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ANIMAL PRODUCTION |
Animal and Range Sciences Department, North Dakota State University, Fargo, ND 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 • forage • lamb • steer
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). To achieve acceptable levels of production, many producers supplement cattle with feeds that predominantly provide either energy or protein (Bodine et al., 2001). When low-quality diets are not limited in quantity, protein is often the most limiting nutrient (Campling, 1970; McCollum and Horn, 1990). Protein supplementation of low-quality forage diets may substantially improve animal performance (McCollum and Horn, 1990; Owens et al., 1991). Köster et al. (1996) reported the effective use of low-quality forages might be limited by inadequate degradable intake protein.
Beet molasses, a by-product of sucrose extraction from sugar beets, is used as a supplement for cattle (Heldt et al., 1999). Beet molasses contains 75 to 85% of DM, 50 to 52% sucrose, 8.5 to 12% CP (predominantly betaine and glutamine), and approximately 2% N (Hungerford, 1982; NRC, 2000). Concentrated separator byproduct (CSB) is produced by removal of residual sugars from beet molasses. Ruminants may respond differently to CSB compared with molasses because of its lower concentration of sucrose and greater CP and ash concentrations (23.0 vs. 50.0%; 19.0 vs. 8.5%; 29.0 vs. 11.3%, DM basis, respectively; Wiedmeier et al., 1992). Sugars are the predominant carbohydrates found in molasses-based products (Kunkle et al., 1999), and impacts of molasses-based supplements on forage use and animal performance have been variable (Bowman et al., 1995). Little information is available on effects of CSB as a protein source in forage-based diets. The objectives were to evaluate effects of CSB supplementation for low- (corn stover) and high-quality forage (alfalfa) on intake, site of digestion, and microbial efficiency in steers and to evaluate how CSB supplementation, either mixed with forage or offered separately, affects intake, digestibility, and N balance in lambs consuming grass hay.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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A 2 x 2 factorial arrangement of treatments was used. Main effects were forage type (alfalfa or corn stover) and CSB supplementation (0 or 10% CSB). The 4 treatments consisted of 1) coarsely chopped alfalfa hay with 0% CSB, 2) coarsely chopped corn stover with 0% CSB, 3) coarsely chopped alfalfa hay mixed with 10% CSB, and 4) coarsely chopped corn stover mixed with 10% CSB (Table 1). For alfalfa and corn stover with CSB supplementation, the forage was weighed, and 10% CSB (DM basis) was added directly to the forage while it was being chopped (10- to 15-cm chop length; Model No. 45700, Art’s-way Manufacturing Co., Armstrong, IA). Forage and CSB were allowed to mix for 45 min. Steers had free access to water and trace mineralized salt blocks (minimum 955 g of NaCl, 3.5 g of Zn, 2.8 g of Mn, 1.75 g of Fe, 0.35 mg of Cu, 0.07 g of I, and 0.07 g of Co/kg; North American Salt Co., Overland Park, KS) at all times. Diets were fed once daily at 0700 and offered to ensure at least 10% refusals. Orts were collected and weighed once daily.
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Duodenal samples were collected (approximately 200 g) in a manner that allowed for every other hour in a 24-h period to be sampled. Therefore, samples were collected at 0600, 1000, 1400, 1800, and 2200 on d 19; 0200, 0800, 1200, 1600, 2000, and 2400 on d 20; and 0400 on d 21 of each collection period. Duodenal samples were composited within animal and collection period and stored frozen (–20°C). Duodenal samples, intake, and fecal output were used to calculate site of digestion, microbial protein synthesis, and forage escape protein.
