Recent research from our group demonstrated that Bos indicus-influenced suckled beef cows had greater resilience to withstand nutrient restriction and establish pregnancy compared with B. taurus cows exposed to the same conditions. To further understand these findings, differences in metabolic profile between these same B. indicus-influenced and B. taurus females were explored. Suckled beef cows (n = 134) were enrolled in a completely randomized design with a 2 × 2 factorial arrangement of treatments. On day − 21, Angus (AN; Bos taurus) and Brangus (BN; B. indicus-influenced) cows were randomly assigned to 1) a diet that met daily energy maintenance requirements (MAINT), or 2) a diet that restricted intake to 70% of the daily energy maintenance requirements (RESTR). Cows were exposed to an estrus synchronization protocol and received an embryo 7 d after ovulation was pharmacologically induced on day 0. Blood samples were collected on days − 21 and 19 to determine circulating concentrations of non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), insulin, glucose, and IGF-1. Pregnancy status after embryo transfer was determined on day 28. As a consequence of the proposed diets, cows in the RESTR diet had less body condition score (BCS) on day 19 (P = 0.008) across breed types. Moreover, BCS change from day − 21 to 19 was included as independent covariate into subsequent analyses, allowing for the comparison of breed types under an equivalent level of body reserve mobilization. A breed × diet interaction was observed for plasma insulin (P = 0.03) and IGF-1 (P = 0.04) on day 19, where AN–RESTR cows had less plasma concentrations on day 19 compared with AN–MAINT cows. Diets did not impact (P > 0.10) plasma insulin and IGF-1 concentrations in BN cows. No diet or breed effects were observed in circulating concentrations of NEFA, BHB, and glucose (P > 0.10). Across breed types and nutritional treatment, there was positive linear effect (P ≤ 0.04) of plasma concentrations of insulin and IGF-1 on the probability of pregnancy to fixed-time embryo transfer. In summary, the negative impacts of nutrient restriction on the somatotropic axis, independently of body tissue mobilization, were heightened in Bos taurus females compared with B. indicus-influenced cohorts, which corroborate with the differences observed in fertility between these subspecies.

Establishment and maintenance of a successful pregnancy requires signaling from the embryo to the mare, a process known as maternal recognition. Six days after fertilization the trophectoderm (TE), the placental precursor, forms. Signals emanating from the TE to the uterine environment are critical to maternal recognition of pregnancy. The identity of factors necessary for this process remain unknown. A novel equine induced trophoblast cell line (iTr) was created that closely mimics the genotype and phenotype of native equine TE. Transcriptome analysis of iTr revealed expression of growth factor (GF) receptors for Epidermal GF (EGF), Hepatocyte GF (HGF), Fibroblast GF-2 (FGF-2), IGF-1, and IGF-2, suggesting these GF may be important targets during TE development in the early embryo. We hypothesized that treatment of iTr cells with these GF would induce changes in cell proliferation and expression of genes likely involved in maternal recognition. The objectives of this experiment were to evaluate the effect of these GFs on iTr mitotic response and regulation of genes involved in steroidogenesis. Equine iTr cells (n = 3) were cultured with 10 ng/mL EGF, HGF, FGF-2, IGF-1 or IGF-2 for 24 hr with 5-ethynyl-2’-deoxyuridine (EdU) supplementation during the final 2 hr. Subsequently, cells were fixed and EdU positive and total nuclei were enumerated. A parallel plate of iTr cells was treated in a similar manner and lysed for total RNA isolation. Quantitative PCR using gene-specific primers for CYP11A1, PTGS2, PTGES2, and PTGES3 was performed. Data were analyzed by ANOVA with Tukey’s post hoc adjustment using the GLM procedure of SAS. Treatment with EGF, FGF-2, HGF, and IGF-1 increased (P < 0.05) iTr proliferation from control levels of 25.33 ± 1.029% to 38.58 ± 1.605, 45.50 ± 2.937, 38.23 ± 2.007, and 35.38 ± 2.753, respectively. The 2-ΔΔCT method was used to calculate the fold change (FC) using GAPDH as the reference gene for normalization. Expression of CYP11A2, PTGES2, and PTGES3 was not affected by GF, as measured by qPCR. By contrast, PTGS2 transcript abundance increased (P < 0.05) following FGF-2 (FC = 3.327 ± 0.8291) and HGF (FC = 11.88 ± 4.572) treatment. These results indicate that FGF-2 and HGF may simultaneously induce proliferation and prostaglandin production by TE cells. The combined results of these experiments will improve our understanding of TE morphogenesis and its response to uterine-derived growth factors.

