Effects Of Forage Particle Size Research Articles

Portable X-Ray Fluorescence Spectroscopy for Rapid and Cost-Effective Determination of Elemental Composition of Ground Forage.

The recent development of portable X-ray fluorescence spectrometers (PXRF) has created new avenues for rapid plant elemental concentration determination at reduced cost while avoiding hazardous chemicals. A few studies have indicated the potential use of PXRF for homogenous plant tissue analysis. However, there is a lack of information for analysis of heterogeneous plant samples like livestock forage, which consists of a mixture of several species and plant parts, each varying in elemental concentration. Our objective was to evaluate PXRF for forage analysis, specifically the effect of forage particle size and scan time on important elements including P, K, Ca, and Fe determination. Hay samples (n = 42) were oven dried (60°C for 3 days) and ground into three particle sizes (≤0.5 mm, 0.25–0.5 mm and 1–2 mm). Prepared samples were scanned by PXRF using a vacuum (<10 torr) without a filter. Samples were placed in cups over thin prolene X-ray film and scanned for 180 s. A subset (n = 29) were also scanned for 60 and 120 s. PXRF counts for P, K, Ca, and Fe were compared with laboratory Inductively Coupled Plasma Optical Emission Spectroscopy (ICP) determinations, using regression models. Results indicated that these elements could potentially be determined with PXRF (r2 ≥ 0.70) in heterogeneous forage samples. Relationship strength increased with decreasing particle size, however, the relationship was still strong (r2 ≥ 0.57) at the largest particle size. Scanning time did not affect the relationship with ICP concentration for any of the particle sizes evaluated. This work demonstrated that with the right sample preparation PXRF can obtain results comparable to acid digestion and ICP regardless of sample composition, and suggests the potential for in situ determinations.

Short communication: Forage particle size and fat intake affect rumen passage, the fatty acid profile of milk, and milk fat production in dairy cows consuming dried distillers grains with solubles

Four ruminally cannulated Holstein cows averaging (±SD) 116±18 d in milk and 686±52kg of body weight were used in a 4×4 Latin square design with a 2×2 factorial arrangement of treatments to test the effects of forage particle size and concentration of corn oil on milk fat depression. Cows were housed in individual stalls, milked daily at 0700 and 1800h, and individually fed daily at 0900h for ad libitum consumption allowing approximately 10% orts. Four 28-d periods, in which each cow was offered 1 of 4 total mixed rations, included reduced-fat dried distillers grains with solubles at 30% of dietary dry matter and differed in forage particle size by inclusion of chopped grass hay (LONGP) or grass hay pellets (SHORTP) and 0 or 2% corn oil (CO). Dietary treatments were 0% corn oil + short particle size (CO0+SHORTP), 0% corn oil + long particle size (CO0+LONGP), 2% corn oil + short particle size (CO2+SHORTP), and 2% corn oil + long particle size (CO2+LONGP). Dry matter intake and milk yield were not affected by treatment averaging 26.5±1.19kg/d and 32.8±3.34kg/d, respectively. A decrease was found in 3.5% fat-corrected milk with the inclusion of oil resulting in 34.6 and 26.6±2.6kg/d for 0 and 2% oil diets, respectively. An oil × size interaction was found for milk fat concentration resulting in 2.27, 3.02, 3.62, and 3.62±0.23% for CO2+SHORTP, CO2+LONGP, CO0+SHORTP, and CO0+LONGP, respectively. Fat yield was reduced from 1.22 to 0.81±0.09kg/d with 2% oil diets. Cows consuming diets with long particle size spent 29 more minutes eating compared with the cows consuming short particle size (198 and 169±15min/d). Rumination time decreased from 504 to 400±35min/d for cows consuming short particle size compared with long particle size. Total chewing was reduced from 702 to 570±4min/d when cows consumed short particle size. Feeding long particle size decreased rate of passage of dry matter from 3.38 to 2.89±0.42%/h; concomitantly mean retention time increased from 31.7 to 38.4±5.36h for diets containing long particle size. The results of this experiment show that effects of oil on milk fat depression were less severe when cows consumed long particle size, suggesting that dietary manipulations that modify rumen kinetics also affect milk fat production in dairy cows consuming reduced-fat dried distillers grains with solubles supplemented with corn oil.

