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PubMed1982

Effect of water temperature on rumen temperature, digestion and rumen fermentation in sheep.

Three studies were conducted to examine effect of water temperature on rumen temperature, digestion and fermentation in sheep. Four, 2-yr-old wethers were used in a Latin square design among four water temperature treatments: 0, 10, 20 and 30 C. Rumen temperature was depressed most by 0 C water followed by 10 C, 20 C and 30 C water. For 0, 10, 20 and 30 C water, respectively, 108, 96, 96 and 72 min were needed to reach initial rumen temperature. Water temperature had no significant effect on N balance or percentage dry matter digestibility, crude protein digestibility and crude fiber digestibility although lowest digestion coefficients were observed for the 0 C treatment. Numerical differences were observed in rumen pH or volatile fatty acid (VFA) and ammonia-N concentrations at the various water temperatures; however, the effects were not significant. Rumen pH was maximally depressed at 2 h postfeeding for 0 C water, 3 h for 10 C water, 4 h for 20 C water, and 3 and 4 h for 30 C water. By 4 h postfeeding, the 0 C water treatment produced the highest concentration of all VFA and ammonia-N; however, by 4 h not all of the VFA or ammonia-N concentrations had reached maxima for 10, 20 or 30 C water treatments. The 0 C water treatment produced the lowest concentrations of ammonia-N and VFA (except acetate) by 5 h postfeeding.

Animals↗
PubMed1983

Influence of feed intake level on site of digestion in steers fed a high concentrate diet.

A high concentrate diet was fed at 1.2, 1.5, 1.8 and 2.1% of body weight to four Angus steers (258 kg) equipped with cannulas in the proximal duodenum and distal ileum. As level of feed intake increased, flow of N, nonammonia N, microbial N and feed N to the small intestine increased linearly (P less than .05). Bypass of feed N increased from 44 to 71% of fed N. At the highest intake level, ruminal protein degradation and protein solubility were almost equal. At lower intake levels, feed protein degradation exceeded N use by microbes, but at the higher level of intake, microbial protein synthesis exceeded N available from protein degradation. Microbial efficiency increased as feed intake was increased to 1.8% of body weight. Apparent digestion of N in the small intestine increased with feed intake. Starch digestion in the rumen increased slightly with feed intake while organic matter and acid detergent fiber (ADF) digestibility declined. At the highest level of feed intake, no ADF disappearance occurred in the rumen. Results suggest that level of feed intake markedly alters 1) bypass and supply of intestinally digested protein, 2) need for degradable N in the rumen, 3) efficiency of microbial growth and 4) ruminal fiber digestion. Both retention time and contingent characteristics of fermentation in the rumen appear to be involved in these alterations.

Abomasum↗
PubMed1983

A study of the relationship between performance and dietary component digestibilities by swine fed different levels of dietary fiber.

A 49-d feeding trial, using 192 growing-finishing pigs (avg initial wt, 32 kg), was conducted to identify pigs of widely differing average daily gains (ADG) when fed 16% crude protein diets containing either 0, 7.5 or 15% corn cobs. There were linear decreases in both ADG (P less than .01) and gain/feed (P less than .001) with increasing levels of dietary corn cobs. Average daily feed intake increased linearly (P less than .001), but average daily digestible energy (DE) intake tended to decrease (P less than .08) with increasing dietary fiber level. Gain/DE was not apparently affected by dietary treatment. At the end of the feeding trial, 27 pigs, nine from each dietary treatment, were selected on the basis of ADG to represent pigs of above average, average and below average performance during the feeding trial. Previous ADG of the pigs selected for these were .93, .81 and .69 kg, respectively. In these pigs, plasma levels of glucose decreased (P less than .01) linearly, but urea N tended to increase (P less than .08) linearly with increasing level of dietary corn cobs. A digestion trial was conducted to determine if previous performance of the selected pigs could be related to the digestibilities of dietary components and the retention of N by these pigs. Nitrogen and dry matter (DM) digestibilities and dietary DE decreased linearly with increasing level of dietary corn cobs. The digestibilities of dietary neutral detergent fiber (NDF) and acid detergent fiber (ADF) decreased both linearly and quadratically with increasing level of corn cobs. Regardless of dietary treatment, no significant differences in any of these criteria were observed among pigs selected on the basis of widely differing ADG during the feeding trial.

