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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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0.31) by treatment. Similarly, no differences (P 0.62) were observed for NDF or ADF total tract digestion. Bacterial OM at the duodenum increased (P = 0.01) with canola-containing diets compared with the control diet and increased (P = 0.08) in steers consuming ground canola compared with whole canola. Apparent and true ruminal CP digestibilities were increased (P = 0.01) with canola supplementation compared with the control diet. Canola supplementation decreased ruminal pH (P = 0.03) compared with the control diet. The molar proportion of acetate in the rumen tended (P = 0.10) to decrease with canola supplementation. The molar proportion of acetate in ruminal fluid decreased (P = 0.01), and the proportion of propionate increased (P = 0.01), with ground canola compared with whole canola. In situ disappearance rate of hay DM, NDF, and ADF were not altered by treatment (P 0.32). In situ disappearance rate of canola DM, NDF, and ADF increased (P = 0.01) for ground canola compared with whole canola. Similarly, ground canola had greater (P = 0.01) soluble CP fraction and CP disappearance rate compared with whole canola. No treatment effects were observed for ruminal fill, fluid dilution rate, or microbial efficiency (P 0.60). The results suggest that canola processing enhanced in situ degradation but had minimal effects on ruminal or total tract digestibility in low-quality, forage-based diets.
Key Words: canola • digestion • low-quality hay • processing • steer • supplementation
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). The oil is composed primarily of oleic acid (52.8%), linoleic acid (23.5%), and linolenic acid (10.5%; Khorasani et al., 1991). Moore et al. (1986) reported that fat levels >4% in forage-based diets resulted in decreased ADF, DM, and OM digestibility. Khorasani et al. (1992) reported that supplementation of ruminally protected canola seed, at levels >3% of the diet, decreased concentrations of total ruminal VFA and molar proportions of acetate, propionate, and butyrate.
When forage quality is low, protein supplementation is often needed to improve performance of livestock (McCollum and Horn, 1990). Canola seed contains moderate amounts of CP and may be used to increase CP intake. Köster et al. (1996) demonstrated a linear and quadratic increase in forage OM intake with increasing levels of degradable intake protein (DIP). Those researchers also reported that supplemental protein increased total tract nutrient digestibility.
Data from cattle fed whole canola suggest that the seeds are relatively resistant to digestion in the rumen and intestine unless processed (Khorasani et al., 1992; Hussein et al., 1995). By processing canola seed, contents are accessible to ruminal and intestinal enzymatic degradation and absorption (Aldrich et al., 1997a).
Although much research has been conducted with supplementing canola to alter diet composition, little research exists on the value of whole or processed canola as a supplement to ruminants consuming low-quality forage diets. Therefore, our objectives were to investigate the effects of whole and processed canola seed on intake, digestion, ruminal fermentation, duodenal protein supply, and microbial efficiency in steers fed low-quality forage.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Khorasani et al., 1992; Whitney et al., 2000). Canola supplements were fed before hay at 0600 and were calculated on a daily basis corresponding to the intake of the previous day. All animals had free access to water throughout the duration of the study.
Sample Collection
Steers were housed in an enclosed, climate-controlled room in individual pens during the 14-d adaptation period and in individual tie stalls during the 7-d collection period. Diet samples were collected weekly throughout the period and composited. Feed refusals (10% of total hay) were taken daily, before the morning feeding, throughout collection period. Five days before and throughout the collection period, 8.0 g of chromic oxide were dosed ruminally twice daily at 0600 and 1800 via gelatin capsule (Torpac, Inc., Fairfield, NJ) and used as a marker of digesta flow.
Total fecal output was collected using stainless steel fecal trays placed directly behind each steer. Daily fecal samples (10% of output) were composited within steer and stored (–20°C) during collections. Fecal samples were then thawed and mixed in a rotary mixer (Model H-600, Hobart Manufacturing Co., Troy, OH). After mixing, a subsample was taken and frozen (–20°C) until analyses.
