J. Anim Sci. 2008. 86:1263-1270. doi:10.2527/jas.2007-0388
© 2008 American Society of Animal Science
Effect of fat supplementation and wheat pasture maturity on forage intake and digestion characteristics of steers grazing wheat pasture1
D. A. Chabot,
C. D. Chabot,
L. K. Conway and
S. A. Soto-Navarro2
Department of Animal and Range Sciences, New Mexico State University, Las Cruces 88003
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Abstract
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Nine ruminally cannulated mixed-breed steers were used in a split-plot design to evaluate effects of fat supplementation and forage maturity on intake, digestibility, and ruminal fermentation. Treatment was the main plot, and stage of forage maturity was the subplot. Treatments were supplements containing mineral pack (M) offered at 114 g/d; M plus fiber as soybean hulls-wheat middlings (MF) offered at 0.50% BW; and MF plus tallow (MFT) offered at 0.625% BW. Stages of wheat maturity were mid-March (MAR) and early April (APR). Steers grazed in a single wheat pasture with supplements offered individually at 0700 h daily. There were supplement type x forage maturity interactions (P < 0.05) for forage OM, CP, and NDF intakes. During MAR, forage OM, CP, and NDF intakes were not affected (P > 0.05) by supplementation. During APR, forage OM, CP, and NDF intakes differed (MF = M > MFT, P < 0.05). There was also supplement type x forage maturity interaction (P = 0.04) for forage OM digestibility. The OM digestibility differed during MAR (M = MF > MFT, P < 0.05) and during APR (MF > M > MFT, P < 0.05). Crude protein digestibility was affected by supplement type (M > MF > MFT, P < 0.05) and stage of forage maturity (MAR > APR, P < 0.01). Rates of DM and NDF ruminal disappearance were not affected (P > 0.05) by supplement or forage maturity. Supplementation increased (P < 0.05) ruminal propionate concentration (19.7, 21.4, and 25.1 ± 0.49 mol/100 mol for M, MF, and MFT, respectively). Tallow can be used in supplements for cattle grazing wheat pasture to increase energy intake without negatively affecting forage intake or ruminal fermentation, particularly if used in the early stage of wheat maturity.
Key Words: cattle • fat supplementation • stocker • wheat pasture
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INTRODUCTION
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Growing cattle on winter wheat pasture is a production program common in the southern Great Plains. Wheat pasture (Triticum aestivum) is a high-quality forage that contains over 20% CP and over 70% DM digestibility (Mader and Horn, 1986
; Branine and Galyean, 1990). Wheat pasture allows moderately high BW gains (Werrell et al., 1990) at a relatively low cost (Torell et al., 1999), and allows maturation of muscle and bone while restricting fat deposition (Hersom et al., 2004). However, an intramuscular lipid content of 3% is needed for acceptable beef palatability in the United States (Savell and Cross, 1988). If backgrounding systems restrict fat deposition, and intramuscular fat at finishing is difficult to deposit, then cattle need more days on feed and must be slaughtered at heavier weights to achieve acceptable carcass quality (Lewis et al., 1990; Choat et al., 2003). Management schemes to increase intramuscular fat deposition during grazing may reduce days on feed at finishing and improve carcass quality. Intramuscular fat deposition normally increases with increasing energy intake (Owens et al., 1995). Fat supplementation increases diet energy density, ADG, G:F, and carcass fat deposition in feedlot cattle (Zinn and Plascencia, 1996). However, palatability problems and decreased fiber digestibility have been associated with feeding fats to ruminants (Johnson and McClure, 1973). These negative effects probably occur because of a toxic effect of long chain fatty acids on ruminal bacteria (Henderson, 1973). Because the fiber content of immature wheat forage is low, fat supplementation may not have a major negative effect on fiber digestibility of wheat forage. Moreover, it might decrease production of methane by ruminal fermentation, resulting in greater ruminal concentration of propionate (Zinn and Plascencia, 1996) and decreased energy losses (Czerkawski, 1973). The objective of this experiment was to evaluate effects of fat supplementation and wheat pasture maturity on intake, digestibility, and rumen fermentation characteristics.
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MATERIALS AND METHODS
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Treatments and Procedures
All procedures and experimental protocols were approved by the New Mexico State University Institutional Animal Care and Use Committee.
