Responses in the rumen microbiome of Bos taurus and indicus steers fed a low-quality rice straw diet and supplemented protein.

Bos indicus typically perform better than Bos taurus when consuming a low-quality diet; however, the response to supplementation is generally greater in B. taurus. The underlying mechanisms supporting these responses have not been fully elucidated. Characterization of differences in rumen prokaryotic populations and their functional role in the two subspecies may provide additional insight. Ten cannulated steers (5 Angus and 5 Brahman) were used in concurrent 5 × 5 Latin squares. Animals were offered ad libitum access to rice straw (4.7% CP). Treatments consisted of an unsupplemented control diet and two levels (50 or 120 mg N/kg BW) of isonitrogenous supplements (30% CP), that were either high (H; 74%) or low (L; 26%) in undegradable intake protein. Rumen samples were collected at 0 and 4 h postfeeding and separated into liquid and solid fractions. Rumen bacterial taxa were sequenced utilizing a Roche 454 platform based on the 16s rRNA gene. At 97% sequence similarity, 97,826 operational taxonomic units were identified, which included 24 phyla, 108 families, and 255 genera. Analysis included SAS PROC mixed model, QIIME, and PICRUSt. Across all samples, Bacteroidetes and Firmicutes accounted for 65% and 28% of total bacterial abundance, respectively. The families Prevotellaceae (P = 0.05) and Ruminococcaceae (P = 0.004) and the genera Prevotellaceae (family; P = 0.003) within the phyla Bacteroidetes differed significantly in relative abundance with added protein when compared to the control. Consistent differences in the relative abundance of family and genus taxa between B. indicus and B. taurus suggest roles the symbiotic rumen microbiome may have in the capacity of B. indicus to utilize low-quality forage over a range of supplement types and levels including (Prevotella, Ruminococcus [family], Sphingobacteriaceae [family], Bacteroidales [order], Pontibacter, Bacteroides, Succiclasticum, Barnesiella, and Xylanibacter). Overall bacterial community diversity differences across parameters were limited. Rice straw is recalcitrant to bacterial digestion because of high levels of silica in the epidermis making this straw more resistant to bacterial attachment. Thus, this analysis represents the bacterial diversity and function of the rumen under conditions depleted CP, recalcitrant fiber matrix and restricted digestibility which appear to limit the microbial population to those capable of attaching and digesting complexed structural carbohydrates, resulting in reduced plasticity, and more evenness in diversity across parameters.

Effect of monensin withdrawal on intake, digestion, and ruminal fermentation parameters by Bos taurus indicus and Bos taurus taurus steers consuming bermudagrass hay.

Effects of monensin withdrawal and cattle subspecies on the utilization of bermudagrass hay (14.3% CP, 72.3% NDF, and 36.9% ADF) were evaluated using ruminally cannulated steers (5 [BI] and 5 [BT]). Subspecies were concurrently subjected to a 2-period, 2-treatment crossover design. Treatments consisted of either 0 mg·steer·d-1 monensin with no previous monensin feeding (CON) or withdrawal from 200 mg·steer·d-1 monensin (MON) fed individually in 0.91 kg dried distillers' grains with solubles for 42 d. Withdrawal was evaluated for a 28-d period. Ruminal fluid was collected 2 h after feeding on d 0, 1, 4, 7, 14, and 21 after withdrawal for determination of pH, VFA, ruminal NH-N (RAN), rate of NH production, and CH production rate. Hay, ort, and fecal grab samples were collected d 23 through 28 after withdrawal for determination of intake and digestion. No subspecies × monensin, subspecies × day, or subspecies × monensin × day interactions were observed ( ≥ 0.11). An effect of day after monensin withdrawal was observed ( < 0.01) for total VFA concentration, with an increase following withdrawal followed by a decrease and then stabilization. Monensin × day after monensin withdrawal interactions ( ≤ 0.01) were observed for the acetate:propionate (A:P) ratio and molar percent of acetate and propionate. There was a decrease in molar percent of propionate between d 1 and 4 from 19.1 to 18.0; however, it remained greater ( ≤ 0.10) for MON than CON through d 7. Withdrawal increased molar percent of acetate from 68.3 to 69.8 between d 0 and 4 for MON steers. The A:P ratio was less ( ≤ 0.01) on d 0 for MON than for CON (3.4 vs. 4.0), but by d 4, it increased to 3.8 and was not different ( = 0.14) from CON. By d 14, no differences ( ≥ 0.88) remained for acetate, propionate, or the A:P ratio. After monensin withdrawal, monensin reduced ( < 0.01) RAN by 12.3% (2.09 vs. 1.83 m for CON and MON, respectively). Monensin withdrawal and cattle subspecies had no effect ( ≥ 0.23) on rate of NH production or CH production rate. Monensin withdrawal had no effect ( ≥ 0.45) on intake or digestibility parameters. Greater forage OM intake ( = 0.09; 21.2 vs. 19.2 g/kg BW) and OM digestibility ( < 0.01; 72.4 vs. 63.0%) resulted in greater ( < 0.01) total digestible OM intake (16.8 vs. 13.2 g/kg BW) in BT steers than in BI steers. These results suggest that BT steers are better able to utilize bermudagrass hay than BI steers. Upon monensin withdrawal, steers previously fed monensin continue to have a reduced A:P ratio for at least 7 d.