A meta-analysis and meta-regression of the effect of forage particle size, level, source, and preservation method on feed intake, nutrient digestibility, and performance in dairy cows

A meta-analysis of the effect of forage particle size (FPS) on nutrient intake, digestibility, and milk production of dairy cattle was conducted using published data from the literature (1998–2014). Meta-regression was used to evaluate the effect of forage level, source, and preservation method on heterogeneity of the results for FPS. A total of 46 papers and 28 to 91 trials (each trial consisting of 2 treatment means) that reported changes in FPS in the diet of dairy cattle were identified. Estimated effect sizes of FPS were calculated on nutrient intake, nutrient digestibility, and milk production and composition. Intakes of dry matter and neutral detergent fiber increased with decreasing FPS (0.527 and 0.166kg/d, respectively) but neutral detergent fiber digestibility decreased (0.6%) with decreasing FPS. Heterogeneity (amount of variation among studies) was significant for all intake and digestibility parameters and the improvement in feed intake only occurred with decreasing FPS for diets containing a high level of forage (>50%). Also, the improvement in dry matter intake due to lowering FPS occurred for diets containing silage but not hay. Digestibility of dry matter increased with decreasing FPS when the forage source of the diet was not corn. Milk production consistently increased (0.541kg/d; heterogeneity=19%) and milk protein production increased (0.02kg/d) as FPS decreased, but FCM was not affected by FPS. Likewise, milk fat percentage decreased (0.058%) with decreasing FPS. The heterogeneity of milk parameters (including fat-corrected milk, milk fat, and milk protein), other than milk production, was also significant. Decreasing FPS in high-forage diets (>50%) increased milk protein production by 0.027%. Decreasing FPS increased milk protein content in corn forage-based diets and milk fat and protein percentage in hay-based diets. In conclusion, FPS has the potential to affect feed intake and milk production of dairy cows, but its effects depend upon source, level, and the method of preservation of forages in the diet.

Effect of feed forage particle size and dietary urea on excretion of phosphorus in lactating dairy cows

Thirty six multiparous Danish Holstein cows, 222 days from calving with a standard deviation (±) of 102 days, 627±7kg of body weight, and 32±3kg/d energy corrected milk were used to investigate the effect of forage particle size (FPS) and dietary urea supplementation on excretion of phosphorus (P) in feces and urine when cows were fed P below requirement. Dietary P content was 2.5gP/kg DM in all treatments. Treatments (CONTROL, SHORT and LOW-N) were all based on the same content of forage ingredients but varied in FPS and dietary urea content. In CONTROL and SHORT rumen degradable protein was optimized according to the Nordic protein evaluation system by supplementing dietary urea, whereas urea was excluded in LOW-N in order to obtain a supply of rumen degradable protein below requirements. It was hypothesized that dietary factors that reduce saliva secretion via reduced chewing activity will reduce the inevitable loss of endogenous P (IL) of P and that dietary factors that reduce the supply of rumen degradable protein in the form of dietary urea will result in a decrease in rumen microbial incorporation of P and in turn increase digestibility of P and hereby reduce IL of P. In SHORT FPS of grass hay was reduced to a theoretical particle size of 3mm, as compared to 40–60mm in CONTROL and LOW-N. Rations were fed for ad libitum intake for 16d and balance trials were conducted on d 15 and 16. Indigestible neutral detergent fiber was used as an internal marker to estimate fecal output and total tract digestibilities. The obtained negative P balances confirmed that dairy cows were fed below P requirement, indicating that treatment effects on fecal P excretion mainly originated from variations in IL. Fecal P excretion was not reduced with reduced forage particle size despite reduction in chewing time. Fecal excretion of P was not affected by reduced dietary urea supply below requirement despite a reduction in digestibility of OM. Therefore, the results of the present study do not support the concept that fecal loss of endogenous P is affected by FPS. Nor do the results support the concept that fecal loss of endogenous P is affected by supply of rumen degradable protein.

Effects of Rumen Acid Load from Feed and Forage Particle Size on Ruminal pH and Dry Matter Intake in the Lactating Dairy Cow

