Forage Particle Size Research Articles

Intake, digestion and selection of roughage with different staple lengths by sheep and goats

The diet selection, ingestive and digestive responses of goats and sheep offered a single forage, which was prepared with three staple lengths: long (L), medium (M) and short (S) (mean particle size (mm): 13.29, 7.26 and 0.69, respectively) were studied in three experiments. The sheep (Scottish Blackface wethers) increased their dry matter intake (sheep DMI: 60.1, 61.1 and 66.2 g DM/(kg W 0.75) per day for L, M and S) and reduced mean retention time (MRT) of the undigested residues (sheep MRT: 54.6, 52.9 and 45.9 h for L, M and S) and digestive efficiency (sheep DM digestibility: 0.524, 0.522 and 0.493 for L, M and S) with the reduction in forage particle size. The respective responses of goats (feral crosses) were not modified with forage staple length (goat DMI: 68.1, 65.9 and 67.3 g DM/(kg W 0.75) per day for L, M and S); (goat MRT: 38.7, 39.3 and 41.1 h for L, M and S); (goat DM digestibility: 0.495, 0.475 and 0.480 for L, M and S). However, both species had similar intakes of digestible dry matter (DDMI) on all staple lengths (mean DDMI: 32.0 and 32.6 g DDM/(kg W 0.75) per day for sheep and goats). On the longer staple lengths (L and M) goats masticated the fibre into smaller particles than did sheep and had ( P<0.01) a greater proportion of small particles in their boli (mean: 0.45 and 0.30 for goats and sheep). The selection of components within the forage offered was different for the two species. Goats consumed forage of lower nitrogen (N) ( P<0.01) and in vitro organic matter digestibility (OMD) ( P<0.05) and higher neutral detergent fibre (NDF) ( P<0.01) contents than sheep. This was associated with the residues from sheep having a coarser texture than those of goats. When the forages of different staple lengths were offered in pairs to the animals, there was no evidence for selection of forage types by either species. It would appear that the greater ability of goats to chew efficiently provides a reason for the different responses to staple length in intake, digestibility and MRT by the two species.

Effects of Forage Particle Size and Grain Fermentability in Midlactation Cows. II. Ruminal pH and Chewing Activity

Our study investigated the effects of, and interactions between, level of dietary ruminally fermentable carbohydrate (RFC) and forage particle size on rumen pH and chewing activity for dairy cows fed one level of dietary NDF. Also, correlations between intake, production, chewing, and ruminal pH parameters were investigated. Eight cows (61 days in milk) were assigned to four treatments in a double 4×4 Latin square. Treatments were arranged in a 2×2 factorial design; finely chopped alfalfa silage (FS) and coarse alfalfa silage (CS) were combined with concentrates based on either dry, cracked-shelled corn (DC; low RFC) or ground, high-moisture corn (HMC; high RFC). Diets were fed ad libitum as a total mixed rations with a concentrate:forage ratio of 60:40. Diets averaged 18.7% crude protein, 24.0% neutral detergent fiber, 18.3%, acid detergent fiber and 27.4% starch on a DM basis. Mean particle size of the four diets were 6.3, 2.8, 6.0, and 3.0mm for DCCS, DCFS, HMCCS, and HMCFS, respectively. Decreasing forage particle size decreased ruminal pH from 6.02 to 5.81, and increasing level of RFC decreased pH from 5.99 to 5.85. Minimum daily ruminal pH decreased from 5.66 to 5.47 when level of RFC was increased, and decreased from 5.65 to 5.48 when forage particle size decreased. Time below pH 5.8 per day increased from 7.4h to 10.8h when level of RFC increased, and increased from 6.4h to 11.8h when forage particle size was decreased. Area below 5.8 showed the same relationship with RFC and forage particle size. Also, forage particle size affected the postprandial pH pattern. Cows spent more time eating when fed CS compared with FS (274 vs. 237min/d), and time spent eating decreased when level of RFC was increased (271 vs. 241min/d). Decreasing forage particle size decreased time spent ruminating (485 vs. 320min/d), rumination periods (15.3 vs. 11.7), and duration of rumination periods (29 vs. 26min). Increasing level of RFC increased time spent ruminating per kg NDF intake (68.5 vs. 79.5min/kg). Milk fat percentage was correlated to mean ruminal pH (r=0.41), time spent below pH 5.8 (r=−0.55), and area below 5.8 (r=−0.57), but not to intake or chewing variables. DMI of particles retained on a screen equivalent in size to the top screen of the Penn State particle separator was the intake parameter explaining most of the variation in mean ruminal pH (r=0.27) and was correlated to time spent ruminating (r=0.61) and chewing (r=0.61).

