Mature Beef Cows Research Articles

387 Impacts of rumen protected omega-6 fatty acid supplementation on cow reproduction and calf growth

Abstract Maternal nutrition during pregnancy is crucial for proper fetal development. Rumen protected omega-6 (ω-6) fatty acids (FA) may improve health and reproductive success in beef cattle. Previous research studied the effects of supplementing ω-6 on cow production either during late gestation or post-breeding but not during both stages. Our objective was to determine the effects of ω-6 supplementation during late gestation and post-breeding on cow reproduction and calf pre-weaning growth. Eighty cows were assigned to either a saturated FA control (C) or rumen protected ω-6 supplements for 40 d before parturition (PRE) and/or 35 d after artificial insemination (AI, POST) using a 2 × 2 factorial: PRE C-POST C(n = 19); PRE C-POST ω-6(n = 19); PRE ω-6-POST ω-6(n = 17); PRE ω-6-POST C(n = 18). Cows were fed ad libitum hay and water when on/off supplementation periods. Supplements were provided in low moisture tubs. Individual animal intake of supplement was measured by a GrowSafe system. Cow body weights and plasma FA concentrations were measured prior to and after supplementation during each period. Calves were weighed at birth, branding, 150 d old and weaning. Reproductive measurements included postpartum estrus activity, estrus response at fixed-time AI (FTAI), and pregnancy rates. Blood plasma for progesterone analysis was collected on d 7 post-AI on all cows. Corpus luteum (CL) area was measured on d 7 via transrectal ultrasonography on a subset of cows during the POST period (PRE ω-6-POST ω-6 n = 8; PRE C-POST C n = 8; PRE C-POST ω-6 n = 8; PRE ω-6-POST C n = 8). The relationship between supplement intake and plasma FA concentration was analyzed via linear regression, and all other variables were analyzed via ANOVA. Supplement intakes within treatments and between the PRE and POST supplemental periods were highly variable. Body weights remained similar for cows (P = 0.52), but POST ω-6 calves had larger weaning weights than POST C calves (P = 0.02). There was a positive linear relationship (r2 = 0.14, P < 0.03) between supplement intake and plasma FA for PRE ω-6 and POST ω-6. Positive linear relationships between intake and plasma ω-6 FA concentration were observed for PRE C (r2 = 0.11, P < 0.05), PRE ω-6 (r2 = 0.2, P < 0.007) and POST ω-6 (r2 = 0.31, P = 0.0005). Post-partum estrus activity was similar (P = 0.81) between PRE C and PRE ω-6 cows, and estrus response at FTAI was similar (P = 0.13) between POST C and POST ω-6 cows. POST ω-6 cows had larger CL areas than POST C cows (P = 0.03); however, blood progesterone concentrations at d 7 did not differ between treatments (P = 0.65). There was no difference in conception to FTAI between POST C and POST ω-6 (P = 0.08). These results indicate that free choice ω-6 FA supplementation during late gestation and post-AI result in large variation in intake between cows that influence plasma concentrations, but did not markedly alter reproductive measures in mature beef cows.

The veterinarian’s role in reducing GHG emissions from beef and dairy production

The beef and dairy industries make significant contributions to sustainability objectives by providing our society with nutri­tious food, supporting farmers’ livelihoods, generating billions of dollars in economic activity, and contributing to healthy ecosystems. However, cattle production also generates negative environmental impacts, including greenhouse gas (GHG) emis­sions. Veterinarians have a unique opportunity to interface with beef and dairy farmers to assist with the implementation of products and practices that reduce GHG emissions, such that their clients can be more profitable and more sustainable. In general, the GHG intensity of beef and dairy production can be reduced by increasing output yields of beef and milk, while re­ducing inputs and maximizing efficiency. Some of the specific interventions include: early entry of feeder cattle to a feedlot, dry manure management, optimized inorganic nitrogen fertil­izer use, increased fat in the ration, use of anti-methane feed additives and ionophores, sourcing low-carbon corn, select­ing genetics for high feed efficiency, raising moderate/small mature beef cows and feed efficient dairy cows, improving pregnancy rate and reducing dystocia, conducting pregnancy checks, implementing artificial insemination, promoting herd health products and practices to reduce death loss, using growth-promoting implants, and utilizing SOP Lagoon®. As a trusted source of scientific information, veterinarians can be a conduit of information for producers and contribute to the ongoing effort to improve the resiliency of the beef and dairy industries.

