Weaning,yearling, and preharvest ultrasound measures of fat and muscle area in steers,bulls, and heifers

Longissimus muscle area and fat thickness were measured following weaning, at yearling, and prior to harvest using real-time ultrasound, and corresponding carcass measurements were recorded 3 to 7 d following the preharvest scan in composite steers (n = 116, 447 +/- 19 d), bulls (n = 224, 521 +/- 11 d), and heifers (n = 257,532 +/- 12 d). Although fat deposition was limited in bulls and heifers from weaning to yearling, coefficients of variation ranged from 8.46 to 13.46% for muscle area, and from 27.55 to 38.95% for fat thickness, indicating that significant phenotypic variance exists across genders. Residual correlations, adjusted for the effects of year of birth, gender, and age at measurement, were high and ranged from 0.79 to 0.87 among ultrasound and carcass measures of muscle area. Residual correlations among ultrasound and carcass measures of fat thickness were also high, ranging from 0.64 to 0.86. Weaning and/or yearling ultrasound muscle area yielded similarly accurate predictions of carcass muscle area. Yearling ultrasound fat thickness accounted for 13% more of the observed variance in carcass fat thickness than the weaning ultrasound measure in single-trait prediction models. When both weaning and yearling ultrasound measures were used to predict carcass fat thickness, partial R2 values were 0.15 and 0.61 for weaning and yearling ultrasound fat thickness, respectively. The difference between predicted and carcass measures with respect to muscle area (fat thickness) was less than 6.45 cm2 (2.5 mm) for 80.2 to 88.9% (90.3 to 95%) of animals. Preharvest ultrasound measures yielded standard errors of prediction of less than 4.95 cm2 for muscle area and 1.51 mm or less for fat thickness. These results indicate that ultrasound measures taken between weaning and yearling provide accurate predictors of corresponding carcass traits in steers, bulls, and heifers.     

Feedlot and Carcass Performance of Angus-, Brangus-, Gelbvieh-, and Gelbray-Sired Crossbred Steers

Feedlot and carcass traits were evaluated for steers (n = 231) sired by Angus (A), Brangus (BA), Gelbvieh (G), and Gelbray (GB) bulls (n = 29) out of first cross (F₁) Brahman-Hereford cows. Steers were produced over 4 y and were born during spring and fall calving seasons. Brahman inheritance was 25% in A- and G-sired steers, and 44% in BA- and GB-sired steers. After weaning, steers were stockered before entering the feedlot. Steers produced in 1993 and 1994 were fed in Louisiana and individually harvested at a targeted backfat thickness of 10 mm. Steers born in 1995 and 1996 were fed in Oklahoma and group harvested at an average backfat thickness of 10 mm. Data were analyzed separately by feedlot location because of significant location and sire breed x location effects. Angus-sired steers had smaller (P<0.05) longissimus areas (LMA) and higher (P<0.01) marbling scores(MS) and quality grades than G-sired steers across both locations. Tenderness was more desirable (P<0.05) for A-sired steers compared with G-sired steers when fed in Louisiana. Angus- and G-sired steers had larger (P<0.01) LMA than BA- and GB-sired steers across both locations. Tenderness was similar (P>0.10) between steers with 25% and 44% Brahman inheritance. These data suggest that more desirable carcass quality and tenderness can be achieved with the use of A sires, relative to the other sire breeds, when mated to F₁ Brahman-Hereford dams. Improved carcass cutability resulted with the use of G sires, and in steers with 25% Brahman inheritance.     

Canola Meal Compared with Urea in a Barley and Potato Processing Residue Finishing Diet for Feedlot Steers

Five combinations of canola meal and urea were compared in a titration study using yearling beef steers (n = 120, initial weight = 383 kg ± 6.25) consuming barley and potato processing residue-based diets. The steers were allotted to 20 pens in a randomized block design and fed for 86 d. Diets were formulated to contain 30% potato processing residue, 45% barley, 15% corn silage, and 10% supplement (DM basis). Nitrogen source was the only difference in the diets. Supplements were formulated to be isonitrogenous with the N source being either urea or canola meal (C) to provide a calculated dietary CP of 11.5%. Treatments were: 100% urea supplement (0C); 25% canola meal supplement, 75% urea supplement (25C); 50% canola meal supplement, 50% urea supplement (50C); 75% canola meal supplement, 25% urea supplement (75C); and 100% canola meal supplement (100C). Average daily gain and DMI were similar for all treatments (P>0.05). Gain to feed ratio was larger (P<0.05) for 75C than 0C (163.2 vs 151.5 g/kg). Marbling scores were greater (P<0.05) from steers fed 0C than from those fed 50C or 75C. Longissimus muscle area and hot carcass weights were greater for 25C than 0C (P<0.05). Longissimus muscle area for 100C was also larger than 0C (P<0.05). The yield grade of 25C steers was lower (P<0.05) than that found in the 0C, 50C, and 100C steers (P<0.05). The 25C treatment had the highest apparent NDF digestibility of all treatments (P<0.05). Additional return of $14.50 per steer fed canola was found (P>0.05). The changes in carcass composition toward a leaner carcass with natural protein (the 25C fed steers) indicate potential benefits from the use of canola meal in barley and potato processing residue-based diets instead of urea as the sole supplemental N source.     

