J. Anim Sci. 2007. 85:3383-3390. doi:10.2527/jas.2006-741
© 2007 American Society of Animal Science
Effects of dry matter intake restriction on diet digestion, energy partitioning, phosphorus retention, and ruminal fermentation by beef steers
J. H. Clark*,
K. C. Olson
,1,2,
T. B. Schmidt
,
M. L. Linville*,
D. O. Alkire*,
D. L. Meyer*,
G. K. Rentfrow
,
C. C. Carr* and
E. P. Berg#
* Division of Animal Sciences, University of Missouri—Columbia 920 East Campus Drive, Columbia, MO 65201;
and
Department of Animal Sciences and Industry, 139 Call Hall, Kansas State University, Manhattan 66506;
and
Department of Animal and Dairy Sciences, Mississippi State University, Mississippi State 39762;
and
Department of Animal and Food Sciences, University of Kentucky, Lexington 40546; and and
# Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
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Abstract
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Two experiments were conducted to determine the effects of DMI restriction on diet digestion, ruminal fermentation, ME intake, and P retention by beef steers. In Exp. 1, twelve Angus x steers (average initial BW = 450 ± 18 kg) were assigned randomly to 1 of 3 diets that were formulated to promote a 1.6-kg ADG at intake levels corresponding approximately to 100% (ad libitum, AL), 90% (IR90), or 80% (IR80) of ad libitum DMI. In Exp. 2, twelve crossbred steers (average initial BW = 445 ± 56 kg) fitted with ruminal cannulae were randomly assigned to 1 of 2 diets that were formulated to promote a 1.6-kg ADG at AL or IR80. All diets delivered similar total NE, MP, Ca, and P per day. During both experiments, fecal DM output by IR80 was less (P 
0.03) than that of AL; IR90 was similar (P = 0.51) to AL during Exp. 1. Digestion of DM by IR80 cattle was greater (P 0.03) than that of AL during both experiments; IR90 was similar (P = 0.31) to AL during Exp. 1. Metabolizable energy intake was similar (P 
0.20) among treatments during both experiments, whereas P retention was similar (P 0.46) among treatments during Exp. 1. Total VFA and the molar proportion of acetate of AL were greater (P 0.03) than that of IR80 during Exp. 2; however, IR80 had a greater (P = 0.03) molar proportion of propionate. Under the conditions of these studies, restricting DMI while holding NE, ruminally degradable protein, and MP intakes constant decreased fecal DM output and changed ruminal fermentation patterns in finishing steers. Improvements in performance associated with programmed-feeding regimens of the type studied here do not appear to be related to changes in diet digestion or ME intake.
Key Words: beef steer • digestion • energy partitioning • intake restriction
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INTRODUCTION
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Limit-feeding refers to the practice of restricting intake of some dietary component to a level less than ad libitum based on known or predicted animal eating behavior (Galyean, 1999
). It is generally assumed that performance of feedlot cattle will be economically most favorable at ad libitum DMI; however, maximum production efficiency may occur at some level of DMI that is less than ad libitum. Benefits associated with programmed restriction of DMI include improved diet digestion (Galyean et al., 1979), improved feed efficiency (Sainz et al., 1995; Rossi et al., 2001; Schmidt et al., 2005), reduced feed costs (Knoblich et al., 1997; Loerch and Fluharty, 1998), and improved ADG (Schmidt et al., 2005). In most circumstances, programmed DMI restriction has been detrimental to performance of growing and finishing cattle. When DMI and energy intake were restricted concomitantly, ADG decreased (Plegge, 1987; Murphy and Loerch, 1994; Rossi et al., 2001), HCW was reduced (Hicks et al., 1990; Rossi et al., 2001), and carcass quality decreased (Hicks et al., 1990; Sainz et al., 1995; Rossi et al., 2001). This manner of DMI restriction also reduced external carcass fatness (Albin and Durham, 1967; Sainz et al., 1995; Rossi et al., 2001) and decreased USDA yield grade (Sainz et al., 1995). Restricting DMI without restricting protein or energy intake relative to ad libitum feeding improved G:F, increased ADG, and did not affect carcass value (Schmidt et al., 2005).
The objective of our research was to evaluate the effects of restricting DMI to 90 or 80% of ad libitum, while holding NE and MP intakes constant relative to cattle fed ad libitum, on diet digestion, nutrient retention, ruminal fermentation, and energy balance.