212 Genome-Wide Association Study Investigating the Genomic Components of Efficiency in Beef Cows

Abstract Efficiency of mature beef cows consuming high-forage diets is not comparable with standard definitions of beef cattle efficiency such as feed conversion or residual feed intake in the feedlot setting. This study aimed to conduct a genome-wide association study (GWAS) to identify regions of the bovine genome associated with efficiency in mature beef cows. Ninety-eight black Angus cows were managed under extensive feeding programs over a two-year period. Using rump fat at calving, calving date, and calf weaning weight as a percentage of the body weight of the dam, a weighted percentile scoring system was used to rank efficiency. Eighty-three of the cows were retained for the GWAS. The 20 most and 20 least efficient cows (HD dataset, n=40) were genotyped with the Illumina BovineHD BeadChip (777,000 SNPs) while the remaining cows were genotyped with the Neogen GGP Bovine 100K chip (LD dataset, n = 43). The LD dataset was imputed to the HD SNP array density using Beagle5.4 (FULL dataset, n = 83). Three separate GWAS were conducted using GAPIT (version3). The first GWAS was performed on the HD dataset using a quantitative phenotype determined by the ranking system. The second GWAS was performed with the HD dataset using a qualitative phenotype (efficient vs non-efficient cows). For the final GWAS, the FULL dataset with ranked phenotypes was used. Five models were evaluated for each GWAS, including the general linear model (GLM), mixed linear model (MLM), multiple loci mixed model (MLMM), fixed and random model circulating probability unification (FarmCPU), and Bayesian-information and linkage-disequilibrium iteratively nested keyway (BLINK). The model that best represented each dataset as determined by quantile-quantile plots was used for downstream analysis. Although results of the GWAS were not significant (Bonferroni threshold), associations were identified on BTA10, 16, 17, 25, 27 and 29. Positional candidate genes in the associated regions include: FOXN3, UPB1, SNX29, DDX54, LOC112444612, RITA1, and TACC1. Further functional analyses are required to confirm these findings; however, this work provides a foundation for identifying genes and gene mutations influencing this newly described phenotype.

358 The Effects of Varying Levels of Cotton Gin Byproduct and Wet brewers’ Grains on Growth Performance of Growing and Finishing Steers

Abstract The abundance of craft breweries provides widespread availability of wet brewers grains (WBG) to be used by beef cattle producers as a potential feedstuff. Cotton gin byproduct (CGB) is a feedstuff typically reserved for mature beef cows due to its low and variable feed value. Both WBG and CGB have high cost of transportation but are sometimes used by producers near supply centers due to their low price. The objective of this study was to analyze animal performance of growing Angus steers fed total mixed rations with varying amounts of CGB and WBG. Sixty-four Angus steers (365 ± 26 kg) were allotted and blocked by initial body weight (BW) in a randomized complete block design to 8 dietary treatments and fed in 2 phases, growing phase (GP) and finishing phase (FP) (84-d and 69-d, respectively). Dietary treatments were arranged in a 2 x 4 factorial with two levels of CGB (0 or 25% of DM) and 4 levels of WBG (0, 10, 20 or 30% of DM). The control and base of all treatments were corn, corn silage and soybean meal. Body weights were recorded on two consecutive days at the beginning and end of GP and FP. Feed samples were collected, and refusals were weighed weekly. Data were analyzed using the MIXED procedure of SAS 9.4 with main effects of CGB, WBG, and the interaction. The linear, quadratic, and cubic effects of increasing levels of WBG and CGB were tested with polynomial contrasts. Average daily gain (ADG) did not differ among dietary treatments (0, 25% CGB and 0, 10, 20, 30% WBG) for GP, (1.67, 1.61, and 1.67, 1.57, 1.74, and 1.60 kg/d, respectively) (P > 0.3031), FP (1.53, 1.61 and 1.56, 1.53, 1.61, and 1.58 kg/d) or the overall trial (1.61, 1.62 and 1.62, 1.55, 1.68, and 1.60 kg/d). The addition of CGB increased GP dry matter intake (DMI; 11.06 vs 11.99 kg/d; P = 0.0011), while the addition of WBG linearly decreased GP DMI (11.81, 11.69. 11.81, and 10.81 kg/d; P = 0.0292). There was an interaction between CGB and WBG (P = 0.0206), with increasing levels of WBG at 0% CGB exhibiting a cubic effect (P = 0.0127), but no effect at 25% CGB. Inclusion of CGB decreased feed efficiency (FE) in the GP (6.77 vs. 7.69; P = 0.0008) but had no carry-over effect in the FP. There was no effect of WBG on FE in GP or FP. In conclusion, CGB increased DMI, reduced FE, and maintained ADG. Increasing quantities of WBG did not reduce ADG or FE, but decreased DMI with increasing feeding level. Therefore, WBG and CGB can be considered viable options for cattle producers seeking to lower input costs.

Cull Beef Cow from Southern Portugal: High Amount of n-3 PUFA

The goal of this research work was to characterize carcass, meat quality traits, proximate composition and lipid profile of cull beef cows reared in extensive systems across various seasons. Mature beef cows (n=65) with mean age of 14.12 years and culled from commercial farms were slaughtered in the Spring, Summer, Autumn and Winter, after a finishing period of about 4 weeks. The meat quality traits were analyzed at 7 d postmortem in Longissimus thoracis, Longissimus lumborum, Semimembranosus, Psoas major and Semitendinosus muscles. The highest carcass yield was obtained in Winter (P <0.05), but the Intramuscular Fat (IMF) means were similar in the different seasons. The meat samples showed high average Warner-Bratzler shear forceWBSF (between 5.41-6.86kg), which may be considered as tough (according to the scale used), except for the Longissimus thoracis which showed intermediate average (5.13kg). However, Psoas major obtained the highest overall acceptance scores. Samples of meat from animals kept in extensive system, natural conditions of Southern Portugal, present high amounts of n-3 PUFA. In Autumn and Summer, portions of 100 g/day of meats with 4.03% and 4.25% of IMF with 1.12 and 2.20% of n-3 PUFA in total fatty acids, can provide between 72.96 and 143.31mg of n-3 PUFA or 31.99 and 61.21mg/d of EPA plus DHA, which corresponds to 12.47% and 24.48% of the requirements recommended by EFSA authorities (250mg/d of EPA plus DHA).

