Influence of forage type, ratio of forage to concentrate, and methionine hydroxy analog on performance of dairy cows.

In a 2-yr study, 44 primiparous and 77 multiparous cows were assigned to one of 12 dietary treatments (2 X 3 X 2 factorial). Treatments were two forages (alfalfa or smooth bromegrass), three percentages of grain (40, 50 or 60% of diet DM), and two percentages of methionine hydroxy analog (0 or .15% of diet DM). Feeds were offered as total mixed diets. Data collection began 4 d postpartum and continued through 116 d postpartum. Dry matter intake was not affected by percentage of concentrate or forage source even though NDF of the diets ranged from 25.6 to 48.8% and ADF ranged from 15.7 to 36.8%. Cows fed bromegrass hay produced 1.5 kg/d more FCM and 1.2 kg/d more SCM than those fed alfalfa hay. Concentrate percentage in the diet increased milk yield (28.9, 30.4 and 31.3 kg/d at 40, 50 and 60%, respectively). Methionine hydroxy analog increased milk fat percentage and yield for cows fed diets of 50 and 60% concentrate with alfalfa hay but not for those fed diets of 50 and 60% concentrate with bromegrass hay. Effect of methionine hydroxy analog was not significant for milk fat or yield when diets of 40% concentrate were fed.     

Effect of source of neutral detergent fiber and starch on nutrient utilization by dairy cows

Two diets were formulated to contain 30% NDF (DM basis) but differed in source of NDF and type of concentrate. One diet contained approximately 70% alfalfa silage and 30% corn grain (89% of NDF from forage) and the other diet contained about 50% alfalfa silage and 50% barley grain (65% of NDF from forage). Diets were fed to 12 cows in a short production trial, a total collection digestion experiment, and a rate of passage study. Cows fed the alfalfa-corn diet produced more 4% FCM (22.4 vs. 20.7 kg/d) than did cows fed the alfalfa-barley diet. Intake of DM (3.7% of BW), NE1 (35 Mcal), and NDF (1.1% of BW) were similar between diets, but due to differences in diet composition, intake of ADF was greater by cows fed alfalfa-corn than by cows fed alfalfa-barley. Digestibilities of DM, NDF, and CP were not affected by diet, but hemicellulose digestion was higher and cellulose and ADF digestibilities were lower by cows fed alfalfa-barley diets. Cows fed alfalfa-corn diet had a higher ruminal acetate to propionate molar ratio. No effect of diet was observed on turnover kinetics of the forage, concentrate, or liquid markers. These data show that forage to grain ratio and source of starch must be considered prior to recommending that diets be balanced for NDF.     

Production of volatile fatty acids in the rumen and cecum-colon of steers as affected by forage:concentrate and forage physical form

Contribution of cecal and ruminal VFA to metabolizable energy was investigated in steers with cannulas in both the rumen and cecum. Animals were fed ad libitum so that data would be applicable to the lactating dairy cow. Diets assigned within a 4 x 4 Latin square were: 20% long alfalfa hay and 80% concentrate; 15% pelleted alfalfa, 5% hay and 80% concentrate; 80% hay and 20% concentrate; 60% pellets, 20% hay and 20% concentrate. Intake of DM was unaffected by diet. Cecal fluid pH, osmolality, and concentrations of valerate and isovalerate were unaffected by diet. Concentrations of total VFA, acetate, propionate, butyrate, and lactate in the cecum increased with proportion of grain in the diet. The high grain diets depressed cecal ammonia concentration and acetate to propionate ratio. Acetate production in the cecum was higher with the high grain diets whereas that in the rumen was lower. Production of propionate and butyrate in both the cecum and rumen was unaffected by diet. Cecal VFA provided 8.6% of metabolizable energy intake, on average. Contribution of ruminal VFA to total metabolizable energy was affected by diet, accounting for 72, 51, 74, and 52% of metabolizable energy from the 20% hay, 20% pelleted alfalfa, 80% hay, and 80% pelleted alfalfa, respectively. Cecal VFA were an important source of energy for ad libitum-fed steers; this contribution would undoubtedly increase with increasing feed intake.     

