Scott L. Kronberg

Diversification and ecosystem services for conservation agriculture: Outcomes from pastures and integrated crop-livestock systems

Conservation agriculturalsystems relyon threeprinciplesto enhance ecosystem services: (1) minimizing soil disturbance, (2) maximizing soil surface cover and (3) stimulating biological activity. In this paper, we explore the concept of diversity and its role in maximizing ecosystem services from managed grasslands and integrated agricultural systems (i.e., integrated crop–livestock–forage systems) at the field and farm level. We also examine trade-offs that may be involved in realizing greater ecosystem services. Previous research on livestock production systems, particularly in pastureland, has shown improvements in herbage productivity and reduced weed invasion with increased forage diversity but little response in terms of animal production. Managing forage diversity in pastureland requires new tools to guide the selection and placement of plant mixtures across a farm according to site suitability and the goals of the producer. Integrated agricultural systems embrace the concept of dynamic cropping systems, which incorporates a long-term strategy of annual crop sequencing that optimizes crop and soil use options to attain production, economic and resource conservation goals by using sound ecological management principles. Integrating dynamic cropping systems with livestock production increases the complexity of management, but also creates synergies among system components that may improve resilience and sustainability while fulfilling multiple ecosystem functions. Diversified conservation agricultural systems can sustain crop and livestock production and provide additional ecosystem services such as soil C storage, efficient nutrient cycling and conservation of biodiversity.

Bovine Muscle n-3 Fatty Acid Content Is Increased with Flaxseed Feeding

We examined the ability of n−3 FA in flaxseed-supplemented rations to increase the n−3 FA content of bovine muscle. Two groups of animals were used in each of two separate trials: (i) Hereford steers supplemented (or not) with ground flaxseed (907 g/d) for 71 d, and (ii) Angus steers supplemented (or not) with ground flaxseed (454 g/d for 3 d followed by 907 g/d for 110 d). For the Hereford group, flaxseed-supplemented rations increased 18∶3n−3 (4.0-fold), 20∶5n−3 (1.4-fold), and 22∶5n−3 (1.3-fold) mass as compared with the control, and increased total n−3 mass about 1.7-fold. When these data were expressed as mol%, the increase in 18∶3n−3 was 3.3-fold and in 20∶5n−3 was 1.3-fold in the phospholipid fraction, and 18∶3n−3 was increased 4-fold in the neutral lipid fraction. For the Angus group, flaxseed ingestion increased masses and composition of n−3 FA similarly to that for the Herefords and doubled the total n−3 FA mass. The effect of cooking to a common degree of doneness on FA composition was determined using steaks from a third group of cattle, which were Angus steers. We demonstrated no adverse effects on FA composition by grilling steaks to an internal temperature of 64°C. Because n−3 FA may affect gene expression, we used quantitative real-time reverse transcriptase-polymerase chain reaction to quantify the effect of feeding flaxseed on heart-FA binding protein, peroxisome proliferator activated receptor γ (PPARγ) and α (PPARα) gene expression in the muscle tissue. PPARγ mRNA level was increased 2.7-fold in the flaxseed-fed Angus steers compared with the control. Thus, we demonstrate a significant increase in n−3 FA levels in bovine muscle from cattle fed rations supplemented with flaxseed and increased expression of genes that regulate lipid metabolism.

Comparison of Sheep and Goat Preferences for Leafy Spurge

The objective of these studies was to compare preference for leafy spurge (Euphorbia esula L.) by sheep and goats. Study 1 was a choice test that paired leafy spurge with either arrowleaf balsamroot (Balsamorhiza sagittata (Pursh)Nutt.) or crested wheatgrass (Agropyron cristatum (L.)Gaertn.) for a 30 minute feeding period. Study 2 consisted of 3 grazing trials on spurge-infested pastures. Differences between sheep and goat grazing were measured using capacitance meter estimates of standing crop and ocular estimates of composition; counts of grazed and ungrazed leafy spurge stems; and bite counts to estimate botanical composition of diets. The paired choice study showed that selection for leafy spurge was affected by the interaction (P < 0.0001) of animal species and the choice alternative. Goats preferred leafy spurge (80% of consumption) compared to arrowleaf balsamroot, but demonstrated a relative avoidance (33% of consumption) of leafy spurge when paired with crested wheatgrass. Sheep always avoided leafy spurge compared to the alternative forage and consumed an average of only 28% of their intake from leafy spurge during the 30 minute test. In the grazing trials goats took 64% of their bites from leafy spurge compared to 20% for sheep. This represented a relative preference for spurge by goats compared to a strong relative avoidance by sheep. Sheep avoided areas in the pasture that had high densities of flowering spurge stems while goats were relatively unresponsive to stem densities. Goat grazing reduced the number of flowering stems. Stem numbers were 90 vs. 23 flowering stems m2 (P = .04) in sheep- and goat-grazed pastures, respectively. Goats appear to have a greater potential for biological control of leafy spurge than sheep. This advantage may be particularly important in areas where leafy spurge is relatively unpalatable, which the present study site represented.

