Performance of dairy cows fed diets with similar proportions of undigested neutral detergent fiber with wheat straw substituted for alfalfa hay,corn silage,or both

This study evaluated the effects of feeding diets that were formulated to contain similar proportions of undigested neutral detergent fiber (uNDF) from forage, with wheat straw (WS) substituted for corn silage (CS), alfalfa hay (AH), or both. The diets were fed to lactating dairy cows and intake, digestibility, blood metabolites, and milk production were examined. Thirty-two multiparous Holstein cows (body weight = 642 ± 50 kg; days in milk = 78 ± 11 d; milk production = 56 ± 6 kg/d; mean ± standard deviation) were used in a randomized block design with 6-wk periods after a 10-d covariate period. Each period consisted of 14 d of adaptation followed by 28 d of data collection. The control diet contained CS and AH as forage sources (CSAH) with 17% of dietary dry matter as uNDF after 30 h of incubation (uNDF₃₀). Wheat straw was substituted for AH (WSCS), CS (WSAH), or both (WSCSAH) on an uNDF₃₀ basis, and beet pulp was used to obtain similar concentrations of NDF digestibility after 30 h of incubation (NDFD₃₀ = 44.5% of NDF) across all diets. The 4 diets also contained similar concentrations of net energy for lactation and metabolizable protein. Dry matter intake was greatest for WSCS (27.8 kg/d), followed by CSAH (25.7 kg/d), WSCSAH (25.2 kg/d), and WSAH (24.2 kg/d). However, yields of milk, 3.5% fat-corrected milk (FCM), and energy-corrected milk did not differ, resulting in higher FCM efficiency (kg of FCM yield/kg of dry matter intake) for WSAH (1.83) and WSCSAH (1.79), followed by CSAH (1.69) and WSCS (1.64). Milk protein percentage was greater for CSAH (2.84%) and WSCS (2.83%) than for WSAH (2.78%), and WSCSAH (2.81%) was intermediate. The opposite trend was observed for milk urea nitrogen, which was lower for CSAH (15.8 mg/dL), WSCS (15.8 mg/dL), and WSCSAH (17.0 mg/dL) than for WSAH (20 mg/dL). Total-tract NDF digestibility and ruminal pH were greater for diets containing WS than the diet without WS (CSAH), but digestibility of other nutrients was not affected by dietary treatments. Cows fed WSAH had less body reserves (body weight change = −13.5 kg/period) than the cows fed the other diets, whereas energy balance was greatest for those fed WSCS. The results showed that feeding high-producing dairy cows diets containing different forage sources but formulated to supply similar concentrations of uNDF₃₀ while maintaining NDFD_30, net energy for lactation, and metabolizable protein constant did not influence milk production. However, a combination of WS and CS (WSCS diet) compared with a diet with CS and AH improved feed intake, ruminal pH, total-tract NDF digestibility, and energy balance of dairy cows.     

Effect of partial replacement of forage neutral detergent fiber with by-product neutral detergent fiber in close-up diets on periparturient performance of dairy cows

The objective of this study was to determine the effect of partial replacement of forage neutral detergent fiber (NDF) with by-product NDF in close-up diets of dairy cattle on periparturient metabolism and performance. Holstein cows (n = 45) and heifers (n = 19) were fed corn silage-based diets containing 1) 30% oat hay, or 2) 15% oat hay and 15% beet pulp from d −21 relative to expected parturition until parturition. After parturition, all animals received the same lactation diet. Animals were group-fed from d −21 to −10 relative to expected parturition and fed individually from d −10 until 14 d in milk. Animals were required to have at least 5 d of prepartum dry matter intake (DMI) data to remain on the study. Data were analyzed as a randomized design and subjected to ANOVA using the MIXED procedure of SAS. Close-up diet did not affect DMI, total tract nutrient digestibility, energy balance, or serum content of nonesterified fatty acids and β-hydroxybutyrate during the last 5 d prepartum. Prepartum body weight and body condition score were similar between treatments. There was no carryover effect of close-up diet on DMI, energy balance, milk yield, body weight, body condition score, or serum content of nonesterified fatty acids and β-hydroxybutyrate during the first 14 d in milk. In summary, partial replacement of forage NDF (oat hay) with by-product NDF (beet pulp) did not affect periparturient metabolism or performance.     

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.     

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.     