Adaptation of skeletal muscle to exercise is partially mediated by satellite cells (SCs) residing near the myofiber. Exercise stimulates production of growth factors (GF) that induce SCs to enter the cell cycle, differentiate, and fuse to the nearby myofiber. Growth factors responsible for entry of equine SCs (eqSCs) into the cell cycle are unknown. The objective of the study was to examine the effects of GFs expressed by skeletal muscle on eqSCs time to S-phase entry in vitro. Biopsies were obtained from the gluteal muscle of mature thoroughbred geldings (n=8), eqSCs isolated, and myogenicity confirmed. Following 24 h attachment to an entactin-collagen-laminin matrix, eqSCs were washed exhaustively and incubated with Dulbecco’s Modified Medium containing 1% fetal bovine serum, 1% penicillin-streptomycin, and 0.2% gentamicin supplemented with either 10 ng/mL Epidermal GF (EGF), 10 ng/mL Fibroblast GF-2 (FGF-2), 25 ng/mL Hepatocyte GF (HGF), 100 ng/mL IGF-1, 10 ng/mL IGF-2, 10 ng/mL IL-6, or an equivalent amount of 0.1% BSA. Parallel plates were maintained and cells co-incubated with 5-ethynyl-2’-deoxyuridine (EdU), a thymidine analog, for 2 h prior to fixation at either 0, 24, 48 or 72 h post-treatment. Incorporation of EdU was detected by click chemistry (AlexaFluor 488 EdU Detection kit; ThermoFisher) and total nuclei detected by Hoechst 33342. Epifluorescent micrographs were obtained and the percentage of cells in S-phase calculated as (number of EdU positive)/(number of nuclei) x 100. Results were analyzed by ANOVA with Tukey’s posthoc adjustment using the GLM procedure of SAS. As time in culture progressed, the percentage of EdU positive eqSC increased from 0 ± 0.85 % at 0 h post-treatment to 11.65 ± 0.85 and 34.71 ± 0.85% at 48 and 72 h post-treatment, respectively (P < 0.0001). At 48 h in treatment, only IGF-2 (14.42 ± 0.89) increased (P = 0.05) the percentage of cells in S-phase compared to control (10.54 ± 0.89). After 72 h in treatment, FGF-2 (40.34 ± 1.65) and HGF (41.73 ± 1.65) increased (P < 0.0004) the percentage of cells in S-phase relative to control (29.19 ± 1.65). Control and IGF-2 treated cells were not different 72 h post-treatment. These results indicate that following isolation, adult eqSCs require 72 to 96 h to enter S-phase of the cell cycle irrespective of treatment. Of the GF tested, only IGF-2 accelerated entry into S-phase while FGF-2 and HGF served as mitogens at 72 h.

To evaluate maternal and fetal system influence on early embryonic and fetal development in Bos indicus and Bos taurus cattle, a reciprocal embryo transfer approach was used in a completely randomized design with a 2 × 2 × 2 factorial arrangement of treatments in order to generate 55 pregnancies over 2 consecutive years (n = 55). Recipient cows were placed into the University of Florida Feed Efficiency Facility, containing a GrowSafe feed intake monitoring system, and were randomly assigned to 1) a diet to meet daily maintenance requirements (MAINT) or 2) a diet that restricts intake of nutrients to 70% of energy maintenance requirements (RESTR). Angus (AN) and Brangus (BN) embryo donors were superovulated and artificially inseminated with female sexed-sorted semen from the same breed. Embryos were then randomly transferred 7 d after insemination (d 7) to either AN or BN recipients fed the respective diets for 20 d. Recipients remained on the dietary scheme until d 91, at which time cows were commingled and fed a common diet that met their energy and protein requirements to the same feeding regime until calving. Transrectal ultrasonography was performed to assess fetal crown to rump length (CRL) weekly from d 42 to 91. Blood samples were collected weekly from d 28 to 91 to determine plasma concentrations of pregnancy-specific protein B (PSPB). All analyses were performed using the MIXED procedure of SAS. There was an effect of diet (P < 0.001) and day (P < 0.001) on recipient BW, with RESTR recipients having lower BW than MAINT. Similarly, diet altered recipient BCS from d 70 to 91 (diet × day, P = 0.005). Embryos from BN donors transferred to recipients fed the RESTR diet resulted in a greater (embryo breed × diet, P < 0.001) plasma concentrations of PSPB. Although no effects of embryo breed (P > 0.05) or diet (P > 0.05) were observed on fetal morphometries, fetuses from AN recipients had greater CRL on d 91 (breed × day, P = 0.021) when compared with BN recipients (167.7 ± 1.8 vs. 160.7 ± 1.6 mm, respectively). No effect of recipient breed, embryo breed, or diet was detected on gestation length (P > 0.05) or birth weight of the offspring (P > 0.05). In conclusion, Bos indicus genotype was a significant factor altering concentrations of PSPB during early gestation, whereas Bos taurus recipient genotype positively impacted early fetal growth.