Nine mixed-breed steers (575 ± 29.5 kg of BW) fitted with ruminal cannulas were used in a split-plot design. Treatment was the main plot, and experimental period was the subplot. Steers were assigned randomly to 1 of 3 supplements (Table 1): 1) mineral pack supplement (M) offered at 114 g/steer daily, 2) M plus fiber supplement based on soybean hulls-wheat middlings (MF) offered at 0.50% BW, and 3) MF plus tallow supplement (MFT) consisting of the fiber supplement offered at 0.50% BW and tallow offered at 0.125% of BW [at feeding, MF supplement (80%) and liquid tallow (20%) were mixed by hand]. The M supplement contained 7.9% wheat middlings and was designed to deliver 200 mg/head of monensin daily. The MF supplement contained 48.9% wheat middlings and 40.8% soybean hulls and also was designed to deliver 200 mg/steer daily of monensin. Because of differences in the estimated BW used at the time of formulating the supplements and BW at the time of the experiment, monensin intake was 92.3, 172.9, and 171.1 mg/steer daily for M, MF, and MFT, respectively. The experiment consisted of two 15-d experimental periods; the first 10 d were used for adaptation to wheat pasture grazing and supplement, and the last 5 d for sample collection. Experimental periods occurred during mid March (MAR) and early April (APR). Steers grazed a single wheat pasture (Pounds Plus B, Kelly Green Seeds Inc., Farwell, TX; wheat, triticale, and oat mixture; Triticum aestivum, Triticosecale rimpaui, and Avena sativa, respectively), with supplements offered individually once daily at 0700 h. Steers were allowed access to their supplement for 30 min, after which uneaten supplement was placed into their rumens through the ruminal cannula.
Total fecal output was collected using fecal bags on d 10 through 15 of each collection period. Fecal bags were emptied and weighed twice daily at 12-h intervals. A 10% (wet basis) subsample of feces was collected from each steer daily during both collection periods.
All steers were placed in a holding pen for ruminal evacuations at 0700 h on d 1 of each period. Digesta was placed in plastic bags lining 133-L plastic containers. After evacuation, steers returned to pasture and were allowed to graze for 60 min. Masticate samples were subsequently collected and a 10% sub-sample was retained to estimate in situ and in vitro digestibility and to label forage with Yb. In situ digestibility was determined in both periods using masticate samples collected on d 1 of period 1. Masticate samples were dried in a forced-air oven (50°C) to a constant weight, ground in a Wiley Mill (2-mm screen), and composited on an equal, dry-weight basis within treatment. Five-gram samples were sealed in dacron bags (10 x 20 cm, 50 ± 15 µm pore size; Ankom, Fairport, NY). On d 10 through 13 of each period, composited forage in situ bags were ruminally incubated within nylon lingerie washing bags (30.5 x 25.4 cm) for 72, 48, 36, 24, 18, 12, 8, 4, 2, and 0 h. All bags were removed at 0 h and rinsed with tap water to remove large particulate matter. In situ bags were then rinsed in a top-loading washing machine (delicate cycle). The machine was filled with 45 L of cold water, the bags were agitated for 1 min, and the machine was drained, and then spun for 2 min. This cycle was repeated 5 times for all bags. Bags were dried in a forced-air oven at 50°C, weighed, and stored at room temperature for analysis of DM, CP, NDF, NDIN, and purines.
On d 14 of each period, CoEDTA (200 mL; Uden et al., 1980) was dosed intraruminally at 0600 h as a marker of fluid passage rate. Ruminal fluid samples were collected at 0 (before dosing), 3, 6, 9, 12, 18, and 24 h after dosing. Ruminal fluid pH was determined immediately after collection, and the samples were then acidified with 7.2 N NH2SO4 at a rate of 1 mL/100 mL of ruminal fluid and frozen (–10°C) in whirl pack bags for later analysis of Co, ammonia, and VFA. Also on d 14, Yb-labeled wheatgrass (1 kg; Sindt et al., 1993) was intraruminally dosed at 0600 h as a marker of particulate passage rate. Ruminal content samples were collected at 0 (before dosing), 3, 6, 9, 12, 18, 24, 36, and 48 h after dosing.
Wheat forage was labeled with Yb as described by Sindt et al. (1993). In brief, wheat forage was allowed to soak in a tub with 64.22 g of Yb/kg of wheat forage for 12 h at 25°C. Excess marker solution was strained through 4 layers of cheesecloth. Tap water was added to the feed, and pH was adjusted to 4.5 with HCl. Then feed plus water was allowed to soak for an additional 6 h and was rinsed with tap water 4 times. During rinsing, excess tap water was strained through 4 layers of cheesecloth, and labeled wheat forage was dried in a forced-air oven at 55°C for 48 h.
At 0600 h on d 15 of each experimental period, a 2-kg subsample of ruminal contents was obtained and mixed with 1 L of saline solution (0.9% NaCl, wt/vol) for isolation of bacterial cells (Zinn and Owens, 1986). Ruminal content samples were frozen (–10°C) for later proximate analysis.