Effect of energy level and feeding frequency on site of digestion and postruminal nutrient flows in steers

Four cannulated (rumen, proximal duodenum, terminal ileum) Simmental steers were fed ground corn and corn silage (low forage) or alfalfa hay and corn silage (high forage) diets twice or 12 times daily to examine effects of energy level and feeding frequency on nutrient digestion. Site of organic matter digestion was shifted from the rumen to the small intestine, and total tract organic matter digestion was increased when steers were fed the low forage diet. Although intakes and flows at all sites within the tract of NDF and ADF were greater when the high forage diet was fed, digestion of these components (percentage total tract digestion) within respective sites was unaffected by energy level. Nonbacterial N flows at the duodenum increased when steers were fed the low forage diet and when fed 12 times daily. Total amino acid flows at the duodenum tended to be increased when steers were fed the low forage diet. Results suggest that dietary energy level can impact on site of nutrient digestion and supply of nutrients at different sites within the digestive tract. However, feeding frequency had minimal effect on site or extent of nutrient digestion. The lack of interaction between energy level and feeding frequency in this experiment may be related to the level of DM intake and nature of the diets fed.     

Effects of fiber source and method of feeding on chewing activities, digestive function, and productivity of dairy cows

This experiment was conducted to evaluate the effects of supplementing a silage-based diet with hay on chewing, digestive function, and productivity of dairy cattle. Eight multiparous rumen-cannulated Holstein cows were fed, in a crossover design, three diets containing 60% high moisture shelled corn-based concentrate and either: 1) 40% alfalfa silage (37% DM; 21% CP; 44% NDF); 2) 25% alfalfa silage and 15% long alfalfa grass hay (16% CP; 57% NDF) with hay offered with 15% chopped alfalfa grass hay. Milk production (kg/d) was increased from 17.3 for diet 1 to 18.9 and 18.3 for diets 2 and 3, respectively. No change in milk fat composition resulted (mean, 3.62%). Rumination occurred in proportion to NDF intake (mean, 69.08 min/kg of NDF) regardless of diet; consequently, rumination increased from 4.6 to 5.4 h/d when diets were supplemented with hay with no effect of method of allocating hay. Rumen parameters and in sacco and total collection techniques indicated that supplemental hay mediated an improvement in fiber digestion, regardless of method of allocation of hay.     

Partial replacement of forage with nonforage fiber sources in lactating cow diets. II. Digestion and rumen function

Replacement of forage with cereal byproducts may be a viable alternative for feeding dairy cows. The objective of this experiment was to evaluate total tract digestion and rumen fermentation profile when diets were formulated to contain low-forage neutral detergent fiber (NDF) (12.6% forage NDF, 18.8% total NDF), adequate NDF from forages (20% forage NDF, 24.4% total NDF) or low-forage NDF with high levels of NDF from cereal byproducts (12.7% forage NDF, 35.1% total NDF). Sodium bicarbonate (0.8% of dry matter) was factorialized over these diets. Total tract apparent digestibilities of organic matter (OM) and carbohydrates were determined in 73 Holsteins. Eight rumen-cannulated cows were used concurrently to evaluate rumen fermentation profile and in situ degradation of forages. Bicarbonate did not increase NDF or OM digestibility, but increased intake of digestible OM. Rumen fermentation parameters were determined by dietary alfalfa NDF content. Adding alfalfa NDF to the low-forage, high-starch diet increased in situ degradation of forage NDF more than adding byproduct NDF. However, increased ruminal forage NDF degradability was not reflected in greater total tract NDF digestibility. Replacement of dietary starch with NDF from byproducts decreased OM digestibility, but energy intake was similar across diets due to increased intake.     