Genetic parameters for ultrasound and carcass measures of yield and quality among replacement and slaughter beef cattle.

Real time ultrasound (RTU) measures of longissimus muscle area and fat depth were taken at 12 and 14 mo of age on composite bulls (n = 404) and heifers (n = 514). Carcass longissimus muscle area and fat depth, hot carcass weight, estimated percentage lean yield, marbling score, Warner-Bratzler shear force, and 7-rib dissectable seam fat and lean percentages were measured on steers (n = 235). Additive genetic variances for longissimus muscle area were 76 and 77% larger in bulls at 12 and 14 mo than the corresponding estimates for heifers. Heritability estimates for longissimus muscle area were 0.61 and 0.52 in bulls and 0.49 and 0.47 in heifers at 12 and 14 mo, respectively. The genetic correlations of longissimus muscle area of bulls vs heifers were 0.61 and 0.84 at 12 and 14 mo, respectively. Genetic correlations of longissimus muscle area measured in steer carcasses were 0.71 and 0.67 with the longissimus muscle areas in bulls and heifers at 12 mo and 0.73 and 0.79 at 14 mo. Heritability estimates for fat depth were 0.50 and 0.35 in bulls and 0.44 and 0.49 in heifers at 12 and 14 mo, respectively. The genetic correlation of fat depth in bulls vs heifers at 12 mo was 0.65 and was 0.49 at 14 mo. Genetic correlations of fat depth measured in bulls at 12 and 14 mo with fat depth measured in steers at slaughter were 0.23 and 0.21, and the corresponding correlations of between heifers and steers were 0.66 and 0.86, respectively. Live weights at 12 and 14 mo were genetically equivalent (r(g) = 0.98). Genetic correlations between live weights of bulls and heifers with hot carcass weight of the steers were also high (r(g) > 0.80). Longissimus muscle area measured using RTU was positively correlated with carcass measures of longissimus muscle area, estimated percentage lean yield, and percentage lean in a 7-rib section from steers. Measures of backfat obtained using RTU were positively correlated with fat depth and dissectable seam fat from the 7-rib section of steer carcasses. Genetic correlations between measures of backfat obtained using RTU and marbling were negative but low. These results indicate that longissimus muscle area and backfat may be under sufficiently different genetic control in bulls vs heifers to warrant being treated as separate traits in genetic evaluation models. Further, traits measured using RTU in potential replacement bulls and heifers at 12 and 14 mo of age may be considered different from the corresponding carcass traits of steers.     

Effects of Prenatal Androgenization and Implantation on the Performance and Carcass Composition of Lactating Heifers in the Single-Calf Heifer System

Two experiments were conducted to evaluate feedlot performance of heifers and calves and the lactational characteristics and carcass composition and quality of heifers while in the single-calf heifer (SCH) system. In Exp. 1, 24 lactating Angus × Holstein heifers were slowly adapted to an 85% concentrate diet, and one-half of the heifers were implanted with Finaplix-H®, both at 11 wk postpartum. Heifer-calf pairs were then placed in feedlot pens, equipped with pinpointer feeding devices, and fed an 85% concentrate diet for 102 d. The control (C) and implanted (I) heifers had similar (P=0.27) daily gains and similar (P=0.30) DMI; however, I heifers consumed 8.9% less (P<0.05) DM as a percentage of BW. Pair efficiency of feed conversion tended to be higher (P<0.09) for I heifers than for C heifers. Hot carcass weight tended to be higher (P<0.10) for the I heifers. Ribeye area was 13% greater (P<0.05) and marbling score was 8.7% lower (P<0.01) for the I heifers than for the C heifers. In Exp. 2, 26 lactating Angus × Simmental heifers were used in the SCH system. Heifer adaptation to a high concentrate diet began 3 to 4 wk prepartum. Two to 3 d postpartum, 16 control (C) and 10 prenatally androgenized (PA) heifer-calf pairs were weighed, and eight C and five PA heifers were implanted with Synovex-H®. They were then placed in feedlot pens equipped with pinpointer feeding devices. By 1 wk postpartum, all heifers were adapted to an 85% concentrate diet and fed until they possessed approximately 1.1 cm s.c. fat cover over the 12th and 13th ribs. Heifers were slaughtered 12 h postweaning. The PA heifers tended to consume more (P<0.11) DM than C heifers. Gain:feed (G:F) was similar (P=0.35) for the C and PA heifers; however, the C heifers tended to have an improved (P<0.08) pair G:F. Heifer G:F and pair G:F were both similar (P=0.53) for the I and nonimplanted heifers. Most carcass measurements were unaffected by treatment; however, the I heifers tended to have higher marbling scores (P<0.07).     

