Applied Animal Science最新文献

{"title":"Evaluating and improving the pasture factor based on herbage allowance and nutritive value to estimate the daily herbage intake of stockers grazing bermudagrass","authors":"P. Woli ,&nbsp;C.R. Long ,&nbsp;L.O. Tedeschi ,&nbsp;F.M. Rouquette Jr","doi":"10.15232/aas.2024-02633","DOIUrl":"10.15232/aas.2024-02633","url":null,"abstract":"<div><h3>Objective</h3><div>The critical herbage allowance (^cHA), de- fined as the herbage allowance (HA) level below which DMI becomes limiting, is a key variable defining the pas- ture factor used in a daily gain model (DGM) to estimate the daily DMI of stockers grazing bermudagrass (<em>Cynodon dactylon</em> [L.] Pers.) as constrained by HA and nutritive value. Our objective was to evaluate the DGM containing the ^cHA function using a new, comprehensive database.</div></div><div><h3>Materials and Methods</h3><div>We evaluated the DGM with its ^cHA function, using the observed and model-predicted ADG values involving 1,032 stocker calves in 33 grazing trials conducted at Overton, Texas. Based on evaluation results, we then modified the ^cHA function by incorporat- ing an enhancement factor (κ). By running the DGM with a potential κ value and evaluating it using the ADG data several times iteratively, we derived the best κ value.</div></div><div><h3>Results and Discussion</h3><div>Evaluation results showed that the DGM containing the original ^cHA function con- sistently underpredicted ADG, as the function was too restrictive to DMI. This issue indicated that the ^cHA func- tion needed to be less restrictive. After multiple iterations of DGM running and testing, we derived 0.75 for κ. With the modification of the ^cHA function through the incor- poration of κ (= 0.75), the DGM performance improved significantly. The modeling efficiency increased by about 31%, the modeling error decreased by about 16%, and the estimated DMI increased from 1.9% BW to 2.1% BW for stockers grazing bermudagrass.</div></div><div><h3>Implications and Applications</h3><div>By incorporating κ into the ^cHA function in the DGM, this study addressed the issue of consistent underprediction of ADG. By in- cluding the improved ^cHA function in an herbage intake prediction system, the DGM users can more accurately explore the effects of various management and environ- mental factors on daily DMI and ADG of stockers grazing bermudagrass.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Pages 39-46"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparison of alternative backgrounding and feedlot system strategies on performance of May-born, Red Angus cross yearling steers in the Nebraska Sandhills","authors":"Dempster M. Christenson,&nbsp;Jacki A. Musgrave,&nbsp;Rick N. Funston","doi":"10.15232/aas.2024-02613","DOIUrl":"10.15232/aas.2024-02613","url":null,"abstract":"<div><h3>Objective</h3><div>Our objective was to examine the physical performance and economic outcomes of differing backgrounding and feedlot systems on May-born yearling steers.</div></div><div><h3>Materials and Methods</h3><div>Steers weaned in January (n = 392) were blocked by BW and randomly assigned to 1 of 2 backgrounding treatments for 4 mo: given ad libitum meadow hay and 1.81 kg/d of a 33% CP supplement (HI) or allowed to graze dormant subirrigated meadow with 0.45 kg/d supplement (LO). In May, one-half of the steers from each backgrounding treatment were blocked by BW and transported to a feedlot system (S-YRL) before slaughter at 18.5 mo of age. The remaining steers grazed upland range (L-YRL), were transported to a feedlot mid-September, and were slaughtered at 21.5 mo of age. The net return of treatment for each study year was applied to 12 consecutive years of economic conditions.</div></div><div><h3>Results and Discussion</h3><div>There were no interactions between treatments. Backgrounding period ADG was 0.24 ± 0.03 kg/d greater among HI calves than among LO calves, which led to 31 ± 3.6 kg greater BW after backgrounding and 20 ± 7.7 kg greater BW at slaughter. However, LO calves had $209.46 ± $12.82 per head greater net return. Greater nutritional value in S-YRL steers at an earlier age led to 0.38 ± 0.03 kg/d greater ADG after the backgrounding period and 0.01 ± 0.003 greater G:F. However, L-YRL steers entered the feedlot 4 mo later with 99 ± 7.5 kg greater BW, a tendency for 0.08 ± 0.04 kg/d greater ADG in the feedlot, 39 ± 9.7 kg greater BW at slaughter, and $148.86 ± $38.72 per head greater net return. Marbling score, LM area, and YG were greater or tended to be greater for L-YRL steers, which led to greater empty body fat.