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.     

Models to predict the risk of subacute ruminal acidosis in dairy cows based on dietary and cow factors: A meta-analysis

The present research aimed at developing practical and feasible models to optimize feeding adequacy to maintain desired rumen pH conditions and prevent subacute ruminal acidosis (SARA) in dairy cows. We conducted 2 meta-analyses, one using data from recent published literatures (study 1) to investigate the prediction of SARA based on nutrient components and dietary physical and chemical characteristics, and another using internal data of our 5 different published experiments (study 2) to obtain adjustments based on cow status. The results of study 1 revealed that physically effective neutral detergent fiber inclusive of particles >8 mm (peNDF >8) and dietary starch [% of dry matter (DM)] were sufficient for predicting daily mean ruminal pH {y = 5.960 – (0.00781 × starch) + (0.03743 × peNDF >8) – [0.00061 × (peNDF >8 × peNDF >8)]}. The model for time of pH suppression (<5.8 for ruminal pH or <6.0 for reticular pH, min/d) can be predicted with additionally including DMI (kg/d): 124.7 + (1.7007 × DMI) + (20.9270 × starch) + (0.2959 × peNDF >8) – [0.0437 × (DMI × starch × peNDF >8)]. As a rule of thumb, when taken separately, we propose 15 to 18% peNDF >8 as a safe range for diet formulation to prevent SARA, when starch or NFC levels are within 20 to 25% and 35 to 40% ranges, respectively. At dietary starch content below 20% of DM, grain type was insignificant in affecting ruminal pH. However, increasing dietary starch contents by using corn as the sole grain source could lead to more severe drops of pH compared with using grain mix based on barley and wheat, as underlined by an interaction between starch content and grain type. Data from study 2 emphasized an increased risk of SARA for cows in the first and second lactation with lower mean pH (0.2 units) and double amounts of time at pH <5.8 compared with the cows with ≥3 parities. Given that a lower ruminal pH is expected in these high-risk cows, it is advisable to keep the lower end of recommended starch (20%) and higher peNDF >8 (18%) contents in the diet of these cows. Overall, the present study underlines the possibility of predicting SARA based on dietary factors including peNDF >8 and starch contents, as well as DMI of the cows, which can be practically implemented for optimal diet formulation for dairy cows. With more data available, future studies should attempt to improve the predictions by including additional key dietary and cow factors in the models.     

Invited review: Current perspectives on eating and rumination activity in dairy cows

Many early studies laid the foundation for our understanding of the mechanics of chewing, the physiological role of chewing for the cow, and how chewing behavior is affected by dietary characteristics. However, the dairy cow has changed significantly over the past decades, as have the types of diets fed and the production systems used. The plethora of literature published in recent years provides new insights on eating and ruminating activity of dairy cows. Lactating dairy cows spend about 4.5 h/d eating (range: 2.4–8.5 h/d) and 7 h/d ruminating (range: 2.5–10.5 h/d), with a maximum total chewing time of 16 h/d. Chewing time is affected by many factors, most importantly whether access to feed is restricted, intake of neutral detergent fiber from forages, and mean particle size of the diet. Feed restriction and long particles (≥19 mm) have a greater effect on eating time, whereas intake of forage neutral detergent fiber and medium particles (4–19 mm) affects rumination time. It is well entrenched in the literature that promoting chewing increases salivary secretion of dairy cows, which helps reduce the risk of acidosis. However, the net effect of a change in chewing time on rumen buffing is likely rather small; therefore, acidosis prevention strategies need to be broad. Damage to plant tissues during mastication creates sites that provide access to fungi, adhesion of bacteria, and formation of biofilms that progressively degrade carbohydrates. Rumination and eating are the main ways in which feed is reduced in particle size. Contractions of the rumen increase during eating and ruminating activity and help move small particles to the escapable pool and into the omasum. Use of recently developed low-cost sensors that monitor chewing activity of dairy cows in commercial facilities can provide information that is helpful in management decisions, especially when combined with other criteria. Although accuracy and precision can be somewhat variable depending on sensor and conditions of use, relative changes in cow behavior, such as a marked decrease in rumination time of a cow or sustained low rumination time compared with a contemporary group of cows, can be used to help detect estrus, parturition, and some illnesses. This review provides a comprehensive understanding of the dietary, animal, and management factors that affect eating and ruminating behavior in dairy cows and presents an overview of the physiological importance of chewing with emphasis on recent developments and practical implications for feeding and managing the modern housed dairy cow.     

