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ANIMAL PRODUCTION |
Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: desugared molasses • digestion • cattle • forage • intake • supplementation
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). Beet molasses, a by-product of sucrose extraction from sugar beets, has traditionally been used as a base ingredient for molasses blocks (Greenwood et al., 2000) and is frequently used as a source of supplemental energy and protein for cattle consuming low-quality forages (Heldt et al., 1999). Animal response to dietary additions of CSB may be different compared with beet molasses because CSB has a lower concentration of sucrose (23.0 vs. 50.0%, DM basis) and greater CP (19.0 vs. 8.5%, DM basis) and ash (29.0 vs. 11.3%, DM basis; Wiedmeier et al., 1992; NRC, 2000). Previous research with cooked molasses blocks containing CSB (Greenwood et al., 2000) or CSB fed separately, mixed, or both (Lawler-Neville et al., 2006) with the low-quality forage portion of the diet has resulted in increased intake, digestion, or both. Research with medium quality forages (Titgemeyer et al., 2004) supplemented with CSB-based cooked molasses blocks indicated minimal intake and digestion responses across a range of forage qualities. Recently, Lawler-Neville et al. (2006) reported that additions of 10% CSB (DM basis) to forage-based diets increased intake independent of forage quality, and Loe et al. (2002) reported that including CSB at 5% of DMI increased intake and gain in newly received feedlot steers. Little information is available on the effects of CSB as a dietary supplement on use of medium-quality forages offered either ad libitum (AL) or at restricted (RE) levels of intake. Therefore, our objectives were to evaluate the influence of CSB on intake, digestion, fermentation, and microbial efficiency in beef steers fed medium-quality grass hay diets at 2 levels of intake and with and without CSB addition. |
MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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The North Dakota State University Institutional Animal Care and Use Committee approved all surgical and animal management procedures used in this experiment. Four ruminally and duodenally cannulated beef steers (332 ± 2.3 kg) were used in a 4 x 4 Latin square design. Treatments were arranged in a 2 x 2 factorial. Factors were intake level (AL vs. RE) and dietary CSB addition (0 vs. 10% CSB). For the RE treatments, intake was based on 1.25% of steer BW, which is in the range often observed in grazing situations (Caton et al., 1988; Johnson et al., 1998). Restricted intake levels were adjusted each period as BW changed. Weights were measured at the end of each experimental period and were not adjusted to a common shrink or fill.
Diets
For the 10% CSB diet, CSB (DM basis) was added directly to the hay, while chopping the big round bales (3.8-cm screen, model No. 457000, Art’s-way Mfg. Co., Armstrong, IA). Control hay was chopped without the addition of CSB. After chopping and mixing, hay was stored in concrete bays under roof.
Animals were housed in individual stanchions and had ad libitum access to water. Nutrient composition of the diets is presented in Table 1. Trace-mineralized salt blocks (minimum 980 g of NaCl, 3.50 g of Zn, 2.80 g of Mn, 1.75 g of Fe, 0.35 g of Cu, 0.07 g of I, and 0.07 g of Co/kg; North American Salt Company, Overland Park, KS) were offered free choice throughout the entire experiment. Diets were offered once daily (0600) with AL-fed animals offered feed to provide a minimum of 10% of the feed as refusals. Diet sampling began 2 d before the beginning of each collection period and continued daily throughout collections. Orts were weighed daily for AL-fed steers. Ten percent of the daily orts were accumulated, mixed, subsampled, analyzed, and used in digestibility calculations.
