Technical note: Effects of filter bags on neutral detergent fiber recovery and fiber digestion in vitro.

Filter bags facilitate the measurement of amylase-treated neutral detergent fiber (aNDF) and in vitro (IV) undigested aNDF (uNDF) by eliminating the transfer of residues from beakers into filtration crucibles. The objectives of this study were to (1) determine effects of filter bags on recovery of aNDF and (2) evaluate effects of filter bags on IV uNDF. For study 1, 6 samples each of grass hay (GR), alfalfa (AL), and corn silage (CS) were selected. Large standard deviations (SD) of ash-free aNDF (aNDFom) for samples in each forage type indicated compositional diversity (15.1, 7.45, and 12.9% of DM for GR, AL, and CS, respectively), and starch SD for CS was 16.4% of DM. Samples were weighed into Berzelius beakers or filter bags [25-µm pores (F57) or 6-µm pores (F58); Ankom Technology, Macedon, NY] for measurement of aNDF and aNDFom. All samples were extracted with neutral detergent, thermostable α-amylase, and sodium sulfite, and then soaked in boiling water and then acetone. Residues from beakers were filtered through a sea sand-covered GF/D filter (Whatman, Marlborough, MA) in Gooch crucibles (CR). Filter bags were extracted in a pressurized chamber at 100°C. The aNDF values did not differ between F57 and CR, but F58 was greater than CR for CS and AL. For GR, F58 was greater than CR for aNDFom. For study 2, diverse samples with large SD of aNDFom (20.7, 7.45, and 12.9% of DM for GR, AL, and CS, respectively) were weighed as loose powder into medium bottles (LS) or F57 bags, which were weighted to prevent floating. Blended ruminal fluid from 3 steers fed a 30% aNDFom diet was used as inoculum. Three samples of 1 forage type were randomly assigned to 1 of 6 IV runs using both treatments (LS and F57), and 3 bottles of each sample-treatment combination were removed after 12 h and 2 were removed after 120 h to measure uNDF. For LS, residues were extracted as in study 1 for CR. For F57, bags were rinsed in cold water and extracted as described in study 1. After 12 h, uNDF of F57 was greater than LS in CS, AL, and overall types. Ash-free uNDF (uNDFom) after 12 h of F57 was greater than LS in CS and overall types. After 120 h, F57 was greater than LS for uNDF of CS, but no differences were detected for uNDFom. The SD of uNDFom, but not uNDF, was higher after 12 and 120 h for F57 compared with LS. From 6 to 96 h, overall gas production of F57 was less than LS, and F57 was less than LS for CS from 3 to 96 h. Overall, LS gave greater maximum and faster rates of gas production than F57, as did AL and CS, but lag did not vary. Results indicate that filter bags affected aNDF and aNDFom measurement and inhibited fermentation for some materials.

Stage of lactation and corresponding diets affect in situ protein degradation by dairy cows.

The influence of stage of lactation and corresponding diets on rates of protein degradation (kd) is largely unstudied. Study objectives were to measure and compare in situ ruminal kd of crude protein (CP) and estimate rumen CP escape (rumen-undegradable protein; RUP) of selected feeds by cows at 3 stages of lactation fed corresponding diets, and to determine the incubation times needed in an enzymatic in vitro procedure, using 0.2 units of Streptomyces griseus protease per percent of true CP, that predicted in situ RUP. Residue CP was measured after in situ fermentation for 4, 8, 12, 24, 36, 48, and 72 h of 5 protein sources and 3 total mixed rations, which were fed to the in situ cows. Two nonlactating (dry) cows and 2 cows each at 190 (mid) and 90 (peak) days of lactation were used. Each pair of cows was offered free-choice diets that differed in composition to meet their corresponding nutrient requirements. Diets had decreasing proportions of forages and contained (dry matter basis) 11.9, 15.1 and 16.4% CP and 54.3, 40.3 and 35.3% neutral detergent fiber, for dry, mid, and peak TMR (TMR1, TMR2, and TMR3), respectively. Intakes were 10.3, 21.4, and 23.8kg of dry matter/d, respectively. Kinetic CP fractions (extractable, potentially degradable, undegradable, or slowly degradable) were unaffected by treatment. Lag time and kd varied among feeds. The kd was faster for all feeds (0.136/h) when incubated in dry-TMR1 cows compared with mid-TMR2 (0.097/h) or peak-TMR3 (0.098/h) cows, and no differences in lag time were detected. Calculated RUP, using estimated passage rates for each cow based on intake, differed between dry-TMR1 (0.382) and mid-TMR2 (0.559) or peak-TMR3 (0.626) cows, with a tendency for mid-TMR2 to be different from peak-TMR3. Using the average kd and lag time obtained from dry-TMR1 to calculate RUP for mid-TMR2 and peak-TMR3 cows using their passage rates reduced RUP values by 6.3 and 9.5 percentage units, respectively. Except for that of herring meal, in vitro residue CP at 6, 12, and 48h of enzymatic hydrolysis was correlated (r=0.90) with in situ RUP of peak-TMR3, mid-TMR2, and dry-TMR1, respectively. Although confounded within treatments, stage of lactation, diet, and intake appeared to affect CP degradation parameters and RUP. Using kd from nonlactating cows, or the RUP calculated from them, may bias diet evaluation or ration formulation for lactating cows. In addition, enzymatic in vitro predictions of RUP should be measured using incubation times that are appropriate for lactating cows.