106 Serial Evaluation ofA. Marginale Positivity Rate Within a Single Herd of Mature Beef Cows

Abstract Anaplasmosis is an economically devastating disease in cattle that is caused by the rickettsial pathogen Anaplasma marginale. Infected cattle can serve as biological reservoirs for the organism, thus enabling further transmission of the disease to naive individuals via ticks, biting flies and contaminated needles. It is estimated that this disease causes over $300 million in expenses for the U.S. cattle industry annually. As a result, a better understanding of this disease and its prevalence is needed. As part of an ongoing collaborative effort between the University of Arkansas and the Kansas State University (KSU) College of Veterinary Medicine, general surveillance testing of beef cattle herds in Washington county, Arkansas previously indicated a possible 30% positivity rate for A. marginale in 2019. The objective of this study was to utilize both quantitative polymerase chain reaction (qPCR) and competitive enzyme-linked immunosorbent assay (cELISA) tests to determine the whole-herd prevalence of A. marginale within the University of Arkansas Washington county research herd. In the fall of 2020, the entire fall-calving herd (168, apparently healthy, mature beef cows) was sampled and tested. Both whole blood and serum samples were collected from each animal. qPCR testing was completed on each whole blood sample submitted at the KSU College of Veterinary Medicine, while cELISA testing was completed on each serum sample by the University of Arkansas. Of the68 cows tested, 20 cows tested seropositive, with a % Inhibition of 30 or above (mean = 45%). Confirmatory qPCR testing on all seropositive samples, however, indicated that all cows were negative for active infection with A. marginale. Subsequently, in the spring of 2022, all available cows that had previously tested seropositive for A. marginale were retested using the same protocol as previously described, except that all qPCR testing was completed by University of Arkansas Veterinary Entomology Lab. Of the 17 mature cows still in inventory, that had previously tested seropositive for A. marginale, only 7 were still seropositive with a % inhibition of 30 or above (mean = 39%). However, confirmatory qPCR testing on all 7 seropositive samples indicated that all cows were negative for active infections with A. marginale. Because of its lower cost, compared with qPCR testing, ELISA testing is commonly recommended to and utilized by producers and veterinarians as a first-line diagnostic for individual and herd health evaluation and management. Information gathered by this study indicates that cELISA testing alone may not provide an accurate depiction of actual infection rates within a herd, and that further investigation into possible causes of false positivity are required. As part of this study, additional assays investigating the specificity of the commercial Anaplasmosis cELISA and possible cross-reaction with other endemic rickettsial pathogens will be performed.

136 Relationship of Mature Beef Cows on an Unprocessed Hay Diet to Residual Intake and Greenhouse Gas Exchange During Gestation and Lactation

Abstract The objective of this study was to compare residual feed intake (RFI) and greenhouse gas exchange in mature beef cows during gestation and lactation when consuming an unprocessed, grass hay diet. Twenty-six mature Angus and Angus x Hereford cows (4.5 ± 0.0 yr) were used in two voluntary intake studies. Cows were evaluated during mid-gestation (GEST) and late lactation (LACT). Unprocessed grass hay (GEST = 8.73% CP and 59.25% TDN; LACT = 8.31% CP and 54.50% TDN) and a mineral mix were provided for ad libitum consumption. Individual animal feed intake data was collected for 52 d and 71 d for GEST and LACT respectively using SmartFeed intake units (C-Lock Inc., Rapid City, SD) and a stocking rate of 3 cows per feeder. An open-circuit, gas-quantification system (GreenFeed, C-Lock Inc., Rapid City, SD) was used to collect CH4 production for 9 days per pen for a minimum of 20 visits per cow. Hay intake averaged 13.8 ± 2.3 kg and 16.6 ± 2.0 kg during GEST and LACT, respectively. The Pearson correlation coefficient for hay intake among the two stages of production was 0.65 (P < 0.01). Metabolic body weight, average daily gain, and ultrasound ribeye area explained 46% of the variation in GEST DMI (P < 0.01), and milk yield, metabolic body weight, and average daily gain explained 64% of the variation in LACT DMI (P < 0.01). Each one kg additional milk production resulted in 0.7 kg greater hay intake during LACT (P < 0.01). There was a moderate correlation between GEST and LACT CH4 (r = 0.64) and a moderate correlation between CH4 production within each stage of production and DMI for that same stage of production (r = 0.58 and 0.63 for GEST and LACT, respectively). Hay intake was moderately correlated between stages of production although highly sensitive to milk yield.