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For each period, steers were allowed 14 d for adaptation to the diet, followed by a 7-d collection period. To measure total fecal output, the steers were fitted with fecal collection bags during each collection period. Bags were emptied twice daily at 0600 and 1600. For each 24-h period, total fecal excretion was determined, and feces were mixed, subsampled (10% of total daily output), and composited within steer and period. Fecal samples were dried in a forced-air oven at 55°C for at least 72 h and ground in a Wiley Mill (No. 4 Wiley Mill, Thomas Scientific, Swedesboro, NJ) to pass a 2-mm screen. To provide an indigestible marker of digesta flow, the steers were dosed with chromic oxide (16 g/d) via gelatin capsules through the ruminal cannula at 0600 and 1800. Dosing began on d 9 and continued through d 18. Duodenal fluid samples (approximately 200 g) were collected from d 15 through 18 of each collection period, in a system that allowed for every other hour in a 24-h period to be sampled (Caton et al., 1994). Digesta were composited within steer and period and stored frozen (–20°C) until analyses. After the study, duodenal samples were lyophilized (Genesis model 25 LL, Virtis Co., Gardiner, NY).
At the morning feeding on d 19 of each period, 200 mL of CoEDTA (850 mg of Co; fluid-phase marker; Uden et al., 1980) were ruminally dosed into each steer for estimation of fluid passage rates. Samples of ruminal fluid (approximately 100 mL) from the midventral region were taken at –1, 0, 1, 3, 6, 9, 12, 16, and 24 h postfeeding. Ruminal fluid pH was measured using a portable pH meter (model 2000, Beckman Instruments Inc., Fullerton, CA) with a combination electrode and acidified with 1 mL of 7.2 N H2SO4. Samples were then stored frozen (–20°C) until later analysis.
In situ degradation measurements were conducted on d 18 through 21 of each period. Duplicate in situ bags (Ankom, Fairport, NY; 10 x 20 cm; 50 ± 15 µm pore size) containing 5 g of ground (2-mm screen) forage were ruminally incubated within each steer. Forage containing both 0 and 10% CSB was weighed separately into in situ bags and sealed with a rubber stopper and 2 rubber bands (Caton et al., 1994). Samples were incubated for 0, 2, 4, 8, 12, 16, 24, 36, 48, and 72 h; bags were not anchored in the rumen and, therefore, were inserted beneath the ruminal fiber mat. Samples were inserted in reverse order and removed at 0 h. A blank was included for each incubation time. All bags were suspended in a large-mesh (18 x 24 cm) nylon bag that allowed contact with the ruminal contents. In situ bags were soaked in warm water (60°C) for 20 min before ruminal insertion.
Once collected, the in situ bags were first rinsed with tap water to remove excess ruminal material on the outside of the bags. In situ bags were then placed in a top-loading washer (model WJXR2080TSWW, General Electric, Louisville, KY) and rinsed in cold water for 10 cycles, using the lowest water level and the delicate cycle options. To determine forage DM disappearance, the dacron bags were then dried in a forced-air oven (model No. SB-350, Grieve Co., Round Lake, IL) at 55°C for 48 h and reweighed.
Total ruminal evacuations were conducted on d 21 of each period. Contents were weighed, mixed thoroughly by hand, and subsampled in duplicate. Subsamples were dried in a forced-air oven (55°C) for 72 h. An additional 4-kg sample of ruminal contents was saved for bacterial analysis. Samples were preserved with 2 L of formalin (9 g of NaCl/L of 3.7% formaldehyde) and stored frozen (–20°C) until bacterial cells were isolated. Steers were weighed (not adjusted for shrink or fill) on the last day of each period, and BW was used as a denominator for expressing the intake and fill data.
Laboratory Analyses
Diet, fecal, lyophilized duodenal, and in situ bag residues were analyzed in duplicate for DM, ash, and N by AOAC (1990) procedures 930.15, 942.05, and 984.13, respectively. Neutral detergent fiber (Van Soest et al., 1991) and ADF (Goering and Van Soest, 1970) of diet, duodenal, and fecal samples were determined by procedures modified by Ankom Technology.
