Impacts of a leptin SNP on growth performance and carcass characters in finishing steers studied over time.

A total of 2,948 steers (mean initial BW = 568.9 ± 49.4 kg) were used to evaluate the effect of the LEP R25C SNP genotype on feed intake, growth performance, and carcass characteristics over time. Steers were grouped into 5 blocks, each consisting of 10 pens initially, and then at approximately 24 d prior to the assigned slaughter date, cattle in each pen were randomly selected either to remain in the pen they were in (group A) or to be assigned to a new pen (group B). Steers were allocated to 5 blocks and 6 harvest weeks (-3, -2, 0, 2, 3, and 4 wk) relative to the projected end point. Steers were weighed and ultrasound scanned at 60 and 1 d prior to harvest. Leptin genotype affected ( ≤ 0.011) 12th-rib fat and i.m. fat percentage (IMF) for each slaughter group at both 60 and 1 d prior to slaughter, although rib eye area (REA) was not affected ( = 0.773) by leptin genotype 60 d prior to slaughter in any group. Time affected ( < 0.001) live BW as well as 12th-rib fat, REA, and IMF measured 60 and 1 d prior to each slaughter time. Dry matter intake was also higher ( = 0.003) for cattle of the animals homozygous for the T allele (TT) genotype compared to those with the animals homozygous for the C allele (CC) genotype (9.59 vs. 9.29 ± 0.075 kg). The LEP R25C genotype affected key traits related to carcass fatness; specifically, compared to cattle of the CC genotype, cattle of the TT genotype had a higher ( = 0.016) calculated empty body fat (29.1 vs. 28.8 ± 0.133%) and higher ( = 0.020 calculated yield grade (2.62 vs. 2.52 ± 0.035). Additionally, like for live measures, TT cattle tended ( = 0.093) to have a higher 12th-rib fat (13.2 vs. 12.8 ± 0.26 mm). However, the LEP R25C genotype did not affect KPH ( = 0.854) or marbling score ( = 0.240), nor did it affect any USDA quality measure ( ≥ 0.350). The leptin genotype also affected ( = 0.048) HCW, which was highest for steers of the TT genotype (400.9 vs. 403.5 ± 3.41kg). Results indicate that the leptin R25C genotype and time impacted most traits associated with fatness.

Impact of a leptin single nucleotide polymorphism and ractopamine hydrochloride on growth and carcass characteristics in finishing steers.

A total of 2,958 steers (mean initial BW = 549.6 ± 3.88 kg) were used to test for the interactive effects, of leptin R25C genotypes (CC, CT, or TT) and feeding of ractopamine hydrochloride (RH) on growth performance and carcass traits. Before application of the drug, steers were blocked by arrival at the feed yard, genotyped for the leptin SNP, allotted to genotype-specific pens, and assigned randomly within genotype and block to 0 or 28 d of dietary RH. All pens within a block were slaughtered on the same day. Final BW of steers fed RH was 9.1 kg heavier (P < 0.001), and RH-fed steers had greater (P < 0.001) ADG and greater (P = 0.001) HCW than steers not fed RH. Feeding RH did not (P = 0.723) affect DMI but it did increase (P = 0.001) with increased frequency of the T allele (8.62, 8.70, and 8.82 kg/d for CC, CT, and TT, respectively). Consistent with the effect of leptin on DMI, increased frequency of the T allele also positively affected 12th rib fat (P = 0.001) and empty body fat (P = 0.001). Regardless of RH-feeding duration, TT steers produced a greater (P = 0.001) percentage of USDA yield grade (YG) 4 or higher carcasses (6.46 vs. 2.98%) and a lesser (P = 0.023) percentage of YG 1 carcasses (16.0 vs. 21.9%) than CC steers. In addition, RH-fed steers produced a lesser (P = 0.034) percentage of USDA YG 4 or higher carcasses (3.70 vs. 5.31%) and a lesser percentage (P = 0.019) of USDA Choice or higher carcasses (57.5 vs. 62.5%) than steers fed the control diet. Results indicated that leptin R25C genotype impacted most traits associated with fatness, whereas feeding RH for 28 d affected HCW and ADG positively but impacted marbling and USDA quality grades negatively.