A query for effective mean particle size in dry and high-moisture corns.

The objective of this study was to investigate whether prediction of fermentation potential (FP) of dry and high-moisture (HM) corns could be improved by using a concept of effective (e) mean particle size (MPS). A set of FP standards was created by processing a single lot of Reid Yellow Dent (RYD) corn to achieve MPS of 3,778, 2,786, 2,282, 1,808, 1,410, 806, 586, 378, 308, 226, and 105 µm. In vitro gas production of RYD standards was measured, and peak absolute rate (PAR) of gas production (mL/0.2 g of DM/h) was used to establish a standard relationship between PAR and MPS. To identify factors other than MPS affecting FP, the MPS and nutrient composition of 36 diverse samples of dry (n=18) and HM (n=18) corns were determined. Composition included dry matter (DM), crude protein, soluble crude protein, neutral detergent fiber, starch, NH3-N, prolamin protein, and fat. In vitro gas production of undried, unground dry and HM corns was measured, and PAR, time of peak absolute rate (h), maximum cumulative gas production (mL/0.2 g of DM), gas production fractional rate (h⁻¹), and lag (h) were determined. Nonlinear relationships between MPS, defined as the dependent variable, and PAR, as an independent variable, were used to identify FP deviations unexplained by MPS. When no variation in nutritional composition was present (RYD standards), the relationship between PAR and MPS was described by an exponential decay model [RYD_MPS=9,006 × e((-0.452 × PAR)); R²=0.96]. For diverse dry and HM corn populations, the variation in MPS explained by PAR was diminished (R²=0.50). To investigate factors that diminish the relationship between MPS and PAR in diverse corns, relative residual (rr) MPS was determined [rrMPS = (MPS - RYD_MPS)/MPS], where RYD_MPS was predicted from the PAR of diverse dry and HM corn. The rrMPS was most highly related to prolamin protein [rrMPS(dry)=0.58-0.15 × (prolamin protein, % of DM); R²=0.43] and NH3-N [rrMPS(HM)=0.21+0.08 × (NH3-N, % of total N); R²=0.46] for dry and HM corns, respectively. An eMPS was calculated as eMPS = MPS - MPS × rrMPS, where rrMPS was predicted from prolamin protein or NH3-N concentration in dry and HM corn, respectively. The natural logarithm of eMPS accounted for 84% of the variability in PAR and 53% of the variability in the fractional rate of gas production. Calculating eMPS by adjusting the MPS of dry corn for prolamin and HM corn for NH3-N concentration improved the assessment of industry corn FP.

A ring test of in vitro neutral detergent fiber digestibility: analytical variability and sample ranking.

In vitro neutral detergent fiber (NDF) digestibility (NDFD) is an empirical measurement of fiber fermentability by rumen microbes. Variation is inherent in all assays and may be increased as multiple steps or differing procedures are used to assess an empirical measure. The main objective of this study was to evaluate variability within and among laboratories of 30-h NDFD values analyzed in repeated runs. Subsamples of alfalfa (n=4), corn forage (n=5), and grass (n=5) ground to pass a 6-mm screen passed a test for homogeneity. The 14 samples were sent to 10 laboratories on 3 occasions over 12 mo. Laboratories ground the samples and ran 1 to 3 replicates of each sample within fermentation run and analyzed 2 or 3 sets of samples. Laboratories used 1 of 2 NDFD procedures: 8 labs used procedures related to the 1970 Goering and Van Soest (GVS) procedure using fermentation vessels or filter bags, and 2 used a procedure with preincubated inoculum (PInc). Means and standard deviations (SD) of sample replicates within run within laboratory (lab) were evaluated with a statistical model that included lab, run within lab, sample, and lab × sample interaction as factors. All factors affected mean values for 30-h NDFD. The lab × sample effect suggests against a simple lab bias in mean values. The SD ranged from 0.49 to 3.37% NDFD and were influenced by lab and run within lab. The GVS procedure gave greater NDFD values than PInc, with an average difference across all samples of 17% NDFD. Because of the differences between GVS and PInc, we recommend using results in contexts appropriate to each procedure. The 95% probability limits for within-lab repeatability and among-lab reproducibility for GVS mean values were 10.2 and 13.4%, respectively. These percentages describe the span of the range around the mean into which 95% of analytical results for a sample fall for values generated within a lab and among labs. This degree of precision was supported in that the average maximum difference between samples that were not declared different by means separation was 4.4% NDFD. Although the values did not have great precision, GVS labs were able to reliably rank sample data in order of 30-h NDFD (Spearman correlation coefficient = 0.93) with 80% of the rankings correct or off by only 1 ranking. A relative ranking system for NDFD could reduce the effect of within- and among-lab variation in numeric values. Such a system could give a more accurate portrayal of the comparative values of samples than current numeric values imply.