The effects of administration of recombinant bovine ST (bST) on plasma hormone concentrations of cows, conceptus development, and postnatal calf performance were examined. Lactating beef cows ( = 190) were exposed to a fixed-time AI (TAI) protocol from d -10 to 0 (TAI on d 0). Cows were blocked by breed and stratified by days postpartum and then randomly assigned to receive, subcutaneously 1) 2 injections of saline (1 mL of 0.9% saline), 1 on d 0 at TAI and a second injection on d 14 (CTRL; = 53); 2) an injection of 325 mg of bST on d 0 and a saline injection on d 14 (bST0; = 48); 3) a saline injection on d 0 and an injection of 325 mg of bST on d 14 (bST14; = 49); or 4) 2 injections of 325 mg of bST, 1 on d 0 and a second injection on d 14 (bST0+14; = 40). Pregnancy status, crown-to-rump length (CRL) on Day 35, and crown-to-nose length (CNL) on Day 65 were determined via transrectal ultrasonography. Blood samples were collected on d 0, 7, 14, 21, 35, and 65, relative to TAI, to determine plasma concentrations of progesterone (P4), IGF-1, and pregnancy-specific protein B (PSPB) and also on d 18 and 21 for isolation of peripheral blood leukocytes for RNA extraction and measurement of interferon-stimulated genes transcript abundance. Individual calf BW was determined at birth and every 30 d until weaning. A subset of 24 calves was randomly selected for liver biopsies at birth to determine mRNA expression of target genes. Administration of bST to cows increased ( < 0.0001) concentrations of plasma IGF-1 for 14 d after injection compared with CTRL but did not affect fetal CRL and CNL ( = 0.23). Cows receiving bST only on d 0 had a greater ( = 0.05) transcript abundance in myxovirus resistance 2 on d 21 compared with 2bST cows (2.0- and 0.8-fold for bST0 and 2bST, respectively), whereas cows receiving bST14 and CTRL were intermediate (1.2- and 0.9-fold, respectively). Calf BW did not differ ( ≥ 0.100) among treatments on d 0, 30, 60, 90, 120, and 150 relative to birth. Injection of bST only on d 0 tended ( = 0.062) to increase calf liver mRNA expression of at birth compared with the calves born to cows in other treatments. Therefore, during a TAI protocol, the administration of 1 or 2 injections of 325 mg of bST to lactating beef cows enhanced their plasma concentrations of IGF-1 but failed to improve fetal size and plasma concentrations of maternal PSPB and P4 and had no effect on postnatal calf growth performance.

Untrained Thoroughbred horses (6 mares and 6 geldings; 11 yr [SE 1] and 565 kg [SE 11]) were used to evaluate antioxidant gene expression and enzyme activity in blood and skeletal muscle in response to prolonged exercise after receiving 2 levels of dietary selenium for 36 d: 0.1 (CON; = 6) or 0.3 mg/kg DM (SEL; = 6). Horses were individually fed 1.6% BW coastal bermudagrass hay, 0.4% BW whole oats, and a mineral/vitamin premix containing no Se. Sodium selenite was added to achieve either 0.1 or 0.3 mg Se/kg DM in the total diet. On d 35, horses underwent 2 h of submaximal exercise in a free-stall exerciser. Blood samples were obtained before (d 0) and after 34 d of Se supplementation and on d 35 to 36 immediately after exercise and at 6 and 24 h after exercise. Biopsies of the middle gluteal muscle were obtained on d 0, before exercise on d 34, and at 6 and 24 h after exercise. Supplementation with Se above the NRC requirement (SEL) increased serum Se ( = 0.011) and muscle thioredoxin reductase (TrxR) activity ( = 0.051) but had no effect on glutathione peroxidase (GPx) activity in plasma, red blood cell (RBC) lysate, or muscle in horses at rest. Serum creatine kinase activity increased ( < 0.0001) in response to prolonged exercise but was not affected by dietary treatment. Serum lipid hydroperoxides were affected by treatment ( = 0.052) and were higher ( = 0.012) in horses receiving CON than SEL immediately following exercise. Muscle expression of was unchanged at 6 h but increased ( = 0.005) 2.8-fold 24 h after exercise, whereas muscle TrxR activity remained unchanged. Glutathione peroxidase activity increased in plasma (P < 0.0001) and decreased in RBC lysate ( = 0.010) after prolonged exercise. A Se treatment × time interaction was observed for RBC GPx activity (P = 0.048). Muscle and expression and GPx activity did not change during the 24-h period after exercise. Level of dietary Se had no overall effect on expression of , , , , , , or in muscle following exercise. The impact of prolonged exercise on the activities of antioxidant enzymes varied. Furthermore, changes in enzyme activity did not necessarily align with enzyme gene expression following exercise. A higher level of Se intake elevated Se status of untrained horses, increased GPx activity, and lessened lipid peroxidation following exercise, suggesting that Se may be beneficial for mitigating oxidative muscle damage and aiding in postexercise recovery.