The effect of supplementing zilpaterol hydrochloride on feeding performance and carcass characteristics of steers sorted by leptin genotype.

The focus of this investigation was to identify interactions that may exist among alleles of the leptin gene and supplementation of zilpaterol hydrochloride (ZH). Steers (n = 4,246; initial BW = 389.8 ± 8.8 kg) were genotyped and sorted into 1 of 3 leptin genotype (LG) groups (homozygous normal [CC], heterozygous [CT], or homozygous mutant ) from a candidate pool of 7,506 steers. Steers were allocated into 48 pens of which one-half were fed the ß-adrenergic agonist ZH and the balance, a control diet. During the pretreatment period (d 1 to 102), cattle of the TT genotype exhibited increased (P = 0.02) DMI compared to other genotypes and lower G:F than the CC genotype (P = 0.03). Cattle of the CT genotype had lower (P = 0.02) ADG compared to other genotypes for the treatment period. Cattle fed ZH had improved (P < 0.01) ADG and G:F compared to cattle on the control diet for both the treatment and entire study periods (d 1 to 125). For the entire study period, cattle of the TT genotype had greater (P = 0.03) DMI than the CT allele, with CT cattle having the lowest (P < 0.01) ADG and CC cattle having greatest (P < 0.01) G:F of all alleles. Cattle of the TT genotype had greater (P = 0.03) final shrunk weight than the CT allele. Cattle of the TT genotype had lower (P = 0.04) dressed yield compared to CT cattle and greater (P = 0.01) marbling score compared to CC cattle, with a concurrent increase (P < 0.01) in calculated empty body fat (EBF) over all alleles. Cattle fed ZH had greater (P < 0.01) final shrunk weight, HCW, dressed yield, and LM area coupled with reduced (P < 0.01) marbling score, s.c. fat depth, EBF, and calculated USDA yield grade compared to control steers. Carcasses of the TT allele had a greater (P = 0.01) proportion of Choice carcasses than CT or CC alleles and lesser (P = 0.03) proportion of Select carcasses than CC alleles. Additionally, ZH supplemented cattle had fewer (P < 0.01) carcasses grading Premium Choice or better, Choice, and yield grade 3, 4, and 5 with subsequently more (P < 0.01) carcasses grading Select, Standard, and yield grade 1. Differences in live and carcass performance exist among leptin alleles, which may allow for sorting and improved timeliness of fed beef marketing.

Impact of a leptin single nucleotide polymorphism and zilpaterol hydrochloride on growth and carcass characteristics in finishing steers.

A total of 4,178 steers (mean initial BW = 403.9 ± 16.04 kg) were used to test the interactive effects, if any, of leptin R25C genotypes (CC, CT, or TT) and zilpaterol hydrochloride (ZH) feeding duration on growth performance and carcass traits. Steers were blocked by arrival at the feed yard, genotyped for the leptin SNP, allotted to genotype-specific pens (90 steers/pen), and assigned randomly within genotype and block to 0 or 21 d of dietary ZH. All pens within a block were slaughtered on the same day (132.1 ± 10.9 d on feed). Final BW of steers fed ZH was 6.0 kg heavier (P = 0.008), and ZH-fed steers had greater (P = 0.003) ADG than steers not fed ZH. Feeding ZH decreased DMI in steers with increased frequency of the T allele (9.67, 9.53, and 9.28 kg/d for CC, CT, and TT, respectively), but DMI increased with the frequency of the T allele (9.68, 9.90, and 10.1 kg for CC, CT, and TT, respectively) when ZH was not fed (leptin genotype × ZH, P = 0.011). At the conclusion of the study, ultrasonic fat was greatest for TT steers (11.4 ± 0.28 mm) and least (P = 0.003) for CC steers (11.0 ± 0.25 mm). Regardless of ZH-feeding duration, TT steers produced a greater (P = 0.006) percentage of USDA yield grade (YG) 4 or higher carcasses (5.4 vs. 2.7%) and a lesser (P = 0.006) percentage of YG 1 carcasses (17.7 vs. 26.8%) than CC steers. In addition, ZH-fed steers produced a greater (P < 0.001) percentage of USDA YG 1 carcasses (25.9 vs. 16.2%) and a lesser (P < 0.001) percentage of YG 4 or higher carcasses (1.6 vs. 6.0%) than steers fed the control diet. Marbling scores and the percentage of carcasses grading USDA Choice and Prime were greater in TT than CC steers when fed diets devoid of ZH, but both marbling and quality grades did not differ among leptin genotypes when fed ZH for 21 d (leptin genotype × ZH, P ≤ 0.03). The amount of HCW gain tended to be less (P = 0.095) for steers of the TT genotype (12.7 kg) than either CC (16.3 kg) or CT (17.0 kg) genotypes. Results indicated that leptin R25C genotype impacted most traits associated with fatness whereas feeding ZH for 21 d affected HCW and ADG positively but impacted feed intake, marbling, and USDA quality grades negatively.