Effect of reduced ferulate-mediated lignin/arabinoxylan cross-linking in corn silage on feed intake, digestibility, and milk production.

Cross-linking of lignin to arabinoxylan by ferulates limits in vitro rumen digestibility of grass cell walls. The effect of ferulate cross-linking on dry matter intake (DMI), milk production, and in vivo digestibility was investigated in ad libitum and restricted-intake digestion trials with lambs, and in a dairy cow performance trial using the low-ferulate sfe corn mutant. Silages of 5 inbred corn lines were fed: W23, 2 W23sfe lines (M04-4 and M04-21), B73, and B73bm3. As expected, the W23sfe silages contained fewer ferulate ether cross-links and B73bm3 silage had a lower lignin concentration than the respective genetic controls. Silages were fed as the sole ingredient to 4 lambs per silage treatment. Lambs were confined to metabolism crates and fed ad libitum for a 12-d adaptation period followed by a 5-d collection period of feed refusals and feces. Immediately following the ad libitum feeding trial, silage offered was limited to 2% of body weight. After a 2-d adaptation to restricted feeding, feed refusals and feces were collected for 5 d. Seventy Holstein cows were blocked by lactation, days in milk, body weight, and milk production and assigned to total mixed ration diets based on the 5 corn silages. Diets were fed for 28 d and data were collected on weekly DMI and milk production and composition. Fecal grab samples were collected during the last week of the lactation trial for estimation of feed digestibility using acid-insoluble ash as a marker. Silage, total mixed ration, feed refusals, and fecal samples were analyzed for crude protein, starch, neutral detergent fiber (NDF), cell wall polysaccharides, and lignin. The W23sfe silages resulted in lower DMI in the ad libitum trial than the W23 silage, but DMI did not differ in the restricted trial. No differences were observed for NDF or cell wall polysaccharide digestibility by lambs with restricted feeding, but the amount of NDF digested daily increased for lambs fed the M04-21 W23sfe silage ad libitum. Lambs were less selective against NDF and lignin when offered W23sfe silages. The B73bm3 silage did not affect DMI or digestibility of cell walls at the restricted feeding level, but total daily NDF digested was greater at ad libitum intake. Intake, milk production, and cell wall digestibility were greater for cows fed diets containing W23sfe silages than for those fed W23 silage. Although milk production was greater for the B73bm3 diet, DMI and cell wall digestibility were not altered. Cows were less selective against cell wall material when fed both W23sfe and B73bm3 silages. Reduced ferulate cross-linking in sfe corn silage is a new genetic mechanism for improving milk production.

pH dynamics and bacterial community composition in the rumen of lactating dairy cows.

The influence of pH dynamics on ruminal bacterial community composition was studied in 8 ruminally cannulated Holstein cows fitted with indwelling electrodes that recorded pH at 10-min intervals over a 54-h period. Cows were fed a silage-based total mixed ration supplemented with monensin. Ruminal samples were collected each day just before feeding and at 3 and 6h after feeding. Solid and liquid phases were separated at collection, and extracted DNA was subjected to PCR amplification followed by automated ribosomal intergenic spacer analysis (ARISA). Although cows displayed widely different pH profiles (mean pH=6.11 to 6.51, diurnal pH range=0.45 to 1.39), correspondence analysis of the ARISA profiles revealed that 6 of the 8 cows showed very similar bacterial community compositions. The 2 cows having substantially different community compositions had intermediate mean pH values (6.30 and 6.33) and intermediate diurnal pH ranges (averaging 0.89 and 0.81 pH units). Fortuitously, these 2 cows alone also displayed milk fat depression, along with markedly higher ruminal populations of 1 bacterial operational taxonomic unit (OTU) and reduced populations of another ARISA amplicon. Cloning and sequencing of the elevated OTU revealed phylogenetic similarity to Megasphaera elsdenii, a species reportedly associated with milk fat depression. The higher populations of both M. elsdenii and OTU246 in these 2 cows were confirmed using quantitative real-time PCR (qPCR) with species-specific primers, and the fraction of total bacterial rDNA copies contributed by these 2 taxa were very highly correlated within individual cows. By contrast, the fraction of total bacterial rDNA copies contributed by Streptococcus bovis and genus Ruminococcus, 2 taxa expected to respond to ruminal pH, did not differ among cows (mean= <0.01 and 10.6%, respectively, of rRNA gene copies, determined by qPCR). The data indicate that cows with widely differing pH profiles can have similar ruminal bacterial community compositions, and that milk fat depression can occur at intermediate ruminal pH. The results support recent reports that milk fat depression is associated with shifts in bacterial community composition in rumine and is specifically related to the relative abundance of Megasphaera elsdenii.