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MATERIALS AND METHODS
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The experimental protocols described in this manuscript were reviewed and approved by the University of Missouri Animal Care and Use Committee.
Twelve crossbred steers (average BW = 450 ± 18 kg) were used to evaluate the effects of programmed DMI restriction on diet digestion, nutrient excretion, and energy balance in a completely random design (Exp. 1). Steers were randomly assigned to 1 of 3 dietary treatments (Table 1): ad libitum (AL) DMI, intake restricted to 90% (IR90) of ad libitum DMI, or intake restricted to 80% (IR80) of ad libitum DMI. In a second experiment (Exp. 2), 12 crossbred steers (average BW = 445 ± 56 kg) fitted with ruminal cannulae were used to evaluate the effects of programmed DMI restriction on ruminal fermentation, fluid dilution rate, and energy balance in a completely random design. Steers were randomly assigned to 1 of 2 dietary treatments (Table 2): AL or IR80. All diets for Exp. 1 and Exp. 2 were formulated to promote 1.6 kg of ADG and to deliver similar amounts of NE, ruminally degradable protein, MP, Ca, and P on a daily basis. Desired intakes of DM, NE, ruminally degradable protein, MP, Ca, and P were achieved by varying the ingredient composition of the diets.
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Table 1. Composition (DM basis) of diets formulated to promote a 1.6-kg ADG by beef steers consuming 100 (AL), 90 (IR90), or 80% (IR80) of ad libitum DMI in Exp. 1
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Table 2. Composition (DM basis) of diets formulated to promote a 1.6-kg ADG by beef steers consuming 100 (AL) or 80% (IR80) of ad libitum DMI in Exp. 2
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Experimental Procedures—Experiment 1
Steers were pen-fed their respective treatment diets for 56 d; subsequently, they were placed in individual metabolism stanchions for a period of 25 d. Treatment diets were individually fed once daily at 0800 during the period of stanchion confinement. Intakes were adjusted such that the AL steers consumed their daily allotment of feed in approximately 23 h; intakes of IR90 and IR80 steers were based on the rolling 5-d average intake of the AL steers.
The 25-d confinement period consisted of a 17-d period of adaptation to the environment and diet, followed by an 8-d data collection period. The 8-d data collection period was conducted as follows: individual DMI were recorded on d 1 through 7 and individual collection of total fecal and urinary output was conducted on d 3 through 8.
Treatment diets were randomly subsampled 1x daily immediately prior to feeding. Diet samples were composited within treatment, across day. Feed composites were dried in a forced-air oven (50°C; 96 h) and subsequently ground to pass a 2-mm screen (No. 4 Wiley mill, Thomas Scientific, Swedesboro, NJ). During the period of intake measurement, consumption of targeted amounts of feed was complete for all treatment groups.
Total fecal output was weighed once daily at 0600. After thorough mixing, fecal material was subsampled (approximately 3% of the daily total by weight), weighed, and dried in a forced-air oven (50°C, 96 h). Dried daily fecal samples were ground to pass a 2-mm screen (No. 4 Wiley mill) and composited within animal across day. Collected urine was acidified with 6 N HCl at 4-h intervals to maintain pH 4.0 (Knowlton et al., 2001). Total urinary output was weighed once daily at 0630, homogenized, and subsampled (approximately 3% of the daily total by weight). Daily subsamples were aggregated into a running composite and frozen (–20°C) immediately after collection.
Experimental Procedures—Experiment 2
Steers were adapted to a common, pen-fed finishing diet over 12 d. Subsequently, they were randomly assigned to dietary treatments and placed in individual metabolism stanchions for a period of 24 d. Treatment diets were individually fed once daily at 0800 during the period of stanchion confinement. Intakes were adjusted such that the AL steers consumed their daily allotment of feed in about 23 h; intakes of IR80 steers were based on the rolling 5-d average DMI by AL steers.
The 24-d confinement period consisted of a 14-d period of adaptation to diet and environment, followed by a 10-d data collection period. The 10-d data collection period was conducted as follows: individual DMI were recorded on d 1 through 7; individual collection of total fecal and urinary output was conducted on d 3 through 9; and ruminal fermentation and passage rate were characterized on d 10. During the period of intake measurement, consumption of targeted amounts of feed was complete for all treatment groups. Samples of feed, feces, and urine were collected and processed using methods described for Exp. 1.
