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ANIMAL NUTRITION |
* Department of Animal and Range Sciences, North Dakota State University, Fargo 58105;
and
Dakota Gold Research Association, Sioux Falls, SD 57104
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: calf • creep feed • digestibility • distillers grain • forage • supplementation
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Lardy et al., 2001; Loy et al., 2002). Many researchers have reported calves consume less forage when supplemented with creep feed high in starch (Cremin et al., 1991; Faulkner et al., 1994; Tarr et al., 1994). Faulkner et al. (1994) and Myers et al. (1999) reported that calves fed creep feed had greater feed intake upon feedlot entry. In addition, Myers et al. (1999) reported that calves fed creep feed had decreased respiratory morbidity compared with calves not offered creep feed.
The ethanol industry is expanding rapidly and coproducts such as corn distillers dried grains with solubles (CDDGS) are becoming widely available (Renewable Fuels Association, 2005). Corn distillers dried grains with solubles are relatively high in CP (30.2%, DM basis) and ME (3,749 kcal/kg; Spiehs et al., 2002) and competitively priced compared with other protein and energy sources. Because of the large supply, excellent feed value, and competitive pricing, research on CDDGS is warranted. To our knowledge, there are no peer-reviewed articles that detail inclusion of CDDGS in supplements for nursing calves. Our objectives were to evaluate effects of CDDGS in supplements for nursing calves and advancing season on intake, digestion, microbial efficiency, ruminal fermentation, and performance in nursing calves grazing native rangeland. Our hypothesis was that inclusion of 50% CDDGS would not affect intake, digestion, microbial efficiency, ruminal fermentation, or performance in nursing calves grazing native rangeland compared with a control supplement based on soybean meal, soybean hulls, and wheat middlings.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). Cattle grazed a 64.8-ha pasture that was divided into four 16.2-ha paddocks. Cattle were rotated into a new paddock at the beginning of each period. Precipitation and temperature data were recorded using the average of 2 weather stations located at Leonard, ND (approximately 25 km north of the study site) and Wyndmere, ND (approximately 25 km south of the study site). The weather stations are operated by the North Dakota Agricultural Weather Network (NDAWN, 2004). Long-term average rainfall and temperature data were computed using all previous recordings from the 2 weather stations (3 and 15 yr for Leonard and Wyndmere, respectively) for June, July, and August.
Experiment 1
Animals and Diets.
Nine ruminally and duodenally cannulated, nursing, commercial, Angus steers (145 ± 21 kg of initial BW, 119 ± 7 d of age) were used in a split-plot design. Surgical procedures, animal care, and animal handling protocols were approved by the North Dakota State University Animal Care and Use Committee. Calves were assigned to 1 of 2 treatments: a supplement containing 41% soybean meal, 26.25% wheat middlings, 26.25% soybean hulls, 5% molasses, and 1.5% limestone (control treatment) or a supplement containing 50% CDDGS, 14.55% wheat middlings, 14.55% soybean hulls, 13.9% soybean meal, 5.0% molasses, and 2.0% limestone (CDDGS treatment; Table 1).
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Sample Collection.
Calf responses to treatment and seasonal effects were measured during 3 experimental periods. Collection periods were June 22 to July 6 (June), July 20 to August 3 (July), and August 17 to 31 (August). Body weights were taken on 2 consecutive days at the beginning and end of the experiment and once at the end of each period. Supplement samples were collected twice weekly and composited within period for laboratory analysis. To determine DM flow and total fecal output, chromic oxide (5 g/dose) in gelatin capsules (Torpac Inc., Fairfield, NJ) was administered ruminally twice daily at 0800 and 2000 on d 2 to 11.
Ruminal contents were evacuated on d 1 of each period to determine DM fill. Ruminal contents of each steer were removed, and a sponge was used to remove remaining ruminal fluid. Ruminal contents were weighed, mixed, and sampled for analysis of DM, ash, ADF, and NDF. A 2-kg sample of ruminal contents was taken, and 1 L of 3.7% formaldehyde/0.9% NaCl solution (wt/vol) was added (Zinn and Owens, 1986) for isolation of microbial cells.
On d 1 after ruminal evacuations and before replacing ruminal contents, calves were allowed to graze for 1 h to collect a masticate sample. Masticate samples were frozen (–20°C) in preparation for lyophilization.
Duodenal digesta samples (200 mL) and fecal grab samples were collected on d 7 to 11. Samples were collected at 0, 4, 8, and 12 h after supplementation and were composited within steer for each period. The pasture was 72 km from Fargo, and the working facility did not have electricity; therefore, it would have been difficult to collect samples through the night. Samples were frozen (–20°C) for later analysis.
