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The nutritive value of forage maize (Zea mays L.) may be improved through genetic selection for increased rate of fiber digestion or decreased indigestible fiber concentration. To identify sources of genetic variation, 45 maize inbreds were evaluated for in vitro neutral detergent fiber (NDF) digestion kinetic parameters using stem internode tissue harvested at silking during 2 yr. Near infrared reflectance spectroscopy (NIRS) was also used to estimate NDF digestion kinetic parameters. Maize inbreds varied significantly in NDF concentration and digestion kinetic parameters using either conventional in vitro analysis or NIRS predictions. Using NIRS predictions, inbreds varied in NDF concentration from 497 to 662 g kg -1 dry matter (DM), rate of NDF digestion ranged from 0.037 to 0.077 h -1 , and extent of NDF digestion was 525 to 735 g kg -1 NDF. The ranges for NIRS predicted parameters were less than those observed for the calibration data set by conventional analysis. Correspondence between conventional analysis data and NIRS predictions were good, except for lag time. Digestion kinetics calculated from NIRS predicted residues provided more precise predictions of lag time and fractional rate of digestion when compared with observations derived from conventional analyses, than did direct prediction of these kinetic parameters. Correlations between rate of NDF digestion and 18-h NDF digestibility (r = 0.79) or between potential extent of NDF digestion and 96-h NDF digestibility (r = 0.95) were large enough that these two fermentation intervals might substitute for conducting complete digestion kinetic studies with eight to 10 fermentation times. The substantial genetic variation among these maize inbreds shows good potential for development of silage hybrids with improved fiber digestion parameters. Year and year x genotype interactions were significant suggesting that identification of superior inbred lines will require evaluations in multiple environments.

Discussion of limits to ruminant digestion of plant cell walls largely focuses on the lignification and chemical nature of these walls. We examined the anatomical limitations to digestion of thick-walled fiber particles in grasses. Estimates were made of wall surface area to cell wall volume ratio (SA/CWV), rate of bacterial digestion, and accessibility to bacteria for different types of cell walls. The analysis reveals the following: (i) Bacterial digestion of fiber cells can progress only from the interior (lumen) surface because their middle lamella-primary wall region is consistently found to he indigestible. (ii) Because of secondary wall thickness (c. 1-5 μm), we calculate that at best only 0.45 to 0.60 μm of wall thickness (as little as 20% of the wall in some cells) would he digested within the average residence time of fiber particles in the rumen assuming digestion of wall at the fast rate of 0.02 μm h −1 . (iii) This potential rate of wall digestion overestimates that of typical fiber particles in the rumen because these particles are comprised of many hundreds of cells and relatively few will be disrupted by chewing to give bacteria immediate access to cell lumens. (iv) Digestion of thick-walled cells by bacteria is surface-based and sclerenchyma cells have a particularly low SA/CWV ratio. Calculated ratios for single cells are sclerenchyma (1:5) < stem parenchyma (1.9: 1) < mesophyll (6.7 to 13.3:1). (v) During digestion of secondary walls, an accumulation of toxic levels of phenolic monomers in cell lumens and at the digesting surface is unlikely, but more slowly diffusing phenolic-carbohydrate complexes could reach concentrations toxic to bacteria. The structural limitations described are discussed in relation to future research directions

Near infrared reflectance spectroscopy (NIRS) is rapidly being accepted for routine prediction of forage quality and chemical constituents. Accurate predictions require calibration with samples analyzed by reference methods. This study was conducted to determine whether deviations between values predicted by NIRS and those determined by conventional techniques are random. In all, 108 samples from the basal 150 mm of immature and mature stems of replicated, field-grown cultivars of alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), red clover (Trifolium pratense L.), smooth bromegrass (Bromus inermis Leyss.), and orchardgrass (Dactylis glomerata L.) were studied

Methodology can play a critical rôle in the measurement of digestion kinetics, especially when the objective is to define kinetic parameters for use in formulating rations or modelling animal responses. Measurement of gas production kinetics provides the opportunity to evaluate the rate of digestion of the soluble, more rapidly fermenting fractions of foods but has the potential for being more sensitive to the in vitro procedure used. Differences among procedures that have little impact on digestion of dry matter after 48 h of incubation, may have dramatic effects on fermentation of soluble matter during the first 20 h. Our objective was to develop a method for measuring the kinetics of gas production that would minimize any detrimental effects associated with the in vitro system and provide estimates of digestion kinetics that can be used to both describe foods for ration formulation systems and provide parameters for models of ruminal digestion.