Steers were intraruminally infused at 0745 on d 10 with 6.5 g of Co-EDTA dissolved in 200 mL of water (Uden et al., 1980) and 500 g of Yb-labeled whole shelled corn (Teeter et al., 1984; Sindt et al., 1993). Labeled corn, infused as a particulate phase marker, replaced 500 g of the treatment diet. Random grab samples of whole ruminal contents were collected at 0.25, 4, 8, 12, 16, 20, and 24 h after feeding (0800). Ruminal contents were strained through 4 layers of cheesecloth into a 250-mL beaker; pH was measured immediately using a combination electrode (Hanna Instruments, Ann Arbor, MI). Two 25-mL subsamples of rumen fluid were collected. One 25 mL aliquot of ruminal fluid was acidified with 0.5 mL 6 N HCl and frozen (–20°C) for subsequent VFA and ammonia analysis. A second 25 mL aliquot was also frozen (–20°C) for Co analysis. Ruminal particulate samples were dried in a forced-air oven (50°C, 96 h) and ground to pass a 2-mm screen (No. 4 Wiley mill).
Laboratory Analysis
Ground composite samples of feed and feces were analyzed for DM and P using standard techniques (AOAC, 2003). Nitrogen content of feed and feces were determined using thermal conductivity of nitrogen gas (Leco Model FP-FP-248, Leco Corp., St. Joseph, MI). Gross energy content of feed, feces, and urine was determined by oxygen bomb calorimetry (Parr Instrument Co., Moline, IL). Gaseous energy loss was estimated according to the methods of Blaxter and Clapperton (1965). Acidified ruminal fluid samples were thawed and centrifuged at 20,000 x g for 20 min. The supernatant was decanted for VFA and ammonia analysis. Ruminal VFA concentrations were ascertained via gas chromatography (Varian 3400, Varian Corp., Walnut Creek, CA). Ruminal ammonia concentration was measured using a colorimetric procedure (Broderick and Kang, 1980).
Cobalt and Yb content of ruminal fluid and ruminal particulate matter, respectively, were measured using atomic absorbtion spectrophotometry (Varian Spec-trAA 30, Mulgrove, Victoria, Australia). Ruminal particulate and liquid passage rates were calculated by regressing the natural logarithm of Yb and Co concentration, respectively, on time. Slopes of ln Yb vs. time were positive for 4 of the 6 steers assigned to the IR80 treatment. In contrast, slopes of ln Yb vs. time were negative for AL cattle and appeared to be typical of cattle fed high-concentrate diets (2 to 4%/h). These data were interpreted to indicate that the technique used to estimate particulate passage was not appropriate for cattle limited to 80% of ad libitum intake. As a result, particulate passage data were not analyzed statistically.
Statistical Analysis
Intake, digestion, P retention, fluid dilution, and energy partitioning were analyzed as a completely random design using the GLM Procedure (SAS Inst. Inc., Cary, NC). Ruminal pH, ruminal ammonia, and ruminal VFA measurements were analyzed as a completely random design split-plot in time (Gill and Hafs, 1971; Littell et al., 1998); the MIXED procedure of SAS was used to analyze the effects of steer, intake level, and time. Intake level x time was used as the error term to test whole plot effects. When F-tests were significant (P < 0.05), means were separated using the method of least significant difference.
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RESULTS AND DISCUSSION
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Actual average DMI were 2.55% of BW by AL, 2.38% of BW by IR90 (93% of AL), and 2.02% of BW by IR80 (79% of AL) during Exp. 1. During Exp. 2, actual average DMI were 1.94% of BW by AL and 1.61% of BW by IR80 (83% of AL). Similar intakes of NEm, NEg, and MP were maintained throughout both experiments for all treatment groups.
Diet digestion and energy balance data from Exp. 1 and 2 are reported in Tables 3 and 4, respectively. During both experiments, fecal output (FO) by IR80 steers was lesser (P 0.02) than that by AL steers. Conversely, FO by IR90 steers was similar (P = 0.52) to AL steers and greater (P 0.01) than IR80 steers during Exp. 1. Over both experiments, FO by IR80 cattle was reduced 39 ± 4.7% relative to AL cattle ([DMI – FO]/DMI). The sharp reduction in fecal output by IR80 cattle was accompanied by an increase (P 0.04) in DM digestibility (DMD) compared with AL cattle in Exp. 1 and 2; DMD by IR90 cattle was similar (P = 0.31) to that of AL cattle in trail 1. Galyean et al. (1979) reported similar changes in DMD when a single high-concentrate diet was fed at DMI corresponding to 1x, 1.33x, 1.67x, and 2x maintenance.