Impact of forage fiber content on digestion and digesta passage in lactating dairy cows

Five Holstein cows (5 wk postpartum) were used in a Latin square design (15-d periods) to determine rumen fill and fractional rates of ruminal digestion and passage. Treatments consisted of prebloom, midbloom, and full bloom alfalfa hay, mature bromegrass hay, and corn silage fed in diets containing forage: concentrate in a 60:40 ratio (DM basis) formulated to be isonitrogenous. Intake of DM averaged 4.0% of body weight for prebloom alfalfa and corn silage. Milk yield and DM intake were lower for full bloom alfalfa and bromegrass than for prebloom alfalfa. Digestibility of organic matter was 7.5 percentage units lower for full bloom than for prebloom alfalfa. Weight of DM in the rumen was higher for midbloom and full bloom alfalfa and bromegrass than with prebloom alfalfa. Ruminal retention time of Yb applied to forage was longer for bromegrass than for prebloom alfalfa. Fractional rates of in situ NDF digestion were slower for full bloom alfalfa and bromegrass than for prebloom alfalfa. Results suggest that the point of limitation of feed intake due to gut fill is dependent on forage quality as well as energy demand of the animal. Dry matter fill of the rumen was more closely related to rates of ruminal digestion and passage than to total tract digestibility or maximum digestibility after lengthy in situ fermentation.     

Lactation performance and digestibility of forages and diets in dairy cows fed a hemicellulose extract

Inclusion of hemicellulose extract (HE) in cattle diets have shown potential for improving fiber digestibility and production efficiency. The objective of this research was to evaluate production and digestibility effects of a HE on midlactation cows. Twelve multiparous Holstein cows (142 ± 44 d in milk, 685 ± 19 kg of body weight) including 4 with ruminal fistula were used in a 2 × 2 Latin square design with 21-d periods. Cows were fed a control (CON) diet containing 55% forage [dry matter (DM) basis, 2/3 corn silage and 1/3 alfalfa hay] or a similar diet where 1.0% of the diet DM was replaced with HE (TRT). Dry matter intake averaged 27.1 and 26.9 kg/d, for CON and TRT respectively, and was not affected by addition of extract. The percentage of milk protein (3.40 vs. 3.29%) was greater, whereas the percentage of milk fat (3.91 vs. 3.80%) tended to be greater, for cows fed the CON compared with the TRT diet. Because of numerically greater milk production (38.8 vs. 39.2 kg/d) for cows fed the TRT diet, no differences were observed in component yields other than lactose (1.86 vs. 1.94 kg/d), which tended to be greater for cows fed the TRT ration. Treatment improved neutral detergent fiber (NDF) digestibility (38.6 vs. 48.1%) for the TRT diet compared with the CON diet but did not affect apparent total-tract DM (67.8 vs. 68.5%), crude protein (67.2 vs. 67.9%), acid detergent fiber (ADF; 37.1 vs. 43.3%), or starch (92.8 vs. 92.2%) digestibility. For in situ determinations, Dacron bags containing corn silage, alfalfa hay, and either the CON or TRT ration were incubated in triplicate in the rumens of the cannulated cows at 0, 3, 6, 9, 12, 24, and 48 h on d 18 of each period. Each total mixed ration was incubated only in cows assigned to the corresponding diet. For corn silage, the rate of disappearance of NDF (1.70 vs. 4.27%) and ADF (1.79 vs. 4.66%) increased for cows fed the TRT diet. For alfalfa hay, the disappearance of fraction A of DM, NDF, and ADF decreased and fraction B of DM and NDF increased with treatment. The rate of disappearance for DM (8.03 vs. 11.04%), NDF (6.30 vs. 10.28%), and ADF (5.52 vs. 9.19%) increased for the alfalfa hay in rumens of treated cows. For the total mixed ration, the disappearance of the A fraction of NDF and ADF increased for cows fed the TRT diet. Supplementing diets of lactating dairy cows with an HE has beneficial effects on fiber degradation characteristics and provides opportunities for improving animal performance.     

