Influence of virginiamycin supplementation on growth performance, carcass characteristics, and liver abscess incidence, with 2 different implant strategies in calf-fed Holstein steers

Applied Animal Science 35:628–633 https://doi.org/10.15232/aas.2019-01894 © 2019 American Registry of Professional Animal Scientists. All rights reserved.

PRODUCTION AND MANAGEMENT: Original Research

Influence of virginiamycin supplementation on growth performance, carcass characteristics, and liver abscess incidence, with 2 different implant strategies in calf-fed Holstein steers B. C. Latack,1* L. Buenabad,2 and R. A. Zinn,3 PAS 1 University of California Cooperative Extension, Holtville 92250; 2Department of Nutrition and Biotechnology of Ruminants, Instituto de Investigaciones en Ciencias Veterinarias, Universidad Autónoma de Baja California, Mexicali, Baja California, Mexico 21100; and 3Department of Animal Science, University of California, Davis 95616

ABSTRACT Objectives: Our goal was to determine the effect of virginiamycin supplementation and 2 different implant strategies on growth performance, carcass characteristics, and liver abscess incidence in calf-fed Holstein steers. Materials and Methods: Following an initial 112-d receiving-growing period, 120 Holstein steer calves (287 ± 14 kg) were blocked by BW into 5 groups and randomly assigned within BW groupings to 20 pens (6 steers per pen, 5 pen replicates per treatment). Two levels of supplemental virginiamycin (0 vs. 16 mg/kg, 90% DM basis) and 2 growth implant strategies (Synovex One vs. Synovex Plus on d 1 and 112) were evaluated in a 2 × 2 factorial arrangement of treatments. Results and Discussion: There were no treatment interactions (P > 0.20). Virginiamycin supplementation increased overall (d 1–197) ADG (6.8%, P < 0.01) and BW gain efficiency (6.1%, P < 0.01). Compared with a single long-duration implant, the re-implant program increased initial 112-d (8.3%, P < 0.01) and overall 197-d (7.5%, P < 0.01) ADG. Enhancements in ADG were due to increased DMI (3.4%, P = 0.04) and efficiency of energy utilization (2.9%, P = 0.04). Across all treatments, liver abscess incidence was low, averaging 5.8%. Virginiamycin supplementation increased carcass weight (4%, P = 0.01). Compared with a single long-duration implant, the re-implant program increased carcass weight (2.8%, P = 0.04) but decreased marbling score (9.1%, P = 0.02). Implications and Applications: Virginiamycin supplementation enhanced ADG, BW gain efficiency, and estimated dietary NE. Single long-duration implants may not afford the same growth and gain efficiency response

The authors declare no conflict of interest. *Corresponding author: bclatack@​ucanr​.edu

as conventional re-implant programs for calf-fed Holstein steers. Although, marbling score may be improved. Key words: cattle, feedlot, implant, performance

INTRODUCTION Virginiamycin (VM) is an antimicrobial that inhibits growth of ruminal lactic acid–producing bacteria, reducing lactic acidosis and associated digestive dysfunctions, including liver abscess development (Nagaraja and Chengappa, 1998; Owens et al., 1998). Salinas-Chavira et al. (2009, 2016) observed that supplemental VM increased 340-d gain efficiency and efficiency of energy utilization of calf-fed Holstein steers. Virginiamycin also may have a protein sparing effect (Salinas-Chavira et al., 2016), reducing ruminal protein degradation (Van Nevel et al., 1984; Ives et al., 2002) and enhancing postruminal nutrient uptake (Erasmus et al., 2008). The potential for enhanced efficiency of protein utilization may have particular relevance in calf-fed cattle during the growing phase when metabolizable AA supplies are limiting (Zinn et al., 2000, 2007). Hormonal implants promote ADG, gain efficiency, HCW, and LM area of calf-fed Holstein steers (Perry et al., 1991; Torrentera et al., 2016). Because of the long feeding period, calf-fed Holstein steers are given hormonal implants when they achieve an initial BW of 270 kg and are re-implanted 90 to 100 d before slaughter (Torrentera et al., 2016). With the development of long-duration (more than 220 d) implants, we were interested in comparing a single implant program with a conventional reimplant program. Additionally, as implanted steers may have reduced protein requirements for maintenance (DiConstanzo and Zehnder, 1999), the response to potentially enhance metabolizable protein supply with supplemental VM may differ with different implant strategies. The objective of this trial was to determine the effect of VM supplementation at the label dosage for liver abscess control

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and 2 different implant strategies on growth performance, carcass characteristics, and liver abscess incidence in calffed Holstein steers.