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Table 3. Effect of diets formulated to promote a 1.6-kg ADG when consumed at 100 (AL), 90 (IR90), or 80% (IR80) of ad libitum DMI on diet digestion and energy balance of beef steers in Exp. 1
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Table 4. Effect of diets formulated to promote a 1.6-kg ADG when consumed at 100% (AL) or 80% (IR80) of ad libitum DMI on diet digestion, fluid dilution rate, and energy balance of beef steers in Exp. 2
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Fluid urinary output by IR80 cattle tended to be greater (P < 0.10) during Exp. 1 and was greater (P = 0.04) during Exp. 2 compared with AL cattle. Fluid urinary output was similar (P = 0.86) between IR90 and AL during Exp. 1. Cattle on the IR80 treatment may have compensated for temporally limited access to feed by increasing water consumption. Water intake was not measured during either experiment; however, authors noted that IR80 cattle appeared to spend more time drinking than cattle assigned to other treatments.
Fecal, urinary, and gaseous energy losses were similar (P 0.65) between AL and IR90 steers in Exp. 1, whereas IR80 steers had lesser (P 0.02) fecal and gaseous energy loss and tended to have greater (P < 0.10) urinary energy loss than that of AL and IR90. In Exp. 2, fecal energy loss was similar (P = 0.15) between treatments. Urinary energy loss by AL cattle was lesser (P = 0.04) than that by IR80 cattle; moreover, gaseous energy loss tended (P = 0.08) to be greater by AL compared with IR80.
The effect of programmed DMI restriction on performance of finishing cattle has been studied extensively. Relative to cattle fed ad libitum, cattle held to less than maximal DMI had improved diet digestion (Galyean et al., 1979), improved feed efficiency (Sainz et al., 1995; Rossi et al., 2001), reduced feed costs (Knoblich et al., 1997; Loerch and Fluharty, 1998), and reduced ADG (Plegge, 1987; Hicks et al., 1990; Murphy and Loerch, 1994; Rossi et al., 2001). The aforementioned studies used a single diet to compare ad libitum DMI with DMI restricted to between 80 and 96% of ad libitum DMI. In each case, total energy intake decreased as DMI decreased. Presumably, diet composition was held constant across treatments in these studies to avoid perceived confounding with intake level; however, unequal energy intakes made it difficult to interpret the effects of DMI restriction per se on growth performance.
In our study, we attempted to hold NEm and NEg intakes constant while progressively restricting DMI. Schmidt et al. (2005) used a similar approach. Both studies were predicated on the idea that diet composition could be altered between treatments while still maintaining similar intakes of NEm and NEg between treatments. There were 2 conceptual drawbacks to this experimental approach. First, potential DMI may decrease as dietary NE density increases beyond some point above maintenance (Grovum, 1986). It was possible that DMI of the IR80 diets in our experiments was effectively near ad libitum due to their energy densities. Schmidt et al. (2005) also considered this possibility. They reported that cattle fed 80% of ad libitum DMI completely consumed their daily ration within 7 h of delivery, whereas cattle consuming similar total NEm and NEg required 20 h to completely consume their daily ration. Schmidt et al. (2005) concluded that a daily intake pattern with a more even temporal distribution would have been expected if intake of the restricted diets was near a physiological maximum. In our studies, cattle assigned to the IR80 treatment consumed their daily allotment of feed within 4 h of delivery; feed intake by AL cattle was complete 23 h after delivery. In Exp. 1, IR90 cattle consumed their daily allotment of feed within 12 h of delivery.
The second drawback to our experimental approach was its reliance on conventions of the California Net Energy System (CNES) to estimate the energetic values of feeds. Predictive equations used to estimate NE content of feedstuffs within the CNES were based on energy retention at ad libitum intake (Lofgreen and Garrett, 1968; Garrett, 1980; NRC, 2000). Schmidt et al. (2005) made the assumption that the net energy yield of individual feedstuffs was the same when fed at ad libitum DMI, 90% of ad libitum DMI, or 80% of ad libitum DMI. We also made that assumption in our studies despite the fact that level of intake is one of the primary causes of variation in apparent digestibility of a given diet (Brown, 1966). As DMI decreases, digestibility generally increases (Moe et al., 1965; Colucci et al., 1982; Edionwe and Owen, 1989); however, it is unclear if changes in apparent digestibility are accompanied by changes in ME intake or in efficiency of ME use by the animal.