Ryegrass or alfalfa silage as the dietary forage for lactating dairy cows

Renewed interest exists in using grass forages to dilute the higher crude protein (CP) and lower digestible fiber present in legumes fed to lactating dairy cows. A 3 x 3 Latin square feeding study with 4-wk periods was conducted with 24 Holstein cows to compare ryegrass silage, either untreated control or macerated (intensively conditioned) before ensiling, with alfalfa silage as the sole dietary forage. Ryegrass silages averaged [dry matter (DM) basis] 18.4% CP, 50% neutral detergent fiber (NDF), and 10% indigestible acid detergent fiber (ADF) (control) and 16.6% CP, 51% NDF, and 12% indigestible ADF (macerated). Alfalfa silage was higher in CP (21.6%) and lower in NDF (44%) but higher in indigestible ADF (26%). A lower proportion of the total N in macerated ryegrass silage was present as nonprotein N than in control ryegrass and alfalfa silages. Diets were formulated to contain 41% DM from either rye-grass silage, or 51% DM from alfalfa silage, plus high moisture corn, and protein concentrates. Diets averaged 17.5% CP and 28 to 29% NDF. The shortfall in CP on ryegrass was made up by feeding 7.6% more soybean meal. Intake and milk yields were similar on control and macerated ryegrass; however, DM intake was 8.3 kg/d greater on the alfalfa diet. Moreover, feeding the alfalfa diet increased BW gain (0.48 kg/d) and yield of milk (6.1 kg/d), FCM (6.8 kg/d), fat (0.26 kg/d), protein (0.25 kg/d), lactose (0.35 kg/d), and SNF (0.65 kg/d) versus the mean of the two ryegrass diets. Both DM efficiency (milk/DM intake) and N efficiency (milk-N/N-intake) were 27% greater, and apparent digestibility was 16% greater for DM and 53% greater for NDF and ADF, on the ryegrass diets. However, apparent digestibility of digestible ADF was greater on alfalfa (96%) than on ryegrass (average = 91%). Also, dietary energy content (estimated as net energy of lactation required for maintenance, milk yield, and weight gain) per unit of digested DM was similar for all three diets. Results of this trial indicated that, relative to ryegrass silage, feeding alfalfa silage stimulated much greater feed intake, which supported greater milk production.     

Effects of replacing chopped alfalfa hay with alfalfa silage in a total mixed ration on production and rumen conditions of lactating dairy cows

The effects of replacing chopped alfalfa hay with alfalfa silage in a total mixed ration containing barley grain and corn silage on production and rumen conditions were investigated. Cows received three diets that all contained (dry matter basis) 38.5% barley grain-based energy supplement, 30.5% corn silage, 17.0% protein supplement, and 4.2% sunflower seeds. One diet contained (dry matter basis) 9.8% of chopped alfalfa hay and no alfalfa silage. One diet contained (dry matter basis) 4.9% chopped alfalfa hay and 4.9% alfalfa silage. One diet contained (dry matter basis) 9.8% of alfalfa silage and no chopped alfalfa hay. Contents of crude protein, neutral detergent fiber, acid detergent fiber, and starch, averaged across diets, were 16.7, 41.3, 21.1, and 24.4% DM, respectively, and did not differ significantly among diets. Replacing chopped alfalfa hay with alfalfa silage decreased the proportion of dietary DM passing through the 8-mm screen of the Penn State Particle Separator from 61.9 to 55.2% dry matter and significantly increased dietary physical effective NDF (peNDF) content, calculated as the NDF retained by the two screens of the Penn State Particle Separator, from 20.1 to 23.3% DM. Replacing chopped alfalfa hay with alfalfa silage also reduced dietary DM content, increased rumen pH from 6.27 to 6.47, reduced volatile fatty acid concentrations, numerically increased milk fat concentration and milk fat yield. Milk yield, milk protein concentration, dry matter intake, and rumen ammonia concentration were not affected.     

Wheat straw or alfalfa hay in diets with 30% neutral detergent fiber for lactating Holstein cows.