Laboratory Analyses
Fecal samples were thawed, mixed, and subsampled (10% of total), then fecal, supplement, and masticate samples were dried in a forced-air oven (50°C) for 48 h. Samples were then allowed to equilibrate at room temperature and ground to pass a 2-mm screen (Model 4 Thomas A. Wiley Laboratory Mill, Thomas Scientific, Swedesboro, NJ). Fecal, masticate, and supplement samples were analyzed for DM, OM, and CP (Methods 930.15, 942.05, and 990.02, respectively; AOAC, 1997). Also, NDF analysis was performed according to Robertson and Van Soest (1991) using an Ankom 200 fiber analyzer (Ankom Co.) sequentially.
In vitro OM digestibility of masticate samples and supplements were determined according to procedures described by Tilley and Terry (1963) using composited inoculate from 2 ruminally cannulated steers fed a grass hay diet.
Ruminal fluid samples were centrifuged at 20,000 x g for 20 min and analyzed for NH3-N (Broderick and Kang, 1980), VFA (Goetsch and Galyean, 1983), and Co. Cobalt was determined using an air-plus-acetylene flame using atomic absorption spectroscopy, as described by Uden et al. (1980). Ytterbium was extracted from ruminal samples as outlined by Hart and Polan (1984), and marker concentration was determined by atomic absorption spectroscopy using a nitrous oxide-plus-acetylene flame.
Ruminal bacteria were isolated from a 2-kg sample of rumen contents. Ruminal contents were blended on high speed in a food processor for 1 min, and the mixture was strained through 4 layers of cheesecloth. Feed particles and protozoa in ruminal samples were removed via centrifugation at 1,000 x g for 10 min. Bacteria were separated from the supernatant by centrifugation at 27,000 x g for 20 min. Isolated bacteria was dried in a forced air oven (50°C) and analyzed for DM, ash, N (as described previously), and purines (Zinn and Owens, 1986).
In situ samples were composited by time, steer, and period and analyzed for DM, CP, and purines as described previously. Also, in situ samples incubated at 2 and 12 h were analyzed for NDIN by performing NDF analysis followed by CP analysis on the NDF residue as described previously. Both NDF and CP analysis were performed as described previously.
Calculations
Forage intake was calculated using the total fecal output and forage in vitro OM indigestibility. Forage fecal output (DM) was converted to an OM basis using the OM percentage of feces. Forage fecal output on an OM basis was determined by subtracting the indigestible fraction of the supplement from feces of supplemented steers using in vitro OM indigestibility of the supplement. To determine forage OM intake, forage fecal OM output was divided by forage in vitro OM indigestibility. Liquid dilution rate was calculated by regressing the natural log of Co concentration on sampling time, and particle dilution rate was calculated by regressing the natural log of Yb concentration on sampling time.
In situ DM and NDF disappearance (%/h) were estimated using the model described by Mertens and Loften (1980). In situ CP data were evaluated using the Ørskov and McDonald (1979) model, [d = a + b (1 – e–kd)], where a is the soluble fraction, b is the slowly degradable fraction, d is the extent of digestion, and kd is the rate of degradation. Protein remaining in in situ bags was adjusted for microbial protein contribution. Microbial protein was calculated using the N to purine ratio of ruminally isolated bacteria and purine content of in situ remaining material. Also, the rates of CP ruminal disappearance were calculated from NDIN at 2- and 12-h in situ incubations as described by Mass et al. (1999).
The undegradable intake protein (UIP) values of masticate samples were calculated using the following equation (adapted from Broderick, 1994): UIP (% of DM) = {[kp/(kp + kd)] x in situ slowly degradable CP fraction} + in situ insoluble CP fraction, where kp is the particle dilution rate, and kd is the rate of protein degradation. In situ insoluble CP fraction was calculated by subtracting CP effective degradability from 100. The UIP values were calculated by 2 different approaches. Each approach consisted of the same formula as described previously and only differed on how the kd was estimated. The first approach used kd estimated using the Ørskov and McDonald (1979) model, and the second approach used kd estimated using the Mass et al. (1999) model. Both estimations are reported.
Statistical Analysis
Data were analyzed as a split plot design using the mixed procedure of SAS (SAS Inst. Inc., Cary, NC). Treatment was included in the main plot and period was in the subplot. For intake, digestibility, liquid and particle passage rates, and in situ data, the model included treatment, period, and period x treatment interaction. The repeated effect was period, and animal within treatment was used to test treatment effects. When significant (P < 0.05) F-statistics were noted, means were separated using LSD.