Duodenal and ileal samples (200 mL) were taken over 4 d in a manner that allowed for every other hour in a 24-h period to be sampled. Samples were taken on d 3 at 0800, 1400, and 2000; on d 4 at 0200, 1000, 1600, and 2200; on d 5 at 0400, 1200, 1800, and 2400; and on d 6 at 0600 of the collection period. Samples were composited within steer and frozen (–20°C) until analyses.
In situ DM, CP, NDF, and ADF disappearance were determined using Dacron bags (Ankom Technology, Fairport, NY; 10 x 20 cm, 53 ± 10-µm pore size) containing 5 g of hay, whole canola, or ground canola. In situ bags containing whole or ground canola were incubated in steers receiving that respective diet. Hay was ground in a Wiley mill (Arthur H. Thomas, Philadelphia, PA) to pass through a 2-mm screen. Beginning on d 2, bags were added in a manner that allowed for all bags to be removed at 2000 h. Bags were ruminally incubated in duplicate for 98, 72, 48, 36, 24, 14, 9, 5, 2, and 0 h. After incubation, all bags were removed and rinsed with a hose to remove large particulate matter. Bags were then rinsed using a top-loading washing machine (General Electric, Louisville, KY) on the delicate cycle. Bags were agitated for 1 min, drained, and spun for 2 min. This cycle was repeated (minimum of 6 cycles) until the rinse water was clear. Bags were dried in a forced-air oven (55°C; The Grieve Corporation, Round Lake, IL) for 48 h and stored at room temperature until analyzed.
Liquid dilution rate was determined by dosing 200 mL of CoEDTA (867 mg Co; Uden et al., 1980) intraruminally on d 6 of the collection period. To allow CoEDTA to mix in the rumen, it was given at 2 h before feeding hay. Ruminal fluid samples were collected with a suction strainer at 0, 2, 4, 6, 8, 10, and 12 h postfeeding. After collection, the pH was recorded using a combination electrode (Model 2000 pH/temperature meter, VWR Scientific Products, West Chester, PA), and a sample (200 mL) was acidified with 2 mL of 6.0 N HCl. Samples were then frozen (–20°C) for NH3 and Co analyses. A portion (3 mL) of the initial, nonacidified ruminal fluid sample was collected and added to 0.75 mL of 25% (wt/vol) metaphosphoric acid and frozen (–20°C) until analyzed for VFA.
On d 21, ruminal evacuations were performed to determine ruminal fill. Ruminal contents were removed, weighed, and subsampled. Subsamples were obtained by hand-mixing the ruminal contents in 208-L tubs and taking samples from various locations. A sample was taken for analysis of DM, OM, ADF, and NDF. A second sample (4 kg) was taken, and 2 L of 3.7% formaldehyde/0.9% NaCl were added for isolation of bacterial cells, which were later analyzed for DM, ash, N, and purine (Zinn and Owens, 1986). Samples were stored frozen (–20°C) until analyses.
Laboratory Analyses
Diet, ort, and fecal samples were dried using a forced-air oven (55°C; The Grieve Corporation) for 48 h. Dried samples were ground in a Wiley mill to pass a 2-mm screen. Duodenal and ileal samples were lyophilized (Virtis Genesis 25LL, The Virtis Company, Inc., Gardiner, NY) and ground with a Wiley mill to pass a 1-mm screen.
Diet, ort, duodenal, ileal, and fecal samples were analyzed for DM, ash, and N (methods 930.15, 942.05, and 984.13, respectively; AOAC, 1990). Diet samples were also analyzed for crude fat (method 920.39; AOAC, 1990). Concentrations of NDF and ADF were determined using an Ankom 200 fiber analyzer (Ankom Technology, Fairport, NY). Chromium concentration was analyzed in duodenal, ileal, and fecal samples by the spectrophotometric method (Fenton and Fenton, 1979). Recovery of chromium averaged 114.1 ± 16.8% across treatments. In situ residues were analyzed for DM, N, NDF, and ADF as previously mentioned and also for purines (Zinn and Owens, 1986) for bacterial correction.
