J. Anim. Sci. 2006. 84:E34-E49
© 2006 American Society of Animal Science
An upper limit for caloric density of finishing diets1,2
C. R. Krehbiel3,
J. J. Cranston and
M. P. McCurdy
Department of Animal Science, Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater 74078
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Abstract
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This review assessed the relationships between dietary energy density and animal performance in an effort to evaluate a possible upper limit for energy density in finishing diets for cattle. Data were combined from 49 experiments (69 trials; 243 treatment observations) in which the dietary ME concentration (Mcal/kg of DM) was varied by level of concentrate, grain source, grain processing, and level of supplemental fat. Dietary concentrations of ME were determined using 1) NRC values of ME from diet ingredients; or 2) values derived from the literature, in which ingredient ME had been calculated from animal performance. Procedures for pooling data from multiple studies were used. The dependent variable was fit to a model that included a random slope and intercept clustered by trial. Trial-adjusted dependent variables (animal performance and carcass characteristics) were regressed on the independent variable (dietary ME concentration). Models were fit to cubic equations, and then reduced from cubic to quadratic to linear equations when the cubic and quadratic terms were not significant at P > 0.10. When NRC values were used, the relationship of DMI (% of BW) to dietary ME was linear (DMI decreased as ME increased; R2 = 0.631). However, the slope of ME intake (Mcal/kg of BW0.75) vs. dietary ME content did not differ (P > 0.25) from zero, supporting the concept that ruminants on high-grain diets (2.7 to 3.3 Mcal of ME/kg of DM) eat to maintain constant energy intake. Quadratic relationships were observed (P < 0.05) when ADG and G:F vs. dietary ME concentration were analyzed. Gain:feed was maximized with 3.46 (NRC) to 3.65 (calculated) Mcal/kg of ME from the total diet, 2.99 (NRC) to 3.40 (calculated) Mcal/kg of ME from grain, and 0.43 (NRC) to 0.53 (calculated) Mcal/kg of ME from supplemental fat. Most relationships of carcass traits to dietary ME were not significant (P > 0.10). Increased 12th-rib fat at greater ME and increasing KPH suggests greater fat deposition with increasing caloric density. Assuming that NRC ME values for ingredients commonly used in finishing diets are correct, the upper caloric limit for maximizing ADG and G:F was 3.16 and 3.45 Mcal/kg of DM, respectively. Reaching the upper caloric limit for G:F would require most grains to be processed or fed in high-moisture form. Whether maximizing G:F results in the most desirable carcass composition and yield of retail cuts should be determined.
Key Words: beef cattle • carcass merit • energy density • feedlot performance
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INTRODUCTION
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Modern diets for feedlot cattle contain from approximately 2.70 to 3.45 Mcal of ME/kg of DM. Caloric density of finishing diets varies due to differences in grain level (66 to 88%; Galyean and Gleghorn, 2002
); source, and degree of processing (Owens et al., 1997); roughage level (4.5 to 13.5%; Galyean and Gleghorn, 2002); and fat supplementation (2.5 to 6.5%; Galyean and Gleghorn, 2002; Zinn and Plascencia, 2002), among other factors (e.g., byproducts, protein, liquid supplements). Grains, primarily corn, sorghum, barley, and wheat, are the main constituents of high-concentrate diets, and are often processed to increase ruminal and total tract starch digestibility and ME concentration of the diet (Owens et al., 1997). Feedlot performance and carcass characteristics are also influenced by roughage level and source, due to their effects on DM and NE intake (Galyean and Defoor, 2003). Fat is supplemented to finishing diets (2.5 to 6.5% of DM; Galyean and Gleghorn, 2002) to increase dietary energy density. Although increasing ME intake by supplementing fat has generally increased G:F, supplementing fat above 6 to 7% of DM has resulted in decreased intake to a level at which G:F is maintained or decreased (Zinn, 1989; Krehbiel et al., 1995).
Although effects of dietary energy density on gain and efficiency are well documented, effects on carcass characteristics, body composition, and metabolic control factors are not as well defined. Because dietary energy level might affect rate and composition of gain in finishing cattle, it may be desirable to optimize energy density of finishing diets.
The purpose of this review was to evaluate the published literature and assess the relationship between dietary energy density and animal performance and carcass merit in an effort to evaluate a possible upper limit for energy density in finishing diets for cattle.
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MATERIALS AND METHODS
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To evaluate the role of dietary ME concentration in accounting for changes in performance, carcass characteristics, and body composition by feedlot cattle, data from 49 experiments (69 trials; 243 treatment observations; 8,251 cattle) were compiled in which the dietary ME concentration (Mcal/kg, DM basis) was altered by 1) grain level (or level of roughage); 2) grain type; 3) grain processing method; or 4) level of fat supplementation. There were 187 treatment observations from experiments where ME was altered by grain (or roughage) level, source, or processing (Table 1), and 56 observations from experiments where ME was altered by level of supplemental fat (Table 2). A summary of treatment observations for grain sources and processing methods used is shown in Table 3. Studies screened were limited to peer-reviewed journal articles with the exception of 1 study from an experiment station publication (Gill et al., 1981) and 3 from a feeder’s day report (Brandt et al., 1988a,b,c). These studies were included to provide additional information that was lacking in the peer-reviewed data. Information from a study was included if 1) cattle were given ad libitum access to feed; 2) cattle were fed in a group; 3) diet composition and animal processing were described; and 4) ADG and either DMI or G:F were reported. Whenever weight gains were adjusted for differences in dressing percent, those values were used; otherwise weight gains were based on changes in live weight reported by the authors (Owens et al., 1997). Retained energy (RE; Mcal/d), proportion of fat in gain {proportion of fat = 0.122 x [(RE/ADG) – 0.146]}, and proportion of protein in gain {proportion of protein = 0.248 – [0.0264 x (RE/ADG)]} were calculated using equations from NRC (1996). Hot carcass weight, dressing percent, LM area, 12th-rib fat thickness, KPH fat, yield grade, and marbling score were recorded when reported. Number of animals/treatment, minimums, maximums, mean, and median for diet characteristics and performance and carcass variables are shown in Tables 4, 5, and 6 for combined data; data from experiments for which ME varied due to grain level (roughage level), source, or method of processing; and experiments for which ME varied due to level of supplemental fat, respectively.
