S. Hejazi and F.L. Fluharty
Department of Animal Sciences
High-concentrate diets containing whole shelled corn (WSC) can improve dry matter digestibility (DMD), organic matter digestibility (OMD), and neutral detergent fiber digestibility (NDFD) compared with the same diets containing ground corn. Additionally, feeding WSC resulted in greater nitrogen digestion and retention compared with ground corn. Peanut hulls (PH) resulted in reduced DMD, OMD, and NDFD compared with diets containing either no added fiber or soybean hulls (SBH). Nitrogen digestion was not affected by dietary fiber at 10% of the diet dry matter.
Processing grains by grinding or pelleting disrupts the starch granule and increases starch digestibility in cattle, primarily through increasing the amount of starch digested in the rumen (Nocek and Tamminga, 1991). However, Murphy et al. (1994) reported that feeding rolled corn in all-concentrate diets resulted in decreased ruminal pH for 9 hours after feeding compared with WSC. If ruminal pH remains low, there may be adverse effects on digestion and metabolism. The objective of this experiment was to determine the effects of feeding high-concentrate diets containing either whole or rolled corn, with either no dietary fiber, a highly digestible fiber (soybean hulls), or a relatively indigestible dietary fiber (peanut hulls) on nutrient digestibility and nitrogen (N) metabolism in lambs.
Twelve white-faced (Targhee and Polypay) crossbred wether lambs (initial body weight 53 2 pounds) of moderate growth potential were used in a total collection (urine and feces) metabolism trial. Lambs (two per treatment) were assigned to one of six treatments in a randomized complete block design. The six treatments were 1) whole shelled corn (WSC) with no supplemental fiber, 2) WSC + soybean hulls, 3) WSC + peanut hulls, 4) ground/pelleted corn with no supplemental fiber, 5) ground/pelleted corn + soybean hulls, and 6) ground/pelleted corn + peanut hulls. The diet compositions for this metabolism trial are shown in Table 1. Dietary concentrations of N, vitamins, and minerals were adjusted to allow equal daily intakes of these nutrients. Diets were formulated to meet nutrient requirements (NRC, 1985). Diets were fed once daily at 0800 hours, and lambs were allowed ad libitum access to fresh water.
| Table 1. Composition of diets fed to lambs in metabolism experiment. | ||||||
| Item | Whole corn/
no fiber |
Pelleted corn/
no fiber |
Whole corn/
peanut hulls |
Pelleted corn/
peanut hulls |
Whole corn/
soybean hulls |
Pelleted corn/
soybean hulls |
| (%, Dry matter basis) | ||||||
| Whole corn | 70.000 | . . . | 60.000 | . . . | 70.000 | . . . |
| Ground corn | 15.641 | 85.641 | 15.211 | 75.211 | 6.011 | 76.011 |
| Peanut hulls | . . . | . . . | 10.000 | 10.000 | . . . | . . . |
| Soybean hulls | . . . | . . . | . . . | . . . | 10.000 | 10.000 |
| Soybean meal | 5.700 | 5.700 | 5.840 | 5.840 | 5.440 | 5.440 |
| Blood meal | 2.850 | 2.850 | 2.920 | 2.920 | 2.720 | 2.720 |
| Corn gluten meal | 2.850 | 2.850 | 2.920 | 2.920 | 2.720 | 2.720 |
| Urea | 0.400 | 0.400 | 0.400 | 0.400 | 0.400 | 0.400 |
| Limestone | 1.300 | 1.300 | 1.300 | 1.300 | 1.300 | 1.300 |
| Dicalcium phosphate | 0.250 | 0.250 | 0.250 | 0.250 | 0.250 | 0.250 |
| Monosodium phosphate | . . . | . . . | 0.150 | 0.150 | 0.150 | 0.150 |
| Trace mineral salt | 0.450 | 0.450 | 0.450 | 0.450 | 0.450 | 0.450 |
| Vitamin A, 30,000 IU/g | 0.010 | 0.010 | 0.010 | 0.010 | 0.010 | 0.010 |
| Vitamin D, 3,000 IU/g | 0.010 | 0.010 | 0.010 | 0.010 | 0.010 | 0.010 |
| Vitamin E, 44 IU/g | 0.030 | 0.030 | 0.030 | 0.030 | 0.030 | 0.030 |
| Selenium, 201 ppm | 0.090 | 0.090 | 0.090 | 0.090 | 0.090 | 0.090 |
| Ammonium chloride | 0.400 | 0.400 | 0.400 | 0.400 | 0.400 | 0.400 |
| Lasalocid, 67.5 g/pound | 0.019 | 0.019 | 0.019 | 0.019 | 0.019 | 0.019 |
| Calculated composition | ||||||
| Crude protein, % | 17.025 | 17.025 | 17.020 | 17.020 | 17.010 | 17.010 |
| Calcium, % | 0.545 | 0.545 | 0.569 | 0.569 | 0.590 | 0.590 |
| Phosphorus, % | 0.411 | 0.411 | 0.416 | 0.416 | 0.429 | 0.429 |
| NEm, Mcal/kg1 | 2.082 | 2.082 | 1.863 | 1.863 | 1.975 | 1.975 |
| NEg, Mcal/kg2 | 1.432 | 1.432 | 1.281 | 1.281 | 1.337 | 1.337 |
| 1 Net energy available for maintenance.