Plane of nutrition effects on body, tissue and cellular growth in the neonatal calf are poorly understood. The hypothesis that a low plane of nutrition (LPN) would limit skeletal muscle size by reducing fibre growth and muscle progenitor cell activity was tested. At birth, calves were randomly assigned to either a LPN (20% CP, 20% fat; GE=1.9 Mcal/days) or a high plane of nutrition (HPN; 27% CP, 10% fat, GE = 3.8 Mcal/days) in a 2 × 3 factorial design to test the impact of diet on neonatal calf growth, organ weight and skeletal muscle morphometry with time. Groups of calves (n = 4 or 5) were euthanised at 2, 4 and 8 week of age and organ and empty carcass weights were recorded. Body composition was measured by DXA. Longissimus muscle (LM) fibre cross-sectional area (CSA), fibre/mm2 and Pax7 were measured by immunohistology. Satellite cells were isolated at each time point and proliferation rates were measured by EdU incorporation. Calves fed a HPN had greater (p < 0.05) BW, ADG and hip height than those fed a LPN for 2, 4 or 8 weeks. HPN calves contained a greater (p < 0.05) percentage of fat tissue than LPN calves. Liver, spleen and thymus weights were less (p < 0.05) in LPN calves than HPN animals. Calves fed HPN had larger (p < 0.05) LM CSA at 8 weeks than LPN fed animals with no differences between the groups in numbers of satellite cells per fibre. Proliferation rates of satellite cells isolated from HPN fed calves were greater (p < 0.05) at 2 weeks than LPN fed animals, which exhibited greater (p < 0.05) proliferation rates at 4 weeks than HPN fed calves. We conclude a LPN diet reduces body growth and organ size and metabolically reprograms satellite cell activity.

Skeletal muscle satellite cells (SCs) become mitotically active, proliferate and differentiate to increase muscle size. The objective of the study was to measure the impact of submaximal exercise on horse SC proliferation, as well as the effect of time in culture on proliferation rates. Unfit, female Quarter Horse yearlings (n = 4) maintained on tall fescue pasture were exercised in a round pen for 5 min at a minimum heart rate of 135 beats per minute. Middle gluteal muscle samples were retrieved aseptically via vacuum-assisted biopsy at 24 h pre-exercise, and 24 h, 48 h, 72 h, and 96 h post-exercise. Satellite cells were isolated by pronase E digestion and differential centrifugation. Purity of the SC isolates was 90% or greater as measured by Pax7 immunostaining. Fresh isolates were cultured in Dulbecco's Modified Eagle Medium containing 20% fetal bovine serum, 4 ng/mL fibroblast growth factor-2, and 250000 units penicillin and 250000 mg streptomycin (growth media; GM). During the final 2 h of culture, EdU, a thymidine analog, was included for the measurement of proliferation rates. Cells were fixed with 4% paraformaldehyde in PBS and EdU incorporation was detected by fluorescent chemistry (ClickIt EdU AlexaFluor488). Total nuclei were detected with 4',6-diamidino-2-phenylindole (DAPI). Representative epifluorescent micrographs at 200-fold magnification were captured digitally and the numbers of EdU and DAPI cells were quantified. The percentage of proliferating cells was calculated as number of cells containing EdU divided by the total number of DAPI nuclei multiplied by 100. The percent proliferation was analyzed by ANOVA in the GLM procedure of SAS. The SCs cultured for 48 h in GM showed a greater (P < 0.0001) percentage of proliferating cells (24.01 ± 0.8804) than those cultured in GM for 24 h (0.9670 ± 0.8804). Post-exercise proliferation rates did not differ from pre-exercise values at either 24 h (P > 0.9999) or 48 h (P > 0.2827) of culture. These results demonstrate that muscle SCs isolated from young horses activate and commence proliferation between 24 and 48 h in culture. The submaximal exercise treatment did not affect activation kinetics as indicated by no change in the time to proliferate. The intensity of exercise required to stimulate SC activation in young horses remains unresolved.