Phenotypic and genetic relationships for feed intake, feed efficiency, body composition and cow milk yield measured postweaning and in mature beef cows

Context Providing feed is the largest cost in beef production. Genetic variation exists in feed efficiency traits in young cattle but the genetic associations with feed efficiency traits in cows are poorly understood, but if strong and favourable, they might be used to improve feed efficiency of cows. Aim To examine the phenotypic and genetic relationships among feed intake, feed efficiency, body composition and cow milk yield measured in young cattle and in cows. Methods Data on 1783 young Angus, Hereford, Polled Hereford and Shorthorn bulls and heifers, and for 751 of the females as cows, were used to calculate the phenotypic and genetic relationships among feed efficiency traits, body composition and cow milk yield measured postweaning and in mature cows. The young cattle were tested for feed intake and feed efficiency at approximately 9 months of age and the females, after two calvings, were tested again as non-pregnant, non-lactating cows at approximately 4 years of age. Key results At the postweaning test, the heritability estimates for feed intake, average daily gain, test weight, residual feed intake (RFI), feed conversion ratio, rump fat depth and eye-muscle area were 0.47, 0.32, 0.46, 0.42, 0.28, 0.47 and 0.20 respectively. Corresponding heritability estimates in the cow test were 0.27, 0.35, 0.74, 0.22, 0.30, 0.47 and 0.12. Heritability estimates for 400-day weight, cow 4-year weight and cow milk yield were 0.47, 0.62 and 0.15 respectively. Genetic correlations between traits measured postweaning and the same traits measured in the cow were moderate to high, and for the feed efficiency trait, RFI, was very high (0.95), close to unity. Conclusions Inclusion of postweaning RFI as a selection criterion in beef cattle breeding can be expected to lead to improvement in cow feed efficiency. Implications Most breeding decisions in beef cattle are based on traits measured early in life and for replacement heifers are made with an aim to improve their productivity and profitability as cows. The strong and favourable associations measured between postweaning RFI and cow RFI mean that feed efficiency measured in young cattle can be used as a selection trait to improve cow feed efficiency.

Estimating body weight and body condition score of mature beef cows using depth images.

Obtaining accurate body weight (BW) is crucial for management decisions yet can be a challenge for cow-calf producers. Fast-evolving technologies such as depth sensing have been identified as low-cost sensors for agricultural applications but have not been widely validated for U.S. beef cattle. This study aimed to (1) estimate the body volume of mature beef cows from depth images, (2) quantify BW and metabolic weight (MBW) from image-projected body volume, and (3) classify body condition scores (BCS) from image-obtained measurements using a machine-learning-based approach. Fifty-eight crossbred cows with a mean BW of 410.0 ± 60.3 kg and were between 4 and 6 yr of age were used for data collection between May and December 2021. A low-cost, commercially available depth sensor was used to collect top-view depth images. Images were processed to obtain cattle biometric measurements, including MBW, body length, average height, maximum body width, dorsal area, and projected body volume. The dataset was partitioned into training and testing datasets using an 80%:20% ratio. Using the training dataset, linear regression models were developed between image-projected body volume and BW measurements. Results were used to test BW predictions for the testing dataset. A machine-learning-based multivariate analysis was performed with 29 algorithms from eight classifiers to classify BCS using multiple inputs conveniently obtained from the cows and the depth images. A feature selection algorithm was performed to rank the relevance of each input to the BCS. Results demonstrated a strong positive correlation between the image-projected cow body volume and the measured BW (r = 0.9166). The regression between the cow body volume and the measured BW had a co-efficient of determination (R2) of 0.83 and a 19.2 ± 13.50 kg mean absolute error (MAE) of prediction. When applying the regression to the testing dataset, an increase in the MAE of the predicted BW (22.7 ± 13.44 kg) but a slightly improved R2 (0.8661) was noted. Among all algorithms, the Bagged Tree model in the Ensemble class had the best performance and was used to classify BCS. Classification results demonstrate the model failed to predict any BCS lower than 4.5, while it accurately classified the BCS with a true prediction rate of 60%, 63.6%, and 50% for BCS between 4.75 and 5, 5.25 and 5.5, and 5.75 and 6, respectively. This study validated using depth imaging to accurately predict BW and classify BCS of U.S. beef cow herds.

PSIII-4 Late-Breaking: Genetic Marker Association Study of Heifer Pregnancy in Red Angus Cattle