Genetic parameters for carcass traits and their live animal indicators in Simmental cattle

The objective of this study was to estimate parameters required for genetic evaluation of Simmental carcass merit using carcass and live animal data. Carcass weight, fat thickness, longissimus muscle area, and marbling score were available from 5,750 steers and 1,504 heifers sired by Simmental bulls. Additionally, yearling ultrasound measurements of fat thickness, longissimus muscle area, and estimated percentage of intramuscular fat were available on Simmental bulls (n = 3,409) and heifers (n = 1,503). An extended pedigree was used to construct the relationship matrix (n = 23,968) linking bulls and heifers with ultrasound data to steers and heifers with carcass data. All data were obtained from the American Simmental Association. No animal had both ultrasound and carcass data. Using an animal model and treating corresponding ultrasound and carcass traits separately, genetic parameters were estimated using restricted maximum likelihood. Heritability estimates for carcass traits were 0.48 +/- 0.06, 0.35 +/- 0.05, 0.46 +/- 0.05, and 0.54 +/- 0.05 for carcass weight, fat thickness, longissimus muscle area, and marbling score, respectively. Heritability estimates for bull (heifer) ultrasound traits were 0.53 +/- 0.07 (0.69 +/- 0.09), 0.37 +/- 0.06 (0.51 +/- 0.09), and 0.47 +/- 0.06 (0.52 +/- 0.09) for fat thickness, longissimus muscle area, and intramuscular fat percentage, respectively. Heritability of weight at scan was 0.47 +/- 0.05. Using a bivariate weight model including scan weight of bulls and heifers with carcass weight of slaughter animals, a genetic correlation of 0.77 +/- 0.10 was obtained. Models for fat thickness, longissimus muscle area, and marbling score were each trivariate, including ultrasound measurements on yearling bulls and heifers, and corresponding carcass traits of slaughter animals. Genetic correlations of carcass fat thickness with bull and heifer ultrasound fat were 0.79 +/- 0.13 and 0.83 +/- 0.12, respectively. Genetic correlations of carcass longissimus muscle area with bull and heifer ultrasound longissimus muscle area were 0.80 +/- 0.11 and 0.54 +/- 0.12, respectively. Genetic correlations of carcass marbling score with bull and heifer ultrasound intramuscular fat percentage were 0.74 +/- 0.11 and 0.69 +/- 0.13, respectively. These results provide the parameter estimates necessary for genetic evaluation of Simmental carcass merit using both data from steer and heifer carcasses, and their ultrasound indicators on yearling bulls and heifers.     

Influence of Betaine on Pasture,Finishing, and Carcass Performance in Steers

Two experiments were conducted to investigate the effects of supplemental betaine on steer performance, fat deposition, and carcass characteristics. In Exp. 1 (grazing phase), 80 steers (317 kg) were fed either 1.0 kg of a control supplement (30% CP) or 1.0 kg of the control supplement plus 20 g of betaine per head per day. Betaine supplementation had no effect on overall gain or fat deposition (P>0.10) but increased ADG (P<0.10) during d 46 to 90 (0.64 vs 0.72 kg; control vs betaine, respectively). The pasture groups remained intact and were moved to the feedlot for 141 d and fed a control diet or the control diet plus 20 g of betaine per head per day. Betaine had no overall effect on finishing gain (P>0.10); however, this response was variable by period. Betaine increased final fat thickness and fat thickness change (P<0.10), but did not affect marbling or longissimus area (P>0.10). Supplemental betaine on pasture increased feed intake, final BW, and hot carcass weight (P<0.05) and increased final fat thickness and fat thickness change (P<0.10) during the finishing phase. In Exp. 2, supplemental betaine (40 g/d) was fed to steers (averaging 584 kg) in 11 replications during the last week before harvest. The overall weighted average increase in dressing percentage when betaine was fed was +0.34% (P<0.05). There was no effect (P>0.10) on fat thickness or marbling. Season of year did not affect response.     