MATERIALS AND METHODS Animals, Management, Housing, and Feeding Procedures for animal care and management were conducted under protocol (#20548) approved by the University of California Animal Use and Care Advisory Committee. A total of 120 Holstein steer calves were obtained from a commercial calf ranch (CalfTech, Tulare, CA) at approximately 105 d of age. As part of the rearing program, calves were vaccinated at the calf ranch for bovine rhinotracheitis virus, bovine viral diarrhea virus Types 1 and 2, and parainfluenza-3 virus (2 mL s.c., Bovi-Shield Gold 4, Zoetis Animal Health, New York, NY) on d 25 and 50 and for Moraxella bovis (2 mL s.c., I-Site XP Pinkeye, AgriLabs, St. Joseph, MO) on d 30 and 60. Upon arrival (August 14, 2017) at the University of California Desert Research and Extension Center (Holtville, CA), calves were vaccinated for infectious bovine rhinotracheitis, bovine viral diarrhea, parainfluenza-3, and bovine respiratory syncytial virus (Bovi-shield Gold One Shot, Zoetis Animal Health) and clostridials (Ultrabac 7, Zoetis Animal Health); treated for parasites (Dectomax Injectable, Zoetis Animal Health); and injected with 1,500 IU of vitamin E (as d-α-tocopherol), 500,000 IU of vitamin A (as retinyl-palmitate), 50,000 IU of vitamin D3 (Vital E-AD, Stuart Products, Bedford, TX), and 2.5 mg/kg tulathromycin (Draxxin, Zoetis Animal Health). Following an initial 112-d initial receiving-growing period, calves were blocked by BW into 5 groups and randomly assigned within BW groupings to 20 pens (6 steers per pen, 5 pen replicates per treatment). Pens were 43 m2 with 22 m2 of overhead shade, automatic waterers, and 2.4 m of fenceline feed bunks. Steers were allowed ad libitum access to feed and water. Composition of the basal diet is shown in Table 1. Two levels of supplemental virginiamycin (0 vs. 16 mg/kg, 90% DM basis; V-Max 50, Phibro Animal Health, Teaneck, NJ) and 2 growth implant strategies were evaluated in a 2 × 2 factorial arrangement. The chosen level for supplemental VM (16 mg/kg, 90% DM basis) corresponds to the label dosage recommended for liver abscess control. Implant strategies were (S1) single implant with Synovex ONE (Zoetis Animal Health) versus (SPSP) Synovex Plus (Zoetis Animal Health) initially and re-implanted with Synovex plus on d 112. For calculation of growth performance, initial, interim, and final BW were reduced 4% to account for digestive-tract fill (slaughter weight). Hot carcass weights and liver scores were obtained from all steers at time of slaughter. After carcasses were chilled for 24 h, the following measurements were obtained: (1) LM area (rib-eye area), taken by direct grid reading of the muscle at the 12th rib; (2) s.c. fat over the rib-eye muscle

at the 12th rib taken at a location 3/4 the lateral length from the chine bone end; (3) KPH as a percentage of hot carcass weight; and (4) marbling score (USDA, 1965).

Estimation of Dietary NE Energy gain (EG, Mcal/d) was derived from measures of slaughter weight (W; kg) and ADG (kg/d) according to the equation EG = (0.0557W0.75)ADG1.097 (NRC, 1984). Net energy content of the diet for maintenance and gain were calculated assuming constant maintenance energy (EM, Mcal/d) of 0.086W0.75 (Fox and Black, 1984; NRC, 1988). The NE values of the diets for maintenance and

Table 1. Ingredient and estimated nutrient composition of basal growing-finishing diet fed to Holstein steers Item Ingredient composition (% DM)   Steam-flaked corn   Distillers grains plus solubles   Sorghum Sudan   Alfalfa hay   Molasses, cane   Yellow grease  Limestone  Urea   Trace mineralized salt2   Magnesium oxide   Dicalcium phosphate Nutrient composition, DM basis (%)  NEm3 (Mcal/kg)  NEg3 (Mcal/kg)   CP (%)   Rumen DIP4 (%)   Rumen UIP4 (%)   Ether extract (%)   Ash (%)   Nonstructural carbohydrates (%)   NDF (%)   Calcium (%)   Phosphorus (%)   Potassium (%)   Magnesium (%)   Sulfur (%)

