**2. Materials and Methods**

#### *2.1. Cow Management*

All animal care and experimental protocols were approved by the South Dakota State University (SDSU) Animal Care and Use Committee (approval number 18-081E). Mature, Angus-based, spring-calving cows (*n* = 131) from the SDSU Antelope Range and Livestock Research Station were evaluated for pregnancy in the fall of 2017 and assigned to dietary treatments based on cow age and body condition score (BCS). Groups were randomly assigned to a forage-based or concentrate-based dietary treatment and allotted to two pens based on treatment (Forage (*n* = 64) or Concentrate (*n* = 65)). The uterine environment

created by differing VFA profiles within each cow was considered the experimental unit. Dietary composition of the treatment diets is provided in Table 1.


**Table 1.** Dietary components (dry matter basis) consumed by cows receiving a forage-based (For) or concentrate-based (Conc) diet during mid- and late-gestation.

<sup>1</sup> Diets formulated based on NRC (2000) requirements. <sup>2</sup> Suspension supplement: 20% Crude Protein (≤20% Non-protein nitrogen), 3.55–4.55% Ca, 0.20% P, 0.30% Mg, 1% K, 528.63 ppm Mn, 12.65 ppm Co, 480 ppm Cu, 5.50 ppm Se, 1440 ppm Zn, 88184 IU/kg Vit. A, 24912 IU/kg Vit. D3, 165 IU/kg Vit. E, 400 g/ton monensin.

Feed intake was controlled so that cows in both treatments consumed equal amounts of protein and energy. Cows were provided the treatment diets beginning at approximately day 94 of gestation and continuing until approximately 30 days prior to calving. Both diets were formulated to maintain cow body condition. Body weight (BW) and BCS from the beginning (day 0) and end (day 98) of the treatment period were used to monitor the influence of dietary carbohydrate source on cow performance. Initial BW was recorded after a two-week diet adaptation period to account for differences in gut fill (cows were provided treatment diets that varied in digestibility and intake compared to the pre-treatment diet). Average initial BW of the cows was 598 ± 49.4 kg and 666 ± 52.4 kg for concentrate and forage treatments, respectively (likely due to differences in rumen fill), and average BCS was 5.2 ± 0.39 and 5.3 ± 0.31 for concentrate and forage treatments, respectively. At the completion of the treatment period the average BW of the cows was 639 ± 60.7 kg and 635 ± 57.4 kg, and average BCS was 5.4 ± 0.57 and 5.1 ± 0.38 for concentrate and forage treatments, respectively. At the end of the treatment period, cows were returned to native range pastures and managed as a common group through weaning.

#### *2.2. Offspring Management*

At approximately 60 d of age, all calves were vaccinated with a killed vaccine for clostridial diseases (Vision 7 Somnus with SPUR, Merck Animal Health, Madison, NJ, USA). At approximately 110 days of age, all calves were administered a modified-live vaccine for prevention of bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD), bovine respiratory syncytial virus (BRSV) Types 1 and 2, and parainfluenza-3 (PI3), Haemophilus somnus, and *Mannheimia haemolytica* (Pyramid 5+ Presponse SQ, Boehringer Ingelheim Vetmedica, Inc., St. Joseph, MO, USA). At weaning, all calves were administered an anthelmintic (Dectomax Pour-On Solution, Zoetis, Parsippany, NJ, USA) and were provided boosters of the clostridial disease and respiratory disease vaccines. At this time, a subset of 96 calves (*n* = 24 heifers/treatment, *n* = 24 steers/treatment) closest to the mean weaning weight were shipped to the SDSU Cottonwood Field Station. Calves were fed a common receiving diet consisting of grass hay and dried distiller's grains with solubles during an 83-days

backgrounding period. On day 36 postweaning, calves were weighed and ultrasounded to determine backfat thickness (BF), muscle depth of the *longissimus dorsi*, and intramuscular fat (IMF) measured at the 12th and 13th rib.

