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There is a critical lack of information on the timing of colonization of bovine respiratory diseaserelated bacteria in the upper respiratory tract, potentially affecting calf health and disease onset. The objective of this study was to evaluate the upper respiratory tract and fecal microbiomes of neonatal beef calves during the first 24 h of life compared with their dams at the time of birth. Late-gestation commercial beef cows (n = 28) were assigned to individual, soilsurfaced pens (6.25 x 2.29 m) fitted with canvas tarps on shared fences to limit contact between unrelated pairs. Left nasal (LN), right nasal (RN), fecal, and vaginal swab samples were collected from cows at a single time point promptly after parturition. Swabs of the LN, RN, and rectum were collected from calves at birth (0 h), 6, 12, and 24 h post-parturition. Samples were flash-frozen and stored at -80°C until processing. DNA was extracted from swabs using Power Soil Pro kit. Extracted DNA was used to prepare DNA libraries for full-length 16S rRNA gene sequencing on a MinION Mk1C device. Sequenced reads were classified using Centrifuge and used in microbiome analyses conducted in R to estimate the changes in the microbiome according to animal type (cow versus calf), time of collection, and sample type (nasal, fecal, or vaginal). Upper respiratory microbiomes significantly differed (P < 0.005) between cows and their offspring at birth. In nasal microbiomes, animal type explained 12.6% (P = 0.002) and 18.5% (P = 0.001) of variance in beta diversity in left and right cavities, respectively. Animal type explained 42.1% of the beta diversity variance in fecal microbiomes (P = 0.001). Nasal microbiomes at birth were significantly more dispersed in dams compared with their calves in both the LN (P = 0.03) and RN (P = 0.03). Similarly, fecal microbiomes of dams were significantly more dispersed (P < 0.0001) than those of their offspring. There was a clear transition of the microbial communities associated with calf age in the upper respiratory and fecal niches. Calf age accounted for 2% (P = 0.02), 3.5% (P= 0.001), and 28% (P = 0.001) of the variance in the beta diversity of the LN, RN, and fecal microbiomes, respectively. After adjusting for calf age, the laterality of nasal microbiomes was not significantly (P = 0.682) associated with the composition of microbial communities. In conclusion, calf microbial communities were dissimilar to that of their dam at birth. Additionally, microbial community transition was evident with each subsequent sampling time point, potentially influenced by the presence of the dam. [ABSTRACT FROM AUTHOR]

abscesses present significant challenges for the beef industry, yet understanding of the interplay between diet composition, eating behavior, and ruminal acidosis in finishing cattle and their effects on liver abscess prevalence and growth performance is lacking. Therefore, this study investigated the independent and interactive effects of dietary starch concentration and feed delivery regimen on growth performance, rumen buffering characteristics, carcass outcomes, and prevalence of liver abscesses in finishing beef steers. On d 0, beef steers [n = 720; body weight (BW) = 407 ± 4.53 kg) were sorted into 12 blocks according to BW and assigned to 1 of 4 treatments arranged as a 2 × 2 factorial (12 pens/interaction treatment; 24 pens/main effect) in a randomized complete block design. Treatments were finishing diets with low (49.1%; CON) or high (64.4%; HOT) starch concentration fed to steers receiving consistent feed delivery (REG) or randomized variations (ERR) in feed quantity (85% followed by 115% of the previous 4-d average once per week) and delivery time (delayed for 1, 2, 3, or 4 h twice per week). The 3 steers closest to the median BW in each pen were administered a 3-axis accelerometer ear-tag to quantify time spent ruminating and an indwelling rumen bolus to measure ruminal pH for the first 150 d of the study. Fecal score (1 = hard and dry consistency to 5 = water like consistency) and fecal pH were recorded on d 0, 56, 112, and before harvest. Daily dry