In situ incubations to calculate forage degradabilities were conducted on d 17 through 21 of each sampling period. Dacron bags (Ankom, Fairport, NY; 10 cm x 20 cm; pore size of 53 ± 10 µm) containing approximately 5 g of ground (2-mm screen; Wiley Mill, Arthur H. Thomas, Philadelphia, PA) forage were incubated for 96, 72, 48, 36, 24, 16, 12, 8, 4, or 0 h. At each incubation time, 2 bags containing forage (alfalfa or corn stover) and 1 blank bag were introduced into their respectively treated steers, after soaking in warm tap water for 15 min. All bags were removed at 0800 on d 21. All bags were suspended in a large-mesh (18 cm x 24 cm) nylon bag fitted with a nylon zipper. Mesh bags were not anchored, but were placed at the interface of the fiber mat and liquid portions of the ruminal contents. Dacron bags were sealed with a #8 rubber stopper and two #19 rubber bands. After incubation, all bags were removed and washed in warm tap water to remove large particles, then washed in a washing machine (Model WJXR2080TSWW, General Electric, Louisville, KY) for ten 4-min rinse cycles or until the rinse water was clear (Wilkerson, et al. 1995).
Total ruminal evacuations were conducted on d 21 of each period. On d 21, ruminal fluid was taken, and the contents were mixed and subsampled from multiple locations within the container and composited within steer for laboratory analysis and determination of fluid fill. Ruminal contents were stored at –20°C. Ruminal contents were strained through 4 layers of cheesecloth until 3 L was obtained, which was preserved with 25 mL of 0.15 M NaCl in 37% (vol/vol) formaldehyde/100 mL of strained ruminal fluid. Samples were stored at 10°C until bacterial cells were harvested for determination of bacterial nitrogen to purine ratio.
Laboratory Analyses.
Duodenal samples were lyophilized (Genesis Model 23LL, Virtis, Gardner, NY). Diet, orts, and in situ bags were dried in a forced-air oven (Model No. SB-350, Grieve Co., Round Lake, IL) at 50°C for 48 h; fecal and ruminal subsamples were dried for 72 h or until dry in the same oven. Diet, orts, and fecal samples were then ground (No. 4 Wiley Mill, Thomas Scientific, Swedesboro, NJ) to pass through a 2-mm screen. Duodenal samples were ground with a mortar and pestle. Duodenal, diet, orts, and fecal samples were analyzed for DM, ash, CP, and ADF by AOAC (1990) procedures. Analysis of NDF was conducted by the method of Robertson and Van Soest (1981). In situ samples were composited among like bags (bags within steer and time) for analysis of DM and CP (AOAC, 1990) and NDF (Robertson and Van Soest, 1981). Duodenal samples were analyzed for Cr concentrations by atomic absorption spectroscopy (air-acetylene flame; Williams et al., 1962). Bacterial cells were isolated from 3 L of ruminal fluid by differential centrifugation (Merchen and Satter, 1983), lyophilized, and ground. Dry isolated bacterial cells were analyzed for DM, ash, and N content (AOAC, 1990). Purines were determined on bacterial, duodenal, and in situ samples (Zinn and Owens, 1986).
Calculations.
Intake and fecal output were determined by direct measurement. Duodenal DM flow was calculated by dividing the daily Cr dose by the Cr concentration in the duodenum. Duodenal flows of N were determined by multiplying percent composition by duodenal DM flow. Duodenal bacterial N flow was estimated by multiplying duodenal purine (g/d) content of duodenal samples by the N:purine ratio in isolated bacterial cells (Zinn and Owens, 1986).
In situ rate and lag of potentially degradable NDF were estimated by using the nonlinear model of Mertens and Loften (1980). Rate of CP disappearance (corrected for bacterial attachment using purines) was calculated using the model outlined by Ørskov and McDonald (1979). This model calculates a rapidly degraded CP fraction (fraction A; assumed to be instantaneously degraded) and a slowly degraded CP fraction (fraction B; degradation rates similar to rate of passage). Degradation rates derived from this model are associated with fraction B. Computations of NDF and CP rates of disappearance were calculated using nonlinear procedures (Marquardt method) of SAS (SAS Inst., Cary, NC). Corrections for microbial contamination of in situ residue were made using purines as a microbial marker (Messman et al., 1992).
Statistical Analysis.
