Grazing Beef Cattle Research Articles

The Effects of Harvest Maturity of Eragrostis tef 'Moxie' Hay and Supplemental Energy Source on Forage Utilization in Beef Heifers.

The phenological stage of maturity of grasses and supplementation program can impact forage utilization in grazing beef cattle. However, the potential interaction between harvest maturity of Eragrostis tef (teff) hay and energy supplement source was yet to be fully evaluated. Therefore, our objective was to determine the effects of harvest maturity of teff hay and supplemental energy sources on nutrient intake, apparent total-tract nutrient digestion, nitrogen (N) utilization, and ruminal fermentation characteristics in beef heifers. A split-plot design with teff hay harvest maturity as the whole plot and supplemental energy source as the subplot was administered in a three-period (21 d), three × three Latin square design. Six crossbred beef heifers (804 ± 53.6 kg of body weight; BW) were allocated to two harvest maturities (early- (EH]) or late-heading (LH)) and to two supplemental energy sources (no supplement (CON), or rolled corn grain or beet pulp pellet fed at 0.5% of BW). Data were analyzed using SAS. There was no harvest maturity × energy supplement interaction. Although harvest maturity had no impact on total dry matter intake (DMI), crude protein (CP) intake was greater (p < 0.01) for EH than LH heifers. Total intakes of dry (DM) and organic matter (OM) were also greater (p < 0.01) for supplemented than CON heifers, whereas acid detergent fiber (ADF) intake was greater for beet pulp heifers compared to heifers fed the CON diet and supplemental corn grain. Harvest maturity had no impact on ruminal pH. However, mean ruminal pH was lower (p = 0.04), duration pH < 6.2, and molar proportions of butyrate and branched-chain fatty acids were greater (p ≤ 0.049) for heifers fed corn grain compared to CON and beet pulp diets. Heifers fed EH hay had greater (p ≤ 0.02) apparent total-tract DM, OM, CP, NDF, and ADF digestibility than heifers fed LH hay. Although there was no supplemental energy effect on microbial nitrogen (N) flow, it was greater (p < 0.01) for EH than LH heifers. Apparent N retention, which did not differ, was negative across all diets. In summary, delaying the harvest of teff hay from the EH to LH stage of maturity compromised nutrient supply, which was not attenuated by feeding supplemental corn grain and beet pulp at 0.5% of diet DM. Because N retention was negative across harvest maturity, there might be a need to provide both energy and protein supplements to improve growth performance when feeding teff hay to beef cattle.

Recommendations on visit duration and sample number requirements for an automated head chamber system.

Automated head chamber systems (AHCS; GreenFeed, C-Lock Inc., Rapid City, SD) increasingly are being used for measuring the gas flux of unrestrained cattle. There are a wide range of recommendations for what constitutes a "good" visit (i.e., duration) to an AHCS and how many visits are required for the AHCS to quantify gas fluxes accurately and precisely. Accordingly, the purpose of this experiment was to investigate the effects of visit duration thresholds and the subsequent effects of these thresholds on the number of visits needed to provide adequate estimates of carbon dioxide (CO2) and methane (CH4) emissions, and oxygen (O2) consumption by beef cattle. This analysis utilized data from three previously published experiments with grazing beef steers and one experiment with finishing beef steers, with 103 steers total. When comparing all available visits, there was excellent agreement [Lin's concordance correlation coefficient (CCC) ≥ 0.96] between visits ≥ 3min in duration and those ≥ 2min for the three gases in all four experiments. When data from all four experiments were pooled, there was excellent agreement between visits ≥ 3min and those ≥ 2min and ≥ 1min for all gases (CCC ≥ 0.96). These results suggest that estimates from visits ≥ 2min are like those from visits ≥ 3min. Next, we investigated if including visits ≥ 2min or ≥ 1min would increase the minimal number of visits required to provide excellent agreement with the "gold-standard" (mean of all visits ≥ 3min). For this, we used only one of the experiments and randomly selected visits per animal ranging from n = 5 to 60, in increments of 5. The sole experiment was used because all animals had more than 60 visits. We then assessed the agreement between the "gold-standard" (mean of all visits ≥ 3min [144 ± 55.01 visits per steer]) estimates of CO2, O2, and CH4. The minimum number of visits required to achieve excellent agreement (CCC ≥ 0.90) to the "gold-standard" estimate for all gases was 30 visits ≥ 3min in duration, or 40 visits ≥ 2min in duration. Visits ≥ 1min in duration did not achieve excellent agreement, even when 60 were used. Based on these results, we recommend excluding visits < 3min in duration with 30 minimum visit records per animal. However, if researchers choose to implement a 2-min visit duration threshold then 40 visit records are needed per animal.