Basal diet1  

68.00 10.00 8.00 4.00 4.00 2.50 1.68 1.15 0.40 0.15 0.10 87.9 2.21 1.54 14.3 63.8 36.2 6.70 5.78 58.0 17.7 0.80 0.35 0.77 0.28 0.18

Basal diet supplemented with or without 16 mg/kg virginiamycin (Vmax 50, Phibro Animal Health, Teaneck, NJ). 2 Trace mineral salt contained CoSO4, 0.068%; CuSO4, 1.04%; FeSO4, 3.57%; ZnO, 1.24%; MnSO4, 1.07%; KI, 0.052%; and NaCl, 92.96%. 3 Based on tabular NE values for individual feed ingredients (NRC, 2000). 4 DIP = degradable intake protein; UIP = undegradable intake protein. 1

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gain were obtained by means of the quadratic formula: NEm, Mcal/kg = (−b − √b2 − 4ac)/2c (Zinn and Shen, 1998), where a = −0.877DMI, b = 0.877EM + 0.41DMI + EG, c = −0.41EM, and NEg = 0.877NEm − 0.41.

Statistical Design and Analysis Pens were used as experimental units. Data were analyzed as a randomized complete block design experiment with a 2 × 2 factorial arrangement of treatments (Statistix 10, Analytical Software, Tallahassee, FL).

RESULTS AND DISCUSSION Treatment effects on growth performance and estimated dietary NE are shown in Table 2. There were no interactions (P > 0.20). Virginiamycin supplementation did not affect (P > 0.10) DMI. During the initial 112-d period, VM supplementation increased (P < 0.01) ADG (7.6%) and BW gain efficiency (8.6%). During the subsequent 85-d period, the influence of VM supplementation on ADG and BW gain efficiency were not statistically appreciable (P > 0.10). Nevertheless, VM supplementation increased overall (d 1–197) ADG (6.8%, P < 0.01) and BW gain efficiency (6.1%, P < 0.01). These enhancements in ADG and BW gain efficiency are similar to those observed in previous studies where VM dosage was 40% greater than that used in the present study (22.5 vs. 16 mg/kg, 90% DM basis; Salinas-Chavira et al., 2009, 2016). Differences in initial and overall BW gain efficiency are attributable to increased (P < 0.01) estimated NE value of the diet. The estimated NE values for the nonsupplemented basal diet were consistent (99%) with expected based on growth performance and tabular NE values for the diet (NRC, 2000). However, with VM supplementation, the overall estimated NEm and NEg values based on growth performance for the diet were greater than expected (5 and 6%, respectively, P < 0.01). This effect of VM on the estimated NE value of the diet is consistent with previously reported studies (Montano et al., 2014; Navarrete et al., 2017). Virginiamycin is effective in controlling lactic acid production and modulating rumen pH (Nagaraja and Taylor, 1987; Coe et al., 1999). In calf-fed Holstein steers, rate of BW gain is maximal within the weight range of 270 to 450 kg (Torrentera et al., 2016), corresponding to the initial 112-d period of this study. Feed intake variation during this period of maximal expression of genetic potential for growth heightens risk of associated metabolic disturbances. As well, it has been proposed that VM enhances postruminal nutrient absorption (Erasmus et al., 2008). Parker et al. (1990) observed that VM supplementation increased in vitro ruminant intestinal microvilli length, leading to enhanced nutrient absorption by brush border vesicles. The combined effect of VM on rumen and small intestine health may be the basis for the estimated improvements in the apparent efficiency of energy utilization. These changes may not only reflect improved efficiency of