On d 9, ruminal fluid was collected from each steer to serve as inoculum for in vitro analysis. Ruminal fluid (1,200 mL) was collected with a suction strainer from the midventral region of the rumen. Ruminal fluid was immediately transferred to an insulated container and transported to the North Dakota State University Nutrition Laboratory. Masticate samples were inoculated immediately upon arrival. Ruminal fluid from each steer was used as inoculum for their corresponding masticate sample.
Ruminal fluid samples (210 mL) were collected on d 11 of each period at –1, 1, 2, 4, 8, 12, and 24 h after supplementation. Ruminal fluid was collected with a suction strainer from the midventral region of the rumen, and pH was recorded using a pH meter and combination electrode (Model 2000, Beckman Instruments Inc., Fullerton, CA). A 200-mL sample of ruminal fluid was acidified with 2 mL of 7.2 N H2SO4 and frozen (–20°C) for later analysis. In addition, a 4-mL sample of ruminal fluid was retained, and 1 mL of 25% (wt/vol) HPO3 was added. Samples were frozen (–20°C) for later analysis.
Milk intake was measured on d 16 using a modification of the weigh-suckle-weigh technique described by Boggs et al. (1980). On the evening before measurement, calves were separated from their dams for 3 h. After the 3-h separation, the calf was allowed to suckle the cow completely, then separated for 12 h. After 12 h of separation, the calves were weighed. Then, the calves were allowed to suckle their dams and weighed immediately once suckling had ceased. Milk intake was assumed to be the difference between the 2 weights. To more closely monitor the calves during suckling and to decrease the time from suckling to weighing, calves were assigned randomly to 1 of 2 groups for the weigh-suckle-weigh technique. Milk consumption of the second group was measured immediately after the first group. During the 3-h separation on d 15 of each period, a milk sample (approximately 150 mL) was extracted by hand. Milk samples were frozen (–20°C) for later analysis.
Laboratory Analyses.
Masticate samples were lyophilized (Virtis Genesis 25LL, The Virtis Company Inc., Gardiner, NY) then ground with a Wiley mill (1-mm screen; Model 3, Arthur H. Thomas, Philadelphia, PA). Samples were analyzed for in vitro OM disappearance (IVOMD) using a modified procedure of Tilley and Terry (1963). Ruminal fluid (6 mL) and McDougall’s solution (24 mL) were added to a 0.25-g masticate sample in a 50-mL tube. During the pepsin digestion, tubes were incubated for 24 h instead of 48 h (Tilley and Terry, 1963). Masticate samples were analyzed for DM, ash, N, Ca, P (Methods 930.15, 942.05, 990.02, 968.08, and 965.17, respectively; AOAC, 1990), ADF, and NDF (Ankom, Fairport, NY).
Supplement was dried at 50°C in a forced-air oven for 48 h. Dried samples were ground with a Wiley mill (1-mm screen). Supplement was analyzed for DM, ash, N, Ca, P, ADF, NDF (methods cited previously), and starch (Herrera-Saldana and Huber, 1989). Supplement was analyzed for IVOMD using the same procedure described for masticate samples. Milk was analyzed for total solids, ash, ether extract, and N (Methods 930.15, 989.04, and 991.20, for total solids, ether extract, and N, respectively; AOAC, 1990).
Ruminal contents were dried at 50°C in a forced-air oven for 48 h. Dried samples were ground with a Wiley mill (1-mm screen). Ruminal contents were analyzed for DM, ash, ADF, and NDF (methods previously cited).
Microbial cells were isolated from formalinized ruminal contents. Ruminal contents were blended (Model 37Bl19, Waring, New Hartford, CT), and the mixture was strained through 4 layers of cheesecloth. Feed particles and protozoa were removed via centrifugation at 500 x g for 20 min. The sample was then centrifuged twice at 30,000 x g for 20 min to pellet the bacteria from the supernatant. Isolated bacteria were frozen, lyophilized, and analyzed for DM, ash, N (methods previously cited), and purines (Zinn and Owens, 1986).
Ruminal fluid samples were centrifuged at 20,000 x g for 20 min and the supernatant 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 x 0.5-µm Nukol; Supelco, Bellefonte, PA) and flame ionization detection.
Duodenal samples were lyophilized and ground with a blender until a uniform particle size was produced (Osterizer Galaxie Pulse Matic I6, Sunbeam, Purvis, MS). Duodenal samples were analyzed for DM, ash, N, ADF, NDF, purines (methods cited previously), and Cr (see below).