matter intake (DMI) variability was greatest (P < 0.01; diet × feed delivery interaction) for CON + ERR, intermediate for HOT + ERR, and least for HOT + REG and CON + REG. No additional interactions (P ≥ 0.14) between diet and feed delivery regimen were observed. Feeding HOT increased total liver abscesses (P < 0.01) by 21.7 percentage points and liver scars (P < 0.01) by 12.7 percentage points compared with CON. Additionally, steers consuming HOT had less (P ≤ 0.05) final BW, average daily gain, DMI, gain-to-feed ratio, hot carcass weight, marbling score, and yield grade than CON. Steers fed HOT also had fewer daily rumination minutes (P < 0.01; diet × day interaction), lower fecal pH (P < 0.01; diet × day interaction) lower ruminal pH (P = 0.04), and less desirable fecal scores (P = 0.02) vs. CON. Feed delivery regimen did not affect (P ≥ 0.21) growth performance, rumen buffering characteristics, carcass traits, or liver abscess prevalence. Increasing the concentration of readily fermentable starch fed to finishing steers reduced growth and carcass performance, ruminal pH, and fecal pH, while increasing the proportion of liver abscesses. In contrast, inducing erratic DMI did not affect growth performance or carcass outcomes. [ABSTRACT FROM AUTHOR]

Introduction: The objectives of this study were to evaluate the impacts of two modified-live virus (MLV) vaccination protocols and respiratory disease (BRD) occurrence on the microbial community composition of the nasopharynx in feedlot cattle. Methods: The treatment groups included in this randomized controlled trial included: 1) no viral respiratory vaccination (CON), 2) intranasal, trivalent, MLV respiratory vaccine in addition to a parenteral BVDV type I and II vaccine (INT), and 3) parenteral, pentavalent, MLV respiratory vaccination against the same agents (INJ). Calves (n = 525) arrived in 5 truckload blocks and were stratified by body weight, sex, and presence of a pre-existing identification ear-tag. A total of 600 nasal swab samples were selected for DNA extraction and subsequent 16S rRNA gene sequencing to characterize the microbiome of the upper respiratory tract. Nasal swabs collected on d 28 fromhealthy cattle were used to evaluate the impact of vaccination on upper respiratory tract (URT) microbial communities. Results: Firmicutes were less abundant in INT calves (n = 114; P < 0.05) and this difference was attributed to decreased relative abundance (RA) of Mycoplasma spp. (P = 0.04). Mannheimia and Pasteurella had lower RA in INT (P < 0.05). The microbiome in healthy animals on d 28 had increased Proteobacteria (largely Moraxella spp.) and decreased Firmicutes (comprised almost exclusively of Mycoplasma spp.) compared to animals that were treated for or died from BRD (P < 0.05). Cattle that died had a greater RA of Mycoplasma spp. in their respiratory microbiome on d 0 (P < 0.02). Richness was similar on d 0 and 28, but diversity increased for all animals on d 28 (P > 0.05). [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the serum metabolome at 3 major time points in cattle subjected to a lipopolysaccharide challenge. Steers (n = 10; 379 kg ± 30.7) were challenged intravenously with LPS [0.25 μg/kg body weight (BW)], and plasma was isolated from blood at -2, 0, 2, 4, 6, 8, 10, 12, 18, 24, 36, and 48 h relative to the LPS challenge at 0 h. Samples were selected for metabolomic analysis at -2, 2, and 8 h of the challenge based on oxidative stress markers present in companion studies. Liquid chromatographyelectrospray ionization-high resolution mass spectrometry was used to separate and detect metabolites (50 to 1,400 m/z). Mass spectral features were annotated using MS-DIAL. Total ion count intensities were median normalized, log10 transformed, and analyzed using MetaboAnalyst v.5. Partial least squares-discriminant analysis (PLS-DA), agglomerative clustering (AHC), and an analysis of variance (ANOVA) with a false discovery rate (FDR) adjusted P < 0.05 were conducted. Of the 245 annotated metabolites, 155 differed between time points. Partial Least SquaresDiscriminant Analysis (PLS-DA) and variable importance in projection (VIP) plot were