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Table 1. Summary of grain (roughage) level, source, and processing method data used for mixed model regression analyses
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Table 3. Number of observations for grain source and processing method from data used for mixed model regression analyses
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Table 4. Data ranges for diet characteristics and performance and carcass merit response variables for data used in the combined analyses
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Table 5. Description of data used to determine relationships between performance response by finishing cattle and ME concentration from grain
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Table 6. Description of data used to determine relationships between performance response of finishing cattle and ME concentration from supplemental fat
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Owens et al. (1997) evaluated the effects of grain source and processing method on DMI, ADG, G:F, and feeding value for cattle fed high-concentrate diets. Metabolizable energy values for each grain and processing method were calculated using quadratic procedures from NE equations for medium-framed cattle (NRC, 1984, 1996). In their summary, Owens et al. (1997) reported that all ME values calculated from animal performance, whether adjusted for final BW, were greater than reported by NRC (1996). When the ME for grains processed in various ways were adjusted for BW, values for dry-rolled corn, milo, wheat, high-moisture corn, and whole barley fell within 5% of NRC (1996) values. The observed value for dry-rolled barley was 18% greater than the NRC (1996) estimate. Metabolizable energy values from all steam-flaked grains and high-moisture grain sorghum were from 8 to 24% greater than reported in NRC (1996). Similarly, Zinn (1989) estimated that the NEm and NEg values for supplemental fats were greater than the value for tallow in the NRC (1996). Owens et al. (1997) suggested that it might be desirable to revise current ME values in feed composition tables; therefore, ME values from NRC (1996) and calculated from performance were used to determine relationships between dependent variables (animal performance and carcass merit) and dietary ME concentrations for the present analyses.
Two methods of assigning ME values to diets were used. For the first method, tabular values from NRC (1996) were used and individual ingredient ME (DM basis) was multiplied by the percentage of that ingredient (DM basis) in the diet. When NRC (1996) provided no estimate for a specific processing method, the value for dry-rolled grain was used. For the second method, ME values for various grains and processing methods reported by Owens et al. (1997; BW-adjusted values), and the ME value for fat calculated from the studies by Zinn (1989, 1994) were used to calculate dietary ME. Metabolizable energy values for all other dietary ingredients were from NRC (1996). Owens et al. (1997) used average cattle weights across the feeding period and DMI to compute ME values of grains from various sources and processing methods. Quadratic procedures from appropriate net energy equations for medium-framed cattle (NRC 1984, 1996) were used; an example of the calculations used was included in Appendix 1 of their paper (Owens et al., 1997). Zinn (1989) described calculations used to derive the NEm and NEg values of experimental diets and fat sources fed. For the present review, ME of fat was determined based on the NEg value derived by Zinn (1989) by solving the equation NEg = 1.42 ME – 0.174 ME2 + 0.0122 ME3 – 1.65 (NRC, 1996). Because calculated NEg values from sources of fat commonly fed to finishing cattle generally have been similar, a value of 4.79 Mcal/kg of DM was used to derive ME (Zinn, 1989). The only exception was for tallow soap stock (NEg = 4.50 Mcal/kg of DM; Zinn 1994).
For each data point, the average BW of cattle over the course of the experiment was used to adjust DMI (% of BW) and ME intake (Mcal/kg of BW0.75). This approach has limitations related to differences in animal age (calves vs. yearlings), days on feed before an experiment was initiated, location, and season of year the experiment was conducted, etc., which were not accounted for in the present analysis. In addition, cattle from 60 of the 243 treatment means were not fed an ionophore. It has been suggested (NRC, 1996) that dietary NEm is increased by 12% (ME by 6%; Owens et al., 1997) when an ionophore is fed. Because this value may vary with energy level and source of ionophore, no adjustments were made in calculated ME values for diets in which no ionophore was fed for the present data analysis. Only 8 of the 243 treatment means used did not include at least an initial implant at the beginning of the finishing period. Guiroy et al. (2002) reported that implanted steers and heifers had 4.2 and 3.1% greater apparent ME values compared with nonimplanted cattle. However, there did not appear to be an implant dose response for diet ME use. For the present analysis, no implant or implant dose x dietary ME concentration interaction was assumed.
Procedures described by St-Pierre (2001) for pooling data from multiple studies were used (MIXED procedure of SAS, Release 9.1, SAS Institute Inc., Cary, NC). These procedures have been used and illustrated by Galyean and Defoor (2003). As these authors suggested, experiment and/or trial effects such as differences in cattle factors (age, biological type, sex, management; Plegge et al., 1984), environmental factors (Plegge et al., 1984; Mader et al., 1997), differences attributable to dietary factors other than ME, among many other unknown, random factors are typically important in pooled data analyses.
For the present analyses, the dependent variables of DMI, ME intake, ADG, G:F, RE, proportion of fat and protein in gain, LM area: HCW, 12th-rib fat thickness, marbling score, KPH, yield grade, marbling: 12th-rib fat thickness, and 12th-rib fat thickness: LM area were regressed on the independent variables of dietary ME concentration (calculated from NRC, 1996 values of dietary ingredients), dietary ME concentration (calculated from performance; Zinn, 1989, 1994; Owens et al., 1997), dietary ME concentration from grain, and dietary ME concentration from supplemental fat. Each dependent variable was fit to a model that included a fixed slope and intercept, and a random slope and intercept clustered by trial. An unstructured variance-covariance matrix was assumed for the random intercepts and slopes; when slope-intercept covariance was not significant (P > 0.10) it was removed from the model. Models were fit to cubic functions, and then reduced from cubic to quadratic to linear equations when the cubic and quadratic effects were not significant (P > 0.10). Because SAS was unable to generate slope-intercept covariance estimates with some quadratic and cubic models, these effects were eliminated from the random statement; therefore, it is likely that quadratic and cubic equations subsequently reported may be slightly biased. Trial-adjusted dependent variables were calculated as described by St-Pierre (2001) and were regressed on the independent variables using the regression techniques of the GLM procedure of SAS Release 9.1.
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RESULTS AND DISCUSSION
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Combined Data
Trial-adjusted combined data showing the relationships between DMI, ME intake, and dietary ME concentration are shown in Figure 1. When ME was calculated using NRC (1996) values, a linear relationship was observed between DMI and dietary ME concentration, with DMI (% of BW) decreasing 0.89% for every 1-Mcal increase in dietary ME (Figure 1a). Plegge et al. (1984) summarized data from feedlot trials (617 pens and 14,199 total cattle) conducted at the University of Minnesota. Similar to the present experiment, the mean feeding period DMI of all dietary ingredients was calculated for each pen of cattle, and ME values were assigned to each ingredient according to NRC (1984) for calculating dietary ME density. When mean BW was held constant, DMI (kg/d) was maximized when ME density of the diet was 2.47 Mcal/kg of DM. When relative BW (calculated as shrunk BW/shrunk slaughter weight) was held constant, DMI was maximized when the diet contained 2.78 Mcal/kg of DM, and then declined thereafter. Dietary ME concentration from the summary by Plegge et al. (1984) ranged from 2.0 to 3.4 Mcal/kg of DM, and the relationship between DMI and dietary ME concentration appeared quadratic. Dry matter intake decreased as dietary ME increased from 2.5 (constant BW) or 2.8 (relative BW) to 3.4 Mcal/kg of DM, which is consistent with decreased DMI with increased dietary ME in the present data summary. Dry matter intake decreased across dietary ME values ranging from 2.66 to 3.29 Mcal/kg of DM (calculated from NRC, 1996 values) in the present summary.