Farm-Scale Effectiveness of Feed Additives Supplied through a Mineral Mix for Beef Cattle Grazing Tropical Pastures

The effectiveness of feed additives delivered through free-choice mineral mixtures (MMs) to grazing cattle remains unclear. Two farm-scale and one in vitro experiment (Exp.) were conducted to investigate the effects of salinomycin and virginiamycin, delivered through an MM, on growing bulls grazing tropical pastures. In Exp. 1, 316 zebu (Bos indicus) Nellore bulls (225 ± 26.7 kg liveweight (LW)) were randomly allocated to four treatments: (1) MM no additives (CON), (2) MM with salinomycin at 1950 mg/kg (SLI), (3) MM with salinomycin at 780 mg/kg (SHI), and (4) MM with virginiamycin at 1950 mg/kg (VGN). Over 123 days, these bulls grazed tropical grasses on pastures of guinea grass, palisade grass, or Bermuda grass. No significant treatment effects were observed for oocyst eggs or ruminal parameters. Bulls fed VGN had higher average daily gain (ADG) compared to CON (p = 0.02) and SLI (p = 0.03) but similar compared to SHI (p = 0.07). In Exp. 2, 308 zebu cross bulls (237 ± 23.0 kg LW) grazed Bermuda grass paddocks and were allocated into two treatments: (1) MM with no additives (CON) and (2) MM containing virginiamycin at 2522 mg/kg (VGN). Cattle fed VGN had a significantly higher ADG (p = 0.007). Exp. 3 tested salinomycin’s effectiveness in vitro at different exposure times to MM, revealing no impact of exposure time on short-chain fatty acid production. In conclusion, virginiamycin delivered through free-choice MM can increase grazing beef bulls’ ADG by 12% compared with CON, with no clear link to rumen fermentation or coccidiostat effects.

Transcriptomic Changes in Response to Form of Selenium on the Interferon-Tau Signaling Mechanism in the Caruncular Tissue of Beef Heifers at Maternal Recognition of Pregnancy.

We have reported that selenium (Se) provided to grazing beef cattle in an inorganic (ISe) form versus a 1:1 mixture (MIX) of inorganic and organic (OSe) forms affects cholesterol biosynthesis in the corpus luteum (CL), the abundance of interferon tau (IFNτ) and progesterone (P4)-induced mRNAs in the caruncular (CAR) tissue of the endometrium, and conceptus length at maternal recognition of pregnancy (MRP). In this study, beef heifers were supplemented with a vitamin-mineral mix containing 35 ppm Se as ISe or MIX to achieve a Se-adequate status. Inseminated heifers were killed at MRP (d 17, n = 6 per treatment) for tissue collection. In CAR samples from MIX versus ISe heifers, qPCR revealed that mRNA encoding the thyroid regulating DIO2 and DIO3 was decreased (p < 0.05) and a complete transcriptomic analysis revealed effects on the interferon JAK-STAT1/2 pathway, including decreased expression of mRNAs encoding the classical interferon stimulated genes IFIT1, IFIT2, IFIT3, IRF1, IRF9, ISG15, OAS2, and RSAD2 (p < 0.05). Treatment also affected the abundance of mRNAs contributing to the immunotolerant environment (p < 0.05). In combination, these findings suggest more advanced preparation of the CAR and developing conceptus for implantation and to evade immune rejection by the maternal system in MIX- vs. ISe-treated heifers.

315 Implementation of Large-Scale Climate-Smart Agriculture Practices and Research on Beef and Bison Grazing Lands

Abstract Today’s livestock producers face increasing public scrutiny because animal agriculture is often cited as a major contributor to greenhouse gas (GHG) emissions. However, this negative perception does not take into account the carbon (C) sequestration benefits of grazing livestock nor that grazing lands account for 25% of the global soil sequestration potential of soil C storage. Grazing beef cattle and bison are key to healthy grassland ecosystems and provide the most nutrient dense source of protein available for human consumption. Beef and bison producers who graze their livestock are widely recognized as environmental stewards because they use sustainable grazing practices that maintain grassland health. These practices are considered climate-smart agriculture (CSA) because they promote soil C sequestration and resilience to increased climate variability. Yet, these same producers are generally overlooked in GHG reduction and C sequestration incentives because of a relative lack of cost-effective methods to measure C and GHG sinks and sources. Emerging technologies are beginning to bridge that gap by paving the way to develop, implement, and monitor CSA practices. Furthermore, rangelands in the U.S. dedicated to supporting forage-based livestock production amount to nearly 940 million acres. This is more than double the acres dedicated to row crops and represents enormous potential to contribute to U.S. climate change commitments. Successful implementation and monitoring of CSA land management practices creates potential to develop climate-smart livestock commodities that sustainably provide economic incentives to producers operating resilient livestock grazing systems. Recently, South Dakota State University, along with ten external partners, was awarded a CSA commodity development grant by the USDA and NRCS focused on CSA-raised grazing beef cattle and bison in the Northern Great Plains. Specific objectives include: 1) developing and implementing existing and novel CSA practices alongside custom grazing plans; 2) measuring, monitoring, reporting, and verifying CSA practice impacts on GHG emissions, C sequestration, and ecosystem biodiversity of plants, arthropods, and wildlife; and 3) creating sustainable, value-added market opportunities for producers using CSA practices. To achieve these objectives, the project team is partnering with producers throughout the Northern Great Plains and beyond and will provide incentives for CSA practice implementation. Additionally, emerging and novel technologies will be used to collect large-scale data across producer operations and test sites to determine and refine GHG and C sequestration estimates associated with range beef cattle and bison systems. The long-term goal of this project is to provide CSA beef and bison producers with sustainable, value-added market opportunities that align with consumer preferences and demand.