Season-Long vs Intensive-Early Stocking with Growing Cattle Grazing Bermudagrass Pasture

Our objective was to compare the performance of weaned steer calves managed with intensive-early stocking (IES; 12.4 steers per ha for 70 d) or season-long stocking (SLS; 6.2 steers per ha for 140 d) with and without supplementation (2 × 2 factorial). Beginning on May 15, 90 steers (BW = 217 ± 0.8 kg) were randomly assigned to one of 12 common bermudagrass (Cynodon dactylon [L.] Pers.) pastures (0.81 ha each) fertilized with 168 kg of nitrogen/ha. One of the following four treatments was randomly applied to three pastures: i) SLS plus no supplement, ii) SLS plus 0.45 kg/steer of ground corn daily, iii) IES plus no supplement, and iv) IES plus 0.45 kg/steer of ground corn daily. Steers on IES were lighter (P=0.01) than SLS steers on d 70. By d 140, SLS steers supplemented with corn were 33 kg heavier (P=0.02) than nonsupplemented steers. When using SLS, corn increased the BW gain 0.5 kg/kg of corn fed; however, when IES was used, there was no benefit from corn supplementation. Total BW gain/ha did not differ (P>0.17) among treatments, but SLS with corn supplementation could have the potential to produce more BW gain/ha compared to the other treatments. Grazing systems did not affect feedlot ADG (P>0.53), but IES (175 d on feed) steers did have a higher (P<0.01) feedlot total BW gain than the SLS steers (154 d on feed). Using IES positively affected (P<0.08) dressing percentage and longissimus area compared to SLS; however, these differences in carcass characteristics were probably the result of the longer feeding period.     

Effects of Organic Chromium on Protein Synthesis and Glucose Uptake in Ruminants

In vitro glucose uptake and protein synthesis were measured using serum from feedlot steers fed diets supplemented with organic Cr (OCr); glucose clearance was studied using sheep as a model. Treatments investigated for glucose uptake and protein synthesis were 1) control (0 ppm supplemental Cr), 2) 0.2 ppm supplemental OCr from high Cr yeast, and 3) 0.4 ppm supplemental OCr from high Cr yeast that contained 2,000 ppm Cr (2 mg Cr/g Saccharomyces cerevisiae yeast) added to a 90% concentrate feedlot diet. The form of OCr supplied by high Cr yeast is presumably a glucose tolerance factor (GTF), which potentiates the action of insulin, and consists of Cr³⁺ centrally bound to or associated with cysteine, glutamate, glycine, and nicotinic acid residues. Serum harvested from steers fed 0.2- and 0.4-ppm OCr diets increased (P<0.05) protein synthesis in primary bovine muscle cultures. Glucose uptake rate by muscle cell cultures was increased (P<0.09) by serum from OCr-supplemented steers. Treatments investigated for glucose clearance by lambs were 1) control (0 ppm supplemental Cr), 2) 0.2 ppm, 3) 0.4 ppm, and 4) 0.8 ppm supplemental OCr from high Cr yeast added to a 85% concentrate finishing diet. Glucose clearance in lambs was improved (P<0.05) by addition of 0.2 and 0.8 ppm OCr to the diet. These results are interpreted to suggest that increased carcass muscling in ruminants fed OCr-supplemented diets is a result of improvements in amino acid uptake and glucose metabolism within muscle cells.     

Effect of Sustained-Release Ivermectin on Performance of Grazing Cattle in the Intermountain West

Five studies (trials I to V) were conducted on ranches located in the intermountain west to determine the effect of sustained-release parasite control (Ivomec SR Bolus®, Merial Limited, Rahway, NJ) on cattle performance and fecal nematode egg counts. Cattle in trials I to IV grazed irrigated meadows for 156 d (n=250 yearling heifers), 117 d (n=250 yearling steers), 85 d (n=150 yearling heifers), and 85 d (n=60 calves), respectively. In trial V, yearling steers (n=200) grazed dry high-desert range for 190 d. Weights and fecal samples were taken initially and at the end of each trial. Cattle were paired by weight and randomly assigned to treatment 1) Control: no deworming for the grazing period or 2) SRI: sustained-release ivermectin. For trials I to V, total gain difference (SRI minus Control) and ADG difference were 10.0 kg and 0.064 kg/d (P<0.001), 13.9 kg and 0.119 kg/d (P<0.001), 6.9 kg and 0.082 kg/d (P<0.01), 8.0 kg and 0.095 kg/d (P=0.05), and −0.48 kg and −0.003 kg/d (P=0.86), respectively. For trials I to V, mean initial, final Control, and final SRI fecal egg counts in eggs per gram were 0.4, 15.2, and 0.1; 6.0, 8.3, and 0.0; 75.8, 57.0, and 16.6; 76.0, 39.1, and 0.0; and 1.8, 2.0, and 0.0; respectively. Treatment of cattle grazing irrigated meadows with sustained-release ivermectin resulted in improved weight gain and fecal egg counts that were diminished to near zero. No differences (P>0.05) in weight gains were detected for cattle administered sustained-release ivermectin that grazed dry high desert range.     