Animals↗
PubMed1983

Effect of protein source and lasalocid on nitrogen digestibility and growth by ruminants.

Protein supplements having either a high (soybean meal, SBM) or low (escape protein, EP) extent of ruminal N degradability with or without lasalocid (L) were evaluated in digestion and growth trials. The SBM supplement included soybean meal while EP was a combination of dehydrated alfalfa and distillers dried grains. Nitrogen digestibility of SBM supplements was consistently higher than EP supplements when evaluated with two lamb trials. Digestibility of N was improved 8% in trial one (64.9 vs 60.3%) and 27% in trial two (66.3 vs 52.3%) with SBM vs EP. The addition of L to the supplements improved N digestibility by 6% in trial one (64.5 vs 60.6%) and 13% in trial two (62.9 vs 55.7%). No interactions between protein source and L were measured in either trial. Dry matter digestibility was not changed by protein source or L in either trial. Rumen propionate was increased and acetate to propionate ratio decreased when L was fed. Plasma urea N was lower over a 24 h sampling period when lambs were fed EP supplements compared with SBM supplements (11.07 vs 16.44 mg/100 ml); however, L did not appear to consistently alter the values. When steers were supplemented with the same protein sources during a 105-d winter pasture trial daily gains were not affected (P greater than .10) by either protein source or L (.429, .495, .476 and .514 kg/d for SBM, SBM+L, EP and EP+L, respectively) although numerically there did not appear to be main effect improvements due to EP and L.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Influence of dietary alfalfa:orchardgrass hay and lasalocid on in vitro estimates of dry matter digestibility and volatile fatty acid concentrations of cecal contents and rate of digesta passage in sows.

Four mature crossbred sows were fistulated in the cecum, with two sows fed a corn-alfalfa:orchardgrass hay (46%) diet (CH) and two fed a corn-soybean meal diet (CS). Four experiments were conducted to evaluate buffers, incubation times, buffer pH and substrate and inocula sources in an in vitro, anaerobic, mixed-culture system. In vitro dry matter digestibility (IVDMD) and substrate solubility in buffer (SS) were determined. In Exp. 1, substrates were CH and CS diets with cecal inocula obtained from CH- and CS-fed sows. The bicarbonate (B) buffer resulted in lower (P less than .01) and less variable SS for all treatments. In vitro dry matter digestibility was higher (P less than .01) for the CS diet at both 24 and 48 h incubation. Use of the B buffer also resulted in higher (P less than .001) IVDMD values. In Exp. 2, substrates were either as in Exp. 1 or were freeze-dried cecal contents (CC) from CH- or CS-fed sows. In vitro dry matter digestibility of CC was lower (P less than .006) than IVDMD of diet, while IVDMD was higher (P less than .02) with cecal inocula than fecal inocula. In Exp. 3, substrate-inocula treatments were CH-CH, CH-CS, CS-CH and CS-CS. Substrate solubility was lower (P less than .05) at pH 5.8 than at pH 6.8. In vitro dry matter digestibility was higher when substrate and inocula were from the same source and at pH 5.8. In Exp. 4, CC and inocula were from sows fed CH and CS diets with or without lasalocid. In vitro dry matter digestibility was higher with CC from lasalocid-fed sows and inocula from sows fed no lasalocid. The CH diet resulted in higher acetate (Ac) and lower propionate (Pr) molar proportions than did the CS diet, while lasalocid increased molar proportion Pr and decreased molar proportion Ac in cecal contents from sows fed either diet. Corn-alfalfa:orchardgrass hay-fed sows had a faster rate of digesta passage and shorter cecal retention time than did CS-fed sows.

Animals↗
PubMed1985

Digestibility of fiber components and reproductive performance of sows fed high levels of alfalfa meal.

