Days On Feed Research Articles

51 Lean meat yield of Angus, Brahman and Charolais grain fed steers

Abstract Lean meat yield (LMY) is a key driver of profitability in the beef industry, and it is associated with muscling and feed efficiency (Pethick et al., 2021). No research has studied differences in LMY between British, Continental, and Tropical beef breeds fed for increasing days on feed. The objective of the present study was to compare LMY of Angus, Brahman and Charolais steers with increasing days on feed (DOF). The hypothesis was that Charolais have the greatest LMY throughout the feeding period due to being a later maturing, high muscling breed compared with Angus and Brahman. Angus (n = 30), Brahman (n = 30), and Charolais (n = 29) 12-18 mo-old steers were inducted with a body weight (BW) of 361 ± 5.3 kg, 355 ± 5.3 kg and 317 ± 5.3 kg, respectively. Six animals of each breed were randomly selected for slaughter at 50-d intervals until 200 DOF. Steers were allowed ad libitum access to water and feed (78% rolled barley, 13.76% CP, 12.15 ME MJ/kg DM). Body weight, hot carcass weight (HCW), and LMY were measured at slaughter. All components of the animal were collected, and carcass muscle, fat and bones physically dissected with knives and weighed separately. The LMY as % empty BW (EBW) was calculated as the weight of lean meat separated from the carcass divided by EBW. The LMY as % of HCW was calculated as the weight of lean meat separated from the carcass divided by HCW. Data was analyzed with a model containing the fixed effect of breed, DOF at slaughter, and their interaction. Breed, DOF and their interaction affected LMY expressed as both ratio to EBW and HCW (P < 0.05). Charolais steers had the greatest LMY (% HCW) at 50, 100, and 150 DOF, but similar to Brahman at 0 and 200 DOF (P < 0.05; Figure 1a). Angus steers showed the lowest LMY (% HCW) throughout all DOF (P < 0.05) except at 50 DOF being similar to Brahman (P > 0.05). Furthermore, Charolais had the greatest LMY (% EBW) from 50 to 200 DOF (P < 0.05) but it was similar to Brahman at 0 DOF (Figure 1b; P > 0.05). Angus had the least LMY (% EBW) throughout (P < 0.05) but was not different to Brahman at 50 DOF. Brahman had intermediate LMY (% EBW and % HCW) between Charolais and Angus. Differences between beef breeds suggest that LMY should be considered as another factor to establish an accurate carcass value.

367 Changing the conversation: Evaluating feedyard closeouts and the beef system on a carcass basis

Abstract Beef cattle genetics, management, technologies and nutritional strategies are ever evolving, and current US trends favor feeding cattle to heavier carcass endpoints and optimizing quality grade. The average number of days on feed (DOF) in the US has increased year after year, averaging 195 and 183 DOF for steers and heifers, respectively, as reported by Elanco Benchmark data in 2021. As DOF increase, cattle live performance, including average daily gain and feed efficiency decline; however, hot carcass weight (HCW) becomes significantly heavier. Although a reduction in live feed conversion occurs as cattle are fed for extended DOF, the kilograms of additional live gain that result as kilograms of gain on the carcass, termed carcass transfer, increase linearly. As DOF are extended, carcass transfer has been reported to increase up to 88 %. As a result of genetic advancements, technologies, and feeding longer, HCW has trended heavier over the last 60 yr, with 2024 USDA HCW reported for April as 11.3 and 9.5 kg heavier for steers and heifers, respectively, year after year. According to mandatory price reporting data, approximately 74 % of fat cattle marketed in the US are sold as dressed beef. As we continue to feed to heavier endpoints and longer DOF, the profitability of selling on a carcass-basis increases. With the increase in carcass transfer as DOF extend, this presentation will attempt to address that cattle live performance should be adjusted to a carcass-basis for feedyards to appropriately capture the inflection point at which cost of additional gain equals the price received for the additional gain.

76 Camera vision grading and objective tenderness outcomes of steers fed lubabegron fumarate for the final 56 d of the feeding period

Abstract Limited research has compared no beta-agonist, ractopamine and lubabegron in feedlot cattle. We evaluated carcass quality and yield variables using a camera grading instrument and also examined objective tenderness outcomes. Treatments were negative control (no beta-ligand; CON), Optaflexx (ractopamine hydrochloride, 300 mg·steer-1·d-1 for 35 d; OPT), and Experior (lubabegron fumarate, 36 mg·steer-1·d-1 for 56 d + 4 d removal; 0EXP) fed for 198 d. Additional EXP treatments investigated total days on feed (DOF) of 184 d (-14EXP), 212 d (+14EXP) and 226 d (+28EXP). Carcasses (n = 2,517) were instrument graded 24 h post-mortem. Longissimus tenderness and lipid content were evaluated in a subset (n = 361) of carcasses via slice shear force and ether extract. Statistical analyses were conducted using mixed models; pen was the experimental unit, treatment was the fixed effect, block was a random effect, and means were separated with the Tukey-Kramer adjustment. Longissimus muscle area (LMA) was 4.0 to 6.2 cm2 larger (P < 0.01) for steers fed EXP compared with CON, which did not differ from OPT. Weight corrected LMA (LMA:HCW) was 1.3 cm2/100 kg larger (P < 0.01) for -14EXP compared with CON. Marbling score was 31 to 39 points lower (P < 0.01) for -14EXP compared with CON and OPT, whereas 0EXP, +14EXP and +28EXP were similar to CON and OPT. Total number of fat pieces within the longissimus did not differ (P = 0.11) across treatments, however number of fat pieces in the lateral one-half of the longissimus decreased (P ≤ 0.03) for -14EXP and +28EXP, whereas +14EXP tended (P = 0.09) to decrease compared with CON. Total meat area was 3.7 percentage points greater (P < 0.01) for -14EXP compared with CON; +14EXP and +28EXP tended (P = 0.07) to be greater than CON. Total fat area was 1.6 to 1.8 percentage points less (P ≤ 0.02) for 0EXP, +14EXP, and +28EXP when compared with CON. Compared with CON, dorsal-ventral longissimus distance increased (P < 0.01) by 3.3 to 5.4% for -14EXP, 0EXP, +14EXP and +28EXP. Medial-lateral longissimus distance increased 1.9 to 2.5 % (P < 0.01) for +14EXP and +28EXP compared with CON, whereas -14EXP tended (P = 0.08) to increase. Percentage intramuscular fat (IMF) was similar (P ≥ 0.44) for +14EXP, +28EXP, and OPT compared with CON, whereas 0EXP tended (P = 0.09) to be less. Marbling score and IMF were moderately correlated (r = 0.66). Slice shear force values were 20.1% greater (P < 0.02) for +14EXP compared with CON, whereas 0EXP tended (P = 0.09) to be greater and +28EXP, -14EXP and OPT were similar (P ≥ 0.28) to CON. These findings illustrate the effect of EXP on carcass traits and tenderness in feedlot cattle.