used to visualize treatments and identify compounds driving discrimination between groups. Hierarchical clustering using the Ward method was used to determine metabolite differences present following an endotoxin challenge in cattle. Pathway analyses were also conducted via KEGG Bos taurus pathway library. Based on AHC, 2 clusters were generated where -2 h clustered separate from 2h and 8h. A PLS-DA explained most variation within the model across Component 1 (47.5%), with clear separation of metabolites present at -2 h versus those present at 2 and 8 h post challenge. A VIP plot recognized metabolite differences driven by taurocholic acid, LysoPE (18:3; Lysophospholipid), butyric acid, acitretin, and tauromuricholic acid. Pathway analyses further identified arginine biosynthesis, beta-alanine metabolism, arginine and proline metabolism, and histidine metabolism as the metabolic pathways likely driving differences in the data (FDR P < 0.05). These data suggest that metabolites change drastically following an immune response and identify differences which may be further related to or contributing to oxidative stress in vivo. Additional research could aid in the identification of biomarkers significant to recognizing immune dysfunction and oxidative stress. [ABSTRACT FROM AUTHOR]

Sexed semen artificial insemination is a breeding technique that allows producers to shorten breeding seasons, optimize genetics through use of superior semen, create calves based on sex preference, and increase profitability. Sexed semen is a technology that sorts semen by differences in DNA content between X (female) and Y (male) bearing sperm. However, sexed semen practices have yet to be widely used in beef cows due to reduced sperm numbers, low conception rates, and increased costs. The objective of this study was to determine the effect of time of estrus upon fixed-time artificial insemination (FTAI) of sex-sorted semen on conception rate using two different estrous synchronization protocols. Multiparous commercial beef cows (n = 73) were randomized by age, body condition score (BCS), and days post-partum at the University of Arkansas Livestock and Forestry Research Station in Batesville. Both synchronization treatments (TRT) used a controlled internal drug releasing device (Eazi-breed CIDR; 1.38g progesterone) inserted intravaginally on d -14 of the protocol simultaneous to administration of prostaglandin F2a (PGF; 500μg cloprostenol sodium; Estrumate). In the first treatment (TRT 1; 7&7 Synch), gonadotropin-releasing hormone (GnRH; 86μg gonadorelin; Fertagyl) was administered on d -7. In the second treatment (TRT 2; 8&6 Synch), GnRH was administered on d -6. Both treatments were then administered PGF simultaneous to CIDR removal on d 0, 66 ± 2h before FTAI and administration of GnRH. Standing heat (estrus) was visually detected every 3 h for 30 min intervals between CIDR removal and FTAI. Heat detection patches were used in conjunction with visual detection of estrus. Time of estrus was signified as time of standing immobile when mounted in combination with presenting a patch score of 4 (>75% color removed). Time of estrus (TD) was deviated from time of FTAI and categorized into three equal time groups (Grp 1 = 0 to 11.0 h; Grp 2 = 11.01 to 22.0 h; and Grp 3 = 22.01 to 33.0 h). Conception rate (CR) was determined via ultrasound 37 ± 2 d after FTAI. Data were analyzed using the GLIMMIX procedure of SAS 9.4. CR did not differ by age of dam (P = 0.58), BCS (P = 0.48), or TRT (P = 0.83). However, TD had an effect on CR (P = 0.002); and resulted in CR of 45% (Grp 1), 87% (Grp 2), and 42% (Grp 3). In conclusion, these results indicate artificially inseminating cows with sexed semen between 11.01 and 22.0 h after time of standing estrus will increase pregnancy rates for multiparous commercial beef cattle. [ABSTRACT FROM AUTHOR]