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Figure 1. Relationship of dietary ME concentration calculated from NRC (1996) values of dietary ingredients (a) or from literature values (b and c; Owens et al., 1997; Zinn, 1989, 1994) to trial-adjusted DMI (a and b) or ME intake (c). For Figure 1a, DMI (% of BW) = –0.887 ± 0.094 (dietary ME, Mcal/kg) + 4.86 ± 0.29 (R2 = 0.63; root mean square error [RMSE] = 0.079); Figure 1b, DMI (% of BW) = 1.90 ± 0.49 (dietary ME, Mcal/kg)3 – 18.0 ± 4.7 (dietary ME, Mcal/kg)2 + 56.0 ± 14.8 (dietary ME, Mcal/kg) – 55.0 ± 15.6 (R2 = 0.82; RMSE = 0.063); and Figure 1c, ME intake (Mcal/kg of BW0.75) = 0.289 ± 0.068 (dietary ME, Mcal/kg)3 – 2.75 ± 0.65 (dietary ME, Mcal/kg)2 + 8.71 ± 2.01 (dietary ME, Mcal/kg) – 8.87 ± 2.18 (R2 = 0.34; RMSE = 0.009).
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In contrast to the linear relationship of DMI to ME concentration calculated using NRC (1996) values (Figure 1a
), the cubic function was significant (P < 0.001; R2 = 0.819; Figure 1b) when DMI vs. ME concentration from literature (Zinn, 1989, 1994; Owens et al., 1997) values was evaluated for the combined analysis. For this comparison, DMI decreased to a ME of approximately 3.45 Mcal/kg of DM, and then leveled out thereafter. Values from 3.45 to 3.70 (48 treatment observations) contained an average of 6.09% total dietary fat, 3.42% supplemental fat, and 9.34% roughage. Only 7 of the treatment observations in this range of ME did not contain at least 3.0% supplemental fat, and only 6 of the treatment observations contained greater than 4.0% supplemental fat. Assuming ME values calculated from performance (Zinn, 1989, 1994; Owens et al., 1997) reflect actual ME values of grains and fats, these data might suggest that feeding supplemental fat (approximately 3 to 4%) prevents intake from dropping below approximately 1.9% of BW when dietary ME exceeds 3.45 Mcal/kg of DM. Although it’s unlikely that dietary ME would exceed 3.45 Mcal/kg of DM in commercial feedlot diets, adding fat (3 to 4%) to diets with extensively processed or high-moisture grains may be of benefit for maintaining DMI in feedlot cattle.
In the present data summary, the slope of the regression line for the relationship of ME intake vs. dietary ME concentration did not differ (P = 0.25) from zero when ME values were assigned to each ingredient according to NRC (1996) for the combined analysis (data not shown), suggesting that feedlot cattle consume DM to maintain a constant ME intake. Owens et al. (1995) used ME values for various corn:alfalfa mixtures to illustrate the effects of dietary ME on DMI. The authors concluded that as concentrate:roughage increased, DMI decreased so that ME intake remained constant, consistent with the present summary. Over a wider range of dietary ME concentrations (2.0 to 3.4 Mcal/kg of DM), Plegge et al. (1984) reported that ME intake continued to increase at a decreasing rate until the dietary ME concentration reached approximately 3.0 (constant BW) to 3.2 (constant relative BW) Mcal/kg of DM. When dietary ME values calculated from performance (Zinn, 1989, 1994; Owens et al., 1997) were considered for the present analysis, the cubic function was significant (P < 0.001; Figure 1c). However, this relationship appeared to be driven by potentially influential data points on both ends of the range of dietary ME values. Cattle (365-kg steers, n = 2 observations; and 325-kg heifers, n = 1 observation) consuming greater than 0.34 Mcal/kg of BW0.75 at 3.68 to 3.70 Mcal/kg of DM were being fed 80% steam-flaked wheat with 3.50 to 4.00% supplemental fat and 10% roughage. Cattle (260-kg steers, n = 2 observations) consuming less than 0.27 Mcal/kg of BW0.75 at 2.61 Mcal/kg of DM were fed 68% dry-rolled grain sorghum with 0.05% supplemental fat and 20% roughage from cottonseed hulls (15%) and alfalfa hay (5.0%).
Ferrell and Jenkins (1995) showed that over a wide range of DMI, the relationship between ADG and feed intake appeared to be nonlinear, suggesting that as feed intake increases, the incremental increase in ADG decreases. In the present data summary, when ME values were calculated using NRC (1996) values, a quadratic relationship was observed between ADG and dietary ME concentration, with ADG increasing at a decreasing rate as dietary ME concentration increased (Figure 2a). Taking the first derivative of the quadratic equation and solving for zero indicated that ADG reached an asymptote when dietary ME was 3.16 Mcal/kg of DM. However, the equation relating ADG to dietary ME concentration accounted for only 23% of the variation (P < 0.05). When ME values calculated from performance (Zinn, 1989, 1994; Owens et al., 1997) were considered, the relationship of ADG to dietary ME concentration was linear (Figure 2b) with a positive slope. Only 15.3% of the variation in ADG was accounted for with this equation. Gain:feed was maximized at 3.46 and 3.65 Mcal of ME/kg of DM, respectively, when dietary ME concentration from NRC (1996) and literature values (Zinn, 1989, 1994; Owens et al., 1997) were evaluated as the independent variable (Figures 2c and 2d). These data show that the relationship between G:F and dietary ME is nonlinear in cattle fed high-energy diets, suggesting that as ME increases, G:F increases but at a decreasing rate. It should be cautioned that the calculated maximum for G:F derived from the equation using NRC (1996) values was above the upper range of the data for dietary ME (Figure 2c). Moreover, dietary ME of 3.46 Mcal/kg of DM would be untenable using most practical formulation constraints for modern feedlot diets, which would contain approximately 4% dietary fat and 9% roughage (approximately 5% NDF from roughage on a DM basis; Galyean and Gleghorn, 2002).
