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ANIMAL NUTRITION |
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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Key Words: calf • creep feed • digestibility • forage • intake • 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). 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 fed creep feed.
Many researchers have shown that calves consume less forage when supplemented with creep feed high in starch (Cremin et al., 1991; Faulkner et al., 1994; Tarr et al., 1994). However, Loy et al. (2002) and Soto-Navarro et al. (2004) reported that creep feeding did not influence forage intake. Loy et al. (2002) fed 3 different supplements that were either high in digestible fiber or high in degradable intake protein, and Soto-Navarro et al. (2004) fed a supplement that was high in digestible fiber composed of soybean hulls and wheat middlings. In addition, Soto-Navarro et al. (2004) reported that digestible fiber-based creep feed increased total tract OM digestibility and had no effect on ruminal pH or microbial efficiency.
Measurement of microbial CP synthesis via ruminal and duodenal fistulas has not been reported in nursing calves grazing native range. Estimates of microbial CP supply are important for calculating amount of undegradable intake protein necessary to meet metabolizable protein requirements of nursing calves grazing native range. A better understanding of microbial efficiency and protein supply should lead to more efficient creep feeding programs and optimal BW gains. Therefore, we hypothesized that a wheat middlings, soybean hull-based creep supplement would improve total intake, not alter ruminal fermentation or microbial efficiency, and improve performance in nursing calves grazing native range.
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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 an 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. Long-term average rainfall and temperature data were computed using all previous recordings from the 2 weather stations (3 and 15 yr of data for Leonard and Wyndmere, respectively) for June, July, and August.
Experiment 1
Animals and Diets.
Nine ruminally and duodenally cannulated, nursing, commercial Angus steers (172 ± 23 kg of initial BW; 140 ± 7 d of age) were used in a split-plot design. All surgical procedures, animal care, and animal handling protocols were approved by the North Dakota State University Institutional Animal Care and Use Committee. Calves were allotted randomly to 1 of 2 treatments: 1) control (no supplement; n = 4) and 2) supplemented calves (n = 5).
Supplementation of calves began 2 wk before the start of the study to ensure calves would be adapted to consuming the supplement at the onset of the study. Supplemented calves were fed at 0.45% of BW (DM basis) once daily at 0800. Cow-calf pairs were gathered daily, and calves were sorted into individual pens for feeding. Amount of supplement fed was adjusted at the beginning of each period based on beginning BW for that period. Supplement consisted of 55% wheat middlings, 38.67% soybean hulls, 5% molasses, and 1.33% limestone (DM basis; Table 1). Cattle had ad libitum access to water and a commercial trace-mineralized salt mix (Trouw Nutrition, Willmar, MN; not more than 94% NaCl, not less than 93% NaCl, 0.380% Zn, 0.2% Fe, 0.19% Mn, 0.039% Cu, 0.008% Co, 0.008% I, and 0.0053% Se).
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Ruminal evacuations were performed 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 subsampled for future analysis of DM, ash, ADF, and NDF. A 2-kg sample of ruminal contents was taken and 1 L of formalin/saline solution (3.7% formaldehyde/0.9% NaCl) was added (Zinn and Owens, 1986) for isolation of bacterial cells.
On d 1 after ruminal evacuations and before replacing ruminal contents, calves were allowed to graze for 1 h in order to collect a masticate sample. Masticate samples were frozen (–20°C) in preparation for lyophilization.
Duodenal fluid 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 extremely difficult to collect samples through the night. Samples were frozen (–20°C) for later analysis.
On d 9, ruminal fluid was drawn from each steer to serve as inoculum for in vitro analysis. Ruminal fluid was immediately transferred to an insulated container, and masticate samples were inoculated within 20 to 30 min after ruminal fluid was drawn. Ruminal fluid from each steer was used as inoculum for their corresponding masticate sample.
Ruminal fluid samples (200 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% HPO3 was added to the fluid. 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 nurse the cow dry, 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. Calves were assigned randomly to 1 of 2 groups for the weigh-suckle-weigh technique to more closely monitor the calves during suckling and to decrease the time from suckling to weighing. The milk consumption of the second group was measured immediately following the first. 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 Analysis.