Alpharma Beef Cattle Nutrition Symposium: predictability of feedlot cattle growth performance.

Predicting performance is vital to management and marketing decisions in commercial feedlots. Agreement between performance predicted from NE equations or empirical regression relationships and actual performance is generally very good, suggesting that factors affecting performance by finishing cattle are fairly well documented. The challenge for feedlot managers is to predict performance with limited information at the start of the feeding period. Data on sex and initial shrunk BW (ISBW) are typically available when cattle start on feed. Relationships between ISBW, sex, and performance were evaluated using 3,363 pen records collected over 4 yr from 3 commercial feedlots in the Texas Panhandle. Mixed-model regression was used to account for random effects of feedlot × season × year and fixed effects of ISBW (range = 227 to 451 kg), sex (steer or heifer), and ISBW × sex (P < 0.10 for all variables evaluated). Previously developed equations indicated that with intercept and slope adjustments for sex, ISBW accounted for 76 and 84% of the variation in DMI and final shrunk BW (FSBW), respectively. Similarly, newly developed regression equations that included ISBW, sex, and ISBW × sex accounted for 46 and 81% of the variation in ADG and HCW, respectively. Initial BW was negatively related to G:F (R(2) = 0.22). Including early DMI data (DMI from d 8 to 28) increased R(2) and decreased prediction error for DMI, indicating that updating predictions with interim intake data might prove beneficial. An independent data set (781 lots of steers and heifers) collected during 1 yr from 2 Texas Panhandle feedlots was used to validate equations developed with the larger database. Dry matter intake predicted from ISBW and sex accounted for 69% of the variation in observed DMI (SE of prediction = 0.47; mean bias = 0.42 kg). Predicting DMI with ISBW, sex, and DMI from d 8 to 28 of the feeding period increased r(2) to 0.76 and slightly decreased the SE of prediction (0.42 kg), but the equation had a strong linear bias (-0.174; P < 0.001). The r(2) values for regression of observed on predicted ADG, G:F, FSBW, and HCW were 0.37, 0.08, 0.74, and 0.73, respectively, with positive mean bias (underprediction for all equations). Average daily gain calculated with NE equations from predicted DMI (ISBW and sex equation) and predicted FSBW had a similar r(2) (0.38) but less mean bias (-0.08 kg) than ADG predicted directly from ISBW and sex. Adjustments to equations for animal type, health, and management effects would likely improve predictions. Nonetheless, results suggest that predicting performance from initial BW with adjustments for steers vs. heifers should have considerable utility in practical settings.

Development and evaluation of feeding-period average dry matter intake prediction equations from a commercial feedlot database.