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Figure 2. Relationship of dietary ME concentration calculated from NRC (1996) values of dietary ingredients (a and c) or from literature values (b and d; Owens et al., 1997; Zinn, 1989, 1994) to trial-adjusted ADG (a and b) or G:F (c and d). For Figure 2a, ADG, kg = –0.860 ± 0.384 (dietary ME, Mcal/kg)2 + 5.44 ± 2.32 (dietary ME, Mcal/kg) –7.17 ± 3.50 (R2 = 0.23; root mean square error [RMSE] = 0.067); Figure 2b, ADG, kg = 0.132 ± 0.041 (dietary ME, Mcal/kg) + 0.98 ± 0.13 (R2 = 0.15; RMSE = 0.067); Figure 2c, G:F, kg/kg = –0.089 ± 0.042 (dietary ME, Mcal/kg)2 + 0.619 ± 0.252 (dietary ME, Mcal/kg) – 0.90 ± 0.38 (R2 = 0.63; RMSE = 0.008); and Figure 2d, G:F, kg/kg = –0.074 ± 0.039 (dietary ME, Mcal/kg)3 + 0.700 ± 0.369 (dietary ME, Mcal/kg)2 – 2.14 ± 1.16 (dietary ME, Mcal/kg) + 2.27 ± 1.22 (R2 = 0.67; RMSE = 0.007).
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In a review of growth and development of feedlot cattle, Owens et al. (1995) showed the relationships of fat and protein accretion to RE for bulls and steers fed high-concentrate diets ad libitum. The derived equation for fat accretion (kg/d) = 0.15 RE – 0.0057 RE2 – 0.162 (R2 = 0.94) indicated that as RE increased, fat accretion increased at a decreasing rate. In contrast, the derived equation for protein accretion (kg/d) = 0.267 – 0.072 RE + 0.0094 RE2 (R2 = 0.34) indicated that protein accretion decreased slightly as RE increased. The relationships between RE, proportion of fat in gain, and proportion of protein in gain and dietary ME concentration calculated using NRC (1996) ME values for dietary ingredients are shown in Figure 3. Quadratic functions were significant (P < 0.001) for RE (Figure 3a), proportion of fat in gain (Figure 3b), and proportion of protein in gain (Figure 3c). As described by the first derivative, RE reached an asymptote when dietary ME was 3.27 Mcal/kg of DM. Similar to the data summarized by Owens et al. (1995), the present data indicate that the increase in RE with increasing dietary ME is associated with an increase in the proportion of fat in gain and a slight decrease in the proportion of protein in gain when high-grain diets are fed. Retained energy reached a maximum at approximately the same dietary ME at which ADG was maximized (3.16 Mcal). However, as suggested by Owens et al. (1995), relationships of weight gain and proportion of fat and protein in gain are confounded with BW, because most of the cattle in studies used for the present analyses were fed for constant days on feed, not to a constant final BW. The exponent for empty BW gain (1.097) in the RE equation (RE = 0.0635 x empty BW0.75 x empty BW gain1.097; NRC, 1996) indicates that the energy content of gain increases with increasing rate of gain at any given live BW, although the effect is expected to be relatively small. Therefore, the main determinant of composition of gain appears to be BW.
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Figure 3. Relationship of dietary ME concentration calculated from NRC (1996) values of dietary ingredients to trial-adjusted retained energy (RE; a), proportion of fat in gain (b), and proportion of protein in gain(c). For Figure 3a, RE, Mcal/d = –5.84 ± 1.54 (dietary ME, Mcal/kg)2 + 38.2 ± 9.2 (dietary ME, Mcal/kg) – 53.7 ± 13.8 (R2 = 0.44; root mean square error [RMSE] = 0.436); Figure 3b, Fat in gain, % = –0.121 ± 0.026 (dietary ME, Mcal/kg)2 + 0.833 ± 0.156 (dietary ME, Mcal/kg) – 0.86 ± 0.23 (R2 = 0.81; RMSE = 0.007); and Figure 3c, Protein in gain, % = 0.026 ± 0.006 (dietary ME, Mcal/kg)2 – 0.180 ± 0.034 (dietary ME, Mcal/kg) + 0.40 ± 0.05 (R2 = 0.81; RMSE = 0.001).
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The number of treatment observations available for evaluating relationships of carcass traits to dietary ME ranged from 72 to 160. Relationships of most carcass traits to dietary ME concentration were not significant (P > 0.10; data not shown). Equations derived from relationships for which the cubic and/or linear functions were significant are shown in Table 7. When dietary ME concentration from NRC (1996) and literature values (Zinn, 1989, 1994; Owens et al., 1997) increased, dressing percent increased (P < 0.05), whereas the ratio of marbling: 12th-rib fat decreased (P < 0.05). The relationship of 12th-rib fat to dietary ME concentration was described by a cubic function when dietary ME was calculated from values derived from the literature (Zinn, 1989, 1994; Owens et al., 1997). Twelfth-rib fat increased as ME concentration increased from approximately 2.65 to 2.95 Mcal/kg, remained constant to approximately 3.50 Mcal/kg, and then increased as dietary ME increased to 3.70 Mcal/kg of DM. All grains (corn, grain sorghum, and wheat) fed when diet ME ranged from 3.50 to 3.70 Mcal/kg of DM in this relationship were steam-flaked. Steam flaking was shown to result in greater 12th-rib fat thickness but lower marbling and quality grades in a previous data summary (Owens and Gardner, 2000). However, in several studies in which dry rolling was compared with steam flaking, effects of grain processing on 12th-rib fat and marbling score were small or nonsignificant (Zinn, 1988, 1989; Barajas and Zinn, 1998). In addition, data used for the present analyses were potentially confounded by cattle age and location of study. Therefore, the significance of this response remains in question. When ME values calculated from performance were considered (Zinn, 1989, 1994; Owens et al., 1997), the relationship of KPH to dietary ME concentration was linear with a positive slope (P < 0.001). Woody et al. (1983) reported that increasing the percentage of grain in the diet increased dressing percent, carcass fat, and 12th-rib fat thickness when cattle were adjusted to equal carcass weight. Maturity, marbling score, quality grade, LM area, and KPH fat were not influenced by dietary grain level. From the present analyses, the increased 12th-rib fat at greater ME and increasing KPH might suggest greater fat deposition with increasing caloric density.