Short communication: Evaluation of acid-insoluble ash and indigestible neutral detergent fiber as total-tract digestibility markers in dairy cows fed corn silage-based diets

The objective of this experiment was to evaluate acid-insoluble ash (AIA) and indigestible NDF (iNDF) as intrinsic digestibility markers in comparison with total fecal collection (TC) in dairy cows fed corn silage- and alfalfa haylage-based diets. The experiment was part of a larger experiment, which involved 8 Holstein cows [102 ± 28.4 d in milk, 26.4 ± 0.27 kg/d of dry matter (DM) intake, and 43 ± 5.3 kg/d milk yield]. The experimental design was a replicated 4 × 4 Latin square with the following treatments: metabolizable protein (MP)-adequate diet [15.6% crude protein (CP); high-CP], MP-deficient diet (14.0% CP; low-CP), and 2 other low-CP diets supplemented (top-dressed) with ruminally protected Lys or Lys and Met. Data for the 3 low-CP diets were combined for this analysis. Total feces were collected for 5 consecutive days during each period to estimate total-tract apparent digestibility. Digestibility was also estimated using AIA (digestion with 2 N HCl) and iNDF (12-d ruminal incubation in 25-μm-pore-size bags). Significant diet × digestibility method interactions were observed for fecal output of nutrients and digestibility. Fecal output of nutrients estimated using AIA or iNDF was lower compared with TC and fecal output of DM, organic matter, and CP tended to be higher for iNDF compared with AIA for the high-CP diet. For the low-CP diet, however, fecal output of all nutrients was lower for AIA compared with TC and was higher for iNDF compared with TC. Data from this experiment showed that, compared with TC, AIA underestimated fecal output and overestimated digestibility, particularly evident with the fiber fractions and the protein-deficient diet. Compared with TC, fecal output was overestimated and digestibility of the low-CP diet was underestimated when iNDF was used as a marker, although the magnitude of the difference was smaller compared with that for AIA. In the conditions of the current study, iNDF appeared to be a more reliable digestibility marker than AIA in terms of detecting dietary differences in apparent digestibility of some nutrients, but significant diet × marker interactions existed that need to be considered when estimating total-tract digestibility using intrinsic markers.     

Inclusion of wheat and triticale silage in the diet of lactating dairy cows

The objective of this experiment was to partially replace corn silage with 2 alternative forages, wheat (Triticum aestivum) or triticale (X Triticosecale) silages at 10% of the diet dry matter (DM), and investigate the effects on dairy cow productivity, nutrient utilization, enteric CH₄ emissions, and farm income over feed costs. Wheat and triticale were planted in the fall as cover crops and harvested in the spring at the boot stage. Neutral- and acid-detergent fiber and lignin concentrations were higher in the wheat and triticale silages compared with corn silage. The forages had similar ruminal in situ effective degradability of DM. Both alternative forages had 1% starch or less compared with the approximately 35% starch in corn silage. Diets with the alternative forages were fed in a replicated 3 × 3 Latin square design experiment with three 28-d periods and 12 Holstein cows. The control diet contained 44% (DM basis) corn silage. In the other 2 diets, wheat or triticale silages were included at 10% of dietary DM, replacing corn silage. Dry matter intake was not affected by diet, but both wheat and triticale silage decreased yield of milk (41.4 and 41.2 vs. 42.7 ± 5.18 kg/d) and milk components, compared with corn silage. Milk fat from cows fed the alternative forage diets contained higher concentrations of 4:0, 6:0, and 18:0 and tended to have lower concentrations of total trans fatty acids. Apparent total-tract digestibility of DM and organic matter was decreased in the wheat silage diet, and digestibility of neutral-and acid-detergent fiber was increased in the triticale silage diet. The wheat and triticale silage diets resulted in higher excretion of urinary urea, higher milk urea N, and lower milk N efficiency compared with the corn silage diet. Enteric CH₄ emission per kilogram of energy-corrected milk was highest in the triticale silage diet, whereas CO₂ emission was decreased by both wheat and triticale silage. This study showed that, at milk production of around 42 kg/d, wheat silage and triticale silage can partially replace corn silage DM and not affect DM intake, but milk yield may decrease slightly. For dairy farms in need of more forage, triticale or wheat double cropped with corn silage may be an appropriate cropping strategy.     