Ruminal fluid samples were centrifuged at 20,000 x g for 20 min, and the supernatant was taken for analysis of NH3 (Broderick and Kang, 1980). Ruminal VFA concentrations were quantified by gas chromatography (5890A Series II GC, Hewlett Packard, Wilmington, DE) using a capillary column (15 m x 0.53 mm x 0.5 µm, Nukol, Supelco, Bellefonte, PA). Cobalt was analyzed by an air-plus-acetylene flame using atomic absorption spectroscopy (Model 3030B, PerkinElmer, Inc., Wellesley, MA).
A subsample of ruminal contents from the total evacuations was analyzed for DM as stated previously. A Waring blender (Model 37BL19 CB6, Waring Products, New Hartford, CT) was used to blend ruminal contents. The sample was blended on high speed for 1 min, and the mixture was strained through 4 layers of cheese-cloth. Feed particles and protozoa were removed via centrifugation at 1,000 x g for 10 min. Bacteria were separated from the supernatant by centrifuging at 20,000 x g for 20 min. The bacterial purine to bacterial CP ratio was calculated and averaged across treatments.
Statistical Analysis
In situ DM and NDF rates of disappearance were calculated using the model of Mertens and Loften (1980). In situ CP rate of disappearance was calculated using the nonlinear model of Ørskov and McDonald (1979). Data were analyzed as a completely randomized design using a mixed model (SAS Inst., Inc., Cary, NC). The model included treatment as the fixed effect and steer as the random effect. Data over time (VFA, NH3) were analyzed as a repeated measures design using a mixed model (SAS Inst.). The model included animal, diet, time, diet x time, and animal x diet; the random variable was animal. Means were separated using orthogonal contrasts: control vs. canola supplements and whole canola vs. ground canola.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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. The switchgrass hay contained 5.8% CP, 77.7% NDF, and 47.0% ADF (DM basis). Canola supplements averaged 23.3% CP, 31.3% NDF, 22.2% ADF, and 39.6% crude fat on a DM basis. Wang et al. (1997) reported that canola seed used in their study contained 20.8% NDF, 12.5% ADF, and 44.3% fat. Differences observed for NDF, ADF, and CP between studies may be due to the use of different varieties of canola in these studies.
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0.60; Table 2) among treatments. This is similar to results reported by Hussein et al. (1995), who fed corn silage-based diets, and those reported by Aldrich et al. (1997b), who fed corncob and alfalfa hay-based diets. Bacterial OM flow at the duodenum increased (P = 0.01) with canola supplementation compared with the control and was greater (P = 0.08) in steers fed ground canola than in steers fed whole canola. This is surprising, as others have reported no differences in bacterial OM flow at the duodenum when feeding canola seeds (Ferlay et al., 1992; Aldrich et al., 1997b). The reasons why our data differs from these other studies are not immediately clear, but it is likely due to differences in basal forage quality between our study and those of Ferlay et al. (1992) and Aldrich et al. (1997b).
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0.78) feed OM flow or total OM flow at the duodenum. Ileal and fecal OM flows were also not altered by treatment (P 0.61). With regard to OM digestibility, no differences (P 0.15) were observed for apparent ruminal, true ruminal, or total tract digestibilities. Similarly, Ferlay et al. (1992) reported no differences in total tract OM digestibility when cattle were offered a mixed diet containing 60.5% hay and 39.5% concentrate supplemented with raw or extruded rapeseed (diets contained 8% fatty acids; DM basis). Hussein et al. (1995) reported no differences for apparent and true ruminal OM digestibility. However, those researchers attributed decreased total tract OM digestibility to low digestibility of the seed coat. Lardy et al. (1993) also reported reduced ruminal DM and NDF degradabilities when rapeseed meal was compared with soybean meal as a protein supplement.
Canola was bred from rapeseed when plant breeders selected for plants lower in erucic acid and glucosinolates (Bell, 1982). Aldrich et al. (1997b) reported that ruminal and intestinal OM digestibilities of diets supplemented with canola were similar for whole or crushed canola, but total tract OM digestibility was decreased with canola supplementation compared with a control diet based on ammoniated corn cobs and alfalfa hay. They attributed these differences to greater variation with measurements of ruminal and intestinal digestibilities compared with total tract digestibility. Discrepancies between studies may be related to differences in level of dietary canola seeds. We supplemented canola seeds at 8% of DM, whereas Hussein et al. (1995) and Aldrich et al. (1997b) supplemented canola at 10% of DM. Forage quality also differed among studies.