Effects of Particle Size of Alfalfa-Based Dairy Cow Diets on Site and Extent of Digestion

Effects of ratio of alfalfa silage to alfalfa hay and forage particle size on nutrient intakes, site of digestion, rumen pools, and passage rate of ruminal contents were evaluated in a 4×4 Latin square design with a 2×2 factorial arrangement of treatments. The diets consisted of 60% barley-based concentrate and 40% forage made up either of 50:50 or 25:75 of alfalfa silage:alfalfa hay and alfalfa hay was either chopped or ground. Lactating dairy cows surgically fitted with ruminal and duodenal cannulas were used and offered ad libitum access to a total mixed ration. Intakes of nutrients were increased by increasing ratio of silage to hay but were not affected by particle size of forage. Change in ratio of silage to hay of diets did not affect site and extent of digestion. However, increased forage particle size of the diets improved digestibility of fiber and N in the total tract, and as well as digestibility of organic matter, starch, and acid detergent fiber in the intestine. There was a shift of starch digestion from the rumen to the intestine when forage particle size was increased, although total digestion of starch was not changed. Ruminal microbial protein synthesis and microbial efficiency also improved with increasing forage particle size. Cows fed ground hay versus chopped hay had significantly lower rumen wet mass regardless of the ratio of silage to hay. Reduced forage particle size also lowered ruminal nutrient pool size for cows fed the high silage diet. Ruminal passage rates of liquid and solid were decreased by reducing the ratio of silage to hay, and retention time of solids in the total tract was shortened by reducing forage particle size. These results indicate that manipulating ratio of silage to hay in the diets of dairy cows changed feed intake but had little effect on digestion. In contrast, increased forage particle size in dairy cow diets improved fiber digestion and microbial protein synthesis in the rumen, and shifted starch digestion from the rumen to the intestine. Dietary particle size, expressed as physically effective neutral detergent fiber, was a reliable indication of ruminal microbial protein synthesis and nutrient digestion.

Effects of Forage Particle Size and Grain Fermentability in Midlactation Cows. I. Milk Production and Diet Digestibility

Our study investigated the effects of, and interactions between, level of dietary ruminally fermentable carbohydrate (RFC) and forage particle size on milk production, nutrient digestibility, and microbial protein yield for dairy cows fed one level of dietary NDF. Eight cows (61 days in milk) were assigned to four treatments in a double 4×4 Latin square. Treatments were arranged in a 2×2 factorial design; finely chopped alfalfa silage (FS) and coarse alfalfa silage (CS) were combined with concentrates based on either dry cracked shelled corn (DC; low RFC) or ground high-moisture corn (HMC; high RFC). Diets were fed ad libitum as a total mixed rations with a concentrate to forage ratio of 61:39. Diets based on DC had a predicted NEL content of 1.73Mcal/kg dry matter (DM), while HMC diets contained 1.80Mcal/kg DM. Diets averaged 18.7% CP, 24.0% NDF, 18.3% ADF, and 27.4% starch on a DM basis. Mean particle size of the four diets was 6.3, 2.8, 6.0, and 3.0mm for DCCS, DCFS, HMCCS, and HMCFS, respectively. Increasing level of RFC decreased dry matter intake (DMI) from 25.0 to 23.8kg/d and organic matter intake from 22.3 to 21.1kg/d, but intake was not affected by particle size. Milk production averaged 44.0 and 26.8kg/d solids corrected milk (SCM) and was not affected by diet, but increasing level of RFC tended to increase milk yield. Efficiency of milk production, expressed as SCM/DMI, increased from 1.06 to 1.14 when level of RFC was increased. Milk composition or yield of milk components was not affected by diet, and averaged 3.53% fat, 3.11% protein, 1.55kg/d fat, and 1.36kg/d protein. Total tract digestibility of DM and OM increased from 71.4 to 73.0% and 72.4 to 76.1% for DM and OM, respectively, when level of RFC was increased. Total tract digestibility of fiber was unaffected by diet, but total tract starch digestibility increased from 93.1 to 97.4% when HMC replaced DC. Total urinary excretion of the purine derivatives uric acid and allantoin increased from 415 to 472mmol/d when level of RFC was increased, and calculated microbial N supply increased from 315 to 365g/d. When expressed as per kilogram of digestible OMI, increasing level of RFC tended to increase microbial N supply (20.4 vs. 22.2g/kg). Cow productivity was not affected by forage particle size and ruminally fermentable carbohydrates in this study.