Two experiments were conducted with second-parity sows fed either 5 or 50% alfalfa meal diets (Exp. 1) or 5, 50 or 95% alfalfa meal diets (Exp. 2) beginning 30 d after breeding and continuing through lactation, 21 d postpartum. Diets in both experiments were calculated to be equal in crude protein, but different in metabolizable energy content. Feed intake was restricted to 2 kg/d during gestation and ad libitum during lactation. Sows were tethered in metabolism crates 45 d after breeding. Total feces were collected during two 5-d collection periods, 60 and 100 d after breeding. Digestibilities of dry matter, fiber components (neutral detergent fiber, acid detergent fiber, hemicellulose and cellulose), protein and energy were determined in both experiments for all diets and periods of gestation. In both experiments, there was a reduction (P less than .05) in digestibility of dry matter, fiber components, protein and energy with increasing fiber levels for both periods of gestation. In Exp. 1, the decrease in digestibility of dry matter, neutral detergent fiber, acid detergent fiber, cellulose and energy was greater at 100 d gestation than at 60 d in sows fed 50% alfalfa. In Exp. 2, 50 and 95% dietary alfalfa reduced 60-d digestibilities of dry matter, all fiber constituents, energy and protein; these digestibilities were further reduced (P less than .05) at 100 d of gestation. In Exp. 1, weight gains of sows fed 5 and 50% alfalfa diets from breeding to 109 d gestation, were 42 and 18 kg/sow (5 greater than 50% level, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1986

Effects of dietary nitrogen level and ileal antibiotic administration on digestion and passage rates in beef heifers. I. High-concentrate diets.

Four beef heifers (211 kg) fitted with ruminal, duodenal and ileal cannulae (T-type), were fed a high-concentrate diet with a low (L) or high (H) level of N (1.71 and 2.18%, respectively), and received daily doses of either saline (S) or an antibiotic (A) mixture (2 g neomycin sulfate and .25 g bacitracin) into the terminal ileum in a 4 X 4 Latin-square experiment. Added N increased ruminal NH3-N concentration and tended to increase efficiency of microbial growth and to decrease ruminal disappearance of organic matter, starch and protein. Administration of antibiotics into the ileum reduced nucleic acid content of feces (P less than .05), tended to reduce digestion of organic matter and starch in the hindgut and total tract and increased ileal pH (P less than .05). Ileal administration of antibiotics increased ruminal escape of feed N by 26 and 42% with the low and high N diets, respectively, and increased ruminal passage rate of particulates. Ruminal N digestion was inversely related to ruminal particulate passage rate (r = -.49; P less than .06). Ruminal liquid passage rate was inversely related to rate of fluid passage through the hindgut and was reduced by ileal administration of antibiotics with the low N diet, but increased by antibiotics with the high N diet. Results indicate that administration of antibiotics into the terminal ileum alters digestive function earlier in the digestive tract including ruminal passage rates and digestion of N in the rumen. Responses were partially modulated by dietary N level.

Animals↗
PubMed1986

Factors affecting starch digestibility with special emphasis on sorghum and corn.

Starch exists inside the endosperm of cereals enmeshed in a protein matrix, which is particularly strong in sorghum and corn. Starch digestibility is affected by the plant species, the extent of starch-protein interaction, the physical form of the granule, inhibitors such as tannins, and the type of starch. Among the cereals, sorghum generally has the lowest starch digestibility. The resistance to digestive action of the hard peripheral endosperm layer is largely responsible for this effect. Processing methods such as steam-flaking and reconstitution are effective in raising sorghum digestibility to near that of corn. Waxy sorghum shows consistently higher feeding value than normal sorghum. Both the starch granules and the protein matrix around them are more digestible in waxy grain. The development of new heterowaxy or waxy sorghum hybrids may further increase sorghum feed efficiency.

Animal Feed↗
PubMed1987

Effect of wheat and high-moisture sorghum grain fed singly and in combination on ruminal fermentation, solid and liquid flow, site and extent of digestion and feeding performance of cattle.