This experiment compared growth, physiological, and reproductive responses of beef heifers with (MI) or without (CON) access to a creep-feeder, as a manner to stimulate metabolic imprinting while nursing their dams. On day 0, 60 Angus × Hereford heifers were ranked by BW and age (140 ± 3 kg and 68±3 days), and assigned to pairs so all ranking criteria were similar between heifers within each pair. On day 1, pairs were randomly assigned to MI (n=15) or CON (n=15). From day 1 to 51, MI pairs and their dams were allocated to 15 drylot pens where heifers had ad libitum access to a corn-based supplement through a creep-feeder. The CON pairs and their dams were maintained in an adjacent single drylot pen. From day 52 to 111, treatments were managed as a single group on a semiarid range pasture. On day 111, heifers were weaned and allocated to two pastures (one pasture/treatment), receiving hay and a corn-based concentrate until day 326. Heifer BW was recorded before and at the end of the creep-feeding period (day 1 to 51), and on days 112 and 326. On days 0, 51, 111, 187, 261, and 325, jugular blood was collected and real-time ultrasonography for longissimus muscle depth and backfat thickness assessment was performed. Blood was also collected every 10 days from days 113 to 323 for puberty evaluation via plasma progesterone. Liver and subcutaneous fat biopsies were performed on days 51, 111, 261 and 325. Average daily gain was greater (P<0.01) for MI than CON from day 1 to 51, tended (P=0.09) to be greater for CON than MI from day 112 to 326, while BW on day 326 was similar between treatments. On day 51, MI had greater (P ⩽ 0.01) plasma IGF-I and glucose concentrations, as well as mRNA expression of hepatic pyruvate carboxylase and adipose fatty acid synthase than CON. On days 261 and 325, plasma insulin concentrations were greater (P ⩽ 0.03) in CON than MI. Mean mRNA expression of hepatic IGF-I and adipose peroxisome proliferator-activated receptor gamma were greater (P ⩽ 0.05) in MI than CON. No treatment effects were detected for puberty attainment rate. In conclusion, supplementing nursing heifers via creep-feeding for 50 days altered physiological and biochemical variables suggestive of a metabolic imprinting effect, but did not hasten their puberty attainment.

The objective of this study was to examine the effects of alternative finishing strategies on beef steak color and cooked meat characteristics. Beef steers (n = 64 pens; 8 steers/pen) were allocated to a randomized complete block design with a 2 × 2 factorial treatment arrangement and initial body weight serving as the blocking factor. Factor 1 consisted of dietary treatment with cattle either being fed a conventional feedlot diet (CON) or a diet that included Programmed Nutrition Beef Program supplements. Cattle in the Programmed Nutrition (PN) treatments were fed in two-stages: 1) the basal diet with Programmed Nutrition Beef Receiver from d 1 to 20 and the basal diet with Programmed Nutrition Beef Finisher from d 21 to harvest. Factor 2 consisted of the inclusion (EGP+) or absence (EGP-) of an exogenous growth promoting program. Steers in the EGP+ treatments were implanted initially with Component E-S, reimplanted with Component TE-IS, and fed 400 mg · d(-1) · steer(-1) of ractopamine hydrochloride for the final 28 d before harvest. Steers were harvested on d 175 of feeding and 1 strip loin was removed from 2 carcasses selected at random from each pen for transport to Kansas State University. After 14 d of aging, loins were fabricated into 2.54-cm thick steaks for objective and trained sensory panel measurement of cooked meat characteristics and objective color measurements during 7 d retail display. There were no interactions (P > 0.10) between feeding strategy and exogenous growth promotants for all objective measures of color and cooked meat characteristics. Throughout the display period, PN steaks were darker (P = 0.02) than CON steaks, but surface percentages of oxymyoglobin and metmyoglobin and metmyoglobin reducing ability were unaffected by feeding strategy (P > 0.10). Loins and steaks from PN cattle possessed decreased moisture loss during aging and cooking (P < 0.01). Trained sensory panel evaluation of cooked meat revealed a dietary program × growth promotant interaction for myofibrillar tenderness, connective tissue amount, and overall tenderness (P = 0.01). Compared to the CON/EGP- and PN/EGP- treatments, steaks from the CON/EGP+ and PN/EGP+ treatments were evaluated by panelists as being less myofibrillar and overall tender (P < 0.05). The alternative feeding strategies presented in this study can favorably impact water-holding capacity without negatively compromising retail display discoloration.