</div></div><div><h3>Implications and Applications</h3><div>Backgrounding with greater inputs decreased net return, whereas extended grazing followed by a relatively shorter feedlot period decreased feed costs and increased net return.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Pages 104-118"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"\"April\" Cover","authors":"","doi":"10.1016/S2590-2865(25)00024-2","DOIUrl":"10.1016/S2590-2865(25)00024-2","url":null,"abstract":"","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Page OFC"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Call for Submissions","authors":"","doi":"10.1016/S2590-2865(25)00029-1","DOIUrl":"10.1016/S2590-2865(25)00029-1","url":null,"abstract":"","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Pages iv-vi"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluating the effects of acidosis and bacterial inoculum concentrations on the development of liver abscesses in beef × dairy steers","authors":"Kallie D. Childress ,&nbsp;Kristin E. Hales ,&nbsp;T.G. Nagaraja ,&nbsp;Ty E. Lawrence ,&nbsp;Raghavendra G. Amachawadi ,&nbsp;Nicole C. Burdick Sanchez ,&nbsp;Aubrey C. Thompson-Smith ,&nbsp;Ashlee N. Hanratty ,&nbsp;Colten W. Dornbach ,&nbsp;Mina Abbasi ,&nbsp;Xiaorong Shi ,&nbsp;Maddie S. Grant ,&nbsp;Michael L. Galyean ,&nbsp;Paul R. Broadway","doi":"10.15232/aas.2024-02641","DOIUrl":"10.15232/aas.2024-02641","url":null,"abstract":"<div><h3>Objective</h3><div>We evaluated the association of diet type, ruminal acidosis bout frequency, and intraruminal bacterial inoculum concentration on liver abscess (LA) development in steers.</div></div><div><h3>Materials and Methods</h3><div>Beef × dairy steers (n = 40, initial BW = 107 ± 11 kg) were assigned randomly to 1 of 5 treatments that included intraruminal inoculation of either a high dose (HD; 100 mL of 1 × 10⁸ and 100 mL of 1 × 10⁹ cfu per steer) or a low dose (LD; 100 mL of 1 × 10⁶ and 100 mL of 1 × 10⁷ cfu per steer) of <em>Fusobacterium necrophorum</em> ssp. <em>necrophorum</em> and <em>Salmonella enterica</em> serovar Lubbock, respectively. Treatments included the following: NCON = high-forage diet with no bacterial inoculation; CON+HD = high-forage diet with a single HD inoculation; 2AD+HD = 2 acidotic diet cycles with a single HD inoculation; 4AD+3LD = 4 acidotic diet cycles with a series of 3 LD inoculations; and 4AD+HD = 4 acidotic diet cycles with a single HD inoculation. Steers were slaughtered 21 d after the last bacterial inoculation. Animal was the experimental unit. Continuous data were analyzed using mixed models, and categorical data were analyzed as binomial proportions with treatment, time, and their interactions as the fixed effects.</div></div><div><h3>Results and Discussion</h3><div>Incidence of LA were 0%, 37.5%, 37.5%, 50%, and 12.5% for NCON, CON+HD, 2AD+HD, 4AD+3LD, and 4AD+HD, respectively, but the difference among treatments was not significant. Although no difference was observed in rumenitis among treatments, steers with LA presented rumenitis scores that were 8 percentage points greater than steers without LA. Steers consuming the high-forage diet also were presented with rumenitis. Hematocrit values were greater in NCON, 2AD+HD, and 4AD+HD than CON+HD or 4AD+3 LD. Similarly, neutrophil:lymphocyte ratio differed among treatments, with a greater ratio for CON+HD and 2AD+HD than for NCON, 4AD+3LD, and 4AD+HD.</div></div><div><h3>Implications and Applications</h3><div>A key finding of this study was that steers fed a high-forage diet given a high dose of <em>F. necrophorum</em> and <em>S. enterica</em>, even in the absence of the acidotic diet, developed LA.