328 Assessment of chronically ill or injured feedlot cattle populations at eight United States and nine Canadian feedlots and implications for cattle welfare

Abstract Cattle health management in the feedlot sector continues to evolve and improve cattle welfare by promoting an understanding of illness and injury to minimize their effects. Many papers have focused on treating individual ill or injured cattle in cattle feeding facilities. However, care, treatment, and outcomes for chronically ill or injured cattle (“chronic cattle”) have received little attention in the literature. The purpose of this descriptive study was to present demographics, diagnoses, and outcomes of chronic cattle in 17 feedlots in the U.S. and Canada and discuss potential risk factors and welfare implications. Individual chronic cattle information and treatment records from 17 feedlots (U.S.: 8; Canada: 9) over 7 yr (2014 – 2020) were retrospectively retrieved from a large feedlot consulting and data-management service (Feedlot Health Management Services, a division of TELUS Agriculture Solutions Inc.). Chronic cattle were defined as those that had spent time in a feedlot’s designated chronic pen. Descriptive results are presented as means ± standard deviations. U.S. feedlots averaged 31,280 ± 23,231 cattle/yr, had an average chronicity rate of 2.24 ± 2.42 % (median 1.53%), and contributed 52,709 chronic cattle to the dataset. Canadian feedlots averaged 21,913 ± 10,497 cattle/yr, had an average chronicity rate of 1.41 ± 0.82% (median 1.10%), and contributed 15,940 chronic cattle to the dataset. U.S. chronic cattle were sourced across all seasons primarily from auctions and ranches, had an average arrival weight of 163 ± 59 kg, and an average days on feed (DOF) of 362 ± 172 d. Canadian chronic cattle were primarily auction-sourced in the fall, weighed 272 ± 95 kg at arrival, and averaged 246 ± 141 DOF. Chronic cattle were treated at least once for respiratory issues (U.S.: 46.3%; Canada: 26.9%), bullers (U.S.: 34.5%; Canada: 5.8%), musculoskeletal issues (U.S.: 2.2%; Canada: 1.4%), lameness (U.S.: 1.7%; Canada: 28.1%), metabolic issues (U.S.: 0.5%; Canada: 4.5%), or other diagnoses (U.S.: 2.2%; Canada: 6.3%), with many cattle treated for multiple issues (U.S.: 12.5%; Canada: 27.0%). Outcomes for chronic cattle were shipped (U.S.: 73.1%; Canada: 52.5%), railed (U.S.: 8.1%; Canada: 20.7%), euthanized (U.S.: 0.7%; Canada: 9.9%) died unassisted (U.S.: 18.1%; Canada: 16.2%), or transferred (U.S.: < 0.1%; Canada: 0.8%). These results are some of the first to describe chronic cattle populations and present interesting trends for further analysis. For example, differences in buller and lameness rates could reflect actual differences but may be artifices of the dataset and feedlot definitions. Additionally, high marketed cattle rates (shipped and railed) indicate positive outcomes for most cattle, but variable mortality rates merit further scrutiny.

A review of foot-related lameness in feedlot cattle

Lameness is the second most prevalent morbidity in North American feedlot cattle and is both an animal welfare and economic concern. Lameness accounts for 30%–40% of all feedlot treatments with greater than 70% being foot-related lameness (FRL). This review focused on foot rot (FR), digital dermatitis (DD), and toe tip necrosis syndrome (TTNS). While there are significant study-to-study differences regarding the prevalence of FR, DD, and TTNS, it is unequivocal that FR is the most prevalent. Poor pen conditions are risk factors for both FR and DD, but the epidemiology of the two diseases is quite different. Whereas FR is diagnosed throughout the feeding period, DD typically occurs after 80 days on feed (DOF). TTNS is the least prevalent of the three FRL, but has the greatest negative effect on animal welfare and production performance. Most TTNS cases occur within 50 DOF with treatment failure leading to a significant loss in production performance and even death. This review provides an overview of the epidemiology of lameness in feedlot cattle with emphasis on the prevalence and risk factors associated with FR, DD, and TTNS.