173 Awardee Talk: Spot Sample Protocol for Gas Quantification of Grazing Beef Cattle Using a Greenfeed

Abstract Through a natural digestive process called enteric fermentation, cattle produce greenhouse gases that are an environmental concern and an energetic loss. Gas fluxes can be quantified with several techniques; however, an open circuit gas quantification system (OCGQS) allows for unencumbered quantification of methane (CH4), carbon dioxide (CO2), and oxygen (O2) from grazing cattle. In the literature, there is wide variation in the minimum number of spot samples recommended to evaluate gas fluxes of an individual animal, while no recommendations have been made to evaluate metabolic heat production. The objective of this study was to characterize the minimum number of spot samples needed to accurately quantify metabolic heat production and CH4, CO2, and O2 gas fluxes in grazing beef cattle. A minimum of 100 spot samples each were collected from seventeen grazing animals using a OCGQS (GreenFeed, C-Lock, Inc). The mean gas fluxes were computed starting from the first 10 visits (forward) and increasing by increments of 10 until 100 visits was reached. Mean gas fluxes were also computed starting from visit 100 moving back in time in increments of 10 (reverse) using the same approach. Mean gas fluxes were used to calculate individual animal metabolic heat production for each interval with both the forward and reverse approaches. Pearson and Spearman correlations were computed between the full 100 visits and each shortened visit interval. The minimum number of spot samples was determined when correlations with the full 100 visits were greater than 0.95. The 0.95 correlation threshold was met between 30 and 40 visits for all gas fluxes and metabolic heat production. Therefore, mean forward and reverse gas fluxes and metabolic heat production were also computed starting at 30 visits and increasing by 2 until 40 visits and vice versa. The results indicated that the minimum number of spot samples needed for accurate quantification of CH4, CO2, and O2 gas fluxes are 38, 40, and 40, respectively. Using gas fluxes collected by the OCGQS, metabolic heat production can be calculated after 36 spot samples. The practical calculation of metabolic heat production will require 40 spot samples given the necessary number of spot samples for component gases in the calculation. Animals met the required number of spot samples for quantification of metabolic heat production, CH4, CO2, and O2 in 29.5 ± 8.7, 30.5 ± 9.1, 31.8 ± 9.2, and 31.8 ± 9.2 days, respectively. Large variation existed around the number of days needed to achieve the recommended number of spot samples. For this reason, protocols for the OCGQS should be based on the total number of spot samples, rather than a test duration.

426 Forages Containing Plant Secondary Compounds Can Improve Digestibility, Rumen Ammonia and Rumen Metabolites of Pasture: an in Vitro Continuous Culture Case Study

Abstract Forages containing plant secondary metabolites (PSM) have been investigated for use in reducing nitrogen waste in feedlot and dairy cattle diets but use as supplements to grazing beef cattle to capture the positive effects of PSM is unclear. Here we investigate potential improvement in rumen digestibility and metabolome, rumen ammonia production and flow from feed protein due to PSM bioactivity in forages used to supplement pasture grass using in vitro methods. Can PSM-containing forages offer a practical way to improve range nutrition and provide delivery of phytochemical benefits? Phytochemical- containing forages birdsfoot trefoil (BFT), sainfoin (SAN), small burnet (SMB) and cicer milkvetch (CMV) supplemented grass pasture diets (200 g/kg of DM). In vitro true dry matter digestibility was determined using 2-stage in vitro methods. Randomly assigned diets of PAS supplemented with one of the PSM-containing forage diets (PAS+X) or not supplemented (PAS) were randomly applied to in vitro dual flow continuous culture (CC) vessels inoculated with grazing beef cow rumen fluid as a metabolic host. For 2-stage digestibility, SMB digestibility exceeded that of CMV, followed by BFT and SAN. The grass diet (PAS) was the least digestible (Table 1). Saponin was detected in CMV samples, which is a new finding. For CC, compared with PAS, minimum culture pH for PAS+CMV was highest (P &amp;lt; 0.02) but no differences were observed in pH between PAS, and PAS+BFT and PAS+SAN. Compared with PAS, the molar proportion of the fatty acid propionate increased with PAS+CMV(P = 0.03) in contrast to the acetate- to- propionate ratio found highest for PAS and decreased for all diets with supplementation of PSM forages. Concentration of rumen NH3–N flow to rumen fluid per gram of protein intake was lower (P &amp;lt; 0.01) with PAS+CMV and PAS+SMB, compared with grass only. Feeding CMV and SMB to grazing cattle may improve nutrient utilization, metabolome, and environmental sustainability of beef cattle production by improving diet digestibility and reducing ammonia waste.

357 The Influence of Supplemental Protein Levels on Beef Cattle Grazing Winter Foothill Rangelands: Cow and Subsequent Calf Performance

Abstract Angus based bred cows [n = 150; initial shrunk body weight (BW) = 615 ± 6.61 kg; initial body condition score (BCS) = 5.2] were used in an 84-d winter grazing experiment that took place over two consecutive years. Cattle were stratified by age and body condition and, within stratum, randomly assigned to one of three protein supplementation treatments: 1) no supplement, 2) cows fed 0.20% BW· d-1 of a 30% protein supplement, and 3) cows fed 0.40% BW · d-1 of a 30% protein supplement. Protein supplement was a 30% CP canola-based pelleted supplement with 9 units protein from urea. Cows were gathered three-times weekly and provided supplement on a replicated pen basis. Performance data were analyzed as a completely randomized design with linear and quadratic contrasts used for mean separation (reps = 5; n = 7). Body weights and BCS were recorded every 28-d period throughout the study and calf BW were obtained at birth and weaning. A treatment × period interaction was detected for body weight change (P &amp;lt; 0.01) where a linear response (P &amp;lt; 0.01) where increasing protein status resulted in modest weight gains relative to the control treatment. BCS also exhibited a linear response for two of the three weight periods (P &amp;lt; 0.01) where level of BCS lost was least in cows with the higher supplemental protein levels. A year × period interaction was detected where cows from year two exhibited less BW change on days 28, 56, and 84 of the study (P &amp;lt; 0.01) and had greater BCS (P &amp;lt; 0.01) than those from year one during these periods. In addition, we observed a treatment × year interaction where cows from year two experienced less BW change and had greater BCS than cows from year one (P &amp;lt; 0.01). No treatment × year interactions were detected for birth weight, average daily gain (ADG), or adjusted 205-d weight in calves. A tendency was noted for cows offered 0.4% BW· d-1 supplement to have heavier calves at birth than their counterparts (P = 0.09) over both years. A year effect was detected where calves born in year two had increased ADG and adjusted 205-d weights compared with those from year one. A tendency (P = 0.09) for the calves in year two of the study to have heavier weights at birth compared with those from year one was also noted. In summary, increasing levels of supplemental protein resulted in linear improvements of BW and BCS of grazing beef cattle during the winter. While birth weights of calves tended to differ due to the gestational nutrition of the dam, calf growth and weaning weights were not affected.