Effect of monensin inclusion on intake, digestion, and ruminal fermentation parameters by Bos taurus indicus and Bos taurus taurus steers consuming bermudagrass hay.

Effects of monensin inclusion and cattle subspecies on utilization of bermudagrass hay (13.7% CP, 77.3% NDF, and 38.8% ADF) were evaluated using ruminally cannulated steers (5 [BI] and 5 [BT]; 398 kg BW). Subspecies were concurrently subjected to a 2-period, 2-treatment crossover design. Treatments were 0 (CON) or 200 mg·steer·d monensin (MON) in 0.91 kg dried distillers' grains with solubles. Periods were 70 d in length: 20 d of adaptation, 22 d of sample collection, and 28 d for withdrawal of treatment. Steers were group housed during adaptation and moved to individual covered pens for sampling. Hay, ort, and fecal grab samples were collected d 21 through 25 for determination of intake and digestion. Ruminal fluid was collected with a suction strainer 0, 2, 4, 8, and 12 h after feeding on d 42 for pH, VFA, and ruminal NH-N (RAN) analysis. Additionally, at h 2, ruminal fluid and contents were collected for determination of rate of NH production and CH production rate. No subspecies × monensin interactions were observed ( ≥ 0.12). Monensin had no effect ( ≥ 0.16) on intake or digestibility parameters. No subspecies effect ( ≥ 0.11) was observed for forage OM intake, total OM intake, or OM digestion. Total digestible OM intake tended to be greater ( = 0.06) for BT steers than for BI steers (14.0 vs. 12.2 g/kg BW). There was an effect of hour after feeding ( ≤ 0.01) on pH, total VFA, acetate:propionate ratio, and molar percent acetate and propionate. Total VFA concentration was greater ( = 0.01) in CON steers than in MON steers (66.5 vs. 62.0 m). Monensin decreased molar percent acetate ( = 0.02) from 72.5 to 71.2% and increased molar percent propionate ( < 0.01) from 16.9 to 18.7%, resulting in a reduced ( < 0.01) acetate:propionate ratio (from 4.34 to 3.85). Although not significantly ( = 0.19), monensin numerically reduced the CH production rate by 15.8%. Greater ( = 0.07) CH production rate tended to be observed in BI steers than in BT steers (21.4 vs. 16.6 µmol CH·mL·h, respectively). Monensin had no effect ( ≥ 0.32) on pH, RAN, or rate of NH production. A subspecies × hour after feeding interaction was observed for RAN, with BT having greater RAN at h 0 and 4, whereas BI had greater RAN at h 2, 8, and 12. Overall, monensin decreased the acetate:propionate ratio and total VFA concentration but had no effect on forage utilization. steers consumed less digestible OM and had a greater CH production rate compared with BT steers, suggesting BT were better able to utilize the available forage resource than BI.

Effect of source and level of protein supplementation on rice straw utilization by Brahman steers.