The mixed procedure of SAS was also used to analyze the ruminal fermentation data (pH, NH3-N, VFA) using a split-split-plot design. Effects in the model included treatment, period, and period x treatment interaction. The repeated effect was time and animal within period x treatment was used as the error term for split-split-plot. Individual steer was the experimental unit in all analyses.
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RESULTS AND DISCUSSION
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Effects of supplement type and stage of forage maturity on OM, CP, and NDF intake and digestibility are shown in Table 2. There were supplement type x forage maturity interactions (P < 0.05) for forage OM, CP, and NDF intakes. During MAR, forage OM, CP, and NDF intakes were not affected (P > 0.05) by supplementation. However, for APR grazing, forage OM, CP, and NDF intakes were greater (P < 0.05) for M and MF supplemented steers than those supplemented with MFT. When total OM intake was expressed as grams per kilogram of BW, a supplement type x forage maturity interaction (P < 0.05) was also observed. During MAR, total OM intake (g/kg of BW) was (P < 0.05) greater for MFT-supplemented steers intermediate for MF-steers and lesser for those receiving M. During APR, total OM intake (g/kg of BW) was greater (P < 0.05) for MF-steers than those receiving M, but MFT was not different (P > 0.05) from M or MFT. A supplement type x forage maturity interaction was observed (P = 0.02) for OM digestibility. During MAR, OM digestibility was greater (P < 0.05) for M and MF than MFT. During APR, OM digestibility was greater for MF intermediate for M and lesser for MFT. Digestibility of CP was greater (P = 0.01) for M and MF than MFT (68.34, 65.91, and 60.45 ± 1.33% for M, MF, and MFT, respectively). Also, CP digestibility was greater (P < 0.01) during MAR than during APR (69.46 and 60.45 ± 1.15% for MAR and APR, respectively). Digestibility of NDF was greater (P < 0.05) for M and MF than for MFT (55.99, 53.81, and 49.00 ± 0.895% for M, MF, and MFT, respectively). Digestibility of NDF was not affected (P = 0.16) by forage maturity (54.10, and 51.77 ± 0.89%, for MAR and APR, respectively).
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Table 2. Effect of supplement type1 and forage maturity2 on OM intake and digestion of beef steers grazing wheat pasture
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Our results for OM intake and digestibility agree partially with results of Horn et al. (1995) who suggested that supplementing cattle grazing wheat pasture with a highly digestible fiber source improves intake, digestibility, and performance. In the present study during MAR, total OM intake increased with supplementation, but OM digestibility was not affected by MF and decreased with MFT. The increase of OM intake by cattle grazing wheat pasture when supplemented with a source of highly digestible fiber is most likely due to the fact that wheat pasture contains excess CP. Supplementing cattle grazing wheat pasture with an energy source improves the ruminal environment by improving the OM:CP ratio and increases the efficiency of the ruminal microbes (Pond et al., 1995). Little information is available on addition of fat to diets of stocker cattle grazing wheat pasture. Most of the information available on addition of fat to cattle grazing has been developed with cattle grazing medium- to low-quality forages. When tallow has been supplemented to cattle consuming medium to low-quality forages, it has decreased fiber digestibility by inhibiting fibrolytic bacteria (Palmquist, 1988) and diminished ruminal fermentation of fiber in sheep (Jenkins et al., 1989). Because wheat pasture forage is highly digestible, similar results to those observed when fat is included in feedlot finishing diets were expected (Zinn and Plascencia, 1996). Our data suggest that supplementing tallow in combination with highly digestible fiber early in the stage of wheat maturity improved OM and NDF intake, but as forage maturity increased, tallow supplementation did not improve OM or NDF intake or OM digestibility as previously observed (Palmquist, 1988).
Interactions of supplement type x forage maturity were not observed (P > 0.10; Table 3) for DM particle flow rate (%/h), ruminal volume (L), fluid dilution rate (%/h), fluid flow rate (L/h), and turnover time (h). Therefore, simple effects are discussed. Ruminal volume (103.9, 92.8, and 72.2 ± 8.07 L) and fluid flow rate (10.3, 9.1, and 8.3 ± 0.5 L/h) tended to decrease (P 
0.08) for MFT compared with M supplemented steers, with MF supplemented steers being intermediate between the other treatments (P 
0.10). Ruminal volume and passage rate were expected to be greater for MFT than M because of the greater OM intake (Table 2
) and DMI (Table 3) observed for MFT. The reason for this discrepancy is not apparent, but we speculate that steers receiving the M treatment may have experienced more thirst after consuming the supplement and therefore consumed more water than the other treatment groups. The ruminal volume of MF and MFT steers agrees with their respective DMI.