Shifts in bacterial community composition in the rumen of lactating dairy cows under milk fat-depressing conditions.

Eighteen ruminally cannulated dairy cattle were fed a series of diets (in 28-d periods) designed to elicit different degrees of milk fat depression (MFD) for the purpose of relating MFD to ruminal bacterial populations. Cows were fed a TMR containing 25% starch (DM basis) supplied as corn silage, a slowly fermented starch (SFS treatment, period 1), then switched to a TMR containing 27% starch, much of it supplied as ground high-moisture corn, a rapidly fermented starch (RFS treatment, period 2). In period 3, the RFS diet was amended with 13.6 mg of monensin/kg of DM (RFS/Mon treatment), and in period 4, the cows were returned to the RFS diet without monensin (RFS/Post treatment). Effect of both starch source and monensin on milk fat percentage varied by cow, and cluster analysis identified 4 pairs of cows having distinct milk fat patterns. Archived ruminal liquors and solids from the 4 pairs were processed to isolate bacterial DNA, which was subjected to automated ribosomal intergenic spacer analysis followed by correspondence analysis to visualize bacterial community composition (BCC). One pair of cows (S-responsive) showed MFD on RFS feeding, but displayed no additional MFD upon monensin feeding and a fat rebound upon monensin withdrawal. The second pair of cows (M-responsive) showed no MFD upon switch from the SFS diet to the RFS diet, but displayed strong MFD upon monensin feeding and no recovery after monensin withdrawal. Both groups displayed major shifts in BCC upon dietary shifts, including dietary shifts that both did and did not change milk fat production. The third pair of cows (SM-responsive) displayed reduction of milk fat on both RFS and RFS/Mon diets, and fat returned to the levels on the RFS diet upon monensin withdrawal; these cows showed a more gradual shift in BCC in response to both starch source and monensin. The fourth pair of cows (nonresponsive) did not display changes in milk fat percentage with dietary treatment and showed only minor shifts in BCC with dietary treatment. Regardless of milk fat response, BCC did not reassemble its original state upon monensin withdrawal, though the difference was strongest in M-responsive cows. One amplicon length (representing a single bacterial species) was elevated in most, but not all, MFD-susceptible (S-, M-, or SM-responsive) cows relative to milk fat-nonresponsive cows, whereas 2 amplicon lengths displayed reduced abundance under MFD conditions. Overall, this study demonstrates an association between MFD and wholesale shifts of microbial communities in the rumen.

Manure nutrient excretion by Jersey and Holstein cows.

The objective of this study was to evaluate feces, urine, and N excretion by Jersey and Holstein cows. Sixteen multiparous cows (n=8 per breed) were fed 2 experimental rations at calving in a switchback experimental design. Diets were 50% forage and based on corn meal (control) or whole cottonseed. Half the cows in each breed started on the control diet and half started on the whole cottonseed diet. Cows were switched to the other diet at 60 d in milk and switched back to their original diet at 165 d in milk. Pairs of cows were moved into open-circuit respiration chambers on d 49, 154, and 271 of lactation for 7-d measurement periods. While in the chambers, total collection of feed refusals, milk, recovered hair, feces, and urine was conducted. No effect of the interaction of diet and breed was observed for measures of nutrient digestibility and manure excretion. Total daily manure excretion was lower in Jersey cows than in Holstein cows, with reductions generally proportional to changes in feed intake. Jersey cows consumed 29% less feed and excreted 33% less wet feces and 28% less urine than Holstein cows. Intake, fecal, and urinary N were reduced by 29, 33, and 24%, respectively, in Jersey cows compared with Holstein cows. Equations from American Society of Agricultural and Biological Engineers underpredicted observed values for all manure measures evaluated (urine, manure solids, N, wet manure), and breed bias was observed in equations predicting excretion of urine, N, and wet manure. Although these equations include animal and dietary factors, intercepts of regression of observed values on predicted values differed between Holsteins and Jerseys for those 3 measures. No breed bias was observed in the prediction of manure solids excretion, however, making that equation equally appropriate for Jerseys and Holsteins. The effect of breed on manure and nutrient excretion has significant nutrient management implications.