Seven ruminally cannulated Brahman steers were used in a 7 × 4 incomplete block design to determine the effects of cottonseed meal (CSM; 43.9% CP, 82.9% RDP) or dried distillers' grains (DDG; 27.5% CP, 43.6% RDP) supplementation on rice straw utilization (47 g/kg CP and 681 g/kg NDF). Treatments consisted of a negative control receiving no supplement (control) and 3 levels (60, 120, and 180 mg N/kg BW) of either CSM or DDG. Periods were 14 d with 8 d for adaptation and 6 d for data collection. Steers had ad libitum access to rice straw and were fed supplements daily. Increased supplementation resulted in a linear increase ( ≤ 0.06) in forage OM intake from 13.5 g/kg BW by controls to 15.5 and 16.1 g/kg BW for 180 mg N/kg BW of DDG and CSM, respectively. No differences between sources were observed ( = 0.84). Total digestible OM intake was increased by supplementation (linear, < 0.01) from 6.9 g/kg BW (control) to 10.0 and 11.2 g/kg BW for 180 mg N/kg BW of CSM and DDG, respectively. A greater response was observed for DDG ( = 0.05) due to greater provision of supplement (g DM/d) to achieve isonitrogenous treatment levels. Total tract OM digestion tended to increase with DDG supplementation (linear, = 0.08) but not CSM supplementation ( = 0.19). Both supplements did not affect NDF digestion ( > 0.40) or calculated forage NDF digestibility ( > 0.40). Ruminal ammonia concentrations peaked 4 h after supplementation/feeding with the greatest concentration (4.0 m) observed for 180 mg N/kg BW of CSM and the lowest concentration at 4 h observed in the control (0.8 m). Provision of CSM resulted in a linear increase ( < 0.01) in average ruminal ammonia, in contrast to the quadratic response ( = 0.02) observed with DDG supplementation. Total VFA production linearly increased for both CSM and DDG supplementation ( = 0.09 and = 0.01, respectively). Protein supplements containing high and low levels of RDP were effective at improving intake and utilization of rice straw by Brahman steers.

Effect of postextraction algal residue supplementation on the ruminal microbiome of steers consuming low-quality forage.

Cattle consuming low-quality forages (LQF) require protein supplementation to increase forage utilization via ruminal fermentation. Biofuel production from algal biomass results in large quantities of postextraction algal residue (PEAR), which has the potential to elicit LQF utilization responses similar to cottonseed meal (CSM); however, its effect on ruminal bacterial communities is unknown. Five ruminally and duodenally cannulated Angus steers in a 5 × 5 Latin square had ad libitum access to oat straw diets. Treatments were infused ruminally and consisted of an unsupplemented control; PEAR at 50, 100, and 150 mg N/kg BW; and CSM at 100 mg N/kg BW. Ruminal samples were collected 4 h after supplementation on d 14 of each period and separated into solid and liquid fractions. Each sample was extracted for genomic DNA, PCR amplified for the V4 to V6 region of the 16S rRNA, sequenced on the 454 Roche pyrosequencing platform, and analyzed using the QIIME pipeline. Weighted UniFrac analysis and Morisita-Horn index demonstrated different community composition between liquid and solid fractions. Measures of richness including observed operational taxonomic units (OTU) and abundance coverage estimator metric decreased with greater PEAR provision (P ≤ 0.09). There were 42 core microbiome OTU observed in all solid fraction samples while the liquid fraction samples contained 30 core OTU. Bacteroidetes was the predominant phylum followed by Firmicutes in both fractions, which together characterized more than 90% of sequences. Relative abundance of Firmicutes increased with PEAR supplementation in the liquid fraction (linear, P = 0.02). Among Firmicutes, Lachnospiraceae, Ruminococcaceae, and Clostridiaceae families increased in the liquid fraction with greater PEAR supplementation (linear, P ≤ 0.03). Prevotella represented over 25% of sequences in all treatments, and relative abundance decreased in the solid fraction with increasing PEAR provision (linear, P = 0.01). Fibrobacter and Treponema decreased in the liquid fraction with increasing PEAR (linear, P < 0.10). Results suggest PEAR supplementation increased forage utilization by increasing members of Firmicutes within the liquid fraction of the rumen microbiome.

Effect of increasing amounts of postextraction algal residue on straw utilization in steers.