PSXII-26 Effect of Different Supplements Plus Phytogenic Additives on Ruminal Bacterial Community of Grazing Beef Cattle

Abstract Changes in ruminal microbial community can affect animal productivity, nutrient utilization efficiency, and environmental impact. This study aimed to evaluate the effect of two levels of supplementation plus a blend of phytogenic additives (essential oils, saponins, and spices) on the ruminal bacterial community in beef cattle grazing tropical pastures. The experiment was conducted at the Beef Cattle Sector of UNESP, Jaboticabal-BR, and lasted 84 days. Nine castrated Nellore steers (body weight of 262 ± 31.2 kg) cannulated in the rumen were assigned to 3 simultaneous 3 × 3 Latin square designs. Animals were kept on pasture of Urochloa brizantha cv. Marandu during the rainy season. The treatments included ad libitum mineral supplementation (MS) as the control group, added mineral supplementation of 0.1% of body weight per day plus Cargill phytogenic blend (AMSP), and energetic-protein supplementation, 0.3% of body weight per day plus Cargill phytogenic blend (EPSP). Ruminal samples were collected on day 26 of each experimental period. A mix of liquid and solid rumen content (6 mL) was taken before supplementation and immediately frozen in liquid nitrogen. Total genomic DNA was extracted using the Quick-DNA Fecal/Soil Microbe kit. The V3-V4 hypervariable regions of the bacterial 16S rRNA gene were amplified using universal primers 341F and 806R. The PCR fragments were submitted to sequencing on an Illumina NovaSeq 6000 PE 250 platform. The sequences were processed using mothur, grouped into operational taxonomic units (OTUs) using a similarity cut-off value of 97%, and the bacterial OTUs were classified using the SILVA database. Bacterial community composition was compared between treatments using a Kruskal–Wallis test and Wilcoxon’s post-hoc test using Rstudio. A total of 27 phyla, 224 families, and 577 genera were assigned by the taxonomic analysis of the ruminal bacterial community (Figure 1). The phyla Bacteroidetes (44.45 ± 9.43) and Firmicutes (42.50 ± 7.18) represent over 86% of the total relative abundance in the rumen of Nellore steers and were not influenced by the supplementation (P ≥ 0.250). The relative abundances of the Spirochaetes phylum, Spirochaetaceae family, and Treponema genus decreased in the rumen of AMSP supplemented animals (P ≤ 0.037) and were similar between MS and EPSP (Figure 2). Additionally, the EPSP supplementation resulted in decreased relative abundances of TM7, TM7 family Incertae sedis, and TM7 genus Incertae sedis relative abundances compared with those in MS (P = 0.031) but not between AMSP and EPSP supplementations. The addition of phytotherapy blend in the supplements led to decreased SR1, SR1 family Incertae sedis, and SR1 genus Incertae sedis abundances in the rumen (P ≤ 0.012). This study indicates that the relative abundance of the dominant phyla was not affected by the supplementation levels, but the addition of the phytogenic blend in the supplement decreased the relative abundances of specific bacterial phyla, families, and genera,

PSXI-30 Ruminal Bacterial Diversity Indexes of Grazing Beef Cattle Receiving Different Supplements Plus Phytogenic Additives