Data were analyzed as a 4 x 4 Latin square design (Cochran and Cox, 1957) with a 2 x 2 factorial arrangement of treatments using the GLM procedure of SAS. The model contained animal, period, forage type, CSB addition, and forage x CSB interaction. Means were separated using the method of LSD.
Experiment 2
Animals, Experimental Design, and Diets.
Five wether lambs (44 ± 1.5 kg) were allocated to a 5 x 5 Latin square. Animal husbandry and handling provided for humane treatment of animals and were approved by the North Dakota Sate University Institutional Animal Care and Use Committee.
The basal forage diet consisted of coarsely chopped (10 to 15 cm) grass hay (predominantly brome hay, Bromus ineris L., 7.7% CP). The 5 treatments were 1) grass hay mixed with 0% added CSB, 2) grass hay mixed with 10% added CSB, 3) grass hay mixed with 20% added CSB, 4) grass hay with 10% CSB offered separately from the hay (10SEP), and 5) grass hay mixed with urea (UREA) to provide N equivalent to that of the 10% CSB treatments. For the 10 and 20% added CSB treatments, 10 or 20% CSB (DM basis), respectively, was added directly to the grass hay while it was being chopped (Model No. 45700, Art’s-way Manufacturing Co.). Hay and CSB were allowed to mix for 45 min. For 10SEP, CSB was offered separately from the grass hay by providing CSB in a small pan immediately before offering fresh hay at the morning feeding in a quantity estimated to be equivalent to the CSB offered in the grass hay mixed with 10% added CSB diet. For UREA, a urea:water solution was added to the forage while mixing in a paddle mixer (Davis Batch Mixer, Model No. S20, Davis Sons Manufacturing Co., Bonner Springs, KS), with a compression sprayer (Model No. 020PEXG, Gilmour Manufacturing Co., Somerset, PA) at equal N levels to the grass hay mixed with 10% added CSB diet.
Sample Collection.
Experimental periods were 17 d in length with a 10-d adaptation period and 7 d for total fecal and urine collections. Water and feed intakes were measured during the collection period. Lambs were fed and watered at 0700, 1200, and 1700 daily to allow for ad libitum consumption. Fecal and urinary output was measured using false-bottomed metabolism crates, permitting separate collection of urine and feces. Urine samples were collected in jugs and feces in floor pans. Samples were weighed at 0700, mixed, composited (10% aliquots) across days within animal and period, and stored (–20°C) until analysis. Urine was pH-tested using litmus paper, and hydrochloric acid (50% wt/vol) was added to maintain a pH of less than 2.0 to inhibit microbial growth and NH3 volatilization.
Laboratory Analysis.
Feed, fecal, and orts samples were dried in a 50°C forced-air oven for 48 h, ground to pass through a 2-mm screen, and subsequently analyzed for DM, ash, CP, ADF, and NDF using the methods previously described for Exp. 1. Urine samples were thawed and analyzed for CP (AOAC, 1990).
Calculations.
Three calculations were used to assess N retention: 1) grams of N retention were measured by subtracting urine and fecal N from N intake, 2) N retention as a percentage of N intake was calculated by dividing N retention by N intake, and 3) N balance was expressed as a percentage of N digested by dividing N balance by the difference of N intake and fecal N output.
Statistical Analysis.
Data were analyzed as a 5 x 5 Latin square using the GLM procedure of SAS. The model included animal, period, and treatment. Contrasts were protected by a significant F-test (P < 0.10). Contrasts were linear and quadratic effects of CSB (0, 10, and 20% CSB); 10% CSB vs. 10SEP; and 10% CSB vs. UREA.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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and 3. When forage x CSB interactions were present (P < 0.10), interaction means are discussed in the text or presented in Table 4 or both. In the absence of interactions, main effects of forage and CSB are discussed.