Two experiments were conducted to determine how varying the proportion of wheat (W) and high-moisture sorghum grain (SG) in 80% grain dies would affect ruminal fermentation, liquid and solid flow, site and extent of digestion (Exp. 1) and feeding performance of cattle (Exp. 2). In Exp. 1, three ruminal, duodenal and ileal cannulated steers (average weight 295 kg), fed at 1.54% of body weight, were used in a six-period crossover design. Treatments were: W, 50W:50SG (W:SG) and SG. Increasing wheat level decreased ruminal pH, molar proportion of acetate, and acetate:propionate ratio (P less than .05) and increased (P less than .05) L-lactate concentration, molar proportions of propionate and valerate and total volatile fatty acid concentration. Ruminal liquid dilution and outflow rates were faster (P less than .05) and retention time was shorter (P less than .05) for the W diet. Duodenal and ileal liquid flow increased (P less than .05), and solid flow decreased (P less than .05), as dietary level of wheat increased. Apparent ruminal digestion (% of intake) of dry matter (DM) and organic matter (OM) was greater (P less than .01) with the wheat-containing diets. Intestinal DM and OM digestion (percent of intake) was higher (P less than .05) with the SG and W:SG diets. Ruminal, small intestine, large intestine and total tract starch digestion (percent of intake) was 93.5, 5.6, .7, 99.8, 71.5, 20.4, 5.7, 97.6; and 48.0, 32.5, 10.5, 91.0 with the W, W:SG and SG diets, respectively. In Exp. 2, group-fed (24 pens) steers (avg initial weight 341 kg) were fed ad libitum once daily for 121 d. Treatments were: W, 67W:33SG, 33W:67SG and SG. Rates of gain (kg/d) with the W (1.32), 67W:37SG (1.33) and 33W:67SG (1.30) diets were similar (P greater than .05), but faster (P less than .05) than those with the SG diet (1.16). Feed intake was lower (P less than .01) with the W and 67W:33SG diets, but the wheat-containing diets were utilized more efficiently (P less than .01). Increasing the proportion of wheat in sorghum grain feedlot diets improved cattle performance by optimizing ruminal and post-ruminal digestion.

Animal Feed↗
PubMed1987

Effects of tallow supplementation and protein withdrawal on ruminal fermentation, microbial synthesis and site of digestion.

The effects of tallow supplementation [0% (NT) vs 7.5% (T)] and crude protein level [8.5% (LP) vs 12.0% (HP)] on ruminal fermentation, microbial protein (MCP) synthesis, digesta passage and site of digestion were estimated using yearling Angus X Simmental steers (390 kg) fitted with ruminal and T-type duodenal cannulae. Chromium-EDTA and ytterbium (Yb) chloride were used as markers of the liquid and solid phases. Passage and site of digestion data were estimated from the concentrations of Yb in the duodenal digesta and feces. Dry matter (DM) intakes were 6.8, 6.5, 6.3 and 6.6 kg/d for the NT-LP, NT-HP and T-HP diets, respectively. Ruminal ammonia concentrations (mg/100 ml) for the NT-LP, NT-HP, T-LP and T-HP diets were 1.22, 4.75, 1.05 and 3.41, respectively. Tallow decreased (P less than .05) acetate (mol/100 mol), increased (P less than .01) propionate (mol/100 mol) and decreased the total volatile fatty acid concentration. Tallow depressed apparent ruminal DM and organic matter (OM) digestibilities only on the HP diet. High protein increased ruminal DM, OM and fiber digestibilities. Tallow and LP tended to shift the site of OM digestion to the lower tract. The liquid and solid dilution rates for the NT-LP, NT-HP, T-LP and T-HP diets were 9.53, 3.37; 5.63, 3.28; 6.66, 5.10 and 6.79, 5.34%/h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Influence of supplemental nitrogen source on digestion of nitrogen, dry matter and organic matter and on in vivo rate of ruminal protein degradation.