Hay CP intake was not affected (P = 0.92) by treatment (Table 3). As expected, total CP intake was increased (P = 0.08) with canola supplementation compared with controls. Treatment did not affect (P 0.22) duodenal, ileal, or fecal CP flow. Supplementation with canola increased (P = 0.01) apparent ruminal and true ruminal CP degradation and decreased (P = 0.01) small intestinal CP digestibility. Lardy et al. (1993) reported lower ruminal DM and NDF degradabilities when rapeseed meal was fed and attributed the lower ruminal digestibility to the lower digestibility of the rapeseed hull.
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). However, no differences were observed in microbial CP flow (P = 0.40; Table 3
). Lardy et al. (1993) reported similar ruminal CP degradability and total tract CP digestibility when rapeseed meal and soybean meal were compared. In addition, those researchers reported no differences in microbial CP flow to the duodenum or in microbial efficiency. In the current study, total tract CP digestibility tended (P = 0.13) to increase with canola supplementation compared with nonsupplemental controls.
Microbial efficiency was not different (P = 0.73) among treatments (Table 3). Several studies have observed minimal differences in microbial efficiency when protein supplements were provided to cattle consuming low- to moderate-quality forages (Caton et al., 1994; Aldrich et al., 1997b; Reed et al., 2004a).
Treatment had no effect (P 0.59; Table 4) on NDF or ADF intake. Duodenal, ileal, and fecal NDF and ADF flows were not different (P 0.59) between treatments. Small intestinal NDF digestibility tended (P = 0.12) to increase with whole canola compared with ground canola. Similar to results reported by Aldrich et al. (1997a), our study indicated no treatment differences (P 0.28; Table 4) for ruminal, large intestinal, or total tract NDF digestibilities. Ferlay et al. (1992) showed that total tract ADF digestibility decreased with canola supplementation (diets contained 8% fatty acids; DM basis) when dairy cows were fed a 60.5% forage to 39.5% concentrate diet. Petit et al. (1997) reported that ADF digestibility tended to decrease in lambs fed an extruded canola supplement with ad libitum access to alfalfa silage.
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; Hussein et al., 1995) or to high levels of fat included in the diet, which can alter ruminal microbial populations and ruminal fermentation characteristics (Ferlay and Doreau, 1992; Aldrich et al., 1997a). Discrepancies between studies are likely due to the amount of fat offered in the diets.
No time x treatment interaction (P 0.24) was present for ruminal fermentation; therefore, main effects of treatment are reported in Table 5. Ruminal pH decreased (P = 0.03) with canola supplementation. Similarly, Albro et al. (1993) reported decreased ruminal pH in steers offered low-quality, mature grass hay (6.5% CP) supplemented with whole or extruded soybeans or with soybean meal and barley. Other studies have reported no difference in pH with supplementation of canola seeds (Hussein et al., 1996; Khorasani and Kennelly, 1998) or rapeseed oil (Ferlay and Doreau, 1992). Unlike our study, which was based on a low-quality forage, these studies utilized moderate-quality forages (corn silage, a mixture of alfalfa and oat silage, and corn silage, respectively).
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; Aldrich et al., 1997a; Khorasani and Kennelly, 1998). Supplementing canola, whether ground or whole, at the level used in this study would not be expected to influence ruminal fermentation because the seeds were not readily fermented. However, Freeman et al. (1992) evaluated the level of protein in supplements based on a 43% CP cottonseed meal supplement or a 22% CP corn grain and cottonseed meal supplement and reported an increase in ruminal NH3 concentration with protein supplementation compared with nonsupplemented controls at every sampling time except 4 h after the supplement was offered. They attributed this increase in ruminal NH3 concentration to protein supplementation supplied to diets consisting of high fiber and low N forages. The lack of NH3 response in our study might have been due to the fact that we only supplied 150 g of supplemental CP/d. Freeman et al. (1992) also observed an increase in total VFA concentration 1 h after supplementation, which they attributed to the fermentation of readily degradable components in the supplement. In our study, canola seed, whether ground or whole, was not readily fermented, which may explain the lack of response of total VFA.