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) and N (Table 3) intakes (g/d) were greater (P = 0.01) for alfalfa compared with corn stover and 10% CSB compared with 0% CSB (P = 0.08; P = 0.05 for OM and N, respectively). Organic matter intakes (g/kg of BW) were greater (P = 0.01) for alfalfa vs. corn stover but not different (P = 0.11) between 0 and 10% CSB. By design, nitrogen intakes (g/kg of BW) were greater for alfalfa compared with corn stover (P = 0.01) and 10% CSB compared with 0% CSB (P = 0.08). Bowman et al. (1995) indicated that low protein or high fiber forages or both may need supplemental feeds to meet livestock nutrient requirements. Molasses is often used as a supplement to low-quality forages to stimulate intake (McLennan et al., 1981) and improve performance (Stephenson and Bird, 1992). Whereas different than molasses in nutrient composition, recent data indicates feeding CSB may also increase intake (Greenwood et al., 2000; Loe et al., 2002; Shellito et al., 2006). Greenwood et al. (2000) reported increased OM intake when steers consuming prairie hay were supplemented with 417 g/d (as-fed basis) of cooked molasses blocks based on beet molasses, cane molasses, or CSB. Loe et al. (2002) reported 9.8% greater DMI (kg/d or % BW) when 5% CSB was included in 44% concentrate feedlot rations for newly received calves. Shellito et al. (2006) reported that DMI tended (P = 0.12) to increase in steers offered medium-quality brome hay ad libitum and supplemented with 10% CSB compared with nonsupplemented controls. Shellito et al. (2006) also reported increased N intake with 10% CSB (DM basis) inclusion.
Total and nonmicrobial duodenal flow (g/d) of OM (Table 2) and N (Table 3) were unaffected by CSB inclusion; however, microbial flows of OM and N were increased (P = 0.02) with 10% CSB inclusion. These data differ from Shellito et al. (2006) who reported 10% CSB increased total and feed duodenal N flow, whereas microbial N flow remained similar to 0% CSB. Total, microbial, and nonmicrobial N flows to the duodenum were greater (P < 0.01) for alfalfa compared with corn stover presumably because of large differences in CP concentration between the basal forages in this study.
Shellito et al. (2006) reported no differences in OM digestion with 10% CSB inclusion. We report similar results in the current study, in which total tract and apparent ruminal OM digestion were not affected (P = 0.71 and 0.16, respectively) by CSB. Steers consuming 10% CSB had increased (P = 0.09) true ruminal OM digestion. Total, apparent ruminal, and true ruminal OM digestion were greater (P < 0.04) in alfalfa compared with corn stover. A CSB x forage source interaction occurred (P = 0.05) for postruminal OM digestion measured as a percent of intake. When corn stover was fed alone, postruminal OM digestion (percentage of intake) was greater (P < 0.02) compared with all other treatments (18.8, 8.9, 9.4, and 10.1% for corn stover, corn stover with CSB, alfalfa, and alfalfa with CSB, respectively). Postruminal OM digestion (percentage of intake) for corn stover with 10% CSB was similar to alfalfa and alfalfa with 10% CSB. Alfalfa and alfalfa with 10% CSB were not different (P = 0.88).
Forage x CSB interactions were present for total tract (P = 0.01), ruminal (P = 0.02; P = 0.06 for apparent and true respectively), and postruminal (P = 0.02; P = 0.10 for percentage of intake and percentage of entering, respectively) N digestion (Table 4). These interactions resulted from large negative ruminal and concomitant large postruminal N digestion in the corn stover-fed steers. Total tract N digestion was lowest in corn stover, intermediate in corn stover with 10% CSB, and greatest in alfalfa and alfalfa with 10% CSB treatments. This ranking in total tract N digestion should be expected, as it follows the dietary CP concentration, in which corn stover was lowest and alfalfa with 10% CSB the greatest. Additionally, Greenwood et al. (2000) reported steers consuming prairie hay and molasses blocks based on CSB as a supplement had greater total tract N digestion compared with controls. Shellito et al. (2006) reported a tendency for increased total tract N digestion and no differences in ruminal digestion using 10% CSB to supplement medium-quality hay. Differences in digestion between our results and those of Shellito et al. (2006) may be explained by differences in forage CP concentration. Shellito et al. (2006) fed grass hay (12.5% CP) and reported a tendency for increased total tract digestion. In our study, we report increased ruminal N digestion and decreased postruminal N digestion for the corn stover treatments (3.3% CP). However, no differences in N digestion were noted when feeding alfalfa (17.5% CP). From this, one could conclude that addition of CSB has a greater effect on digestion when fed in combination with low-quality forages. Large negative ruminal N digestion values have also been reported by other researchers (Caton et al., 1993; Olson et al., 1994) in cattle grazing pasture and native range.