Fecal samples were dried at 50°C in a forced-air oven for 48 h. Dried samples were ground with a Wiley mill (1-mm screen). Fecal samples were analyzed for DM, ash, N, ADF, NDF (methods cited previously), and Cr (see below).
We assumed that milk OM digestibility was essentially 100% and had negligible effects on fecal output. This assumption is consistent with that of recently published papers (Loy et al., 2002; Gelvin et al., 2004; Soto-Navarro et al., 2004).
Chromium concentrations were determined in duodenal and fecal samples by the spectrophotometric method (Fenton and Fenton, 1979). Dry matter flow to the duodenum was calculated by dividing the amount of Cr dosed by the concentration of Cr in duodenal DM. Fecal DM flow was calculated by dividing the amount of Cr dosed by the concentration of Cr in fecal DM. Disappearance was calculated by subtracting flow from intake, or amount entering, and dividing by intake. Forage intake was calculated using total forage fecal OM flow and forage in vitro OM indigestibility. Forage fecal DM flow was determined by subtracting the indigestible fraction of the supplement from feces of supplemented calves using in vitro DM indigestibility of the supplement. Forage fecal DM flow was converted to an OM basis using the analyzed ash concentration of feces. To determine forage OM intake, forage fecal OM flow was divided by forage in vitro OM indigestibility.
Experiment 2
Animals and Diets.
Sixteen intact, nursing, commercial, Angus steers (181 ± 36 kg of initial BW, 141 ± 15 d of age) were used in a split-plot design. All animal care and handling protocols were approved by the North Dakota State University Animal Care and Use Committee. Calves were assigned randomly to 1 of 2 treatments. Treatments and supplements were the same as in Exp. 1 (Table 1
), and the calves consumed the supplement for the same period of time. Calves grazed the same pastures as in Exp. 1; therefore, forage species and trace mineralized salt were the same as in Exp. 1.
Sample Collection.
Calf responses to treatment and seasonal effects were measured during 3 experimental periods. Collection periods were June 22 to July 6 (June), July 20 to August 3 (July), and August 17 to 31 (August). To determine ADG and G:F, BW were determined on 2 consecutive days at the beginning and end of the experiment and once at the end of each period. Unconsumed supplement was weighed back daily for calculation of DMI. Supplement samples were collected twice weekly and composited within period for laboratory analysis.
Calves were fitted with fecal collection bags on d 7 to 12 of each collection period. Fecal bags were weighed and emptied twice daily at 12-h intervals. Samples from a minimum of 5 d were collected from each calf. Fecal samples (10% of output) were composited within steer and across days for each period. Samples were frozen (–20°C) for later analysis.
Milk intake was measured on d 16 using a modification of the weigh-suckle-weigh technique described by Boggs et al. (1980). Techniques for measurement of milk intake were similar to those described for Exp. 1. A milk sample was not collected for Exp. 2; however, milk composition for Exp. 1 was averaged within treatment and period for calculation of milk OMI for Exp. 2.
Upon weaning (218 d of age), calves were transported to the North Dakota State University Beef Unit and fed in a common pen until slaughter (407 d of age). Hot carcass weight was measured immediately, and 12th rib s.c. fat thickness, LM area, KPH, and marbling score were collected approximately 24 h after slaughter. Yield grade was calculated as follows (Boggs and Merkel, 1979): yield grade = 2.5 + (0.9843 x 12th-rib fat thickness) + (0.2 x KPH) + (0.0084 x HCW) – (0.0496 x LM area).
Laboratory Analyses.
Laboratory analyses of fecal and supplement samples was the same as in Exp. 1. Forage intake was calculated using total forage fecal OM flow and forage in vitro OM indigestibility. Forage fecal DM flow was determined by subtracting the indigestible fraction of the supplement from feces of supplemented calves using in vitro DM indigestibility of the supplement. Forage fecal DM flow was converted to an OM basis using the analyzed ash concentration of feces. To determine forage OM intake, forage fecal OM flow was divided by forage in vitro OM indigestibility. Forage in vitro OM indigestibility values were extrapolated from Exp. 1 for similar treatments and periods.
Statistical Analysis
Data for both experiments were analyzed as a split-plot design using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). The model contained fixed effects for treatment, period, and treatment x period interaction. Compound symmetry was used as the covariance structure because it was the better fitting structure, and the random effect of calf within treatment was used to test for treatment effects. Residual error was used for testing the effects of period and treatment x period.