Twenty-four Holstein cows near peak lactation were fed diets formulated to contain 30% NDF with forage NDF from chopped wheat straw or chopped alfalfa hay in proportions of 0:3, 1:2, 2:1, and 3:0 in an 8-wk trial to evaluate effects of fiber source on lactational performance. Concentrate was based on highly degradable carbohydrate in steam-flaked sorghum grain. Forage to concentrate ratio decreased from 49:51 to 28:72 when straw was substituted for alfalfa hay. Milk yield (38.4 kg/d) and DMI (23.1 kg/d) were not influenced by forage source. Milk fat percentage decreased and milk protein percentage increased linearly with increasing straw. Yields of 3.5% FCM and fat showed linear and quadratic responses, because they appeared to be reduced only on the 0:3 diet, and protein yield showed a quadratic response and was highest for the 1:2 diet. Digestibility of NDF averaged 43.5, 45.4, 40.7, and 31.2%, and acetate to propionate ratio was 3.0, 2.4, 2.2, and 1.9 with increasing dietary straw. Passage rates were not influenced by diet and averaged 9.3, 7.6, 6.1, and 4.7%/h for fluid, grain, alfalfa hay, and wheat straw, respectively. It is suggested that the ratio of forage NDF to ruminally degradable starch be maintained greater than or equal to 1:1 when diets based on low quality forage are fed to cows in early lactation.     

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 x 4 Latin square design with a 2 x 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.     

Response of lactating dairy cows to diets containing wet corn gluten feed or a raw soybean hull-corn steep liquor pellet

We evaluated effects of wet corn gluten feed (WCGF) and a novel product (SHSL) containing raw soybean hulls and corn steep liquor on performance and digestion in lactating dairy cows. In Experiment 1, 46 multiparous Holstein cows were assigned to control (C), WCGF (20% of diet DM), or SHSL (20% of diet DM). Diets were fed as a total mixed ration beginning after calving. The C diet contained (dry matter [DM] basis) 30% alfalfa hay, 15% corn silage, 32% corn, 9.3% whole cottonseed, 4.4% solvent soybean meal (SBM), and 3.3% expeller SBM. The WCGF replaced 10% alfalfa hay, 5% corn silage, and 5% corn grain, while expeller SBM replaced solvent SBM to maintain diet rumen undegradable protein. The SHSL replaced 10% alfalfa hay, 5% corn silage, 3% solvent SBM, and 2% corn. Dietary crude protein averaged 18.4%. Milk, energy-corrected milk (ECM), DM intake (DMI), and ECM/DMI were similar among diets during the first 13 wk of lactation. During wk 14 through 30 postpartum, WCGF and SHSL improved milk, ECM, milk component yield, and ECM/DMI. In Experiment 2, 6 cows were used to evaluate digestibility and rumen traits. Dry matter intake and total tract digestibilities of DM, fiber, and crude protein were not different among diets. Diets did not affect ruminal liquid dilution rate, pH, or concentrations of total volatile fatty acids or ammonia, but acetate:propionate was higher for C (3.38) than for WCGF (2.79) or SHSL (2.89). The WCGF and SHSL products can serve as alternative feedstuffs in diets fed to lactating dairy cattle.     

Effects of alfalfa hay of varying fiber fed at 35 or 50% of diet on lactation and nutrient utilization by dairy cows.

Five alfalfa hays (four from Arizona and one from California), varying in percentages of ADF (26, 28, 32, and 38%), were fed to 40 lactating Holstein cows averaging 90 DIM. Cows were in 10 groups of 4 cows each; groups were based on 14-d pretreatment milk yield. Each hay was included in TMR to provide 50 or 35% of DM. Diets were fed for ad libitum intake for 70 d. Feeding behavior of 2 cows per treatment was electronically monitored for 14 d. Total tract digestibilities of DM, ADF, and NDF were determined using Cr2O3, and ruminal in situ loss of DM, ADF, and NDF of hays was estimated using 4 cows fitted with ruminal fistulas. Dry matter intake, 3.5% FCM, changes in BW, rectal temperatures, and milk composition (except milk fat) were not affected by ADF in hays or concentrate percentage. However, milk yield decreased as ADF in hay increased, particularly at 50% concentrate. At 50% concentrate, milk yield of cows fed hays of 26 to 28% ADF averaged 30.7 kg/d, and the mean for cows fed 32 and 38% ADF hays was 27.6 kg/d. Milk fat percentages tended to be lower on higher concentrate. Eating time was longer as hay ADF increased and tended to decrease on high concentrate, but there were no significant effects of treatment on number or length of meals. In situ disappearance of DM, ADF, and NDF decreased as hay ADF increased, but total tract digestibilities of ADF and NDF were greater in hay of higher fiber content, particularly in cows fed 35% hay.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of sarsaponin on digestion and passage rates in cattle fed medium to low concentrate