The objective of the study was to examine the effect of Brahman genetics on collagen enzymatic crosslinking gene expression and meat tenderness. Steers were randomly selected to represent a high percentage Brahman genetics (n = 13), Half-Blood genetics (n = 13), Brangus genetics (n = 13), and a high percentage Angus genetics (n = 13). Muscle samples from the Longissimus lumborum muscle were collected at weaning and harvest and reverse transcription quantitative PCR (qPCR) analysis was conducted to measure the mRNA expression of lysyl oxidase (LOX), bone morphogenetic protein 1 (BMP1), and cystatin C (CYS). Steaks from subject animals were collected at harvest, aged for 14 d and subjected to collagen analysis, Warner-Bratzler Shear Force (WBS) and trained sensory panel analysis (tenderness, juiciness, and connective tissue). Data indicated that Half-Blood and Brahman steers had greater (P<0.05) WBS values and tended to receive decreased (P < 0.06) panel tenderness scores than Angus and Brangus steers. Panelists tended to detect more connective tissue in Brahman and Half-Blood steaks when compared to Angus and Brangus steaks (P < 0.07). Crosslinking gene expression data revealed that at weaning Half-Blood steers had more (P < 0.05) mRNA expression of CYS and LOX than Angus and Brangus steers. At weaning and harvest, all genetic groups had similar mRNA expression of BMP1 (P > 0.10). At harvest, Brangus and Angus steers had greater LOX mRNA expression than Brahman cattle (P < 0.05). Pearson's correlation coefficients indicated that only weaning CYS mRNA expression was correlated to WBS, panel tenderness and connective tissue scores (P < 0.05). Expression of LOX was only correlated to these measures at harvest, and BMP1 was correlated to these traits at both time periods (P < 0.05). These results indicate that collagen crosslinking enzyme activity, as indicated by mRNA levels, early in an animal's life may account for some of the variation seen in steak tenderness due to Brahman genetic influence.

Brahman × British crossbred steers (n = 40 and 38 in yr 1 and 2, respectively) were used to evaluate the effects of calf management systems following early weaning (EW) on growth performance, muscle gene expression, and carcass characteristics. On the day of EW (d 0), steers were stratified by BW and age (95 ± 14 kg; 74 ± 14 d) and randomly assigned to a control treatment that was normally weaned (NW) on d 180 (n = 10 steers/yr) or to 1 of 3 EW treatments: 1) EW and limit fed a high-concentrate diet at 3.5% of BW (as-fed basis) in drylot until d 180 (EW180; n = 10 steers/yr), 2) EW and limit fed a high-concentrate diet at 3.5% of BW (as-fed basis) in drylot until d 90 and then grazed on bahiagrass pastures until d 180 (EW90; n = 10 steers/yr), or 3) EW and grazed on annual ryegrass pastures until d 60 (yr 1; n = 10 steers) or 90 (yr 2; n = 8 steers) and then on bahiagrass pastures until d 180 (EWRG). Early-weaned steers on ryegrass and bahiagrass pastures were supplemented with high-concentrate diet at 1.0% of BW (as-fed basis) until d 180. From d 180 to 270 (yr 1), all EW steers remained in their respective treatments, whereas NW steers were provided high-concentrate diet at 1.0% of BW (as-fed basis) on bahiagrass pastures. In yr 1, feedlot finishing period began on d 270. In yr 2, the study was terminated on d 180. In both years, EW180 steers were heaviest (P < 0.0001) on d 180. On d 180 of yr 1, EWRG steers were lightest (P < 0.0001) and EW90 steers were heavier (P = 0.05) than NW steers, whereas EW90, EWRG, and NW steers had similar BW on d 180 of yr 2 (P ≥ 0.14). On d 90, muscle PPARγ mRNA expression tended (P = 0.07) to be greater for EW180 steers and was greater (P = 0.008) for EW90 vs. EWRG steers but similar (P = 0.25) between EW180 and NW steers. On d 180, PPARγ mRNA was greater (P ≤ 0.06) for EW180 vs. NW, EW90, and EWRG steers. From d 274 to 302, EW180 steers had the least ADG (P ≤ 0.09), whereas EW90 steers had similar (P = 0.19) ADG compared with EWRG steers but greater (P = 0.03) ADG than NW steers. At slaughter, carcass characteristics did not differ (P ≥ 0.22) among treatments. In summary, EW steers provided a high-concentrate diet in drylot for at least 90 d were heavier at the time of normal weaning than NW steers and EW steers grazed on ryegrass pastures for 60 to 90 d and supplemented with concentrate at 1.0% of BW. Feeding a high-concentrate diet immediately after EW enhanced the muscle PPARγ expression but did not enhance marbling at slaughter.