Intake and milk production of cows fed diets that differed in dietary neutral detergent fiber and neutral detergent fiber digestibility

The objectives of this study were to determine how feeding diets that differed in dietary neutral detergent fiber (NDF) concentration and in vitro NDF digestibility affects dry matter (DM) intake, ruminal fermentation, and milk production in early lactation dairy cows. Twelve rumen-cannulated, multiparous Holstein cows averaging 38 ± 15 d (±standard deviation) in milk, and producing 40 ± 9 kg of milk daily, were used in a replicated 4 × 4 Latin square design with 28-d periods. Treatment diets were arranged in a 2 × 2 factorial with 28 or 32% dietary NDF (DM basis) and 2 levels of straw NDF digestibility: 1) LD, untreated wheat straw (77% NDF, 41% NDF digestibility) or 2) HD, anhydrous NH₃-treated wheat straw (76% NDF, 62% NDF digestibility). All 4 diets consisted of wheat straw, alfalfa silage, corn silage, and a concentrate mix of cracked corn grain, corn gluten meal, 48% soybean meal, and vitamins and minerals. Wheat straw comprised 8.5% DM of the 28% NDF diets and 16% DM of the 32% NDF diets. Cows fed 28% NDF and HD diets produced more milk, fat, and protein than those consuming 32% NDF or LD diets. Dry matter intake was greater for cows consuming 28% NDF diets, but intakes of DM and total NDF were not affected by in vitro NDF digestibility. Intake of digestible NDF was greater for cows consuming HD diets. Ruminal fermentation was not affected by feeding diets that differed in NDF digestibility. Ruminal NDF passage rate was slower for cows fed HD than LD. No interactions of dietary NDF concentration and in vitro NDF digestibility were observed for any parameter measured. Regardless of dietary NDF concentration, increased in vitro NDF digestibility improved intake and production in early lactation dairy cows.     

Effects of physically effective fiber on digestion and milk production by dairy cows fed diets based on corn silage

Effects of physically effective (pe) neutral detergent fiber (NDF) content of dairy cow diets on nutrient intakes, site and extent of digestion, microbial protein synthesis and milk production were evaluated in a double 3 x 3 Latin square design using 6 lactating dairy cows with ruminal and duodenal cannulas. During each of 3 periods, cows were offered 1 of 3 diets that were chemically similar but varied in peNDF content (high, medium, and low) by altering corn silage particle length. The peNDF contents were determined using the Penn State Particle Separator and were 11.5, 10.3, and 8.9%, for the high, medium, and low diets, respectively, and the physical effectiveness factors for the long, medium, and fine silages were 84.1, 72.6, and 67.2%, respectively. Increased forage particle length increased intake of peNDF but did not affect intakes of nutrients including dry matter, NDF, starch, and nitrogen. Except for starch, apparent digestibilities of nutrients in the total tract were linearly increased with increasing dietary peNDF. Fiber digestion was affected by dietary peNDF to a greater extent than were the other nutrients. However, increased digestibility due to increased dietary peNDF did not significantly improve milk production or milk composition. Increased dietary peNDF also increased numerically rumen microbial protein synthesis due to increased amount of organic matter fermented in the rumen. These results indicate that increasing the peNDF content of a corn silage based diet improves digestibility, especially digestibility of fiber, in the total tract. Dietary particle size, expressed as peNDF, is positively associated with nutrient digestibility when level of peNDF in the diet is low.     

Effects of prepartum roughage neutral detergent fiber levels on periparturient dry matter intake, metabolism, and lactation in heat-stressed dairy cows

Heat stress of lactating cattle results in dramatic reductions in dry matter intake (DMI). As a result, energy input cannot satisfy energy needs and thus accelerates body fat mobilization. Decreasing the level of roughage neutral detergent fiber (NDF) in prepartum diets, and thereby increasing the amount of nonfiber carbohydrates, may provide an adequate supply of energy and glucose precursors to maintain and minimize the decrease in DMI while reducing mobilization of adipose tissue. The effects of 3-wk prepartum diets containing different amounts of roughage NDF on DMI, blood metabolites, and lactation performance of dairy cows were investigated under summer conditions in Thailand. Thirty cross-bred cows (87.5% Holstein × 12.5% Sahiwal) were dried off 60 d before their expected calving date and were assigned immediately to a nonlactating cow diet containing the net energy for lactation recommended by the National Research Council (2001) model. The treatment diets contained 17.4, 19.2, and 21.0% DM as roughage NDF from bana grass (Pennisetum purpureum × Pennisetum glaucum) silage. Levels of concentrate NDF were 39.8, 40.2, and 38.6% of dietary NDF, so the levels of dietary NDF were 28.9, 32.1, and 34.2% of DM. After parturition, all cows received a lactating cow diet containing 12.7% roughage NDF and 23% dietary NDF. During the entire experiment, the minimum and maximum temperature-humidity index averaged 77.7 and 86.8, respectively, indicating conditions appropriate for the induction of extreme heat stress. As parturition approached, DMI decreased steadily, resulting in a 12.9, 25, and 32.8% decrease in DMI from d −21 until calving for nonlactating cows fed prepartum diets containing 17.4, 19.2, and 21% roughage NDF, respectively. During the 3-wk prepartum period, intakes of DM and net energy for lactation and concentrations of plasma glucose and serum insulin were higher for cows fed diets containing less roughage NDF. In cows fed the 3-wk prepartum diets containing less roughage NDF, calf birth weights, milk yield, and 4% fat-corrected milk were higher, whereas periparturient concentrations of serum nonesterified fatty acids and plasma β-hydroxybutyrate were lower. There was a carryover effect of the prepartum diet on serum nonesterified fatty acids and plasma β-hydroxybutyrate during the first 7 d in milk, and therefore on milk production. These results suggest that feeding diets containing decreased amounts of roughage NDF during the 3-wk prepartum period may minimize the decrease in DMI and lipid mobilization as parturition approaches. This strategy may thus minimize the effect of hormonal factors and heat stress on periparturient cows.     