Association between forage particle size at initial feeding and the weigh-back and chewing activity in dairy cattle

A field trial was conducted at the University of Florida Dairy Research Unit (USA) to determine the relationship between initial coarse portion (ICP) particle size of a total mixed ration (TMR) and orts (weigh-back coarse portion, WBCP) of the same TMR. Additionally, the relationship between the ICP of a TMR and the proportion of cows chewing their cud 2.0 hours after feeding was determined. A random representative sample of TMR was taken from the feed bunk at initial feeding and 8 h later (weigh-back) every day from the same barn for 75 days. Samples were analysed for particle size content using a particle size evaluator. Proportion of the largest particles of the TMR was recorded. Additionally, the proportion of cows ruminating 2.0 hours after the morning feeding was recorded each day. Correlation and regression models between ICP and WBCP, and between ICP and the proportion of ruminating cows were calculated. The mean and standard deviation for ICP, WBCP and proportion of cows cud chewing were 14.2ñ6.6, 29.9ñ13.2 and 18.4ñ5.0%, respectively. The Pearson correlation coefficient between ICP and WBCP was 0.53, and the correlation coefficient between the proportion of cows chewing their cud and ICP in the TMR was 0.19. Initial coarse proportion was a predictor for WBCP (p&lt;0.01), but was not a predictor of the proportion of cows ruminating 2 h after the morning feeding (p&gt;0.05). These findings are suggestive of sorting of the TMR by the cows. Sorting was significantly higher (p&lt;0.01) as the coarse proportion at the initial feeding increased, but this difference was likely of little biological significance.

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 23 factorial arrangement of treatments. The dietary factors were extent of barley grain processing, coarse (1.60mm) or flat (1.36mm); forage-to-concentrate (F:C) ratio, low (35:65) or high (55:45) (dry matter basis); and forage particle length, long (7.59mm) or short (6.08mm). 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.

Effects of fibre level and particle size on rumen microbial fermentation and protein metabolism using liquid and solid associated bacteria

The effects of fibre level (F) and forage particle size (S) on ruminal fermentation profile is often mediated through changes in feed intake, rates of digestion or passage, ruminal pH and/or bacteria population. Therefore, most in vivo studies have confounded the direct effect of F or S with changes in the rumen environment. In vitro systems allow to control several fermentation conditions independently (pH, flow rates, intake). Total, bacterial and dietary nitrogen (N) flows are generally calculated using liquid associated bacteria (LAB), although solid associated bacteria (SAB) represent about 80% of total bacterial population in the rumen (Olobobokun and Craig, 1988). The objective of this experiment was to study the effects of F and S on microbial fermentation and N metabolism using LAB or SAB values in a dual flow continuos culture system.