Ruminal fluid samples were thawed at room temperature and centrifuged at 20,000 x g for 10 min at 4°C. Supernatant from the initial centrifugation step was mixed with 25% (wt/vol) metaphosphoric acid (5 mL of ruminal fluid and 1 mL of metaphosphoric acid) and recentrifuged at 20,000 x g for 10 min. The fluid portion was filtered through a 0.45-µm filter into 12 x 75-mm storage tubes and taken for VFA analysis; 2-ethylbutyric acid was used as the internal standard (Goetsch and Galyean, 1983). Determination of VFA was conducted by gas chromatography (model GC-9A, Shimadzu Scientific Instruments, Columbia, MD; Supelco 21687 Chromosorb WAW packed column; 140°C; N gas carrier). Supernatant from the initial centrifugation was analyzed for Co and ammonia concentration. The Co analysis (Uden et al., 1980) was conducted by atomic absorption spectroscopy using an air-plus-acetylene flame (model No. 3030B, Perkin Elmer, Norwalk, CT), and ammonia was determined colorimetrically (Broderick and Kang, 1980).
To dislodge particulate-associated bacteria, samples of whole-ruminal contents fixed with formalin were blended (model 37BL19 CB6, Waring Products, New Hartford, CT) with 0.9% saline (approximately 1 part saline:2 parts ruminal contents) for approximately 1 min. Blended contents were strained through 4 layers of cheesecloth. Bacteria-rich fluid fractions were then prepared by differential centrifugation (Merchen and Satter, 1983), lyophilized, and ground (mortar and pestle). Isolated bacterial cells were analyzed for DM, ash, and N (AOAC, 1990). Purine analysis was conducted on bacterial, duodenal, and in situ residue by the procedure of Zinn and Owens (1986).
Samples of feces and duodenal digesta were analyzed for DM, ash, CP, NDF, and ADF, as outlined previously. Samples were then prepared for Cr analysis, which was conducted by the spectrophotometric procedure of Fenton and Fenton (1979).
Calculations and Statistical Analyses
Intake and fecal output were determined by direct measurement. Duodenal DM flow was calculated by dividing the daily marker dose by the marker concentration at the duodenum. Nutrient digestibilities were calculated from differences in nutrient flow of digesta at various sites of the gastrointestinal tract. True ruminal OM digestibilities were calculated from duodenal flows after corrections were made for bacterial contributions.
Duodenal flows of OM, NDF, ADF, N, and purines were determined by multiplying the specific component composition by duodenal DM flow. Duodenal bacterial N flow was estimated by multiplying the duodenal purine flow by the N:purine ratio in isolated bacterial cells. Rate of fluid passage was determined by regressing the natural log of ruminal Co concentrations on time (Grovum and Williams, 1973). The absolute value of the slope was defined as the fluid dilution rate. Fluid volume was determined by dividing Co dose by the estimated marker concentration at time zero.
Rates of in situ degradation of DM, NDF, and ADF were determined by fitting the percentage residual fraction (DM, NDF, or ADF) remaining to the nonlinear model of Mertens and Loften (1980). Rate of in situ N disappearance (corrected for bacterial attachment using purines) was calculated using the model outlined by Ørskov and McDonald (1979). This model was also used to divide the total forage N into rapidly (fraction A) and slowly degraded (fraction B) N fractions. The calculated rate of N degradation is associated with fraction B because the disappearance of fraction A is assumed to be nearly instantaneous. Computations associated with models used for in situ DM, NDF, ADF, and N degradation rates were conducted using the nonlinear (Marquardt method) procedures of SAS (SAS Inst. Inc., Cary, NC).