Effects of dietary neutral detergent fiber and starch ratio on rumen epithelial cell morphological structure and gene expression in dairy cows

This study was designed to investigate the effect of dietary neutral detergent fiber to starch ratio on rumen epithelial morphological structure and gene expression. Eight primiparous dairy cows including 4 ruminally fistulated cows were assigned to 4 total mixed rations with neutral detergent fiber to starch ratios of 0.86, 1.18, 1.63, and 2.34 in a replicated 4 × 4 Latin square design. The duration of each period was 21 d including 14 d for adaptation and 7 d for sampling. Rumen epithelial papillae were collected from the ruminally fistulated cows for morphological structure examination and mRNA expression analysis using quantitative real-time PCR of several genes related to volatile fatty acid absorption and metabolism, and cellular growth. Increasing dietary neutral detergent fiber to starch ratio resulted in a linear increase in the thickness of the stratum spinosum and basale. In contrast, expression of HMGCS2 (encoding the rate-limiting enzyme in the synthesis of ketone bodies) decreased linearly, whereas the expression of MCT2 (encoding a transporter of volatile fatty acid) increased linearly with increasing dietary neutral detergent fiber to starch ratio. As dietary neutral detergent fiber to starch ratio increased, expression of IGFBP5 (a gene related to the growth of rumen epithelial papillae) decreased, whereas IGFBP6 expression increased. Both of these IGFBP genes are regulated by short-chain fatty acids. Overall, the data indicate that dietary neutral detergent fiber to starch ratio can alter the thickness of the rumen epithelial papillae partly through changes in expression of genes associated with regulating volatile fatty acid absorption, metabolism, and cell growth.     

Modification of a rumen fluid priming technique for measuring in vitro neutral detergent fiber digestibility

Recently, we developed an alternate method to measure in vitro neutral detergent fiber (NDF) digestibility (ivNDFD) based on a primed rumen fluid inoculum. Pretreating rumen fluid inoculum with cellulose and holding the inoculum until it generated 0.3 mL of gas/mL of rumen fluid before inoculating forage samples improved ivNDFD assay repeatability but depressed ivNDFD means. Our objective in this study was to determine if pretreating rumen fluid with a mixture of carbohydrates and urea would affect the ivNDFD mean and variance. We also used the modified procedure as a reference assay to calibrate near-infrared reflectance spectroscopy (NIRS) to predict 24-, 30-, and 48-h ivNDFD. Two experiments were completed. In experiment A, 3 ivNDFD assays modified from the method of Goering and Van Soest were evaluated over 24, 28, 48, 54, and 72 h by using dried, ground alfalfa (1 mm) or wheat straw (0.5 g) sealed in Ankom F57 forage fiber bags. Bags were placed individually in 125-mL Erlenmeyer flasks and incubated with Goering and Van Soest media and 10 mL of rumen fluid. Rumen fluid was collected before feeding from 2 cannulated cows fed a high-forage diet and was prepared in 1 of 3 ways: 1) pooled rumen fluid was strained and used immediately to inoculate flasks (modified Goering and Van Soest method); 2) strained, pooled fluid was combined with buffer, reducing solution, and 1.25 mg of primer/mL of rumen fluid and allowed to produce 0.12 mL of gas/mL of rumen fluid before sample inoculation [Combs-Goeser (CG) method]; or 3) the CG method was used without the primer mixture (unprimed method). The assay was repeated 5 times, with 5 time points (24, 28, 48, 54, and 72 h) and 2 subsamples per time point for each method. Neutral detergent fiber was analyzed using an Ankom²⁰⁰ forage fiber analyzer and ivNDFD was determined as follows: ivNDFD (% of NDF) = 100 × [(NDF_0h - NDF_residue)/(NDF_0h)]. Results were analyzed using a mixed model procedure, and data were blocked by method to obtain repetition sums of squares, which were compared by an F-test to assess interassay error. Repetition sums of squares were reduced with the CG method compared with the Goering and Van Soest method (19 vs. 228), and mean ivNDFD estimates were similar at 28, 48, and 54 h. In experiment B, 24-, 30-, and 48-h ivNDFD data for 54 feeds were determined in triplicate using the CG method, and corresponding samples were then scanned with an NIRS instrument. Calibrations were computed using partial least squares regression techniques. The NIRS calibration equation R² values were 0.93, 0.93, and 0.89 for 24-, 30-, and 48-h ivNDFD. Results suggest that the modified ivNDFD method using rumen fluid primed with a mixture of carbohydrate and urea (CG method) reduced interassay error.     