94 Effects of orally administered Megasphaera elsdenii during finishing diet realimentation on feedlot steer fecal consistency, clinical depression, and rumination

Abstract The objective of the study was to determine the effects of oral administration of Megasphaera elsdenii NCIMB 41125 (ME) during finishing diet realimentation on fecal consistency, clinical depression, and rumination of feedlot steers. Steers [n = 60; initial body weight (BW) = 591 kg ± 38 kg] were assigned to microbial supplement treatment in a randomized complete block design. Treatments were 1) no ME (CON); and 2) orally administered microbial supplement (1 x 1010 colony forming units ME/capsule; LP) immediately before diet reintroduction. Preceding study initiation, steers consumed a finishing diet with 88% concentrate [dry matter (DM) basis] primarily consisting of whole shelled corn and corn silage for 200 d. Steers were transported from a local feedyard 27 km and upon arrival offered ad libitum long stem hay. Forty-eight h after arrival, steers were reintroduced to a 90% concentrate (DM basis) finishing diet with consisting of dry-rolled corn, dried distiller’s grains plus solubles, liquid supplement, and wheat hay. The diet was introduced initially at 1.5% BW on 0 d, and daily delivery was increased until cattle reached their intake plateau at which point a slick bunk management system was employed. At initial processing, all steers received respiratory and clostridial vaccines and were fitted with wireless rumination tags to track daily rumination throughout the 42-d study. Fecal consistency (FCS) and clinical depression scores (CD) were collected starting 24 h after diet initiation, and subsequent collections occurred at 24 h intervals until 168 h. Fecal consistency was recorded on 20 random pen surface fecal samples and CD was recorded for individual steer. Categorical distributions for FCS and CD were analyzed with the Fisher’s Exact Test. Rumination data was analyzed as a linear mixed model with fixed effects of treatment, days on feed (DOF), and their interaction with a random effect of block and DOF as a repeated measure. For all analyses, P ≤ 0.05 was declared significant and 0.05 > P ≤ 0.10 was considered a tendency. No difference (P ≥ 0.49) was observed for CD at all time points. Additionally, no difference (P ≥ 0.12) was observed for FCS at 24, 48, 72, 120, 144, and 168 h. Fecal consistency tended (P = 0.10) to differ at 96 h, with CON exhibiting a 67% decrease in FCS 1 and 2. No significant (P ≥ 0.78) treatment × DOF interaction was noted for daily minutes ruminating. A significant (P < 0.01) DOF effect was realized for daily minutes ruminating. Minutes ruminating differed (P < 0.01) between treatments, with CON steers ruminating 6% more minutes daily than LP steers. Oral administration of ME had minimal effects on FCS and CD and decreased daily rumination time in feedlot steers during finishing diet realimentation.

Carcass and non-carcass component yields of trenbolone acetate + estradiol-17β implanted steers vs. non-implanted steers across serial harvest endpoints

ObjectiveWe investigated incremental growth of carcass and non-carcass components and tissue partitioning of implanted or non-implanted steers. Materials and MethodsSteers (n = 80; 271 ± 45 kg) were paired and randomized to harvest date (d 0, 42, 84, 126, 168, 210, 252, 294, 336, or 378), and individuals within pairs were randomized to CON (negative control) or REV (Revalor-XS, Merck Animal Health, on d 0 and 190) treatments. Non-carcass components were removed, cleaned, and weighed. Growth coefficients were calculated using the allometric equation Y = bXa. Results and DiscussionEmpty body weight (EBW), and hot carcass weight (HCW) were 6% greater (P < 0.01) in REV steers versus CON. No treatment effects (P ≥ 0.12) occurred for fill or dressed carcass yield (DY); however, EBW, HCW, and DY increased (P ≤ 0.01) and percentage fill decreased as an effect of days on feed (DOF). Absolute fill weight did not change across DOF (P = 0.82). Implanted steers had greater (P ≤ 0.05) absolute mass of blood, head, hide, oxtail, liver, spleen, bladder, heart, reticulum, omasum, stomach, small intestine, intestines, gastrointestinal tract (GIT), total splanchnic tissue, and total offal. Implanted steers also had smaller (P ≤ 0.05) absolute mass of thymus glands and kidney-pelvic- heart fat (KPH) than non-implanted steers. Non-carcass components with lowest growth coefficients included small intestine (0.02), large intestine (0.12), and brain and spinal cord (0.13). However, KPH (2.01) accumulated at more than 2 times the rate of the empty body, whereas cod fat (1.42) and GIT fat (1.61) grew notably faster than the empty body. Implication and ApplicationsResults suggest that Revalor-XS increased body and carcass weights and altered many non-carcass components and their growth co- efficients, ultimately playing key biological, nutritional, and financial roles across sectors of the beef industry.

Effect of extended days on feed on carcass gain, efficiency, and quality of individually fed beef steers.

Crossbred steers (n = 114, initial BW = 334kg; SEM = 5kg) were serially harvested to evaluate the change in carcass composition by feeding cattle 21 or 42 d longer than the 2014 industry average subjective measure of finish, 1.27cm of 12th rib fat thickness. Carcass ultrasound measurements were collected on 76 steers at 1, 78, and 134 days on feed (DOF) to project appropriate harvest date. Steers were sorted into three harvest groups, and serially harvested at 142, 163, or 185 DOF, with the first harvest date selected based on an estimated 12th rib fat thickness of 1.27cm via ultrasound measurement. Steers were fed using an individual animal feeding system, to determine individual performance metrics. Steer DMI did not differ (P ≥ 0.31) between harvest groups, while carcass-adjusted ADG and G:F decreased linearly (P ≤ 0.04) as DOF increased. Carcass weight increased linearly (P < 0.01) as DOF increased from 142 to 185 DOF, with steers gaining an additional 36kg of HCW when fed an additional 42 DOF. Carcass LM area quadratically increased (P = 0.04) to 163 DOF and remained constant to 185 DOF. Marbling score was not different (P = 0.14) between harvest groups; however, the opportunity to grade USDA Premium Choice was improved for steers fed to 185 DOF. Calculated YG and 12th rib fat thickness increased linearly (P < 0.01) as DOF increased, with distributions across YG 1 through 5 differing between harvest groups (P < 0.01), and 185-d carcasses having the greatest frequency of YG 4 carcasses. As cattle are fed for additional DOF, live ADG and G:F decline, while HCW and LM area increase.