This study evaluated starch dilution with different sources of fiber from terminal implant to harvest on feedlot cattle performance, rumen buffering characteristics, and carcass outcomes. Steers (n = 416) were allocated to 48 pens in a randomized complete block design and assigned to 1 of 4 dietary treatments. Treatments were steam-flaked corn-based diets: CON; 7.5% corn stalks fed for the entire feeding period or CON followed by CS; 14.8% corn stalks, WD; 9.5% wet distillers grains with solubles and 7.5% corn stalks, or NR; 19.0% wet distillers grains with solubles and 0.0% corn stalks fed from terminal implant to harvest. Steers were transitioned to CS, WD, and NR over 6 d using a two-ration system. Within each pen, 2 steers received an indwelling rumen pH bolus and a 3-axis accelerometer ear-tag to quantify rumination. Treatment differences were considered statistically significant when P < 0.10. Dry matter (DM) and metabolizable energy (ME) intake were greatest for cattle consuming CS, intermediate for WD and CON, and least for NR (P < 0.01). The average daily gain (ADG) did not differ among treatments (P = 0.18); however, feed efficiency (G:F) was least for NR, intermediate for WD, and greatest for CS and CON (P = 0.10). Steers consuming CS had more (P = 0.08) 12th rib fat than NR, WD, or CON, but no other differences (P = 0.24) in carcass characteristics were observed. A treatment × day interaction (P < 0.01) was observed for daily rumination time and ruminal pH. Results suggest that increasing the concentration of corn stalks in the diet post-terminal implant increased DM and ME intake and rumination; replacing corn stalks with wet distillers grains with solubles improved G:F and reduced rumination with minimal impacts on ruminal pH. [ABSTRACT FROM AUTHOR]

Liver abscesses (LAs) are a common and important problem in cattle because of their association with decreased growth and production, low carcass quality, and the significant economic losses associated with liver condemnation. Fusobacterium necrophorum has traditionally been considered the primary etiologic agent of LA formation in cattle, but recent evidence has demonstrated that LA microbial communities are far more polymicrobial than previously believed. Here, we characterize microbial communities within multiple LAs from the same animal, provide evidence that some LAs may be seeded from the hindgut, identify biomarkers throughout the gut-liver axis that predict the presence of LAs, and demonstrate the impact of tylosin on microbial communities in the rumen, ileum, and colon. 16S rRNA gene sequencing was used to characterize communities from LA purulent material, as well as from the luminal and epithelia, communities in three gut locations (rumen, ileum, colon) within the same animals. A combination of QIIME2 and phyloseq were used to analyze sequence data, and microbial community composition was compared based on generalized UniFrac distances. Taxa discriminant of LA occurrence were identified using linear discriminant analysis effect size (LEfSe). Despite being the most abundant genus when averaged across all LA communities, Fusobacterium spp. was not the predominant taxa in the majority of LAs. In fact, members of Bacteriodetes (largely Bacteroides, Porphyromonas) were the predominant taxa in more than one-half of all LA communities. Importantly, multiple LAs from the same animal had remarkably similar community structure, and multiple taxa including Bifidobacterium spp., widely considered beneficial to gut barrier function in humans, were differentially abundant in both the foregut and hindgut between cattle that did and did not have LAs. Further, tylosin had little impact on the diversity and composition of microbial communities within LAs but did alter communities in the rumen and small intestine. In particular, members of the family Lachnospiraceae were more abundant in the rumen and hindgut of animals given tylosin. Together, these results provide additional evidence challenging the traditional theory of LA etiology (that bacterial translocation occurs exclusively from the rumen) and provides evidence that barrier dysfunction in the gut may be the underlying cause of LA formation. [ABSTRACT FROM AUTHOR]