Influence of Both Endophyte Infestation in Fescue Pastures and Calf Genotype on Subsequent Feedlot Performance of Steers

Three experiments were conducted to determine the influence of both the concentration of endophytic fungus infestation in tall fescue pastures and calf genotype on the subsequent health and performance of steers in the feedlot. In Exp. 1 and 2, Angus steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte infestations for 182 d (Exp. 1) or 78 d (Exp. 2) with 12 steers per treatment. Steers were transported 1,600 km to Texas in October (Exp. 1) and July (Exp. 2), were fed a 93% concentrate diet during the finishing period, and were harvested at an estimated backfat thickness of 12 mm. In both trials, DMI over the entire feeding period and carcass characteristics were not affected (P>0.05) by endophyte infestation. In both trials, pasture ADG decreased, and feedlot ADG and gain to feed ratio increased as the previous pasture endophyte infestation increased (P<0.05). Serum cholesterol concentrations tended (P<0.10) to decrease with increasing endophyte infestation during the first 14 d in the feedlot. In Exp. 3, Angus and Brahman × British crossbred steers grazed fescue pastures in Georgia containing low, moderate, or high endophyte in each of 2 yr. Six steers of each breed group were on each treatment each year. Steers were transported to Texas in late August of each year, were fed a 93% concentrate finishing diet, and were harvested at an estimated individual backfat thickness of 12 mm. As endophyte infestation increased, serum urea N concentrations and gain to feed ratios increased (P<0.05), whereas pasture ADG, initial BW, transit shrink, serum cholesterol concentrations, final BW, and carcass weights decreased (P<0.05) in Angus steers, but not in Brahman-cross steers. In these studies, the adverse effects of high endophyte infestations in fescue pastures appeared to carry over to the feedlot for ca. 14 d. However, steers from highly infested pastures can compensate for poor pasture performance with improved performance in the feedlot when no adverse health effects occur. Any impact of the endophyte seems to be similar in Brahman-cross and Angus steers.     

Estimation of Protein Requirements of Feedlot Steers

Feedlot performance, carcass characteristics, and diet composition data were collected from a survey of finishing steer experiments (40 experiments; 347 kg average initial weight; data excluded Holstein steers). Data were analyzed by weighted (observations/mean) analyses of variance to determine effects of protein intake and implanting strategy on feedlot performance and carcass characteristics. Implanting strategies were defined according to prevalent or last implant type used: no implant (None); medium-potency implants (Medium): zeranol 72 mg per dose, steroid-based implants (Synovex-S or Compudose) or trenbolone acetate (TBA) alone; high-potency implants (High): TBA in combination with either steroids or zeranol. Regression procedures were utilized to estimate CP and DIP, or MP requirements. Implant effects were independent (P>0.60) of dietary protein effects and included faster (P<0.05) gains at higher intakes (P<0.05) that resulted in improved (P<0.05) feed efficiencies. Steers responded to higher dietary CP (13.3 vs 11.4%) by increasing intake (P<0.05) which resulted in faster (P<0.05) and more efficient (P=0.09) gains. Compared to nonimplanted steers, implanted steers had heavier (P<0.05) carcasses with larger (P<0.05) ribeyes and lower (P<0.05) marbling scores. Nonimplanted steers fed 13.3% CP diets had heavier (P<0.05) carcasses than nonimplanted steers fed 11.4% CP diets. Maintenance MP requirements of nonimplanted steers were greater than those of implanted steers and similar to established MP requirements. Diets of steers implanted with high-potency implants must be supplemented to contain more than 7.5 g MP/kg BW^0.75/d, especially at heavy (>450 kg) initial BW, to maximize implant response. Implanted steers have a greater ability to respond to increased dietary protein because of reduced protein requirements for maintenance.     