320 Effects of Sorting Strategy on Within-Pen Variation and Profitability

Abstract Decreasing variation in a pen of feedlot cattle reduces overfeeding, increases carcass quality and uniformity, and improves economic returns. The objective of this study was to evaluate the effect of sorting by body weight (BW) or expected days on feed (DOF) on pen performance and profitability. Ninety-six Angus-cross steers (initial BW = 360 ± 28 kg) were randomly assigned to sorting by BW or DOF determined using the Davis Growth Model and initial body measurements for BW, hip height, back fat thickness (BF), and ribeye area. Steers within BW and DOF sort groups were randomly assigned to one of two replicates. Within replicate, BW groups were divided into light and heavy pens (initial BW = 323 and 366 kg, respectively), and DOF groups were divided into short and long pens (DOF = 119 and 160 d, respectively), for a total of 8 pens with 12 steers in each pen. Pen feeding was managed using the slick bunk method and time of marketing was determined based on observation of an average pen BF of 1.1 cm. Steers were harvested at a commercial abattoir and individual carcass characteristics were recorded. Profit was calculated as carcass value minus feed costs. For comparison of sorting treatments, pen was the experimental unit, and treatment means and variances were compared using a t-test and F-test, respectively. Steers were harvested in three groups: both heavy-BW sort pens and both short-DOF sort pens were harvested after 84 d, both long-DOF sort pens and one light-BW sort pen were harvested after 104 d, and the final light-BW sort pen was harvested after 116 d on the finishing ration. There were no differences in mean initial BW (P = 0.95) or initial percent empty body fat (EBF; P = 0.28), but variation in initial BW was reduced (P &amp;lt; 0.01) for the BW sort group. Final mean BW did not differ between sort groups (P = 0.54), but variance in final BW and hot carcass weight was less (P &amp;lt; 0.01) for the group sorted by BW. Final percent EBF also did not differ between groups (P = 0.41), but percent EBF variance was 2.4 %-units for DOF and 2.9 %-units for BW sorted pens, although differences were not statistically significant. There were no differences in average daily gain or feed conversion rate between sort groups. Variation in yield grade, BF, and marbling score were numerically reduced for the DOF group; however, differences were not statistically significant (P &amp;gt; 0.10). Average profit per steer was $ 321.42 and $ 235.05 for DOF and BW sorted groups, respectively. Sorting by DOF increased profitability by 26% by increasing harvest BW, improving uniformity, and decreasing overweight carcasses.

PSXII-20 Differences in Fat Accretion Rate of Different Depots of Angus, Brahman and Charolais Feedlot Steers

Abstract Understanding accretion rate of intramuscular and subcutaneous fat in feedlot steers is crucial to ensure that carcasses are meeting market specifications and therefore optimizing profitability. Intramuscular fat (marbling) and subcutaneous fat (P8 and rib) are key areas of assessment on the live animals and carcasses determining quality. The objective of the present study was to determine fat accretion rate in three popular breeds of cattle with contrasting accretion rate throughout the feedlotting period. We hypothesized that Angus would have the fastest fat accretion rate being early maturing. Thirty of each Angus, Brahman and Charolais steers were entered into a feedlot (344 ± 5.3 kg initial BW) and six of each breed randomly selected for slaughter at 50-day intervals for 200 days on feed (DOF). Ultrasound scanning and BW were measured at each slaughter point, measuring fat thickness at the rib and P8 site, intramuscular fat (IMF), kidney fat and the eye muscle area (EMA). Body weight, intramuscular fat (%), P8 and rib fat (mm) all had significant interactions between DOF and breed (P &amp;lt; 0.001). At the start of the feeding period, Charolais were lighter than Angus and Brahman (P &amp;gt; 0.001). However, Charolais (663.7 ± 9.31 kg) and Angus were the heavier (680.4 ± 8.68 kg) than Brahman (539.4 ± 8.68 kg) at 200 DOF (P &amp;lt; 0.05). The interaction for P8 and rib fat was due to all breeds having similar fat thickness at 0 DOF (P &amp;gt; 0.05) but Angus had greatest (21.38 ± 0.882 mm, 17.12 ± 0.549 mm), Brahman intermediate (16.73 ± 0.883 mm and 10.38 ± 0.550 mm) and Charolais thinnest (9.97 ± 0.966 mm, 7.23 ± 0.600 mm) P8 and rib fat, respectively, at 200 DOF (P &amp;lt; 0.05). Similarly, IMF was similar between breeds at 0 DOF (P &amp;gt; 0.05), but Angus had greater IMF (7.76 ± 0.287 %; P &amp;lt; 0.001) compared with Brahman (5.08 ± 0.287 %) and Charolais (5.18 ± 0.314 %), which were not different amongst them (P &amp;gt; 0.10). Results of the present study demonstrated the contrasting fat metabolisms of each genotype with Angus steers showing the fastest fat accretion rate for all fat depots, whereas Brahman steers showed intermediate and Charolais slowest subcutaneous fat accretion rate. However, both Brahman and Charolais steers showed similarly low IMF and kidney fat accretion rates. Fat accretion rate of each depot and whole body should be considered in mathematical simulation models of animal growth.