nutrient uptake but also reduced energy expenditure for maintenance of intestinal health. Compared with a single long-duration implant (Synovex One), the re-implant program (Synovex Plus initially followed by a re-implant with Synovex Plus on d 112) provided for greater initial 112-d (8.3%, P < 0.01) and overall 197-d (7.5%, P < 0.01) ADG. Enhancements in ADG were due, in part, to increased initial (3.4%, P = 0.02) and overall (3.4%, P = 0.04) DMI and, in part, to increased initial 112-d (4%, P = 0.05) and overall (2.9%, P = 0.04) estimated dietary NE. Accordingly, compared with a single long-duration implant, the re-implant program enhanced (P < 0.01) initial 112-d and overall 197-d gain efficiency by 4.2 and 3.6%, respectively. Based on growth equations for implanted calf-fed Holstein steers (ADG = 1.242 − 0.003278AW + 0.00002264AW2 − 0.00000002964AW3, where AW is average weight; r2 = 0.80; Torrentera et al., 2016), expected initial 112-d and final 85-d ADG for SPSP re-implant treatment are 1.64 and 1.42 kg, in close agreement with those observed (104 and 99%, respectively). In contrast, with the S1 single longduration implant treatment, ADG was 96 and 89% of that projected, during the initial and final periods, respectively. Overall (197 d), ADG was 102 and 93% of that projected for the SPSP versus S1 implant strategies, respectively. Treatment effects on carcass characteristics, liver abscess incidence, and morbidity are shown in Table 3. There were no treatment interactions. Supplemental VM increased carcass weight (4%, P = 0.01), KPH (2%, P = 0.04), and yield grade (12.4%, P = 0.05) but did not affect (P > 0.10) LM area and marbling score. The effects of VM on carcass weight are consistent with that reported by Gorocica and Tedeschi (2017). Liver abscess incidence was low, averaging 5.8%. And, although numerically lower (29%) for VM-supplemented steers, the difference was not statistically appreciable (P = 0.68). Virginiamycin is labeled for reduction of liver abscess at the 13.5 to 16 mg/kg dosage level (90% DM basis). Effectiveness of VM in preventing liver abscesses is associated with its ability to control harmful bacteria populations, improving rumen health and integrity (Rogers et al., 1995). The magnitude of the reduction in liver abscess incidence in the present study is consistent with that reported in a recent 16,000-head meta-analysis evaluating the effect of VM on liver abscess incidence (29%, Tedeschi and Gorocica-Buenfil, 2018). Implant program did not affect (P > 0.10) KPH, fat thickness, LM area, and retail yield. Compared with the S1 single long-duration implant, the SPSP re-implant strategy increased carcass weight (2.8%, P = 0.04) but decreased marbling score (9.1%, P = 0.02). Implant program did not affect liver abscess incidence (P > 0.10). The basis for decreased marbling with SPSP versus S1 is uncertain. However, Parr et al. (2011) likewise observed improved marbling in steers receiving a single long-acting implant program versus a conventional re-implant program. Smith et al. (2017) postulated that enhanced mRNA expression

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Table 2. Main effects of implant program and supplemental virginiamycin (VM) on growth performance and dietary NE in calffed Holstein steers during the final 197 d of a 309-d feeding period Synovex One1 Item

0 mg/kg VM

Pen replications 5 Days on test 197 Weight,2 kg    Initial 286   112 d 452  Final 566 ADG (kg)     1–112 d 1.49   112–197 d 1.32   1–197 d 1.42   DMI (kg/d)   1–112 d 8.33   112–197 d 9.45   1–197 d 8.82 ADG/DMI     1–112 d 0.179   112–197 d 0.140   1–197 d 0.161 Estimated dietary NE (Mcal/kg)  Maintenance     1–112 d 2.15   112–197 d 2.24   1–197 d 2.18  Gain     1–112 d 1.47   112–197 d 1.55   1–197 d 1.50 Estimated/expected dietary NE  Maintenance     1–112 d 0.97   112–197 d 1.01   1–197 d 1.00  Gain     1–112 d 0.97   112–197 d 1.02   1–197 d 0.98

Synovex Plus1

16 mg/kg VM   5 197

          289 473     586     1.65     1.32 1.51         8.36   9.50 8.86       0.198   0.140   0.171  

0 mg/kg VM

P-value

16 mg/kg VM

5 197

  288 472 586   1.66 1.33 1.52   8.67 9.52 9.03   0.191 0.140 0.168

5 197

  286 480 607   1.74 1.48 1.63   8.59 10.1 9.23   0.203 0.147 0.177

SEM      

1.5 4.2 5.8   0.037 0.049 0.028   0.11 0.19 0.13   0.003 0.005 0.002

Implant      

0.72 <0.01 <0.01   <0.01 0.11 <0.01   0.02 0.11 0.04   0.03 0.45 0.19

Virginiamycin      

0.72 <0.01 <0.01   <0.01 0.15 <0.01   0.82 0.14 0.38   <0.01 0.52 <0.01

2.31 2.29 2.29   1.62 1.60 1.59

               