Grain Level, Source, and Processing Method
Figure 4 shows the relationship between DMI and performance response and ME concentration from grain calculated using NRC (1996) values. Similar to the combined data set, a linear relationship was observed between DMI and dietary ME concentration, with DMI decreasing 0.61% for every unit increase in dietary ME concentration from grain (Figure 4a). Decreased feed intake appears to be a consistent response of finishing cattle to increased dietary energy density, most likely reflecting chemostatic intake regulation or potentially increased metabolic acid load. Although the relationship was generally weak, the cubic function was significant (P = 0.03) for the relationship between ME intake and ME concentration from grain when NRC (1996) values were used (Figure 4b). Metabolizable energy intake decreased from 1.68 to 2.09, remained constant to approximately 2.65, and then decreased from 2.65 to 2.95 Mcal/kg of DM. Evaluating treatment observations indicated that at the lower ME level, treatment observations (n = 12) contained from 52 to 68% grain, and an average of 21.6% roughage. Treatment observations (n = 43) from 2.65 to 2.95 Mcal/kg of DM from grain contained from 79 to 91% grain, and an average of 7.40% roughage. Ten treatment observations were from experiments in which no roughage was fed. These observations are consistent with data reporting increasing ME intake with increasing roughage, and decreasing intake with all concentrate diets. Several potential mechanisms for this response have been discussed, including energy dilution, ruminal or metabolic acidosis, and rate of passage, among other factors (Owens et al., 2002; Galyean and Defoor, 2003). In contrast, greater roughage levels can depress intake of ME by cattle consuming high-concentrate diets. Peak ME intakes were reached with 17 to 25% of the diet DM being corn silage or other roughage sources (Owens et al., 2002).
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Figure 4. Relationship of ME concentration from grain calculated from NRC (1996) values to trial-adjusted DMI (a), ME intake (b), ADG (c), and G:F (d). For Figure 4a, DMI (% of BW) = 3.71 ± 0.23 – 0.608 ± 0.086 (ME from grain, Mcal/kg; R2 = 0.78; root mean square error [RMSE] = 0.080); Figure 4b, ME intake (Mcal/kg of BW0.75) = –0.109 ± 0.029 (ME from grain, Mcal/kg)3 + 0.770 ± 0.199(ME from grain, Mcal/kg)2 –1.81 ± 0.46 (ME from grain, Mcal/kg) + 1.71 ± 0.35 (R2 = 0.15; RMSE = 0.012); Figure 4c, ADG, kg = – 0.083 ± 0.033 (ME from grain, Mcal/kg)2 + 0.322 ± 0.121 (ME from grain, Mcal/kg) + 0.72 ± 0.25 (R2 = 0.22; RMSE = 0.071); and Figure 4d, G:F, kg/kg = –0.037 ± 0.018(ME from grain, Mcal/kg)2 + 0.219 ± 0.089 (ME from grain, Mcal/kg) – 0.16 ± 0.11 (R2 = 0.70; RMSE = 0.008).
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When dietary ME was calculated using NRC (1996) values in the present summary, a quadratic relationship was observed between ADG and dietary ME concentration, with ADG increasing at a decreasing rate as dietary ME concentration increased (Figure 4c). As described by the quadratic equation, ADG reached an asymptote when ME from grain was 2.59 Mcal/kg of DM. In addition, when ME concentration from grain calculated from NRC (1996) was evaluated as the independent variable, G:F was maximized at 2.99 Mcal of ME/kg of DM from grain (Figure 4d). Woody et al. (1983) studied the effects of increasing grain in the diet on ADG and G:F. Regression analysis indicated that ADG increased 0.009 kg for each percentage unit increase in grain level between 30 and 70%. Similarly, feed conversion (kg of daily DMI/kg of ADG) was improved by 0.058 kg of diet DM for each percentage unit increase in grain over the same range. Dry matter intakes remained relatively constant as the percentage of grain in the diet increased to approximately 80%, and then decreased. Average daily gain was improved until grain level reached 80%, and then decreased due to lower DMI. These data are consistent with the present summary. Similarly, in a review of the effects of feedlot management and nutrition on performance and carcass traits, Owens and Gardner (2000) showed that increasing concentrate levels increased ADG and G:F to a plateau.
Although the range in ME concentration associated with grain level, source, and method of processing was greater when the literature values were used (Owens et al., 1997), relationships of animal performance to ME concentration from grain were generally similar as when NRC (1996) values were considered (data not shown). The one exception was for the relationship of ME intake to dietary ME from grain, which increased by 0.01 Mcal/kg of BW0.75 for every unit increase in ME concentration from grain, similar to the results of Woody et al. (1983). Discrepancies between estimated maximum ADG and G:F between NRC (1996) and calculated (Owens et al., 1997) ME values from grain most likely reflect the lack of values provided by NRC (1996) for processed grains.
Fat Level
Fat is supplemented to finishing cattle diets (2.5 to 6.5% of DM; Galyean and Gleghorn, 2002) to increase dietary energy density. Although increasing ME intake by supplementing fat has generally increased G:F, supplementing fat above 6 to 7% of DM has resulted in decreased intake to a level at which G:F is maintained or decreased. Zinn and Plascencia (2002) studied the effects of increasing tallow fatty acids (0, 3, 6, and 9%) on growth performance of steer calves fed a high-energy diet. Increasing level of fat supplementation linearly decreased ADG, DMI, and dietary NE. Observed/expected dietary NEm was 1.03 with 3% supplemental fat and declined to 0.90 with 9% supplemental fat. The authors concluded that the feeding value of total fatty acids was proportional to total fatty acid intake. When total dietary fatty acid intake was less than 6%, the NE value of total fatty acid was consistent to the tabular values for tallow. Above 6%, the energy intake, ADG, and the NE value of total fatty acids decreased.
Figure 5 shows the relationship between DMI and performance response and ME concentration from supplemental fat calculated using the NRC (1996) value for tallow. Similar to the overall data set, a linear relationship was observed between DMI and ME concentration from supplemental fat, with DMI decreasing 0.26% for each unit increase in dietary ME concentration from fat (Figure 5a). In contrast, the slope describing the relationship of ME intake to ME from supplemental fat did not differ (P = 0.69) from zero (data not shown).
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Figure 5. Relationship of ME concentration from supplemental fat calculated from the NRC (1996) value for tallow to trial-adjusted DMI (a), ADG (b), and G:F (c). For Figure 3a, DMI (% of BW) = 2.08 ± 0.05 – 0.262 ± 0.063 (ME from fat, Mcal/kg; R2 = 0.52; root mean square error [RMSE] = 0.042); Figure 3b, ADG, kg = –0.609 ± 0.305 (ME from fat, Mcal/kg)2 + 0.352 ± 0.142 (ME from fat, Mcal/kg) + 1.31 ± 0.57 (R2 = 0.24; RMSE = 0.050); and Figure 3c, G:F, kg/kg = –0.074 ± 0.021 (ME from fat, Mcal/kg)2 + 0.064 ± 0.009 (ME from fat, Mcal/kg) + 0.15 ± 0.004 (R2 = 0.61; RMSE = 0.005).