Masticate samples were lyophilized (Virtis Genesis 25LL; The Virtis Company, Inc., Gardiner, NY) then ground with a Wiley mill (Model 3, 1 mm screen; 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 as described by 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 as was described for masticate samples. Milk was analyzed for total solids, ash, ether extract, and N (methods 930.15, 989.04, 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).
Bacterial cells were isolated from ruminal contents that contained 1 L of formalin/saline solution. Ruminal contents were blended (Model 37Bl19; Waring, New Hartford, CT), and the mixture was strained through 4 layers of cheesecloth. Feed particles and protozoa in ruminal samples 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 collect 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 supernatant taken for analysis of NH3 (Broderick and Kang, 1980). Ruminal VFA concentrations (Goetsch and Galyean, 1983) were quantified by gas chromatography (Hewlett Packard 5890A Series II GC, Wilmington, DE) using a capillary column.
Duodenal samples were lyophilized (Virtis Genesis 25LL) 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 previously cited), and Cr (Fenton and Fenton, 1979).
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, and Cr (methods previously cited).
Milk OM contribution to the feces was not accounted for. We assumed that milk OM digestibility was high. This method is consistent with that of recently published papers (Loy et al., 2002; Gelvin et al., 2004; Soto-Navarro et al., 2004).
Dry matter flow to the duodenum was calculated by dividing the amount of Cr dosed by the concentration of Cr in the duodenal contents. Fecal DM flow was calculated by dividing the amount of Cr dosed by the concentration of Cr in the feces. Disappearance was calculated by subtracting flow from intake, or amount entering, and dividing by intake, or amount entering.
Forage intake was calculated using total forage fecal DM 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 (153 ± 28 kg of initial BW; 133 ± 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 Institutional Animal Care and Use Committee. Calves were allotted to 1 of 2 treatments: 1) control (no supplement; n = 8) and 2) supplemented calves (n = 8). Supplemented calves received the same supplement as supplemented calves in Exp. 1 (Table 1
) and consumed supplement for the same duration 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 24 to July 8 (June), July 15 to July 29 (July), and August 5 to 19 (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 to determine ADG and G:F. 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 subsamples (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 as 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 OM intake (OMI) for Exp. 2.
Upon weaning, calves were transported to the North Dakota State University Beef Unit and fed in a common pen until slaughter. Hot carcass weight was collected within 30 min after slaughter. Twelfth rib fat thickness, LM area, KPH, and marbling score were collected approximately 24 h after slaughter. Yield grade was calculated as follows: yield grade = 2.5 + (0.9843 * 12th rib fat thickness) + (0.2 * KPH) + (0.0084 * HCW) – (0.0496 * LM area).
Laboratory Analysis.
Laboratory analysis of fecal and supplement samples was the same as Exp. 1. Forage intake was calculated using total forage fecal DM 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 Proc Mixed procedure of SAS (SAS Inst., Cary, NC). The model contained fixed effects for treatment, period, and treatment x period. Compound symmetry was used as the covariance structure, and calf within treatment was used to test for treatment effects. Residual error was used for testing 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 (SAS Inst., Cary, NC). The model included fixed effects for treatment, period, and treatment x period interactions. 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 mostly due to magnitude; therefore, P-values were not presented and means were averaged across sampling time. Period means were separated using linear and quadratic contrasts.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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).
Experiment 1
There were no treatment x period interactions detected for any components of the grazed forage (Table 2). Grazed diet composition was not affected (P = 0.22 to 0.99) by treatment. Grazed diets averaged 12.4% CP (OM basis) and 50.3% IVOMD. In comparison, Loy et al. (2002) reported averages of 10.2% CP (OM basis) and 53% IVOMD over a 2-yr period in the same pasture. There was a quadratic effect (P = 0.001 to 0.01) for OM, CP, IVOMD, NDF, and Ca with advancing season. Organic matter, CP, and Ca were greatest in July, whereas IVOMD and NDF were least in July. Acid detergent fiber (P = 0.04) declined linearly as season advanced, and P (P = 0.18) was not affected by season.