Similar to results reported by Shellito et al. (2006), microbial efficiency (g of microbial N/kg of OM truly fermented) was not affected (P < 0.37) by forage type or CSB addition. Researchers using corn condensed distillers solubles as a supplement to low-quality hay found no differences in microbial efficiency (Gilbery et al., 2006). Our microbial efficiency values (10.9 ± 0.8) are in expected ranges for forage fed beef steers (Caton et al., 1994; NRC, 2000; Lardy et al., 2004a). Addition of 10% CSB increases microbial protein supply as indicated by greater (P = 0.02) microbial N flows in CSB-fed steers. Differences in microbial efficiency because of CSB supplementation were lacking because of increases in intake; however, we still observed an increase in metabolizable protein supply to the lower tract. This increase resulted in increased N digestion in diets containing corn stover as previously discussed.
In situ rate of NDF disappearance (%/h; Table 5) was greater (P = 0.08; 8.4 vs. 6.8 ± 0.5 %/h, respectively) when CSB was added to the diet. This result differs from Shellito et al. (2006) who reported no differences in NDF disappearance with the addition of 10% dietary CSB. This may be explained by increased ruminal digestion because of CSB supplementation in steers consuming corn stover; however, interactions would be expected if CSB was increasing digestion with corn stover, but not alfalfa. These effects may also be explained by differences in rate of NDF digestion. As expected rate of NDF disappearance (%/h) was different between alfalfa and corn stover (11.4 vs. 3.9 ± 0.5 %/h). Interactions (P < 0.01) were present for all measurements associated with in situ CP disappearance. Interactions for fraction A, fraction B, and rate (%/h) of CP disappearance were due to magnitude and not changing treatment ranking. For fraction A, inclusion of CSB resulted in greater (P < 0.01) disappearance, whereas in fraction B, CSB inclusion reduced (P < 0.01) disappearance. Rate of CP disappearance (%/h) was greater (P < 0.01) when CSB was included in the diet. Inclusion of 10% CSB did not alter CP disappearance (fraction A or fraction B) in the study conducted by Shellito et al. (2006). Alfalfa had greater (P = 0.01) fraction B and rate (%/h) of CP disappearance compared with corn stover. Corn stover had a more (P = 0.01) highly degradable fraction B when compared with alfalfa.
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) on forage, total, and water intakes are presented in Table 7. Forage intake (g/d and g/kg of BW) increased with CSB supplementation (P < 0.01). Forage intake was greater for 10% CSB compared with UREA and the 10SEP treatment (P = 0.04). Forage and total DMI were greatest (P < 0.01) for 20% CSB. Water intakes were greater for CSB-containing diets (P < 0.01) compared with 0% CSB. Intake of water was greatest for 20% CSB (P < 0.01).
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reported increased forage OM, NDF, and N intakes for steers fed cooked molasses blocks. Forage intake responses resulting from CP supplementation may be related to basal forage quality. Swanson et al. (2000) suggested that forage quality averaging 6.7% CP may not be low enough to stimulate an intake response to supplementation. However, in our study, DMI increased with CSB supplementation for this trial even though the basal forage CP content was 7.7%. Although responses to CP supplementation have been variable (Guthrie and Wagner, 1988; Heldt et al., 1999), differences in degradable intake protein, rather than basal forage quality may be a more important factor affecting total feed intake (Bodine et al., 2001). Marston and Lusby (1995) noted that gestating cows fed a soybean meal based protein supplement consumed 1 kg/d more hay (DM basis) and had greater hay DM digestibilities compared with cows fed an energy supplement based on soybean hulls.