Four dairy cows with duodenal cannulae were fed diets consisting of sorghum silage (67% of dietary dry matter) at 85% of ad libitum intake with 0 (control diet) or 44 ppm (dry matter) sarsaponin (sarsaponin diet) in a crossover experiment. Digestion coefficients for organic matter were low but increased by addition of sarsaponin both in the rumen (43.7 versus 32.4%) and total tract (52.1 versus 48.2%). Digestibilities of starch and nitrogen in the rumen and total tract and passage rates of fluid, concentrate, and silage tended to be greater for the sarsaponin diet. Extent of ruminal digestion of organic matter was related to passage rate of concentrate (correlation .81) and fluid (correlation .75). In a second study, diets contained 50% concentrate either with or without sarsaponin added at 44 ppm. Ruminal pH for animals given sarsaponin tended to be lower 4, 8, and 12 h after feeding. In situ rate constants of dry matter disappearance tended to be greater with the control diet for corn, alfalfa, and prairie hay and lower for milo and soybean meal. Lag time of digestion tended to be longer with the sarsaponin diet for corn, milo, soybean meal, and corn gluten meal but shorter for alfalfa and prairie hay. Although sarsaponin may increase ruminal digestion of medium to low concentrate diets, in situ data indicate that effects may differ with type of feed.     

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 4x4 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 source and amount of fiber on kinetics of digestion and specific gravity of forage particles in the rumen.

This experiment investigated the relationship between kinetics of digestion and change in specific gravity during in situ incubation. Nine cows were fed three sources of fiber (corn silage, alfalfa silage, or alfalfa hay) in diets formulated to contain 25, 30, or 35% NDF in three simultaneous 3 x 3 Latin squares. Method of alfalfa preservation did not influence rate of digestion or rate of increase in specific gravity of forage particles measured by a flotation technique. Prior to incubation, specific gravity of forage particles was in increasing order: alfalfa hay, alfalfa silage, and then corn silage. Essentially, all particles with a specific gravity less than 1.0 shifted to a higher specific gravity fraction by hydration within the first 4 h of incubation. From 4 to 56 h of incubation, percentage of residual DM that settled in solution having specific gravity of 1.3 increased linearly from 21 to 27% for corn silage but exponentially from 3 to 20% for alfalfa forages. Fractional rates of DM and NDF digestion and increase in percentage of residual DM having a specific gravity greater than 1.3 increased with the amount of fiber in the alfalfa diets and were correlated positively, suggesting that rate of increase in specific gravity, which affects rate of passage from the rumen, is influenced by rate of digestion of forage particles.     

Effects of varying forage and concentrate carbohydrates on nutrient digestibilities and milk production by dairy cows.