Ruminal data over sampling time were analyzed as a repeated measures (split-split-plot) design using the MIXED procedures of SAS. The model included fixed effects for treatment, period, and treatment x period interaction. The repeated effect was sampling time and animal within period x treatment was used as the error term for the split-split-plot. Two-way and 3-way interactions involving sampling time were usually significant and largely due to magnitude; therefore, P values are not presented, and means were averaged across sampling time. Period means were separated using linear and quadratic contrasts. Equal spacing was assumed when constructing contrast coefficients (Steel and Torrie, 1980).
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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).
Experiment 1
Masticate Composition.
There were no treatment x period interactions detected for any components of the grazed forage. Organic matter, CP, IVOMD, NDF, Ca, and P levels of the grazed diet were not different (P = 0.12 to 0.89) between the treatments (Table 2). Calves consuming CDDGS selected forage that was greater (P = 0.08) in ADF. Loy et al. (2002) and Reed et al. (2005) reported no differences in grazed diet quality between treatments on the same pasture as our study. Grazed diets averaged 12.8% CP (OM basis) and 57.9% IVOMD. In comparison, Loy et al. (2002) reported averages of 10.2% CP (OM basis) and 53% IVOMD over a 2-yr period, and Reed et al. (2005) reported averages of 12.4% CP (OM basis) and 50.3% IVOMD in the same pasture used on the current study. Crude protein of the grazed forage decreased linearly (P = 0.001) as season progressed, which is likely due to increased forage maturity. In vitro OM disappearance (P = 0.02) and NDF (P = 0.03) responded quadratically over season. In vitro OM disappearance was greatest in July and least in August, whereas NDF was least in July and greatest in August. Advancing season did not affect (P = 0.18 to 0.65) OM, ADF, Ca, or P of the grazed forage.
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). Treatment ranking did not change; therefore, the interaction was due to magnitude of change and not likely biologically significant. For cows nursing calves fed the control supplement, percent solids were less (P = 0.02) in June compared with July, and milk solids in August were similar (P = 0.21 and 0.22) to both June and July. For cows nursing calves fed CDDGS, percent solids were similar (P = 0.28) for June and July, which were both less (P = 0.006 and 0.05) compared with August. Cows nursing control and CDDGS calves had similar (P = 0.31 and 0.93) percent solids for June and August, and cows nursing control calves had greater (P = 0.05) percent solids in July.
There were no other treatment x period interactions (P = 0.12 to 0.60) detected for milk composition. Milk OM, CP, and fat content were not affected (P = 0.11 to 0.68) by treatment. Reed et al. (2005) reported no differences in milk composition in cows nursing calves consuming either no supplement or a wheat middling, soybean hull-based supplement, and Faulkner et al. (1994) reported no differences in milk composition in cows nursing calves consuming no supplement, 1 kg/d corn, 1 kg/d soybean hulls, or unlimited intake of corn or soybean hulls. Milk OM increased linearly (P = 0.002), and CP (P = 0.003) and fat (P = 0.03) responded quadratically as season advanced. Milk CP was greatest in July and least in August, and fat content was greatest in July and least in June.
Intake.
A treatment x period interaction was not detected (P = 0.58) for supplement OM intake (OMI; kg/d). Supplement OM intake (kg/d) was not affected (P = 0.59) by treatment (Table 3). Supplement was fed at 0.45% of BW (DM basis), and level of supplement was adjusted according to BW at the beginning of each period; therefore, supplement OMI was not different between treatments and increased linearly (P = 0.004) as season progressed. Supplement intake would have only been different if BW differed between treatments.
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; Loy et al., 2002). There was a quadratic affect (P = 0.003) for milk OMI across season. Milk OMI was greatest in July and least in August. It is not apparent why milk OMI was greatest in July; however, it was expected that milk OMI would be least in August because the cows were nearing the end of lactation (Clutter and Nielsen, 1987) and forage CP and IVOMD were least in August.
A treatment x period interaction was not detected (P = 0.57) for forage OMI (kg/d). Forage OMI (kg/d) was not different (P = 0.46) between treatments. Forage intake was likely not affected by treatment because nutrient profiles of the supplements were similar and feeding rates were the same. Faulkner et al. (1994) reported no differences in forage DM intake for calves consuming soybean hulls or corn in creep feed. Also, Loy et al. (2002) reported no differences in forage intake when feeding 3 different supplements that were high in digestible fiber or in degradable intake protein (DIP). Soto-Navarro et al. (2004) and Reed et al. (2005) fed digestible fiber-based supplements and reported no differences in forage intake compared with nonsupplemented controls. However, many researchers reported that calves supplemented with creep feed high in starch consume less forage compared with controls (Cremin et al., 1991; Faulkner et al., 1994; Tarr et al., 1994). Forage OMI increased linearly (P = 0.001) as season advanced. This effect is likely due to increasing rumen function and calf size. Similarly, Loy et al. (2002) and Reed et al. (2005) reported linear increases in forage OMI in nursing calves grazing the same pasture as the current study.