Seven Holstein steers (340 kg) fitted with ruminal, duodenal and ileal cannulae were used to measure the influence of supplemental N source on digestion of dietary crude protein (CP) and on ruminal rates of protein degradation. Diets used were corn-based (isonitrogenous, 12% CP on a dry matter basis, and isocaloric, 80% total digestible nutrients) with urea, soybean meal (SBM), linseed meal (LSM) or corn gluten meal (CGM) as supplemental N. Ruminal ammonia N concentrations were higher (P less than .05) in steers fed LSM than in those fed CGM, but did not differ from those in steers fed urea or SBM (11.7, 6.7, 9.1 and 9.2 mg/100 ml, respectively). Due to the high degradability of urea, ruminal digestion of dietary CP was greater (P less than .05) in steers fed urea than in those fed CGM, but intermediate in steers fed SBM and LSM (58.4, 48.8, 53.1 and 53.9%, respectively). Flow of bacterial nonammonia N to the duodenum was highest (P less than .05) in steers fed SBM or LSM, intermediate (P less than .05) for urea and lowest (P less than .05) for CGM (86.8, 86.1, 76.3 and 65.9 g/d, respectively). Efficiency of bacterial protein synthesis was lowest in steers fed CGM and differed (P less than .05) from SBM (15.6 vs 21.8 g N/kg organic matter truly digested, respectively). Rate of ruminal digestion for SBM-CP differed (P less than .05) from that of CGM-CP but not from that of LSM-CP (17.70, 5.20 and 10.13%/h, respectively). The slow rate of ruminal degradability of CGM resulted in increased amounts of dietary protein reaching the intestinal tract but lower amounts of bacterial protein, thus intestinal protein supply was not appreciably altered.

Animal Nutritional Physiological Phenomena↗
PubMed1988

Effects of dietary fiber of young adult genetically lean, obese and contemporary pigs: rate of passage, digestibility and microbiological data.

Twenty-one genetically lean, obese or contemporary slaughter weight castrated male pigs (6 mo old; seven of each genotype) were assigned to individual tether stalls and fed either a control diet (low fiber) or a diet containing 80% alfalfa meal (high fiber) at 1.50% of initial body weight for 71 d (1.75% for d 1 to 4). Apparent dry matter digestibility of the diets was estimated by determining acid insoluble ash in fecal samples. Fecal cellulolytic bacteria and total viable bacteria were enumerated at d 0, 14, 35, 49 and 70. Fecal inocula were used to determine 48-h in vitro digestibility of alfalfa meal fractions on the same days. Digesta rate of passage was determined by feeding a pulse dose of chromium-mordanted alfalfa fiber to the pigs fed the high-fiber diet. In vivo digestibility of both diets was less for the obese pigs than for the lean or contemporary genotypes. In vitro digestibility of alfalfa fiber fractions was not different between the genotypes fed either diet. When the high-fiber diet was fed, in vitro digestibility increased for all genotypes from d 0 to d 14, but not thereafter. The numbers of cellulolytic bacteria for all three genotypes were greater when pigs were fed the high-fiber diet (23.0 X 10(8), 51.6 X 10(8), 37.2 X 10(8) per gram fecal dry weight; obese, lean and contemporary, respectively) compared to the low-fiber diet (3.0 X 10(8), 3.2 X 10(8), 3.4 X 10(8), respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Combinations of high-moisture harvested sorghum grain and dry-rolled corn: effects on site and extent of digestion in beef heifers.

To determine the effects of blends of high-moisture harvested sorghum grain (HMS) and dry-rolled corn (DRC) on site and extent of digestion, high-grain diets were fed to Angus-Hereford heifers (315 kg) in a 5 x 5 latin square. The grain portion consisted of ratios (HMS:DRC) of 0:100, 25:75, 50:50, 75:25 and 100:0. Heifers were equipped with ruminal, duodenal and ileal T-type cannulas. Digestibilities of OM (P less than .05) and non-ammonia nitrogen (NAN; P less than .01) in the total tract declined linearly as HMS replaced DRC. Chyme flow (liters/d) through the duodenum increased linearly (P less than .01), and true ruminal OM disappearance tended to decline linearly (P less than .10) as HMS replaced DRC. A quadratic response (P less than .05) in extent of starch disappearance (g/d) in the rumen was noted; blends were lower than either individual grain. Ruminal escape of feed N tended to be quadratic (P less than .10); values for individual grain types were greater than blends. Microbial efficiency increased linearly (P less than .05) as HMS replaced DRC. Extent of starch digestion in the rumen averaged 82.7% compared to only 2.9% in the small intestine and 5.7% in the large intestine. Altering the ratio of HMS to DRC appeared to have more effect on ruminal fermentation than on digestion in the small intestine; most starch and nitrogen responses were quadratic. Increases in ruminal pH and chyme flow, potentially caused by increased salivary flow, may cause non-linear changes in the solubility of proteins in HMS and DRC, when fed as blends, altering the digestibility of protein and starch from values predicted from the individual grains.