Rumen function and grazing behavior of early-lactation dairy cows supplemented with fodder beet

Fodder beet (FB) is a source of readily fermentable carbohydrate that can mitigate early spring herbage deficits and correct the negative energy balance experienced during early lactation in pastoral dairy systems of New Zealand. However, the low-fiber and high-soluble carbohydrate content of both FB bulb and spring herbage are factors that promote subacute ruminal acidosis, impairing rumen function and limiting the marginal milk production response to supplement. In a crossover experiment, 8 Holstein Friesian × Jersey early-lactation dairy cows were used to test the effect of supplementing 16 kg of dry matter (DM) of a grazed perennial ryegrass herbage with 6 kg of DM/d of FB bulb (FBH) versus herbage only (HO) on changes in rumen function and grazing behavior. Following 20 d of adaptation to diets, DM disappearance (%) of FB bulb (FBH cows only) and herbage were measured in sacco, separately. Cows were fasted overnight, and the ruminal contents were bailed the following morning (~0930 h) again to determine the pool size of volatile fatty acids, ammonia, and particle size of digesta, as well as to estimate the rate of ruminal outflow and degradation of neutral detergent fiber. The FBH diet did not alter DM intake, milk yield, or milk solid (fat + protein) production compared with HO. Supplementation of herbage with FB reduced ruminal pH compared with HO between ~0800 h and 1300 h each day. During each period, 1 cow experienced severe subacute ruminal acidosis (pH <5.6 for >180 min/d) during final adaptation to the target FB allocation. The FBH diet reduced the ruminal pool of acetate and ammonia, but increased the ruminal pool of butyrate and lactate compared with HO. When fed FB, rumination and grazing time increased and grazing intensity declined compared with cows fed HO. Despite increased rumination, the comminution of large particles declined 28% between the first and second rumen bailing when cows were fed FB, and in sacco DM disappearance of perennial ryegrass declined 18% compared with cows fed HO. These results indicate that grazing dairy cows supplemented with FB (40% of daily intake) increase rumination and mastication intensity to counteract reduced ruminal degradation of ryegrass herbage due to low ruminal fluid pH.     

Effects of physically effective fiber on chewing activity and ruminal pH of dairy cows fed diets based on barley silage

The objective of this study was to investigate the effects of physically effective neutral detergent fiber (peNDF) content of dairy cow diets containing barley silage as the sole forage source on feed intake, chewing activity, and ruminal pH. The experiment was designed as a replicated 3 × 3 Latin square using 6 lactating dairy cows with ruminal cannulas. Cows were offered 1 of 3 diets (high, medium, and low peNDF) obtained using barley silage that varied in particle length: long (theoretical cut length of 9.5 mm), medium (equal proportions of long and fine silages), and fine (theoretical cut length of 4.8 mm). The peNDF contents were determined using the Penn State Particle Separator and were 13.8, 11.8, and 10.5%, for the high, medium, and low diets, respectively. The physical effectiveness factors (defined as proportion retained on 19- and 8-mm screens) for the long and fine silages were 0.84 and 0.68, respectively. Increased forage particle size increased intake of peNDF but did not affect intake of DM and NDF. Ruminating and total chewing time were linearly increased with increasing dietary peNDF. Mean ruminal pH, area between the curve and a horizontal line drawn at pH 5.8 or 5.5, and time that pH was below 5.8 or 5.5 were not affected by peNDF content. Intake of peNDF was not correlated to any chewing activity but proportion of long particles on the 19-mm sieve tended to be correlated to ruminating chews (r = 0.36) and ruminating time (r = 0.36). These results indicate that increasing the peNDF content of diets increases chewing time. However, increased chewing time does not always improve ruminal pH status. Increasing chewing time and thus increasing salivary secretion may not fully overcome the effects of feed digestion and the production of fermentation acids that lower rumen pH. The results suggest that dietary peNDF and fermentable OM intake are critical in regulating rumen pH. Dietary particle size, expressed as peNDF, was a reliable indication of chewing activity.     