Increasing physically effective fiber content of dairy cow diets through forage proportion versus forage chop length: Chewing and ruminal pH

A study was conducted to evaluate whether the risk of acidosis in dairy cows can be lowered by increasing the physically effective fiber (peNDF) concentration of the diet, either through increased theoretical chop length of alfalfa silage or higher proportion of forage in the diet. The experiment was designed as a replicated 4 × 4 Latin square using 8 ruminally cannulated lactating dairy cows. Treatments were arranged in a 2 × 2 factorial design; 2 forage particle lengths (FPL) of alfalfa silage (short and long) were combined with low (35:65) and high (60:40) forage:concentrate (F:C) ratios [dry matter (DM) basis]. Dietary peNDF concentration (DM basis) was determined from the sum of the proportion of dietary DM retained either on the 2 sieves (8 and 19 mm) or on the 3 sieves (1.18, 8, and 19 mm) of the Penn State Particle Separator multiplied by the neutral detergent fiber concentration of the diet. The dietary peNDF concentrations were altered by changing the F:C or the FPL, and ranged from 10.7 to 17.5% using 2 sieves, or from 23.1 to 28.2% using 3 sieves. Intake of peNDF was increased by increasing FPL but not by increasing F:C ratio because of the reduction of DM intake at the higher F:C ratio. Chewing activity, including number of chews and chewing time, increased with increasing F:C ratio or FPL. Mean ruminal pH was elevated by 0.4 and 0.2 units with increasing F:C ratio and FPL, respectively. Lowering the F:C ratio decreased the duration that ruminal pH was below 5.8 (1.2 vs. 8 h/d). Increased F:C ratio or FPL reduced ruminal volatile fatty acids concentration from 137 to 122 or from 133 to 126 mM, respectively, whereas acetate:propionate ratio was increased from 2.55 to 3.46 with increasing F:C ratio. Dietary peNDF concentration measured using 2 sieves was correlated to chewing time (r = 0.57) and mean ruminal pH (r = 0.75), whereas dietary peNDF concentration measured using 3 sieves was correlated to mean ruminal pH (r = 0.83) and negatively correlated to the time that pH was below 5.8 (r = −0.78). This study shows that the risk of ruminal acidosis is high for cows fed a low F:C diet. Increasing the proportion of forage in the diet helps prevent ruminal acidosis through increased chewing time, a change in meal patterns, and decreased ruminal acid production. Increasing FPL elevates ruminal pH, but in low forage diets, increased FPL does not alleviate subacute acidosis because the fermentability of the diet is high and changes in chewing activity are marginal.     

Physically adjusted neutral detergent fiber system for lactating dairy cow rations. II: Development of feeding recommendations