Ruminal metabolism of leafy spurge in sheep and goats: A potential explanation for differential foraging on spurge by sheep, goats, and cattle.

Leafy spurge (Euphorbia esula) is an introduced forb that is invading western rangelands. Goats (Capra hircus) readily graze the plant, but cattle (Bos tarus) generally and sheep (Ovis aries) locally appear to develop conditioned flavor aversions to leafy spurge. They either avoid the plant entirely or graze it reluctantly. We hypothesized that: (1) a diterpene diester that can occur in leafy spurge was an aversive agent, and (2) diet selection differences among ruminant species may be partly a function of differential ruminai metabolism of aversive phytochemicals, and further that cattle and sheep may be reluctant to graze leafy spurge because their ruminai microbes do not metabolize certain leafy spurge chemicals as do ruminai microbes in goats. Sheep did not develop an aversion to a novel food when its consumption was followed by an intravenous injection of ingenol 3,20-dibenzoate (P=0.34). Sheep did develop an aversion to a novel food when its intake was followed by a dose of leafy spurge fermented with sheep ruminai digesta, but not when followed by a dose of leafy spurge fermented with goat ruminai digesta (P= 0.03). This suggests that goat ruminai microbes may modify leafy spurge such that it does not elicit an aversion in sheep.

Toxic and aversive diterpenes of Euphorbia esula.

Leafy spurge (Euphorbia esula L.), a plant introduced into the Great Plains of North America from Europe, has become a serious economic and ecological threat to the productivity of agricultural and natural areas. Cattle, the predominant livestock species on the Great Plains, as well as common wild ruminant species in this region appear to consume little if any leafy spurge. This is likely because they experience a toxic response after consuming small amounts of this plant, and they consequently learn to avoid it. Domestic sheep and goats can consume considerable amounts of leafy spurge and are used to help control it, but even these species may suffer a toxic response at high levels of intake. Toxic diterpene ingenols have been isolated from leafy spurge tissues, but compounds in this plant have not been evaluated with respect to their capacity to induce food aversion learning in ruminants. We conducted bioassay-guided fractionations of leafy spurge in an attempt to isolate toxic and aversive compounds. These bioassay-guided fractionations led to identification of ingenol and one of its diesters as two toxic compounds in leafy spurge that are potentially aversive to cattle.

Rodent and Ruminant Ingestive Response to Flavonoids in Euphorbia esula

Euphorbia esula, common name leafy spurge, was chemically evaluated for aversive phytochemicals that appear to minimize herbivory by rodents and cattle. A middle-layer extract elicited food aversions in rats as did the petroleum ether extract of the initial methanol extract. Kaempferol-3-0-β- glucuronic acid and quercetin-3-0-β-glucuronic acid were separated and identified from the middle-layer residue. This study is the first report of quercetin-3-0-β-glucuronic acid in leafy spurge. Together these flavonoidal glucosides were mildly aversive to rats but showed less aversive activity when tested separately. The middle-layer extract produced no aversive response from cattle, while the petroleum ether extract elicited strong aversions in cattle. Flavonoidal compounds from leafy spurge that were aversive to rats, a monogastric mammal, were not aversive to cattle, a ruminant. Microbial degradation of the compounds before they reach the intestines and are absorbed into the bloodstream is likely a key advantage for cattle compared to rats.

Integrated crops and livestock in central North Dakota, USA: Agroecosystem management to buffer soil change

Integrated crop–livestock systems have been purported to have numerous agronomic and environmental benefits, yet information documenting their long-term impact on the soil resource is lacking. This study sought to quantify the effects of an integrated crop–livestock system on near-surface soil properties in central North Dakota, USA. Soil bulk density, electrical conductivity, soil pH, extractable N and P, potentially mineralizable N, soil organic carbon (SOC) and total nitrogen (TN) were measured 3, 6 and 9 years after treatment establishment to evaluate the effects of residue management (Grazed, Hayed and Control), the frequency of hoof traffic (High traffic, Low traffic and No traffic), season (Fall and Spring) and production system (integrated annual cropping versus perennial grass) on near-surface soil quality. Values for soil properties were incorporated into a soil quality index (SQI) using the Soil Management Assessment Framework to assess overall treatment effects on soil condition. Residue management and frequency of hoof traffic did not affect near-surface soil properties throughout the evaluation period. Aggregated SQI values did not differ between production systems 9 years after treatment establishment (integrated annual cropping=0.91, perennial grass=0.93; P =0.57), implying a near-identical capacity of each system to perform critical soil functions. Results from the study suggest that with careful management, agricultural producers can convert perennial grass pastures to winter-grazed annual cropping systems without adversely affecting near-surface soil quality. However, caution should be exercised in applying results to other regions or management systems. The consistent freeze/thaw and wet/dry cycles typical of the northern Great Plains, coupled with the use of no-till management, modest fertilizer application rates and winter grazing likely played an important role in the outcome of the results.