There were not (P = 0.80 and 0.76 for kg/d and % of BW, respectively) treatment x period interactions for total OMI. Total OMI (kg/d, P = 0.53; and % of BW, P = 0.98) was not affected by treatment. Across season, total OMI increased linearly (P = 0.001 and P = 0.03 for kg/d and % of BW, respectively). Supplement and forage OMI (kg/d) increased linearly as season progressed, but milk OMI was least in August; therefore, increased total OMI (kg/d) was due to increased intake of supplement and forage. Supplement was offered at the same percentage of BW throughout the study; therefore, increased total OMI (% of BW) was only due to increased forage intake.
Organic Matter Flow and Disappearance.
A treatment x period interaction was not detected (P = 0.20) for total duodenal OM flow (g/d). Total duodenal OM flow was not affected by treatment (P = 0.88; Table 3). Similarly, Soto-Navarro et al. (2004) and Reed et al. (2005) reported no differences in total duodenal OM flow between nonsupplemented calves and calves consuming a fiber-based supplements while consuming brome hay (7.43% CP; Soto-Navarro et al., 2004) or grazing native range (12.4% CP; Reed et al., 2005). Total duodenal OM flow (g/d) increased quadratically (P = 0.005) across season. Increased total duodenal OM flow was caused by a linear increase in OMI as season advanced. Reed et al. (2005) reported a linear increase in total duodenal OM flow; however, Soto-Navarro et al. (2004) reported no difference in total duodenal OM flow with advancing season.
There was a (P = 0.08) treatment x period interaction for true ruminal OM disappearance (g/d). True ruminal OM disappearance was 1,219, 1,742, and 2,067 g/d for control calves in June, July, and August, respectively, and was 1,166, 1,880 and 1,650 g/d for CDDGS calves in June, July, and August, respectively. There were no differences between treatments in June (P = 0.81) or July (P = 0.51), but true ruminal OM disappearance (g/d) was greater (P = 0.06) for control calves in August. A treatment x period interaction was also detected (P = 0.004) for true ruminal OM disappearance (% of intake). True ruminal OM disappearance was 59.4, 69.4, and 68.4% of intake for control calves in June, July, and August, respectively, and was 64.7, 74.2 and 59.2% of intake for CDDGS calves in June, July, and August, respectively. There were no differences between treatments in June (P = 0.25) or July (P = 0.28), but true ruminal OM disappearance (% of intake) was greater (P = 0.05) for control calves in August. The control supplement was greater in DIP (65 vs. 49% calculated DIP, % of CP, for control and CDDGS, respectively), which might have had a positive influence on OM digestion in August, when forage quality was decreased. Soto-Navarro et al. (2004) and Reed et al. (2005) supplemented calves with a fiber-based creep feed and reported no differences in true ruminal OM disappearance between nonsupplemented and supplemented calves.
There was a (P = 0.02) treatment x period interaction for intestinal apparent OM disappearance (g/d). Intestinal apparent OM disappearance (g/d) was 1,015.1, 683.2, and 591.3 g/d for control calves in June, July, and August, respectively, and was 878.5, 649.1, and 844.3 g/d for CDDGS calves in June, July, and August, respectively. There were no differences between treatments in June (P = 0.29) or July (P = 0.78), but intestinal apparent OM disappearance was less (P = 0.05) for control calves in August compared with CDDGS calves. Control calves had greater true ruminal OM disappearance in August and less intestinal apparent OM disappearance compared with CDDGS calves.
Treatment x period interactions were not detected (% of entering, P = 0.17; % of intake, P = 0.32) for intestinal apparent OM disappearance. Intestinal apparent OM disappearance was not affected (% of entering, P = 0.55; % of intake, P = 0.60) by treatment and declined quadratically (% of entering, P = 0.06; % of intake, P = 0.01) across season. Decreased intestinal apparent OM disappearance was the result of decreasing milk intake, which was assumed to be more digestible than either forage or supplement.
There was no (P = 0.11) treatment x period interaction for apparent total tract OM disappearance (% of intake). Apparent total tract OM disappearance was not affected (P = 0.72) by treatment and decreased linearly (P = 0.001) as season advanced (Table 3). Decreased apparent total tract OM disappearance is likely caused by declining milk intake and forage IVOMD both of which decreased quadratically as season advanced. Similar results were reported by Reed et al. (2005) in calves grazing the same pasture as the current study.
Nitrogen Intake and Flow.