Five Holstein cows with ruminal cannulas were used in a 5 x 5 Latin square design to determine the effect of replacing forage NDF with soyhull NDF and varying concentrations of nonstructural carbohydrates on nutrient digestion and milk production. Diets in which NDF percentage from forage (corn silage: alfalfa hay, 1:1) was 80 (control), 70, or 60 were formulated by substituting soyhulls for forage; total forage was 43.2, 36.7, and 31.1% of the diets, respectively, but total NDF was 31%. Nonstructural carbohydrates were formulated to be 47 (control), 35, or 25% by substituting soyhulls, roasted soybeans, and Ca soaps for concentrate. Ruminal acetate: propionate ratio decreased linearly when diets lower in forage NDF were fed, but it increased quadratically when dietary nonstructural carbohydrates were reduced. Apparent digestibility of OM increased quadratically, but NDF digestibility and lactation performance were unaffected when diets lower in forage NDF were fed. Digestibility of NDF increased linearly when nonstructural carbohydrates were reduced, perhaps because of greater digestibility of soyhull NDF and smaller negative associative effects. Fat from soybeans and Ca soaps was increased as nonstructural carbohydrates decreased. Added fat probably increased fatty acid digestibility and decreased milk protein percentage. Greater FCM production without correspondingly greater feed intake or BW loss increased feed efficiency as nonstructural carbohydrates decreased. In dairy rations containing soyhulls, 60% of dietary NDF from forage should maintain lactation performance, and decreasing nonstructural carbohydrates to 25 to 35% of feed DM, coupled with adding dietary fat, may decrease negative associative effects and improve efficiency of milk production.     

Replacing chopped alfalfa hay with alfalfa silage in barley grain and alfalfa-based total mixed rations for lactating dairy cows

The effects of replacing chopped alfalfa hay with alfalfa silage in a fine barley grain and alfalfa-based total mixed ration (TMR) were evaluated. Diets contained (dry matter basis) 53.0% commercial energy supplement, 10.3% commercial protein supplement, and 9.7% corn silage. Diets varied in inclusion of chopped alfalfa hay and alfalfa silage, and contained either 20.0% chopped alfalfa hay and 7.0% alfalfa silage, 10.0% chopped alfalfa hay and 17.0% alfalfa silage, or 27.0% alfalfa silage. Contents of crude protein, neutral detergent fiber (NDF), acid detergent fiber, and minerals did not differ among diets. Replacing chopped alfalfa hay with alfalfa silage decreased dietary dry matter, and increased dietary soluble protein and physical effective NDF calculated as the proportion of dietary NDF retained by the 8- and 19-mm screens of the Penn State Particle Separator (peNDF(NDF)) from 13.3 to 15.6% DM. Replacing chopped alfalfa hay with alfalfa silage did not affect dry matter intake, rumen pH, rumen volatile fatty acids, blood lactate, milk fat, and milk protein percentage, but did decrease blood glucose, tended to increase blood urea, and numerically decreased milk yield and milk protein yield. A wider range in peNDF(NDF) and a higher inclusion of corn silage might have resulted in greater differences in rumen fermentation and milk production among diets. The pH of rumen fluid samples collected 4 h after feeding varied from 5.90 to 5.98, and milk fat percentage varied from 2.50 to 2.60% among diets. These values suggest that mild subacute ruminal acidosis was induced by all diets.     

Effect of alfalfa maturity on fiber utilization by high producing dairy cows

Six ruminally cannulated cows were used in a replicated 3 x 3 Latin square to study the effect of alfalfa maturity on utilization of DM and fiber. Cows were fed three diets based on alfalfa hay at early vegetative, late bud, or full bloom maturities. Forage:concentrate ratios were: 68:32, 53:47, and 45:55 for diets with early vegetative, late bud, and full bloom hays. Concentrations of NDF in the early vegetative and late bud diets was higher (32.6%) than NDF in the full bloom diet (27.9%) after accounting for feed refusals. Fat-corrected milk yield was similar, but fat percentage was higher for the diet with early vegetative hay than the diets with late bud or full bloom alfalfa. Dry matter intake was higher for the diet with early vegetative hay than the diets with late bud or full bloom hay (26.1, 24.4, and 24.8 kg/d). Ruminal dacron bag incubations of the three hays suggest that the high digestibility of the early vegetative hay was due to more soluble DM, more potentially digestible DM and fiber, and a faster rate of digestion. These factors compensated for the faster passage of the early vegetative hay and resulted in a higher intake and better utilization of DM and fiber.