Bovine Respiratory Disease (BRD) is the most devastating disease affecting cattle producers in North America. Vaccines and antimicrobials are commonly used to prevent and treat BRD. However, it is still a growing problem. The four common BRD opportunistic pathogens, Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis, are present in the upper respiratory tract of healthy cattle as well, and how they move to the lung are unknown. The apparent role of the respiratory microbiome in BRD has led to many microbiome studies. However, most culture-independent studies have focused on the opportunistic pathogens, and little is known about the potential bacterial probiotics in the prevention and treatment of BRD. This study aims to identify potential probiotics to treat and prevent BRD by analyzing respiratory microbiotas (nasal swabs (NS): healthy: n=94, BRD: n=94; nasopharyngeal swabs (NPS): healthy: n=25, BRD: n=36; and bronchoalveolar lavage (BAL): healthy: n=22, BRD: n=29) from clinically healthy calves at feedlot entrance and calves at BRD diagnosis. Amplicon sequence variants (ASVs) were classified as potential probiotics if selected as a top predictor by a machine learning technique (random forest) and significantly more abundant in healthy controls (log2fold change = 2 and P<0.05) based on DESeq2. ASV98_Corynebacterium was a potential probiotic in all three locations. ASV121_JG30-KF-CM45_unclassified, ASV32_Corynebacterium, and ASV64_Serinicoccus were potential probiotics in NPS and BAL. Additional taxa were potential probiotics in a single location, including ASV114_ Streptococcus_luteciae and ASV233_Facklamia in NS; and ASV150_Facklamia, ASV26_Corynebacterium, ASV306_Facklamia, and ASV44_Dietzia in NPS. SPARCC network analysis revealed that ASV114_ Streptococcus_luteciae was the top hub taxa in healthy calves' NS, and ASV32_Corynebacterium and ASV26_ Corynebacterium were in the top five hub taxa of healthy calves' NPS, indicating that these ASVs are key members of their respective communities. Furthermore, SPARCC found ASV32_Corynebacterium is negatively correlated with ASV2_Mycoplasma (-0.25) in NS and ASV5_Mycoplasma_hyorhinis (-0.23) in NPS (P <0.05). Additionally, ASV26_Corynebacterium is negatively associated with ASV62_Ureaplasma (-0.37) and ASV5_Mycoplasma_hyorhinis (-0.21) in NPS and ASV12_Histophilus_somni in (-0.29) in BAL (P <0.05). [ABSTRACT FROM AUTHOR]

Two groups (light = 740 lbs and heavy = 942 lbs) of Akaushi cross steers (n = 20), were ultrasounded for carcass traits by an Ultrasound Guidelines Council Certified Technician every 28 days to quantify differences in intramuscular fat deposition occurring in three distinct muscles (longissimus dorsi, biceps femoris and semitendinosus). Cattle were fed at the West Texas A&M University Research Feedlot and scanned with an Aloka 500 ultrasound unit using Beef Image Analysis (BIA) Feedlot software from Designer Genes Technologies, Inc. (Harrison, AR). Carcass ultrasound measurements included 12-13th rib ribeye area (REAU), subcutaneous fat thickness (FTU), intramuscular fat percentage along the longissimus dorsi (IMFULD), rump fat thickness (RFU) as well as intramuscular fat percentage of the biceps femoris (IMFUBF) and semitendinosus (IMFUST). A difference was detected in IMFULD for the duration of the study (P < 0.05). However, no differences occurred from day 0 to day 56 (P = 0.34), or from day 84 to day 140 (P = 0.17) for IMFULD. There was a slight numerical decrease (0.1505%) in IMFUBF from day 0 to day 56, with an increased difference from day 56 to day 84 (P < 0.05). There was a positive change from 4.113% to 5.728% in the heavy group (P = 0.08) and a change from 4.113% to 4.456% in the light group (P = 0.42) for IMFUBF. There was a significant change in IMFUST from day 56 to 84 (P < 0.05). Of note, there was a decrease in IMFULD, IMFUBF and IMFST from day 140 to day 168 which could be associated with adverse winter weather events. The data present a positive increase throughout all muscles studied for beef cattle while on feed, though weather events have the possibility to negatively affect gains more rapidly than progressive effects associated with feed and growth. [ABSTRACT FROM AUTHOR]