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Pages 93-103"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Review: Sustainable phosphorus use in the United States beef cow-calf industry—Requirements, forage, soil, and water content, supplementation, and nutritional recommendations for producers","authors":"J.M. Warner ,&nbsp;G.E. Fike ,&nbsp;A.G. Schwartz ,&nbsp;J.W. Waggoner ,&nbsp;S.K. Johnson","doi":"10.15232/aas.2024-02643","DOIUrl":"10.15232/aas.2024-02643","url":null,"abstract":"<div><h3>Purpose</h3><div>The objective is to explain the current understanding of the biological importance of P to beef cattle congruent with current established requirements as well as describe the current management toward P supplementation, nutritional recommendations, quantify forage, soil, and water mineral concentrations, and identify existing knowledge gaps specific for improving sustainable use of the mineral in United States cow-calf production.</div></div><div><h3>Sources</h3><div>Peer-reviewed literature, abstracts, experiment station progress reports, technical bulletins, and reports were the primary sources of information reviewed.</div></div><div><h3>Synthesis</h3><div>Phosphorus is essential for beef cattle productivity and health as well as a potential water contaminant. Although efforts have been made in recent years to improve our understanding of requirements for growing and finishing beef cattle, relatively little work has been done focused on the cow-calf segment of the industry. Because grazing beef cattle frequently use surface water sources, producers play a critical role in minimizing P introduction to waters. Soil and forage P levels and responses to supplementation vary widely and studies including both animal and agronomic components of P utilization are very limited. Concurrently, data directly evaluating the effect of specific best management practices for improving sustainable P use within cow-calf production systems on surface water quality are few and would be beneficial for industry guidance and producer adoption.</div></div><div><h3>Conclusions and Applications</h3><div>Long-term cow-calf studies reporting intake and production outcomes that also include soil and forage P levels are needed for developing industry benchmarks and accurate supplementation recommendations. Best management practices implemented holistically are key for minimizing the industry’s use of supplemental P while optimizing animal health and production, particularly in areas where public water quality is of concern.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Pages 129-145"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluation of Saccharomyces cerevisiae fermentation product on the prevention of digital dermatitis using an experimental infection model in cattle","authors":"K. Anklam ,&nbsp;M. Aviles ,&nbsp;J. Buettner ,&nbsp;S. Henschel ,&nbsp;R. Sanchez ,&nbsp;S. Ordaz ,&nbsp;I. Yoon ,&nbsp;J. Wheeler ,&nbsp;G. Dawson ,&nbsp;D. Doepfer","doi":"10.15232/aas.2024-02567","DOIUrl":"10.15232/aas.2024-02567","url":null,"abstract":"<div><h3>Objective</h3><div>The objective of this research was to evaluate the efficacy of a feed supplement, <em>Saccharomyces cerevisiae</em> fermentation product (SCFP, NutriTek, Diamond V, Cedar Rapids, IA), on the prevention of digital dermatitis (DD) lesions in Holstein Friesian steers. For this research, an experimental infection model was used to reliably induce DD lesions in cattle.</div></div><div><h3>Materials and Methods</h3><div>A blind completely randomized study was conducted using a digital dermatitis infection model. Following 7 d of hydropic skin maceration in a wrap, the hind feet of 49 Holstein Friesian steers (24 control and 25 SCFP) were inoculated with bovine DD lesion homogenate and remained wrapped until clinical signs of DD were observed or until the protocol endpoint. Pellets containing SCFP (12 g/d NutriTek) or control supplements were mixed in the steers’ respective daily total mixed ration and fed throughout the duration of the study.</div></div><div><h3>Results and Discussion</h3><div>Seven days after inoculation, all 49 steers developed an M1 (early focal bacterial keratolysis of the epidermis) or M2 (ulcerated/active) lesion on at least 1 hind foot. Treponeme species were detected by polymerase chain reaction, and invasive spirochetes were observed by histology in skin biopsies of the experimentally induced DD lesions. In this DD induction model, the relative risk of steers to develop M2 lesions in the control group was 1.53 (1.09–2.15, 95% CI) times greater than the SCFP group, although SCFP supplementation did not significantly affect the size of the M2 lesions. The multivariable regression analysis, adjusted for risk factors, confirmed that the control steers were significantly more likely to develop M2 lesions than the SCFP steers.