Technical note: effect of sample processing procedures on measurement of starch in corn silage and corn grain.

Methods for processing feedstuffs before analysis can affect analytical results. Effects of drying temperature (corn silage), preservation method (corn grain), and grinding method (corn silage and grain) on starch analysis values were evaluated. Corn silage samples dried at 55 or 105 degrees C and grain samples dried at 55 degrees C were ground to pass the 1-mm screen of an abrasion mill or cutting mill and analyzed for free glucose and starch corrected for free glucose. Starch analyses were performed in triplicate to assess the effect of treatment on precision of starch determination. Drying at 105 degrees C decreased free glucose and tended to decrease starch detected in silage. Decreased free glucose and starch values in silages dried at 105 degrees C may have been caused by the destruction of glucose and production of Maillard products through nonenzymatic browning. Maillard products with reducing activity could potentially interfere with the glucose oxidase-peroxidase glucose detection method used. Compared with the cutting mill, grinding samples through the abrasion mill increased the precision of starch measures in silage, likely due to the effect of the finer particle size produced by the abrasion mill allowing more accurate subsampling of a more homogeneous matrix. Starch values were greater for grain ground with an abrasion mill than with a cutting mill, with the difference greater for dry-rolled than for high-moisture corn. For starch analysis of corn silage and corn grain, drying at lower temperatures (55 degrees C) in forced-air ovens and grinding through the 1-mm screen of an abrasion mill or its equivalent is recommended.

Influence of fermentation methods on neutral detergent fiber degradation parameters.

The effect of 3 fermentation methods, in situ (IS) in 4 lactating cows (average pH of 5.8), in vitro (IVn) with media pH of 6.8, or in vitro (IVa) with media pH adjusted to 6.0 using citric acid, on fiber degradation parameters was studied using feeds ground to different particle sizes. Corn silage (CS), grass silage (GS), barley grain (B), sugar beet pulp (BP), and rapeseed cake (RC) were ground using a shear mill. Silages were ground through 8-, 4-, 2-, or 1-mm screens, B and BP through 4-, 2-, or 1-mm screens, and RC through 2- or 1-mm screens. The amylase-treated NDF (aNDF) content of samples ground using a 1-mm screen was 399, 431, 197, 480, and 251 g/kg of DM for CS, GS, B, BP, and RC, respectively, but increased with increasing screen size. Materials were incubated for 0, 6, 12, 24, 48, and 96 h IS, IVn, or IVa. Inoculum for IVn and IVa was prepared as a composite from the cows used for IS. The potentially degradable aNDF (D(0)), indegradable aNDF (I), lag time (L), and fractional rate of degradation of potential degradable aNDF (k(d)) were estimated using PROC NLIN in SAS. Except for RC, fermentation methods affected most degradation parameters, especially k(d) and L. The IVn, IVa, and IS methods resulted in k(d) values of 0.291, 0.105, 0.080 h(-1) and 0.262, 0.107, 0.103 h(-1) for BP and RC, respectively, demonstrating a decreasing rate of degradation for these feeds when fermented under suboptimal pH. In CS, GS, and B, no difference was found in k(d) between the IVn and IVa methods, which suggests that differences in pH did not alter k(d) in vitro. The k(d) values obtained for CS, GS, and B were 0.058, 0.109, 0.168, and 0.028, 0.054, and 0.069 h(-1) for the IVn and IS methods, respectively, indicating that the IS method using cows fed at production levels can underestimate the potential rate of NDF degradation. Using the IVa method, L was 12.1, 9.1, 7.8, and 2.5 h for CS, GS, BP, and RC, respectively, which was higher than L obtained from the IVn and IS methods for all feeds except B, where L in all methods were near the parameter boundary of zero hour in NLIN. It was concluded that fermentation methods were more important than grinding screen size on estimates for feed aNDF degradation and that the individual aNDF degradation parameters for the 5 feeds were affected differently by fermentation methods.

In vitro fermentation vessel type and method alter fiber digestibility estimates.