Animal Feed↗
PubMed1989

A review of the use of intrinsically 14C and rare earth-labeled neutral detergent fiber to estimate particle digestion and passage.

Methodology that allows simultaneous measurement of dynamic events affecting NDF digestion in passage from the rumen should improve our understanding of factors influencing intake and digestion. Ideally, particle flow is measured with a marker indelibly attached to or intrinsically part of the feed. If flow measurements are to reflect physiological conditions, marked and unmarked feed must be digested and passed with identical fractional rates. Application of 14C-labeled plant fiber to the study of ruminal dynamics has been slow because of expense and difficulty in producing 14C-labeled plant material. Recently, alfalfa was intrinsically labeled with 14C under field conditions to produce plant material similar in composition to unlabeled material. Carbon-14 specific activity was similar in all particle sizes, and in indigestible and digestible NDF. Greater concentrations of ytterbium (Yb) were associated with smaller vs larger particles. Larger differences in turnover rates among animals than differences attributable to treatments force comparisons of markers to be made within animal or with in vitro systems. The uncertainty about how extrinsic markers respond under various environments resulting from interaction of feed properties and gut function, and the high error inherent in measuring dynamic systems, raise serious questions on the interpretability of results. Advantages of 14C-labeled NDF over other markers include simultaneous measurements of particle breakdown, digestion and passage rates as well as the potential to study microbial attachment, VFA, CO2 and CH4 production and rate of incorporation of labeled metabolites into tissues.

Animals↗
PubMed1989

Voluntary consumption and digestion of diets high in endophyte-infected fescue by growing Holstein steers.

Holstein steers (112 to 258 kg BW) were fed diets high in endophyte-infected fescue (80 to 100%) in 15 latin square experiments to determine the relationships among BW, forage composition, voluntary consumption and digestion. Fescue DM intake (kg/d) increased linearly (P less than .05) with increasing BW (-.513 + .0275 BW; R2 = .69). Regressing log fescue intake (DM) on log BW resulted in a BW exponent of 1.1034 (R2 = .66) but did not account for any more variation in intake than the simple regression did. The percentage NDF in fescue was not related (P greater than .10) to fescue intake (kg/d) and was correlated only slightly with fescue intake as a percentage of BW (r = -.13; P less than .10). Adding the percentage of fescue in the diet or NDF in the fescue to the regression of DM intake on BW did not increase explained variation. Organic matter intake (kg) and digestibility (%) were not related (P greater than .10). Based on standardized partial regression coefficients, differences in voluntary intake accounted for 60% of the variation in the total quantity of OM digested, whereas differences in digestibility accounted for 40%. In conclusion, ingestibility of endophyte-infected fescue hay in relation to changing BW did not vary greatly. Concentrations of chemical constituents such as NDF and ADL in fescue were poorly correlated with feed consumption and digestibility.

Acremonium↗
PubMed2000

Effects of barley grain processing on extent of digestion and milk production of lactating cows.