</div></div><div><h3>Implications and Applications</h3><div>The DD experimental infection model used in the present study is useful for testing additional intervention strategies in cattle. The protective effect of SCFP against developing experimentally induced M2 DD lesions suggests that SCFP can be considered as a nutritional intervention to mitigate the risk of DD infection. Additional research is warranted to evaluate the potential mode of action to support the use of SCFP supplementation in the prevention of the development and transmission of DD lesions in cattle under field conditions.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Pages 47-64"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Review: History of chromium in animal nutrition in the United States","authors":"J.W. Spears","doi":"10.15232/aas.2024-02653","DOIUrl":"10.15232/aas.2024-02653","url":null,"abstract":"<div><h3>Purpose</h3><div>The purpose of this paper is to review animal research studies with chromium (Cr) sources that are permitted or approved by the US Food and Drug Administration (FDA).</div></div><div><h3>Sources</h3><div>Research in peer-reviewed journals was the source of information reviewed.</div></div><div><h3>Synthesis</h3><div>Chromium tripicolinate (Chromax) and chromium propionate (KemTRACE Cr) are permitted by FDA for supplementation to swine diets at a level up to 0.20 mg Cr/kg diet. Chromium propionate (CrProp) is permitted by FDA for supplementation to cattle diets at a level up to 0.50 mg Cr/kg diet, and is approved for supplementation to adult horses at a level of 4 mg Cr/d, and broiler and turkey diets at a level not to exceed 0.20 mg Cr/kg diet. Chromium supplementation in swine has increased litter size in sows. In lactating dairy cows, CrProp supplementation has increased milk production and reproductive performance, and increased ADG and hot carcass wt in finishing steers. Improved gain and feed efficiency have been reported in broilers and turkeys supplemented with CrProp. In adult horses, CrProp supplementation increased insulin sensitivity following oral or i.v. carbohydrate administration.</div></div><div><h3>Conclusions and Applications</h3><div>Studies in lactating dairy cows, finishing steers, broilers, and turkeys have indicated that CrProp supplementation can improve performance. Supplementation of Cr picolinate (CrPic) has increased litter size in sows in several studies. Animal responses to Cr supplementation have been variable and research is needed to determine factors that affect responses to Cr supplementation. Chromium propionate may be beneficial in preventing insulin resistance or improving insulin sensitivity in insulin-resistant horses.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 2","pages":"Pages 65-75"},"PeriodicalIF":1.4,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143683794","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Targeted durations of tylosin phosphate on incidence and severity of liver abscesses in feedlot cattle*","authors":"L.F.B.B. Feitoza ,&nbsp;A.N. Baker ,&nbsp;R.L. Thorn ,&nbsp;L.S. Monteiro ,&nbsp;F. Nasiu ,&nbsp;T.G. Nagaraja ,&nbsp;Q. Kang ,&nbsp;J.S. Drouillard","doi":"10.15232/aas.2024-02574","DOIUrl":"10.15232/aas.2024-02574","url":null,"abstract":"<div><h3>Objective</h3><div>Our objective was to assess the effects of feeding tylosin phosphate at 60 mg∙steer⁻¹∙d⁻¹ for the first 30 or 60 d of the finishing phase on the incidence and severity of liver abscesses, performance, and carcass characteristics in feedlot steers.