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Table 3. Effect of supplement type1 and forage maturity2 on DM intake, ruminal volume, fluid dilution rate, fluid flow rate, turnover time, and particulate flow rate in beef steers grazing wheat pasture
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Fluid flow rate (7.9 and 10.6 ± 0.54 L/h) increased (P = 0.02) and turnover time (12.5 and 7.4 ± 0.99 h) decreased (P = 0.02) for steers grazing wheat during the APR compared with MAR grazing. Fluid flow rate increased as stage of maturity advanced, probably because during APR forage particles were retained longer. Fluid dilution rate (9.1 and 14.3 ± 1.6%/h) tended to increase (P = 0.09) for steers grazing wheat pasture during APR as compared with when they grazed wheat in MAR. Particle flow rate was expected to decrease with increasing NDF intake and coarseness of forage, and decreasing forage digestibility with advancing stage of maturity. Welch (1982) suggested that coarseness, greater particle size, or both, decreases particle passage rate.
Ruminal CP kinetics, in situ DM and NDF disappearance, and wheat pasture UIP are shown in Table 4. An interaction was observed for in situ soluble CP fraction. Soluble CP fraction was not affected (P = 0.98) by supplement type during MAR. However, during APR, MF had a greater (P = 0.05) CP soluble fraction than M and MFT. An interaction was also observed (P = 0.01) for the CP slowly degradable fraction. The slowly degradable fraction was not affected (P = 0.10) by supplement type in MAR. In APR, MF had a smaller (P = 0.04) slowly degradable fraction than M and MFT. These results are inverse to the soluble fraction, and this might be due to the availability of the CP after subtracting the soluble fraction. Another interaction was observed (P = 0.01) for degradation rate of the slowly degradable fraction. Rate of degradation was not affected (P = 0.57) during MAR. But during APR, MF tended (P = 0.07) to have a slower degradation rate than M. The slower degradation rate for MF is likely due to the smaller amount of CP available for digestion after subtracting the soluble fraction. We also observed that degradation rate increased (P = 0.01) with advancing stage of maturity (3.21 and 9.67 ± 0.58%/h for MAR and APR, respectively). We were able to visually observe that as the forage matured, the coarseness of the wheat increased. Therefore, it can be speculated that the increased coarseness increased the physical friction, which contributed to remove more material from the in situ bags. The greater removal of material resulted in a greater rate of CP disappearance. When CP degradation rate was estimated using the NDIN technique, APR tended (P = 0.07) to be greater than MAR (2.36 and 2.96 ± 0.38%/h). An interaction for CP effective degradability was observed (P = 0.02). During MAR, in situ effective degradability was greater (P = 0.05) for MF than MFT. However, during APR treatment did not affect (P > 0.10) CP effective degradability. The high in situ CP degradation is consistent with the high ammonia concentration observed in this study.
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Table 4. Effect of supplement type1 and forage maturity2 on CP kinetic parameters, rate of in situ DM and NDF ruminal disappearance of wheat pasture masticates, and UIP from wheat masticates in beef steers grazing wheat pasture
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Rates of DM and NDF ruminal disappearance were not affected (P > 0.05) by supplement type or stage of forage maturity. Supplemental fat in excess of 2 to 3% of dietary DM intake inhibits fibrolytic bacteria (Palmquist, 1988). Also, the depressing effect of fat on fiber digestion might also be partially due to physical coating of fiber particles, forming a lipid barrier that impedes enzyme penetration (MacLeod and Buchanan-Smith, 1972). In the present study, fat supplementation (DM basis) was calculated to be 6.85% for MAR and 8.08% for APR. However, no differences in in situ DM or NDF disappearance were noted when tallow was added to the supplement.
