Our objectives were to evaluate the dose/payout pattern of trenbolone acetate (TBA) and estradiol-17β (E₂) implants and feeding of zilpaterol hydrochloride (ZH) on performance and carcass ...characteristics of finishing beef steers. A randomized complete block design was used with a 3 x 2 factorial arrangement of treatments. British x Continental steers (n = 168; initial BW = 362 kg) were blocked by BW and allotted randomly to 42 pens (7 pens/treatment; 6 pens/block; 4 steers/pen). The main effects of treatment were implant no implant (NI); Revalor-S (REV-S; 120 mg of TBA + 24 mg of E₂); and Revalor-XS (REV-X; 200 mg of TBA + 40 mg of E₂) and ZH (0 or 8.3 mg/kg of DM for 20 d with a 3-d withdrawal before slaughter). Blocks were split into 2 groups, and block groups were fed for either 153 or 174 d. No implant x ZH interactions were noted for cumulative performance data. Overall, shrunk final BW (567, 606, and 624 kg for NI, REV-S, and REV-X, respectively), ADG (1.25, 1.51, and 1.60 kg), and G:F (0.14, 0.16, and 0.17) increased (P < 0.05) as TBA and E₂ dose increased. Implanting increased (P < 0.05) DMI, but DMI did not differ (P > 0.10) between REV-S and REV-X (8.8 for NI vs. 9.4 kg/d for the 2 implants). From d 1 to 112 of the feeding period, implanting increased (P < 0.05) ADG and G:F, but REV-S and REV-X did not differ (P > 0.10). From d 112 to end, ADG increased by 19% (P < 0.05) and G:F was 18% greater (P < 0.05) for REV-X vs. REV-S. Carcass-adjusted final BW (29-kg difference), ADG (0.2-kg/d difference), and G:F (0.02 difference) were increased (P < 0.05) by ZH, but daily DMI was not affected by feeding ZH. Hot carcass weight was increased (P < 0.05) by ZH (19-kg difference) and implant, with REV-X resulting in the greatest response (HCW of 376 for NI vs. 404 and 419 kg for REV-S and REV-X, respectively; P < 0.05). An implant x ZH interaction (P = 0.05) occurred for dressing percent (DP). Without ZH, implanting increased DP, but DP did not differ (P > 0.10) between REV-X and REV-S. With ZH, REV-X increased (1.7%; P < 0.05) DP vs. NI and REV-S. Marbling score, 12th-rib fat, and KPH were not affected (P > 0.10) by implant or ZH. Overall, treatment increased steer performance and HCW in an additive fashion, suggesting different mechanisms of action for ZH and steroidal implants. In addition, a greater dose of TBA + E₂ and extended payout improved steer performance and HCW.
Abstract
Based on principles of the California Net Energy System, the dry matter intake (DMI) by feedlot cattle can be subdivided into DMI required for maintenance and DMI required for gain. Thus, if ...DMI along with body weight at a compositional endpoint and shrunk weight gain are known, dietary concentrations of net energy for maintenance and gain (NEm and NEg, respectively) can be calculated from growth performance data. Close agreement between growth performance-predicted and tabular NEm and NEg values implies the system can be used to accurately predict growth performance and be used to evaluate marketing and management decisions. We used 747 pen means from 21 research studies conducted at Texas Tech University and South Dakota State University to assess the agreement between growth performance-predicted NEm and NEg values and those calculated from tabular energy values for feeds reported by the 2016 National Academies of Science, Engineering, and Medicine publication on beef cattle nutrient requirements. Regression of growth performance-predicted values on tabular values with adjustment for random effects of study indicated that the intercepts of the two regressions did not differ from zero, and the slopes did not differ from one. Residuals (tabular minus growth performance-predicted values) for NEm and NEg averaged −0.003 and −0.005, respectively. Nonetheless, the precision of growth performance-predicted values was low, with approximately 40.3% of performance-predicted NEm values and 30.9% of NEg values falling within 2.5% of the corresponding tabular value. Residuals for NEm were divided into quintiles to evaluate dietary, growth performance, carcass, and energetics variables that might help explain lack of precision in growth performance-predicted values. Among the variables considered, gain:feed ratio was the most discriminating, with differences (P < 0.05) among each of the quintiles. Despite these differences, however, gain:feed ratio did not explain important percentages of variation in components of growth performance-predicted NEm values like maintenance energy requirements (r2 = 0.112) and retained energy (r2 = 0.003). Further research with large datasets that include dietary composition, growth performance and carcass data, and environmental variables, along with fundamental research on maintenance requirements and energy retention, will be required to identify ways to improve the precision of growth performance-predicted NE values.
