F.L. Fluharty and B.A. Dehority
Department of Animal Sciences
Supplementing an energy-limiting orchardgrass hay diet with either corn or beet pulp had no affect on rumen bacterial or fungal concentrations or nylon bag digestibility of orchardgrass hay. Ruminal pH was lower in the beet pulp supplemented diet (P < 0.05). The concentration of total protozoa was higher (P < 0.01) with the corn supplement, and the percentage of Entodinium was lower (P < 0.05) and Isotricha higher (P < 0.01) with the beet pulp supplement. Both beet pulp and corn are suitable sources of supplemental energy for an energy-limiting, high-forage diet when fed at 20 and 30% of the diet, respectively.
When cattle are fed an all forage diet, energy can be limiting if the forage is of low nutritional value. Normally, these diets are supplemented with corn; however, this tends to lower the rumen pH, encourage the growth of non-fibrolytic microorganisms, and lower dry matter and fiber digestion of the forage. The feeding of beet pulp, a highly digestible fiber, may encourage growth of the cellulolytic and hemicellulolytic microorganisms (bacteria and fungi). This, in turn, should increase the extent of digestion of the forage.
It has been assumed that by using the newer techniques of molecular biology the concentration of cellulose enzymes produced by bacteria and fungi in the rumen can be increased. This would result in an increase in forage cellulose digestion. However, it also seems probable that increasing the number of cellulolytic microorganisms would accomplish the same end result. This study was designed to feed a highly digestible source of cellulose and determine whether the numbers of cellulolytic organisms are increased. The objective of this experiment was to compare the effects of using corn and sugar beet pulp (highly digestible cellulose) as supplements for cattle fed a nutritionally limited forage diet.
Six Holstein steers (initial weight 827 pounds and 9 to 10 months old) were used in a crossover design experiment to determine the effects of the type of energy source added to a forage-based diet on ruminal digestibility and microbial numbers. A one-stage ruminal fistulation was performed on the steers according to the procedure of McGilliard (1982) 3 to 4 weeks before the initiation of the experiment. Surgery was performed using procedures approved by The Ohio State University Institutional Animal Care and Use Committee. Research protocols concerning animal care followed guidelines recommended in the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (Consortium, 1988). Steers were housed individually in pens for the duration of the experiment. The pens were constructed of metal gates, had slatted concrete floors, concrete feed bunks, and automatic water cups. The animals were fed an all-forage diet at a level slightly above their maintenance requirement level. Feed was offered once daily, with feed intakes recorded daily.
There were four experimental periods of 4 weeks duration. All steers were fed the forage control diet for the first 4 weeks (Period 1) to allow for diet adaptation. At the beginning of week 5, three steers were supplemented with beet pulp, and three steers were supplemented with ground corn. The steers remained on these diets from weeks 5 to 8 (Period 2). During weeks 9 to 13 (Period 3), the steers once again were fed the all-forage diet. From weeks 13 to 16 (Period 4), the steers once again were supplemented with either sugar beet pulp or corn grain, with the steers receiving the supplement source that they did not receive during Period 2.
On the Monday of weeks 4, 8, 12, and 16 just before feeding, six dacron bags containing 4-gram samples of orchardgrass hay (ground to pass a 2 mm screen) were placed in the rumen of each steer. Dacron bags were 8 cm x 14 cm, with a pore size of 51 micro-m. The bags were double-stitched and glued on both sides to cover stitch lines. Two bags containing the orchardgrass hay were removed from each steer after 12, 24, and 48 hours incubation for dry matter (DM) and neutral detergent fiber (NDF) analyses. Upon removal, bags were rinsed with cold tap water to remove debris and then placed in a 55oC forced-draft oven for 3 days to dry. After drying, bags containing
orchardgrass were weighed for determination of DM disappearance by difference (AOAC, 1984). Half-gram samples of the hay then were removed from each bag for determination of residual NDF according to the method of Van Soest et al. (1991). At 0, 3, 6, 12, and 24 hours after feeding, ruminal samples for pH measurements were taken using a 150 ml bottle. Ruminal pH was determined immediately, using a Fisher Model 805 Accumet pH meter.