Algal biomass has been identified as a third-generation biofuel. Significant quantities of the coproduct postextraction algal residue (PEAR) remain after lipid extraction. After extraction, PEAR is concentrated in protein (17.9% CP on a DM basis and 32.5% CP on an ash-free basis), suggesting it may be an alternative to cottonseed meal (CSM) as a protein supplement. Our objectives were to determine the optimal level of PEAR supplementation to steers consuming straw and to compare the effects of PEAR supplementation on straw utilization and N metabolism with an isonitrogenous level of CSM. Five steers (198.2 ± 6.1 kg of BW), in a 5 × 5 Latin square, had ad libitum access to oat straw (80% NDF and 4.5% CP on a DM basis). Treatments were infused ruminally once daily and included no supplemental protein (CON); PEAR at 50, 100, and 150 mg N/kg BW; and CSM at 100 mg N/kg BW. Provision of PEAR increased total digestible OM intake (TDOMI) quadratically (P = 0.01) from 0.9 (CON) to 1.6 kg/d (100 mg N/kg BW of PEAR). Organic matter digestibility (OMD) increased quadratically (P < 0.01) with supplementation and was maximized (55% OMD) at 50 mg N/kg BW of PEAR. At isonitrogenous levels of PEAR and CSM, TDOMI was similar (P = 0.13) as was OMD (P = 0.50). Negative N balance was observed for all treatments except PEAR provided at 100 or 150 mg of N/kg BW. Nitrogen balance was quadratic (P < 0.01) with the greatest retention (1.84 g N/d) occurring at 100 mg N/kg BW of PEAR. There were no differences (P ≥ 0.22) between isonitrogenous PEAR and CSM supplementation in measurements of ruminal ammonia or VFA concentrations. Straw utilization was maximized when PEAR was provided at 100 mg N/kg BW. Our observations suggest cattle provided PEAR utilize straw in a manner similar to those supplemented CSM, indicating PEAR has potential to substitute for CSM as a protein supplement in forage-based operations.

Influence of maternal plane of nutrition on mares and their foals: determination of mare performance and voluntary dry matter intake during late pregnancy using a dual-marker system.

Thirty pregnant mares (538 to 695 kg BW; 4 to 19 yr of age) were used to evaluate the effects of plane of nutrition on DMI of hay and mare performance (BW, BCS, and rump fat) during the last third of pregnancy. Mares were divided into 4 blocks by their expected foaling date and randomly assigned within block to either a hay or concentrate plus hay diet (concentrate fed at 0.75% BW, as-fed basis) with 15 mares per treatment. Treatments began 110 d before expected foaling date (230 d of gestation) and terminated at parturition. Mares were housed by block and allowed ad libitum access to coastal Bermuda grass (C. dactylon) hay, and concentrate-supplemented mares were fed twice daily in individual stalls. Performance variables were recorded every 14 d, with the last measurements obtained before foaling being considered a prepartum measurement. To evaluate DMI of hay, a dual-marker system was used at 9, 10, and 11 mo of gestation. Titanium dioxide was dosed at 10 g for 14 d. Fecal grab samples were obtained on the last 4 d twice daily via rectal palpation at 12-h intervals with times advancing 3 h each day to account for diurnal variation and to ultimately represent a 24-h period. Fecal samples were analyzed for TiO2 using a colorimetric procedure. Fecal, concentrate, and hay samples were also analyzed for acid detergent insoluble ash. Treatment tended to influence prepartum BW (P = 0.09) and affected prepartum BCS (P < 0.01) and rump fat (P = 0.01), with hay-fed mares having decreased BW and BCS from d 0 (beginning of feeding trial or d 230 of gestation) until parturition, whereas mares fed concentrate gained BW and BCS (P < 0.01). Mares fed only hay consumed 2.3% BW of forage compared with 1.8% BW for concentrate-fed mares (P < 0.01). Regardless of treatment, month of gestation influenced forage intake (P < 0.06), with mares consuming less during the 10th month of gestation and more in the 11th month (1.9% and 2.2% BW, respectively). These data indicate that the altered plane of nutrition of mares in late gestation influenced mare performance. Furthermore, DMI of hay was influenced by both diet and month of gestation. Continued research investigating manipulation of maternal nutrition and its effects on DMI would be beneficial to completely understand the relationships of these observations.

Effect of frequency and amount of rumen-degradable intake protein supplementation on urea kinetics and microbial use of recycled urea in steers consuming low-quality forage.