366 Effects of Acidosis Bout Events on Animal Growth and Development, and the Effectiveness of Liver Abscess-Controlling Antibiotic on Diminishing Its Incidence

Abstract Ruminal acidosis is a common metabolic disorder that affects feedlot and dairy cattle and occurs when the supply of organic acids from fermentation exceeds its absorption, accumulating acid content in the rumen. Virginiamycin (VM) has inhibitory effects on primary liver abscess-causing bacteria. In feedlot animals, dietary VM has been shown to reduce rumen acidosis and improve feed conversion actively. This study evaluated ruminal pH over 150 days on feed (DOF) of growing and finishing beef cattle and investigated the relationships between ruminal pH and growth and development outcomes and the effectiveness of the continuous or intermittent provision of VM in 120 Angus-crossbred steers. Steers received VM (240 mg/d) as follows: no VM (T000); VM in the last 50 d (T001); VM for the last 100 d (T011); VM in the first 50 d (T100); VM in the first 100 d (T110); and VM for 150 d (T111). Animals were fed a grower-type diet (metabolizable energy [ME]: 2.45 Mcal/kg; crude protein [CP]: 12.2 % dry matter basis [DM]) for 50 d before the adaptation of a finisher-type diet (ME: 2.60 Mcal/kg; CP: 10.6% DM) over a 17-d period. The finisher-type diet was fed for the remaining 84 days. On d -1 and d 82 each animal received an indwelling pH bolus to record ruminal pH at 10-min intervals. Acidosis bout event was categorized as if the pH stayed below 5.6 for 3 hours. Data were analyzed using a random coefficient statistical model, binary data was analyzed using the logit link function and correlations were analyzed using PROC CORR in SAS (Table 1). Duration under pH 5.8 and 5.6 tended to have a negative correlation with gain to feed (G/F; P ≤ 0.080), and % of the time that pH remained below 5.6 when under 5.8 was negatively correlated with G/F (P = 0.007) and tended to have a negative correlation with average daily gain (ADG; P = 0.081). Similarly, acidosis bouts event and duration of bout event (DURB) tended (P ≤ 0.074) to have a negative correlation with G/F, while ADG was negatively correlated (P = 0.035). The number of acidosis bout events and probability of acidosis bout events to occur increase linearly (R2 = 0.89, P &amp;lt; 0.001, and R2 = 0.77; P &amp;lt; 0.001, respectively) as DOF progressed. The probability of an acidosis bout event decreased by 46% for the T111 treatment compared with T000 (35.43% vs. 18.82%; P = 0.049). Acidosis bout event seems to affect the growth and development of beef steers negatively, and it appears to be more critical as DOF progress. Administration of VM at 240 mg/d throughout the whole feeding period seems to reduce the incidence of acidosis bout events.

246 Evaluation of Live Growth Performance and Carcass Characteristics of Late Finishing Phase Beef Cattle with Varying Degrees of Pulmonary Hypertension

Abstract Late feedlot death caused by congestive heart failure has been quantified extensively through epidemiological studies however, these models do not consider losses or gains associated live growth performance, carcass quality, and consumer rejection of meat products. To address these gaps in the literature, we conducted two studies to characterize effects of pulmonary hypertension on four populations of feedlot cattle. In study one, reproductively intact (INT, n = 19), and ovariectomized (OVX, n = 18) yearling Sim-Angus heifers were selected on heart failure risk according to their pulmonary arterial pressure. Heifers were gradually transitioned onto a feedlot ration and fed to an acceptable harvest body composition determined using both 12th rib subcutaneous fat and body weight. Cattle were weighed biweekly and ADG was calculated by regressing body weight by days on feed (DOF). Pulmonary arterial pressure (PAP) was measured approximately every 3 months by a qualified veterinarian. Cattle were harvested at a commercial harvesting facility where carcass data and muscle samples were collected. In study two, weaned sim-angus steers (n = 41) were selected on heart failure risk categories using the same methodology outline above. Twenty steers were administered a steroidal growth promoting implant upon receiving (IMP) and twenty were untreated (NAT). Steers were fed to an average of 610 kg and data were collected using the same methodology outlined above. Data were analyzed using ANOVA, linear model, and Pearson correlation functions in R statistical software where PAP was used as a fixed continuous variable. Data were analyzed by study with the exception of live growth performance regression and correlations where data were combined. Linear regression within the combined datasets showed that initial mean PAP (P &amp;lt; 0.001), diastolic pressure (P &amp;lt; 0.001), and sex (P &amp;lt; 0.001) positively influenced ADG throughout the duration of the finishing period. Furthermore, initial PAP was moderately correlated with ADG (R = 0.38, P &amp;lt; 0.001). Gain to feed (G:F) was positively correlated with initial diastolic PAP (R = 0.31, P &amp;lt; 0.006). Neither initial mean PAP nor diastolic pressures impacted dry matter intake (DMI; P &amp;gt; 0.90), but sex was associated with DMI where steers had significantly decreased DMI (P = 0.003). Within study two, longissimus muscle objective color values were influenced by PAP where a* (redness; P &amp;lt; 0.001) and b* (yellowness; P &amp;lt; 0.04) values were negatively correlated with final PAP. These data begin to demonstrate the close relationship between live growth performance and pulmonary hypertension. More research is needed to better understand how cellular energy metabolism is potentially contributing to increased growth performance but negatively influencing muscle health in the form of oxygen binding capacity and inflammation.