Interactions Between Forage and Wet Corn Gluten Feed as Sources of Fiber in Diets for Lactating Dairy Cows

Twelve early lactation Holstein cows (4 fistulated) were used in replicated 4 × 4 Latin squares with 4-wk periods to determine the effective neutral detergent fiber (NDF) content of wet corn gluten feed and to measure the effect of forage particle size on ruminal mat consistency and passage rate of wet corn gluten feed. Diets were 1) 23.3% NDF (17.4 percentage units of NDF from alfalfa silage), 2) diet 1 plus 11.1 additional percentage units of NDF from alfalfa silage, 3) diet 1 plus 10.7 percentage units of NDF from wet corn gluten feed, and 4) 8.6 percentage units of NDF from alfalfa silage plus 8.9 percentage units of NDF from coarsely chopped alfalfa hay and 10.7 percentage units of NDF from wet corn gluten feed. The calculated effective NDF factor for wet corn gluten feed, using change in milk fat concentration per unit change in NDF, was 0.74 compared with an assumed 1.0 for alfalfa silage. Rumination activity was measured to calculate a physically effective NDF factor for wet corn gluten feed, which was only 0.11 compared with 1.0 for alfalfa silage. Physically effective NDF also was determined for wet corn gluten feed by wet sieving; 22% of the particles were retained on the 3.35-mm screen or greater. Ruminal mat consistency increased and passage rate of wet corn gluten feed decreased with added hay. The inclusion of chopped alfalfa hay to a diet containing wet corn gluten feed increased ruminal mat consistency, rumination activity, and slowed passage rate, resulting in greater ruminal digestion of NDF from wet corn gluten feed. Depending on the response variable, the effectiveness of NDF from wet corn gluten feed varied from 0.11 to 0.74.

Effect of forage particle size and feeding frequency on fermentation patterns and sites and extent of digestion in dairy cows fed mixed diets

This trial aimed at studying the effects and possible interactions between forage particle size and feeding frequency on the site and extent of digestion and ruminal fermentations throughout the day in dairy cows fed mixed diets. Two forage particle sizes (chopped, C, or ground and pelleted, G, dehydrated alfalfa) and two feeding frequencies (two (2) or six (6) times daily) were combined in a 2×2! arrangement. Four mid-lactation cows with cannulae in the rumen and proximal duodenum were used in a 4×4 Latin square design. They were fed at 95% of ad-libitum intake with three hours access to the manger after each meal distribution. On a dry-matter (DM) basis, the four diets consisted of 40% dehydrated whole-crop maize, 4% long perennial ryegrass hay, 25% dehydrated alfalfa and 31% concentrate (69% wheat). Dry-matter intake averaged 22.2 kg day −1. No interaction between forage particle size and feeding frequency was found. Feeding G rather than C diets reduced chewing time (22.4 vs. 26.2 min kg −1 DM), total and ruminal digestibilities of organic matter (OM) and cell-wall constituents ( p<0.10), and increased the non-ammonia nitrogen flow into the duodenum per unit of digestible OM intake ( p<0.05). Feeding G diets also reduced the molar proportion of acetic acid and increased the molar proportions of propionic and valeric acids. These changes in ruminal digestion were associated with a lower fibrolytic activity and modifications in ruminal environment. The daily means of pH and ammonia concentration were decreased, while the range of pH during the day and the time when pH and ammonia concentration were low (<6.0 and 2.9 mmol l −1, respectively) were increased. At the same time, the proportion of fluid in the reticular contents and the fractional outflow rate of liquids and small particles were decreased. Increasing feeding frequency did not affect carbohydrate digestion and mean ruminal parameters, although post-feeding variations of pH, osmolality and ammonia concentration were much less pronounced. It is concluded that reduced forage particle size can sharply affect the quantity and the nature of digestive end-products by altering chemical and physical conditions in the rumen. However, the magnitude of this effect is not dependent on the amount of fermentable OM entering the rumen in one meal.

The effect of forage source and particle size on finishing yearling steer performance and ruminal metabolism.