Measured ME density of treatment diets was similar (P > 0.10) between AL and IR90 during Exp. 1. During Exp. 1 and 2, measured ME density of IR80 diets was greater (P < 0.01) than that of AL. This was the expected result of intentionally restricting DMI without reducing energy intake relative to ad libitum feeding. Conversely, ME intake was similar (P 0.20) between treatments in both Exp. 1 and 2. This observation led us to conclude that, under the conditions of our studies and those described by Schmidt et al. (2005), the methodology used by the CNES to estimate ME and NE values of feedstuffs is valid at DMI between 80 and 100% of ad libitum. Our diets were formulated to supply similar ME intakes at 80, 90, and 100% of ad libitum DMI.
Schmidt et al. (2005) held ME and MP intakes constant while varying DMI between 80 and 100% of ad libitum. They reported that cattle restricted to 80% of ad libitum DMI had greater ADG, greater G:F, and similar carcass characteristics compared with cattle fed ad libitum. Schmidt et al. (2005) proposed that the primary basis for improved growth performance by the DMI-restricted cattle was increased diet digestibility. Reduced rates of digesta passage and longer digesta residence times in the gut are characteristic of both low relative DMI and high relative diet digestibility (Moe et al., 1965; Colucci et al., 1982; Edionwe and Owen, 1989); however, fluid dilution rate was similar (P = 0.42) between AL and IR80 steers in Exp. 2 (Table 4
).
Although diet digestion by IR80 cattle was improved in our studies compared with AL cattle, ME intake was similar (P 0.20) between treatments. We concluded from this information that the basis for improved performance by DMI-restricted cattle, as reported by Schmidt et al. (2005), must be beyond the point of ME within the classical energy partitioning scheme (Maynard et al., 1979). Our data were interpreted to indicate that, for a given rate of gain, cattle managed for a low relative DMI may have a lesser heat increment than cattle managed for a high relative DMI.
Energy balance of intake-restricted cattle has not been extensively studied. As DMI increases above maintenance requirements, the effective ME concentration of feeds decreases (Moe, et al. 1965). The converse of this phenomenon may occur during programmed intake restriction (Plegge, 1987), but does not explain why cattle that are fed similar amounts of energy and protein do not perform equally when the amount of DMI is varied.
The weight of visceral organs and their contribution to the maintenance energy requirement increases as DMI increases (Ferrell et al., 1976). Sainz and Bentley (1997) reported that steers limited to 70% of ad libitum DMI had smaller livers than steers fed ad libitum; moreover, their visceral mass contained less protein and RNA. The numbers of liver cells per kilogram of BW were the same for limit-fed steers and steers fed ad libitum; however, cell size was smaller in limit-fed cattle. Johnson et al. (1990) estimated that portal drained viscera accounted for 24% of total energy expenditure by sheep. The liver accounted for 20 to 26% of energy use by the portal drained viscera. If sustained visceral organ mass reduction is characteristic of DMI restriction, maintenance energy requirements may be smaller in limit-fed animals compared with animals fed ad libitum. Improved ADG and G:F by cattle limited to 80% of ad libitum DMI, as reported by Schmidt et al. (2005), may have resulted partially from a lesser maintenance requirement.
Nutrient retention by intake-restricted beef cattle has not been widely studied. Effects of DMI restriction on P retention by feedlot steers in our study were reported in Table 5. By design, intake of P during Exp. 1 was similar (P > 0.47) among treatments; moreover, retention characteristics were not changed by intake restriction. Fecal P, urinary P, and retained P, expressed as a percentage of P intake, were not different (P 0.11) when DMI was held to 80, 90, or 100% of ad libitum DMI. Based on this information, we concluded that strategies used to influence P retention by conventionally fed beef cattle would likely be effective in limit-fed beef cattle as well.