Abstract Heifer pregnancy (HPG) is lowly heritable, yet economically relevant in beef cattle production systems. Hence, identifying single nucleotide polymorphisms (SNP) associated with phenotype could increase the amount of information used in the genetic evaluation of the trait. Using RNA-sequence data from lactating Holstein cows, a set of SNP (n = 69) were discovered among embryo mortality conceptuses (Conceptus-SNP) associated with maternal recognition of pregnancy on day 16 after artificial insemination (AI). To further study these SNP, our objective was to conduct analyses to identify markers associated with HPG in Red Angus. Phenotypic records and genotypes were provided by the Red Angus Association of America (RAAA). For phenotypes, a total of 59,387 cattle records, from the June 2022 RAAA genetic evaluation, were used in the analysis. For genotype data, a 47,860 SNP panel (excluding SNP on the X-chromosome) were formed by combining the historical RAAA genotype data (96,162 animals with genotypes) and genotypes from whole genome sequence of 30 prominent Red Angus AI sires. Markers were mapped to the ARS-UCD1.2 bovine reference genome and then imputed to 47,860 SNP panel using findhap software. A subset of SNP (n = 2,169 SNP; Conceptus-SNP and the multi-breed selected reduced panel [MSRP]) were extracted from the imputed genotypes file. Using PLINK software, genotype quality control procedure was performed so that animals with call rate < 0.9 were removed. A marker was removed if: it had minor allele frequency < 0.01, not in Hardy–Weinberg equilibrium (P < 0.00001), or in high linkage disequilibrium (r2 > 0.95). The final genotype file contained 96,667 animals with 2,137 SNP. A Bayes Cπ single-step super hybrid model (π = 0.99), using the BOLT software package, was used to estimate marker’s posterior probability of inclusion (PPI), the marker significance criterion in predicting HPG. A marker’s PPI was calculated as the average probability from four different Gibbs sampling chains of 75,000 iterations that included 5,000 iterations as burn-in. Markers rs42576394 (18:60583784) and rs42942055 (14:34249373) had PPI of 25.5 and 7.1%, respectively; suggesting association with HPG. None of the Conceptus-SNP had a detectable association with HPG; however, these Conceptus-SNP may be much more informative for genotype to phenotype association analyses for the trait of stayability. Such a trait would be measured with lactating mature beef cows and potentially more similar to the lactating Holstein cows from which the markers were discovered.

PSXIII-8 Grazing Behavior of Cows Grazing Natural Grassland Under Silvopastoral Systems or Full sun

Abstract The objective of this study was to evaluate the grazing behavior of mature beef cows grazing natural grassland in silvopastoral systems (SPS) in comparison with pasture systems in full sun (FS) during the austral summer in South America. A total of fifty-five Braford crossbred multiparous suckled cows (352 ± 43 kg) were randomly assigned to two treatments, with two replicates, in a complete randomized design: SPS (n=28) and FS (n=27). Global positioning system (GPS) devices were placed in six randomly selected cows per treatment (three per replicate) to track geolocation every five minutes during five consecutive days. Data were analyzed using the Java program GRAZEACT to determine total distance traveled (km), area explored (ha), and animal activities (h/d). Type of animal activity was defined by GRAZEACT based on movement velocity, being categorized as: resting (velocities< 3 m/min), grazing (3< velocities< 25 m/min), and traveling (velocities >25 m/min). Each of these variables were automatically calculated for four time periods: Night Pre-Dawn hours (00:00-06:00 h), Daytime hours (06:00-20:00 h), Night Post-Sunset hours (20:00-24:00 h), and 24 h. There was a treatment effect for distance traveled, explored area, grazing and resting in the 24 h period (P ≤ 0.0154). Specifically, cows grazing SPS had a greater distance traveled (P = 0.044) and area explored (P < 0.0001) during the daytime hours compared to cows grazing FS. In accordance to this, for the same period, SPS cows had lesser resting time (P < 0.0001) and spent an extra 1.5 h grazing (P < 0.0001) compared with their FS counterparts. In conclusion, SPS changed spatial and temporal grazing behavior. The provision of shade by SPS allowed a greater grazing activity through the daytime hours, period associated with greater temperatures during summer, most-likely by improving thermal comfort of animals.

The glutamate metabotropic receptor 5 (GRM5) gene is associated with beef cattle home range and movement tortuosity

BackgroundThe grazing behaviour of herbivores and their grazing personalities might in part be determined genetically, but there are few studies in beef cattle illustrating this. In this study, we investigated for first time the genetic variation within a candidate ‘grazing gene’, the glutamate metabotropic receptor 5 gene (GRM5), and tested associations between variation in that gene and variation in grazing personality behaviours (GP-behaviours) displayed by free-ranging cows during winter grazing in the steep and rugged rangelands of New Zealand. Mature beef cows (n = 303, from 3 to 10 years of age) were tracked with global positioning system (GPS) and, with 5-minutes (min) relocation frequency, various GP-behaviours were calculated. These included horizontal and vertical distances travelled, mean elevation, elevation range, elevation gain, slope, home range and movement tortuosity, variously calculated using daily relocation trajectories with repeated measurements (i.e., 7 to 24 days (d)) and satellite-derived digital elevation models (DEM). The different GP-behaviours were fitted into mixed models to ascertain their associations with variant sequences and genotypes of GRM5.ResultsWe discovered three GRM5 variants (A, B and C) and identified the six possible genotypes in the cattle studied. The mixed models revealed that A was significantly associated with elevation range, home range and movement tortuosity. Similarly, GRM5 genotypes were associated (P < 0.05) to home range and movement tortuosity, while trends suggesting association (P < 0.1) were also revealed for elevation range and horizontal distance travelled. Most GP-behaviour models were improved by correcting for cow age-class as a fixed factor. The analysis of GP-behaviours averaged per cow age-class suggests that grazing personality is fully established as beef cows reached 4 years of age. Home range and movement tortuosity were not only associated with GRM5 variation, but also negatively correlated with each other (r = − 0.27, P < 0.001).ConclusionsThere seems to be a genetically determined trade-off between home range and movement tortuosity that may be useful in beef cattle breeding programmes aiming to improve the grazing distribution and utilisation of steep and rugged rangelands.