Contrary to the reports of Hussein et al. (1995) and Petit et al. (1997), who found no differences in the molar proportions of acetate, propionate, or butyrate in the rumen, we found decreased (P = 0.10) acetate with canola supplementation, compared with the nonsupplemented control, and decreased (P = 0.01) acetate with ground canola supplementation, compared with whole canola. Similarly, Albro et al. (1993) reported decreased ruminal acetate concentrations in steers supplemented with whole or extruded soybeans or soybean meal and barley. The ruminal proportion of propionate, conversely, increased (P = 0.01) with ground canola compared with whole canola. These changes in the ruminal proportions of VFA are similar to the findings of Ferlay and Doreau (1992) with rapeseed oil supplementation. This shift in molar proportions of VFA (Ferlay and Doreau, 1992) was attributed to a decrease in ruminal fiber digestion. However, in our study, we did not observe a decrease in ruminal fiber digestion with canola-supplemented steers.
Butyrate was not affected (P = 0.34) by treatment, which is in agreement with the observation of Hussein et al. (1995), who fed 2 forage levels (30 and 70% of DM as corn silage) supplemented with 3 forms of canola seed at 10% of dietary DM. This observation also agrees with that of Aldrich et al. (1997a), who fed alfalfa silage-based diets (45% of DM) and supplemented canola seed at 11.2% of DM. Ferlay and Doreau (1992) reported decreased butyrate concentrations in rapeseed oil-supplemented diets compared with nonsupplemented controls. Khorasani et al. (1992) included ruminally protected canola at levels of 0, 4.5, 9, 13.2, or 17.4% to cows fed a 60 to 40% (DM basis) concentrate to forage ration and reported a quadratic response in ruminal butyrate concentrations. In their study, the greatest increase in butyrate occurred at 4.5% canola, and the lowest occurred at 17.4% canola; 9 and 13.2% were intermediate.
In situ ruminal disappearance did not differ (P 0.32) among treatments for hay DM, NDF, or ADF (Table 6). Degradation rates of CP or of soluble and slowly degradable CP fractions were not affected (P 0.73) by treatment. These data are in agreement with that of Khorasani et al. (1992) when fat supplementation did not exceed 5%. Similarly, Ferlay et al. (1992) reported no differences for the rate of in situ DM, NDF, or ADF degradation of hay when cows consumed grassland hay and were supplemented with rapeseed.
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incubated whole and ground canola ruminally in dairy cows and found increased in situ DM degradabilities for ground canola. They also reported increased DM disappearance of ground canola in the first 16 h of incubation and a slowing of the rate of disappearance thereafter. This result may imply that processing increased access of the ruminal microorganisms to readily fermentable material found in canola seed but did little to improve fermentation of less digestible material. Grinding also increased (P = 0.01) the soluble CP fraction and degradation rate of canola when compared with whole canola seed. The slowly degradable CP fraction was not different (P = 0.49) among treatments. Canola residues were not corrected for microbial CP based on previous literature stating that feeds higher in N content have less underestimation of N degradability because of bacterial contamination (Michalet-Doreau and Ould-Bah, 1992; Wanderley et al., 1993; Beckers et al., 1995).
No differences (P 0.42) were observed for total ruminal fill or fluid dilution rate across treatments (Table 7). Mathis et al. (2000) and Reed et al. (2004b) reported a linear decrease in ruminal DM fill with increasing protein level. In contrast, Sunvold et al. (1991) reported increased ruminal DM fill and no differences for fluid dilution rate when steers were supplemented with wheat middlings. Albro et al. (1993) reported approximately a 50% increase in DM fill 5 h after supplementation with whole or extruded soybeans or soybean meal and barley. Protein supplementation seems to have variable effects on ruminal DM fill, and results may be impacted by the extent of processing, the basal forage, the intake level of the basal forage, the basal forage fiber level, and animal characteristics such as animal age and physiological status (Owens and Goetsch, 1988).
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Footnotes |
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3 Current address: Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003.
2 Corresponding author: glardy{at}ndsuext.nodak.edu
Received for publication July 31, 2005. Accepted for publication October 5, 2005.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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