The objective of this study was to evaluate the effects of level of concentrate acidogenic value (AV) and forage particle size on ruminal pH and feed intake in lactating dairy cows. Two isoenergetic (net energy for lactation=1.5±0.01Mcal/kg) and isonitrogenous (crude protein=17.4±0.1% dry matter) concentrates with either a low AV or high AV were formulated and fed in a total mixed ration with either coarsely or finely chopped corn silage and alfalfa haylage ad libitum. Four rumen-fistulated cows (114±14 d in milk) were randomly assigned to 1 of the 4 treatments in a 4×4 Latin square with a 2×2 factorial treatment arrangement. Each period consisted of 3-wk (14-d treatment adaptation and 7-d data collection). Increasing the concentrate AV decreased the mean pH (from 6.07 to 5.97) and minimum pH (from 5.49 to 5.34). Cows fed high-AV diets spent a longer time below pH 5.6 (135.1 vs. 236.7min/d; low-AV diet vs. high-AV diet, respectively) and pH 5.8 (290.0 vs. 480.6min/d; low-AV diet vs. high-AV diet, respectively) than cows fed low-AV diets. Increasing forage particle size had no effect on the mean and minimum ruminal pH. There was an interaction between concentrate AV and forage particle size on maximum ruminal pH. Increasing forage particle size increased the maximum pH for cows fed the high-AV concentrate (6.69 vs. 6.72; low-AV diet vs. high-AV diet, respectively) and had no effect on the maximum pH for cows fed the low-AV concentrate (6.98 vs. 6.76; low-AV diet vs. high-AV diet, respectively). Increasing the concentrate AV did not affect dry matter intake but reduced neutral detergent fiber intake from 9.7 to 8.8kg/d. Milk fat content was negatively correlated with time and area below pH 5.6 (time below, r=−0.51; area below, r=−0.56) and pH 5.8 (time below, r=−0.42; area below, r=−0.54). These results suggest that coarse forage particle size can attenuate drops in ruminal pH. However, the ameliorating effects of forage particle size on drops in ruminal pH were more apparent for high-AV diets than for low-AV diets. The AV approach combined with physically effective neutral detergent fiber would therefore improve the formulation of diets and help to mitigate subacute ruminal acidosis in dairy cows.

Effects of Forage Particle Size, Forage Source, and Grain Fermentability on Performance and Ruminal pH in Midlactation Cows

Our study investigated the effects of, and interactions between, forage particle size, level of dietary ruminally fermentable carbohydrate (RFC), and level of dietary starch on performance, chewing activity, and ruminal pH for dairy cows fed one level of dietary NDF. Twelve cows (48 DIM) were assigned to six treatments in a replicated 6×6 Latin square. Treatments were arranged in an incomplete 2×2×2 factorial design. Factors were: dry cracked shelled corn (DC, low RFC) or ground high-moisture corn (HMC; high RFC), finely chopped or coarse silage, and alfalfa silage as the only forage or a 50:50 ratio (DM basis) of alfalfa and corn silage. Diets combining HMC with only alfalfa silage were not included in the experiment. Diets were fed for ad libitum intake as a TMR with a concentrate:forage ratio of 61:39. Diets based on only alfalfa silage and diets based on a mix of alfalfa and corn silage averaged 18.6 and 15.8% CP, 25.8 and 24.7% NDF, 17.7 and 14.8% ADF, and 29.1 and 37.3% starch, respectively. Mean particle sizes were 5.3, 2.7, 5.6, and 2.8mm for coarse alfalfa, fine alfalfa, coarse corn silage, and fine corn silage, respectively. Decreasing forage particle size decreased DMI (23.3 vs. 21.6kg) and organic matter intake (22.0 vs. 20.2kg). Increasing RFC decreased DMI (22.8 vs. 21.0kg) and organic matter intake (21.5 vs. 20.0kg). Decreasing forage particle size increased energy-corrected milk for alfalfa based diets (34.9 vs. 37.4kg). Percentage of milk fat decreased with decreasing forage particle size (3.07 vs. 2.90%) and increased level of RFC (3.04 vs. 2.57%). Percentage of protein increased when corn silage partially replaced alfalfa silage (2.84 vs. 2.90%) but decreased when HMC replaced DC (2.90 vs. 2.84%). Apparent total tract digestibility of DM (66.7 vs. 68.5%), OM (65.9 vs. 70.7%), and starch (88.9 vs. 93.4%) increased when level of RFC was increased. Increasing level of RFC decreased mean ruminal pH from 5.82 to 5.67 and decreased minimum pH. Hours per day at which pH was <5.8, and area <5.8, increased when corn silage partially replaced alfalfa silage (2.6 vs. 4.4h and 8.9 h×pH vs. 11.4 h×pH) and decreased further when level of RFC was increased (4.4 vs. 6.4h and 11.4 h×pH vs. 14.3 h×pH). Decreasing forage particle size in HMC diets increased hours and area <5.8, but for DC diets, the effect of forage particle size depended on forage source. Interactions were found between level of physically effective fiber, forage source, and level of RFC on production and pH, complicating the inclusion of these effects in dairy ration formulation and evaluation.