Two finishing trials and a metabolism trial were conducted to evaluate the effect of forage source and particle size in dry-rolled corn finishing diets. In Exp. 1, 224 crossbred yearling steers (BW = 342+/-11 kg) were used in a randomized complete block design consisting of seven treatments. Treatments were an all-concentrate diet or diets containing equal NDF levels provided by alfalfa hay or wheat straw (three treatments each) with each forage source ground to pass through a .95-, 7.6-, or 12.7-cm screen. Steers fed diets containing forage had greater (P < .05) DMI than steers fed an all-concentrate diet. Steers fed alfalfa diets gained faster (P < .05) with a greater (P < .05) concentrate efficiency than steers fed either all-concentrate or straw diets. In Exp. 2, 120 crossbred yearling steers (BW = 307+/-2 kg) were used in a completely randomized design and fed dry-rolled corn diets containing 10% alfalfa ground to pass through either a .95- or 7.6-cm screen. Alfalfa particle size had no effect on performance or carcass measurements. In Exp. 3, six ruminally fistulated steers (BW = 508+/-34 kg) were used in a 6 x 6 Latin square design and fed an all-concentrate diet or diets containing equal NDF levels provided by alfalfa hay, wheat straw, or ground corncobs with alfalfa and straw ground to pass through either a 2.54- or 12.7-cm screen. Steers fed straw diets spent more time (P < .10) chewing than those receiving the other diets. In conclusion, forage particle size had no effect on finishing cattle performance or ruminal metabolism data. However, cattle consuming different forage sources in dry-rolled corn finishing diets may not respond similarly in animal performance.

Effect of forage particle size and intake level on fermentation patterns and sites and extent of digestion in dairy cows fed mixed diets

The aim of this study was to examine the effects and possible interactions between forage particle size and intake level on the site and extent of digestion and on ruminal fermentations in dairy cows fed mixed diets. Two forage particle sizes (chopped [C] or ground and pelleted alfalfa [G]) and two intake levels (ad libitum [H] and 80% of ad libitum [L]) were combined in a 2×2 factorial arrangement. Four mid-lactating cows equipped with ruminal and duodenal cannulas were used in a 4×4 Latin square design. On a dry matter (DM) basis, the four diets consisted of 18% maize silage, 25% dehydrated pelleted whole-crop maize, 25% dehydrated alfalfa and 32% concentrate. They were distributed twice daily with three hours access after each distribution. Dry matter intake averaged 21.9 kg day −1 for the H level. Feeding G rather than C diets reduced chewing time (22.1 vs. 27.7 min kg −1 DM). Feeding G diets sharply reduced organic matter (OM) and cell-wall constituents digestibilities ( P<0.01) with these effects being greater at H than at L intake ( P<0.10). Starch digestibility and the site of digestion of OM and carbohydrate were unaffected, but non ammonia nitrogen flow into the duodenum was increased ( P<0.05). Feeding G diets did not affect ruminal fermentation at the L intake level but the molar proportion of acetic acid was decreased and that of propionic acid was increased at the H intake level. When feeding GH diet, these changes in ruminal digestibility and fermentation patterns were associated with a reduced rumen retention time and lower cellulolytic activity which, in turn, were related to modifications in the ruminal environment. The range of pH during the day and hours below 5.6 were increased, whereas ruminal NH 3 was decreased compared to the three others diets. When cows were fed at H level the digestibilities of OM and cell-wall constituents were depressed ( P<0.01), along with the percentage of digestible materials disappeared in the rumen. Efficiency of microbial synthesis remained unaffected but the ruminal degradability of feed nitrogen tended to be lowered ( P<0.10). The H level increased ruminal content but did not change ruminal retention time. Lower ruminal digestibilities were mainly related to a depressed rate of digestion at H level. It is concluded that reducing the forage particle size can strongly affect the quantity and the nature of the digestive end-products by altering ruminal conditions. However, the magnitude of these digestive effects is dependent on the amount of fermentable OM ingested.