A treatment x period interaction was not detected (P = 0.81) for N intake. Total N intake (g/d) was not affected (P = 0.66; Table 4) by treatment. The supplements were similar in CP and supplement, milk, and forage intakes were similar between treatments resulting in similar N intakes between treatments. There was a quadratic affect (P = 0.01) for N intake with advancing season. Nitrogen intake was 91.0, 111.1, and 95.3 g/d in June, July, and August, respectively. Nitrogen intake increased from June to July because of increased supplement, milk, and forage intake, although forage CP was lower in July. Nitrogen intake decreased from July to August because of decreased milk intake and forage CP.
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A treatment x period interaction was not detected (P = 0.92) for duodenal microbial N flow (g/d). Duodenal microbial N flow was not affected (P = 0.50) by treatment. Duodenal microbial N flow linearly increased (P = 0.003) as season progressed. Increased duodenal microbial N flow across season is possibly the result of increased intake of fermentable OM. Reed et al. (2005) reported increased duodenal microbial N flow in supplemented compared with nonsupplemented calves and a quadratic increase across season. However, Soto-Navarro et al. (2004) reported no differences between supplemented and nonsupplemented calves.
There was (P = 0.05) a treatment x period interaction for nonmicrobial nitrogen flow (g/d). Nonmicrobial nitrogen flow was 72.1, 53.9, and 54.8 g/d for control calves in June, July, and August, respectively; and was 62.7, 53.9, and 63.8 g/d for CDDGS calves in June, July, and August, respectively. There were no differences (June, P = 0.12; July, P = 0.99; August, P = 0.11) between treatments within periods. The interaction may be a result of greater undegradable intake protein in CDDGS and increasing levels of supplementation with advancing season.
Composition of Microbial Isolates and Microbial Efficiency.
In the microbial isolate (Table 4), treatment x period interactions were not detected for N (% of DM, P = 0.27), N (% of total duodenal N, P = 0.40), or N:purine ratio (P = 0.39). Nitrogen (% of DM, P = 0.59 and % of total duodenal N, P = 0.54) was not affected by treatment and increased quadratically (% of DM, P = 0.01; % of total duodenal N, P = 0.03) with advancing season. Reed et al. (2005) reported no differences in N with advancing season. Nitrogen:purine ratio was not affected (P = 0.90) by treatment and increased quadratically (P = 0.001) across season. Nitrogen:purine ratio followed a similar pattern as N intake across season. Similarly, Reed et al. (2005) reported a quadratic increase in N:purine across season.
There was (P = 0.08) a treatment x period interaction for OM:purine ratio. Organic matter:purine ratio was 9.5, 12.0, and 11.8 for control calves in June, July, and August, respectively, and was 10.6, 12.3, and 11.8 for CDDGS calves in June, July, and August, respectively. Organic matter:purine ratio was greater (P = 0.07) for CDDGS calves in June, but there were no differences (P = 0.57 and 0.99) between treatments in July and August.
A treatment x period interaction was detected (P = 0.009) for microbial efficiency. Microbial efficiency was 17.2, 15.7, and 13.9 g of microbial N per kilogram of OM truly fermented in the rumen for control calves in June, July, and August, respectively, and was 17.3, 13.1, and 16.6 g of microbial N per kilogram of OM truly fermented in the rumen for CDDGS calves in June, July, and August, respectively. Microbial efficiency was not different (P = 0.94) between treatments for June, was greater (P = 0.06) in control calves in July, and was less (P = 0.04) for control calves in August. Microbial efficiency values were greater than those reported by Soto-Navarro et al. (2004) and Reed et al. (2005) whose treatments included a control (nonsupplemented) or a supplement based on wheat middlings and soyhulls. The CP content of our supplement was greater than that of previously mentioned studies [30% CP vs. 12.1 and 17.4 % CP for Soto-Navarro et al. (2004) and Reed et al. (2005), respectively]. Increased CP in the supplement increased microbial efficiency compared with previous research on this forage type, which may lead to increased calf performance.
Nitrogen Disappearance.
There were no treatment x period interactions for apparent (P = 0.27) or true (P = 0.30) ruminal N disappearance (% of intake). Ruminal N disappearance (% of intake) was not affected (apparent, P = 0.56 true, P = 0.55) by treatment although the control supplement was greater in calculated DIP compared with the CDDGS supplement (65.0 vs. 46.1% calculated DIP, % of CP, for control and CDDGS, respectively). Apparent and true ruminal N disappearance responded quadratically (P = 0.003) to season, being least in June and greatest in July.