Replacement of corn silage with shredded beet pulp and dietary starch concentration: Effects on performance,milk fat output,and body reserves of mid-lactation dairy cows

We aimed to evaluate the interaction between dietary starch concentration, varied by replacing wheat bran with dry ground corn, and replacement of corn silage (CS) with shredded beet pulp (BP) on production, milk fat output, milk fatty acid profile, and body reserves in dairy cows. Sixty-four Holstein dairy cows (140 ± 26 d in milk) were randomly assigned to 8 pens (8 animals per pen). Treatments were arranged in a 2 × 2 factorial arrangement with 2 concentrations of starch and 2 sources of fiber and were allotted to 8 pens (2 pens per treatment). Treatments were (1) 15% dry ground corn and 24% CS, (2) 15% dry ground corn and 24% BP replacing CS, (3) 30% dry ground corn and 24% CS, and (4) 30% dry ground corn and 24% BP replacing CS. The trial lasted for 47 d and final 7 d of experimental period was used for data and sample collection. Cows fed the BP-based diets had greater dry matter intake than those offered the CS-based diets, whereas no effects were observed with starch concentration. Milk yield increased by 1.8 kg/d with BP-based diets compared with CS-based diets and by 2.5 kg/d when cows received the high-starch compared with low-starch diets. Interactions between dietary starch concentration and forage substitution were detected for milk fat concentration and yield as BP inclusion lowered milk fat output with high-starch diet. Milk trans-18:1 concentration was lower with 15% dry ground corn and 24% CS compared with other diets. In conclusion, the effects of dietary starch concentration (22 and 32% dry matter) and forage substitution on production responses were independent except for milk fat output and milk trans 18:1 isomers. Substituting CS with BP is effective at increasing milk yield regardless of starch concentration; however, milk fat yield is lower when BP is used with high-starch concentration.     

Milk production and nitrogen excretion of dairy cows fed different amounts of protein and varying proportions of alfalfa and corn silage

Four trials were conducted to determine the effect of dietary protein amount on lactation performance and N utilization. Each trial used one of the following alfalfa-to-corn-silage ratios for the forage part of the diet: 100:0, 75:25, 50:50, and 25:75. All trials utilized 16 mid-lactation Holstein cows (days in milk averages ranging from 80 to 140 among trials) in a replicated 4 × 4 Latin square design with 3-wk periods, including 2 wk for adaptation and 1 wk for data collection. Diets consisted of 50% forage and 50% concentrate (dry matter basis) and were formulated to contain 15.00, 16.25, 17.50, or 18.75% protein in each trial. The analyzed protein content of the diets was 15.7, 16.9, 18.0, and 19.2% when averaged across trials. Milk yield was similar among dietary protein levels in each trial, ranging from 35.2 to 36.1 kg/d when data were combined across trials. Changes in milk fat and protein due to the protein content of the diet were small and inconsistent. Both milk urea nitrogen and blood urea nitrogen concentrations increased linearly as the protein content of the diet was increased, ranging from 9.9 to 13.1 and from 9.9 to 13.8 mg/dL, respectively, across trials. As dietary protein was increased from the lowest to the highest concentrations when data were combined and analyzed, mean fecal N concentration increased from 2.8 to 3.0%, and urinary N from 5.8 to 7.3 g/L. At the same time, mean total N excretion increased from 484 to 571 g/d, and conversion of intake N to milk N decreased from 0.27 to 0.22, resulting in an average change of 18%. Of the N excreted, urinary N accounted for an increasing proportion, ranging from 41 to 48%, as dietary protein was increased. Overall, based on N utilization as well as milk production, 17% protein in diets utilizing various proportions of alfalfa and corn silage as the forage source appeared sufficient for cows producing 38 kg/d of milk in this study.     

Effects of an esterase-producing inoculant on fermentation, aerobic stability, and neutral detergent fiber digestibility of corn silage