Selected vessel types and conditions used for in vitro fermentation were compared to evaluate their effects on determinations of neutral detergent fiber (NDF) digestibility (NDFD) in 2 replicate 48-h fermentations. Treatments included 50-mL polyethylene centrifuge tubes with gas-release valves (treatment 1); 50-mL polyethylene centrifuge tubes with continuous gassing with CO2 (treatment 2); 50-mL polyethylene centrifuge tubes sealed, oriented horizontally, and shaken continuously parallel to the long axis of the tube, with manual gas release (treatment 3); 125-mL Erlenmeyer flasks with continuous gassing with CO2 (treatment 4); and 125-mL serum vials sealed with stoppers and crimp seals with (treatment 5) or without (treatment 6) manual gas release. Goering and Van Soest medium and blended ruminal inoculum from 4 lactating cows were used. Substrates were alfalfa hay, corn silage, ryegrass hay, and soyhulls. Gas was released and measured in treatments 3 and 6 at 3.0, 5.5, 9.0, 11.5, 23.5, 29.5, and 47.5 h by using a syringe with a hypodermic needle. Vessels from each treatment were harvested at 0, 6, 12, 24, 30, and 48 h for NDF analysis, with NDFD calculated as 1 - [(residual NDF, g - residual NDF in fermentation blank, g)/sample NDF, g]. Medium pH did not decline below 6.3 for any treatment. Average values for NDFD for 24 through 48 h were 0.576, 0.639, 0.688, 0.668, 0.679, and 0.681 for treatments 1 through 6, respectively (standard error of the difference = 0.008). The lowest NDFD was noted for treatment 1, which differed from all other treatments; treatments 3, 4, 5, and 6 did not differ by treatment or by the interaction of treatment and substrate. Treatments 1 and 2 gave lower NDFD values than the other treatments, but these differences were not consistent and differed by substrate, with alfalfa showing the fewest differences among treatments and soyhulls the most. Net energy of lactation values for substrates, as predicted from differences in 48-h NDFD, were 7 to 15% lower for treatment 1 than for the average of all other treatments. Slopes of the gas production per gram of substrate dry matter curves differed between treatments 3 and 5. In conclusion, measured NDFD was altered by fermentation treatment, with polyethylene tubes + gas-release valves giving the lowest values. Consequently, NDFD values may not be comparable across fermentation methods, but the effect will vary among feedstuffs. The combination of methods used for sealing, gassing, or agitating vessels may have a greater impact on NDFD than does vessel type.

Chemical and physical characteristics of corn silages and their effects on in vitro disappearance.

Estimating the available energy in corn silage provides a unique challenge because the silage contains variable proportions of grain and stover, each of which can differ in availability due to chemical composition and physical form. The objectives of this study were to investigate relationships among chemical components and their relationships with in vitro disappearance of ground and unground dried silages, and to quantify minimally fragmented starch in corn silage and investigate its impact and that of mean particle size (MPS) on in vitro disappearance of unground silages. Thirty-two corn silages were selected to provide diversity in dry matter, protein, fiber, and MPS. Detergent fibers were highly correlated with each other and with nonfiber carbohydrates, and were used to develop prediction equations between these constituents. Sieves with apertures > or =4.75 mm were used to isolate intact kernels and large kernel fragments, which were collected and analyzed to measure minimally fragmented starch (Starch>4.75). Dividing Starch>4.75 by total starch defined the proportion of minimally fragmented starch (Starch>4.75/Total), which ranged from 9 to 100% with a mean of 52%. Starch>4.75/Total was positively correlated with MPS (r = 0.46). The inverse of Starch>4.75/Total is an index of kernel fragmentation. Silages were prepared as whole material or ground to pass through a 4- or 1-mm screen of a cutter mill. In vitro dry matter disappearance (IVDMD) was greater for ground than for whole samples (71.7 and 61.2%, respectively). Increased IVDMD for ground samples was attributed to greater in vitro neutral detergent fiber (NDF) and neutral detergent solubles (NDS) disappearances. The IVDMD of ground samples was related to NDF and acid detergent lignin (R2 = 0.80). The IVDMD of whole corn silage was related to acid detergent lignin, Starch>4.75, MPS, and dry matter. When IVDMD was partitioned into in vitro digestible NDS (IVdNDS) and in vitro digestible NDF, the IVdNDS of whole was not uniform or completely fermented. The difference in IVdNDS between ground and whole was related to Starch>4.75/Total. In conclusion, the proportion of minimally fragmented starch provides a corn silage fragmentation index that is related to the in vitro digestion of whole silages that, if validated by in vivo trials, may be a useful quantitative substitute for the qualitative processing adjustment factor that is used currently in summative equations for estimating the total digestible nutrients of corn silages.

Challenges in measuring insoluble dietary fiber.