Abstract The addition of phytogenic compounds that have antimicrobial activity in cattle supplements can promote changes in ruminal bacterial diversity. This study aimed to evaluate the effect of two levels of supplementation plus a blend of phytogenic additives (essential oils, saponins, and spices) on the measures of alpha and beta diversity in the rumen of beef cattle grazing tropical pasture. The experiment was carried out in the Beef Cattle Sector of UNESP, Jaboticabal-BR. The trial lasted 84 days and nine castrated Nellore steers (body weight of 262 ± 31.2 kg) cannulated in the rumen were assigned in 3 simultaneous 3 × 3 Latin square designs. Animals were kept on the pasture of Urochloa brizantha cv. Marandu in the rainy season. The treatments were: ad libitum mineral supplementation (MS) as control group; added mineral supplementation, 0.1% of body weight per day plus Cargill phytogenic blend (AMSP); and energetic-protein supplementation, 0.3% of body weight per day plus Cargill phytogenic blend (EPSP). Ruminal samples were collected on day 26 of each experimental period. A mix of liquid and solid rumen content (6 mL) was taken before supplementation, placed in cryogenic tubes, and immediately frozen in liquid nitrogen. All samples were stored at −80 °C until DNA extraction and analysis. Total genomic DNA was extracted using the Quick-DNA Fecal/Soil Microbe Miniprep kit. The V3-V4 hypervariable regions of the bacterial 16S rRNA gene were amplified primers 341F (CCTACGGGNGGCWGCAG) and 806R (GGACTACHVGGGTWTCTAAT). The PCR fragments were submitted to sequencing on an Illumina NovaSeq 6000 PE 250 platform. The sequences were processed using mothur, grouped into operational taxonomic units (OTUs) using a similarity cut-off value of 97%, and the bacterial OTUs were classified using the SILVA database. Alpha diversity indices including Shannon, Simpson, Fisher, Chao1, and ACE, were calculated using the phyloseq package, while beta diversity was determined using the vegan package, both in Rstudio. Alpha diversity indices were compared between treatments using a non-parametric Kruskal–Wallis test and Wilcoxon’s post-hoc test. Beta diversity was tested using permutational multivariate analysis of variance (PERMANOVA) based on the Bray-Curtis similarity index. The AMSP and EPSP did not affect measures of alpha diversity (Figure 1), such as Shannon and Fisher indices (P = 0.219) as well as the richness index measured using Chao1 and ACE (P ≥ 0.363). A negative effect of supplementation on alpha diversity (P = 0.004) was only observed with Simpson’s Index of Diversity. Additionally, the supplementation did not change the beta-diversity of the ruminal bacterial community based on Bray–Curtis similarity index (P = 0.510; Figure 2). In conclusion, the addition of phytogenic compounds in the two levels of supplementation showed only a minor impact on the alpha diversity in the rumen of grazing beef cattle.

91 Grazing management–Tools for Improving the Efficiency of Grazing Beef Production

Abstract The beef sector is facing mounting challenges related to its perceived impact on climate change and other negative ecological externalities that can occur from the rearing of beef cattle. This would include greenhouse gas emissions (GHG), soil degradation, eutrophication of water ways and a decrease in biodiversity, to name a few. Within the industry, the largest contributor of GHG comes from the grazing sector, predominantly in the form of enteric methane (CH4) produced during the reticulo-rumen fermentation process. This presents a unique challenge, as the grazing sector is one where animal scientists have low precision with respect to experimental design and data collection, and where producers assert a lower level of dietary control relative to confined operations. While enteric CH4 inhibitors are getting closer to regulatory approval, their ability to reduce emissions in grazing systems is still relatively unknown due to the “pulse” supplementation strategy being unstudied to date. Therefore, management decisions that improve the quality of the forage base are the most practical strategies to reduce enteric CH4 production. This would include strategies such as adaptive grazing management, inclusion of high-quality forages, and improved forage diversity as potential tools to reduce emissions, dependent on geographic location. Furthermore, how the human dimension influences soil-plant-animal interrelationships may lead to beneficial ecological outcomes such as carbon sequestration and soil health. Therefore, potential “win-win” outcomes may be achieved. However, climatic gradients, and more specifically moisture, can influence or limit outcomes and thus interpreting research should be done on a geographical and climatic specific basis. The objective of this presentation is to outline and examine how management decisions can influence the efficiency and environmental impact of U.S. beef production, and to identify potential limitations and knowledge gaps in need of future research.

PSVIII-A-3 Activity Behavior and Growth Performance During Summer of Grazing Beef Heifers with Divergent Residual Feed Intake

Abstract Concerns about sustainability of beef production systems generate an interest in improved feed efficiency; however, there is a lack of research evaluating cattle activity budgets in response to the interaction between residual feed intake (RFI) and environment while grazing. Lying behavior and activity can provide insight into how animals interact with the environment and serve as an indicator of animal comfort. Furthermore, exposure to severe environmental factors can change behavioral patterns and impair animal performance. Therefore, this study evaluated activity budgets and performance in grazing beef heifers with divergent residual feed intake (RFI) during the summer season. From July to August 2022, forty-four crossbred beef heifers [358 ± 4.78 kg of body weight (BW); approximately 14 months of age] previously tested for RFI in drylot and classified as more (n = 21; LOW-RFI = -0.9 ± 0.70) or less feed efficient (n = 23; HIGH-RFI = 1.3 ± 1.00) were grazed at 2.72 AUM/ha over 7 wk in Alberta, Canada. IceRoboticTM pedometers (IceQube+) were used to track 24-hr heifer activity budgets [n = 43; total steps and lying and standing time (min/d and min/h) for 36 d]. Full BW was obtained on d -1, 0, 14, 28, 42, and 43 while fat scan on rib and rump were measured by ultrasound (Aloka 500 V diagnostic real-time) on d 0 and 42. Air temperature, relative humidity, wind speed and solar radiation information were collected within 1 km of the grazed area to calculate the Comprehensive Climate Index (CCI). Based on CCI, weather conditions were considered to impose risk to cause mild, moderate, severe, and extreme stress for 5, 18, 7, and 1 days, respectively. For BW, average daily gain (ADG), rump (RF) and rib fat (RiF), the data were analyzed as a completely randomized design, while behavior activity included repeated measures. An RFI x day interaction was observed for lying and standing times (P = 0.02) and total steps (P = 0.001). Greater number of steps (P &amp;lt; 0.01) and an increased standing time (P &amp;lt; 0.01) were observed in HIGH-RFI heifers. RFI × hour interaction was observed for lying and standing times (P = 0.006), where LOW-RFI heifers spent more time lying at 10:00 am (P &amp;lt; 0.01). Furthermore, LOW-RFI heifers had decreased number of steps per hour throughout the study (P = 0.03; 178 vs 191 ± 4.1). No effects were observed for ADG, BW, RF, and RiF (P &amp;gt; 0.24). In summary, selected activity behaviors differed between beef heifers with divergent residual feed intake while summer grazing. Further studies are needed to investigate the effects of continuous changes in weather conditions to better understand the environmental impacts on animal behavior while selecting for more efficient beef cattle.