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). Milk composition was not affected by treatment or period. Similarly, Faulkner et al. (1994) reported no differences in milk composition in calves consuming no creep, 1 kg/d of corn or soyhulls, or unlimited intake of corn or soyhulls. It is unlikely that calf nutrition will affect milk composition. There was a treatment x period interaction (P = 0.04) for milk OMI. Milk OMI was 0.69, 1.05, and 0.28 kg/d for control calves in June, July, and August, respectively, and was 0.41, 0.67, and, 0.60 kg/d for supplemented calves in June, July, and August, respectively. For control calves, milk OMI (kg/d) was not different (P = 0.11) between June and July and lower (P = 0.06 and 0.002) for August compared with June and July. However, for supplemented calves, there were no differences (P = 0.15 to 0.66) between periods. There were no differences (P = 0.15 and 0.11) between treatments during June and August, but control calves had greater (P = 0.08) milk OMI (kg/d) during July.
There were no treatment differences for forage OMI (kg/d; P = 0.70; Table 3). Soto-Navarro reported no differences in milk or forage OMI when feeding a supplement similar to the one in the current study, and Loy et al. (2002) reported no differences in milk or forage intake between supplemented and control calves grazing the same pasture as used in our study. In addition, Gelvin et al. (2004) reported no differences in milk or forage OMI between supplemented and control calves grazing native range in western North Dakota.
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There were no treatment x period interactions for duodenal OM flow or ruminal OM disappearance (Table 3). Total duodenal OM flow (g/d) was not different (P = 0.69) between control and supplemented calves. Apparent ruminal OM disappearance (% of intake) was greater (P = 0.02) in supplemented calves compared with controls. In contrast, Soto-Navarro et al. (2004) reported no differences in apparent ruminal OM disappearance in supplemented vs. control calves consuming a soybean hulls, wheat middlings-based supplement, and brome hay. True ruminal OM disappearance (% of intake) was not affected (P = 0.13) by treatment. This result concurs with the findings of Soto-Navarro et al. (2004). Several studies have found that cereal grain supplementation reduces forage OM digestibility (Hannah et al., 1989; Vanzant et al., 1990; Pordomingo et al. 1991). Pordomingo et al. (1991) reported that in situ forage OM disappearance was greatest for steers fed corn at 0.2% of BW and least for those fed corn at 0.4 and 0.6% of BW. Degradable intake protein supplementation of low quality forage-based diets generally increases OM digestion (Köster et al., 1996; Bodine et al., 2000; Bandyk et al., 2001). Supplementation increased apparent ruminal OM digestion and had no effect on true ruminal OM digestion, perhaps because the supplement was based on digestible fiber sources, greater in CP (17.4%), and lower in starch than most common cereal grains. Apparent and true ruminal OM disappearance (% of intake; P = 0.23 and P = 0.29 for apparent and true, respectively) were not affected by advancing season.
Intestinal apparent OM disappearance (% of entering) was not different (P = 0.32) between treatments and was lower (P = 0.09) as a percentage of intake in supplemented compared with control calves (Table 3). The decrease in intestinal apparent OM disappearance (% of intake) reflects increased ruminal apparent OM disappearance in supplemented calves. Soto-Navarro et al. (2004) reported no differences in intestinal apparent OM disappearance (% of intake) between treatments, along with no differences in ruminal OM disappearance. Intestinal OM disappearance (% of entering and % of intake) decreased linearly (P = 0.001) as season progressed. Decreased intestinal apparent OM disappearance could be caused by decreasing milk intake, which is more digestible than forage and supplement.
There was a treatment x period interaction for apparent total tract OM disappearance (% of intake; P = 0.03). Apparent total tract OM disappearance was 73.5, 64.2, and 63.2% of intake for control calves in June, July, and August, respectively, and was 73.0, 72.0, and 72.8% of intake for supplemented calves in June, July, and August, respectively. For control calves, apparent total tract OM disappearance was greater (P = 0.004 and 0.002) in June compared with July and August, and July and August were similar (P = 0.71). However, for supplemented calves, there were no differences (P = 0.67 to 0.94) across periods. There was no difference (P = 0.87) between treatments during June, but for July and August, supplemented calves had greater (P = 0.01 and 0.003) apparent total tract OM disappearance (% of intake).