  2.24 2.30 2.25   1.55 1.61 1.56

  2.34 2.35 2.33   1.64 1.65 1.63

  0.029 0.052 0.025   0.025 0.046 0.022

  0.05 0.25 0.04   0.05 0.25 0.04

  <0.01 0.32 <0.01   <0.01 0.32 <0.01

1.05 1.04 1.04   1.06 1.05 1.05

               

  1.02 1.05 1.02   1.02 1.06 1.03

  1.06 1.07 1.06   1.08 1.09 1.07

  0.013 0.024 0.012   0.016 0.030 0.015

  0.05 0.25 0.04   0.05 0.25 0.04

  <0.01 0.32 <0.01   <0.01 0.32 <0.01

Interaction      

0.21 0.18 0.99   0.36 0.17 0.71   0.64 0.22 0.55   0.36 0.51 0.82     0.27 0.95 0.61   0.27 0.95 0.61     0.27 0.95 0.61   0.27 0.95 0.61

Synovex-One implant (Zoetis Animal Health, New York, NY) given on d 1. Synovex-Plus implant (Zoetis Animal Health) given on d 1 and 112. 2 Shrunk BW (full weight × 0.96). 1

of adipogenic genes with slower-release long-acting implants may explain differences between implant strategies on marbling score.

APPLICATIONS In addition to potential benefits in liver abscess reduction, lower-dosage-level virginiamycin supplementation (16 mg/kg) enhanced ADG and gain efficiency and estimated dietary NE of calf-fed Holstein steers. The effect was most noticeable during the growing phase when ADG

was greatest. A single long-duration implant may not afford the same growth and gain efficiency response as conventional re-implant strategies for calf-fed Holstein steers. Although, marbling score may be improved.

ACKNOWLEDGMENTS This project was supported through the University of California Agricultural Experiment Station with Hatch funding from the USDA National Institute of Food and Agriculture (CA-D-ASC-6578-H).

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Table 3. Main effects of implant program and supplemental virginiamycin (VM) on carcass characteristics of calf-fed Holstein steers Synovex One1 0 mg/kg VM

Item Carcass wt (kg) DP KPH fat2 (%) Fat thickness (cm) LM area (cm2) Marbling score3 Retail yield4 (%) Yield grade Abscessed liver (%)

346 61.1 1.97 0.53 91.5 4.59 52.7 1.76 10.0

Synovex Plus1

16 mg/kg VM   357 60.9 2.00 0.61 89.6 4.37 51.9 2.04 0.00

                 

P-value

0 mg/kg VM

16 mg/kg VM

SEM

Implant

Virginiamycin

Interaction

353 60.2 1.97 0.43 90.6 3.88 52.6 1.78 6.67

371 61.0 2.02 0.54 92.9 4.27 52.2 1.93 12.0

4.51 0.356 0.018 0.060 1.68 0.154 0.243 0.104 5.52

0.04 0.34 0.66 0.20 0.48 0.02 0.68 0.64 0.45

<0.01 0.45 0.04 0.12 0.91 0.60 0.05 0.06 0.68

0.51 0.17 0.66 0.85 0.24 0.07 0.55 0.54 0.19

Synovex-One implant (Zoetis Animal Health, New York, NY) given on d 1. Synovex-Plus implant (Zoetis Animal Health) given on d 1 and 112. 2 KPH fat as a percentage of carcass weight. 3 Using 3.0 as minimum slight, 4.0 as minimum small, 5.0 as minimum moderate, 6.0 minimum modest, and so on (USDA, 1997). 4 Estimated retail yield of boneless, closely trimmed retail cuts from the round, loin, rib, and chuck [% of hot carcass weight (HCW); Murphey et al., 1960] = 52.56 − 1.95 × s.c. fat − 1.06 × KPH + 0.106 × LM area − 0.018 × HCW. 1