We evaluated the effect of frequency and amount of rumen-degradable intake protein (DIP) on urea kinetics in steers consuming prairie hay. Five ruminally and duodenally fistulated steers (366 kg of BW) were used in a 5 x 5 Latin square and provided ad libitum access to low-quality prairie hay (4.7% CP). Casein was provided daily in amounts of 61 and 183 mg of N/kg of BW (61/d and 183/d) and every third day in amounts of 61, 183, and 549 mg of N/kg of BW per supplementation event (61/3d, 183/3d, and 549/3d). Periods were 18-d long with 9 d for adaptation and 9 d for collection. Steers were in metabolism crates for total collection of urine and feces. Jugular infusion of (15)N(15)N-urea followed by determination of urinary enrichment of (15)N(15)N-urea and (14)N(15)N-urea was used to determine urea kinetics. Treatment means were separated to evaluate the effects of increasing DIP supplementation and the effects of frequency at the low (61/d vs. 183/3d) and at the high (183/d vs. 549/3d) amounts of DIP provision. Forage OM and total digestible OM intakes were linearly (P < or = 0.05) increased by increasing DIP provision but were not affected by frequency of supplementation at either the low or high amounts. Production and gut entry of urea linearly (P < or = 0.006) increased with DIP provision and tended to be greater (P < or = 0.07) for 549/3d than 183/d but were not different between 61/d and 183/3d. Microbial N flow to the duodenum was linearly (P < 0.001) increased by increasing DIP provision. Additionally, 183/d resulted in greater (P = 0.05) microbial N flow than 549/3d. Incorporation of recycled urea-N into microbial N linearly (P = 0.04) increased with increasing DIP. Microbial incorporation of recycled urea-N was greater for 549/3d than 183/d, with 42 and 23% of microbial N coming from recycled urea-N, respectively. In contrast, there was no difference due to frequency in the incorporation of recycled urea-N by ruminal microbes at the low level of supplementation (i.e., 61/d vs. 183/3d). This study demonstrates that urea recycling plays a substantial role in the N supply to the rumen and to the animal, particularly in steers supplemented infrequently with high levels of protein.

Effect of rumen-degradable intake protein supplementation on urea kinetics and microbial use of recycled urea in steers consuming low-quality forage.

We evaluated the effect of increasing amounts of rumen-degradable intake protein (DIP) on urea kinetics in steers consuming prairie hay. Ruminally and duodenally fistulated steers (278 kg of BW) were used in a 4 x 4 Latin square and provided ad libitum access to low-quality prairie hay (4.9% CP). The DIP was provided as casein dosed ruminally once daily in amounts of 0, 59, 118, and 177 mg of N/kg of BW daily. Periods were 13 d long, with 7 d for adaptation and 6 d for collection. Steers were in metabolism crates for total collection of urine and feces. Jugular infusion of (15)N(15)N-urea, followed by determination of urinary enrichment of (15)N(15)N-urea and (14)N(15)N-urea was used to determine urea kinetics. Forage and N intake increased (linear, P < 0.001) with increasing DIP. Retention of N was negative (-2.7 g/d) for steers receiving no DIP and increased linearly (P < 0.001; 11.7, 23.0, and 35.2 g/d for 59, 118, and 177 mg of N/kg of BW daily) with DIP. Urea synthesis was 19.9, 24.8, 42.9, and 50.9 g of urea-N/d for 0, 59, 118, and 177 mg of N/kg of BW daily (linear, P = 0.004). Entry of urea into the gut was 98.9, 98.8, 98.6, and 95.9% of production for 0, 59, 118, and 177 mg of N/kg of BW daily, respectively (quadratic, P = 0.003). The amount of urea-N entering the gastrointestinal tract was greatest for 177 mg of N/kg of BW daily (48.6 g of urea-N/d) and decreased (linear, P = 0.005) to 42.4, 24.5, and 19.8 g of urea-N/d for 118, 59, and 0 mg of N/kg of BW daily. Microbial incorporation of recycled urea-N increased linearly (P = 0.02) from 12.3 g of N/d for 0 mg of N/kg of BW daily to 28.9 g of N/d for 177 mg of N/kg of BW daily. Provision of DIP produced the desired and previously observed increase in forage intake while also increasing N retention. The large percentage of urea synthesis that was recycled to the gut (95.9% even when steers received the greatest amount of DIP) points to the remarkable ability of cattle to conserve N when fed a low-protein diet.

Effect of supplementation frequency and supplemental urea level on dormant tallgrass-prairie hay intake and digestion by beef steers and prepartum performance of beef cows grazing dormant tallgrass-prairie.