Objectives of this review are to define criteria for evaluating insoluble dietary fiber (IDF) methods, discuss their relevance in meeting the nutritional needs of ruminants and herbivores, describe problems with empirical IDF methods, and assess their relative merits. The challenge for the researcher, nutritionist, and analyst is to select fiber methods that are relevant and reproducible. Without relevance, there is no reason to measure IDF, and without reproducibility, there is no value in doing so. Insoluble dietary fiber is a complex matrix of chemical components, and there are no primary standards that can be used to establish the validity of methods. Thus, the definition of fiber is crucial in determining method relevance. For ruminants and nonruminant herbivores, the appropriate physiological definition for selecting IDF methods may be as follows: the organic fraction of the diet that is indigestible or slowly digesting and occupies space in the gastrointestinal tract. Crude fiber does not match this definition, and its use should be abandoned. Acid detergent fiber does not measure all IDF but is useful when included with other dietary fiber methods to describe some feeds. Several current methods, including amylase-treated neutral detergent fiber (aNDF) and enzymatic-gravimetric methods, are relevant for measuring IDF. In a collaborative study, aNDF obtained a standard deviation of reproducibility (SD(R)) of 1.3%. Enzymatic-gravimetric methods of measuring IDF have been evaluated using too few feed materials to make statistically valid conclusions, but the SD(R)f IDF, for the few feeds evaluated, were similar to aNDF (0.9 to 2.4%). The enzymatic-chemical method of measuring IDF as the sum of insoluble nonstarch polysaccharides and lignin agrees with NDF, but the SDR of neutral sugar analysis using acid hydrolysis and chromatography is greater (3.2%) than other dietary fiber methods. Empirical methods--such as those used to measure IDF, although based on nutritional concepts--actually define the fraction being measured and must be followed exactly, without modification. The selection of a suitable method for IDF depends on the purpose of analysis. Analysis of sugars in insoluble polysaccharides provides more information but is less reproducible and more expensive to obtain. For routine nutritive evaluation of feeds and formulation of rations, aNDF seems to be a reasonable choice for measuring IDF based on relevance and reproducibility.

Efficacy of carbohydrate sources for milk production by cows fed diets based on alfalfa silage.

The effectiveness of three carbohydrate sources, high-moisture ear corn (HMEC), cracked shelled corn (CSC), and a 50:50 mixture of HMEC plus dried citrus pulp (DCP), fed with or without supplemental rumen-undegraded protein as expeller soybean meal (ESBM), was assessed in 48 multiparous dairy cows. All diets contained (dry mater [DM] basis) 50% alfalfa silage, 10% ryegrass silage, 28% NDF, and one of six concentrates: A) 38% HMEC; B) 38% CSC; C) 19% DCP plus 19% HMEC; D) 27% HMEC plus 12% ESBM; E) 27% CSC plus 12% ESBM; or F) 13% DCP, 13% HMEC, and 12% ESBM. Diets A, B, and C averaged 19% crude protein, of which 53% was nonprotein nitrogen (NPN), and diets D, E, and F averaged 22% crude protein, of which 40% was NPN. Cows were fed a high-energy covariate diet for 2 wk, blocked into eight groups of six, based on covariate protein yield, then randomly assigned to diets that were fed for 12 wk. Feeding ESBM increased DM intake, yields of milk, fat-corrected milk, fat, protein, SNF, and milk and blood urea concentration and decreased weight loss. There were no production differences between HMEC and CSC. However, DM intake, yields of milk, fat-corrected milk, fat, protein, lactose, SNF, and milk SNF content all were lower on the diets containing DCP versus HMEC and CSC. A 6 x 6 Latin square trial conducted at the same time with six ruminally cannulated cows showed similar effects of diet on DM intake and milk production. Ruminal ammonia was elevated by ESBM but not ruminal total amino acids and branched-chain volatile fatty acids. Ruminal propionate was highest on HMEC diets and lowest on DCP diets; acetate, butyrate and acetate-to-propionate ratio were lowest on HMEC diets and highest on DCP diets. These results indicated that, compared to HMEC and CSC, feeding the pectin-rich carbohydrate source DCP altered ruminal fermentation but depressed intake and milk production in lactating cows.

Mechanical maceration of alfalfa.

Maceration is an intensive forage-conditioning process that can increase field drying rates by as much as 300%. Because maceration shreds the forage and reduces its rigidity, improvements in bulk density, silage compaction, and ensiling characteristics have been observed. Macerating forage also increases the surface area available for microbial attachment in the rumen, thereby increasing forage digestibility and animal performance. Feeding trials with sheep have shown increases in DMI of 5 to 31% and increases in DM digestibility of from 14 to 16 percentage units. Lactation studies have demonstrated increases in milk production and BW gain for lactating Holstein cows; however, there is a consistent decrease in milk fat percentage when dairy cattle are fed macerated forage. In vitro studies have shown that maceration decreases lag time associated with NDF digestion and increases rate of NDF digestion. In situ digestibility studies have shown that maceration increases the size of the instantly soluble DM pool and decreases lag time associated with NDF digestion, but it may not consistently alter the rate or extent of DM and NDF digestion.