On average, dietary net energy values calculated from growth performance and carcass data agree with those calculated from tabular net energy values of feeds, but the precision of growth performance-predicted values is low. Further experimentation related to energy requirements of beef cattle as well as analysis of growth performance and carcass data could provide tools for improving the precision of growth performance-predicted net energy values.
Lay Summary
Feedlot growth performance and carcass data can be used to estimate dietary net energy values. The degree to which growth performance-predicted values agree with tabular energy values for feeds is an indication of how accurately the California Net Energy System can be used to predict cattle growth performance. Using data from 747 pens of cattle in feedlot research studies, we found that growth performance-predicted and tabular net energy values agreed on average, but the precision of growth performance-predicted estimates was less than desired for practical application. Based on analysis of residuals, differences in gain:feed ratio were strongly related to growth performance-predicted net energy values. Research is needed on approaches to improve the precision of growth performance-predicted net energy values.
One experiment was conducted to evaluate the influence of glycerin (GLY) on animal performance and health when used as a partial replacement for roughage in receiving diets. The second experiment was ...conducted using ruminally and duodenally cannulated steers in a 4 × 4 Latin square to determine the site of nutrient digestion and ruminal fermentation characteristics when GLY replaced roughage at 0%, 2.5%, 5%, and 10% of diet DM. In Exp. 1, steers (initial BW = 245 ± 2.3 kg) were fed treatment diets over a 42-d period that consisted of a control diet based on steam-flaked corn with GLY inclusion in replacement of dietary roughage at 0%, 5%, and 10% of diet DM. A linear reduction in DMI was observed as GLY increased (P = 0.01). Glycerin incorporation tended to improve G:F in a linear manner (P = 0.07); efficiency was improved 5.4% and 4.7% at 5% and 10% GLY. The number of animals receiving treatment for bovine respiratory disease did not differ among treatments. Furthermore, there were no differences among treatments for mortality or the frequency of steers that were seropositive for serum antibody titers to infectious bovine rhinotracheitis on d 28. In Exp. 2, apparent OM and apparent and true starch digestibility increased linearly (P < 0.05) as GLY concentration increased, whereas true OM digestibility responded in a quadratic (P < 0.01) manner. Bacterial OM and bacterial starch flow responded quadratically (P ≤ 0.02), and flow increased from 0% to 5% GLY inclusion and decreased thereafter. Feed OM flow responded quadratically (P ≤ 0.05), where it decreased from 0% to 2.5% GLY and increased from 2.5% to 10% GLY inclusion. Feed starch (P = 0.02) and total starch (P = 0.02) flow from the duodenum decreased linearly as the concentration of GLY increased in the diet. Bacterial N flow to the duodenum responded quadratically (P < 0.01); it increased with increasing GLY in the diet up to 5% and then decreased from 5% to 10%. The acetate to propionate (A:P) ratio in the ruminal fluid decreased (P < 0.05) as the concentration of GLY in the diet increased, which could have implications on improved G:F. The decrease in the A:P ratio as GLY increased in the diet, coupled with the linear decrease in DMI and improvement in G:F with GLY addition up to 5% of DM in place of roughage, implies that GLY is a viable dietary ingredient in growing and receiving diets.
Ghrelin is a peptide hormone produced in the gut that is implicated in signaling appetite and regulating dry matter intake (DMI). The objective of this experiment was to determine the change in acyl ...ghrelin, total ghrelin, and the ghrelin ratio (acyl ghrelin/total ghrelin) over an 84-d DMI and average daily BW gain (ADG) measurement period and to determine the association of those ghrelin measurements with DMI, ADG, ADG:DMI ratio (G:F), and residual feed intake in finishing beef steers and heifers. Blood samples were collected on day 0 and day 83 before feeding and between 0730 h and 1130 h. Samples were analyzed for acyl and total ghrelin using commercially available RIA. DMI in steers was greater during the last 35-d period of the experiment compared with the first 35 d (P < 0.01) and was greater than heifers regardless of period (P < 0.01). Steers had greater acyl ghrelin concentrations on day 0 than heifers, but concentrations decreased by day 83 to equal concentrations in heifers (P < 0.01). Total ghrelin concentrations were lower on day 0 in heifers but increased by day 83 and did not differ from steers on day 83 (P < 0.01). A mixed model analysis was used to determine the association of ghrelin concentrations and ratio with production traits, independent of breed and sire effects. There was an interaction of day 0 acyl ghrelin concentrations with time of sample collection for 84-d DMI (P < 0.01), ADG (P < 0.01), and G:F (P = 0.09), indicating a general positive association of acyl ghrelin with production traits, but the association weakened as time of sample collection increased. The mean ghrelin ratio tended (P = 0.08) to be positively associated with DMI in the last 35-d period. The ghrelin ratio on day 0 interacted with time of sample collection for ADG and G:F (P < 0.05), indicating an overall positive association of the ghrelin ratio with ADG and G:F. Results indicate that ghrelin is associated with DMI, ADG, and feed efficiency of finishing beef cattle, and data lend more evidence that ghrelin is involved in appetite regulation of ad libitum fed cattle.