Intake prediction equations were developed from a commercial feedlot database consisting of 3,363 pen means collected from 3 feedlots over a 4-yr period. The objective was to predict feeding-period average DMI from variables known at the start of the feeding period, including initial BW, sex, and average DMI from d 8 to 28 of the feeding period. Equations were evaluated within the same database using bootstrapping and cross-validation techniques. Bootstrapping evaluations of equations that included initial BW and sex explained approximately 57.0 to 73.2% of the variation in observed DMI with 90.5 to 96.6% accuracy, but DMI was overpredicted by 0.21 kg/d. Accuracy and precision improved with addition to the models of average DMI from d 8 to 28 of the feeding period; these models accounted for 68.0 to 83.0% of variation in observed DMI with model accuracy between 95.2 and 99.5% and overprediction of DMI by 0.05 kg/d. Cross-validation of developed equations confirmed the robust nature of chosen variables and the decrease in prediction error as sex and average DMI from d 8 to 28 were added to models based on initial shrunk BW (SBW). Bootstrapping and cross-validation evaluations were also conducted on the NRC (1996) NE(m)-based intake prediction equations with and without the NRC-recommended 4% decrease in predicted DMI and a 12% increase in dietary NE(m) concentration associated with the feeding of monensin. The average metabolic SBW used in these equations was computed from initial SBW and a predicted final SBW developed from the pen database. When these evaluations were performed, model precision decreased compared with simpler equations that included initial BW and sex, but using both adjustments for use of monensin improved the accuracy of the NRC equation. Nonetheless, the systematic bias proportion of the mean square error of prediction for bootstrapping analyses increased from 4.6 to 11.1% in the model with no adjustments to 16.3 to 38.9% in the model with both monensin adjustments, demonstrating these adjustments are less than optimal. Overall, variables that are typically available to feedlot managers when cattle are started on feed (e.g., initial BW, sex, and an early indication of DMI) were important predictors of feeding-period average DMI by pens of cattle.

Evaluation of the National Research Council (1996) dry matter intake prediction equations and relationships between intake and performance by feedlot cattle.

Intake prediction equations of NRC based on initial BW and dietary NE(m) concentration were evaluated with a commercial feedlot database consisting of 3,363 pen means collected from 3 feedlots over a 4-yr period. The DMI predicted by NRC equations had significant (P < 0.01) mean and linear biases across the range of observed DMI in the database. In general, DMI was overpredicted by the NRC equations. Adjustment of the NE(m)-based prediction by use of a 12% increase in NE(m) concentration and a 4% decrease in predicted DMI associated with the feeding of monensin decreased bias. Dry matter intake predicted by the NE(m)-based monensin-adjusted, NE(m)- based, and initial BW equations explained 67, 66, and 64% of the variation in observed DMI, respectively. Relationships between ADG and G:F with DMI as a percentage of BW and NE(g) intake also were examined in the same data set. Across the wide range of average shrunk BW in the database (334.4 to 548.0 kg), ADG was positively related to DMI as a percentage of BW (P < 0.01); however, this relationship was not strong (r(2) = 0.17). Likewise, G:F showed little relationship with DMI as a percentage of BW (P < 0.01; r(2) = 0.05). By accounting for differences in maintenance energy requirements of pens with varying average BW, NE(g) intake was strongly and positively related to ADG (linear and quadratic, P < 0.01; R(2) = 0.70); however, G:F showed little relationship with NE(g) intake (P = 0.02; r(2) = 0.01). Our evaluations with measurements of DMI by cattle in commercial feedlots indicated the shortcomings of current published equations for predicting DMI and suggest the need for development of new equations with improved accuracy and precision. Furthermore, our data indicate that increasing NE(g) in- take increased ADG in a quadratic manner but did not affect G:F by pens of cattle in feedlots. These findings suggest a diminishing returns effect of energy intake on energy retention.

Effects of wet corn gluten feed and roughage levels on performance, carcass characteristics, and feeding behavior of feedlot cattle.