Estimations of UIP were greater (P = 0.02) for MAR than for APR when estimated using CP disappearance adjusted for microbial protein using purines. However, when the NDIN technique was used, no effects of treatment or period were observed. The UIP estimates are in close agreement for MAR. However, for APR the values estimated using the NDIN technique are from 18.7 to 27.6 percentage points greater than those estimated with the purine technique. Such discrepancy was due to the greater CP degradation rate estimated for APR using the purine technique. These data do not agree with Gunter et al. (1993) who estimated UIP on duodenal chyme of heifers grazing midgrass prairie rangeland or sideoats grama/sweetclover pasture and found a greater extent of ruminal N degradation with NDIN than with purines technique. The usual method to estimate UIP is the in situ bag method (Broderick, 1994). In this discussion, the in situ bag method is being termed the purines method because microbial contamination has been corrected using purines as the correction method (Zinn and Owens, 1986). The in situ bag technique for UIP estimation and the purine microbial correction method are labor intensive and expensive. Sniffen et al. (1992) hypothesized that NDIN is the primary UIP fraction of feedstuff. Mass et al. (1999) evaluate Sniffen’s hypothesis with 6 hay sources ranging from low to high quality and 2 (low and high quality) range masticates and concluded that in situ NDIN provide estimates of forage UIP that are equal to those estimated using the purine technique. In this particular study, the NDIN method used incubation times closer to the estimated time that the wheat forage remained in the rumen. Therefore, that can be a criterion to decide which method is more accurate. Even though, this paper reports about 90% in situ CP effective degradability, UIP values were estimated to be between 35 and 70%. The fast passage rates observed in this experiment is the cause of the high UIP estimates. Therefore a considerable amount of protein bypasses the rumen and is available for absorption in the small intestine of cattle grazing wheat pasture. This protein bypass may explain why Vogel et al. (1989) and Smith et al. (1989) failed to observe improved performance of cattle grazing wheat pasture with bypass protein supplementation.
Supplement and wheat pasture stage of maturity effects on ruminal pH, ammonia, total VFA, and VFA molar proportions are shown in Table 5. Ruminal pH decreased (P < 0.05) and ruminal ammonia concentration tended to decrease (P = 0.12) with advancing stage of maturity of wheat pasture. Because total OM intake, OM digestibility, and total VFA concentration were not affected by stage of maturity, the decrease of pH was not expected and causes are not apparent. The tendency of ruminal ammonia concentration to decrease with advancing stage of forage maturity was due to the lower numerical CP intake during APR compared with MAR. Protein content of wheat pasture decreases rapidly with advancing stage of maturity (Johnson et al., 1973; Reuter and Horn, 2000).
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Table 5. Effect of supplement type1 and forage maturity2 on ruminal pH, ammonia, and VFA molar proportion in beef steers grazing wheat pasture
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Total ruminal VFA concentration was not affected (P = 0.26) by supplement type or (P = 0.40) stage of wheat pasture maturity. However, an interaction (P = 0.01) was observed for ruminal acetate molar proportion. During MAR, acetate molar proportion was smaller (P = 0.01) for MFT than M and MFT. However, for APR, acetate molar proportion was smaller for M and MFT than MF. Ruminal propionate molar proportion increased (P = 0.01) for MFT supplemented steers (19.7, 21.4, and 25.1 ± 0.49 mol/100 mol for M, MF, and MFT, respectively). Additionally, an interaction (P = 0.01) was observed for acetate:propionate ratio. During MAR, acetate:propionate ratio was smaller (P < 0.05) for MFT intermediate for MF and greater for M. However, for APR, acetate molar proportion was smaller (P < 0.05) for MFT than for M and MF. The acetate:propionate molar proportion was smaller for MFT during both periods due to the decrease on acetate molar proportion and the increase on propionate molar proportion observed during both period. Fat supplementation increases propionate concentration and decreases methane production in feedlot diets (Zinn and Plascencia, 1996). Ruminants use propionate for gluconeogenesis (Fahey and Berger, 1988). Smith and Crouse (1984) demonstrated that glucose provides 50 to 75% of the acetyl units for in vitro lipogenesis in the intramuscular fat depot. Therefore, elevated propionate concentration from fat supplementation may be a key component in triggering intramuscular adipocyte development in young calves grazing wheat pasture.
In conclusion, tallow can be used in wheat pasture supplements to increase energy intake without negatively affecting forage intake, or ruminal fermentation, particularly if used early in the stage of wheat maturity. Tallow supplementation slightly (2.7 percentage units) decreased OM digestibility during MAR grazing; however, the negative effect on OM digestibility was more severe during APR (5.8 percentage units). In addition to increasing energy intake, tallow promotes a greater ruminal propionate concentration. Additional studies are needed to determine if this regimen influences performance and carcass composition.
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Footnotes
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1 This research was supported by the New Mexico Agricultural Experiment Station. 
2 Corresponding author: ssoto{at}nmsu.edu
Received for publication July 2, 2007.
Accepted for publication January 14, 2008.
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LITERATURE CITED
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AOAC. 1997. Official Methods of Analysis. 16th ed. Assoc. Off. Anal. Chem., Arlington, VA.