This experiment evaluated effects of an inoculant containing esterase-producing bacteria on fermentation, aerobic stability, in situ dry matter digestibility (DMD), and neutral detergent fiber (NDF) digestibility (NDFD) of corn silage. Two corn hybrids grown on adjacent fields [Croplan Genetics 851RR2 (CS1) and Vigoro 61R36 (CS2)] were harvested at approximately 39% dry matter. Each forage was conserved in quadruplicate in 20-L mini silos with or without application of an inoculant at a level to achieve 1.0 × 10⁴ cfu/g of Lactobacillus casei and 1.0 × 10⁵ cfu/g of Lactobacillus buchneri. After 110 d of ensiling, silos were opened and silages were analyzed for chemical composition, fermentation indices, microbial counts, and aerobic stability. In situ DMD, 24-h and 48-h DMD, and NDFD were measured by incubating ground (6-mm) samples in triplicate in each of 2 lactating, fistulated dairy cows fed a corn silage-based diet. Inoculation decreased concentrations of total fermentation acids and lactate, as well as lactate to acetate ratio, and increased propionate concentration compared with the uninoculated control in CS1 but not CS2. Inoculation tended to decrease yeast counts of CS1 but increased yeast counts and tended to increase the mold counts of CS2. Consequently, inoculation improved the aerobic stability of CS1 by 57.3 h (98%) but decreased that of CS2 by 20.5 h (20%). Inoculation also increased the potentially degradable fraction of CS1 and the total degradable fraction, 24-h and 48-h DMD, and 48-h NDFD of CS2. Inoculation of CS1 modified the fermentation, improved the aerobic stability, and increased the potentially degradable DM fraction. Inoculation of CS2 did not affect fermentation, but decreased the aerobic stability and increased the total degradable DM fraction, 24-h and 48-h DMD, and 48-h NDFD.     

Corn silage versus corn silage:alfalfa hay mixtures for dairy cows: effects of dietary potassium, calcium, and cation-anion difference

Corn silage (CS) has replaced alfalfa hay (AH) and haylage as the major forage fed to lactating dairy cows, yet many dairy producers believe that inclusion of small amounts of alfalfa hay or haylage improves feed intake and milk production. Alfalfa contains greater concentrations of K and Ca than corn silage and has an inherently higher dietary cation-anion difference (DCAD). Supplemental dietary buffers such as NaHCO₃ and K₂CO₃ increase DCAD and summaries of studies with these buffers showed improved performance in CS-based diets but not in AH-based diets. We speculated that improvements in performance with AH addition to CS-based diets could be due to differences in mineral and DCAD concentrations between the 2 forages. The objective of this experiment was to test the effects of forage (CS vs. AH) and mineral supplementation on production responses using 45 lactating Holstein cows during the first 20 wk postpartum. Dietary treatments included (1) 50:50 mixture of AH and CS as the forage (AHCS); (2) CS as the sole forage; and (3) CS fortified with mineral supplements (CaCO₃ and K₂CO₃) to match the Ca and K content of the AHCS diet (CS-DCAD). Feed intake and milk production were equivalent or greater for cows fed the CS and CS-DCAD diets compared with those fed the AHCS diet. Fat percentage was greater in cows fed the CS compared with the AHCS diet. Fat-corrected milk (FCM; 3.5%) tended to be greater in cows fed the CS and CS-DCAD diets compared with the AHCS diet. Feed efficiencies measured as FCM/dry matter intake were 1.76, 1.80, and 1.94 for the AHCS, CS, and CS-DCAD diets, respectively. The combined effects of reduced feed intake and increased FCM contributed to increased feed efficiency with the CS-DCAD diet, which contained 1.41% K compared with 1.18% K in the CS diet, and we speculate that this might be the result of added dietary K and DCAD effects on digestive efficiency. These results indicate no advantage to including AH in CS-based diets, but suggest that improving mineral supplementation in CS-based diets may increase feed efficiency.     

Effect of partitioning the nonfiber carbohydrate fraction and neutral detergent fiber method on digestibility of carbohydrates by dairy cows

Many nutrition models rely on summative equations to estimate feed and diet energy concentrations. These models partition feed into nutrient fractions and multiply the fractions by their estimated true digestibility, and the digestible mass provided by each fraction is then summed and converted to an energy value. Nonfiber carbohydrate (NFC) is used in many models. Although it behaves as a nutritionally uniform fraction, it is a heterogeneous mixture of components. To reduce the heterogeneity, we partitioned NFC into starch and residual organic matter (ROM), which is calculated as 100 ? CP ? LCFA ? ash ? starch – NDF, where crude protein (CP), long-chain fatty acids (LCFA), ash, starch, and neutral detergent fiber (NDF) are a percentage of DM. However, the true digestibility of ROM is unknown, and because NDF is contaminated with both ash and CP, those components are subtracted twice. The effect of ash and CP contamination of NDF on in vivo digestibility of NDF and ROM was evaluated using data from 2 total-collection digestibility experiments using lactating dairy cows. Digestibility of NDF was greater when it was corrected for ash and CP than without correction. Conversely, ROM apparent digestibility decreased when NDF was corrected for contamination. Although correcting for contamination statistically increased NDF digestibility, the effect was small; the average increase was 3.4%. The decrease in ROM digestibility was 7.4%. True digestibility of ROM is needed to incorporate ROM into summative equations. Data from multiple digestibility experiments (38 diets) using dairy cows were collated, and ROM concentrations were regressed on concentration of digestible ROM (ROM was calculated without adjusting for ash and CP contamination). The estimated true digestibility coefficient of ROM was 0.96 (SE = 0.021), and metabolic fecal ROM was 3.43 g/100 g of dry matter intake (SE = 0.30). Using a smaller data set (7 diets), estimated true digestibility of ROM when calculated using NDF corrected for ash and CP contamination was 0.87 (SE = 0.025), and metabolic fecal ROM was 3.76 g/100 g (SE = 0.60). Regardless of NDF method, ROM exhibited nutritional uniformity. The ROM fraction also had lower errors associated with the estimated true digestibility and its metabolic fecal fraction than did NFC. Therefore, ROM may result in more accurate estimates of available energy if integrated into models.     