Two experiments were conducted to evaluate the effects of feeding different levels of wet corn gluten feed (WCGF) and dietary roughage on performance, carcass characteristics, and feeding behavior of feedlot cattle fed diets based on steam-flaked corn (SFC). In Exp. 1, crossbred steers (n = 200; BW = 314 kg) were fed 4 dietary treatments (DM basis): a standard SFC-based diet containing 9% roughage (CON) and 3 SFC-based diets containing 40% WCGF, with either 9, 4.5, or 0% roughage. A linear (P = 0.04) increase in final BW and DMI (P < 0.01) was observed in diets containing WCGF as dietary roughage increased. Steers fed WCGF and higher levels of roughage had greater (P = 0.01) ADG than steers fed lower levels of roughage. Steers fed the CON diet had lower (P = 0.04) daily DMI and greater (P = 0.03) G:F than those fed WCGF. Most carcass characteristics of steers fed CON did not differ (P > 0.10) from those of steers fed WCGF. Based on feed disappearance and visual scan data, consumption rate did not differ (P > 0.10) among treatments; however, feeding intensity (animals present at the bunk after feeding) was greater for steers fed CON (P < 0.01) than for steers fed WCGF. In Exp. 2, yearling crossbred steers (n = 1,983; BW = 339 kg) were fed 4 dietary treatments (DM basis): a standard SFC-based control diet that contained 9% roughage (CON) and 3 SFC-based diets containing either 20% WCGF and 9% roughage or 40% WCGF with 9 or 4.5% roughage. Steers fed the CON diet tended to have lower final BW (P = 0.14), ADG (P = 0.01), and DMI (P < 0.01) than steers fed diets containing WCGF. Steers fed the 20% WCGF diet had greater (P = 0.08) G:F than steers fed the 40% WCGF diets. With 40% WCGF, increasing roughage from 4.5 to 9% decreased (P < 0.01) G:F and increased (P = 0.06) DMI. Gain efficiency was improved (P < 0.01) for steers fed CON vs. those fed diets containing WCGF, whereas HCW (P = 0.02) and dressing percentage (P < 0.01) were greater for steers fed WCGF. Percentage of cattle grading USDA Choice was greater (P = 0.02) for cattle fed WCGF. Results suggest that replacing SFC with up to 40% WCGF increased ADG and decreased G:F when 4.5 to 9.0% roughage was supplied. More CON steers were present at the feed bunk during the first hour after feeding than WCGF steers, suggesting that including WCGF at 40% of the diet affected feeding behavior.

Effects of source of supplemental zinc on performance and humoral immunity in beef heifers.

Two experiments were conducted to evaluate receiving-period performance, morbidity, and humoral immune response, as well as finishing performance and carcass characteristics of heifers fed different sources of supplemental Zn. In Exp. 1, 97 crossbred beef heifers (initial BW = 223.4 kg) were fed a 65% concentrate diet with no supplemental Zn (control) or 75 mg of supplemental Zn/kg of DM from Zn sulfate, Zn methionine, or Zn propionate. During a 35-d receiving period, heifers were monitored daily for signs of bovine respiratory disease. Serum samples were collected for Zn analysis on d 0, 14, and 28. After the receiving period, heifers were adapted to and fed a high-concentrate diet with no supplemental Zn for 42 d. Heifers were then assigned to finishing diet treatments, with the same concentrations and sources of supplemental Zn as during the receiving period and fed for an average of 168 d. Serum samples also were obtained on d 0 and 56 of the finishing period and at the end of the study. During the receiving period, control heifers had a greater (P < or = 0.05) BW and G:F on d 35 than heifers in the other treatments, but no differences were observed among treatments for morbidity or serum Zn concentrations (P > or = 0.50). For the finishing period, DMI and ADG did not differ among treatments; however, overall G:F tended (P = 0.06) to be less for control heifers than for heifers in the 3 supplemental Zn treatments. On d 56 of the finishing period, control heifers tended (P = 0.06) to have a lower serum Zn concentration than heifers in the 3 supplemental Zn treatments. In Exp. 2, 24 crossbred beef heifers (initial BW = 291.1 kg) were fed the same 4 treatments as in Exp. 1 for a 21-d period. The humoral immune response to treatments was determined by measuring specific antibody titers after s.c. injection of ovalbumin on d 0 and 14. Body weights and blood samples for serum Zn concentration and ovalbumin IgG titers were collected on d 0, 7, 14, and 21. Serum Zn concentration and specific ovalbumin IgG titers did not differ (P > 0.10) among the 4 treatments on any sampling day. Results from these 2 studies showed no major differences among the sources of supplemental Zn for receiving period morbidity, ADG, DMI, and humoral immune response of beef heifers; however, a lack of supplemental Zn during an extended finishing period tended to negatively affect G:F.