133 Ranking Mature Beef Cows for Residual Intake Using an Unprocessed Grass Hay Diet and Its Relationship to Greenhouse Gas Exchange

Abstract The objective of this study was to compare high and low residual feed intake (RFI) beef cows when consuming an unprocessed, grass hay diet (93% DM, 8.73% CP, 2.11 Mcal ME, and 59.25% TDN). Relationships of hay intake to carbon dioxide (CO2) and methane (CH4) production were also evaluated. Thirty-six mature Angus and Angus x Hereford cows were assigned randomly to five pens (n = 6 or 9) and individual feed intakes were collected for 52-d using SmartFeed intake units (C-Lock Inc., Rapid City, SD) at a stocking rate of 3 cows per feeder. An open-circuit, gas-quantification system (GreenFeed, C-Lock Inc., Rapid City, SD) was used to collect CO2 (7611.63±714.09 g) and CH4 (283.64±37.10 g) production for 9 days of collection per pen for a minimum of 20 visits per cow (n = 22 cows, 36.18±14.24 visits). Data collection on cows included (means ± SD) dry matter intake (DMI; 13.86±2.16 kg), metabolic body weight (MBW, 111.65±9.28 kg), average daily gain (ADG, 0.77±0.29 kg), and rib eye area by ultrasound (REA, 46.62±6.34 cm).To calculate RFI (0.03±1.71), a multiple regression model was used to predict DMI (PDMI = ADG + REA + MBW; R2=0.50, P = 0.001). Cows were categorized into three RFI classes: low (n = 7), moderate (n = 6), and high (n = 9). Differences between RFI and RFI class and DMI and RFI class were analyzed using PROC MIXED in SAS (SAS, Cary, NC). Low RFI cows (-1.81 kg) consumed 12.08 kg hay DM daily and high RFI cows (1.59 kg) consumed 15.27 kg hay DM daily (P &amp;lt; 0.001). Correlations between DMI and daily gas exchange were estimated using PROC CORR in SAS (SAS, Cary, NC). Pearson Correlation Coefficients were significant between DMI and CO2 (r=0.58, P = 0.004), and CH4 (r=0.70, P &amp;lt; 0.001) production. Differences in feed intake for high and low RFI rankings were similar to previously reported literature when growing cattle consumed energy-dense diets.

Immuno-phenotyping of Canadian beef cattle: adaptation of the high immune response methodology for utilization in beef cattle.

The high immune response (HIR) methodology measures the genetic performance of the adaptive immune system to identify and breed animals with balanced and robust immunity. The HIR methodology has previously been used in dairy and swine to reduce disease but has not been fully investigated in beef cattle. The first objective of the current study was to examine whether the HIR methodology as standardized for use in dairy cattle was appropriate for use in beef cattle. The second objective was to determine the earliest age for immune response phenotyping of beef calves. In this study, beef calves (n = 295) of various ages, as well as mature beef cows (n = 170) of mixed breeds, were immunized using test antigens to assess their antibody- (AMIR) and cell-mediated immune responses (CMIR). Heritability for AMIR and CMIR was estimated at 0.43 and 0.18, respectively. The HIR methodology was appropriate for use in beef cattle; beef calves as young as 2–3 wk of age were capable of mounting AMIR responses comparable with those seen historically in mature Holstein dairy cows. Three-week-old beef calves mounted CMIR responses comparable with those of Holstein cows, but 9-mo-old calves and mature beef cows had significantly higher CMIR responses than Holsteins. The HIR methodology can be used to measure both AMIR and CMIR in beef calves as young as 3 wk of age.

An assessment of global ruminant methane-emission measurements shows bias relative to contributions of farmed species, populations and among continents

Global ruminant methane (CH4)-mitigation strategies rely on data from in vivo CH4-emission measurements. This survey of 415 peer-reviewed studies of in vivo enteric-CH4 measurements from farmed ruminants details research objectives, diets, and methodology as well as groups within ruminant species. The survey results have been evaluated in relation to ruminant population data and the contributions of each species to CH4 emissions. Despite the highest estimated total CH4 emissions from ruminants in Asia, South America and Africa (accounting for 37%, 23% and 17% of total enteric-CH4 emissions respectively), the number of in vivo studies of CH4 measurements were 15%, 9% and 1% of global studies respectively. Globally, the most studied species were cattle (64%) and sheep (22%), whereas goats and buffalo accounted for 7% and 5% of studies respectively. These species account for 75%, 7%, 5% and 12% of total enteric-CH4 emissions respectively. Most cattle studies were with Bos taurus and only 12% of the cattle studies were with Bos indicus. Respiration chambers have been used in 51% of studies and, despite the development of other methodologies, they remain the dominant technique for measurement of enteric-CH4 production. Most studies involved animals fed high-forage diets; these were 56% of the studies with cattle, 73% with sheep, 47% for goats, but only 15% of studies with buffalo. The evaluation of diets as a mitigation strategy was the prime objective of all regions. The number of studies that have measured CH4 from cattle aligns with their contribution to enteric emissions; however, buffalo, Bos indicus cattle and mature beef cows were under-represented relative to their global populations and contribution to global emissions. Dominance of measurements from cattle was evident in all continents.