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A quadratic relationship was observed between ADG and supplemental fat ME content (Figure 5b). As described by the quadratic equation, ADG reached an asymptote when ME from fat was 0.26 Mcal/kg of DM. In addition, when ME concentration from supplemental fat was evaluated as the independent variable, G:F was maximized at 0.43 Mcal of ME/kg of DM from fat (Figure 5c). Maximum ADG and G:F were achieved at the equivalent of 3.99 and 6.75% supplemental fat, respectively, when the NRC (1996) ME value for tallow was used. When ME values derived from Zinn (1989, 1994) were used, ADG and G:F were maximized at the equivalent of 4.56 and 6.80% supplemental fat, respectively. These data are in agreement with the level of supplemental fat currently being used in feedlot diets by consulting nutritionists (Galyean and Gleghorn, 2002), and support the plateau in G:F observed above 6 to 7% supplemental fat.
With the exception of ME intake, relationships of animal performance and carcass composition to ME concentration from supplemental fat were generally similar when NRC (1996) values or literature values (Zinn, 1989, 1994) values were used. All intercepts and R2 values were nearly identical, with regression coefficients nearer to zero for literature values, reflecting the greater ME values from supplemental fat.
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CONCLUSIONS
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Assuming that NRC (1996) ME values for ingredients commonly used in finishing diets are correct, the upper caloric limits for maximizing ADG and G:F were 3.16 and 3.45 Mcal/kg of DM, respectively. As suggested by Owens et al. (1997), adding values to the NRC for all grains commonly fed in finishing diets and processed by varying methods would be beneficial for defining caloric limits. It appears from the present data analysis that reaching the upper caloric limit for maximizing G:F would require most grains to be processed and/or fed in high-moisture forms. Although the relationships of most carcass traits to dietary ME content were not significant, increasing proportion of fat in gain, increasing KPH, and increased 12th-rib fat at greater ME suggest greater fat deposition with increasing caloric density, consistent with the data for nonruminants (Pettigrew and Moser, 1991; Azain, 2001). It should be determined whether maximizing G:F results in the most desirable carcass quality and yield of retail cuts.
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Footnotes
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1 Invited review. Presented at the "Alpharma Beef Cattle Nutrition: Challenging the Limits of Caloric Intake in Feedlot Cattle" symposium held at the American Society of Animal Science Annual Meeting, Cincinnati, OH, July 24–28, 2005. 
2 Approved for publication by the Director, Oklahoma Agric. Exp. Sta. This research was supported by the Oklahoma Agric. Exp. Sta. under project H-2438.
3 Corresponding author: clint.krehbiel{at}okstate.edu
Received for publication August 26, 2005.
Accepted for publication December 22, 2005.
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LITERATURE CITED
|
|---|
Axe, D. E., K. K. Bolsen, D. L. Harmon, R. W. Lee, G. A. Milliken, and T. B. Avery. 1987. Effect of wheat and high-moisture sorghum grain fed singly and in combination on ruminal fermentation, solid and liquid flow, site and extent of digestion and feeding performance of cattle. J. Anim. Sci. 64:897–906.[Abstract/Free Full Text]
Azain, M. J. 2001. Fat in swine nutrition. Pages 95–105 in Swine Nutrition, A. J. Lewis and L. L. Southern, ed. CRC Press, Boca Raton, FL.
Barajas, R., and R. A. Zinn. 1998. The feeding value of dry-rolled and steam-flaked corn in finishing diets for feedlot cattle: Influence of protein supplementation. J. Anim. Sci. 76:1744–1752.[Abstract/Free Full Text]
Bartle, S. J., R. L. Preston, and M. F. Miller. 1994. Dietary energy source and density: Effects of roughage source, roughage equivalent, tallow level, and steer type on feedlot performance and carcass characteristics. J. Anim. Sci. 72:1943–1953.[Abstract]
Bock, B. J., R. T. Brandt, Jr., D. L. Harmon, S. J. Anderson, J. K. Elliott, and T. B. Avery. 1991a. Mixtures of wheat and high-moisture corn in finishing diets: Feedlot performance and in situ rate of starch digestion in steers. J. Anim. Sci. 69:2703–2710.[Abstract]
Bock, B. J., D. L. Harmon, R. T. Brandt, Jr., and J. E. Schneider. 1991b. Fat source and calcium level effects on finishing steer performance, digestion, and metabolism. J. Anim. Sci. 69:2211–2224.[Abstract]
Bradshaw, W. L., D. D. Hinman, R. C. Bull, D. O. Everson, and S. J. Sorensen. 1996. Effects of barley variety and processing methods on feedlot steer performance and carcass characteristics. J. Anim. Sci. 74:18–24.[Abstract]
Brandt, R. T., Jr., and S. J. Anderson. 1990. Supplemental fat source affects feedlot performance and carcass traits of finishing yearling steers and estimated diet net energy value. J. Anim. Sci. 68:2208–2216.[Abstract]
Brandt, R. T., Jr., S. J. Anderson, and J. K. Elliott. 1988a. Effect of supplemental fat on performance and carcass traits of finishing cattle fed milo or wheat processed by two methods. Pages 16–19 in Cattle Feeders’ Day Rep. Prog. 555. Kansas State Univ., Manhattan.
Brandt, R. T., Jr., S. J. Anderson, and J. K. Elliott. 1988b. Mixtures of high moisture corn and steam rolled wheat for finishing cattle. Pages 32–34 in Cattle Feeders’ Day Rep. Prog. 555. Kansas State Univ., Manhattan.
Brandt, R. T., Jr., S. J. Anderson, and J. K. Elliott. 1988c. Relative feeding value of milo as affected by processing method. Pages 29–31 in Cattle Feeders’ Day Rep. Prog. 555. Kansas State Univ., Manhattan.
Brown, M. S., C. R. Krehbiel, G. C. Duff, M. L. Galyean, D. M. Hallford, and D. A. Walker. 2000. Effect of degree of corn processing on urinary nitrogen composition, serum metabolite and insulin profiles, and performance by finishing steers. J. Anim. Sci. 78:2464–2474.[Abstract/Free Full Text]
Clary, E. M., R. T. Brandt, Jr., D. L. Harmon, and T. G. Nagaraja. 1993. Supplemental fat and ionophores in finishing diets: Feedlot performance and ruminal digesta kinetics in steers. J. Anim. Sci. 71:3115–3123.[Abstract]
Defoor, P. J., M. L. Galyean, G. B. Salyer, G. A. Nunnery, and C. H. Parsons. 2002. Effects of roughage source and concentration on intake and performance by finishing heifers. J. Anim. Sci. 80:1395–1404.[Abstract/Free Full Text]
Ferrell, C. L., and T. G. Jenkins. 1995. Body composition effects on maintenance, feed intake and efficiency. Pages 23–30 in Symposium: Intake by Feedlot Cattle. Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater.