Treatment x period interactions were not detected for apparent intestinal N disappearance (P = 0.38 and 0.25 for % of entering and % of intake, respectively). Intestinal N disappearance was not affected (P = 0.97 and 0.67 for % of entering and % of intake, respectively) by treatment. Intestinal N disappearance (% of entering) responded quadratically (P = 0.04) to season, being greatest in June and least in August. Intestinal N disappearance (% of intake) also responded quadratically (P = 0.003) to season and was greatest in June and least in July. This pattern coincides with ruminal N disappearance (% of intake), which was least in June and greatest in July, indicating a shift in site of digestion.
There was not (P = 0.72) a treatment x period interaction for apparent total tract N disappearance (% of intake). Treatment did not affect (P = 0.31) apparent total tract N disappearance (% of intake). Apparent total tract N disappearance (% of intake) responded quadratically (P = 0.06) to season and was least in August. The ratio of forage OMI to total OMI continually increased throughout the season, whereas the percentage of milk and creep OMI to total OMI decreased; this likely explains the decrease in apparent total tract N disappearance in August. As percentage of forage in the diet increased, N digestibility likely decreased.
Treatment x period interactions were not detected for apparent total tract NDF (P = 0.25) or ADF (P = 0.25) disappearance (data not shown). Apparent total tract NDF (50.0 and 52.6% of intake for control and CDDGS, respectively; P = 0.22) and ADF disappearance (44.6 and 48.2% of intake for control and CDDGS, respectively; P = 0.23) were not affected by treatment. The supplements had similar levels of CP, starch, and fiber (Table 1), which likely led to no differences in fiber digestion. Grazed forage IVOMD declined with advancing season; however, apparent total tract NDF and ADF disappearance were not affected (NDF, 53.4, 48.8, and 51.8% of intake for June, July, and August, respectively, P = 0.38; ADF, 49.0, 40.3, 44.5% of intake for June, July, and August, respectively, P = 0.97). Reed et al. (2005) reported a quadratic response across season for apparent total tract NDF and ADF disappearance (% of intake) with the lowest disappearance occurring in July.
Ruminal Fermentation.
There was no treatment x period interaction (P = 0.16) for ruminal pH (Table 5). Ruminal pH was less (P = 0.05) for CDDGS compared with control calves; however, ruminal pH was not affected (P = 0.15) by grazing period. Ørskov (1982) and Mould and Ørskov (1983) indicated that ruminal pH below 6.2 reduces the activity of cellulolytic bacteria and ruminal fiber digestion. Ruminal fiber digestion was likely not affected by ruminal pH, because pH was greater than 6.2 for both treatments during all collection periods. Supplement may have a more adverse effect on ruminal pH with advancing season because of declining forage quality. Mould et al. (1983) suggested that readily fermentable carbohydrates more adversely affect the ruminal environment in animals fed low-quality forages compared with animals fed greater-quality forages.
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There was not a treatment x period interaction (P = 0.34) for total VFA. Total ruminal VFA concentrations were not different (P = 0.28) between treatments. Similarly, Faulkner et al. (1994) reported no differences in total VFA when supplementing either corn or soybean hulls to nursing calves grazing fescue. Numerous researchers have reported increased total VFA concentrations in supplemented compared with nonsupplemented calves (Faulkner et al., 1994; Gelvin et al., 2004; Soto-Navarro et al., 2004). Total VFA responded quadratically (P = 0.08) to season. Total VFA concentrations were least in July and greatest in August.
There was not a treatment x period interaction (P = 0.87) for molar proportions of ruminal acetate. Acetate (mol/100 mol) was decreased (P = 0.09) by CDDGS treatment and responded quadratically (P = 0.001) to season (Table 5). There was not a treatment x period interaction (P = 0.23, Table 5) for molar proportions of propionate. Overall CDDGS treatment increased (P = 0.03) molar proportions of propionate. Propionate responded quadratically (P = 0.001) to season. Propionate was similar in June and July and less in August. This result may have been caused by increasing the relative proportion of forage in the diet.
A treatment x period interaction was not detected (P = 0.30) for ruminal acetate:propionate ratio. Acetate:propionate ratio was greater (P = 0.01) for control compared with CDDGS calves. The control treatment was greater in DIP, which could have caused greater ruminal fiber digestion resulting in greater acetate:propionate. Acetate proportions were numerically greater, and propionate proportions were numerically less for control compared with CDDGS calves causing an increased acetate:propionate ratio. Acetate:propionate responded quadratically (P = 0.001) to season, being least in July and greatest in August.