Technical note: Evaluation of a novel enzymatic method to predict in situ undigested neutral detergent fiber of forages and nonforage fibrous feeds

The purpose of this study was to optimize the conditions of a previously proposed enzymatic method used to estimate in situ undigested neutral detergent fiber (uNDF). We used a multi-step enzymatic approach, in which samples were first solubilized in NaOH solutions as a preincubation (PreInc) phase. After rinsing, samples were incubated (24 h at 39°C) in a buffered solution (pH 6) containing hemicellulase, cellulase, and Viscozyme L enzymes (Sigma-Aldrich s.r.l., Milan, Italy), followed by incubation (24 h at 39°C) in a buffered solution (pH 5) containing xylanase. Two sets of experiments were performed: a calibration trial (that tested different PreInc conditions on 9 selected forages) and a validation trial (that verified the results by testing multiple samples of 6 different forage types and a group of fibrous by-products). In the calibration trial, samples (300 mg in Ankom F57 filter bags; Ankom Technology Corp., Fairport, NY) were preincubated at 39°C in a 0.1 M NaOH solution for 90, 180, or 240 min, or in 0.2, 0.5, 1.0, or 2.0 M NaOH solution for 90 min. The results indicated that the best PreInc method, in terms of intra-laboratory repeatability and estimation of reference in situ values, was 90 min in a 0.2 M NaOH solution. Thus, we used this PreInc condition to determine enzymatic uNDF of 257 samples in the validation trial. Although the selected method generally had good accuracy in predicting in situ uNDF, inconsistencies were noted for certain forage types. Overall, when enzymatic uNDF was used to predict the in situ uNDF of all samples, the regression was satisfactory (intercept = 7.098, slope = 0.920, R² = 0.73). The regression models developed for alfalfa hays, corn silages, and small grain silages had also acceptable regression performances and mean square error of prediction (MSEP) values, and the main sources of MSEP variation were error due to incomplete (co)variation and random error. Even when R² values were >0.70, the MSEP value of the regression model for grass hays was 149.55, and that for nonforage fibrous feeds was 155.16. Although enzymatic uNDF partially overestimated the in situ uNDF, particularly in grass silages, the proposed procedure seems to be promising for accurately predicting in situ uNDF, because it generally had good repeatability and provided satisfactory estimates of in situ uNDF.     

Effects of barley silage chop length on productivity and rumen conditions of lactating dairy cows fed a total mixed ration

Barley silage, cut at the early dough stage, was chopped long (19 mm) or short (10 mm), ensiled, and incorporated into total mixed rations (TMR). The TMR contained (dry matter [DM] basis) either 58.0 or 41.4% concentrate and either short- or long-chopped barley silage. Reducing chop length of barley silage decreased the proportion (asis basis) of TMR particles retained by the 8- and 19-mm screens of the Penn State Particle Separator (PSPS) from 66.9 to 52.7% in the high concentrate TMR and from 74.8 to 60.9% in the low concentrate TMR. Chop length reduction decreased dietary physically effective fiber, calculated as the NDF retained by the 8- and 19-mm screens of the PSPS, from 29.2 to 25.2% DM in the high concentrate TMR and from 34.9 to 30.6% DM in the low concentrate TMR. Reduction in chop length did not affect rumen pH, total rumen volatile fatty acids, milk yield, and milk composition, but increased DM intake from 19.4 to 20.1 kg/d at the high level of concentrate and from 16.9 to 17.7 kg/d at the low level of concentrate and increased rumen propionate. Increasing the concentrate inclusion rate reduced rumen pH from 6.52 to 6.35, did not affect total volatile fatty acids, reduced the acetate-to-propionate ratio from 3.1 to 2.7, increased milk yield from 28.7 to 31.3 kg/d, reduced milk fat content from 3.48 to 2.94%, and increased milk protein content from 3.11 to 3.27% across chop lengths.