PSVIII-A-4 Evaluation of Blood Parameters Associated to Environmental Stress in Grazing Beef Heifers with Divergent Residual Feed Intake

Abstract There is considerable interest in improved feed efficiency to enhance sustainability in beef production, but a lack of understanding exists on the interaction between residual feed intake (RFI) and environment while grazing. Increasing variation in environmental conditions has been documented in western Canada with summers becoming warmer. This study evaluated blood parameters and rumen temperature (RT) of grazing beef heifers with divergent residual feed intake (RFI) during summer (July to August) of 2022. Forty-four crossbred beef heifers (358 ± 4.78 kg body weight; approximately 14 months of age) previously tested for RFI in drylot and classified as more (n = 21; LOW-RFI = -0.9 ± 0.70) or less feed efficient (n = 23; HIGH-RFI = 1.3 ± 1.00) were grazed at 2.72 AUM/ha over 7 wk in Alberta, Canada. Rumen temperatures were automatically recorded throughout the study using the Smart Rumen Bolus by Moonsyst. Plasma was collected every 14 ± 1 d for 42 d to determine concentrations of blood urea nitrogen (BUN), non-esterified fatty acids (NEFA), insulin-like growth factor 1 (IGF-1), β-Hydroxybutyric acid (BHBA), leptin (LEP), free triiodothyronine (fT3), haptoglobin (HP), heat shock protein 70 (HSP70), and gamma-aminobutyric acid (GABA). Environmental conditions were assessed by calculating the Climate Comprehensive Index using temperature, wind speed, solar radiation, and humidity data from a weather station within 1 km of the grazed pastures. Daily weather conditions were considered to impose risk to cause mild, moderate, severe, and extreme stress for 8, 21, 8, and 1 days, respectively. Plasma and RT data were analyzed as a completely randomized design with repeated measures. An RFI × day interaction was observed for BUN (P = 0.018). LOW-RFI had greater (P = 0.02) BUN on d 42 compared with HIGH-RFI heifers (42.5 vs. 32.6 mg/dL, respectively), while GABA tended to be greater (P ≤ 0.09) for HIGH-RFI heifers on d 0 and 42. Free T3 concentrations were greater (P = 0.04; 8.54 vs. 7.78 pmol/L, respectively), whereas HP was less (P = 0.01) in LOW-RFI heifers. However, HP concentrations were below the threshold for inflammation throughout the study. There was also an effect of day (P &amp;lt; 0.01) for fT3, IGF-1, LEP, NEFA, HSP70, and BHBA. Leptin and HSP70 concentrations were greatest on d 14 and 28, whereas BHBA was the greatest (P &amp;lt; 0.01) and IGF-1 the least on d 42 (P &amp;lt; 0.01). An RFI × hour interaction was detected for RT (P = 0.0003), where HIGH-RFI heifers had greater RT throughout the day. In summary, weather conditions in western Canada changed blood parameters of replacement beef heifers during summer. Feed efficient heifers had decreased RT and greater plasma concentrations of fT3, which could be associated with metabolic homeostasis and regulation of thermogenesis.

315 Awardee Talk: Late Gestational Nutrient Restriction Alters Postnatal Nutrient Delivery and Calf pre-Weaning Growth in the Primiparous Beef Female

Abstract Nutrient requirements increase dramatically in the late gestation beef female to allow for proper growth and function of the uteroplacenta, fetus, and mammary gland. In fall- and spring-calving systems, late gestation grazing beef cattle often have limited forage nutrient availability. Late gestational nutrient restriction research generally associates decreased prenatal nutrient delivery with programming fetal growth and development, resulting in poor postnatal outcomes. However, the effects gestational nutrient partitioning may have on programming the mammary gland to decrease postnatal nutrient delivery is far less understood. In a fall-calving experiment, primiparous females were individually fed either 100% or 70% of energy and protein requirements from d 160 of gestation until parturition. Nutrient restricted females lost body weight and condition and had less nutrients in maternal circulation during late pregnancy. Calf birth weight was not affected, but nutrient restricted dams had less vigorous calves and 40% less colostrum yield. Colostrum of nutrient restricted females was more concentrated with IgG, and calf 48-h serum IgG indicated that offspring of both treatments had successful passive transfer of immunity. Colostrum of nutrient restricted females had less total lactose, but similar total protein and triglycerides compared with control females. Even when females were fed to meet their energy and protein requirements during lactation, late gestational nutrient restriction reduced milk yield by 15% and decreased milk protein concentration during the first 150 d of lactation. Reduced milk production was partially explained by a 19% reduction in blood flow supplying the mammary gland during this time. Less total lactose, protein, and triglycerides provided by the milk resulted in calf body weight diverging by 42 d of age, and calves born to nutrient restricted dams were 13% smaller at weaning. Interestingly, calf metabolic status pre-weaning was not as severely altered as expected considering milk nutrient and calf growth differences. By d 21 of lactation, metabolic status of previously nutrient restricted dams had returned to concentrations similar to control dams. During lactation, previously nutrient restricted females gained maternal weight faster and increased body condition, but had still not fully recovered to that of control females by weaning. Females were managed together and followed through their second parity to examine effects during the subsequent parity. Previously nutrient restricted dams still weighed less, were in thinner body condition, and had less mammary blood flow during their second lactation. Lactational performance and second parity calf growth were similar between treatments. While late gestational nutrient restriction may not always reduce fetal growth, our results illustrate that impaired postnatal nutrient delivery mechanisms in the cow and calf deserve continued consideration. Additionally, persisting effects in the second parity on maternal size, fleshing ability, and mammary blood flow demonstrate the possibility of long-term programming effects on the dam.