Extending Interval from Seventeen to Nineteen Days in the Melengestrol Acetate - Prostaglandin Estrous Synchronization Program for Heifers

Two experiments were conducted to determine whether extending the interval between removal of melengestrol acetate (MGA) from feed and injection of prostaglandin F_2α (PGF) from 17 to 19 d would affect synchronization of estrus, conception, and pregnancy rates of beef heifers. In both experiments, heifers were fed MGA for 14 d, and PGF was given at either 17 or 19 d after cessation of MGA feeding. Heifers were observed for estrus and artificially inseminated for 5 d after PGF injection. In Exp. 1, 240 yearling heifers were randomly assigned to either a 17- or a 19-d treatment group according to estrous status and day of the estrous cycle. In Exp. 2, 1409 yearling heifers on a cooperating ranch were randomly assigned to the same two treatment groups without knowledge of estrous status. The PGF injection at 19 d (Exp. 1) caused a higher (P<0.05) percentage of heifers to exhibit estrus by 72 h after the injection compared with heifers receiving the injection at 17 d. A greater percentage (P<0.01) of heifers in the 19-d group were in the late luteal phase of the estrous cycle at the time of PGF injection compared with the heifers in the 17-d group, and pregnancy rates were higher for the heifers in the late luteal phase. In Exp. 2, heifers injected with PGF at 19 d after MGA had a greater (P<0.05) percentage in estrus (10%) during the 5-d breeding period, and had higher (P<0.05) pregnancy rates in 5 d (7.6%) and 50 d of breeding (5.5%), compared with heifers injected with PGF 17 d after withdrawal of MGA. These results indicate that the PGF injection given at 19 d after removal of MGA from the diet increases synchronized estrous response and results in higher pregnancy rates in heifers compared with the 17-d injection treatment.     

Relationships Among Growth Characteristics of Replacement Angus Heifers

Angus heifers (n = 88) were used over 3 yr to determine the relationship between two sets of traits considered to be indicators of growth. Data were collected at weaning (7 to 8 mo), yearling (10 to 11 mo), andprebreeding (13 to 14 mo) and included BW, hip height (HH), hip width (HW), pelvic height (PH), pelvic width (PW), lactate dehydrogenase (LDH) activity, longissimus area (LA), and backfat thickness (BKFAT). Measurements were grouped into two sets of traits; Set 1 included BW, HH, HW, and LDH activity; Set 2 included PH, PW, LA, and BKFAT. Weight was correlated (P < 0.01) with all variables studied except LDH activity. At weaning, heifers with lower LDH activity had a larger PH just prior to the breeding season. The first canonical variate between Set 1 measurements at weaning or yearling was correlated (r > 0.8; P < 0.01) with Set 2 measurements at prebreeding. Additional linear combinations of Set 1 traits at weaning and yearling were correlated (r > 0.48; P < 0.01) with Set 2 traits at prebreeding. These results suggest that the Set 1 measurements, as early as at weaning, could be used as indicators of Set 2 variables at prebreeding. The canonical coefficients of Set 1 traits were used to rank heifers as either above or below the mean. Ranking heifers based on Set 1 measurements at weaning resulted in a greater (P < 0.01) percentage of heifers calving as 2-yr olds. Correlations between Set 1 and Set 2 traits suggest that external measurements coupled with LDH activity could be used in identifying replacement beef heifers that have larger pelvic dimensions at breeding and a greater frequency of calving as 2-yr olds.     

Leptin as a predictor of carcass composition in beef cattle

Our objective was to determine if serum concentrations of leptin could be used to predict carcass composition and merit in feedlot finished cattle. Two different groups of crossbred Bos taurus steers and heifers were managed under feedlot conditions near Miles City, MT. The first group consisted of 88 1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise composite gene combination steers (CGC) harvested at the ConAgra processing facility in Greeley, CO. The second group (Lean Beef Project; LB) consisted of 91 F2 steers and heifers born to Limousin, Hereford, or Piedmontese by CGC F1 cows crossed to F1 bulls of similar breed composition and harvested at a local processing facility in Miles City, MT. Blood samples were collected approximately 24 h before harvest (CGC) or approximately 3 d before and at harvest (LB). No differences in serum concentrations of leptin were detected (P > 0.10) between Hereford, Limousin, or Piedmontese F2 calves nor between LB steers and heifers. Positive correlations (P < 0.01) existed between serum leptin and marbling score (r = 0.35 and 0.50), fat depth measured between the 12th and 13th rib (r = 0.34 and 0.46), kidney, pelvic, and heart fat (KPH) (r = 0.42 and 0.46), and quality grade (r = 0.36 and 0.49) in CGC and LB cattle, respectively. Serum leptin was also positively correlated with calculated yield grade for CGC steers (r = 0. 19; P = 0. 10) and LB cattle (r = 0.52; P < 0.01). Longissimus area was not correlated with serum leptin in CGC steers (r = 0.12; P > 0.10). However, a negative correlation existed between longissimus area and serum leptin in the LB cattle (r = -0.45; P < 0.01). Serum concentrations of leptin were significantly associated with carcass composition (marbling, back fat depth, and KPH fat) and quality grade in both groups of cattle studied and may provide an additional indicator of fat content in feedlot cattle.     