Branine, M. E., and M. L. Galyean. 1990. Influence of grain and monensin supplementation on ruminal fermentation, intake, digesta kinetics and incidence and severity of frothy bloat in steers grazing winter wheat pasture. J. Anim. Sci. 68:1139–1150.[Abstract/Free Full Text]
Broderick, G. A. 1994. Quantifying forage protein quality. Pages 200–228 in Forage Quality, Evaluation, and Utilization. G. C. Fahey, Jr., ed. American Society of Agronomy, Crop Science Society of America, Soil Science of America, Madison, WI.
Broderick, G. A., and J. H. Kang. 1980. Automated simultaneous determination of ammonia and total amino acids in ruminal fluid and in vitro media. J. Dairy Sci. 63:64–75.[Abstract/Free Full Text]
Choat, W. T., C. R. Krehbiel, G. D. Duff, R. E. Kirksey, L. M. Lauriault, J. D. Rivera, B. M. Capitan, D. A. Walker, G. B. Donart, and C. L. Goad. 2003. Influence of grazing dormant native range or winter wheat pasture on subsequent finishing cattle performance, carcass characteristics, and ruminal metabolism. J. Anim. Sci. 81:3191–3201.[Abstract/Free Full Text]
Czerkawski, K. L. 1973. Effect of linseed oil fatty acids and linseed oil rumen fermentation in sheep. J. Agric Sci. (Camb.) 81:517–531.
Fahey, G. C., Jr., and L. L. Berger. 1988. Carbohydrate nutrition of ruminants. Pages 269–297 in The Ruminant Animal-Digestive Physiology and Nutrition. D. C. Church, ed. Waveland Press Inc., Prospect Heights, IL.
Goetsch, A. L., and M. L. Galyean. 1983. Influence of feeding frequency on passage of fluid and particulate markers in steers fed a concentrate diet. Can. J. Anim. Sci. 63:727–730.
Gunter, S. A., F. T. McCollum III, R. L. Gillen, and L. J. Krysl. 1993. Forage intake and digestion by cattle grazing midgrass prairie rangeland or sideoats grama/sweetclover pasture. J. Anim. Sci. 71:3432–3441.[Abstract]
Hart, S. P., and C. E. Polan. 1984. Simultaneous extraction and determination of ytterbium and cobalt ethylenediaminetetrs-acetate complex in feces. J. Dairy Sci. 67:888–892.[Abstract/Free Full Text]
Henderson, C. 1973. The effects of fatty acids on pure cultures of rumen bacteria. J. Agric. Sci. (Camb.) 81:107–112.
Hersom, M. J., G. W. Horn, C. R. Krehbiel, and W. A. Phillips. 2004. Effect of live weight gain of steers during winter grazing: I. Feedlot performance, carcass characteristics, and body composition of beef steers. J. Anim. Sci. 82:262–272.[Abstract/Free Full Text]
Horn, G. W., M. D. Cravey, F. T. McCollum, C. A. Strasia, E. G. Krenzer Jr., and P. L. Claypool. 1995. Influence of high-starch vs. high-fiber energy supplements on performance of stocker cattle grazing wheat pasture and subsequent feedlot performance. J. Anim. Sci. 73:45–54.[Abstract]
Jenkins, T. C., T. Gimenez, and D. L. Cross. 1989. Influence of phospholipids on ruminal fermentation in vitro and on nutrient digestion and serum lipids in sheep. J. Anim. Sci. 67:529–537.[Abstract/Free Full Text]
Johnson, R. R., and K. E. McClure. 1973. High fat rations for ruminants. II Effect of fat added to corn plant material prior to ensiling on digestibility and voluntary intake of the silage. J. Anim. Sci. 36:397–406.[Abstract/Free Full Text]
Johnson, R. R., M. McGeehan, E. Williams, and H. C. Young Jr. 1973. Studies on the nutritive value of wheat pasture. Page 13 in Oklahoma State Univ. Res. Rep., MP-90. Oklahoma Agric. Exp. Stn., Stillwater.
Lewis, J. M., T. J. Klopfenstein, and R. A. Stock. 1990. Effects of rate of gain during winter on subsequent grazing and finishing performance. J. Anim. Sci. 68:2525–2529.[Abstract]
MacLeod, G. K., and J. G. Buchanan-Smith. 1972. Digestibility hydrogenated tallow, saturated fatty acids and soybean oil-supplemented diets by sheep. J. Anim. Sci. 35:890–895.[Abstract/Free Full Text]
Mader, T. L., and G. W. Horn. 1986. Low-quality roughage for steers grazing wheat pasture. II. Effect of wheat forage intake and utilization. J. Anim. Sci. 62:1113–1119.[Abstract/Free Full Text]
Mass, R. A., G. P. Lardy, R. J. Grant, and T. J. Klopfenstein. 1999. In situ neutral detergent insoluble nitrogen as a method for measuring forage protein degradability. J. Anim. Sci. 77:1565–1571.[Abstract/Free Full Text]
Mertens, D. R. and J. R. Loften. 1980. The effect of starch on forage fiber digestion kinetics in vitro. J. Dairy Sci. 63:1437–1446.[Abstract/Free Full Text]
Ørskov, E. R., and I. McDonald. 1979. The estimation of protein degradability in the rumen from incubation measurements weighed according to rate of passage. J. Agric. Sci. 92:499–503.