Bovine respiratory disease (BRD) detection is a major challenge in feedlot cattle management. In a pilot study, two dogs were trained using sets of three samples to identify nasal swabs from cattle that developed signs of BRD after feedlot arrival. Cattle arrived at the feedlot in four lots and included a mixture of bulls (n=306) and steers (n=89). In the final stage of training, Dog A accuracy was 0.82 (95% CI: 0.79-0.85) and Dog B accuracy was 0.63 (95% CI: 0.60-0.67). A Kruskal-Wallis test identified differences in accuracy across lots (P < 0.001). Differences between pairs were identified by Wilcoxon tests. Accuracy for Lot 2 (0.53, 95% CI: 0.46-0.59) was lower than all other lots. The greatest accuracy, 0.96 (95% CI: 0.92-1.00), was for sets where the positive sample came from a different lot than both negative samples, and differed from accuracy for all lots except Lot 4. A Wilcoxon test detected no differences (p = 0.76) in accuracy between sets that consisted of all bulls (0.73, 95% CI: 0.69-0.76) and sets that were a mixture of bulls and steers (0.72, 95% CI: 0.69-0.75). After training, in a double-blind detection test, unfamiliar samples (n=123) were presented to the dogs as 41 sets. Each set was evaluated twice by each dog. Accuracy for Dog A was 0.39 (95% CI: 0.28-0.50), no better than chance; however, Dog B's accuracy was 0.45 (95% CI: 0.34-0.56), better than the 0.33 expected by chance. In the detection test, neither sample lot (p = 0.33) nor sex (p = 0.11) impacted performance for either dog. Dogs' consensus accuracy was 0.54 (95% CI: 0.38-0.69). Overall, dogs showed some ability to discriminate between BRD-affected and healthy cattle using nasal swabs, however multiple compounding factors may have influenced canines' decision making in this trial. [ABSTRACT FROM AUTHOR]

Modified-live virus (MLV) respiratory vaccines are commonly administered to beef cattle upon arrival in feedlots to prevent bovine respiratory disease (BRD) but their impact on respiratory microbial communities is unknown. The objective of this study was to evaluate the impact of intranasal and parenteral MLV vaccination and health status on the respiratory microbiome of feedlot cattle with a high-risk of BRD. Crossbred beef calves were blocked by truckload and stratified by arrival body weight, sex, and ranch tag status. Cattle were randomly assigned to 1 of 3 treatment groups: no vaccination, intranasal MLV, or parenteral MLV. Nasopharyngeal swabs were collected on d 0 and 28, and upon treatment for BRD. A subset of these samples (n=600) was selected from an equal number of healthy and morbid cattle among vaccine treatment groups. Additionally, all chronically ill cattle and mortalities were selected for sequencing. After DNA extraction, 16S rRNA gene sequencing was used to characterize the microbiome of the upper respiratory tract. The overall composition of respiratory tract microbial communities in all treatment groups was similar to previously described respiratory communities. Members of the families Pasteurellaceae and Mycoplasmataceae, which include common respiratory pathogens (Mannheimia, Pasteurella, Histophilus, Mycoplasma), were prevalent in all communities. However, the proportions of these important taxa differed between cattle that developed BRD and cattle that remained healthy. Morbid cattle had lower (P< 0.05) phylum members Proteobacteria and higher (P< 0.05) Tenericutes than cattle that remained healthy. Cattle that received an intranasal vaccine had a higher (P< 0.05) abundance of Proteobacteria and lower (P< 0.05) abundance of Tenericutes compared to both control and parenteral cattle. Results indicate that intranasal vaccination had a significant impact on respiratory microbial communities, while parenteral vaccination did not. These results add to our understanding of the impacts of MLV vaccination on the health and productivity of feedlot cattle. [ABSTRACT FROM AUTHOR]