•Plasma ghrelin was measured at the beginning and end of a feeding period.•Acyl and total ghrelin association with production traits were examined.•Day 0 acyl ghrelin was positively associated with feed intake and ADG.•Time of sample collection affected the associations on day 0.•Ghrelin physiology could be a mechanism contributing to production variation
ABSTRACT
Two experiments were conducted to study the effects of monensin dose on growth performance and Escherichia coli O157:H7 shedding in finishing beef cattle. In Exp. 1, 198 heifers (298 ± 1.1 ...kg BW) were allocated to 1 of 2 treatments consisting of 1) 200 mg/heifer daily of monensin and 2) 400 mg/heifer daily of monensin and fed for 151 d. In Exp. 2, 199 steers (430 ± 1.9 kg BW) were stratified by BW and allocated to 1 of 2 treatments consisting of 1) 0 mg/steer daily of monensin and 2) 400 mg/steer daily of monensin and fed for 128 d. For both experiments, there were 4 pen replicates per treatment. For Exp. 1 and Exp. 2, the model included the fixed effect of treatment for growth performance measures and the fixed effects of treatment, time, and treatment × time interaction, respectively, for E. coli O157:H7 shedding. In Exp. 1, final BW was 1.9% greater for heifers fed 400 mg/d monensin than for heifers fed 200 mg/d monensin (P = 0.05). Furthermore, ADG was 4.9% greater (P = 0.05) and G:F was 3.1% greater (P = 0.04) when the heifers were fed 400 mg/d monensin vs. 200 mg/d monensin. Pen prevalence for E. coli O157:H7 (P = 0.96) and the percentage of animals in the pen shedding E. coli O157:H7 at enumerable levels (P = 0.82) did not differ between heifers fed 200 mg/d monensin and heifers fed 400 mg/d monensin over the 4 sampling periods. For Exp. 2, steers fed the supplement containing monensin had a 1.9% greater final BW (P = 0.04) and a 5.2% greater ADG (P = 0.02) than steers fed a control supplement without monensin. No differences in DMI or G:F were noted across the treatments (P ≥ 0.14). Escherichia coli O157:H7 percentage of enumerable cattle within the pen was greater for the steers fed monensin than the control steers not fed monensin than the control steers not fed monensin (P = 0.02) over the 4 sampling periods. However, the percentage of animals in the pen shedding E. coli O157:H7 (prevalence positive) did not differ between treatments (P = 0.18), nor did the average fecal counts (P = 0.45). In conclusion, feeding a higher dose (400 mg/d) of monensin improved final BW and ADG compared with a low dose of monensin or a no-monensin control in steers and heifers across multiple years. The percentage of animals shedding E. coli O157:H7 at enumerable levels was greater for steers fed the monensin supplement than for steers fed the control supplement, yet the presence of monensin, irrespective of the dose, did not affect the percentage of animals in the pen shedding E. coli O157:H7.