Apparent total tract OM disappearance was greater (P = 0.01) for supplemented compared with control calves (Table 3). The supplemented calves consumed a diet (forage plus supplement) that was greater in IVOMD; this likely caused the increase in apparent total tract OM disappearance. Also, the supplement was based on digestible fiber sources and was relatively high in CP [17.39%; 69.89% degradable intake protein (DIP), % of CP], which may have positively influenced fiber digestion. Apparent total tract OM disappearance (% of intake) decreased linearly (P = 0.01) as season progressed. Decreased apparent total tract OM disappearance was likely caused by declining milk intake and forage IVOMD, which both decreased quadratically across season.
There was not a treatment x period interaction for N intake (P = 0.11). Total N intake (g/d) was not affected (P = 0.19) by treatment (Table 4). Soto-Navarro et al. (2004) reported a tendency for greater N intake in supplemented vs. control calves when feeding a similar supplement to the current study and brome hay. Nitrogen intake was not affected (P = 0.11) by season.
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). Duodenal total N flow (g/d; P = 0.19) and nonbacterial N flow (g/d; P = 0.48) were not affected by treatment. Duodenal bacterial N flow (g/d) was greater (P = 0.01) in supplemented compared with control calves. Supplementation likely increased energy and DIP supply and consequently microbial growth.
There was a quadratic effect for duodenal total N (P = 0.06) and duodenal bacterial N (P = 0.02) flow across season (Table 4). Duodenal nonbacterial nitrogen flow (g/d) increased linearly (P = 0.002) across season, which likely reflects increased undegraded intake protein as season progressed.
There were no treatment x period interactions for components of the bacterial isolate (Table 4). In the bacterial isolate, N (% of DM, P = 0.02 and % of total duodenal N flow, P = 0.05) was greater in supplemented compared with control calves, but N (% of DM, P = 0.35 and % of total N, P = 0.30) was not affected by season. In the bacterial isolate, N:purine (P = 0.37) and OM:purine (P = 0.95) ratios were not affected by treatment.
Microbial efficiency (grams of N per kilogram of OM truly digested) was not affected (P = 0.56) by treatment (Table 4). Microbial efficiency values were greater than those reported by Soto-Navarro et al. (2004; 11.8 and 12.0 g of N/kg of OM truly digested for control and supplemented, respectively) in nursing calves. Microbial efficiency was not affected (P = 0.12) by season.
There was a treatment x period interaction (P = 0.03) for apparent ruminal N disappearance (% of intake). Apparent ruminal N disappearance was 32.5, 14.2, and –48.9% of intake for control calves in June, July, and August, respectively, and was 13.4, 31.6, and 14.9% of intake for supplemented calves in June, July, and August, respectively. For control calves, apparent ruminal N disappearance was similar (P = 0.37) during June and July and less (P = 0.001 and 0.007) in August compared with June and July. For supplemented calves, there were no differences (P = 0.32 to 0.94) between periods. For June and July, there were no differences (P = 0.32 and 0.36) between treatments. However, during August, supplemented calves had greater (P = 0.004) apparent ruminal N disappearance (% of intake). Apparent ruminal N disappearance (% of intake) was negative for control calves in August. This was likely due to N recycling to the rumen, which caused greater levels of N leaving the rumen than was consumed.
There was a treatment x period interaction (P = 0.02) for true ruminal N disappearance (% of intake). True ruminal N disappearance was 52.1, 42.2, and 10.1% of intake for control calves in June, July, and August, respectively, and was 48.2, 60.2, and 45.0% of intake for supplemented calves in June, July, and August, respectively. For control calves, true ruminal N disappearance for June and July was similar (P = 0.43) and less (P = 0.004 and 0.02) during August compared with June and July. For supplemented calves, there were no differences (P = 0.18 to 0.77) between treatments. For June and July, there were no differences (P = 0.74 and 0.14) between treatments; however, during August, supplemented calves had greater (P = 0.009) true ruminal N disappearance (% of intake).