The kinetics of gas production during ruminal fermentation may provide valuable information about foods that can be used to formulate diets and model animal responses. However, measurement of digestion kinetics is affected by methodology and techniques must be established that provide accurate and precise estimates of kinetic parameters. Because gas production measurements provide the opportunity to estimate the digestion kinetics of both soluble and insoluble matter in foods, it would be desirable to use this technique on a wide variety of forages, grains, supplements, and by-product foods. Applying an in vitro technique to such a wide variety of substrates raises questions about the type of inoculum that should be used. The objective of our study was to evaluate the effects of donor animal and its diet on the measurement of gas production kinetics using both forage and concentrate substrates.

Analysis of the fibrous composition of feeds by the Goering and Van Soest procedure requires that samples be filtered in the presence of mineral acids and organic solvents. In this process, it is desirable to use a manifold that not only is resitant to these reagents, but also is inexpensive and easy to construct

Use of sodium sulfite to reduce nitrogenous contamination in fiber analysis was evaluated. The effects of sodium sulfite on analytical accuracy and precision were examined for amylase-treated neutral detergent fiber (aNDF), sequentially determined acid detergent fiber (sADF), and acid detergent lignin (sADL) in animal feeds. In one experiment, 0.5 g sodium sulfite was added per sample during neutral detergent (ND) extraction. The treatment consistently reduced aNDF, sADF, and sADL values of 180 alfalfa samples and improved precision (decreased within-sample variance of replicated analyses). The greatest effect was on precision of sADL analysis, with within-sample variance reduced by more than 50%. In a second experiment, 24 animal feeds were analyzed for a aNDF, sADF, and sADL with and without addition of 0.5 g sodium sulfite per sample during ND extraction. Nitrogen contents of the recovered fiber fractions were determined. Sodium sulfite reduced fiber and lignin values and decreased nitrogen concentration in residues. Within-sample variance was lower in all analyses. In a third experiment, 23 animal feeds were analyzed for aNDF with sodium sulfite at 0, 0.25, 0.5, and 1.0 g per sample. Average aNDF of feeds was reduced by each additional increment of sodium sulfite; however, 1.0 g sodium sulfite resulted in only a slight reduction in aNDF compared with 0.5 g. Therefore, 0.5 g sodium sulfite per sample should be added to samples prior to aNDF analysis.

Two experiments were designed to determine the effect of gas production during in vitro digestion on functional specific gravity (FSG) of forage particles. In Exp. 1, FSG of ground alfalfa hay decreased from 1.123 to 1.049 between 3 and 9 h of incubation and increased thereafter to reach a plateau at 1.309 after 30 h of incubation. Gas production peaked at 6 h, but gas associated with particles increased until 9 h of incubation. Gas associated with solid residue was correlated to gas production (r = -.67) but also was influenced by gas holding capacity and rate of escape from the particles. In Exp. 2, measurements were performed on ground alfalfa hay, alfalfa silage, and bromegrass hay containing 42.6, 35, and 66.4% NDF, respectively. Gas production seemed to be related to the amount of readily available substrate. Although at 9 h of incubation more gas was produced by alfalfa silage (.235 mL.min-1.g of DM-1) than by bromegrass hay and alfalfa hay (.087 and .187 mL.min-1.g of DM-1, respectively), gas associated with particles was greater for alfalfa hay (.416 mL/g of DM) than for bromegrass hay and alfalfa silage (.256 and .281 mL/g of DM, respectively). The increase in FSG was more rapid for alfalfa silage than for the hays. After 27 h of digestion, gas associated with particles (milliliters per gram of DM) and FSG were .164, 1.226; .147, 1.235; and .001, 1.467 for bromegrass hay, alfalfa hay, and alfalfa silage, respectively. Gas produced during fermentation delayed the increase in specific gravity of forage particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals on pasture do not always have the opportunity for ad libitum consumption. Our objectives were to determine effects of intake level on digestibility of 12 grass hays, and to relate differences in intake and digestibility to proportions of leaf blade, leaf sheath and stem. In each of two periods, 24 wethers were offered one of 12 hays at three consecutive levels of feeding: (L1) ad libitum, allowing 15% refusal; (L2) restricted to 100% of hay consumed ad libitum by individual wether during L1; and (L3) 1.8% of BW on a DM basis. Hays offered included two sorghum-sudan, four barley, four oat and two pearl millet. Hays were similar in NDF concentration but differed in morphological composition Organic matter intake averaged 1.99 +/- .04, 1.79 +/- .04 and 1.52 +/- .01% of BW for L1, L2 and L3, respectively. Organic matter digestibilities averaged 71.8 +/- .55 72.4 +/- .60 and 72.3 +/- .65% for L1, L2 and L3, respectively. Intake SEM within hays were lower with restricted intakes (L3), whereas the opposite was observed for the SEM for digestibility. Forage morphological composition within feeding level influenced intake and digestibility by altering diet selection capabilities of wethers. Wethers did not consume equal NDF amounts, ranging form .95 to 1.47% of BW, because hays differed in morphological composition. Ash-free ADF and 72% sulfuric acid lignin were higher (P less than .01) in stem than in blade or sheath. In vivo digestibilities measured under restricted feeding conditions were related more closely (P less than .05) to in vitro estimates of digestibility than were digestibilities measured under ad libitum conditions (r = .72, .79 and .85 for L1, L2 and L3, respectively). This study demonstrates that variation in morphological characteristics of forages may account for part of the difference in voluntary intake of forages of similar chemical composition. New knowledge in this area will be valuable in developing improved forage quality prediction procedures.