Protein supplements often include both nonprotein N (NPN) and true protein sources (Murphy et al., 1994), and combinations of protein sources may be best in supplying amino acids to the ruminant animal (Titgemeyer et al., 1989). Feeding a liquid molasses-based supplement at greater levels (above 25% diet DM) in low-quality diets may reduce palatability (Wiedmeier et al., 1994) and cause digestive disturbances (Ensminger et al., 1990). Although reductions in intake were noted (Wiedmeier et al., 1994) when CSB was added at greater than 25% of dietary DM, this response was not observed when CSB was offered at 20% in brome hay-based diets in the current trial. Swanson et al. (2000) reported an increase in water intake in protein-supplemented lambs, which concurs with the current study. Meyer et al. (1955) reported that fattening steers consumed 35% more water when fed 0.77 kg of salt (9% of the total diet). The observed response in greater water intakes for this study were likely a result of the greater ash component of CSB (Wiedmeier et al., 1992).
Digestibility.
Total tract digestibilities of DM, OM, NDF, ADF, and N are presented in Table 8. Dry matter, OM, and N digestion increased (P = 0.01, 0.02, and 0.01 for DM, OM, and N digestion, respectively) with CSB supplementation. There was a tendency (P = 0.12) for greater DM digestion for 10% CSB compared with UREA. Organic matter digestion for 10% CSB was greater (P = 0.09) when compared with UREA. Neutral detergent fiber and ADF digestion were not affected by CSB supplementation, which was similar to results reported by Wiedmeier et al. (1992). Digestion of N increased (P = 0.01) with CSB supplementation. When 10% CSB was offered separately from the forage, more (P = 0.01) N was digested than when it was mixed with hay. Nitrogen digestion between 10% CSB and UREA were similar (P = 0.55).
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). However, this is not always the case. Putnam et al. (1964) reported that when urea and molasses were fed to steers, digestibilities of DM, crude fiber, ether extract, and N-free extract were not affected. Although molasses-type liquid feeds usually contain high proportions of soluble carbohydrates (Wing et al., 1988), supplemental degradable intake protein is typically responsible for improving low-quality forage digestion in cattle (Heldt et al., 1999). Responses in fiber digestion due to protein supplementation are variable. Mathis et al. (2000) reported that cattle consuming bermudagrass, bromegrass, or forage sorghum hay supplemented with sodium caseinate (supplemental degradable intake protein) had similar NDF digestibilities, whereas Greenwood et al. (2000) reported that NDF and OM digestion were greater when beet molasses was used as the base ingredient in molasses blocks when compared with cane molasses or CSB. Experiment 1 found no differences in OM digestion when steers consumed CSB. Leupp et al. (2005) reported increased OM digestion with the supplementation of cooked molasses blocks. Negative associative effects of nonstructural carbohydrates on fiber digestibility are well documented (Highfill et al., 1987; Sanson et al., 1990; Pordomingo et al., 1991). These responses could be due to pH inhibition of fiber fermentation (Mertens, 1977; Burgwald-Balstad et al., 1995; Lardy et al. 2004b); however, other researchers have reported conflicting results as to effects of pH on fiber fermentation (Henning et al., 1980; Van der Linden et al., 1984; Pordomingo et al., 1991). In our study, it is unlikely that CSB provided enough soluble carbohydrates to dramatically reduce ruminal fiber digestion. In Exp. 1, N digestion increased when cattle fed low-quality forage (corn stover) and consumed CSB. When Leupp et al. (2005) supplemented cattle with cooked molasses blocks, increased N digestion was observed compared with control steers. In regards to N digestion, we did not observe a difference between CSB and urea supplementation. Use of urea or other NPN sources has increased N digestibility above control-fed animals (Ammerman et al., 1972; Lee et al., 1987). Furthermore, the ability of NPN to improve forage digestion is due to the supply of ruminal ammonia, the main source of N used by most cellulolytic bacterial strains (Petersen, 1987; Owens et al., 1991; Russell et al., 1992).
Nitrogen Balance.