On the Monday of weeks 4, 8, 12, and 16, just before feeding, 500 ml of whole ruminal contents were collected for measuring the concentration of total and cellulolytic bacteria per gram of ruminal contents, total and cellulolytic fungi per gram of ruminal counts, and protozoa counts. For enumeration of the bacteria, a 20 gram subsample was diluted 10X with the anaerobic dilution solution (ADS) of Bryant and Burkey (1953). The mixture was agitated for 3 minutes in a Waring blender under a steady stream of CO2 and then diluted through a series of 9.0 ml ADS tubes, as described by Dehority (1969). Using the 10-7 through 10-11 ADS dilution tubes as inocula, total and cellulolytic bacterial concentrations were determined according to the MPN procedure of Dehority et al. (1989). Total and cellulolytic fungi concentrations were determined according to the MPN procedure of Obispo and Dehority (1992). For protozoa counts, a 10 ml subsample of the whole ruminal contents was taken with a 10 ml measuring pipet (inside diameter, 8 mm) that had the end cut off. The subsample was preserved by adding an equal volume of 50% Formalin and was stored in an 8 x 150 mm culture tube until protozoa counts were determined according to the procedure of Dehority (1984). Statistical analysis was performed using the repeated measures procedures of SAS (1988) for a crossover design experiment blocked by period.
The diet composition is shown in Table 1. The diets were formulated to contain the same concentrations of protein, vitamins, and minerals so that any observed differences could be attributed to the supplemental energy sources.
| Table 1. Diet composition. | |||
| Item | Control diet | Beet pulp diet | Corn diet |
| (%, Dry matter basis) | |||
| Grass hay | 90.00 | 60.00 | 70.00 |
| Beet pulp | . . . | 30.00 | . . . |
| Whole shelled corn | . . . | . . . | 20.00 |
| Ground oats | 2.00 | 2.55 | 2.00 |
| Soybean meal | 4.30 | 3.90 | 4.20 |
| Urea | 0.50 | 0.50 | 0.50 |
| Limestone | 1.30 | 0.85 | 1.50 |
| Dicalcium phosphate | 0.80 | 1.10 | 0.70 |
| Trace mineral salt1 | 0.50 | 0.50 | 0.50 |
| Vitamin A, 30,000 IU/g | 0.01 | 0.01 | 0.01 |
| Vitamin D, 3,000 IU/g | 0.01 | 0.01 | 0.01 |
| Vitamin E, 44 IU/g | 0.03 | 0.03 | 0.03 |
| Selenium premix, 201 mg of SE/kg | 0.05 | 0.05 | 0.05 |
| Dynamate2 | 0.40 | 0.40 | 0.40 |
| Magnesium oxide | 0.10 | 0.10 | 0.10 |
| Calculated analysis | |||
| Crude protein,% | 12.10 | 12.12 | 12.11 |
| Calcium, % | 0.89 | 0.92 | 0.88 |
| Phosphorus, % | 0.44 | 0.45 | 0.44 |
| Potassium, % | 2.14 | 1.54 | 1.78 |
| NEm, Mcal/kg | 1.03 | 1.26 | 1.28 |
| NEg, Mcal/kg | 0.49 | 0.70 | 0.71 |
| 1 Contained > 93% NaCl, 0.35% Zn, 0.28% Mn, 0.175%
Fe, 0.035% Cu, 0.007% I, and 0.007% Co.
2 Magnesium sulfate and potassium sulfate. International Minerals and Chemical Co., Terre Haute, IN. | |||
Effects of beet pulp and corn supplementation on the ruminal microbial population are shown in Table 2. There were no differences (P > 0.05) in numbers of bacteria or fungi due to source of energy supplementation. Mansfield et al. (1994) also reported that beet pulp and corn resulted in similar concentrations of ruminal bacteria. However, Mansfield et al. (1994) fed higher energy diets to their cattle, and beet pulp replaced only half of the corn. Therefore, the comparison of beet pulp to corn was confounded by the presence of corn in their beet pulp diet. However, Mansfield et al. (1994) reported that the molar proportion of ruminal acetate was higher when beet pulp was fed, which was indicative of a more efficient fiber digestion compared with corn.
Corn resulted in a greater (P < 0.05) concentration of protozoa and a greater (P < 0.05) percentage of Entodinium compared with beet pulp (Table 2). Because Entodinium are starch digesting protozoa, this increase in both total numbers and concentration of Entodinium is not surprising. Beet pulp resulted in a greater (P < 0.05) percentage of Isotricha compared with corn. Isotricha are normally associated with diets high in digestible fiber. Therefore, this result indicated that the beet pulp was a readily available source of fiber in the rumen. There were no differences (P > 0.05) in total protozoa numbers due to energy supplementation source. This was not surprising, because the diets were formulated to be equal in energy intake.