Effects of phase-feeding of crude protein on performance, carcass characteristics, serum urea nitrogen concentrations, and manure nitrogen of finishing beef steers.

As cattle mature, the dietary protein requirement, as a percentage of the diet, decreases. Thus, decreasing the dietary CP concentration during the latter part of the finishing period might decrease feed costs and N losses to the environment. Three hundred eighteen medium-framed crossbred steers (315 +/- 5 kg) fed 90% (DM basis) concentrate, steam-flaked, corn-based diets were used to evaluate the effect of phase-feeding of CP on performance and carcass characteristics, serum urea N concentrations, and manure characteristics. Steers were blocked by BW and assigned randomly to 36 feedlot pens (8 to 10 steers per pen). After a 21-d step-up period, the following dietary treatments (DM basis) were assigned randomly to pens within a weight block: 1) 11.5% CP diet fed throughout; 2) 13% CP diet fed throughout; 3) switched from an 11.5 to a 10% CP diet when approximately 56 d remained in the feeding period; 4) switched from a 13 to an 11.5% CP diet when 56 d remained; 5) switched from a 13 to a 10% CP diet when 56 d remained; and 6) switched from a 13 to an 11.5% CP diet when 28 d remained. Blocks of cattle were slaughtered when approximately 60% of the cattle within the weight block were visually estimated to grade USDA Choice (average days on feed = 182). Nitrogen volatilization losses were estimated by the change in the N:P ratio of the diet and pen surface manure. Cattle switched from 13 to 10% CP diets with 56 d remaining on feed or from 13 to 11.5% CP with only 28 d remaining on feed had lower (P < 0.05) ADG, DMI, and G:F than steers fed a 13% CP diet throughout. Steers on the phase-feeding regimens had lower (P = 0.05) ADG and DMI during the last 56 d on feed than steers fed 13.0% CP diet throughout. Carcass characteristics were not affected by dietary regimen. Performance by cattle fed a constant 11.5% CP diet did not differ from those fed a 13% CP diet. Serum urea N concentrations increased (P < 0.05) with increasing dietary CP concentrations. Phase-feeding decreased estimated N excretion by 1.5 to 3.8 kg/steer and nitrogen volatilization losses by 3 to 5 kg/steer. The results suggest that modest changes in dietary CP concentration in the latter portion of the feeding period may have relatively small effects on overall beef cattle performance, but that decreasing dietary CP to 10% of DM would adversely affect performance of cattle fed high-concentrate, steam-flaked, corn-based diets.

Effects of copper and zinc source on performance and humoral immune response of newly received, lightweight beef heifers.

Two experiments were conducted to evaluate the effects of Cu and Zn source on performance, morbidity, and humoral immune response in lightweight, newly received beef heifers. A 2 x 2 factorial arrangement of treatments was used in both experiments, with either a sulfate or a polysaccharide mineral complex (SQM) source of both Cu and Zn as the factors. Supplemental Cu and Zn were included in the receiving diet at concentrations designed to provide 10 mg of Cu/kg and 75 mg of Zn/kg (DM basis). In Exp. 1, 219 newly received beef heifers (British x Continental, average initial BW = 208 kg) were given ad libitum access to a 65% concentrate diet for 35 d to determine treatment effects on DMI, ADG, G:F, and bovine respiratory disease (BRD) morbidity. In Exp. 2, 24 heifers (average initial BW = 272 kg) were fed a diet with no supplemental Cu or Zn for 35 d, followed by fasting-refeeding-fasting stress, after which the same treatment diets used in Exp. 1 were fed for 21 d to examine the effects on humoral immune response (plasma IgG titer determined by ELISA on d 7, 14, and 21) to an ovalbumin (OVA) vaccine given on d 0 and 14. Copper source x Zn source interactions were not detected in either experiment. In Exp. 1, neither Cu nor Zn source affected (P > 0.10) DMI, ADG, G:F, or BRD morbidity. In Exp. 2, d 14 (P = 0.02) and 21 (P = 0.06) OVA titers were greater for heifers that received SQM Zn compared with heifers receiving ZnSO4, but heifers receiving CuSO4 had greater OVA titers than did heifers on the SQM Cu treatment on d 14 (P = 0.01) and 21 (P = 0.001). In summary, neither supplemental Cu nor Zn source affected performance or morbidity of lightweight, newly received heifers; however, source of both Cu or Zn affected the humoral immune response to OVA, although source effects were not consistent for the two minerals.