Nitrogen intake, excretion, and balance are reported in Table 9. A linear response in N intake was observed with increasing CSB supplementation (P < 0.01). Nitrogen intake was greater (P < 0.01) for 10% CSB when compared with UREA. No differences (P = 0.55) in N intake between 10% CSB and 10SEP were observed.
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Fecal and urinary N excretion increased as CSB in the diet increased (P < 0.01); however; quadratic effects (P < 0.05) for increasing CSB were detected. Salisbury et al. (2004) reported similar increases in N excretion in wethers supplemented with either ruminally undegradable or degradable intake protein. Fecal and urinary N excretion for 10% CSB fed separately were lower (P < 0.06) compared excretion for 10% CSB. Likewise, fecal and urinary N excretion for urea supplement were lower (P < 0.01) when compared with 10% CSB. There were linear (P = 0.01) and quadratic (P = 0.09) responses to increasing CSB in N balance (g/d) in which 0, 10, and 20% CSB supplementation had 0.6, 0.5, and 2.9 g/d of N balance, respectively.
When forage CP is low to moderate, as in the current study (7.7% CP), rumen-degradable CP is most likely to be limiting (Castillo et al., 2001), causing an increase N recycling to the rumen and reductions in N loss in urine. However, when CSB is added, more N would be absorbed as ammonia or more AA deaminated, causing an increase in urine N loss (Castillo et al., 2001) similar to the results noted in this experiment.
Nitrogen balance when expressed as a percentage of N intake and as a percentage of N digested increased (P < 0.08) with CSB supplementation. Concentrated separator by-product fed separately from forage resulted in greater N balance (P < 0.05), whereas the UREA treatment had the least amount of N retained.
Although urinary and fecal N losses were greater in CSB-fed wethers, N retention (g/d) increased (linear; P = 0.01, quadratic P = 0.09) with increasing CSB. These results were similar to previous studies in which protein supplements increased N retention (Phillips et al., 1995) when comparing different levels of CP supplementation. Phillips et al. (1995) saw no differences among treatments when N retention was expressed as a percentage of N consumed or N absorbed when cottonseed meal and corn gluten meal were used as protein supplemental sources. Cheema et al. (1991) observed an increase in N absorption and N retention with subsequent increases in dietary CP level.
For all N balance calculations N was retained in the body to a greater extent when 10% CSB was fed separately, indicating that some mechanism by which protein is being absorbed or utilized is different from when it is consumed in a mixture with hay compared with feeding separately. Although study design does not permit a clear elucidation of the factors responsible for the improved N balance in the 10SEP treatment, the time lapse (45 min) between CSB and hay intake may have contributed to the response. At feeding, when CSB was offered separately, little to no forage was consumed initially. Licking of CSB may have activated the esophageal groove and resulted in a larger portion of the CSB N to bypass the rumen and reticulum and allow for lower tract digestion. Garza and Owens (1989) reported that 60 to 80% of drinking water consumed by heifers bypassed the rumen. Perhaps a similar mechanism is allowing CSB fed separately to reach the lower tract for digestion. Furthermore, greater N digestion in 10SEP treatment may partially explain why greater N retention was observed in 10% CSB-fed wethers.
In summary, it appears that CSB can be effectively used in ruminant diets as a protein supplement. Including CSB in steer diets increased OM and N intake and microbial N flow to the duodenum. True ruminal N digestion increased when steers consumed corn stover with CSB. Digestion and N retention in wethers were improved with CSB additions. Feeding CSB to wethers separately from forage improved N retention compared with mixing similar amounts of CSB with the forage and offered it as a mixed diet. Mechanisms for this response are unclear; however, improving the ability to predict responses to CSB will allow greater use of a supplemental protein source that improves intake and digestion of lower-quality forages.
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Footnotes |
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2 Present address: 1915 10th Street South, Moorhead, MN 56560.
3 Present address: 3410 Corral Drive #206, Rapid City, SD 57702.
4 Corresponding author: Joel.Caton{at}ndsu.nodak.edu
Received for publication December 28, 2005. Accepted for publication March 11, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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