Beet pulp resulted in lower (P < 0.05) ruminal pH at 3, 6, and 12 hours after feeding compared with corn (Table 3). Additionally, the mean daily ruminal pH was lower (P < 0.05) with beet pulp compared with hay. In general, diets high in starch resulted in a lower ruminal pH compared with diets high in fiber. However, beet pulp fiber has a very small particle size compared with whole shelled corn or orchardgrass hay.
| Table 2. Effects of diet on ruminal characteristics of steers. | ||||
| Item | Beet pulp | Corn | Hay | SEM |
| Number 108/ml | ||||
| Cellulolytic bacteria | 4.82 | 7.32 | 3.82 | 0.98 |
| Total bacteria | 59.00 | 62.83 | 207.50 | 89.74 |
| Number 102/ml | ||||
| Cellulolytic fungi | 16.60 | 39.14 | 11.45 | 61.73 |
| Total fungi | 198.55 | 168.38 | 93.82 | 107.29 |
| Protozoa | ||||
| Total number (x 104/ml) | 45.25c | 67.76d | 32.31c | 6.47 |
| Distribution, % | ||||
| Entodinium | 89.33a | 92.35ab | 94.94b | 1.30 |
| Diplodinium | . . . | 0.66 | 0.05 | 0.18 |
| Epidinium | 7.62 | 6.40 | 3.81 | 1.09 |
| Isotricha | 2.93c | 0.59d | 1.11d | 0.43 |
| Dasytricha | . . . | . . . | 0.05 | 0.03 |
| abMeans with different superscripts differ (P < 0.05).
cdMeans with different superscripts differ (P < 0.01). | ||||
When pelleted beet pulp is ingested and the pellet breaks down, the result is a much greater surface for bacterial adhesion compared with an equal weight of corn or hay. This increase in surface area coupled with the greater daily intake of supplemental beet pulp fed in the present study probably resulted in a greater proportion of highly digestible substrate for the ruminal microorganisms during the first 12 hours after feeding. Additionally, the NDF digestibility of beet pulp was reported to be 81% (Torrent et al., 1994). Therefore, in the present study, beet pulp provided a greater amount of highly digestible substrate compared with corn, which explains the lower ruminal pH.
| Table 3. Effects of diet on ruminal characteristics of steers. | ||||
| Hour | Beet pulp | Corn | Hay | SEM |
| pH | ||||
| 0 | 6.58 | 6.52 | 6.65 | 0.07 |
| 3 | 6.30a` | 6.47ab | 6.69b | 0.07 |
| 6 | 6.07c | 6.25cd | 6.50d | 0.08 |
| 9 | 6.07 | 6.21 | 6.21 | 0.09 |
| 12 | 6.27c | 6.44d | 6.43d | 0.03 |
| 24 | 6.75 | 6.69 | 6.73 | 0.04 |
| meane | 6.34a | 6.43ab | 6.54b | 0.04 |
| Dry matter digestibility, % | ||||
| 12 | 31.37 | 31.37 | 31.16 | 1.59 |
| 24 | 46.07 | 45.02 | 42.67 | 1.45 |
| 48 | 59.92 | 55.73 | 55.94 | 3.05 |
| meane | 45.79 | 44.04 | 43.26 | 1.66 |
| ab Means with different superscripts differ (P < 0.05).
cd Means with different superscripts differ (P < 0.01). e Hour effect (P < 0.001). | ||||
Lower ruminal pH normally would result in decreased ruminal fiber dry matter digestibility. However, there was no decrease (P > 0.05) in ruminal dry matter digestibility when beet pulp was fed compared with corn (Table 3). Carey et al. (1993) reported that both beet pulp and corn resulted in increased dry matter digestibility (DMD) compared with a control brome hay diet. The lower ruminal pH observed with beet pulp without a resulting decrease in ruminal dry matter digestibility in the present study could be due to a greater proportion of ruminal acetate production with beet pulp as reported by Mansfield et al. (1994). Several investigators have reported an increased fiber digestibility when corn is replaced with beet pulp. Petit and Tremblay (1995a) reported that the diet digestibility of dry matter (DM) and NDF was greater for cows fed beet pulp compared with corn in grass silage-based diets. These authors also suggested that beet pulp resulted in improved microbial protein synthesis in the rumen compared with high-starch, grain-based supplements. However, Van Vuuren et al. (1993) reported that, although beet pulp resulted in greater NDF digestibility compared with corn, the efficiency of microbial protein synthesis was greater with corn compared with beet pulp. Petit and Tremblay (1995b) found that beet pulp improved the nitrogen utilization of low-quality timothy silage compared with corn supplementation. Additionally, Petit and Tremblay (1995b) reported that beet pulp resulted in an average increase of 7.7 pounds/day of fat- corrected milk production compared with corn or oats and barley supplementation. Sanson (1993) reported that beet pulp had no negative effects on dry matter intake (DMI) of lambs fed a low-quality hay, whereas corn supplementation reduced the DMI of this same hay. Furthermore, lambs whose diet was supplemented with beet pulp had a greater estimated hay DMD compared with lambs supplemented with corn.
The authors wish to thank Michigan Sugar Company, Caro, Michigan, for their generous support of this research.
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