A mathematical nutrition model adequately predicts beef and dairy cow intake and biological efficiency.

The beef cow-calf sector accounts for 70% of feed consumed and greenhouse gases emitted for the beef industry, but there is no straightforward method to measure biological efficiency in grazing conditions. The objective of this study was to evaluate a mathematical nutrition model to estimate the feed intake and biological efficiency of mature beef cows. Data from dams (N = 160) and their second and third progeny (312 pairs) were collected from 1953 through 1980. Individual feed intake was measured at 28-d intervals year-round for dams and during 240-d lactation for progeny. Body weights of progeny were measured at 28-d intervals from birth to weaning, and of dams at parturition and weaning each production cycle. The milk yield of dams was measured at 14-d intervals. Dam metabolizable energy intake (DMEI) and milk energy yield (MEL) of each cow were predicted using the Cattle Value Discovery System beef cow (CVDSbc) model for each parity. Biological efficiency (Mcal/kg) was computed as the ratio of observed or predicted DMEI to observed calf weaning weight (PWW). Pearson correlation coefficients were computed using corr.test function and model evaluation was performed using the epiR function in R software. Average (SD) dam weight, PWW, DMEI, and observed MEL were 527 (86) kg, 291 (47) kg, 9584 (2701) Mcal/production cycle, and 1029 (529) Mcal, respectively. Observed and predicted DMEI (r = 0.93 and 0.91), and observed and predicted MEL (r = 0.58 and 0.59) were positively correlated for progeny 2 and 3, respectively. The CVDSbc model under-predicted DMEI (mean bias [MB] = 1,120±76 Mcal, 11.7% of observed value) and MEL (MB = 30±25 Mcal, 2.9% of observed value). Observed and predicted progeny feed intake were not correlated (r = 0.01, P-value = 0.79). Observed and predicted biological efficiency were positively correlated (r = 0.80 and 0.80, P-value ≤ 0.05) for parity 2 and 3, respectively, and the CVDSbc model under-predicted biological efficiency by 11% (MB = 3.59±0.25 Mcal/kg). The CVDSbc provides reasonable predictions of feed intake and biological efficiency of mature beef cows, but further refinement of the relationship between calf feed intake and milk yield is recommended to improve predictions. Mathematical nutrition models can assist in the discovery of the biological efficiency of mature beef cows.

PSXIII-29 Late-Breaking: Relationships between feed efficiency traits, gas emissions, and calculated heat production and respiratory quotients in mature beef cows

Abstract This research evaluated relationships between feed efficiency measurements including residual feed intake (RFI), gain to feed ratio (G:F) and enteric gas production of methane (CH4), carbon dioxide (CO2), oxygen, (O2) along with calculated respiratory quotient (RQ) and heat production (HP) of mature beef cows. Sixty pregnant multiparous Angus beef cows were measured for individual intake for 10 weeks leading up to parturition. Cows were individually fed using the Insentec feeding system to measure individual feed intake. Pens of cows were rotated weekly to the C-Lock Greenfeed trailer (C-Lock Inc.) to measure gas production for a minimum 2 periods per group. Cows were weighed, body condition scored, and ultrasound performed for rib and rump fat depth every 28 days and calf birth weight was recorded. Pearson correlations were conducted to determine relationships between gas exchange measurements and feed efficiency measures. The model for RFI included ADG, pregnancy corrected BW, and ultrasound measures of rib and rump fat (R2= 0.32). Methane emissions were 263±40.3 g CH4/d in dry lot, and daily enteric CH4 emissions per kg of pregnancy corrected body weight ranging from 0.26 to 0.53 g CH4/kg pcBW. Pearson correlations found positive correlations between DMI and CH4 and CO2 (P ≤ 0.001). Pregnancy corrected BW was also positively correlated with total O2 consumption and calculated HP (P ≤ 0.001) and negatively correlated with RQ (P = 0.04). However, RFI and feed conversion ratio were not significantly correlated with gas measurements, or calculated HP or RQ (P ≥ 0.1), although DMI/kg of BW tended (P = 0.098) to be negatively correlated with O2 consumption. In conclusion, accurately identifying feed efficiency in mature beef cows continues to be a challenge. However, the inclusion of gas exchange measures and calorimetry measurements may be able to better assess metabolic efficiency in mature beef cattle.