PSI-30 A Novel Direct-Fed Microbial Influences Growth Performance, Health Parameters, and Carcass Characteristics in Feedlot Finishing Steers

Abstract Non-hormone-treated beef steers (n = 1,625; 370.6 ± 8.4 kg) were used to determine the impact of a direct-fed microbial (DFM) on growth performance, carcass characteristics, health parameters, and cost of gain in finishing beef cattle. Steers were sorted into 3 optimal marketing groups for each day of enrollment and randomly assigned, within block to 1 of 2 treatments (12 replicates per treatment). Treatments included: 1) Control (no DFM), 2) BDP (BOVAMINE DEFEND Plus containing (50 mg· animal-1· /day-1; Lactobacillus animalis, Propionibacterium freudenreichii, Bacillus licheniformis, and Bacillus subtilis). Steers averaged 133 days on feed (DOF) at time of harvest. Both pens within a block were harvested on the same day. Steers were weighed in drafts on a certified scale by pen at closeout. Hot carcass weights and liver scores were collected at the time of slaughter. Data were analyzed as a completely randomized block design and pen was considered the experimental unit. Dry matter intake and final body weight were not different across treatments. Total outs (dead animals and removed) throughout the experiment were less (P &amp;lt; 0.01) for BDP steers. Performance tended to be greater as ADG (P &amp;lt; 0.06) and FE (P &amp;lt; 0.01) were better for steers receiving BDP treatment. Hot carcass weight and quality grade were not different across treatments; however, total liver abscesses were found to be less (P &amp;lt; 0.01) in steers receiving BDP compared with controls. These data suggest that BOVAMINE DEFEND Plus supplementation improves growth performance during the finishing phase, reduces overall mortality, and increases return on investment of feedlot cattle.

158 Effect of Weaning Strategy and Backgrounding Length on Growth Performance, Carcass Characteristics, and Mrna Expression in the Longissimus Muscle of Beef Steers

Abstract This study aimed to investigate the effect of the weaning strategy (WS; early, at 130 ± 21 d vs normal, at 187 ± 20 d) and backgrounding length (BGL; short vs long) on growth performance, carcass characteristics, and relative mRNA expression in the longissimus muscle (LM) of beef steers. Angus × SimAngus-crossbred steers [n = 120; body weight (BW) = 130 ± 11.2 kg] were used in randomized complete block design. Steer calves were blocked by age and BW and randomly assigned to 1 of 4 treatments (2×2 factorial arrangement). Treatments consisted of early or normal weaned steers with either a short or a long BGL. Early weaned steers were ad libitum-fed a grain-based diet for 49 d until nursing calves were normally weaned. Subsequently, steers were ad libitum-fed a hay-based diet for 214 d or a concentrates-based diet for 95 d, for the long or the short BGL, respectively. Steers were finished on a high grain diet until harvested at a common 12th rib fat thickness. Longissimus muscle biopsies were performed on days 1, 57, 112, 168, 255. Data were analyzed using PROC MIXED in SAS. Early weaned steers were heavier (P &amp;lt; 0.01; Table 1) at the beginning of the backgrounding and finishing period. When the finishing phase began, steers with a long BGL were heavier (P &amp;lt; 0.01; Table 1) than steers with a short BGL. There was a WS × BGL interaction (P = 0.01; Table 1) for final BW, where normal weaned steers with a long BGL were the heaviest among treatments. In the finishing phase, steers with a long BGL had greater DMI and ADG, but lower G:F (P &amp;lt; 0.01; Table 1) than steers with a short BGL. There was WS × BGL interaction (P = 0.03; Table 1) for days on feed (DOF) in the finishing phase, where early weaned steers with a short BGL required less days on DOF to reach harvesting target than the remaining treatments. No interactions or treatment effects (P ≥ 0.11; Table 2) were detected for marbling score (MS). For the mRNA expression of ZFP423, a WS × d interaction was detected (P &amp;lt; 0.01; Figure 1). Day×WS interaction (P &amp;lt; 0.01) was observed for ZFP423 mRNA expression, early weaned steers showed a greater expression at d 112 and a decreased expression at d 255. For DLK1, a BGL×d interaction occurred (P &amp;lt; 0.01; Figure 2). In d 57 steers with a short BGL presented a greater DLK1 mRNA expression than steers with long BGL, whereas in d 255, this was inverted. Overall, data from this experiment does not support the implementation of different WS and BGL as a method to improve the MS of beef carcasses.

312 Evaluation of Dietary Roughage Manipulation During the Feeding of Ractopamine Hydrochloride as a Method to Improve Ruminal Health and Control Liver Abscess Severity in Feedlot Steers