Effects of live cultures of Lactobacillus acidophilus (strains NP45 and NP51) and Propionibacterium freudenreichii on performance, carcass, and intestinal characteristics, and Escherichia coli strain O157 shedding of finishing beef steers.

In Exp. 1, 240 beef steers (initial BW = 332.8 kg) were used to determine the effects of Lactobacillus acidophilus (LA) plus Propionibacterium freudenreichii (PF) on performance, carcass, and intestinal characteristics; serum IgA concentrations; and the prevalence of Escherichia coli O157 (EC). Cattle were fed a steam-flaked corn-based, 92% concentrate diet, and the four direct-fed microbial (DFM) treatments (12 pens/treatment) included in a randomized complete block design were as follows: 1) control, lactose carrier only (CON); 2) 1 x 10(9) cfu of LA NP51 plus 1 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51H); 3) 1 x 10(9) cfu of LA NP51 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA51); and 4) 1 x 10(6) cfu of LA NP51 plus 1 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51L). No differences (P > 0.10) were detected for pen-based performance data. The average lamina propria thickness for LA51 and LA45-51H steers was less (P = 0.02) than the average for CON and LA45-51L steers. Moreover, LA51 and LA45-51H steers had a lower (P = 0.06) prevalence of EC shedding than CON and LA45-51L steers. In Exp. 2, 660 steers fed 91% concentrate, steam-flaked corn-based diets were used to determine the effects of the following DFM treatments (10 pens/treatment) on performance, carcass, and intestinal characteristics: 1) control, lactose carrier only (CON); 2) 5 x 10(6) cfu of LA NP51 plus 5 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51L); and 3) 1 x 10(9) cfu of LA NP51 plus 5 x 10(6) cfu of LA NP45 plus 1 x 10(9) cfu of PF NP24 per animal daily (LA45-51H). Steers were from two weight groups (WG). One group (SDOF; BW at arrival = 351.5 kg) had grazed before arrival, and the other group (LDOF; BW at arrival = 314 kg) had been in a grower yard. A split plot was used with WG as the whole-plot factor and DFM in the split plot. There was an interaction of WG and DFM for ADG (P = 0.05) and for carcass-adjusted ADG (P = 0.08). The simple-effect ADG and carcass-adjusted ADG means for DFM treatments differed (P < or = 0.01) between WG classifications. Within SDOF, ADG for CON and LA45-51L did not differ (P = 0.70), but both were less (P < or = 0.08) than for LA45-51H. Overall, these data indicate that live cultures of LA plus PF did not greatly affect feedlot performance and carcass characteristics. Some of the DFM used decreased fecal EC shedding, which might be related to the results for ileal lamina propria thickness.

Effects of roughage source and concentration on intake and performance by finishing heifers.