Effects of High Dietary Calcium Propionate and Dietary Cation-Anion Balance on Calcium Metabolism and Longissimus Muscle Tenderness in Finishing Steers,

Forty-eight Angus and Angus-cross steers (initial BW = 657 ± 5.7 kg) were used in a 2 × 2 factorial design to determine whether feeding an anionic diet or high dietary concentrations of a soluble calcium (Ca propionate) source or both would alter Ca metabolism and subsequently longissimus tenderness. Treatments consisted of 1) control, 2) 4% Ca propionate (CaProp), 3) 2% NH ₄Cl (anionic diet), and 4) CaProp plus 2% NH₄Cl. Experimental diets were fed for 7 d prior to slaughter. Steers were individually fed using electronic Calan gate feeders. Blood samples were obtained on d 3 and 7 at 2 h post feeding for plasma Ca determination. A striploin steak was obtained from each carcass at 48 h post harvest for muscle Ca analysis and Warner-Bratzler shear force (WBSF) determination. Addition of CaProp or NH₄Cl to the high concentrate finishing diet reduced (P < 0.01) ADG and DMI during the 7-d feeding period. The anionic diet reduced ADG to a greater extent than did CaProp. Average daily gain and DMI were lowest for steers fed both NH₄Cl and CaProp, indicating that their effects were additive. Carcass characteristics were not affected by CaProp, but the anionic diet tended to reduce hot carcass weights (P=0.13) and longissimus areas (P=0.09). Plasma Ca concentrations were slightly greater in steers fed CaProp on d 3 (P < 0.10) and 7 (P < 0.01) of the study. The anionic diet did not affect plasma Ca. Muscle Ca concentrations and WBSF values were not affected by either CaProp or the anionic diet. Results indicate that beef tenderness was not enhanced in steers fed a diet high in CaProp or those fed an anionic diet.     

Prediction of Future Carcass Traits in Stocker Cattle at the Conclusion of Grazing

Prediction of eventual carcass traits in stocker cattle at the conclusion of grazing could be useful for culling, co-mingling of animals, feedlot pen assignments, and making management decisions in the feedyard. Ultrasound measures of 12th to 13th rib longissimus area (ULA) and fat thickness (UFAT), and off-pasture BW (OPBW) were collected from yearling cattle (n = 261) at the conclusion of grazing in two experiments that evaluated stocking rate and grazing management effects on rye (Secale cereale L.) annual ryegrass (Lolium multiflorum Lam.) pastures. Carcasss data were subsequently recorded at harvest following feedyard finishing to a visual 1-cm backfat. Correlations were analyzed to determine relationships between carcass traits and ULMA, UFAT, body condition measure (BCM), and OPBW. Ultrasound measures, breed type (BRDT; n = 4), gender (steers and heifers), and feedlot days on feed (DOF) were evaluated in multiple regression models to determine whether these variables influence eventual carcass percentage retail product, kilograms retail product (KRP), hot carcass weight (HCW), and marbling score. Ultrasound FAT and BCM were negatively correlated with percentage retail product, KRP, and HCW and were positively correlated with marbling score. All reduced regression models had R² values of between 0.15 and 0.63, and models with inputs of UFAT and OPBW consistently had the numerically greatest R² values and least RMSE. Multiple regression analyses indicated that prediction of carcass traits from stocker cattle ultrasonic measurements at the conclusion of grazing were possible, but improvement in the models will be necessary to reduce error and improve reliability.     

Intramuscular Fat Deposition in Steers Is Accelerated at a Set Body Weight

Seventy-two Angus crossbred steers (average initial BW, 351 ± 5.5 kg) were used to ascertain the breakpoint in BW above which intramuscular fat deposition was accelerated. Steers were randomly assigned to one of three treatments in an unbalanced study; treatment groups represented a BW at which steers would enter the feedlot (363, 408, or 454 kg). Until entering the feedlot, steers were grazed on pasture and supplemented to achieve 0.8 kg gain/d. Intramuscular fat deposition, measured ultrasonically, and live BW were acquired on d 0 and at 28-d intervals thereafter on each animal until harvest. In the feedlot, steers were fed a 13.4% CP concentrate diet until they reached a final BW of approximately 567 kg. After slaughter, carcass data were collected. No differences (P < 0.05) in ADG on pasture (0.85 ± 0.14 kg) or in the feedlot (1.70 ± 0.07 kg) occurred among treatments. There was good agreement between predicted and measured carcass quality grade (QG) (5.5 and 5.2, respectively). Based on broken-line analysis, deposition of intramuscular fat began to increase at approximately 378 kg regardless of BW at entry into the feedlot. The breakpoint BW for increased intramuscular fat accretion rate was calculated as 64% of mature BW of these steers.     