Ruminal N disappearance (apparent, P = 0.08 and true, P = 0.02; % of intake) was greater in supplemented compared with control calves (Table 4). Similarly, Reed et al. (2004) reported increased apparent and true ruminal N disappearance (% of intake) with increasing field pea supplementation for moderate quality forage diets fed to steers. Also, Köster et al. (1996) reported a quadratic increase in apparent ruminal N disappearance with the addition of DIP to low-quality forage diets. Apparent ruminal N disappearance (% of intake) decreased linearly (P = 0.01) as season progressed. True ruminal N disappearance (% of intake) decreased quadratically (P = 0.08) as season progressed and was similar between June and July and least in August. Declining ruminal N disappearance was likely affected by CP content of grazed forage and milk intake.
There was a treatment x period interaction (P = 0.02) for intestinal apparent N disappearance (% of intake). Intestinal apparent N disappearance was 51.4, 60.7, and 107.1% of intake for control calves in June, July, and August, respectively, and was 64.8, 48.9, and 59.0% of intake for supplemented calves in June, July, and August, respectively. For control calves, intestinal apparent N disappearance (% of intake) was similar (P = 0.53) for June and July and greater (P = 0.002 and 0.006) during August compared with June and July. It is likely that N recycling to the rumen during August caused increased intestinal apparent N disappearance (107.1% of intake). Increased N recycling to the rumen can cause N flow to the intestine to be greater than intake and thus cause level of intestinal N disappearance to be high. For supplemented calves, there were no differences (P = 0.24 to 0.66) between periods. For June and July, there were no differences (P = 0.34 and 0.40) between treatments, but control calves had greater (P = 0.003) intestinal apparent N disappearance (% of intake) during August.
Intestinal apparent N disappearance (% of intake) was lower (P = 0.08) in supplemented compared with control calves (Table 4). Lower intestinal apparent N disappearance in supplemented calves resulted from greater ruminal N disappearance in supplemented calves, since more N was utilized in the rumen there was less available to the intestine. Soto-Navarro et al. (2004) also observed decreased intestinal N disappearance (% of intake) in supplemented calves and suggested that lower intestinal N disappearance (% of intake) in supplemented calves resulted from a tendency toward greater N intake in supplemented compared with control calves because N (g/d) disappearing intestinally was similar between treatments. Intestinal apparent N disappearance (% of entering) was not different (P = 0.32) between supplemented and control calves. Intestinal N disappearance (% of intake) responded quadratically (P = 0.08) across season and was least in July and greatest in August.
There was a treatment x period interaction (P = 0.06) for apparent total tract N disappearance (% of intake). Apparent total tract N disappearance was 83.9, 74.9, and 58.4% of intake for control calves in June, July, and August, respectively; and was 78.2, 80.5, and 73.8% of intake for supplemented calves in June, July, and August, respectively. For control calves, apparent total tract N disappearance was similar (P = 0.16) for June and July and less (P = 0.001 and 0.02) during August. For supplemented calves, there were no differences (P = 0.24 to 0.68) between periods. For June and July, there were no differences (P = 0.32 and 0.33) between treatments, but apparent total tract N disappearance (% of intake) was greater (P = 0.01) for supplemented calves during August.
Apparent total tract N disappearance (%) was not different (P = 0.12) between treatments and decreased linearly (P = 0.003) across season (Table 4). Soto-Navarro et al. (2004) reported similar results in supplemented vs. control nursing calves consuming brome hay. The percentage of forage OMI to total OMI continually increased throughout season, whereas the percentage of milk and creep OMI to total OMI decreased; this likely explains the decrease in apparent total tract N digestibility across season. As percentage of forage in the diet increased, digestibility and protein quality likely decreased.