At the conclusion of the backgrounding phase, all calves were transported approximately 526 km to Brookings, SD for the finishing phase of the study. Upon arrival, calves were vaccinated against clostridia perfringens type A (Clostridium Perfringens Type A Toxoid; Elanco, Greenfield, IN, USA). The calves were finished in an Insentec monitoring system (Insentec, Marknesse, The Netherlands) to monitor individual feed intake (steers and heifers were fed separately in two pens) at the SDSU Cow-Calf Education and Research facility. Calves were stepped up to their finishing diets over 14-days; final diets are shown in Table 2. Diet ingredients were sampled weekly and monthly composites were used to determine the dry matter [10], crude protein [11], neutral detergent fiber [12], acid detergent fiber [13], ash [14], crude fat [15]. Tabular values for diet ingredients were used to calculate energy content of diets.

**Table 2.** Dietary components and nutrient composition of finishing diet <sup>1</sup> consumed by offspring of cows receiving a forage-based or concentrate-based diet during mid- and late-gestation.


<sup>1</sup> Diet formulated based on NRC (2000) requirements. <sup>2</sup> Dried distiller's grains w/solubles fed to heifers included melengestrol acetate (MGA, Zoetis, Parsippany, NJ, USA) at a rate sufficient to provide 0.50 mg·hd−1·day−1; steers received dried distiller's grains w/solubles without MGA. <sup>3</sup> Suspension supplement: 30.8% protein (26.6% non-protein nitrogen), 8% Ca, 0.2% P, 0.4% Mg, 7.1% K, 15.6 ppm Co, 337.6 ppm Cu, 33.8 ppm I, 723.8 ppm Mn, 3.2 ppm Se, 1107.8 ppm Zn, 9502 IU/kg Vit A, 2381 IU/kg Vit D3, 848 IU/kg Vit E, 512.3 g/ton monensin.

Cattle were weighed at 28-days intervals during the finishing period to monitor performance (hereafter referred to as Period 1, Period 2, etc.). Calves were administered an initial growth promoting implant on day 23 of the finishing period containing 100 mg trenbolone acetate (TBA) and 14 mg estradiol benzoate (EB) (Synovex-Choice, Zoetis Inc., Parsippany, NJ, USA). Cattle were re-implanted with 100 mg TBA and 14 mg EB (Synovex-Choice, Zoetis Inc., Parsippany, NJ, USA) and a second ultrasound was conducted on day 80 of the finishing period. Ultrasound measures collected during the backgrounding period and finishing period were compared to determine changes in composition. The second ultrasound was also used to predict harvest date. The harvest target was determined when the predicted BF was approximately 1.27 cm, resulting in three harvest dates at day 131, day 145, and day 180 of the finishing period. Cattle were weighed the morning of slaughter to determine final live BW and shipped 235 km to a commercial harvest facility.

#### *2.3. Carcass Evaluation and Sample Collection*

All cattle were tracked individually through the harvest process. Following carcass chilling (approximately 24 h), hot carcass weight (HCW), ribeye area (REA), 12th rib BF, USDA Yield Grade, marbling score, carcass maturity, and USDA Quality Grade were evaluated according to the United States Standards for Grades of Carcass Beef [16]. Objective color measurements (*L*\*, *a*\*, and *b*\*) were also recorded at the exposed REA of each carcass using a handheld Minolta colorimeter (Model CR-310, Minolta Corp., Ramsey, NJ, USA; 50 mm diameter measuring space, D65 illuminant). A strip loin (IMPS #180) was collected from each carcass and transported to the SDSU Meat Science Laboratory, portioned into 2.54-cm steaks, and vacuum packaged. Four steaks were aged for either 3, 7, 14, or 21 days at 4 ◦C and then frozen at −10 ◦C for evaluation of Warner-Bratzler shear force (WBSF). Additional steaks were utilized to determine fatty acid profile using Fatty Acid Methyl Ether (FAME) synthesis, crude fat percentage using ether extraction, and consumer palatability of 14-d aged samples using a trained sensory panel.