Interactions of Tallow and Hay Particle Size on Yield and Composition of Milk from Lactating Holstein Cows

An 18-wk lactation study was conducted to determine whether the effects of tallow on the lactation performance of dairy cows were influenced by particle size of hay in the ration. A total mixed ration containing 50% concentrate, 25% corn silage, and 25% alfalfa hay (dry matter basis) was fed to Holstein cows. Four total mixed rations were developed based on differences in the percentage of tallow in the concentrate and particle size of alfalfa hay: 1) 0% tallow, long-cut hay; 2) 0% tallow, short-cut hay; 3) 5% tallow, long-cut hay; and 4) 5% tallow, short-cut hay. Ration had no effect on dry matter intake, body weight gain or change in body condition score. Tallow increased milk and milk protein yields but reduced milk protein concentration. However, the effects of tallow on milk and milk protein yields were the same, regardless of hay length in the ration. A tendency for an interaction of tallow and hay particle size was detected for fat-corrected milk (FCM) because tallow increased FCM more when hay was short. Ration had no effect on volatile fatty acids in ruminal samples collected via a stomach tube. In this study, the effects of tallow on milk yield and composition from Holstein cows were the same, regardless of hay particle size in the ration. The tendency for tallow to increase FCM more when hay was short suggests at least a limited role of forage particle size in the determination of how fat supplements in dairy rations affect lactation performance.

Effects of forage type and protein supplementation on voluntary intakes and particle breakdown of forages by dry dairy cows

There is now considerable evidence of residual effects of both energy and protein supply during the dry period on performance in the next lactation. Changes in forage intake and eating/rumination behaviour in the dry period have been implicated in predisposition to metabolic disorders in the subsequent lactation. In particular, there is a close association between intake either side of calving (Grummer, 1995). The primary objective of this experiment was to identify the effects, and interactions, of pre-partum energy and protein supply on forage intake and particle size reduction (as an index of rumination behaviour) of cows in the dry period.Fifty-two Holstein-Friesian cows, calving from September to November 1996, were used in a continuous design experiment The cows were dried off 8 weeks before their anticipated calving date and grazed on bare pasture for one week before training to use Calan gates (using grass silage only).

Interactions Among Forages and Nonforage Fiber Sources

Source, amount, and physical characteristics of dietary forage can interact with nonforage fiber sources and influence ruminal and total tract fiber digestion, passage, and performance of dairy cows fed diets containing substantial nonforage fiber in place of forage. Dietary NDF from forage can be reduced to ≤60% and still provide sufficient amounts of effective fiber for FCM production that is similar to or superior to that with high forage diets. Because of small particle size and high specific gravity, increased ruminal rate of passage may be responsible for lower ruminal NDF digestibility of nonforage fiber sources fed at high dietary amounts. As the amount of soybean hulls increased from 50 to 95% of a pelleted mix for dairy cows, passage rate increased by 8%. In five studies, the digestion of soybean hull diets was improved by the addition of coarse forage. Fiber digestibility might have improved because coarse hay increased ruminal retention time of nonforage fiber sources and allowed more complete digestion. Addition of coarsely chopped alfalfa hay to diets based on silage containing 25% soybean hulls increased ruminal mat consistency by 49% and tended to slow the ruminal escape rate of soybean hulls by 16%. When high percentages of nonforage fiber are fed, the amount of dietary forage is necessarily low, and forage particle size should be adequate to stimulate rumination and entrap small feed particles. The amount and particle size of forage in the diet interacts with the substituted nonforage fiber source to determine the net impact on the rate of ruminal digestion and passage of nonforage fiber.

Net flux of nutrients across splanchnic tissues in wethers consuming grasses of different sources and physical forms ad libitum.