Effect of supplementation frequency and supplemental urea level on forage use (Exp. 1) and performance (Exp. 2 and 3) of beef cattle consuming low-quality tallgrass-prairie were evaluated. For Exp. 1 and 2, a 2 x 2 factorial treatment structure was used, such that two supplements (30% CP) containing 0 or 30% of supplemental degradable intake protein (DIP) from urea were fed daily or on alternate days. In Exp. 1 and 2, supplement was fed at 0.41% BW daily or at 0.83% BW (DM basis) on alternate days. For Exp. 3, a 2 x 4 factorial treatment structure was used, such that four supplements (40% CP) containing 0, 15, 30, or 45% of supplemental DIP from urea were fed daily or 3 d/wk. Supplements were group-fed at 0.32% BW daily or at 0.73% BW (DM basis) 3 d/wk. In Exp. 1, 16 Angus x Hereford steers (initial BW = 252 kg) were blocked by BW and assigned to treatment. Urea level x supplementation frequency interactions were not evident for forage intake, digestion, or rate of passage. Forage OM intake (OMI) and total digestible OMI (TDOMI) were not significantly affected by treatment. Total-tract digestion of OM (P = 0.03) and NDF (P = 0.06) were greater for steers supplemented daily. In Exp. 2, 48 Angus x Hereford cows (initial BW = 490 kg) grazing winter tallgrass prairie were used. Significant frequency x urea interactions were not evident for BW and body condition (BC) change; similarly, the main effects were not substantive for these variables. In Exp. 3, 160 Angus x Hereford cows (initial BW = 525 kg) grazing dormant, tallgrass prairie were used. Supplement refusal occurred for cows fed the highest urea levels, particularly for cows fed the supplement with 45% of the DIP from urea 3 d/wk, and supplement refusal increased closer to calving. A frequency x urea interaction (P = 0.02) was observed for prepartum BW changes. As supplemental urea level increased, prepartum BW loss increased quadratically (P = 0.02); however, a greater magnitude of loss occurred when feeding supplements containing > or = 30% of DIP from urea 3 d/ wk. Cumulative BC change followed a similar trend. In conclusion, moderate protein (< or = 30% CP) supplements with < or = 30% of supplemental DIP from urea can be fed on alternate days without a substantive performance penalty. However, infrequent feeding of higher protein (> 30% CP) supplements with significant urea levels (> 15% of DIP from urea) may result in decreased performance compared with lower urea levels.

Ruminal and host adaptations to changes in frequency of protein supplementation.

The effect of altering supplementation frequency on host N balance and key N transactions in the ruminal ecosystem were monitored. Four ruminally fistulated beef steers (BW = 513 kg; SEM = 6.5) were used in a 2 x 2 crossover design with two periods and two supplementation frequency treatments. Supplementation frequencies were 2 and 7 d/wk. Steers were fed tallgrass prairie hay (73.1% NDF, 5.3% CP) ad libitum. Supplement (42% CP; DM basis) was fed at 0.36% BW/d to steers supplemented 7 d/wk. Steers supplemented 2 d/wk received the same amount of supplement per week, but it was equally split among the two supplementation events. Steers supplemented 7 d/wk had higher forage (P < 0.02) and total digestible OM intake (P < 0.06), total N intake, fecal N excretion, and N retention. Although both supplementation frequencies were characterized by positive N balance, the decrease in N retention in the steers supplemented 2 d/wk was due to higher (P < 0.01) urinary N loss. Ruminal fluid was sampled at 0, 2, 4, 6, 12, 24, 48, and 72 h after supplementation beginning on a day when both treatments were supplemented. Frequency x hour interactions (P < 0.02) were observed for ruminal N metabolism criteria. Counts of peptide- and AA-fermenting bacteria peaked at 2 h and returned to nadir by 12 h for steers supplemented 7 d/wk. Steers supplemented 2 d/wk peaked at 6 h with a greater population and returned to nadir at 48 h. Ruminal ammonia concentrations followed a similar trend. Specific activity of ammonia production was lower (P < or = 0.05) immediately after supplementation for steers supplemented 2 d/wk, but by 12 h was the same as for 7 d/wk steers. Ruminal peptides and free AA peaked at 2 h for steers supplemented 2 d/wk and were generally higher (P < or = 0.05) during the first 6 h compared with steers supplemented 7 d/wk. Total VFA concentration was not different (P = 0.35) due to supplementation frequency. Frequency x hour interactions (P < 0.01) were observed for all molar proportions of VFA. The molar proportion of acetate and acetate:propionate ratio were lower (P < 0.01) and the molar proportions of propionate and butyrate were higher for steers supplemented 2 d/wk from 4 h to 24 h. In conclusion, forage use and N balance improved with supplementation 7 d/wk, but supplementation 2 d/wk was associated with some desirable shifts in select ruminal events that may contribute to moderating potential negative impacts of supplementing infrequently.