Effects of Particle Size of Alfalfa-Based Dairy Cow Diets on Chewing Activity, Ruminal Fermentation, and Milk Production

Effects of forage particle size measured as physically effective NDF and ratio of alfalfa silage to alfalfa hay of diets on feed intake, chewing activity, particle size reduction, salivary secretion, ruminal fermentation, and milk production of dairy cows were evaluated using 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, comprised either of 50:50 or 25:75 of alfalfa silage:alfalfa hay, and alfalfa hay was either chopped or ground. Various methods were used to determine physically effective NDF content of the diets. Cows surgically fitted with ruminal and duodenal cannulas were offered ad libitum access to these total mixed diets. The physically effective NDF content of the diets was significantly lower when measured using the Penn State Particle Separator than when measured based on particles retained on 1.18-mm screen. Intake of DM was increased by increasing the ratio of silage to hay but was not affected by physically effective NDF content of diets. Eating time (hours per day) was not affected by the physically effective NDF content of diets, although cows spent more time eating per unit of DM or NDF when consuming high versus low alfalfa hay diets. Ruminating time (hours per day) was increased with increased physically effective NDF content of the diets. Rumen pH was affected more by changing dietary particle size than altering the ratio of silage to hay. Feeding chopped hay instead of ground hay improved ruminal pH status: time during which ruminal pH was above 6.2 increased and time during which ruminal pH was below 5.8 decreased. Milk production was increased by feeding higher concentrations of alfalfa silage due to increased DM intake, but was not affected by dietary particle size. Feed particle size, expressed as mean particle length or physically effective NDF was moderately correlated with ruminating time but not with eating time. Although physically effective NDF and chewing time were not correlated to mean rumen pH, they were negatively correlated to the area between the curve and pH 5.8, indicating a positive effect on reducing the risk of acidosis. Milk fat content was correlated to rumen pH but not to physically effective NDF or chewing activity. These results indicate that increasing physically effective NDF content of the diets increased chewing activity and improved rumen pH status but had limited effect on milk production and milk fat content.

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.

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).

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.

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.

Effects of Forage Particle Size and Long Hay for Cows Fed Total Mixed Rations Based on Alfalfa and Corn

A 2 × 2 factorial arrangement of treatments, in which particle length of alfalfa silage in the TMR and supplementary long alfalfa-grass hay were the factors, was used to determine whether hay benefits lactating cows and whether its effects depend on fibrosity of the main forage source. Without supplementary hay, TMR contained 45% forage, including corn silage, and 26 to 27.5% NDF. When hay was fed, the amount of alfalfa silage in the corresponding TMR was reduced. In the production trial, 40 cows (20 multiparous) were fed the diets for 8 wk in early lactation. No interactions of silage length and hay occurred on any production variables except lactose concentration in the milk of multiparous cows. Addition of hay to the diet enhanced DMI, without effect on production, so efficiency of milk production was reduced. Shorter alfalfa silage enhanced DMI by multiparous cows, reduced SCM and FCM in primiparous cows, and depressed fat test in both groups. Milk composition and component production generally were unaffected. Five rumen-fistulated cows in early to midlactation each were given the four treatments during four 3-wk periods. Hay enhanced rumination when short alfalfa silage was fed but tended to reduce it on long alfalfa silage. Hay also depressed rumen pH and enhanced VFA concentrations. Alfalfa silage length had minimal effects on rumination and no effect on fermentation, and neither hay nor silage length affected digestion of silage DM or NDF in the rumen. Addition of hay to the diet may not be beneficial for cows fed TMR, but longer term feeding studies are needed.

Effect of Particle Size of Forage and Rumen Cannulation upon Chewing Activity and Laterality in Dairy Cows

Three ruminally cannulated Holstein dairy cows housed in free stalls (with .7% slope) were fed three total mixed rations, differing in silage particle size, in a 3 × 3 Latin square design. Observations on cow behavior were made every 5min during 24h for each of three periods. Additional observations of six cows (three intact, three cannulated) housed under identical conditions yielded information concerning recumbent rumination activity and laterality. Results indicated that decreasing particle size of forage reduced time spent ruminating, whether standing or recumbent, and had no effect upon rumination rate or number of rumination bouts per 24-h period. Eating time was unaffected by treatment. Effect of forage particle size upon baseline rumination activity appeared to be most pronounced from 0800 to 2000h, although maximum rumination activity occurred during nighttime hours. Ruminally cannulated cows demonstrated increased right-side laterality (70%) compared with intact cows (47%), but the cows tend to ruminate while lying on their left side. The percentage of time spent ruminating while recumbent on the left side was similar (55%) for intact and cannulated cows.