Apparent total tract NDF (59.2 and 65.4% of intake for control and supplemented calves, respectively; P = 0.001) and ADF (54.2 and 61.8% of intake for control and supplemented calves, respectively; P = 0.001) disappearance increased in supplemented compared with control calves. The supplement was high in digestible fiber, which may have had a positive influence on fiber digestion. In addition, DIP in the supplement may have had a positive influence on total tract NDF and ADF disappearance in supplemented calves. The supplement in our study was 17.4% CP with a calculated DIP (% of CP) of 69.89%. Apparent total tract NDF (P = 0.001) and ADF (P = 0.07) disappearance (% of intake) responded quadratically across season. Apparent total tract NDF disappearance was 64.4, 57.6, and 64.9% of intake for June, July, and August, respectively. Apparent total tract ADF disappearance was 57.7, 54.9, and 61.3% of intake for June, July, and August, respectively. Similarly, grazed forage IVOMD responded quadratically across season and was least in July.
There was not a treatment x period interaction for ruminal pH (P = 0.72). Ruminal pH was not different (P = 0.40) between treatments (Table 5). Soto-Navarro et al. (2004) reported similar results. Ruminal pH was likely not affected by supplementation because the supplement in our study and that of Soto-Navarro et al. (2004) was based on wheat middlings and soyhulls, which are relatively low in starch and high in potentially fermented fiber components. Others have reported reductions in ruminal pH when supplementing nursing calves with supplements containing greater levels of rapidly fermented carbohydrates (Cremin et al., 1991; Faulkner et al., 1994; Gelvin et al., 2004).
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). Similarly, Gelvin et al. (2004) and Soto-Navarro et al. (2004) reported increased ruminal NH3 concentrations in supplemented calves. Gelvin et al. (2004) suggested the increase was due to increased CP intake from a field-pea based supplement, and Soto-Navarro et al. (2004) suggested increased ruminal NH3 concentrations were due to numerically greater N intakes in supplemented calves. Others have reported decreased ruminal NH3-N concentrations in nursing calves when fed unlimited vs. limited levels of corn-based supplements (Cremin et al., 1991; Faulkner et al., 1994), as well as soybean hull-based supplements (Faulkner et al., 1994). Satter and Slyter (1974) suggested that the concentration of ruminal NH3-N necessary for maximal growth of ruminal microorganisms is 3.57 mM. In our study, the control calves averaged 2.68 mM, and the supplemented calves averaged 3.89 mM of ruminal NH3-N, which may help to explain decreases in NDF and ADF digestion in control calves. Ruminal NH3 concentration responded quadratically (P = 0.001) to advancing season and was highest in July and least in August. This result follows the same pattern as grazed forage CP.
There was not a treatment x period interaction for total VFA (P = 0.32). Total VFA concentrations were not different (P = 0.21) between treatments (Table 5). In contrast, Faulkner et al. (1994), Gelvin et al. (2004), and Soto-Navarro et al. (2004) reported increased total VFA concentrations in supplemented compared with control calves, suggesting that supplements were more rapidly fermented than forage. Gelvin et al. (2004) and Faulkner et al. (1994) fed supplements that were greater in starch than our study, which likely explains differences in total VFA. Soto-Navarro et al. (2004) fed a similar supplement to the supplement in our study, but they fed a lower quality forage (7.43% CP) compared with our study (10.8% CP).
There were treatment x period interactions for acetate:propionate (P = 0.006), acetate (P = 0.001), butyrate (P = 0.003), isobutyrate (P = 0.001), valerate (P = 0.001), and isovalerate (P = 0.007) molar proportions. For acetate:propionate, acetate, butyrate, and valerate, treatment ranking never changed across period; thus, the interactions were caused by magnitude of change. For isobutyrate and isovalerate, supplemented calves had greater molar proportions in June and July and lower proportions in August compared with control calves.
Molar proportions of acetate decreased (P = 0.001), and molar proportions of propionate increased (P = 0.002) in supplemented compared with control calves (Table 5). Therefore, the acetate:propionate decreased (P = 0.001) in supplemented compared with control calves. Lower acetate:propionate in supplemented calves has been reported by numerous researchers (Faulkner et al., 1994; Tarr et al., 1994; Gelvin et al., 2004). Decreased molar proportions of acetate likely reflect the trend for decreased forage intake in supplemented calves, and increased proportions of propionate in supplemented calves are likely the result of consumption of a more energy dense diet.