2 Net energy available for gain. | ||||||
The trial consisted of two 14-day periods during which lambs were placed in metabolism crates (63 inches x 21 inches) designed to allow for separation and collection of feces and urine. Lambs were allowed 7 days to adapt to the crates before initiation of the experiment and were housed in the crates throughout the experiment. The assignment of lambs to Period 2 was random with the restriction that no lamb received the same diet in both periods. Therefore, there were four lambs represented in each of the six diet treatments.
Each 14-day experimental period consisted of 9 days of adaptation and 5 days for total collection of feces and urine. Feed and orts were sampled and collected daily from days 10 to 14 of the experimental period. Total feces were collected and weighed, and a 10% aliquot was retained and composited for each lamb within each period. Feces were stored frozen during the collection period. Urine was collected into containers with sufficient 6 N HCL added to maintain a pH below 3.0. A 5% aliquot of urine was retained daily and composited for each lamb within each period.
Feed and fecal samples were dried in a forced-air oven at 131oF, ground to pass a 2-mm screen, and analyzed for DM, OM, N (AOAC, 1984), NDF (Van Soest et al., 1991), and starch using enzymatic hydrolysis and glucose oxidase (Fleming and Reichert, 1980). Urine was analyzed for N using the macro-Kjeldahl technique (AOAC, 1984). Digestibilities and N retention were calculated by difference.
Statistical analysis was performed using the GLM procedure of SAS (1988) for a 2 x 3 factorial experiment blocked by initial weight. The model contained effects due to block, period, corn processing, fiber source, and the corn processing x fiber source interaction. Animal served as the experimental unit. Treatment means were compared using the PDIFF statement of SAS (1988) when protected by a significant (P < 0.05) F-value.
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).
There were no significant (P > 0.05) corn processing x fiber source interactions. Therefore, only the main effects of corn processing and dietary fiber source have been reported. The apparent digestibilities of dry matter (DM), organic matter (OM), and NDF were greater (P < 0.001) for WSC compared with ground corn in high-concentrate diets (Table 2). Anderson et al. (1988) suggested that the smaller particle size of ground feedstuffs would cause a greater surface area and result in potentially higher digestion compared with whole feedstuffs. However, the data obtained in this study indicated that other factors also were involved. Heating during processing (grinding and pelleting) may result in decreased digestibility due to structural changes from heat through formation of Maillard products where a reaction between sugar aldehyde groups and free amino groups makes dietary protein unavailable in the rumen. Furthermore, Anderson et al. (1988) found the DMD of a ground soyhull diet to be lower than that of a whole soyhull diet and attributed this finding to the fact that digestibility is inversely related to the rate of passage. Therefore, it may be that the greater apparent digestibility of WSC compared with ground corn in the present study was due to an increased ruminal retention time of the WSC. Furthermore, WSC has a "fiber effect" on ruminal papillae, which can lead to greater surface area for absorption of volatile fatty acids compared with processed corn. This effect is thought to be the result of physical stimulation of the papillae similar to what is observed on forage diets.