Crossbred sheep (n 16, 8.5 months of age and 33 (SE 0.9) kg) were used in a 21 d experiment (2 x 2 factorial) to determine effects on net flux of nutrients across the portal-drained viscera (PDV) and liver of ad libitum consumption of bermudagrass (Cynodon dactylon; B) v. ryegrass (Lolium multiflorum)-wheat (Triticum aestivum; RW) hay, coarsely chopped (CC) or finely ground and pelleted (GP). Crude protein concentrations were 86, 81, 113 and 119 g/kg and neutral-detergent fibre concentrations were 710, 688, 654 and 672 g/kg (dry matter basis) for B-CC, B-GP, RW-CC and RW-GP respectively. Digestible energy intake (6.0, 9.6, 10.2 and 13.8 MJ/d) differed (P < 0.01) with grass source and form, and digestible N intake values were 4.4, 7.0, 8.4 and 14.1 (SEM 0.82) g/d for B-CC, B-GP, RW-CC and RW-GP diets respectively. Consumption of O2 by the PDV (118, 165, 144 and 155 mmol/h) and splanchnic bed (196, 273, 247 and 266 mmol/h for B-CC, B-GP, RW-CC and RW-GP respectively) was greater (P = 0.07) for GP than for CC. The ratio splanchnic heat energy production: digestible energy intake was greater (P = 0.06) for B than for RW (0.374, 0.300, 0.278 and 0.219 for B-CC, B-GP, RW-CC and RW-GP respectively). alpha-Amino-N release by the PDV (P < 0.01; 11.6, 12.8, 23.0 and 18.7 mmol/h) and uptake by the liver (P = 0.07; 15.2, 6.1, 17.0 and 19.3 mmol/h for B-CC, B-GP, RW-CC and RW-GP respectively) were greater for RW than for B. Release of NH3-N by the PDV was greater (P = 0.02) for CC than for GP (12.5, 6.2, 15.7 and 8.9 mmol/h), and hepatic urea-N release differed between grass sources (P = 0.03) and physical forms (P = 0.07; 22.6, 12.7, 31.4 and 24.8 mmol/h for B-CC, B-GP, RW-CC and RW-GP respectively). In conclusion, decrease in forage particle size elicited by grinding and pelleting did not affect the difference between grass sources in splanchnic tissue heat energy production relative to digestible energy intake.

A Simple Method for the Analysis of Particle Sizes of Forage and Total Mixed Rations

A simple separator was developed to determine the particle sizes of forage and TMR that allows for easy separation of wet forage into three fractions and also allows plotting of the particle size distribution. The device was designed to mimic the laboratory-scale separator for forage particle sizes that was specified by Standard S424 of the American Society of Agricultural Engineers. A comparison of results using the standard device and the newly developed separator indicated no difference in ability to predict fractions of particles with maximum length of less than 8 and 19mm.The separator requires a small quantity of sample (1.4L) and is manually operated. The materials on the screens and bottom pan were weighed to obtain the cumulative percentage of sample that was undersize for the two fractions. The results were than plotted using the Weibull distribution, which proved to be the best fit for the data.Convenience samples of haycrop silage, corn silage, and TMR from farms in the northeastern US were analyzed using the forage and TMR separator, and the range of observed values are given.

Portal and hepatic fluxes in sheep and concentrations in cattle ruminal fluid of 3-(4-hydroxyphenyl)propionic, benzoic, 3-phenylpropionic, and trans-cinnamic acids.

Extraction methods and HPLC procedures were developed for analysis of potential ruminal metabolites of dietary phenolics (reduced phenolics). Hepatic portal venous blood from wethers fed bromegrass, bermudagrass, ryegrass-wheat, and alfalfa hays also was analyzed for hippuric (HA), 3-(4-hydroxyphenyl)propionic (4OHPPA), benzoic (BA), 3-phenylpropionic (PPA), and t-cinnamic (CA) acids. Additionally, mesenteric arterial and hepatic venous blood was analyzed and, in conjunction with blood flow measurements, fluxes for portal-drained viscera (PDV) and liver were calculated. Ruminal fluid from four steers fed two levels of forage and two forage particle sizes in a Latin square design was analyzed for PPA and CA. 3-Phenylpropionic and benzoic acids were the most concentrated reduced phenolics identified in hepatic portal venous blood. Concentrations of PPA in ruminal fluid varied with ruminal disappearance of p-coumaric and ferulic acids. Additionally, hepatic portal venous concentrations of PPA were correlated (P < .05) with p-coumaric acid (r = .57) and ferulic acid (r = .67) intakes. Net release of PPA from PDV was observed, suggesting absorption of PPA from the gut. The liver removed PPA and BA with less efficiency. Given the relatively high concentrations of PPA in blood of ruminants, specific effects of this reduced phenolic on liver metabolism of ruminants should be assessed.