Owens, F. N., D. R. Gill, D. S. Secrist, and S. W. Coleman. 1995. Review of some aspects of growth and development of feedlot cattle. J. Anim. Sci. 73:3152–3172.[Abstract]
Palmquist, D. L. 1988. The feeding value of fats. Page 293 in Feed Science. E. R. Ørskov, ed. Elsevier Science Publishers, New York, NY.
Pond, W. G., D. C. Church, and K. R. Pond. 1995. Basic Animal Nutrition and Feeding. 4th ed. John Wiley & Sons Inc., New York, NY.
Reuter, R. R., and G. W. Horn. 2000. Changes in growth performance of steers and nutritive value of wheat pasture from fall/winter grazing to graze-out. Anim. Sci. Res. Report No. P-980:20–27. Oklahoma Agric. Exp Stn., Stillwater.
Robertson, J. B., and P. J. Van Soest. 1991. Methods for dietary fiber, neutral detergent fiber, and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:3583–3597.[Abstract]
Savell, J. W., and H. R. Cross. 1988. The role of fat in the palatability of beef, pork, and lamb. Page 345–355 in Designing Foods: Animal Product Options in the Marketplace. National Academy Press, Washington, DC.
Sindt, M. H., R. A. Stock, T. J. Klopfenstein, and D. H. Shain. 1993. Effect of protein source and grain type on finishing calf performance and ruminal metabolism. J. Anim. Sci. 71:1047–1056.[Abstract]
Smith, M. E., W. A. Phillips, and G. W. Horn. 1989. Protein supplementation of growing ruminants on wheat pasture. Proc. Western Section Meeting Am. Soc. Anim. Sci. 40:256–259.
Smith, S. B., and J. D. Crouse. 1984. Relative contribution of acetate, lactate, and glucose to lipogenesis in bovine intramuscular and subcutaneous adipose tissue. J. Nutr. 114:792–800.[Abstract/Free Full Text]
Sniffen, C. J., J. D. O’Connor, P. J. Van Soest, D. J. Fox, and J. B. Russell. 1992. A net carbohydrate and protein system for evaluating cattle diets: II Carbohydrates and protein availability. J. Anim. Sci. 70:3562–3577.[Abstract]
Tilley, J. M. A., and R. A. Terry. 1963. A two-stage technique for the in vitro digestion of forages. J. Br. Grassl. Soc. 18:104–111.
Torell, R., W. Riggs, B. Bruce, and B. Kuasnicka. 1999. How good is wheat pasture for grazing lightweight calves? Nevada Agric. Ext. Svc. Fact Sheet 99–40.
Uden, P., P. E. Colucci, and P. J. Van Soest. 1980. Investigation of chromium, cerium, and cobalt as markers in digesta. Rate of passage studies. J. Sci. Food Agric. 31:625–632.[Medline]
Vogel, G. J., G. W. Horn, W. A. Phillips, C. A. Strasia, and J. J. Martin. 1989. Effects of supplemental protein on performance of stocker cattle grazing wheat pasture. Pages 208–216 in Anim. Sci. Res. Rep., MP-90. Oklahoma Agric. Exp. Stn., Stillwater.
Welch, J. G. 1982. Rumination, particle size and passage rate from the rumen. J. Anim. Sci. 54:885–894.[Abstract/Free Full Text]
Werrell, M. A., D. J. Undersander, C. E. Thompson, and W. C. Bridges Jr. 1990. Effects of time of season and cottonseed meal and lasalocid supplementation on steers grazing rye pastures. J. Anim. Sci. 68:1151–1157.[Abstract/Free Full Text]
Zinn, R. A., and F. N. Owens. 1986. A rapid procedure for purine measurement and its use for estimating net ruminal protein synthesis. Can. J. Anim. Sci. 66:157–166.
Zinn, R. A., and A. Plascencia. 1996. Effects of forage levels on the comparative feeding value of supplemental fat in growing-finishing diets for feedlot cattle. J. Anim. Sci. 74:1194–1201.[Abstract]
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Abstract
INTRODUCTION