Forty clinically normal lactating Holstein cattle from a herd involved in a natural outbreak of chronic nitrate toxicosis were divided into 2 equal groups according to production, stage of lactation, age, and apparent pregnancy state (pregnant or nonpregnant). One group was fed a low-nitrate ration (average of 356 ppm on dry matter basis in concentrate; less than 400 ppm in free-choice hay for 1st 5 wks of study). The 2nd group was fed a high-nitrate (HN) ration (average of 1,600 ppm in protein concentrate-amemded corn silage; 4,000 ppm in free-choice hay for the 8-week study). At the end of the study, the 2 groups were classified according to their starting reproductive status: nonpregnant (open); early pregnant (less than 60 da); midpregnant (average of 105 da). Milk production, milk fat, and milk nitrate concentrations were similar for cows fed both rations. Serum progesterone concentration (SPC) was depressed (P less than 0.05) in cows fed the HN ration. This effect was prominent in open, luteal phase cows, less prominent but still apparent in early pregnant cows, and absent in midpregnant cows. The early reproductive problems of chronic nitrate toxicosis may be due to depression of SPC. A possible mechanism of inhibition of luteal progesterone synthesis by inhibition of cytochrome P-450 is presented.

Many novel solutions to the nationwide problem of solid waste disposal have been proposed. A recent one which has been studied is the feeding of paper products to farm animais such as dairy cattle as a source of cellulose (MERTENS et ai. 1971a). Cattle will consume rations containing up to 20 weight % paper and assimilate up to 90% of the dry matter of certain of them such as brown cardboard (MERTENS et ai. 1971b). Office paper has also been advantageously incorporated in sheep rations (NISHIMUTA et,ai. 1969). It is known that compounds such as the polychlorinated biphenyls (PCB's) are used as dye carriers in specialt'y printing inks. High concentrations of PCB's have been reported as present in carbonless copying paper (MASUDA et al. 1972). It is possible that these compounds may survive when specialty paper products are regenerated for use in other paper products such as cardboard. Paperboard has been reported to contain PCB-type compounds (ANONYMOUS 1972). These compounds could be transferred to cows' milk or meat as residues. Contamination of food by contact is possible if the paper material becomes part of a food container. Electron capturing peaks in extracts of cereal grains have been traced to the presence of corresponding compounds in cloth bags (LEVl and NOWICKI 1972). Certain metals may also be present in paper as constituents of the ink or as a result of the printing process. Furthermore deep rooted trees may absorb unusual elem~Its from lower soil horizons (ROBINSON et ai. 1958) which may then be present in paper. In the work reported a survey of about i00 papers and paper products has been made for the presence of chlorinated organic compounds using gas chromatography with electron affinity and electrolytic conductivity detectors and the combination gas chromatography-mass spectrometry. Metals and other elements in paper were also determined by spark source mass spectrometry. Experimental

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 6 h 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 =