Factors influencing particle size distributions in finely ground forage

Two studies were conducted to assess the possibility of using particle size distribution following grinding as a routine procedure of forage evaluation. It was concluded that although differences in particle size distribution could be detected when different feeds were ground, it would be difficult to standardize the technique since particle size distributions were influenced by type of mill used for grinding, particle size of forage before grinding, and moisture content of the forage. Key words: Forages, grinding, particle size, moisture, mill

Forage level and particle size effects on orchardgrass digestion by steers: II. Ruminal digestion kinetics of cell wall components

Four steers (502 +/- 49 kg) with ruminal cannulas were used in a 4 x 4 Latin square experimental design with a 2 x 2 factorial arrangement of treatments to determine the effects of the dietary forage:concentrate ratio (96:4 and 60:40) and forage particle size (long hay and coarsely ground hay) on in situ ruminal digestion kinetics of orchardgrass hay DM and cell wall neutral monosaccharides, uronic acids, acetyl groups, and hydroxycinnamic acids. Dacron in situ bags containing orchardgrass hay were fermented for 0, 4, 8, 12, 18, 24, 48, and 96 h. Digestion profiles of DM and cell wall monomers in undigested residues recovered from the rumen were analyzed using a first-order, exponential equation to estimate the indigestible fraction (fi), the insoluble, potentially digestible fraction (fd), and the fractional rate constant (kd) of digestion of fd. Initial results indicated that fi was not consistently influenced by diet fed to the steers; thus, in situ digestion profiles were analyzed to estimate single fi and fd values common to all steers and diets and different estimates of kd for each steer x diet combination (16 total). Estimates of fi (percentage of original) for cell wall components were ranked in the following order: galactose (12.6), ferulic acid (13.9), arabinose (14.5), total uronic acids (15.4), glucose (19.8), xylose (28.4), p-coumaric acid (34.6), and acetyl groups (35.8).(ABSTRACT TRUNCATED AT 250 WORDS)

Forage level and particle size effects on orchardgrass digestion by steers: I. Site and extent of organic matter, nitrogen, and cell wall digestion

Four steers (502 +/- 49 kg) with ruminal, duodenal, and ileal cannulas were used in a 4 x 4 Latin square experimental design with a 2 x 2 factorial arrangement of treatments to determine the effects of dietary forage:concentrate ratio (96:4 [96F] and 60:40 [60F]) and forage particle size (long hay [L] and coarsely ground hay [G]) on site and extent of digestion of OM, N, and plant cell wall monomeric components. Orchardgrass hay was the forage source used and was the sole source of cell wall material fed to steers (DMI = 88.6 g/kg BW.75). Diurnal variation in ruminal pH was greater when steers consumed 60F vs 96F (P < .01) and greater for G vs L (P < .10). Ruminal fluid volumes (liters) and daily outflows (liters/day) were greater (P < .05) when steers consumed 96F or L. True ruminal OM digestion (percentage of intake) was greater (P < .05) when steers consumed 60F (69.0) vs 96F (59.5) or L (65.8) vs G (62.7). Efficiency of net bacterial CP synthesis (grams of N/kilogram of true ruminal OM disappearance) was greater (P < .05) when steers consumed 60F (33.8) vs 96F (30.8). Total tract digestibilities of NDF and ADF were 63.3 and 53.0% when steers consumed 96F and were decreased (P < .05) to 52.3 and 43.8% when steers consumed 60F. Total tract digestibilities of plant cell wall arabinose, galactose, glucose, xylose, and uronic acids were 78.7, 69.7, 70.8, 67.6, and 79.7% when steers consumed 96F and were decreased (P < .05) when steers consumed 60F. Ruminal digestion accounted for greater than 90% of total tract digestion of all cell wall monosaccharide components when steers consumed 96F but accounted for 6 to 20 percentage units less of total digestion when steers consumed 60F. Total tract disappearances of cell wall acetyl groups, ferulic acid, and p-coumaric acid were 62.4, 79.4, and 50.6% when steers consumed 96F and were decreased (P < .05) to 49.7, 73.2, and 42.2% when steers consumed 60F. Addition of concentrate to diets, but not forage processing, decreased total tract digestibilities of cell wall components and shifted site of digestion to the lower gastrointestinal tract.