Beef Cattle Grazing Native Grasslands May Follow Three Different Supplement Response Patterns

Previous studies on winter supplementation of growing cattle grazing stockpiled native Campos grasslands suggest that forage allowance (FA), herbage mass, and weather conditions before and during the supplementation period could all affect supplement feed efficiency (SFE)—that is, the difference or change in average daily gain (ADG) between supplemented (S) and control (C) animals (ADGchng, kg) per unit (kg) of supplement dry matter (DM) intake. In this study, we analyse data from fifteen collated winter supplementation trials carried out in Uruguay between 2004 and 2018. The working hypotheses of this research paper were: (i) that average substitution rates are positive, and (ii) that ADGchng is not constant throughout the supplementation period and that its variation may be attributed to sward, animal or weather variables. There were two main objectives: (i) to estimate the average supplement substitution rate (sSbR, kg forage, f, dry matter, DM intake reduction: kg supplement DM intake) and potential herbage intake substitution rate (hSbR, kg fDM intake reduction: kg fDM intake of control animals), and its association with SFE, and, (ii) to assess the existence of different phases and supplementation response patterns and its association with other relevant variables. Estimated substitution rates were always positive (sSbR = 0.3–1.1 kg/kg; hSbR = 0.1–0.3 kg/kg) and were negatively and moderately associated with SFE. Supplementation proved to be a dynamic process where three possible supplementation responses over the supplementation period were identified (linear, quadratic and Weibull). While linear patterns did not appear distinctly associated with any particular set of variables, quadratic models were mostly associated with herbage biomass and substitution rates, whereas Weibull models were the clearest in their association with frosts. Regardless of the response pattern, at the beginning of the trials it was the animals’ body weight and supplement quality that most influenced supplement response, whereas towards the end, supplementation intake, supplemented animals’ ADG and forage quality played a more relevant role. The estimated parameters and response patterns are expected to be used as inputs in decision support systems for livestock farmers in the future.

Energy-protein supplementation and grazing dynamics of growing beef cattle grazing stockpiled native grasslands in winter: Doctoral thesis abstract

The weight loss of growing beef cattle grazing native grasslands in winter may be reverted by supplementing with energy and protein. To render this practice profitable, its efficiency -SFE- difference in average daily gain- ADG - between supplemented - S - and control - C animals- ADGchng - supplement response - per kg of dry matter -DM intake- must be controlled. Twenty-five trials carried out in Uruguay between 1993 and 2018 were gathered. The average SFE was 0.21 ± 0.076 kg/ADGchng/kg DM, from an average ADGchng of 0.38 ± 0.180 kg/animal/day. No association was found between SFE and supplementation rate nor type (p &lt; 0.05), but forage allowance negatively affected it while herbage mass positively affected it, yet in a smaller magnitude. Weather conditions during trials affected SFE (p &lt; 0.05), with greater SFE in winters with lower temperatures and more frosts. Another collated analysis using only 15 of the original 25 trials was performed to estimate supplement substitution rates (sSbR) and to assess the existence of different phases and ADGchng evolution patterns. sSbR were 0.3-1.1 kg/kg and were negatively associated with SFE. Three responses were identified (linear, quadratic and Weibull). Quadratic patterns were closely associated with sward biomass and substitution rates, while Weibull were associated with frosts. Finally, a grazing-down experiment was performed comparing S and C animals in their grazing dynamics. No differences were found between the horizontal dynamics, and when the upper grazing horizon was depleted by &gt; 80 %, the subsequent horizon was being depleted by 50 %. Supplementation is a highly reliable technology for improving the performance of growing beef cattle.

Resistência anti-helmíntica em nematódeos gastrointestinais de bovinos de corte em uma região tropical: efeito no ganho de peso vivo do gado de pasto no México

ABSTRACT This study aimed to determine the efficacy and parasite resistance of levamisole (LV) and ivermectin (IVM) in beef cattle naturally infected with gastrointestinal nematodes, as well as the effect on the liveweight gain in a tropical wet region of Oaxaca, Mexico. From November 2019 to January 2020, sixty-six grazing calves were randomly allocated into three groups of twenty-two animals each, treated with LV or IVM or an untreated control group (day 0). Feces were collected 1 day before treatment and 15 days after treatment. The liveweight gain from each animal was recorded at days 0, 15, 30 and 45 post treatment. The LV group presented the highest reduction of eggs per gram (EPG) of feces, followed by the IVM group. Resistance to IVM was detected, although LV resistance was also suspected. The IVM group had significantly higher effective treatment at 93.5%, resulting in an increase (P&lt;0.05) of liveweight gain of 16.1kg, followed by the LV group (92.4%) with 17.1kg, compared to the untreated control group. A significant (P &lt; 0.05) negative correlation was observed between EPG and weight gain for the LV (�� = -0.46) and IVM groups (�� = -0.32). LV and IVM showed a lack of efficacy against gastrointestinal nematodes, as well as an adequate capacity for EPG reduction but with IVM resistance and detrimental effects on growth performance in grazing beef cattle.