Abstract The objective of this study was to determine if additional roughage inclusion to feedlot steer finishing diets during the feeding of ractopamine hydrochloride (RH) is an effective method to improve rumen health and control liver abscess severity. Steers [n = 64; initial shrunk body weight (SBW) = 633 kg ± 35.1 kg] were sourced from an unrelated trial and remained in their previous study pens; pens (n = 8) were assigned to dietary treatment in a completely randomized design. All steers on trial were fed a common 7% [dry matter (DM) basis] roughage equivalent (RE) finishing diet composed of dry-rolled corn, dried distillers grains plus solubles, corn silage, and grass hay for the 58 d preceding study initiation. Steers were fitted with rumination tags to track daily rumination. Dietary treatments were CON: no diet change; and 12R: 5% (DM basis) RE addition to diet via grass hay during the feeding of RH. Steers were fed RH (300 mg/steer/d), finished on treatment diets for 28 d, and harvested at a commercial beef processor. Growth performance, efficiency of dietary net energy (NE) utilization, and continuous carcass data were analyzed with pen as the experimental unit (EU) and fixed effect of treatment. Minutes ruminating was analyzed as an analysis of covariance with individual animal as the EU, fixed effects of treatment, days on feed (DOF) and their interaction, and baseline minutes ruminating as a covariate in the model. Liver abscess prevalence, rumen health, and categorical carcass data were analyzed with the Fisher’s exact test to determine differences between treatments. No difference (P ≥ 0.19) was observed for final SBW, average daily gain, dry matter intake, feed conversion efficiency, dressing percentage, hot carcass weight, calculated yield grade, marbling score, 12th rib fat thickness, calculated empty body fat, observed dietary NE for maintenance and gain, observed-to-expected dietary NE for maintenance and gain, or distribution of liver abscess prevalence, ruminitis score, or USDA yield grade. Ribeye area tended (P = 0.10) to differ between treatments with 12R steers exhibiting a 3.5% larger ribeye. Distribution of USDA quality grade differed (P = 0.003) between treatments with 12R steers having 25% more carcasses grading USDA average choice or better. A treatment × DOF interaction (P = 0.045) was observed for minutes ruminating per day. Daily minutes ruminating was increased (P ≤ 0.05) for 12R on d 1, 2, and 20 and tended to be increased (P ≤ 0.10) for 12R on days 10, 13, 24, and 25. Inclusion of an additional 5% RE to finishing cattle diets during a 28 d RH feeding period can be a management strategy to decrease risk of digestive upsets without sacrificing growth performance or carcass quality.

Characteristics of intramuscular collagen in calf-fed Nellore bulls and steers throughout the finishing phase

This study evaluated collagen solubility and gene expression of biomarkers for intramuscular collagen (IMCT) deposition and remodeling in the Longissimus muscle of bulls and steers through the finishing phase. Thirty-six Nellore calves were used (18 bulls and 18 steers), and six of each sexual condition were randomly assigned to be harvested at 0, 100, or 200 days on feed (DOF) to evaluate collagen characteristics in different time points throughout the finishing phase. Bulls showed a greater collagen solubility than steers (P = 0.03). The gene expression of fibrogenic markers (TGFβ1, COL1A1, and COL3A1) and IMCT remodeling mediators (MMPII, TIMPII, and LOX) were not affected by sexual condition or DOF (P > 0.05). Our data indicate that young Nellore bulls have a higher percentage of soluble intramuscular collagen, possibly due to higher collagen remodeling associated with a faster growth rate and muscle hypertrophy. Moreover, castration and DOF did not modify mRNA levels of fibrogenic and collagen remodeling markers.

Effect of weaning strategy and backgrounding management on growth performance, carcass characteristics, and mRNA expression in the longissimus muscle of beef steers.

We evaluate the effect of the weaning strategy (WS; early, 130 ± 21 d vs. normal, 187 ± 20 d) and backgrounding management (BGM) on growth, carcass characteristics, and relative mRNA expression in the longissimus muscle (LM) of beef steers. One hundred and twenty Angus × SimAngus-crossbred steers (body weight (BW) = 130 ± 11.2 kg) were used in a randomized complete block design. Steers, blocked by age and BW, were randomly assigned to one treatment (2 × 2 factorial). Treatments consisted of early weaned (EW) or normal weaned (NW) steers subsequently backgrounded (BG) on either a forage-based (FB) or concentrates-based (CB) diet. The EW steers (d 0) were ad libitum-fed a grain-based diet for 49 d until nursing calves were NW. Steers were ad libitum-fed either a FB diet for 214 d or a CB diet for 95 d afterward. Steers were finished on a high-grain diet until harvested at an estimated constant 12th-rib fat thickness (1.5 cm). Expression of mRNA in the LM was measured over time. Data were analyzed using PROC MIXED in SAS. The EW steers were heavier (P ˂ 0.01) at the beginning of the backgrounding and finishing period. When the finishing phase began, steers FB were heavier (P ˂ 0.01) than CB steers. There was a tendency for a WS × BGM interaction (P = 0.08) for final BW, where NW-FB steers were heavier than the steers on the other three treatments, which do not differ between them. In the finishing phase, steers BG on a FB diet had greater dry matter intake and average daily gain, but lower gain-to-feed ratio (P ˂ 0.01). There was a WS × BGM interaction (P = 0.03) for days on feed (DOF) in the finishing diet, where backgrounding steers in a FB diet decreased DOF required to reach the harvesting target among EW steers, but not within NW steers. No interactions or treatment effects (P ≥ 0.17) were detected for marbling score (MS). For ZFP423, EW steers showed a greater mRNA expression on d 112 and a lower expression on d 255 than NW steers (P ˂ 0.01). In d 57, steers BG on a CB diet presented a greater delta-like homolog 1 mRNA expression than steers BG on a FB diet, whereas in d 255, this was inverted (P ˂ 0.01). For CCAAT/enhancer binding protein D (C/EBPD) mRNA expression, a tendency for a WS × BGM interaction was observed (P = 0.06), where a greater expression of C/EBPD was observed in steers BG on a FB diet among EW steers, but not within NW steers. In this study, early grain feeding followed by different BGM does not support MS improvements of beef carcasses.

The effects of a nutritional packet (live yeast, vitamins C and B1, and electrolytes) offered to steers in a calf-fed system on growth performance, nutrient digestion, feeding behavior, carcass characteristics, and ruminal variables.