LITERATURE CITED Coe, M. L., T. G. Nagaraja, Y. D. Sun, N. Wallace, E. G. Towne, K. E. Kemp, and J. P. Hutcheson. 1999. Effect of virginiamycin on ruminal fermentation in cattle during adaptation to a high concentrate diet and during an induced acidosis. J. Anim. Sci. 77:2259–2268. https:​/​/​doi​.org/​10​.2527/​1999​.7782259x. DiConstanzo, A., and C. M. Zehnder. 1999. Estimation of protein requirements of feedlot steers. Prof. Anim. Sci. 15:116–123. https:​/​/​ doi​.org/​10​.15232/​S1080​-7446(15)31739​-3. Erasmus, L. J., C. Muya, S. Erasmus, R. F. Coertze, and D. G. Catton. 2008. Effect of virginiamycin and monensin supplementation on performance of multiparous Holstein cows. Livest. Sci. 119:107–115. https:​/​/​doi​.org/​10​.1016/​j​.livsci​.2008​.03​.005. Fox, D. G., and J. R. Black. 1984. A system for predicting body composition and performance of growing cattle. J. Anim. Sci. 58:725–739. https:​/​/​doi​.org/​10​.2527/​jas1984​.583725x. Gorocica, M. A., and L. O. Tedeschi. 2017. 498 Virginiamycin increases performance and carcass weight of feedlot cattle under Mexican conditions. J. Anim. Sci. 95(Suppl. 4):243. https:​/​/​doi​.org/​10​.2527/​ asasann​.2017​.498. Ives, S. E., E. C. Titgemeyer, T. G. Nagaraja, A. del Barrio, D. J. Bindel, and L. C. Hollis. 2002. Effects of virginiamycin and monensin plus tylosin on ruminal protein metabolism in steers fed corn-based finishing diets with or without wet corn gluten feed. J. Anim. Sci. 80:3005–3015. https:​/​/​doi​.org/​10​.2527/​2002​.80113005x. Montano, M. F., O. M. Manriquez, J. Salinas-Chavira, N. Torrentera, and R. A. Zinn. 2014. Effects of monensin and virginiamycin supplementation in finishing diets with distiller dried grains plus solubles on growth performance and digestive function of steers. J. Appl. Anim. Res. 43:417–425. https:​/​/​doi​.org/​10​.1080/​09712119​.2014​.978785. Murphey, C. E., D. K. Hallett, W. E. Tyler, and J. C. Pierce. 1960. Estimating yields of retail cuts from beef carcasses. J. Anim. Sci. 19(Suppl. 1):1240.

Nagaraja, T. G., and M. M. Chengappa. 1998. Liver abscesses in feedlot cattle: A review. J. Anim. Sci. 76:287–298. https:​/​/​doi​.org/​10​ .2527/​1998​.761287x. Nagaraja, T. G., and M. B. Taylor. 1987. Sensitivity and resistance of ruminal bacteria to antimicrobial feed additives. Appl. Environ. Microbiol. 53:1620–1625. Navarrete, J. D., M. F. Montano, C. Raymundo, J. Salinas-Chavira, N. Torrentera, and R. A. Zinn. 2017. Effect of energy density and virginiamycin supplementation in diets on growth performance and digestive function of finishing steers. Asian-Australas. J. Anim. Sci. 30:1396–1404. https:​/​/​doi​.org/​10​.5713/​a jas​.16​.0826. NRC. 1984. Nutrient Requirement of Beef Cattle. 6th rev. ed. Natl. Acad. Press, Washington, DC. NRC. 1988. Nutrient Requirement of Dairy Cattle. 6th rev. ed. Natl. Acad. Press, Washington, DC. NRC. 2000. Nutrient Requirement of Beef Cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC. Owens, F. N., D. S. Secrist, W. J. Hill, and D. R. Gill. 1998. Acidosis in cattle: A review. J. Anim. Sci. 76:275–286. https:​/​/​doi​.org/​10​ .2527/​1998​.761275x. Parker, D. S., H. Tapper, H. Mason, and H. Tuer. 1990. The effect of inclusion of virginiamycin in food on glucose and alanine transport by intestinal brush border membrane vesicles of sheep. Anim. Prod. 50:576–577. (Abstr.) https:​/​/​doi​.org/​10​.1017/​S0308229600018894. Parr, S. L., K. Y. Chung, J. P. Hutcheson, W. T. Nichols, D. A. Yates, M. N. Streeter, R. S. Swingle, M. L. Galyean, and B. J. Johnson. 2011. Dose and release pattern of anabolic implants affects growth of finishing beef steers across days on feed. J. Anim. Sci. 89:863–873. https:​/​/​ doi​.org/​10​.2527/​jas​.2010​-3447. Perry, T. C., D. G. Fox, and D. H. Beerman. 1991. Effect of an implant of trenbolone acetate and estradiol on growth, feed efficiency and carcass composition of Holstein and beef steers. J. Anim. Sci. 69:4696–4702. https:​/​/​doi​.org/​10​.2527/​1991​.69124696x.

