mill. Samples were then analyzed in duplicate for nitrogen (Leco CN-2000; Leco Corporation, St. Joseph, MI), and fiber (NDF and ADF; Ankom 200 Fiber Analyzer, Ankom Co., Fairport, NY) as indicators of vegetation quality.
Objective 1.- All the data from the 2 SmartFeed Pro self-feeder (C-Lock Inc., Rapid City, SD) trailers and the HOBO weather station have been downloaded and converted into a usable format. The effects of age class on intake related variables displayed an age class x year interaction (P < 0.05), therefore, data is displayed for each year independently (Table 2). Daily supplement intake, feeding time, and intake rate decreased linearly (P < 0.05) as age class increased in the 1st yr, while daily intake CV, and feeder visits per day had a quadratic (P < 0.01) response to age class. In yr 2, there was no effect (P > 0.09) of age class on daily intake or daily intake CV. Visits per day, and intake rate decreased (P < 0.01) linearly as age class increased, while feeding time increased (P < 0.01) linearly with increasing age class.
When evaluating the effects of environmental conditions and age class on supplement intake, we found a single top model containing year, temperature, and temperature x age class interaction received 100% of the AICc total weight (Table 3). Our top model reveals that temperature interacts with age class, where young animals increase supplement intake as temperature decreases, while older animals decrease supplement intake as temperature decreases (Figure 1). Year represented an additive effect where cows had higher average daily supplement intakes in yr 2 than in yr 1.
The few studies that have quantified supplement intake in mixed age herds have shown older cows spend more time at the feeder and consume more supplement than younger cows (Earley et al., 1999; Sowell et al., 2003). However, our results contradict this conventional idea with higher daily supplement intake by younger cows in yr 1, and increased visits per day, and intake rate (P < 0.05) by younger cows in both yr. Our research suggests that temperature alone can interact with cow age in altering supplement intake behavior. Our top model supports this idea, as mean temperatures in yr 1 were substantially lower than yr 2 (-9.6 vs -2.0 °C; Table 4), potentially resulting in greater energetic needs for young cows to maintain homeothermy.
Specific factors such as cow age, environmental conditions, and supplement form need to be evaluated to determine the influence they play on supplement intake behavior. By providing a supplement delivery system that optimizes uniformity of consumption and minimizes economic inputs, we can effectively improve the efficiency of beef cattle production systems.
Objective 2.- All GPS fix and sensor data for all 30 individuals have been downloaded and converted to a usable format for both years. HOBO temperature sensors were located at each transect location with a HOBO weather station located in the pasture that records temperature, precipitation, wind speed and direction. All temperature and weather data has been downloaded and converted into a usable format. Data will be analyzed and formatted into a journal manuscript in May 2018.
Objective 3.- Collection of pre-grazing vegetation data was completed 11/4/16 for year 1. Post-grazing data collection during year 1 was completed 4/8/17. Collection of pre-grazing vegetation data was completed 10/1/17 for year 2. Post-grazing data collection during year 2 was completed 4/23/18. In total, 450 plots along 75 transects were sampled pre- and post- grazing for both years of the research trial. All data collected in the field (total production, production by species, cover by species and VOR) pre- and post- grazing for year 1 and pre- grazing in year 2 have been recorded in a relational data base. All pre-grazing vegetation samples for both years have been ground and analyzed for fiber and crude protein. Data will be analyzed and formatted into a journal manuscript in May 2018.
Table 1. Supplement composition for cattle winter grazing rangeland in 2016 & 2017 at the Thackeray ranch, Havre MT (as-fed basis)
Table 2. Average daily supplement intake and behavior by age class for cattle winter grazing rangeland in 2016 & 2017 at the Thackeray ranch, Havre MT
Table 3. Model selection for models evaluating the effects of environmental conditions and age class on supplement intake for cattle winter grazing rangeland in 2016 & 2017 at the Thackeray ranch, Havre MT
Table 4. Mean, minimum and maximum temperature (°C) during winter grazing period for 2016 & 2017 at the Thackeray ranch, Havre MT
Figure 1. Model output and confidence intervals (85%) evaluating the interaction of temperature x age class on supplement intake of cattle during the winter grazing period for 2016 & 2017 at the Thackeray ranch, Havre MT
Educational & Outreach Activities
The objectives of our research proposal and preliminary results from the supplement and intake control system, SmartFeed Pro self-feeder (C-Lock Inc., Rapid City, SD), have been featured in several presentations and meetings across Montana: The Northern Ag Research Center (NARC) Advisory Committee meeting, NARC Field Day, Montana Nutrition Conference, the Stillwater Range Association, Montana Stock Growers mid-year meetings, Montana State University Extension Agent Training, and the Crazy Mountains Livestock Association Meetings. There have been 2 accepted Western Section of American Society of Animal Science proceeding papers from this project that will be presented at the annual meetings in Bend, OR June of 2018. Additionally, photographs of our research cattle using the equipment specifically designed for our research project are featured on the C-Lock inc. website, advertised as the world’s most portable feed intake and supplement control system.