Effects of a nutritional packet strategically offered to calf-fed system steers on growth performance, nutrient digestibility, feeding behavior, ruminal variables, and carcass characteristics were evaluated. Angus crossbred steer-calves (N = 60; body weight [BW] = 234 ± 4 kg) were used in a randomized complete block design (block = BW) and stratified into two treatments: 1) control; and 2) 30 g/steer-daily (dry matter [DM] basis) of a nutritional packet containing (steer-daily basis): Live yeast (Saccharomyces cerevisiae; 1.7 × 1010 CFU), vitamin C (Ascorbic acid, 162 mg), vitamin B1 (thiamin hydrochloride, 400 mg), sodium chloride (2.4 g), and potassium chloride (2.4 g). Animals were offered (electronic feed-bunks [SmartFeed, C-Lock Inc., Rapid City, SD]), a steam-flaked corn-based finishing diet to ad libitum (individual intake), once daily for 233 d. Treatments were offered during the first and last 60 days on feed (DOF). The GLIMMIX procedure of SAS was used, with steer as the experimental unit, treatment and phase (for feeding behavior and digestibility) as fixed effects, and BW-block as a random effect. Steers offered the nutritional packet had 14% less (P < 0.01) intake and 18% greater (P = 0.01) feed efficiency during the initial 30 DOF. Intake (days 0 to 233) was 6% greater (P = 0.02) for steers offered the nutritional packet, while BW gain was not different (P ≥ 0.44). Greater (P = 0.02) dressing percent (61.1% vs. 62%) for steers offered the packet was observed, while other carcass variables were not different (P ≥ 0.33). Digestibility of DM, organic matter, and fiber were greater (P < 0.01) for steers offered the packet. Steers offered the packet spent 13% less time eating during the first 60 DOF, while during the last 60 DOF a 14% greater meal frequency and 12.3% smaller mean meal size (treatment × phase interaction, P < 0.02) were observed. Steers offered the packet had a reduced (P ≤ 0.01) mean meal duration during both phases. Regardless of treatment, a decreased rumination (P ≤ 0.03) and chewing (P ≤ 0.01) activities were observed for the last 60 DOF compared to the first 60 DOF. Ruminal papillae area was 30% greater (P = 0.02) and the total volatile fatty acid (VFA) tended (P = 0.09) to be greater for steers offered the nutritional packet. The nutritional packet offered to calf-fed steers improved feed efficiency during the initial 30 d after arrival, while inducing superior overall intake, nutrient digestibility, dressing percentage, ruminal papillae area, and total ruminal VFA.

Associations between pen management characteristics and bovine respiratory disease incidence in the first 45 days post-arrival in feedlot cattle

&#x0D; The purpose of this study was to utilize retrospective commer­cial feedlot data to evaluate the potential associations between pen housing management factors and first treatment BRD inci­dence during the first 45 days on feed (DOF). Our study popula­tion included 1,733 cohorts of feedlot cattle representing 188,188 total animals from 2018 to 2020. Our explanatory variables of interest in this study were pen area per animal and bunk space per animal. These variables were categorized as either having below, adequate, or above recommended pen area/bunk space per animal-based guidelines from the central United States. Our data were analyzed with a generalized linear mixed model utilizing a binomial link function. Results demonstrated that pen housing management factors were significantly (P &lt; 0.05) associated with BRD incidence in the first 45 DOF, but their ef­fects were modified by relevant cattle demographic factors (co­hort size at arrival, average arrival weight, sex, and quarter of arrival). For example, cohorts with an average arrival weight between 900 to 1,000 lb. (409 to 453 kg) had a higher probability of BRD incidence in the first 45 DOF when provided below rec­ommended pen area per head compared to similar weighted co­horts that had adequate, or above, recommended pen area per head. Our results from this study identify potential situations where pen housing management factors, combined with cattle demographics, may impact the risk of BRD in feedlot cattle. Further defining these situations may allow feedlot managers to utilize these estimates to manage feedlot cattle health more effectively.

PSV-A-11 The Effect of Days on Feed for Feedyard Performance, Health, Carcass, and Organ Characteristics of Angus X Holstein Heifers

Abstract The objective of this study was to evaluate the effect of days on feed (DOF) on performance, health, carcass, and organ characteristics of composite Angus x Holstein heifers (n = 3,676). At time of arrival (d 0), heifers from a single source were placed into large (~300 animal) pens at two commercial feedlot locations in the Texas Panhandle. At administration of final implant (Revalor® 200; d 240), heifers, within lot, were randomly assigned to one of four smaller pens, creating a block (location A block n = 6, location B block n = 7). Pens within blocks were randomly assigned to treatment (323, 344, 365, or 386 DOF). Data were analyzed using DOF as the fixed effect; block was nested within location as a random effect. Linear and quadratic effects were also tested; pen was experimental unit (n = 52). Heifer DMI did not differ across DOF (P = 0.72). Heifer ADG decreased linearly (1.52, 1.37, 1.31, and 1.27 kg/d; P ≤ 0.01). Heifer HCW (372, 387, 401, and 414 kg), longissimus dorsi muscle area (88.63, 89.55, 90.80, and 91.95 cm2), marbling score (535, 553, 563, and 594) and percentage of Prime QG (6.6, 11.2, 12.8, and 19.0 %) linearly increased (P ≤ 0.01) as DOF increased. Frequency of liver scores (edible, minor, or major abscess) did not change over DOF (P ≥ 0.82). Frequency of ideal heart score linearly decreased with DOF (53.0, 44.3, 25.7, and 15.0 %; P ≤ 0.01). Frequency of YG 3 did not change (P = 0.68), however YG 4 linearly increased with DOF (6.2, 12.0, 14.0, and 22.5 %; DOF P ≤ 0.01). Data collected in this trial indicate that DOF led to increased HCW, LM area, marbling, YG, and QG with minimal changes to DMI or liver scores for Angus x Holstein heifers.