Data were analyzed as a 4 x 4 Latin square with a 2 x 2 factorial arrangement of treatments. Intake, digestion, fill, and passage rate were analyzed using GLM of SAS, with the model containing the effects of period, animal, intake, CSB addition, and intake level x CSB interactions. In the absence of intake level x CSB interactions, the main effects of intake and CSB are presented. In situ disappearance was analyzed as just described, with the additional factor of incubated forage type (with or without added CSB) included in the model. Ruminal fermentation was analyzed as a split-plot within a 4 x 4 Latin square. The model contained effects for animal, period, treatments, and time. Animal x period x intake x CSB was used as the error term for testing the main-plot effects.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). By design, RE steers had lower (P = 0.01) DM and OM intake compared with AL-fed steers. Main effects of CSB level on DMI were not different. There were no differences in OM intake (4,619.8 and 4,785.8 ± 138.0; P = 0.43) expressed as g/d or g/kg of BW (14.2 and 14.3 ± 0.62; P = 0.86) between control and CSB-supplemented diets. However, within AL-fed steers, CSB tended (P = 0.12) to improve DMI (6,018 vs. 6,585 ± 195 g/d for 0 and 10% CSB, respectively). Lawler-Neville et al. (2006) reported that steers fed 10% CSB consumed more OM (6,660 vs. 5,683 ± 330 g) and N (184.4 vs. 141.5 ± 13.0 g) compared with nonsupplemented steers fed either corn stover or alfalfa-based diets. Additionally, Loe et al. (2002) reported that receiving steers consumed 9.8% more feed when 5% CSB was included in feedlot diets.
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; Greenwood et al., 1998). From experiments using CSB as an ingredient within cooked molasses blocks, Greenwood et al. (2000) reported increases in forage and total intake, total tract OM and N digestibilities, ruminal ammonia, and total VFA concentrations in steers fed 5.9% CP prairie hay (Greenwood et al., 2000). In research with steers fed medium (8.4% CP) to high (19.2% CP) quality forages and cooked molasses blocks containing CSB, Titgemeyer et al. (2004) found little change in intake and digestion measurements, which would tend to agree with the current study.
Response of cattle consuming forage-based diets to protein supplementation has been variable (Guthrie and Wagner, 1988; McCollum and Horn, 1990; Heldt et al., 1999) and may be explained by differences in degradable intake protein (DIP) of the basal feedstuff and supplement (Mathis et al., 2000; Bodine et al., 2001). In the study conducted by Mathis et al. (2000), the basal forage CP (8.2%) content may have been adequate to meet the DIP requirements; consequently, intake responses to DIP were not observed. Similarly, the forage used in the current study was medium quality (12.5% CP). Variation in intake due to protein supplementation may be dependent on forage CP and DIP content; however, data from our laboratory indicate that when CSB is mixed with the basal diet, intake in both low and high-quality forage-based diets are increased (Lawler-Neville et al., 2006). In addition, including 5% CSB into receiving diets for beef steers has resulted in increased intake and gain (Loe et al., 2002).
Total tract digestion of DM and OM was not affected (P = 0.84 and 0.85, respectively) by either intake level or CSB supplementation (Table 2
). Ruminal and post-ruminal digestion of DM and OM were not affected by CSB supplementation (P = 0.93, 0.60, 0.81, and 0.99, respectively); however, ruminal digestion of DM and OM was greater for AL-fed compared with RE-fed (P = 0.01) steers. Postruminal digestion of DM and OM was lower (P < 0.02) for AL-fed compared with RE-fed steers. Total tract digestion of NDF and ADF (data not shown) followed trends in OM digestion (P = 0.27 and 0.35, respectively) and averaged 57.3 ± 1.54, and 49.4 ± 1.72 for NDF and ADF, respectively.
Concentrated separator by-product and molasses have similar nutrient digestibility coefficients in forage-based diets (Wiedmeier et al., 1992). In a study using 4 Holstein cows, Wing et al. (1988) reported that peak digestibility of DM and OM occurred when a molasses-type liquid feed was added at 6% of the diet DM.