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Table 5. Effect of diets formulated to promote a 1.6-kg ADG when consumed at 100% (AL), 90% (IR90), or 80% (IR80) of ad libitum DMI on P retention by beef steers in Exp. 1
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There were no treatment x time interactions (P > 0.21) observed for total ruminal VFA concentration or molar proportions of individual VFA. Therefore, main effect means were reported (Table 6). Steers assigned to the AL treatment had greater (P < 0.01) total ruminal VFA concentration than IR80 steers. The temporal pattern of total ruminal VFA concentration (data not shown) indicated that VFA concentrations were similar (P > 0.41) between treatments at 0.25, 4, and 8 h after feeding. Conversely, total ruminal VFA concentration of IR80 steers was lesser (P < 0.05) than that of AL steers at 12, 16, 20, and 24 h after feeding. Authors presumed that this effect was related to the observation that IR steers consumed their feed within 4 h of delivery, whereas AL steers consumed their daily allotment of feed over a 23-h period. The rate of ruminal fermentation by IR80 steers may have slowed 8 to 12 h postfeeding without continued input of substrate.
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Table 6. Effect of diets formulated to promote a 1.6-kg ADG when consumed at 100 (AL) or 80% (IR80) of ad libitum DMI on concentration of VFA in ruminal fluid of beef steers in Exp. 2
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The average ruminal molar proportion of acetate was greater (P = 0.03) in AL cattle than in IR80 cattle (Table 6). Conversely, IR80 cattle had a greater (P = 0.03) average molar proportion of propionate than did AL cattle. The molar proportions of butyrate and total minor VFA were similar (P 0.31) between treatments. Differences in the proportions of fermentation end products were reflective of dietary ME density; however, this observation had no impact on total ME intake (Table 4).
Treatment x time interactions were detected for ruminal pH and for ruminal ammonia concentration (Figures 1 and 2, respectively). Ruminal pH was similar (P> 0.10) between treatments at 0.25, 8, 12, 16, 20, and 24 h postfeeding; however, IR80 cattle had lesser (P < 0.01) ruminal pH 4 h postfeeding than did AL cattle. Our data were interpreted to indicate that the nadir in ruminal pH of IR80 cattle occurred sooner after feeding compared with AL cattle (4 vs. 8 h) and that the nadir in ruminal pH was lower (P < 0.02) for IR80 than for AL cattle (5.45 vs. 5.73).
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Figure 1. Effect of diets formulated to promote a 1.6-kg ADG when consumed at 100% (AL) or 80% (IR80) of ad libitum DMI on ruminal pH of beef steers in Exp. 2 (treatment x time, P < 0.01).
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Figure 2. Effect of diets formulated to promote a 1.6-kg ADG when consumed at 100% (AL) or 80% (IR80) of ad libitum DMI on ruminal ammonia concentration of beef steers in Exp. 2 (treatment x time, P < 0.01).
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Ruminal ammonia concentration of IR80 cattle was greater (P < 0.01) than that of AL cattle at 0.25 and 4 h postfeeding but similar (P > 0.10) between treatments at 8, 12, 16, 20, and 24 h postfeeding. Intakes of MP and ruminally degradable protein were held constant between treatments; however, the rapid rate of DMI by IR80 cattle probably contributed to an equally rapid rate of ruminal ammonia-N release.
Murphy et al. (1994) reported that ruminal pH of steers limit-fed high-concentrate diets was not different than that of steers fed high-concentrate diets ad libitum. Moreover, Soto-Navarro et al. (2000) indicated that restricting DMI of a high-concentrate diet did not negatively affect ruminal health or digestion of OM, N, or starch. Under the conditions of our studies, DMI-restricted steers were without feed for 12 to 23 h without causing clinical digestive upset. Schmidt et al. (2005) reported similar results. Feeding programs that promote rapid consumption of a limit-fed diet may have important ramifications for bunk management. Compared with feeding management systems that are designed to reach and maintain maximum DMI, those that impose a predetermined intake level based on body size and desired performance may be accompanied by more stable intake patterns and a reduced need for bunk management expertise.
Steers limited to 80% of ad libitum DMI but not restricted in terms of NE or MP intakes had sharply reduced fecal output and greater diet digestibility compared with steers fed ad libitum. Urinary output appeared to be greater by cattle restricted to 80% of ad libitum DMI; however, this condition did not affect retention of dietary P. In general, fecal energy loss was lesser and urinary energy loss greater by cattle limited to 80% of ad libitum DMI compared with cattle fed ad libitum. There were also temporal changes in ruminal fermentation and in the proportions of end products of ruminal fermentation between treatments. In spite of these changes, ME intake was similar among cattle fed 80, 90, or 100% of ad libitum DMI.