The effects of several supplementation frequencies on forage use and the performance of beef cattle consuming dormant tallgrass prairie forage.

Two experiments were conducted to quantify the impact on forage use and performance of varying supplementation frequency of cattle consuming forage diets across a range of frequencies. In both experiments, a common supplement was used that contained a relatively high concentration of CP (43%) and was fed at the following frequencies: 1) 2 d/wk; 2) 3 d/wk; 3) 5 d/wk; and 4) 7 d/wk. In Exp. 1, 120 Hereford x Angus cows (BW = 537 kg) grazing winter tallgrass-prairie range were supplemented at the various frequencies from December 7 until calving (average calving date = 3/7/99). All treatments provided the same quantity of supplement on a weekly basis (12.74 kg, as-fed) but divided the amount delivered on a given day equally among the number of supplementation events for that treatment. Less BW was lost from December 7 through calving (linear effect, P = 0.02) as frequency of supplementation increased, but the magnitude of difference in weight change was relatively small. Body condition responded similarly through early February (linear effect, P = 0.02), although treatment effects were not as distinct at calving (cubic effect, P = 0.11). In Exp. 2, 16 ruminally fistulated Hereford x Angus steers (BW = 257 kg) were blocked by weight and assigned to one of the four frequencies of supplementation. Steers were offered tallgrass prairie hay (73.5% NDF, 4.8% CP) ad libitum and were supplemented at a rate (relative to BW) similar to that of the cows in Exp. 1. Increasing frequency of supplementation increased (linear effect, P < or = 0.02) forage OM intake, OM and NDF digestion, and digestible OM intake. However, the most prominent differences in forage OM intake tended (cubic effect, P = 0.07) to occur with the two extreme frequencies of supplementation. In conclusion, forage use was improved with an increased frequency of supplementation, but the impact on performance is not likely to be large unless extreme differences in frequency occur.

Effect of ruminal vs postruminal administration of degradable protein on utilization of low-quality forage by beef steers.

An experiment was designed to determine the effects of ruminal and postruminal infusions of ruminally degradable protein (casein) on intake and digestion of low-quality hay by beef steers. Twelve ruminally fistulated Angus x Hereford steers (initial BW = 563 kg) were blocked by weight and assigned to one of three treatments: control (C; hay only) or hay plus ruminal (R) or postruminal (P) infusion of 400 g/d of sodium caseinate. The trial consisted of five periods: 1) 10-d adaptation to the hay diet; 2) 7-d measurement of hay intake (without infusions); 3) 10-d adaptation to protein infusion treatments (intake measurements continued); 4) 7-d measurement of hay intake and digestibility (infusions continued); and 5) 3-d ruminal sampling period (infusions continued). Steers were given ad libitum access to tallgrass-prairie hay (3.4% CP, 76.6% NDF) throughout the study. Casein was administered once daily before feeding, either directly into the rumen or via anchored infusion lines into the abomasum. Hay intake was increased by supplementation (P < 0.01). Ruminal infusion elicited a greater (P = 0.04) increase in hay intake than postruminal infusion. Intake tended (P = 0.11) to be lower in period 4 than in period 2 for control steers but was greater in period 4 than in period 2 (P < or = 0.03) for both R and P steers. The increase in intake between periods 2 and 4 was greater for R than for P steers (P = 0.03). Supplementation improved diet OM digestion (P = 0.04) but not NDF digestion (P = 0.18); however, greater relative error for NDF digestion may have limited the ability to elucidate significant treatment effects. There were no differences in either OM digestion (P = 0.42) or NDF digestion (P = 0.35) between R and P steers. Plasma urea N at 0 and 3 h after feeding on the last day of the experiment was lower (P = 0.05) for C than for R and P steers, but no difference (P = 0.48) was evident between R and P steers. Ruminal ammonia N levels also were increased by supplementation (P < 0.01), with a much larger increase for R than for P steers (P < 0.01). Total VFA concentrations were not affected (P = 0.21) by treatment, but R steers exhibited lower proportions of acetate and higher proportions of isobutyrate, valerate, and isovalerate than P steers (P < 0.01). In conclusion, ruminal and postruminal infusion of a degradable protein source improved forage utilization, although the response in forage OM intake and total digestible OM intake was greater for ruminal infusion than for postruminal infusion.