In our study, we selected a 10% inclusion level of CSB because data from our laboratory (Shellito, 2002) indicated that 10% inclusion increased intake and N retention. Additional work from our laboratory has shown that CSB inclusion into forage-based diets increased true ruminal OM digestion (Lawler-Neville et al., 2006). Reducing intake has been shown to improve digestibility of forage-based diets (Tyrrell and Moe, 1975). In this study, there were no effects of reduced intake on total tract digestion of DM, OM, NDF, and ADF. Reasons for this lack of response are unclear. Perhaps level of dietary restriction was insufficient to result in greater digestion coefficients. However, as discussed later, dietary restriction did increase (P 
0.08) in situ digestion rates and reduce (P = 0.01) passage rate.
No intake level x CSB interactions were present and, by design, N intake was greater for AL-fed (P = 0.01) compared with RE-fed steers and 10% CSB (P = 0.02) compared with 0% CSB-fed steers (Table 3). Total, feed, fecal, and microbial duodenal flow of N was greater (P < 0.02) for AL compared with RE steers. Total and feed (nonbacterial) N flow at the duodenum was increased by CSB supplementation (P 0.06); however, microbial N flow to the duodenum was not affected by CSB (P = 0.80). Total tract digestion of N (CP divided by 6.25) was unaffected by intake level but was increased (P = 0.10) by CSB addition. Ruminal N digestion (apparent and true) and apparent postruminal N absorption (percentage of intake and percentage of entering) were greater (P = 0.04 and 0.03, respectively) in AL- compared with RE-fed steers and were not influenced by CSB additions (P = 0.25 and 0.99, respectively).
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Furthermore, increased apparent total tract N absorption for CSB-fed steers was probably due to increased feed N reaching the duodenum. Total tract digestion of N has been shown to be greater in steers consuming CSB-based molasses blocks compared with controls, while being fed poor quality forage (5.9% CP; Greenwood et al., 2000). Other data from our laboratory indicate that increased microbial N flow to the duodenum can result from CSB supplementation (Lawler-Neville et al., 2006).
In the absence of interactions (P = 0.14 to 0.85), main effects of intake, dietary CSB and type of forage incubated (with or without CSB additions) for in situ disappearance rates of DM, NDF, ADF, and N (CP divided by 6.25) are shown in Table 4. Restricting intake increased the rate of in situ DM, NDF, ADF, and N disappearance (P 0.08). Dietary CSB level did not affect rate of in situ disappearance of any component analyzed (P = 0.20 to 0.68). However, forage containing 10% CSB incubated in situ had a greater DM (P = 0.01) and N (P = 0.01) disappearance rate compared with forage containing no CSB. Digestion rate of NDF and ADF were unaffected by type of forage incubated. The rapidly degraded (fraction A) N fraction was greater (P = 0.01), whereas the slowly degraded (fraction B) N fraction was lower (P = 0.01) for the 10% CSB-incubated forage compared with nonsupplemented forage. In the current study, the differences observed with incubated forage type are likely due to the high ruminal degradability of CSB.
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, in which increases of in situ DM disappearance occurred when feed intake was decreased. When intake decreases, increases in digestibility can be due to several factors, including slower turnover rates of both particles and liquid in the digestive tract (Colucci et al., 1990), changes in the microbial population, or modifications of the ruminal wall such as absorptive capacity or metabolic activity (Fell and Weekes, 1975). Supplementation with CSB did not affect in situ disappearance rates; however, Lawler-Neville et al. (2006) reported that 10% CSB dietary addition increased in situ N disappearance rate.
No intake level x CSB interactions were present (P = 0.39 to 0.94) for ruminal fill and fluid passage rate data; therefore, main effect means are presented in Table 5. Fluid fill, calculated using data obtained from CoEDTA, was not influenced by intake (P = 0.46) or CSB (P = 0.27). Concentrated separator by-product had no effect on passage rate (P = 0.69) or total fill (P = 0.40). Colucci et al. (1990) reported that passage rates of liquid markers were faster at greater intake levels for both sheep and cattle. Ad libitum intakes in this study were also associated (P = 0.01) with a faster liquid passage rate. Total fill (calculated from ruminal evacuation data), DM, and fluid fill were greater (P < 0.05) for AL compared with restricted steers (Table 5).