Feed costs are a major economic expense in finishing and developing cattle; however, collection of feed intake data is costly. Examining relationships among measures of growth and intake, including ...breed differences, could facilitate selection for efficient cattle. Objectives of this study were to estimate genetic parameters for growth and intake traits and compare indices for feed efficiency to accelerate selection response. On-test ADFI and on-test ADG (TESTADG) and postweaning ADG (PWADG) records for 5,606 finishing steers and growing heifers were collected at the U.S. Meat Animal Research Center in Clay Center, NE. On-test ADFI and ADG data were recorded over testing periods that ranged from 62 to 148 d. Individual quadratic regressions were fitted for BW on time, and TESTADG was predicted from the resulting equations. We included PWADG in the model to improve estimates of growth and intake parameters; PWADG was derived by dividing gain from weaning weight to yearling weight by the number of days between the weights. Genetic parameters were estimated using multiple-trait REML animal models with TESTADG, ADFI, and PWADG for both sexes as dependent variables. Fixed contemporary groups were cohorts of calves simultaneously tested, and covariates included age on test, age of dam, direct and maternal heterosis, and breed composition. Genetic correlations (SE) between steer TESTADG and ADFI, PWADG and ADFI, and TESTADG and PWADG were 0.33 (0.10), 0.59 (0.06), and 0.50 (0.09), respectively, and corresponding estimates for heifers were 0.66 (0.073), 0.77 (0.05), and 0.88 (0.05), respectively. Indices combining EBV for ADFI with EBV for ADG were developed and evaluated. Greater improvement in feed efficiency can be expected using an unrestricted index versus a restricted index. Heterosis significantly affected each trait contributing to greater ADFI and TESTADG. Breed additive effects were estimated for ADFI, TESTADG, and the efficiency indices.
Two studies were conducted to evaluate the effects of corn (CDG) and sorghum (SDG) wet distillers grains with solubles on feedlot cattle performance, carcass characteristics, and apparent total tract ...digestion of nutrients. In Exp. 1, 224 steers were used in a randomized complete block design (initial BW 391.1 +/- 9.51 kg) and fed steam-flaked corn (SFC)-based diets consisting of (DM basis) 0% distillers grains (CON), 15% SDG, 30% SDG, 15% CDG, 30% CDG, 15% of a 50:50 blend of SDG and CDG, and 30% of a 50:50 blend of CDG and SDG. Decreased carcass-adjusted final BW and HCW (P < or = 0.05) were noted as the inclusion amount of distillers grains increased in the diet. Body weight gain efficiency did not differ among the CDG, 50:50 SDG and CDG blend, and CON treatments, but G:F was numerically less with either amount of SDG than for CON, and decreased (P < or = 0.05) as distillers grains were increased from 15 to 30%. Cattle fed CON had greater carcass yield grades than those fed the distillers grain diets (P < or = 0.05). In Exp. 2, crossbred beef steers (n = 36; initial BW 567.3 +/- 53.1 kg) were used in a generalized randomized block design and fed SFC-based diets with 0% distillers grains (CON) and 15% (DM basis) CDG or SDG. Digestibility was determined with a pulse dose of Cr(2)O(3). Feeding steers 15% CDG or SDG increased intakes of CP and NDF (P < or = 0.05), but intakes of DM, OM, and starch did not differ among treatments (P >o r = 0.07). Apparent total tract digestibilities of DM, OM, CP, NDF, and starch (P > or = 0.25) did not differ among the 3 treatments. Fecal pH averaged over all sampling times was not affected by treatment, nor were average fecal pH values for prefeeding samples (0, 24, 48, and 72 h after the pulse dose) or for samples taken after feeding (12, 36, and 60 h after the pulse dose; P > or = 0.11). Results suggest that with 15% distillers grains in the DM, G:F was similar for cattle fed the CDG, 50:50 SDG and CDG blend, and CON diets. Feeding 30 vs. 15% distillers grains decreased G:F, but including 15% CDG or SDG in SFC-based diets did not affect apparent total tract digestibilities in feedlot steers.