Methane emissions and growth performance of beef cattle grazing multi-species swards in different pesticide-free integrated crop-livestock systems in southern Brazil

The aim of this study was to assess the growth performance, forage intake and methane (CH4) emissions by beef cattle grazing under different spatiotemporal integrated crop-livestock systems (ICLSs). The experiment was conducted for two years (2017–2018 and 2018–2019) in warm season perennial pastures and cool season annual pastures grazed by beef steers. Three pesticide-free ICLS treatments – livestock-forestry (LF); crop-livestock (CL), and crop-livestock-forestry (CLF) – plus, a livestock control pesticide-free system (L) were conducted in randomized complete block design, with three replicates per treatment. Maize crop rotation was done with cool season cover crop under no-tillage. Eucalyptus trees (Eucalyptus benthamii) were planted in 2013 and intercropped with tree alleys. The animal performance, organic matter (OM) intake and enteric CH4 emission, yield, and intensity were assessed. We found no significant difference (P > 0.05) for average daily gain (ADG), stocking rate (SR), and daily live weight gain (LWG) per area for the different ICLS arrangements and seasons. The ICLS arrangements did not affect (P > 0.05) CH4 emission, yield, and intensity, with averages of 186 g steer−1 day−1, 26 g kg−1 OM intake and 210 g kg−1 of ADG, respectively. The average CH4 emissions per steer per day, per OM intake, per ADG and LWG per area were greater (P < 0.05) for steers when grazing warm season compared to cool season pastures. The integration or not of beef cattle with crops and/or forestry does not influence CH4 emissions, yield, and intensity by beef steers grazing pastures under moderate grazing intensity. Our results reinforce that well-managed integrated systems are a reliable climate-smart agriculture alternative for increasing production, e.g., grain, wood, meat, and mitigating or without increasing greenhouse gas emissions, such as CH4 from enteric fermentation in beef cattle.

Solid supplementation and energy sources for grazing beef cattle: digestion and metabolism

ABSTRACT The objective of this study was to determine the influence of different forms and energy sources for energy protein supplementation for grazing cattle on nutrient intake digestibility, ruminal fermentation, microbial protein synthesis, nitrogen utilisation, urea and creatinine metabolism. Five rumen cannulated crossbred steers were used in a 5 × 5 Latin square experiment design of 21-d periods. Steers were randomly designated to one treatment sequence: BSES (bran sorghum energy supplement); BCES (bran corn energy supplement); BPFES (bran protect fat energy supplement); SBES (solid block energy supplement); SMES (solid molasses energy supplementation). Animals were individually allocated in paddocks covered with Urochloa brizantha and were offered a concentrate at 400 g/100 kg of LW. Steers fed with bran supplements had higher supplement intake and total digestible nutrients compared to steers fed with solid supplements. The animals that received starch-based energy source in supplements had lower concentration of acetate and total volatile fatty acids compared to steers supplemented with protected fat source. Steers fed solid supplements had higher nitrogen excretion compared to steers fed bran supplements. The bran supplements were superior to solid alternatives. Addition of protected fat positively influenced the digestion of grazing beef cattle.

148 Economic Assessment of Beef Cattle Backgrounding in Brazil at Pre and During the Covid-19 Pandemic

Abstract The production costs of beef cattle grazing backgrounding systems between 2018/2019 (pre) and 2020/2021 (during) pandemic were evaluated. A comprehensive mathematical model for the cost of production was used according to the Economic Theory. Costs were collected and allocated into Fixed Cost (FC), Variable Cost (VC), and Total Cost (TC). In addition, analyses were performed concerning total income and profitability. A survey was carried out in 2018 with a rancher in the state of Minas Gerais (Brazil) to define major technical indicators of production. The spot prices used in our analysis were collected in 2018/19 and 2020/21. The base-animal used for such growing phase assessment represented the Nelore breed (Bos indicus), intact males and females, weaned at approximately 7-10 mo, and averaging 195 ± 15 kg of live shrunk BW (body weight), which remained in a grazing system for 12 mo. The average selling weight was 360 ± 15 kg shrunk BW. Animals (n = 34) were separated into three lots according to the ranch of origin and sex. Mineral supplementation was provided for 150 d during the greatest forage supply, while protein supplementation was offered for 210 d during the least forage supply for all animals. After comprehensively accounting for inputs, the cost index was compared between the two periods. The total cost for the 2018/19 production-period was US$ 1.13kg of BW, while an increase of approximately 53% (US$ 1.70kg of BW) was observed for 2020/21. The FC represented in the year 20/21 was 2.66 % less than 2018/19, which represented 22.9% of all costs combined. The VC represented 66.3% of the total cost in 2018/19, in which cattle purchase cost and feed cost represented 58.8% and 7.1%, respectively. For 2020/21, the VC increased to 70.7% of the total cost, in which cattle purchase cost and feed cost represented 62% and 8.5%, respectively. Regardless of the period, the most representative items analyzed were the cattle purchase price and feed costs. There was a 68.9% increase in gross income, followed by a raise in profit from US$ 0.26/kg BW in 2018/19 to US$ 2.9/kg of BW in 2020/21. The factors that influenced profitability the most were the purchase and sale price of animals. The shorter feeder cattle supply during the pandemic induced greater overall costs, although also positively affecting the final sale price of long-yearlings, which generated widened margins. The current cost calculation model showed to be helpful while allowing testing scenarios, possibilities, and helping producers to manage risk in such cattle enterprises.