The study objective was to evaluate health, performance, and antimicrobial costs of heifers where targeted metaphylaxis was guided by a commercial blood leukocyte analyzer compared to a traditional metaphylaxis regimen. Using a randomized complete block design, heifers (n=1,271; initial body weight (BW) = 233.3±1.08 kg) were randomly allocated to treatment pens (n=20; 10 blocks). Treatments were: 1) cattle administered metaphylactic treatment with gamithromycin at arrival (META), and 2) cattle administered metaphylaxis with gamithromycin according to the blood leukocyte analyzer outcome (TARGETED). The blood leukocyte analyzer indicated immune status of individual animals according to the number and proportion of different leukocytes in the blood; red signified "abnormal" and green signified "normal" status. Only cattle with a red outcome were administered antimicrobial in the TARGETED treatment. Of all cattle enrolled in the study, 73% were deemed normal and 27% were deemed abnormal by the chute side blood analyzer. Treatment groups had an equal distribution of normal (META = 73% TARGETED = 74%) and abnormal (META = 28% TARGETED = 26%) cattle enrolled in the study. Cattle were fed a common starter ration for the duration of the 62-d study. Pen riders were blinded to treatment pen status. Data was analyzed using PROC MIXED and GLIMMIX in SAS. Final BW, ADG, and feed conversion were less for TARGETED (P=0.02). However, the arrival processing antimicrobial cost (META = 11.77 and TARGETED = $3.27/heifer) and total antimicrobial cost (META = 17.77 and TARGETED = $9.12/heifer) was reduced (P< 0.01) for TARGETED. TARGETED had an arrival processing antimicrobial cost savings of $8.50/heifer and an overall drug input cost savings of $8.65/heifer. The BRD morbidity rate for normal status heifers was 18.85% and more than abnormal (26.49%; P< 0.01). Normal status heifers had a mortality rate of 3.17 vs. 5.80% for abnormal (P=0.03). In conclusion, drug costs were reduced but performance of TARGETED was also less. [ABSTRACT FROM AUTHOR]

This study evaluated the plasma oxidative products of beef calves challenged with LPS following methionine supplementation (L0 = Control; L1 = 10 g/hd · d; L2 = 20 g/hd · d). Following an initial 40-d feeding period, steers (n = 32; 379kg±30.7) were challenged i.v. with LPS (0.25 µg/kg body weight) on d 41. Blood was collected at -2, 0, 2, 4, 6, 8, 10, 12, 18, 24, 36 and 48 h relative to the LPS challenge at 0 h. Samples were processed to isolate plasma for indicators of oxidative stress with colorimetric assays determining malondialdehyde (MDA) and reactive oxygen species (ROS) concentrations. Data were analyzed as repeated measures using the GLIMMIX procedure of SAS. Concentrations of MDA varied by time (P < 0.001), showing a large increase (P < 0.05) 2 h post-LPS, then decreasing again at 4 h. MDA values decreased (P < 0.05) from h 6 to 18 where values returned to initial concentrations (P < 0.05). A treatment × time interaction (P < 0.001) occurred for ROS concentrations. Concentrations for all treatments were less than the detectable limit at -2, 0, 10, 12, 24, 36, and 48h (P > 0.05). At 2 h post-LPS, ROS was greatest in L0 cattle, least in L2, and intermediate in L1 (P < 0.05), but declined at 4 h in all treatments. Values peaked at 6 h for L1 and L2 cattle, followed by a decline at 8 h (P < 0.05). Control cattle were similar from 4 to 6 h (P > 0.05) but increased again at 8 h (P < 0.05). These data show that oxidative stress from an LPS challenge contributes to increased plasma ROS and secondary lipid oxidation products but may be mitigated by the inclusion of methionine supplements. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the effects of methionine supplementation prior to and during a lipopolysaccharide (LPS) challenge on the performance and inflammatory biomarkers of receiving beef steers. Steers ( n  = 65; 295.8 ± 46.5 kg) were randomly assigned to 3 treatment groups: L0 = Control, receiving no supplement; L1 = 10 g/hd/d rumen-protected methionine (MetaSmart, Adisseo USA Inc., Alpharetta, GA); and L2 = 20 g/hd/d rumen-protected methionine and fed for 40 d at the West Texas A&M University Research Feedlot. On day 40, a subset of steers ( n  = 32; L0 = 10; L1 = 11; L2 = 11) were transported to the USDA Livestock Issues Research Unit, and on day 41 steers were weighed and fitted with indwelling rectal thermometers and jugular catheters. On day 42, steers were challenged i.v. with LPS (0.25 µg/kg BW). Blood samples were collected at -2, 0, 2, 4, 6, 8, 10, 12, 18, 24, 36, and 48 