Peanut hulls resulted in decreased (P < 0.01) DM, OM, and NDF digestibilities compared with the control and SBH diets (Table 2). The PH would be expected to have a low digestibility due to their higher lignin (22 to 24%) content.
Lambs fed WSC had greater apparent N digestion (%), true N digestion (%, P < 0.001), N retention (g/day, P < 0.01), % of N intake (P < 0.01), and % of N digested (P < 0.05) compared with lambs fed ground corn (Table 3). Fecal N (g/day) was greater (P < 0.001) for ground corn compared with whole corn (Table 3). The greater fecal N with ground corn was an indication of increased mucosal cell sloughing in the intestines compared with whole corn. Other possibilities included an inability of the enzymes in the small intestine to degrade a larger supply of ruminal bypass feed protein and increased large intestine bacterial production. Urinary N (g/day), on the other hand, was greater (P < 0.05) for whole corn compared with ground corn (Table 3). Nitrogen intake was greater for lambs consuming whole corn diets, which helps explain the greater urinary N. Furthermore, the increased urinary N with whole corn indicated that the N was absorbed and metabolized prior to excretion. Murphy et al. (1994) reported no differences in nitrogen digestion in cattle when WSC was compared with rolled corn. No dietary fiber resulted in a greater N intake (g/day, P < 0.01) compared with SBH and PH; however, there were no differences (P > 0.10) in diet digestibility due to fiber (Table 3).
| Table 2. Main effects of corn type and fiber source on apparent digestibility. | |||||||
| Corn type | Fiber type | ||||||
| Item | Ground | Whole | SEM | Control | SBH1 | PH2 | SEM3 |
| DMI4, pounds/day | 2.03 | 2.06 | 0.03 | 2.04 | 2.06 | 2.04 | 0.04 |
| Apparent digestibility, % | |||||||
| Dry matter | 74.79a | 85.11b | 0.84 | 82.70c | 80.35c | 76.79d | 1.03 |
| Organic matter | 76.09a | 86.10b | 0.81 | 83.75c | 81.65c | 77.88d | 1.00 |
| NDF5 | 15.55a | 66.49b | 2.75 | 45.93c | 46.75c | 30.37d | 3.36 |
| Starch | 96.17 | 97.39 | 0.86 | 97.90 | 95.94 | 96.50 | 1.05 |
| 1 Soybean hulls.
2 Peanut hulls. 3 SEM = Standard error of mean. 4 Dry matter intake. 5 Neutral detergent fiber. abMeans within a row with different superscripts differ (P < 0.001). cdMeans within a row with different superscripts differ (P < 0.01). | |||||||
| Table 3. Main effects of corn type and fiber source on nitrogen metabolism. | |||||||
| Corn type | Fiber type | ||||||
| Item | Ground | Whole | SEM | Control | SBH1 | PH2 | SEM3 |
| N intake, g/day | 24.25a | 25.71b | 0.43 | 26.65c | 23.98d | 24.30d | 0.53 |
| Fecal N, g/day | 8.23e | 4.95f | 0.35 | 6.37 | 6.87 | 6.53 | 0.43 |
| Apparent digestion, % | 65.14e | 80.57f | 1.57 | 75.91 | 70.11 | 72.54 | 1.92 |
| True digestion, % | 86.20e | 100.56f | 1.57 | 95.04 | 91.63 | 93.46 | 1.92 |
| Urinary N, g/day | 11.09a | 12.59b | 0.49 | 12.76 | 11.43 | 11.34 | 0.59 |
| N retention, g/day | 4.92c | 8.17d | 0.58 | 7.53 | 5.68 | 6.44 | 0.71 |
| % of N intake | 20.32c | 32.14d | 2.10 | 28.58 | 23.47 | 26.64 | 2.57 |
| % of N digested | 30.98a | 39.97b | 2.50 | 32.68 | 32.60 | 36.16 | 3.06 |
| 1 Soybean hulls.
2 Peanut hulls. 3 SEM = Standard error of mean. abMeans within a row with different superscripts differ (P < 0.05). cdMeans within a row with different superscripts differ (P < 0.01). efMeans within a row with different superscripts differ (P < 0.001). | |||||||
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