The effect of flaxseed supplementation on growth, carcass characteristics, fatty acid profile, retail shelf life, and sensory characteristics of beef from steers finished on grasslands of the northern Great Plains

The objective of this trial was to determine if daily supplementation of flaxseed for 85 d to steers finished on grasslands of the northern Great Plains would influence growth and carcass characteristics or the fatty acid profile, tenderness, and sensory characteristics of beef steaks. Eighteen Angus yearling steers (initial BW 399 ± 21 kg) were randomly divided into 3 groups. Steers in treatment 1 (FLX; n = 6) received a daily supplement of ground flaxseed (0.20% of BW), whereas steers in treatment 2 (CSBM; n = 6) received a daily supplement of ground corn and soybean meal (0.28% of BW), with contents of CP and TDN being similar to the supplement for FLX. Control steers (CONT; n = 6) were not supplemented. Treatments were given to each individual steer in side-by-side stalls and were fed from mid-August to November 7, 2007, the day before slaughter. All steers grazed growing forage from early May through the first week of November. Growth rate of steers fed FLX was 25% greater (P < 0.01) than that of steers fed CONT, but was similar (P = 0.45) to that of steers fed CSBM. No differences were observed for carcass characteristics (P ≥ 0.14), tenderness (Warner-Bratzler shear force; P ≥ 0.24), or sensory attributes (P ≥ 0.40) except for a slight off-flavor detected in steaks from steers fed FLX compared with CONT (7.4 vs. 7.8, respectively, with 8 indicating no off-flavor and 1 indicating extreme off-flavor; P = 0.07) and CSBM (7.9; P = 0.01). The n-3 fatty acids α-linolenic acid and eicosapentaenoic acid were 62 and 22% greater, respectively, in beef from steers fed FLX compared with those fed CONT (P < 0.001). The ratio of n-6 to n-3 fatty acids was smaller (P < 0.001) in beef from steers fed FLX compared with the ratios in beef from steers fed CONT and CSBM. Daily supplementation of flaxseed to steers grazing growing vegetation on the northern Great Plains may improve growth rate and enhance the n-3 fatty acid profile of the steaks.

Temperature and Precipitation Affect Steer Weight Gains Differentially by Stocking Rate in Northern Mixed-Grass Prairie

Abstract Cattle weight gain responses to seasonal weather variability are difficult to predict for rangelands because few long-term (>20 yr) studies have been conducted. However, an increased understanding of temperature and precipitation influences on cattle weight gains is needed to optimize stocking rates and reduce enterprise risk associated with climatic variability. Yearling steer weight gain data collected at the USDA-ARS High Plains Grasslands Research Station at light, moderate, and heavy stocking rates for 30 years (1982–2011) were used to examine the effects of spring (April–June) and summer (July–September) temperature and precipitation, as well as prior-growing-season (prior April–September) and fall/winter (October–March) precipitation, on beef production (kg · ha−1). At heavier stocking rates, steer production was more sensitive to seasonal weather variations. A novel finding was that temperature (relatively cool springs and warm summers) played a large predictive role on beef production. At heavier stocking rates, beef production was highest during years with cool, wet springs and warm, wet summers, corresponding to optimum growth conditions for this mixed C3–C4 plant community. The novelty and utility of these findings may increase the efficacy of stocking rate decision support tools. The parsimonious model structure presented here includes three-month seasonal clusters that are forecasted and freely available from the US National Oceanic and Atmospheric Administration up to a year in advance. These seasonal weather forecasts can provide ranchers with an increased predictive capacity to adjust stocking rates (in advance of the grazing season) according to predicted seasonal weather conditions, thereby reducing enterprise risk.

Sheep preference for leafy spurge from Idaho and North Dakota.

Three trials were conducted to determine if low ingestion of some leafy spurge (Euphorbia esula L.) by sheep is primarily due to differences in sheep or in leafy spurge. In the first trial, pastures in Idaho and North Dakota were grazed by sheep originating from both states. Generally, sheep from both states grazed the leafy spurge growing in the Idaho pastures reluctantly but grazed the leafy spurge growing in the North Dakota pastures in proportion to its availability (P = 0.003). In the second trial, ingestion of air-dried leafy spurge by penned sheep was compared by offering samples from the 2 locations simultaneously. Sheep consumed more (P = 0.0001) leafy spurge from North Dakota than from Idaho. In the third trial, penned sheep were simultaneously offered Idaho leafy spurge harvested from fertilized and non-fertilized sites. Initially, equal amounts of fertilized and unfertilized leafy spurge were consumed (P greater than or equal to .68), but by the fourth day sheep had an obvious preference for leafy spurge from the fertilized site (P = 0.01). These trials indicate that preference for leafy spurge by sheep differs depending on site, and that using sheep to manage leafy spurge may be more successful on soils with relatively high fertility.