Latack et al.: Virginiamycin supplementation and implant strategy for calf-fed Holsteins Rogers, J. A., M. E. Branine, C. R. Miller, M. I. Wray, S. J. Bartle, R. L. Preston, D. R. Gill, R. H. Pritchard, R. P. Stillborn, and D. T. Bechtol. 1995. Effects of dietary virginiamycin on performance and liver abscess incidence in feedlot cattle. J. Anim. Sci. 73:9–20. https:​/​ /​doi​.org/​10​.2527/​1995​.7319. Salinas-Chavira, J., A. Barreras, A. Plascencia, M. F. Montano, J. D. Navarrete, N. Torrentera, and R. A. Zinn. 2016. Influence of protein nutrition and virginiamycin supplementation on feedlot growth performance and digestive function of calf-fed Holstein steers. J. Anim. Sci. 94:4276–4286. https:​/​/​doi​.org/​10​.2527/​jas​.2016​-0576. Salinas-Chavira, J., J. Lenin, E. Ponce, U. Sanchez, N. Torrentera, and R. A. Zinn. 2009. Comparative effects of virginiamycin supplementation on characteristics of growth-performance, dietary energetics, and digestion of calf-fed Holstein steers. J. Anim. Sci. 87:4101– 4108. https:​/​/​doi​.org/​10​.2527/​jas​.2009​-1959. Smith, Z. K., K. Y. Chung, S. L. Parr, and B. J. Johnson. 2017. Anabolic payout of terminal implant alters adipogenic gene expression of the longissimus muscle in beef steers. J. Anim. Sci. 95:1197–1204. https:​/​/​doi​.org/​10​.2527/​jas​.2016​.0630. Tedeschi, L. O., and M. A. Gorocica-Buenfil. 2018. An assessment of the effectiveness of virginiamycin on liver abscess incidence and growth performance in feedlot cattle: A comprehensive statistical analysis. J. Anim. Sci. 96:2474–2489. https:​/​/​doi​.org/​10​.1093/​jas/​sky121. Torrentera, N., A. Barreras, V. Gonzalez, A. Plascencia, J. Salinas, and R. A. Zinn. 2016. Delay implant strategy in calf-fed Holstein

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steers: Growth performance and carcass characteristics. Appl. Anim. Res. 45:454–459. https:​/​/​doi​.org/​10​.1080/​09712119​.2016​.1210012. USDA. 1965. Official United States Standards for Grades of Carcass Beef. USDA. Consumer and Marketing Services, Service and Regulatory Announcement No. 99. US Gov. Print. Off., Washington, DC. USDA. 1997. United States Standards for Grading of Carcass Beef. Agric. Market. Serv., USDA, Washington, DC. Van Nevel, C. J., D. I. Demeyer, and H. K. Hendrrickx. 1984. Effect of virginiamycin on carbohydrate and protein metabolism in the rumen in vitro. Arch. Tierernahr. 34:149–155. https:​/​/​doi​.org/​10​.1080/​ 17450398409426938. Zinn, R. A., E. G. Alvarez, M. F. Montano, and J. E. Ramirez. 2000. Interaction of protein nutrition and laidlomycin on feedlot growth performance and digestive function in Holstein steers. J. Anim. Sci. 78:1768–1778. https:​/​/​doi​.org/​10​.2527/​2000​.7871768x. Zinn, R. A., J. F. Calderon, L. Corona, A. Plascenceia, M. F. Mantano, and N. Torrentera. 2007. Phase feeding strategies to meet metabolizable amino acid requirements of calf-fed Holstein steers. Prof. Anim. Sci. 23:333–339. https:​/​/​doi​.org/​10​.15232/​S1080​-7446(15)30986​-4. Zinn, R. A., and Y. Shen. 1998. An evaluation of ruminally degradable intake protein and metabolizable amino acid requirements of feedlot calves. J. Anim. Sci. 76:1280–1289. https:​/​/​doi​.org/​10​.2527/​ 1998​.7651280x.