Drought and other weather-related disasters impact the amount and quality of grains and forages available to beef cattle. The impact of nutrient restriction at specific gestational timeframes on fetal skeletal muscle growth was examined. Crossbred beef cows were fed to NRC recommendations (CCC) or restricted to 60% of said levels for the first 85 or 140 d of pregnancy followed by realimentation to recommended protein and energy levels (RCC and RRC, respectively). Fetal infraspinatus (INF) morphometrics and gene expression analyses were performed at d 85, 140, and 254 of gestation. Results demonstrate that fetal primary myofibers are larger (P < 0.05) after 85 d of maternal caloric restriction by comparison to controls. Realimentation of pregnant dams at d 85 causes an increase (P < 0.05) in RCC INF cross-sectional area (CSA) by comparison to RRC at d 140 but the fibers remain smaller (P < 0.05) than CCC muscle cells. Returning nutrient load to recommended levels at d 140 of pregnancy increases RRC CSA equivalent to CCC fibers at d 254 (343.4 ± 5.2 and 345.2 ± 5.3 μm(2), respectively). Fetal RRC and CCC muscle fibers are smaller (P < 0.05) than RCC fibers at d 254 suggesting the later experienced compensatory growth. Numbers of Paired box 7 (Pax7) immunopositive cells were fewer (P < 0.05) in the nutrient restricted fetuses at d 85 suggesting a loss of muscle progenitor cells. Moreover, mRNA content for the collagen crosslinking enzymes, lysyl oxidase and bone morphogenetic protein 1, were greater (P < 0.05) in the d 85 nutrient restricted fetal INF than CCC suggesting increased connective tissue cell numbers and/or activity. Because myogenesis is acutely regulated by the IGF, mRNA content of these growth factors and their receptors was examined. Fetal IGF1 mRNA content was lower in the d 85 nutrient restriction fetuses (P < 0.05) by comparison to CCC. Levels of INF IGF2 mRNA were greater (P < 0.05) in d 85 NR fetuses than CCC. Continued nutrient restriction through d 140 resulted in a reduction (P < 0.05) in IGF2 expression by comparison to CCC. No treatment effect on IGF1R or IGF2R mRNA content was noted. In summary, NR for 85 d causes an increase in primary INF fiber size that may be a result of increased IGF2 transcription and Pax7-immunopositive cell fusion. Realimentation of NR beef cows supports compensatory growth of the fetal musculature such that normal muscle fiber size and muscle progenitor numbers are achieved before birth.

Inclusion of Bos indicus genetics improves production traits of cattle maintained in hot climates. Limited information exists detailing pregnancy-specific events as influenced by variable amounts of Bos indicus genetics. Three experiments were completed to examine the effect of Bos taurus and Bos indicus genotypes on fetal size and plasma pregnancy-associated glycoprotein (PAG) concentrations. In all experiments, cows were bred by AI after synchronization of ovulation. Fetal measurements were completed by transrectal ultrasonography and plasma PAG concentrations were quantified from plasma harvested the day of each fetal measurement. In Exp. 1, fetal size and plasma PAG concentrations were measured at d 53 of pregnancy in cows composed of various fractions of Angus and Brahman (n = 9 to 21 cows/group). Fetus size was greater in cows containing >80% Angus genetics compared with cows containing <80% Angus influence (3.40 ± 0.28 vs. 2.86 ± 0.28 cm crown-rump length; P < 0.01). Plasma PAG concentrations were reduced (P < 0.01) in cows containing >80% Angus genetics when compared with their contemporaries (6.0 ± 1.5 ng/mL vs. 9.4 ± 1.5 ng/mL). In Exp. 2, fetal measurements and plasma PAG concentrations were determined at d 35 and 62 of pregnancy in Angus and Brangus cows. Breed did not affect fetus size at d 35, but Angus cows contained larger fetuses than Brangus cows at d 62 [3.0 ± 0.03 vs. 2.8 ± 0.03 cm crown-nose length (CNL; P > 0.01)]. Plasma PAG concentrations were not different between breed at d 35 and 62 (P > 0.1). In Exp. 3, fetal measurements and plasma samples were collected at d 33/34, 40/41, 47/48, and 54/55 post-AI in Angus and Brangus cows. Fetus size was not different (P > 0.05) between genotypes on d 33/34, 40/41, and 47/48. Angus fetuses were larger than Brangus fetuses at d 54/55 (2.1 ± 0.03 vs. 1.9 ± 0.03 cm CNL; P = 0.001). Plasma PAG concentrations were less in Angus than Brangus cows at each time point (average 4.9 ± 0.9 vs. 8.2 ± 0.9 ng/mL; P = 0.005). In conclusion, these studies determined that the Bos taurus × Bos indicus genotype impacts fetal size and rate of fetal development by 7 wk of gestation. Plasma PAG concentrations were increased in cattle with Bos indicus genetics in 2 of 3 studies, suggesting that genotype is one of several determinants of PAG production and secretion in cattle.