Effect of Particle Size of Alfalfa Hay on Intake, Digestibility, Milk Yield, and Ruminal Cell Wall of Dairy Cattle

Alfalfa hay was chopped in a tubgrinder containing screens with apertures of 31, 63, or 100mm. The hays were fed with concentrate to lactating cows (Experiment 1) and without concentrate to nonlactating, fistulated cows (Experiment 2). The objective was to find effects of forage particle size upon intake, digestibility, milk yield, and ruminal cell wall. In Experiment 1, there were no significant effects of forage particle size upon forage or total DM intake, digestibility of NDF, cellulose, nitrogen retained, milk yield, or milk fat percent. Digestibility of DM, ADF, and protein increased as particle size decreased. In Experiment 2, forage DM intake was greater for the 63 than the 100-mm forage but digestibility of cell wall and DM were not different among treatments. Ruminal volume for the 31 and 63-mm forages was greater than the 100-mm forage. Ruminal DM and ruminal cell wall were greater for the 63-mm forage than the 100-mm forage, with the 31-mm forage in between. Increased volume, DM, and cell wall probably account for increased intake of the 63-mm forage. Chopping alfalfa to these three sizes had no particularly positive or negative effects on animal productivity.

Effect of Forage Particle Size on In Situ Digestion Kinetics

The effect of forage particle size on in situ DM digestion kinetics was evaluated. Six forages, “Florida-77” alfalfa, “Florigraze” rhizoma peanut, “Tifton-78” bermudagrass, “Mott” dwarf elephantgrass, “Pensacola” bahiagrass, and “Floralta” limpograss were ground through a 2-mm screen and separated into particle size fractions by dry sieving. Mean particle size of forages ranged from 256 to 341 μm. Particle shape appeared different between legumes and grasses. Grasses had mostly rectangular and needle-shaped particles whereas legumes had square or triangular-shaped particles. Three particle sizes (710, 355, and 106 μm) of bermudagrass and rhizoma peanut were chosen for further evaluation. Percent NDF decreased while percent CP increased with decreasing particle size. Five-gram samples were incubated in situ for 0, 2, 4, 6, 12, 18, 24, 30, 36, and 72h. Lag, rate, and extent of DM digestion were determined. Rate and extent of DM digestion of rhizoma peanut increased with decreasing particle size but was unchanged for bermudagrass. Different particle size fractions potentially can have different rates and extents of DM digestion.

Milk Production, Nutrient Digestion, and Rate of Digesta Passage in Dairy Cows Fed Long or Chopped Alfalfa Hay Supplemented with Sodium Bicarbonate ,

Effects of forage particle size and sodium bicarbonate on milk production, ruminal fermentation, ruminal fluid dilution rate, dry matter passage from the rumen, and nutrient digestion were measured in four Holstein cows in a 4×4 Latin-square experiment. Cows were fed ad libitum amounts of a diet of approximately 46% concentrate and 54% alfalfa hay. The 2×2 factorial arrangement of treatments were: 1) long stem alfalfa hay, 2) long stem alfalfa hay + 1.4% sodium bicarbonate (3.0% of concentrate), 3) chopped alfalfa hay (1.3cm), and 4) chopped alfalfa hay + 1.4% sodium bicarbonate.Feed intake, milk yield, and milk composition were similar among treatments. Ruminal pH and concentration and molar percentages of volatile fatty acids were not altered. Decreasing feed particle size reduced ruminal fluid out-flow as estimated by polyethylene glycol and chromium ethylenediamine tetra-acetic acid dilution rates. Digestion of nutrients was decreased with chopped alfalfa hay but was not related to faster rate of passage of smaller size feed particles as determined by rare earth markers. Sodium bicarbonate increased water intake and tended to improve nutrient digestion. Absence of a significant effect of sodium bicarbonate upon rate of passage of chopped hay indicates that feed particles of this size are not significantly affected by small increases of dilution rate of ruminal fluid. Addition of sodium bicarbonate to an alfalfa hay (forage)-based diet did not improve production responses but did increase nutrient digestion.