We concluded from these data that, at a given ME intake, a 20% reduction in DMI can reduce DM manure output by as much as 39%. Moreover, DMI-restriction was associated with a sustainable ruminal fermentation pattern under the conditions of this study, in spite of the fact that steers limited to 80% of ad libitum DMI were without feed for 20 h per d. Improvements in ADG and G:F by DMI-restricted finishing cattle do not appear to be related to changes in diet digestion or ME intake. Further research is warranted to determine if the heat increment of limit-fed cattle is lesser than that of cattle fed ad libitum for a given ADG.
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Footnotes
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2 Thanks are extended to M. F. Smith, R. E. Ricketts, M. S. Kerley, J. E. Williams, P. B. Brooks, D. J. Kemp, and J. P. Porter of the University of Missouri—Columbia, for their support of this research. 
1 Corresponding author: kcolson{at}ksu.edu
Received for publication November 6, 2006.
Accepted for publication August 22, 2007.
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LITERATURE CITED
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Albin, R. C., and R. M. Durham. 1967. Restricted feeding and use of dehydrated alfalfa meal and beef tallow in an all-concentrate ration for fattening steers. J. Anim. Sci. 26:85–88.[Abstract/Free Full Text]
AOAC. 2003. Official Methods of Analysis. 17th ed. Assoc. Off. Anal. Chem., Arlington, VA.
Blaxter, K. L., and L. J. Clapperton. 1965. Prediction of the amount of methane produced by ruminants. Br. J. Nut. 19:511–522.[CrossRef][Medline]
Broderick, G. A., and J. H. Kang. 1980. Automated simultaneous determination of ammonia and amino acids in ruminal fluid and in vivo media. J. Dairy Sci. 63:64–75.[Abstract/Free Full Text]
Brown, L. D. 1966. Influence of intake on feed utilization. J. Dairy Sci. 49:223–230.[Abstract/Free Full Text]
Colucci, P. E., L. E. Chase, and P. J. Van Soest. 1982. Feed intake, apparent diet digestibility, and rate of particulate passage in dairy cattle. J. Dairy Sci. 65:1445–1456.[Abstract/Free Full Text]
Edionwe, A. O., and F. G. Owen. 1989. Relation of intake to digestibility of diets containing soyhulls and distillers dried grains. J. Dairy Sci. 72:1786–1792.[Abstract/Free Full Text]
Ferrell, C. L., W. N. Garrett, and N. Hinman. 1976. Estimation of body composition in pregnant and nonpregnant heifers. J. Anim. Sci. 42:1158–1166.[Abstract/Free Full Text]
Galyean, M. L. 1999. Review: Restricted and programmed feeding of beef cattle definitions, application, and research results. Prof. Anim. Sci. 15:1–6.[Abstract/Free Full Text]
Galyean, M. L., D. G. Wagner, and F. N. Owens. 1979. Level of feed intake and site and extent of digestion of high concentrate diets by steers. J. Anim. Sci. 49:199–203.[Abstract/Free Full Text]
Garrett, W. N. 1980. Energy utilization of growing cattle as determined in seventy-two comparative slaughter experiments. Page 3 in Energy Metabolism, EAAP Publ. No. 26. L. E. Mount, ed. Butterworths, London, UK.
Gill, J. L., and H. D. Hafs. 1971. Analysis of repeated measurements of animals. J. Anim. Sci. 33:331–336.[Abstract/Free Full Text]
Grovum, W. L. 1986. A new look at what is controlling feed intake. Page 1 in Proc. Symp. Feed Intake by Beef Cattle. MP 121. Okla. Agric. Exp. Sta., Stillwater.