Satellite cells are the resident stem cell population of adult skeletal muscle tissue that is responsible for growth and regeneration. The cells typically congregate near the tips of the muscle fi bers and in close proximity to the neural muscular junction (NMJ). Ephrin-A5 is a chemotactic molecule that participates in the correct positioning and formation of the NMJ. The objective of the experiment was to examine the effects of ephrin-A5 signaling on bovine satellite cell (BSC) biology. Primary cultures of BSC demonstrate changes in velocity with time in culture that is unique to the Paired box protein 7 (Pax7):Myogenic factor 5 (Myf5) subpopulation. Treatment of the BSC with ephrin-A5 causes a reduction (P < 0.05) in velocity with a concomitant increase (P < 0.05) in directed migration. The chemoattractant properties of ephrin-A5 occur before myogenic differentiation 1 (MyoD) expression in the myogenic precursors and are abrogated after their differentiation to committed myoblasts. Ephrin-A5 induced migration appears to require components of the Ras homolog gene family member A (RhoA) and Rho-associated protein kinase (ROCK) signaling machinery. Supplementation of culture media with a chemical ROCK inhibitor suppressed (P < 0.05) ephrin-A5 initiated BSC migration. These results contrast with treatment of BSC with hepatocyte growth factor (HGF), a key modulator of myogenic and motogenic activity. Treatment of BSC with HGF had no effect on cell motility or migration immediately after culture establishment. Twenty-four hours after culture establishment, BSC demonstrated an increase (P < 0.05) in transwell migration toward HGF. These results document that temporal and spatial gradients of chemokines and growth factors participate in the localization of BSC within the niche.

Satellite cells support efficient postnatal skeletal muscle hypertrophy through fusion into the adjacent muscle fiber. Nuclear contribution allows for maintenance of the fiber myonuclear domain and proficient transcription of myogenic genes. Niche growth factors affect satellite cell biology; however, the interplay between fiber elasticity and microenvironment proteins remains largely unknown. The objective of the experiment was to examine the effects of hepatocyte growth factor (HGF) and surface elasticity on bovine satellite cell (BSC) activation kinetics in vitro. Young's elastic modulus was calculated for the semimembranosus (SM) and LM muscles of young bulls (5 d; n = 8) and adult cows (27 mo; n = 4) cattle. Results indicate that LM elasticity decreased (P < 0.05) with age; no difference in Young's modulus for the SM was noted. Bovine satellite cells were seeded atop polyacrylamide bioscaffolds with surface elasticities that mimic young bull and adult cow LM or traditional cultureware. Cells were maintained in low-serum media supplemented with 5 ng/mL HGF or vehicle only for 24 or 48 h. Activation was evaluated by proliferating cell nuclear antigen (PCNA) immunocytochemistry. Results indicate that BSC maintained on rigid surfaces were activated at 24 h and refractive to HGF supplementation. By contrast, fewer (P < 0.05) BSC had exited quiescence after 24 h of culture on surfaces reflective of either young bull (8.1 ± 1.7 kPa) or adult cow (14.6 ± 1.6 kPa) LM. Supplementation with HGF promoted activation of BSC cultured on bioscaffolds as measured by an increase (P < 0.05) in PCNA immunopositive cells. Culture on pliant surfaces affected neither activation kinetics nor numbers of Paired box 7 (Pax7) immunopositive muscle stem cells (P > 0.05). However, with increasing surface elasticity, an increase (P < 0.05) in the numbers of muscle progenitors was observed. These results confirm that biophysical and biochemical signals regulate BSC activation.