Gaebe, R. J., D. W. Sanson, I. G. Rush, M. L. Riley, D. L. Hixon, and S. I. Paisley. 1998. Effects of extruded corn or grain sorghum on intake, digestibility, weight gain, and carcasses of finishing steers. J. Anim. Sci. 76:2001–2007.[Abstract/Free Full Text]
Galyean, M. L., and P. J. Defoor. 2003. Effects of roughage source and level on intake by feedlot cattle. J. Anim. Sci. 81(E. Suppl. 2):E8–E16.[Abstract/Free Full Text]
Galyean, M. L., and J. F. Gleghorn. 2002. Summary of the 2000 Texas Tech University Consulting Nutritionist Survey. Pages 1–10 in Plains Nutr. Council Spring Conf. Publ. No. AREC 05–20. Texas A&M Research and Extension Center, Amarillo.
Gill, D. R., F. N. Owens, J. J. Martin, D. E. Williams, R. A. Zinn, and R. J. Hillier. 1981. Roughage levels in feedlot rations. Oklahoma Agric. Exp. Stn., Stillwater. Res. Rep. MP-108:141–146.
Guiroy, P. J., L. O. Tedeschi, D. G. Fox, and J. P. Hutcheson. 2002. The effects of implant strategy on finished BW of beef cattle. J. Anim. Sci. 80:1791–1800.[Abstract/Free Full Text]
Guthrie, M. J., M. L. Galyean, K. J. Malcom-Callis, and G. C. Duff. 1996. Roughage source and level in beef cattle finishing diets. Prof. Anim. Sci. 12:192–198.
Hale, W. H., L. Cuitun, W. J. Saba, B. Taylor, and B. Theurer. 1966. Effect of steam processing and flaking milo and barley on performance and digestion by steers. J. Anim. Sci. 25:392–396.[Abstract/Free Full Text]
Huck, G. L., K. K. Kreikemeier, G. L. Kuhl, T. P. Eck, and K. K. Bolsen. 1998. Effects of feeding combinations of steam-flaked grain sorghum and steam-flaked, high-moisture, or dry-rolled corn on growth performance and carcass characteristics in feedlot cattle. J. Anim. Sci. 76:2984–2990.[Abstract/Free Full Text]
Krehbiel, C. R., R. A. McCoy, R. A. Stock, T. J. Klopfenstein, D. H. Shain, and R. P. Huffman. 1995. Influence of grain type, tallow level, and tallow feeding system on feedlot cattle performance. J. Anim. Sci. 73:2916–2921.[Abstract]
Kreikemeier, K. K., D. L. Harmon, R. T. Brandt, Jr., T. G. Nagaraja, and R. C. Cochran. 1990. Steam-rolled wheat diets for finishing cattle: Effects of dietary roughage and feed intake on finishing steer performance and ruminal metabolism. J. Anim. Sci. 68:2130–2141.[Abstract]
Kreikemeier, K. K., R. A. Stock, D. R. Brink, and R. A. Britton. 1987. Feeding combinations of dry corn and wheat to finishing lambs and cattle. J. Anim. Sci. 65:1647–1654.[Abstract/Free Full Text]
Ladely, S. R., R. A. Stock, K. Goedenken, and R. P. Huffman. 1995. Effect of corn hybrid and grain processing method on rate of starch disappearance and performance of finishing cattle. J. Anim. Sci. 73:360–364.[Abstract]
Lee, R. W., M. L. Galyean, and G. P. Lofgreen. 1982. Effects of mixing whole shelled and steam flaked corn in finishing diets on feedlot performance and site and extent of digestion in beef steers. J. Anim. Sci. 55:475–483.[Abstract/Free Full Text]
Macken, C. N., G. E. Erickson, T. J. Klopfenstein, C. T. Milton, and R. A. Stock. 2004. Effects of dry, wet, and rehydrated corn bran and corn processing method in beef finishing diets. J. Anim. Sci. 82:3543–3548.[Abstract/Free Full Text]
Mader, T., J. Gaughan, and B. Young. 1997. Effects of feeding level and diet energy density on cattle exposed to heat. Pages 85–88 in Nebraska Beef Cattle Report MP 62-A. University of Nebraska, Lincoln.
McCoy, R. A., R. A. Stock, T. J. Klopfenstein, D. H. Shain, and M. J. Klemesrud. 1998. Effect of energy source and escape protein on receiving and finishing performance and health of calves. J. Anim. Sci. 76:1488–1498.[Abstract/Free Full Text]
Ngidi, M. E., S. C. Loerch, F. L. Fluharty, and D. L. Palquist. 1990. Effects of calcium soaps of long-chain fatty acids on feedlot performance, carcass characteristics and ruminal metabolism of steers. J. Anim. Sci. 68:2555–2565.[Abstract]
NRC. 1984. Nutrient Requirements of Beef Cattle. 6th rev. ed. National Academy Press, Washington, DC.
NRC. 1996. Nutrient Requirements of Beef Cattle. 7th rev. ed. National Academy Press, Washington, DC.
Oltjen, R. R., P. A. Putnam, E. E. Williams, Jr., and R. E. Davis. 1966. Wheat versus corn in all-concentrate cattle rations. J. Anim. Sci. 25:1000–1004.[Abstract/Free Full Text]
Owens, F., M. Hinds, and S. Soderlund. 2002. Roughage levels and sources in feedlot diets. Pages 1–19 in Components of Rumen Function and Dysfunction as They Relate to Beef Cattle Production. Proc. Colo. Nutr. Roundtable. Colorado State University, Fort Collins.
Owens, F. N., and B. A. Gardner. 2000. A review of the impact of feedlot management and nutrition on carcass measurements of feedlot cattle. Available: http://www.asas.org/JAS/symposia/proceedings/0940.pdf. Accessed Aug. 26, 2005.
Owens, F. N., D. S. Secrist, and D. R. Gill. 1995. Impact of grain sources and grain processing on feed intake by and performance of feedlot cattle. Pages 235–256 in Symposium: Intake by Feedlot Cattle P-942. Oklahoma State University, Stillwater.