There was a treatment x period interaction (P = 0.09) for molar proportion of butyrate. Treatment ranking did not change across period, thus, we believe the interaction was caused by magnitude of change. Therefore, only main effect means are reported. Butyrate molar proportion was greater (P = 0.001) in CDDGS calves compared with control calves and responded quadratically (P = 0.001) to season (Table 5). Butyrate was greatest in July and least in August. Gelvin et al. (2004), Soto-Navarro et al. (2004), and Reed et al. (2005) reported increased molar proportions of butyrate in supplemented compared with nonsupplemented nursing calves.
A treatment x period interaction was not detected (P = 0.71) for ruminal valerate proportion. Dietary treatment did not influence (P = 0.50) ruminal valerate, whereas valerate proportions decreased (P = 0.001) linearly with advancing season. Gelvin et al. (2004) and Reed et al. (2005) reported increased ruminal molar proportions of valerate in supplemented compared with nonsupplemented calves.
There were no treatment x period interactions for ruminal isobutyrate (P = 0.40), whereas there were for isovalerate (P = 0.07). The treatment x period interaction in isovalerate was mostly due to magnitude differences. Molar proportions of isobutyrate (P = 0.007) and isovalerate (P = 0.01) were less in CDDGS compared with control calves indicating less deamination of branched chain amino acids, an indication of less DIP. Gelvin et al. (2004) and Reed et al. (2005) reported no differences in ruminal isobutyrate and isovalerate in supplemented compared with nonsupplemented nursing calves. Molar proportions of isobutyrate (P = 0.004) and isovalerate (P = 0.07) responded linearly and quadratically to season, respectively. Molar proportion of isobutyrate was greatest in June and least in August, whereas molar proportion of isovalerate was greatest in July and least in August.
Experiment 2
Intake.
A treatment x period interaction was not detected (P = 0.58) for supplement OMI (% of BW). Supplement OMI (% of BW) decreased (P = 0.09) in calves fed CDDGS (Table 6). Creep feed intake is often variable, and in this study there were 2 calves fed CDDGS that regularly did not completely consume all of their supplement. Supplement was fed at 0.45% of BW (DM basis), and level of supplement was adjusted according to BW at the beginning of each period; therefore, there were no differences (P = 0.35) in supplement OMI (% of BW) across season.
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A treatment x period interaction was not detected (P = 0.99) for milk OMI (% of BW). Milk OMI was not different (P = 0.46) between treatments. Numerous researchers have reported no differences in milk intake when comparing supplemented to nonsupplemented calves (Loy et al., 2002; Gelvin et al., 2004; Soto-Navarro et al., 2004) and when comparing calves consuming different types of supplements (Faulkner et al., 1994; Loy et al., 2002). There was a quadratic affect (P = 0.02) for milk OMI across season. Milk OMI decreased from June to July and increased from July to August. This result was unexpected because milk production typically declines as the cow progresses in lactation (Clutter and Nielsen, 1987).
There was not (P = 0.81) a treatment x period interaction for total OMI (% of BW). Total OMI was not affected (P = 0.55) by treatment and increased (P = 0.09) quadratically as season progressed. Supplement was offered at the same percentage of BW throughout the study, and milk OMI (% of BW) declined quadratically; therefore, increased total OMI was only due to increased forage intake.
Calf Performance.
No treatment or treatment x period interactions were detected for final BW, ADG, or G:F (P = 0.27 to 0.99; Table 7). It is likely that there were no differences in performance because the nutrient profiles of the supplements were similar. Other researchers have reported no differences in calf performance when comparing different types of supplements (Faulkner et al., 1994; Loy et al., 2002). Loy et al. (2002) reported no differences in calf performance when comparing an energy supplement, a DIP supplement, and a supplement containing both DIP and rumen undegradable intake protein. Faulkner et al. (1994) reported no differences in calf performance when comparing corn and soybean hull supplements.
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In Exp. 1, there were no differences in OMI, and OM, N, ADF, or NDF disappearance between calves consuming a supplement containing 50% CDDGS or the control supplement. Calves consuming the 50% CDDGS supplement had decreased ruminal acetate:propionate ratio, increased molar proportions of butyrate, and decreased molar proportions of isobutyrate and isovalerate. In Exp. 2, supplement OMI (% of BW) slightly decreased in calves consuming the 50% CDDGS supplement, but there were no differences in performance or carcass composition. Inclusion of 50% dry distillers grains with solubles in supplement for nursing calves produced similar results as the control supplement containing soybean meal, wheat middlings, and soybean hulls and seems to be a suitable ingredient in supplements for nursing calves.
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Footnotes |
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2 Corresponding author: joel.caton{at}ndsu.edu
Received for publication November 4, 2005. Accepted for publication March 9, 2006.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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