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; Colucci et al., 1990). Although CSB did not affect passage rate in this study, Caton et al. (1988) reported that ruminal fluid passage rates were greater and retention times lower in protein-supplemented compared with nonprotein supplemented steers. Additionally, intake restriction has decreased rate of passage and resulted in greater retention times (Tamminga et al., 1979). In the current study, there was no difference in fluid fill (L; P = 0.27), liquid passage rate (%/h; P = 0.69), or total fill (kg; P = 0.40) when the diet contained CSB additions. Others (Hermesmeyer et al., 2002) have reported no difference in liquid dilution or particulate passage rate in steers restricted to 75% of AL intake of wheat middlings.
The absence of interactions allowed for fermentation data to be composited across time and main effects presented (Table 6). Ruminal pH was greater (P = 0.06) for RE steers compared with AL-fed steers but was not affected by supplementation with CSB (P = 0.74). Ruminal ammonia concentration was greater (P = 0.03) in the 0% CSB diets compared with the 10% CSB-fed diets. Total VFA concentration was greater in AL(P = 0.03) and CSB- (P = 0.04) fed steers compared with the RE- and control-fed steers, respectively. Acetate (P = 0.71), propionate (P = 0.83), and butyrate (P = 0.14) proportions were not different between RE and AL intakes. Likewise, acetate (P = 0.27), propionate (P = 0.83), valerate (P = 0.14), and isovalerate (P = 0.15) were not different in control and CSB-fed steers; however, butyrate concentrations were greater (P < 0.01) for CSB-fed steers. The acetate:propionate ratio was not influenced by either intake or CSB (P = 0.31 and 0.72, respectively).
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). In the current study, greater (P = 0.06) ruminal pH values were observed for RE animals compared with AL steers, whereas ruminal pH was similar (P = 0.74) between CSB- and control-fed steers. The greater ruminal pH for restricted steers is probably a result of reduced microbial fermentation because of the lack of substrate availability. Similar to the findings of Greenwood et al. (2000), total molar concentrations of VFA in the current study increased with CSB supplementation; however, increased total VFA concentrations were not enough to produce a change in ruminal pH for CSB-fed steers. These data indicate that the dietary restriction reduces and CSB supplementation increases total VFA concentrations in steers fed medium-quality grass hay.
Previous studies have shown reduced ruminal NH3 concentrations when animals consumed readily fermented carbohydrates. Stakelum et al. (1988) reported that supplements with or without molasses beet pulp reduced ruminal NH3 concentrations. Furthermore, Huhtanen (1987) and Rooke et al. (1987) reported that, in cattle receiving grass silage diets, sugar supplements have decreased ruminal ammonia concentrations and increased microbial protein synthesis. Restricting intake had no effect on ruminal ammonia level, which was similar to the findings of Hermesmeyer et al. (2002).
In summary, CSB can provide a valuable source of supplemental dietary nitrogen for medium and lower-quality forage diets. At different levels of dietary intake, supplementing medium-quality forage with 10% CSB improves N intake, small intestinal protein supply, and increases total ruminal VFA.
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Footnotes |
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2 Present address: 1915 10th Street South, Moorhead, MN 56560.
3 Present address: Colby College, 1040 Golden St., Colby KS 67701.
4 Corresponding author: Joel.Caton{at}ndsu.edu
Received for publication November 30, 2004. Accepted for publication January 15, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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  T. L. Lawler-Neville, S. M. Shellito, T. D. Maddock, M. L. Bauer, G. P. Lardy, T. C. Gilbery, and J. S. Caton Effects of concentrated separator by-product (desugared molasses) on intake, site of digestion, microbial efficiency, and nitrogen balance in ruminants fed forage-based diets J Anim Sci, August 1, 2006; 84(8): 2232 - 2242. [Abstract] [Full Text] [PDF]
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