Owens, F. N., D. S. Secrist, W. J. Hill, and D. R. Gill. 1997. The effect of grain source and grain processing on performance of feedlot cattle: A review. J. Anim. Sci. 75:868–879.[Abstract/Free Full Text]
Pettigrew, J. E., and R. L. Moser. 1991. Fat in swine nutrition. Pages 133–145 in Swine Nutrition. E. R. Miller, D. E. Ullrey, and A. J. Lewis, ed. Butterworth-Heinemann, Stoneham, MA.
Plegge, S. D., R. D. Goodrich, S. A. Hanson, and M. A. Kirick. 1984. Predicting dry matter intake of feedlot cattle. Pages 56–70 in Proc. Minnesota Nutr. Conf. University of Minnesota, Twin Cities.
Ramirez, J. E., and R. A. Zinn. 2000. Interaction of dietary magnesium level on the feeding value of supplemental fat in finishing diets for feedlot steers. J. Anim. Sci. 78:2072–2080.[Abstract/Free Full Text]
Ramirez, R. G., H. E. Kiesling, M. L. Galyean, G. P. Lofgreen, and J. K. Elliott. 1985. Influence of steam-flaked, steamed-whole or whole shelled corn on performance and digestion in beef steers. J. Anim. Sci. 61:1–8.[Abstract/Free Full Text]
Reinhardt, C. D., R. T. Brandt, Jr., T. P. Eck, and E. C. Titgemeyer. 1998. Performance, digestion, and mastication efficiency of Holstein steers fed whole or processed corn in limit- or full-fed growing-finishing systems. J. Anim. Sci. 76:1778–1788.[Abstract/Free Full Text]
Scott, T. L., C. T. Milton, G. E. Erickson, T. J. Klopfenstein, and R. A. Stock. 2003. Corn processing method in finishing diets containing wet corn gluten feed. J. Anim. Sci. 81:3182–3190.[Abstract/Free Full Text]
Shain, D. H., R. A. Stock, T. J. Klopfenstein, and D. W. Herold. 1999. The effect of forage source and particle size on finishing yearling steer performance and ruminal metabolism. J. Anim. Sci. 77:1082–1092.[Abstract/Free Full Text]
Sindt, M. H., R. A. Stock, T. J. Klopfenstein, and D. H. Shain. 1993. Effect of protein source and grain type on finishing calf performance and ruminal metabolism. J. Anim. Sci. 71:1047–1056.[Abstract]
Stock, R. A., D. R. Brink, R. T. Brandt, J. K. Merrill, and K. K. Smith. 1987a. Feeding combinations of high moisture corn and dry corn to finishing cattle. J. Anim. Sci. 65:282–289.[Abstract/Free Full Text]
Stock, R. A., D. R. Brink, R. A. Britton, F. K. Goedeken, M. H. Sindt, K. K. Kreikemeier, M. L. Bauer, and K. K. Smith. 1987b. Feeding combinations of high moisture corn and dry-rolled sorghum to finishing steers. J. Anim. Sci. 65:290–302.[Abstract/Free Full Text]
Stock, R. A., D. R. Brink, K. K. Kreikemeier, and K. K. Smith. 1987c. Evaluation of early-harvested and reconstituted grain sorghum in finishing steers. J. Anim. Sci. 65:548–556.[Abstract/Free Full Text]
Stock, R. A., M. H. Sindt, R. M. Cleale, IV, and R. A. Britton. 1991. High-moisture corn utilization in finishing cattle. J. Anim. Sci. 69:1645–1656.[Abstract]
Stock, R. A., M. H. Sindt, J. C. Parrott, and F. K. Goedeken. 1990. Effects of grain type, roughage level and monensin level on finishing cattle performance. J. Anim. Sci. 68:3441–3455.[Abstract]
St-Pierre, N. R. 2001. Invited review: Integrating quantitative findings from multiple studies using mixed methodology. J. Dairy Sci. 84:741–755.[Abstract]
Theurer, C. B., R. S. Swingle, R. C. Wanderley, R. M. Kattnig, A. Urias, and G. Ghenniwa. 1999. Sorghum grain flake density and source of roughage in feedlot cattle diets. J. Anim. Sci. 77:1066–1073.[Abstract/Free Full Text]
Woody, H. D., D. G. Fox, and J. R. Black. 1983. Effect of diet grain content on performance of growing and finishing cattle. J. Anim. Sci. 57:717–728.[Abstract/Free Full Text]
Zinn, R. A. 1987. Influence of lasalocid and monensin plus tylosin on comparative feeding value of steam-flaked versus dry-rolled corn in diets for feedlot cattle. J. Anim. Sci. 65:256–266.[Abstract/Free Full Text]
Zinn, R. A. 1988. Comparative feeding value of supplemental fat in finishing diets for feedlot steers supplemented with and without monensin. J. Anim. Sci. 66:213–227.[Abstract/Free Full Text]
Zinn, R. A. 1989. Influence of level and source of dietary fat on its comparative feeding value in finishing diets for steers: Feedlot cattle growth and performance. J. Anim. Sci. 67:1029–1037.[Abstract/Free Full Text]
Zinn, R. A. 1991. Comparative feeding value of steam-flaked corn and sorghum in finishing diets supplemented with or without sodium bicarbonate. J. Anim. Sci. 69:905–916.[Abstract]
Zinn, R. A. 1992. Comparative feeding value of supplemental fat in steam-flaked corn- and steam-flaked wheat-based finishing diets for feedlot steers. J. Anim. Sci. 70:2959–2969.[Abstract]
Zinn, R. A. 1993. Influence of processing on the comparative feeding value of barley for feedlot cattle. J. Anim. Sci. 71:3–10.[Abstract]
Zinn, R. A. 1994. Effects of excessive supplemental fat on feedlot cattle growth performance and digestive function. Prof. Anim. Sci. 10:66–72.
Zinn, R. A., E. G. Alvarez, M. F. Montañ o, A. Plascencia, and J. E. Ramirez. 1998. Influence of tempering on the feeding value of rolled corn in finishing diets for feedlot cattle. J. Anim. Sci. 76:2239–2246.[Abstract/Free Full Text]
Zinn, R. A., and A. Plascencia. 1996. Effects of forage level on the comparative feeding value of supplemental fat in growing-finishing diets for feedlot cattle. J. Anim. Sci. 74:1194–1201.[Abstract]
Zinn, R. A., and A. Plascencia. 2002. Influence of level and method of supplementation on the utilization of supplemental tallow fatty acids by feedlot steers. J. Anim. Sci. 80(Suppl. 1):270. (Abstr.)[Abstract/Free Full Text]
Zinn, R. A., and Y. Shen. 1996. Interaction of dietary calcium and supplemental fat on digestive function and growth performance in feedlot steers. J. Anim. Sci. 74:2303–2309.[Abstract]
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Abstract
INTRODUCTION