Effects of barley processing on site and extent of digestion and milk production in dairy cows were evaluated in a 4 x 4 Latin square design with four lactating cows with ruminal and duodenal cannulas. Barley grain was steam-rolled to four thicknesses: coarse, medium, medium-flat, and flat. The processing index (PI), measured as volume weight of barley after processing expressed as a percentage of its volume weight before processing, was 81.0, 72.5, 64.0, and 55.5% for the four treatments, respectively. Diets consisted of 53% concentrate (dry matter basis) containing one of the four processed barleys. Cows were offered ad libitum access to a total mixed ration three times daily. Dry matter intake was quadratically increased with decreasing PI, with maximum intake for cows fed medium-flat barley. Although ruminal digestibilities of organic matter, starch, and crude protein were not affected by grain processing, intestinal and total tract digestibilities were linearly increased as PI of barley was reduced. Milk yield was quadratically increased (25.6, 28.1, 30.8, and 29.0 kg/d) with decreasing PI, and maximum milk yield was for cows fed medium-flat barley. Milk fat and lactose contents were similar, but milk protein content was increased with decreasing PI. These results indicate that the optimal extent of barley processing for dairy cows fed diets supplying adequate fiber was medium-flat, corresponding to a processing index of about 64%. Coarsely or flatly rolled barley is not recommended, because extensive processing did not further improve intake of digestible nutrients, and coarsely processed barley resulted in the lowest intake of digestible organic matter; hence, lowest milk production. Processing index is a reliable and practical method to quantitatively measure extent of steam rolling.

Animal Nutritional Physiological Phenomena↗
PubMed2001

Initial pH as a determinant of cellulose digestion rate by mixed ruminal microorganisms in vitro.

In vitro fermentations of pure cellulose by mixed ruminal microorganisms were conducted under conditions in which pH declined within ranges similar to those observed in the rumen. At low cellulose concentrations (12.5 g/L), the first-order rate constants (k) of cellulose disappearance were successively lower at initial pH values of 6.86, 6.56, and 6.02, but in each case the value of k was maintained over a pH range of 0.3 to 1.2 units, as the fermentation progressed. Plots of k versus initial pH were linear, and k displayed a relative decrease of approximately 7% per 0.1 unit decrease in pH. At high cellulose concentration (50 g/L) and an initial pH of 6.8, cellulose digestion was initially zero order, the absolute rate of digestion declined with pH and digestion essentially ceased at pH 5.3 after only 30% of the added cellulose was digested. Further incubation resulted in a loss of bound N and P, suggesting that at low pH cells lysed or detached from the undigested fibers. Pure cultures of ruminal cellulolytic bacteria also were able to ferment cellulose to a minimum pH of 5.1 to 5.3, but the extent of fermentation was increased by coculture with noncellulolytic bacteria. A model is proposed in which the first-order rate constant of cellulose digestion is determined by the pH at which the fermentation is initiated, and end product ratios reflect greater activity of the noncellulolytic population as pH declines.

Animals↗
PubMed2001

Effects of grain processing, forage to concentrate ratio, and forage particle size on rumen pH and digestion by dairy cows.

Dietary factors that alter the intake of effective fiber were evaluated for their effects on rumen fermentation, digestion, and milk production using a double 4 x 4 quasi-Latin square design with a 2(3) factorial arrangement of treatments. The dietary factors were extent of barley grain processing, coarse (1.60 mm) or flat (1.36 mm); forage-to-concentrate (F:C) ratio, low (35:65) or high (55:45) (dry matter basis); and forage particle length, long (7.59 mm) or short (6.08 mm). Eight lactating cows with ruminal and duodenal cannulas were offered ad libitum access to a total mixed diet and milked twice daily. Dry matter intake was increased by increasing the extent of grain processing. Mean rumen pH was lower for cows fed flatly rolled barley than for cows fed coarsely rolled barley, whereas F:C ratio or forage particle size had no effect on rumen pH. Rumen pH was not correlated with effective NDF intake but tended to be correlated with digestibility of starch in the rumen. Total tract digestibilities of dry matter, organic matter, starch, and neutral detergent fiber were increased by feeding flatly rolled barley or low F:C ratio diets. Milk yield and milk protein content were higher in cows fed flatly rolled barley or low F:C ratio diets. Milk fat content tended to increase with high F:C ratio or long forage particle length but was reduced by feeding flatly rolled barley. In this study, extent of grain processing and intake of ruminal available starch were the most influential factors affecting milk production. Reducing the ratio of F:C improved total digestion and actual milk production. Forage particle length had minimal impact on digestibility and milk production.

Ammonia↗