Effect of diet on populations of three species of ruminal cellulolytic bacteria in lactating dairy cows.

The effects of four contrasting diets were determined on populations of three species of ruminal cellulolytic bacteria (Ruminococcus albus, Ruminococcus flavefaciens, and Fibrobacter succinogenes) using oligonucleotide probes to rRNA. Diets based on alfalfa silage or corn silage as the primary fiber source were formulated to contain either 24 or 32% neutral detergent fiber measured after alpha-amylase treatment. The diets were fed twice daily to four ruminally fistulated, lactating Holstein cows in a trial using a Latin square design. The cows fed the alfalfa silage diets had higher dry matter intakes and milk production and smaller pH fluctuations than did cows fed the corn silage diets (0.3 vs. 0.8 units). The total populations of the three cellulolytic species at 3 h after feeding ranged from 0.3 to 3.9% of the bacterial domain; R. albus was generally the most abundant of the three species. The data are in general agreement with population assessments obtained by some traditional methods of culture enumeration. Although diet and individual cows had major effects on ruminal pH and volatile fatty acid concentrations and on milk production and composition, differences in cellulolytic populations that were attributable to individual cows were larger than those attributable to diet, suggesting that each cow maintained a unique assemblage of cellulolytic species.

A dairy herd model for use in whole farm simulations.

A dairy herd submodel was created for integration with other farm submodels to form DAFOSYM, a dairy farm simulation model. The herd submodel determines the best mix of available feeds to meet the fiber, energy, and protein requirements for each of six animal groups. The groups are early-, mid-, late-, and nonlactating cows, heifers over 1 yr old, and younger heifers. Feed intake, milk production, and manure dry matter and nutrient (N, P, and K) excretions are functions of the nutrient content of the diets. Required feed characteristics include crude protein, rumen degradable protein, acid detergent insoluble protein, net energy of lactation, neutral detergent fiber, total digestible nutrients, P, and K concentrations. Feed intake is predicted with fill and roughage units. These units are functions of feed neutral detergent fiber adjusted for particle size distribution and the relative rate of ruminal digestibility or physical effectiveness of the fiber. The herd submodel predicted feed intakes, nutrient requirements, diets, and manure excretions similar to those recommended or measured for dairy animals. When integrated with other farm components in DAFOSYM, the comprehensive model provides a useful tool for evaluating the long-term performance and economics of alternative dairy farm systems.

Feeding strategy, nitrogen cycling, and profitability of dairy farms.

On a typical dairy farm today, large amounts of N are imported as feed supplements and fertilizer. If this N is not recycled through crop growth, it can lead to large losses to the atmosphere and ground water. More efficient use of protein feed supplements can potentially reduce the import of N in feeds, excretion of N in manure, and losses to the environment. A simulation study with a dairy farm model (DAFOSYM) illustrated that more efficient feeding and use of protein supplements increased farm profit and reduced N loss from the farm. Compared to soybean meal as the sole protein supplement, use of soybean meal along with a less rumen degradable protein feed reduced volatile N loss by 13 to 34 kg/ha of cropland with a small reduction in N leaching loss (about 1 kg/ha). Using the more expensive but less degradable protein supplement along with soybean meal improved net return by $46 to $69/cow per year, dependent on other management strategies of the farm. Environmental and economic benefits from more efficient supplementation of protein were generally greater with more animals per unit of land, higher milk production, more sandy soils, or a daily manure hauling strategy. Relatively less benefit was obtained when either alfalfa or corn silage was the sole forage on the farm or when relatively high amounts of forage were used in animal rations.

Correlation of acid detergent lignin and Klason lignin with digestibility of forage dry matter and neutral detergent fiber.

The acid detergent lignin and Klason lignin methods were compared for their correlation with forage digestibility. Thirty-six forages, including C3 legumes and C3 and C4 grasses, were analyzed for sulfuric acid detergent lignin, Klason lignin, and in vitro digestibilities of dry matter (DM) and neutral detergent fiber (NDF). Twenty of these forages were also fed to lambs at restricted intake for measurement of DM and NDF digestibilities. Lignin concentrations determined by the two lignin methods were positively correlated, and the Klason lignin value was always greater than the acid detergent lignin concentration. The largest differences were observed for grass forages. Digestibilities of forage DM and NDF were negatively correlated with both lignin methods for the in vitro system and the lamb digestibility trials. The degree of correlation for the two lignin methods with digestibility was generally similar across all forages and within forage classes. Slopes of linear regressions of digestibility on lignin concentration did not differ between legumes and grasses. Although the sulfuric acid detergent lignin and Klason lignin procedures gave very different estimates of forage lignin concentration, they were similarly correlated with digestibility and should yield predictions of forage digestibility that have similar accuracy.