h relative to the LPS administration at 0 h. Serum was isolated to determine serum chemistry and inflammatory marker concentrations. Whole blood was used for hematology analysis. There were no differences in DMI or ADG ( P  ≥ 0.75) during 35 d of supplementation. A treatment × time interaction ( P  = 0.01) occurred for rectal temperature, where L2 steers had the greatest temperature following the challenge ( P  ≤ 0.05) compared to L1 and L0 steers. There was a treatment × time interaction ( P  = 0.03) for the change in white blood cells where L0 steers had the greatest change compared to L1 and L2 steers at various timepoints. There was a treatment × time interaction ( P  = 0.02) for the change in tumor necrosis factor-α concentration, where there was a greater increase in concentration in L0 compared to L1 and L2 steers. Additionally, there was a treatment × time interaction ( P  < 0.01) for Macrophage Inflammatory Protein-1β (MIP-1β) concentrations, where concentrations were greater in L0 compared with L1 and L2 steers from 2 to 4 h post-challenge. There was a treatment × time interaction for plasma total protein concentration ( P  < 0.01) where L0 steers had less plasma total protein compared with L1 and L2 steers, while L1 steers had less plasma total protein than L2 steers at -2 h prior to LPS challenge. These data suggest that methionine supplementation may have an immunomodulatory effect in beef steers that may improve response to pathogens., (Published by Oxford University Press for the American Society of Animal Science 2024.)

The objective of this study was to evaluate the impacts of stress challenge duration on metabolic, hematologic, and rumen fermentation parameters of beef steers. Thirty steers (416 ± 19 kg) were used in a randomized complete block design with 2 blocks and 3 treatments. Treatments were intravenous injection of (1) saline at 0, 24, 48, and 72 h ( n  = 10; control); (2) corticotropin-releasing hormone (CRH) and vasopressin (VP) at 0 h and saline at 24, 48, and 72 h ( n  = 10; acute); or (3) CRH and VP at 0, 24, 48, and 72 h ( n  = 10; chronic). Serum samples were collected at various time points for analysis of serum chemistry and nonesterified fatty acids (NEFA). Whole blood was collected for analysis of complete blood count, and ruminal fluid was collected via oral lavage to evaluate volatile fatty acid (VFA) composition. Serum cortisol was greater (treatment × hour; P  ≤ 0.01) for cattle receiving acute and chronic than control at 1 h ( P  < 0.01) and greater for chronic than acute and control at 25, 26, 49, 50, 73, and 74 h ( P  < 0.01). Similarly, there was a treatment × hour interaction ( P  < 0.01) for serum glucose concentrations such that cattle receiving acute and chronic had greater glucose at 1 h than control ( P  < 0.01), and cattle receiving chronic had greater glucose at 25, 49, 73, and 74 h than acute and control ( P  ≤ 0.04). Serum insulin concentrations were greater (treatment × hour P  < 0.01) in chronic and acute than control at 1 h ( P  < 0.01) and greater for chronic compared to acute and control at 25, 49, and 73 h ( P  ≤ 0.01). Serum NEFA tended ( P  = 0.09) to be greater in stressed cattle compared to control. There was a treatment × hour interaction ( P  = 0.003) for total white blood cell count such that chronic had greater concentration than control at 72 h ( P  < 0.01). Conversely, monocyte concentration was less (treatment × hour interaction P  < 0.01) for chronic than acute and control at 144 h ( P  < 0.01) and eosinophil concentration was greater (treatment × hour interaction P  = 0.02) for chronic than control steers at 48 h ( P  = 0.02) and greater for chronic than acute at 72 and 144 h ( P  ≤ 0.03). Minimal differences were observed in VFA concentrations with the exception of acetate (treatment × hour interaction P  = 0.05). These results demonstrate that administration of CRH and VP affects complete blood count and serum chemistry, and longer duration of treatment exposure prolongs the physiological responses to a stress challenge., Competing Interests: The authors declare no conflicts of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)