Hicks, R. B., F. N. Owens, D. R. Gill, J. J. Martin, and C. A. Strasia. 1990. Effects of controlled feed intake on performance and carcass characteristics of feedlot steers and heifers. J. Anim. Sci. 68:233–244.[Abstract/Free Full Text]
Johnson, D. E., K. A. Johnson, and R. L. Baldwin. 1990. Changes in liver and gastrointestinal tract energy demands in response to physiological workload in ruminates. J. Nutr. 120:649–655.[Abstract/Free Full Text]
Knoblich, H. V., F. L. Fluharty, and S. C. Loerch. 1997. Effects of programmed gain strategies on performance and carcass characteristics of steers. J. Anim. Sci. 75:3094–3102.[Abstract/Free Full Text]
Knowlton, K. F., J. H. Herbein, M. A. Meister-Weisbarth, and W. A. Wark. 2001. Nitrogen and phosphorus partitioning in lactating Holstein cows fed different sources of dietary protein and phosphorus. J. Dairy Sci. 84:1210–1217.[Abstract]
Littell, R. C., P. R. Henry, and C. B. Ammerman. 1998. Statistical analysis or repeated measures data using SAS procedures. J. Anim. Sci. 76:1216–1231.[Abstract/Free Full Text]
Loerch, S. C., and F. L. Fluharty. 1998. Effects of programming intake on performance and carcass characteristics of feedlot cattle. J. Anim. Sci. 76:371–377.[Abstract/Free Full Text]
Lofgreen, G. P., and W. N. Garrett. 1968. A system for expressing net energy requirements and feed values for growing and finishing beef cattle. J. Anim. Sci. 27:793–806.[Abstract/Free Full Text]
Maynard, L. A., J. K. Loosli, H. F. Hintz, and R. G. Warner. 1979. Animal Nutrition. 7th ed. McGraw-Hill Book Co., New York, NY.
Moe, P. W., J. T. Reid, and H. G. Tyrrell. 1965. Effect of level of intake on digestibility of dietary energy by high-producing cows. J. Dairy Sci. 48:1053–1061.[Abstract/Free Full Text]
Murphy, T. A., and S. C. Loerch. 1994. Effect of restricted feeding of growing steers on performance, carcass characteristics, and composition. J. Anim. Sci. 72:2497–2507.[Abstract]
Murphy, T. A., S. C. Loerch, and B. A. Dehority. 1994. The influence of restricted feeding on site and extent of digestion and flow of nitrogenous compounds to the duodenum in steers. J. Anim. Sci. 72:2487–2496.[Abstract]
NRC. 2000. Nutritional Requirements of Beef Cattle. 7th rev. ed. Natl. Acad. Press, Washington, DC.
Plegge, S. D. 1987. Restricting intake of feedlot cattle. Page 297 in Proc. Symp. Feed Intake by Beef Cattle. MP 121. Okla. Agric. Exp. Sta., Stillwater.
Rossi, J. E., S. C. Loerch, S. J. Moeller, and J. P. Schoonmaker. 2001. Effects of programmed growth rate and days fed on performance and carcass characteristics of feedlot steers. J. Anim. Sci. 79:1394–1401.[Abstract/Free Full Text]
Sainz, R. D., F. De la Torre, and J. W. Oltjen. 1995. Compensatory growth and carcass quality of growth-restricted and refed beef steers. J. Anim. Sci. 73:2971–2979.[Abstract]
Sainz, R. D., and B. E. Bentley. 1997. Visceral organ mass and cellularity in growth-restricted and refed beef steers. J. Anim. Sci. 75:1229–1236.[Abstract/Free Full Text]
Schmidt, T. B., K. C. Olson, M. L. Linville, J. H. Clark, D. L. Meyer, M. M. Brandt, C. A. Stahl, G. K. Rentfrow, and E. P. Berg. 2005. Effects of dry matter intake restriction on growth performance and carcass merit of finishing steers. Prof. Anim. Sci. 21:332–338.[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]
Soto-Navarro, S. A., C. R. Krehbiel, G. C. Duff, M. L. Galyean, M. S. Brown, and R. L. Steiner. 2000. Influence of feed intake fluctuation and frequency of feeding on nutrient digestion, digesta kinetics, and ruminal fermentation profiles in limit-fed steers. J. Anim. Sci. 78:2215–2222.[Abstract/Free Full Text]
Teeter, R. G., F. N. Owens, and T. L. Mader. 1984. Ytterbium chloride as a marker for particulate matter in the rumen. J. Anim. Sci. 58:465–473.[Abstract/Free Full Text]
Uden, P., P. E. Colucci, and P. J. Van Soest. 1980. Investigation of chromium, cerium, and cobalt as markers in digesta: Rate of passage studies. J. Sci. Agric. 31:625–632.[CrossRef]
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Abstract
INTRODUCTION