</div></div><div><h3>Materials and Methods</h3><div>Steers (n = 462) were randomly assigned to 1 of 3 treatments: no tylosin phosphate (control) or tylosin phosphate, administered in the feed as a type B medicated premix supplement, to provide 60 mg∙steer⁻¹∙d⁻¹ for the first 30 d (T-30) or 60 d (T-60) of the finishing phase (steers were fed the control diet for the remaining days of the finishing phase). Steers were housed in pens with 7 steers per pen and 22 pens per treatment. Cattle BW were recorded at 30-d intervals, and final BW was recorded on d 161 on feed. Steers were processed at a commercial abattoir, and incidence and severity of liver abscesses and carcass characteristics were recorded.</div></div><div><h3>Results and Discussion</h3><div>Incidence of abscessed livers was not affected by targeted durations of tylosin phosphate administration. However, there was a trend for severe abscesses to happen less in T-30 and T-60 than in the control, possibly because of inclusion of tylosin phosphate during the diet transition phase when cattle are likely to experience ruminal acidosis. Steers that received tylosin phosphate had greater BW on d 30 or 60 compared with the control. Steer performance and carcass characteristics were not affected by treatments.</div></div><div><h3>Implications and Applications</h3><div>Administration of tylosin phosphate at 60 mg per animal daily for the first 30 or 60 d of the finishing phase had no effect on the incidence of abscessed livers, although there was a trend for the reduction in severe abscesses in feedlot steers.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 1","pages":"Pages 1-9"},"PeriodicalIF":1.4,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143139427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Myosin heavy chain, myogenic regulatory factors, and steroid hormone receptor responses in serially slaughtered implanted or nonimplanted beef steers","authors":"K.R. Wesley ,&nbsp;L.K. Fuerniss ,&nbsp;J.T. Jobe ,&nbsp;J.P. Hutcheson ,&nbsp;W.T. Nichols ,&nbsp;T.J. Kirkpatrick ,&nbsp;S.L. Pillmore ,&nbsp;K.B. Cooper ,&nbsp;B.J. Johnson ,&nbsp;T.E. Lawrence","doi":"10.15232/aas.2024-02579","DOIUrl":"10.15232/aas.2024-02579","url":null,"abstract":"<div><h3>Objective</h3><div>The objective of this study was to quantify changes in beef steers in myosin-heavy-chain fiber type, myogenic regulatory factors, and steroid hormone receptors over time and in response to implantation in the longissimus dorsi (LD), semitendinosus (ST), and diaphragm (D) muscles.</div></div><div><h3>Materials and Methods</h3><div>Eighty beef steers were paired based on estimated final BW, and individuals received no implant (CON) or Revalor-XS (Merck Animal Health) administered at d 0 and 190 (IMP). Four pairs of steers were randomly assigned to slaughter group at 42-d intervals from d 0 to 378. At slaughter, samples were collected from the LD, ST, and D muscles of each animal for immunohistochemical analysis.</div></div><div><h3>Results and Discussion</h3><div>Proportions of cross-sectional area (CSA) occupied by each myosin-heavy-chain type were not different between implant treatments. Increased days on feed led to increased CSA in all muscles. Total nuclei density tended to be greater in CON steers. Myogenic regulatory factors expressed as a proportion of total nuclei led to no difference due to implant treatment in all variables, except a tendency for increased proportion of myonuclei in the ST of IMP steers. Day influenced all variables in the LD with positive quadratic effects on proportion of myonuclei and MYF5-positive nuclei. In the ST, day affected proportion of myonuclei and PAX7- and MYF5/ PAX7-dual-positive nuclei. All myogenic factors were affected by day in the D. Steroid receptor expression was unaffected by implant status regardless of muscle. Day tended to affect steroid receptor variables in the LD, ST, and D, with varying trends by muscle and variable.</div></div><div><h3>Implications and Applications</h3><div>Implant treatment did not alter the proportion of muscle fiber types, myogenic outcomes relative to total nuclei, or steroid hormone receptors. However, implant administration increased overall CSA by 9% to 16%, suggesting enhanced muscle growth without affecting muscle composition or regulatory mechanisms.</div></div>","PeriodicalId":8519,"journal":{"name":"Applied Animal Science","volume":"41 1","pages":"Pages 10-20"},"PeriodicalIF":1.4,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143139430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}