Molar proportions of butyrate (P = 0.002) and valerate (P = 0.001) increased with supplementation (Table 5). Similarly, Gelvin et al. (2004) reported increased proportions of butyrate and valerate in supplemented calves. Cremin et al. (1991) and Soto-Navarro et al. (2004) reported increased butyrate as a result of supplementation in nursing calves.
Experiment 2
There were no treatment x period interactions for forage OMI (kg/d or % of BW). Forage OMI (kg/d) was not affected (P = 0.30) by treatment; however, forage OMI (% of BW) was greater in control compared with supplemented calves (Table 6). Soto-Navarro et al. (2004) reported no differences in forage OMI when supplementing nursing calves with a supplement similar to the one used in the current study (49% soybean hulls and 44% wheat middlings). Because the supplement was relatively high in digestible fiber and low in starch, negative effects on forage intake were not expected (Soto-Navarro et al., 2004).
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reported no differences in forage intake in nursing calves grazing the same pasture as the one used in the current study when offering 3 different types of supplements. The difference in results may be due to differences in composition of the supplements and intake level. Loy et al. (2002) fed 3 different supplements that were either greater in fiber or DIP than the supplement fed in the current study, and supplement intakes were approximately 50% lower than intakes in the current study. Similar to our results (Exp. 2), Cremin et al. (1991), Faulkner et al. (1994), and Tarr et al. (1994) reported substitution effects of supplementation in nursing calves; forage intake decreased in nursing calves consuming supplements based on corn.
There was a quadratic response for forage OMI (kg/d, P = 0.001; and % of BW, P = 0.001) as season progressed (Table 6). Forage OMI (kg/d) decreased from June to July and increased from July to August. Increased forage OMI (kg/d) in August might be due to increased BW and the need for increased nutrient intake due to declining milk production and forage quality. Forage OMI (% of BW) declined from June to July and increased in August. Others have reported a linear increase in forage OMI (kg/d and % of BW) in nursing calves grazing the same pasture as our study (Loy et al., 2002) or grazing native range in western North Dakota (Gelvin et al., 2004).
There were treatment x period interactions for milk OMI (kg/d, P = 0.02 and % of BW, P = 0.03). Milk OMI (kg/d) was 0.77, 0.31, and 0.30 kg/d for control calves in June, July, and August, respectively, and was 0.42, 0.44, and 0.46 kg/d for supplemented calves in June, July, and August, respectively. Milk OMI (% of BW) was 0.45, 0.18, and 0.16% of BW for control calves in June, July, and August, respectively, and was 0.25, 0.23, and 0.20% of BW for supplemented calves in June, July, and August, respectively. For control calves, milk OMI (kg/d and % of BW) was greater (P = 0.002 and P = 0.006) for June compared with July and August, and July and August were similar (P = 0.96 and 0.77). There were no differences (P = 0.76 to 0.89) between periods for supplemented calves. For June, control calves had greater (P = 0.01 and 0.006) milk OMI (kg/d and % of BW) compared with supplemented calves, and treatments were similar during July and August (P = 0.32 to 0.57).
Milk OMI (kg/d, P = 0.84 and % of BW, P = 0.43) was not different between treatments (Table 6). Numerous researchers have reported no differences in milk intake when comparing supplemented to control calves (Loy et al., 2002; Gelvin et al., 2004; Soto-Navarro et al., 2004). Additionally, Loy et al. (2002) and Faulkner et al. (1994) reported no differences in milk intake among calves offered different types of supplements. As expected, milk OMI (kg/d, P = 0.05 and % of BW, P = 0.004) decreased linearly as season progressed. Declining milk production from the dam is likely due to both declining forage quality and the normal decrease in milk production near the end of lactation (Clutter and Nielsen, 1987). Similarly, Soto-Navarro et al. (2004) reported decreased milk OMI (kg/d and % of BW) as season progressed, and Gelvin et al. (2004) and Loy et al. (2002) reported decreased milk OMI (% of BW) as season progressed.