Three experiments were conducted to evaluate the effects of roughage source and concentration on intake and performance by finishing heifers. In Exp. 1, 12 medium-framed beef heifers (average BW = 389 kg) were used in three simultaneous 4 x 4 Latin square intake trials to evaluate the effects of dietary NDF supply from alfalfa hay, sudan hay, wheat straw, or cottonseed hulls fed in each Latin square at 5, 10, or 15% of dietary DM. Within each roughage concentration, roughage NDF accounted for the majority of variation in NEg intake/kg of BW0.75 among the roughage sources. Averaged across roughage concentrations, NEg intake/kg of BW0.75 tended to be greater (P < 0.10) when heifers were fed cottonseed hulls, sudan hay, or wheat straw than when they were fed alfalfa. In Exp. 2, six medium-framed beef heifers (average BW = 273 kg) were used in a 3 x 3 Latin square design to determine whether diets containing 10% (DM basis) alfalfa, cottonseed hulls, or sudan silage differed in eating rate. Average DM eating rates did not differ (P > 0.10) among roughage sources, which we interpreted to suggest that 90% concentrate diets containing alfalfa, cottonseed hulls, and sudan silage do not differ in the amount of chewing required during eating. In Exp. 3, 105 medium-framed beef heifers (average BW = 275 kg) were used in a 140-d finishing trial to evaluate three methods of dietary roughage exchange. Alfalfa at 12.5% of the dietary DM (ALF12.5) was used as a standard, and cottonseed hulls and sudan silage were each fed at three different levels: exchanged with ALF12.5 on an equal percentage DM basis, an equal NDF basis, or an equal NDF basis, where only NDF from particles larger than 2.36 mm (retained NDF) were considered to contribute to the NDF. No differences (P > 0.10) in ADG, DMI, gain:feed ratio, or NEg intake/kg of BW0.75 were detected between alfalfa and cottonseed hulls exchanged on an equal NDF basis. For sudan silage, exchanging with ALF12.5 on an equal retained NDF basis resulted in no differences (P > 0.10) in ADG, DMI, or NEg intake/kg of BW0.75. These data provide a preliminary indication that depending on the roughage sources evaluated, roughage NDF content and(or) roughage NDF from particles larger than 2.36 mm might provide a useful index of roughage value in high-concentrate finishing diets.

Effects of grain sorghum planting density and processing method on nutrient digestibility and retention by ruminants.

Grain sorghum grown in 38-cm rows (high density [HD]) or 76-cm rows (normal density [ND]) was treated as follows: steam-flaked (SF), high-moisture-harvested followed by rolling and ensiling (HM), or dry-rolled (DR). Resulting grains were evaluated using lambs in two 5 x 5 Latin square digestion trials. Treatment diets contained either SF-HD, SF-ND, HM-HD, HM-ND, or DR-ND grain sorghum in two trials; a 90 or a 60% concentrate diet was fed in each trial. High-density planting increased (P < 0.10) the apparent absorption of P relative to ND planting for both 60 and 90% concentrate diets. Steam flaking decreased (P < 0.10) the apparent absorption of P in the 90% concentrate diet and decreased (P < 0.10) the apparent absorption of N in both the 90 and 60% concentrate diets. Despite differences in N digestibility, steam flaking and HM ensiling resulted in similar (P > 0.10) N retention as a percentage of N intake in both trials. However, changes in the distribution of N between feces and urine among processing methods could affect N content of manure and alter nutrient management strategies. These results indicate that both planting density and grain processing can alter the apparent absorption of grain sorghum P by ruminants. Furthermore, it seems that grain processing can alter the route of N excretion in ruminants without changing total N retention.

Effects of planting density and processing method on laboratory characteristics of grain sorghum for ruminants.

Grain sorghum grown in 38-cm (high-density) or 76-cm rows (normal-density) was steam-flaked, harvested as high-moisture grain followed by rolling and ensiling, or dry-rolled. Chemical composition, enzymatic starch availability, CP insolubility, and IVDMD in a reduced-strength buffer were evaluated. High-density planting increased (P < .10) OM and starch concentration and decreased (P < .0001) CP concentration but did not affect (P > .10) P concentration, enzymatic starch availability, or CP insolubility. High-density planting resulted in lower (P < .10) in vitro ruminal culture pH at 6, 12, and 18 h of incubation when grain sorghum was processed by steam flaking, and lower (P < .10) IVDMD at 6, 12, and 18 h of digestion when grain sorghum was processed by dry rolling. Steam flaking decreased (P < .10) CP concentration and solubility and increased (P < .10) OM concentration. High-moisture ensiling decreased (P < .10) the insolubility of CP but did not otherwise seem to alter the chemical composition of grain sorghum relative to dry rolling. Starch was more available (P < .10), and DM was digested more rapidly and extensively (P < .10) in vitro, in steam-flaked sorghum followed by high-moisture sorghum. Based on these data, it seems that planting density primarily affected chemical composition of grain sorghum, whereas processing primarily affected CP insolubility and rate and extent of starch fermentation.