Effects of Lactation and Prenatal Androgenization on the Performance,Carcass Composition,and Longissimus Muscle Sensory Characteristics of Heifers in the Single-Calf Heifer System

Two experiments were conducted to evaluate feedlot performance, lactational characteristics, and carcass composition and quality of heifers and the performance of their calves in a single-calf heifer (SCH) system. In Exp. 1, 13 [10 lactating (L) and 3 nonlactating (NL)] prenatally androgenized (PA) heifers, born to cows implanted with testosterone propionate (TP) and 19 (13 L and 6 NL) control (C) heifers, born to nonimplanted cows, were used. Heifers were calved and the pairs were placed in feedlot pens to evaluate the effects of PA on feedlot performance and lactation. Heifers were fed an 85% concentrate diet and fed to a compositional endpoint of 1.1 cm of subcutaneous fat cover, at which point calves were weaned and heifers slaughtered approximately 12 h later. The NL heifers consumed 17.0% less (P<0.01) dry matter and were 30.8% more (P<0.01) efficient in feed conversion. When calf performance was included, overall feed efficiency of L heifers was 26.9% greater (P<0.05; 0.151 vs 0.119) than that of the NL feedlot heifers. Prenatal androgenization had no effect on heifer performance. Four percent fat-corrected milk yield averaged 7.79 and 5.62 kg/d for PA and C heifers, respectively. The NL heifers had 11.0% greater (P<0.01) marbling score and yield grades were 3.77 and 3.03 (P<0.05) for NL and L heifers, respectively. Livers (P<0.01) and kidneys (P<0.05) as a percentage of shrunk weight were heavier for L heifers than for NL heifers. Two carcasses were classified as hard-boned (C-maturity) and 74% received a USDA Choice grade. The L heifers tended (P<0.10) to have lower taste panel tenderness scores; however, shearforce was similar (P=0.81) for L and NL heifers. In Exp. 2, 24 Angus × Holstein heifers were utilized in the single-calf heifer system, similar to Exp. 1. Calves were weaned from their dam between d 64 and 89 postpartum. Heifers that had their calves early weaned (EW) gained 44.2% faster (P<0.01) and consumed 10.8% less (P<0.05) DM than L heifers. The EW heifers were 60.0% more (P<0.01) efficient than L heifers. However, when calf performance was included with heifer performance, L heifers were 23.7% more (P<0.05) efficient than EW heifers. The EW heifers had 18.9% heavier (P<0.01) hot carcasses than L heifers. Backfat thickness was 1.07 and 0.66 cm (P<0.01) for the EW and L heifers.     

Case Study: Relationships of Scrotal Circumference and Scrotal Volume to Growth and Semen Traits in Beef Bulls

Breeding soundness examinations (BSE) were performed on 327 bulls at three locations in Wyoming and Montana. Scrotal circumference (SC), scrotal volume (SV), and body condition score (BCS) data were also collected. The animals were classified as yearlings, 2-yr-olds, or mature bulls. Age class and BCS had significant (P<0.01) effects on SC. Age class also accounted for significant (P<0.01) variation in SV. The correlation between SC and SV was 0.88. Scrotal circumference, SV, and pelvic area (PA) were measured and adjusted for age on the 139 yearling bulls at Location 1 (MT) to allow comparison with other age-adjusted traits. The linear regression of SC on age was 0.023 cm/d (P<0.05). Scrotal circumference and age were significant (P<0.01) sources of variation for the percentage of motile sperm (MOT). Composite yearling bulls had larger (P<0.05) adjusted SV, adjusted SC, pelvic height (PH), and percentage of MOT than Red Angus yearling bulls. The simple correlation between adjusted SC and adjusted yearling BW was 0.33 (P<0.05). Actual SC and SV were positively correlated with actual BW, actual hip height (HH), and percentage of MOT. Scrotal volume and percentage of MOT were positively correlated (0.22) (P<0.05). Our results indicate that SV could be used interchangeably with SC as a measure of sperm- producing capacity in beef bulls. Results of this study indicate that selecting bulls with larger SC or SV should result in increased yearling BW, greater PA, and bulls with improved fertility.