There was a treatment x period interaction for total OMI (kg/d, P = 0.02). Total OMI (kg/d) was 3.47, 2.37, and 3.20 kg/d for control calves in June, July, and August, respectively, and was 3.23, 3.29, and 4.05 kg/d for supplemented calves in June, July, and August, respectively. For control calves, total OMI (kg/d) was similar (P = 0.42) for June and August and less (P = 0.001 and 0.02) during July. For supplemented calves, total OMI (kg/d) was similar for June and July (P = 0.83) and greater (P = 0.01 and 0.02) in August. Total OMI (kg/d) was similar (P = 0.44) between treatments for June and greater (P = 0.005 and 0.02) in supplemented calves for July and August.
There was a treatment x period interaction for total OMI (% of BW, P = 0.08). Total OMI (% of BW) was 2.09, 1.32, and 1.57% of BW for control calves in June, July, and August, respectively, and was 1.96, 1.69, and 1.87% of BW for supplemented calves in June, July, and August, respectively. For control calves, total OMI (% of BW) was greater (P = 0.001 and 0.005) for June compared with July and August and was similar (P = 0.17) between July and August. For supplemented calves, total OMI (% of BW) was similar (P = 0.11 to 0.61) between periods. Total OMI (% of BW) was similar (P = 0.42 and 0.11) between treatments for June and August and greater (P = 0.03) in supplemented calves during July.
Total OMI (kg/d, P = 0.009 and % of BW, P = 0.08) was greater in supplemented compared with control calves (Table 6). Total OMI (kg/d, P = 0.002 and % of BW, P = 0.001) responded quadratically as season progressed. Total OMI (kg/d and % of BW) decreased from June to July and increased from July to August. The decrease from June to July was mostly due to a decline in milk OMI, whereas the increase from July to August was caused by increased forage OMI.
There were no treatment x period interactions for calf performance (Table 7). There were no differences in initial BW (P = 0.89), final BW (P = 0.95), ADG (P = 0.94), or G:F (P = 0.35) in control vs. supplemented calves. These results are in contrast to results of other researchers. Numerous studies have indicated increased ADG and final BW when comparing nonsupplemented calves with calves receiving unlimited supplement (Prichard et al., 1989; Faulkner et al., 1994; Gelvin et al., 2004). Increased performance has also been reported for calves receiving limited supplement compared with those receiving no supplement (Lardy et al., 2001; Loy et al., 2002).
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). Numerous researchers have evaluated the effects of creep feeding on carcass composition, and results have varied. Large variations in effects of supplementation on carcass characteristics are likely due to variations in type of supplement, supplementation level, and length of time supplemented. For example, Deutscher and Slyter (1978) supplemented calves with a 50:50 mixture of rolled corn and whole oats for approximately 180 d and reported increased carcass weight, dressing percent, carcass grade, marbling score, yield grade, LM area, fat thickness over the 12th rib, and kidney fat. Whereas, Myers et al. (1999) reported no differences in carcass weight, LM area, yield grade, or marbling score between control calves and calves given ad libitum access to ground corn for 55 d, KPH was greater for control compared with supplemented calves. In comparison, calves in the current study were supplemented with a limited amount (0.45% of BW) of wheat middlings and soybean hull-based creep feed for 79 d. The lack of differences in our study could be partially explained by the limited numbers of animals (n = 8). In summary, supplementing nursing calves with wheat middlings and soybean hull-based creep feed increased OMI, total tract OM disappearance, ruminal N disappearance, and tended to increase total tract N disappearance; supplementation had no effects on milk OMI, ruminal pH, total VFA concentration, or microbial efficiency. Supplementation did not affect forage OMI in Exp. 1 and reduced forage OMI in Exp. 2. Supplementation did not affect calf performance and had little effect on carcass composition. Supplementation with a wheat middlings and soybean hull-based creep feed might improve OM and N digestion but might not produce significantly greater BW gains compared with not supplementing.
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Footnotes |
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2 Corresponding author: joel.caton{at}ndsu.edu
Received for publication March 22, 2005. Accepted for publication October 4, 2005.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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