190 Winter vs. year-round supplementation of mature beef cows on feedlot performance and carcass characteristics of steer progeny

Abstract This study evaluated the effects of year-round supplementation of molasses/urea or wheat middlings-based range cubes to mature cows on subsequent feedlot growth, immunity, and carcass characteristics of their steer progeny. On d 0, 82 mature Brangus cows were stratified by BW and BCS (433 ± 47 kg; 4.6 ± 0.77) and randomly allocated into 1 of 6 bahiagrass pastures (13–14 cows/pasture). Treatments were randomly assigned to 2 pastures/treatment and consisted of supplementation with molasses/urea during winter (MOL-W), or year-round supplementation with molasses/urea (MOL-Y) or range cubes (CUB-Y). Supplements were isocaloric and isonitrogenous (75% TDN, 20% CP; DM basis) and offered at a total yearly supplement DM amount of 272 kg/cow. On d 423, all calves were weaned, and 33 steers were randomly selected for the feedlot phase. Steers were penned based on cow prepartum pasture distribution and managed similarly until slaughter (d 661). Data were analyzed as complete randomized design using MIXED procedure of SAS, pasture as the experimental unit, treatment as fixed effect, and pasture(treatment) and steer(pasture) as random effects. Dry matter intake did not differ (P ≥ 0.70), but MOL-Y and MOL-W steers had greater (P = 0.05) overall ADG vs. CUB-Y steers. Plasma haptoglobin concentrations tended (P = 0.06) to be greater for CUB-Y vs. MOL-W, and intermediate for MOL-Y. Serum titers against bovine viral diarrhea virus-1 and parainfluenza-3, hot carcass weight, REA, and YG did not differ (P ≥ 0.16) among treatments, but back fat thickness was greater (P = 0.03) for MOL-W vs. MOL-Y and CUB-Y. The percentage of carcasses grading Choice did not differ (P = 0.35) among treatments, but more carcasses tended (P = 0.08) to grade low Choice for MOL-W vs. CUB-Y and MOL-Y. Therefore, providing molasses/urea supplementation to mature beef cows during winter only or year-round increased steer post-weaning feedlot performance and carcass quality compared to steers born from cows offered year-round supplementation with range cubes.

Clinical effectiveness of enrofloxacin 100 mg/mL injectable solution for the treatment of acute anaplasmosis in cattle caused by Anaplasma marginale

Anaplasma marginale is a gram-negative rickettsial pathogen that can cause clinical anemia and death in cattle. The objective of this study was to evaluate the effectiveness of enrofloxacin (ENR) 100 mg/mL at a single subcutaneous dose of 5.7 mg/lb (12.5 mg/kg) for treatment of acute anaplasmosis (ANA) in mature beef cows (n=67). Following intravenous inoculation with A. marginale-infected blood, cattle were monitored for clinical signs of ANA. Upon meeting case criteria, cattle were randomly assigned to receive ENR or saline (SAL). Treatment success, defined as 28 d post-treatment survival and resolution of abnormal clinical scores, was 81.8% (27/33) and 44.1% (15/34) (P=0.0032) for ENR and SAL treated cows, respectively. Mortality was 47% (16/34) and 3% (1/33) in SAL and ENR, respectively (P=0.0027). Packed cell volume at 7, 14, 21, and 28 d post-treatment was significantly greater in ENR compared to SAL (P&lt;0.05). In this study, ENR improved treatment success compared to SAL, reduced ANA mortality, and maintained greater packed cell volumes post-clinical signs compared to SAL. Extra-label use of fluoroquinolones in food animals is prohibited in the United States, but ENR (Baytril® 100-CA1) was recently conditionally approved for treatment of ANA.

299 Treatment with prostaglandin F2α and an intravaginal progesterone insert in advance of gonadotropin-releasing hormone enhances response to estrus synchronization in mature beef cows

Abstract An experiment was designed to evaluate the effect of treatments in advance of gonadotropin-releasing hormone (GnRH; 100μg gonadorelin) administered at the start of estrus synchronization. We hypothesized that administration of prostaglandin F2α (PG; 500μg cloprostenol) followed by treatment with an intravaginal progesterone-releasing insert (CIDR; 1.38g progesterone) would result in increased follicle size at GnRH, thereby enhancing response to GnRH and overall response to estrus synchronization. Postpartum suckled beef cows (n = 183) in two locations were assigned to one of five treatments based on age, days postpartum, and body condition score. Treatments (Figure 1) were designed as a two-by-two factorial with a control (Treatment 1). Treatments 2–5 received a CIDR insert from Day -17 to Day -10, with (Treatments 2 and 3) or without (Treatments 4 and 5) administration of PG coincident with CIDR insertion on Day -17. Coincident with GnRH administration on Day -10, CIDR inserts were either removed (Treatments 2 and 4) or remained in place until Day -3 (Treatments 3 and 5). On Day -3, estrus detection aids were applied and a representative subset of cows in each treatment were fitted with estrus detection transmitters. Blood samples were collected on Days -27, -17, -10, -3, and 0 for determination of serum estradiol and/or progesterone concentrations via radioimmunoassay. For a representative subset of cows (n = 111), transrectal ovarian ultrasound was performed to assess ovarian follicle size and presence of corpora lutea on Days -17, -10, -3, and 0. Treatment with PG and CIDR in advance of GnRH resulted in improvements (P &amp;lt; 0.05) in several response variables, including follicle size on Day -17 and estrous response prior to AI. Results support the hypothesis that administration of PG and treatment with a CIDR for 7 d prior to GnRH improves likelihood of GnRH response and enhances response of mature cows to estrus synchronization.