ABSTRACT
The objective of this 2-yr study was to evaluate growing and finishing performance as well as carcass characteristics of spring-born steers backgrounded on 3 different systems, using ...feedstuffs readily available in the Midwest: 1) grazing corn residue and being supplemented with dried distillers plus solubles at 2.68 kg DM/steer 6 d/wk (RESIDUE), 2) grazing a late summer–planted oat–brassica forage mix (CCROP), or 3) being fed a corn silage–based diet in a drylot (DRYLOT). Steers (n = 715) were stratified by BW (278 kg ± 23 in yr 1 and 291 kg ± 91 in yr 2) and assigned to treatment and replicate (4 replications per treatment per yr). Steers assigned to DRYLOT were fed a corn silage–based diet for 54 d in yr 1 and 52 d in yr 2 before being transitioned to the finishing diet. Steers assigned to RESIDUE and those assigned to CCROP grazed 65 d in yr 1 and 66 d in yr 2 and then were fed a corn silage–based diet for 21 d in yr 1 and 33 d in yr 2 before being transitioned to the finishing diet. During backgrounding, the ADG (SEM 0.022) of steers assigned to DRYLOT (1.48 kg/d) was greater (P < 0.01) than that of steers assigned to both CCROP (1.05 kg/d) and RESIDUE (0.87 kg/d) and ADG of steers assigned to CCROP was greater (P < 0.01) than that of steers assigned to RESIDUE. At the start of the finishing period, BW of steers assigned to CCROP (381 kg) was greater (P < 0.01, SEM 2.5) than that of steers assigned to DRYLOT (361 kg) and RESIDUE (366 kg). The finishing period lasted 160 d for all treatments. Both 12th-rib fat (P = 0.89) and calculated yield grade (P = 0.39) did not differ among treatments. Finishing G:F of steers assigned to DRYLOT (0.162 kg/kg) was greater (P < 0.01, SEM 0.0015) than that of steers assigned to RESIDUE (0.153 kg/kg) and CCROP (0.153 kg/kg), which did not differ (P = 0.79). In yr 1, HCW of steers assigned to CCROP (402 kg) was greater (P < 0.01, SEM 2.1) than that of steers assigned to both RESIDUE (389 kg) and DRYLOT (391 kg), which did not differ (P = 0.40). This difference in HCW is most likely a result of differences in BW at the start of the finishing phase in yr 1. However in yr 2, HCW of steers assigned to CCROP (400 kg) and RESIDUE (397 kg) did not differ (P = 0.26, SEM 2.1) but were greater (P < 0.01) than that of steers assigned to DRYLOT (367 kg), despite the fact that steers assigned to RESIDUE entered the finishing phase at a lighter BW than steers assigned to CCROP. Marbling was greater (P = 0.01, SEM 3.9) for steers assigned to DRYLOT (429) than for steers assigned to RESIDUE (414), although steers assigned to CCROP (424) were not different (P ≥ 0.10) from steers assigned to DRYLOT or RESIDUE. When cost and price scenarios from the last 5 yr were conducted, no treatment appeared to be consistently superior in terms of cost of gain or net return. Therefore, all 3 systems appear to be viable options for producers.
Effects of 3 ionophores and 2 antibiotics on in vitro H₂S production, IVDMD, total gas production, and VFA profile with or without added S were examined. In Exp. 1, ruminal fluid from 2 ruminally ...cannulated steers fed a steam-flaked corn-based diet (75% concentrate) without ionophore and antibiotics for 28 d before collection was used to inoculate in vitro cultures. Treatments were control (no ionophore or antibiotic), 3 ionophores (lasalocid sodium and monensin sodium at 5 mg/L or laidlomycin propionate at 1.65 mg/L), and 2 antibiotics (chlortetracycline hydrochloride at 5 mg/L and tylosin tartarate at 1.25 mg/L). Cultures also had 0 or 1.75 mg of S/L (from sodium sulfate). No S x ionophore-antibiotic treatment interactions were noted (P > 0.53) for IVDMD, total gas production, and H₂S production. Hydrogen sulfide (μmol/g of fermentable DM) was increased (P < 0.001), and total gas production tended (P = 0.09) to be increased with additional S; however, IVDMD was not affected by added S (P = 0.90). Production of H₂S was not affected by ionophores or antibiotics (P > 0.18). On average, IVDMD (P = 0.05) was greater for ionophores than for antibiotics, whereas total gas production was less for ionophores than for control (P < 0.001) and antibiotics (P < 0.001). Molar proportions of acetate (P < 0.01) and acetate:propionate (P < 0.01) were decreased and propionate was increased (P < 0.001) in ionophore treatments when no S was added, but when S was added there were no differences (P > 0.20) in acetate, propionate, or acetate:propionate between ionophores and control (S x treatment interaction, P = 0.03). In Exp. 2, the effects of ionophore-antibiotic combinations with added S were examined using the same procedures as in Exp. 1. Treatments were control, monensin plus tylosin (MT), and lasalocid plus chlortetracycline (LCTC), with concentrations of the ionophores and antibiotics as in Exp. 1. No differences were observed among treatments for H₂S production (P > 0.55). Treatments MT and LCTC tended (P = 0.06) to increase IVDMD and decreased (P = 0.02) gas production vs. control. Proportion of acetate (P = 0.01) and acetate:propionate (P < 0.01) were decreased and propionate increased (P = 0.01) for both MT and LCTC compared with control. These data suggest that when S is approximately 0.42% of substrate DM, the 3 ionophores and 2 antibiotics we evaluated did not affect production of H₂S gas in an in vitro rumen culture system.
PDF