The objective of this work was to leverage equations derived in a meta-analysis into an ensemble modeling system for estimating dietary physical and chemical characteristics required to maintain desired rumen conditions in lactating dairy cattle. Given the availability of data, responsiveness of ruminal pH to animal behaviors, and the chemical composition and physical form of the diet, mean ruminal pH was chosen as the primary rumen environment indicator. Physically effective fiber (peNDF) is defined as the fraction of neutral detergent fiber (NDF) that stimulates chewing activity and contributes to the floating mat of large particles in the rumen. The peNDF of feedstuffs is typically estimated by multiplying the NDF content by a particle size measure, resulting in an estimated index of effectiveness. We hypothesized that the utility of peNDF could be expanded and improved by dissociating NDF and particle size and considering other dietary factors, all integrated into a physically adjusted fiber system that can be used to estimate minimum particle sizes of TMR and diet compositions needed to maintain ruminal pH targets. Particle size measures of TMR were limited to those found with the Penn State particle separator (PSPS). Starting with specific diet characteristics, the system employed an ensemble of models that were integrated using a variable mixture of experts approach to generate more robust recommendations for the percentage of dietary DM material that should be retained on the 8-mm sieve of a PSPS. Additional continuous variables also integrated in the physically adjusted fiber system include the proportion of material (dry matter basis) retained on the 19- and 8-mm sieves of the PSPS, estimated mean particle size, the dietary concentrations of forage, forage NDF, starch, and NDF, and ruminally degraded starch and NDF. The system was able to predict that the minimum proportion of material (dry matter basis) retained on the 8-mm sieve should increase with decreasing forage NDF or dietary NDF. Additionally, the minimum proportion of dry matter material on the 8-mm sieve should increase with increasing dietary starch. Results of this study agreed with described interrelationships between the chemical and physical form of diets fed to dairy cows and quantified the links between NDF intake, diet particle size, and ruminal pH. Feeding recommendations can be interpolated from tables and figures included in this work.     

Influence of corn silage particle length on the performance of lactating dairy cows fed supplemental tallow

The objective of this study was to determine if the length of chop of processed corn silage influences the impact of supplemental fat on rumen fermentation and performance of dairy cows. We hypothesized that increasing forage particle length may alleviate the interference of fat on rumen fermentation. Sixteen Holstein cows averaging 120 d in milk were used in a replicated 4 x 4 Latin square design with 21-d periods. Treatments were arranged as a 2 x 2 factorial with 0 or 2% tallow (dry matter basis), and corn silage harvested at either 19 or 32 mm theoretical length of cut. The forage:concentrate ratio was 50:50, and diets were formulated to contain 18% crude protein and 32% neutral detergent fiber (dry matter basis). Cows were allowed ad libitum consumption of diets that were fed twice daily as a total mixed ration. Fat supplemented cows had lower dry matter intake and produced less milk fat relative to nonsupplemented cows. No effect of corn silage particle length was observed for dry matter intake and milk fat production. Proportion of trans-10 C18:1 and of trans-10, cis-12 conjugated linoleic acid was highest in milk fat of cows fed 2% supplemental tallow. Rumen pH was not affected by feeding tallow, and tended to be highest for cows eating the 32-mm theoretical length of chop corn silage diets. No effect of treatments was observed for rumen acetate-to-propionate ratio or rumen ammonia concentration. In this study, tallow supplementation had a negative impact on performance of dairy cows regardless of the corn silage particle length. Feeding tallow increased formation of trans-fatty acids in the rumen in the absence of significant changes in the rumen environment.     

Graded replacement of corn grain with molassed sugar beet pulp modulates the fecal microbial community and hindgut fermentation profile in lactating dairy cows

High starch lactation diets not only enhance the risk of subacute ruminal acidosis but also of hindgut acidosis, which increases the risk of dysbiosis and the depression of fiber degradation. We recently showed that replacing corn with molassed sugar beet pulp (Bp) improved fiber degradation in high-producing dairy cattle, possibly because of an improvement of rumen and hindgut conditions for microbes by Bp feeding. However, little is known about the effects of high inclusion rates of Bp on hindgut microbes and fermentation. Thus fecal grab samples were taken from 18 high-yielding Simmental cows after 28 d of feeding 3 different levels of Bp (n = 6) for bacterial 16S rRNA amplicon sequencing. In addition, the reticular pH was continuously monitored with indwelling sensors and eating and ruminating behavior was evaluated with noseband sensors. The Bp inclusion rates were 0 g/kg (i.e., no Bp inclusion as control, CON), 120 g/kg (12Bp), or 240 g/kg (24Bp) replacing corn grain and limestone on a dry matter basis. The amount of time spent eating and ruminating was unaffected by Bp level, and the daily fluctuation in the reticular pH was reduced by 25% with Bp inclusion from 0.8 in the CON diet to 0.6 in 24Bp fed animals. Also, the fecal pH tended to increase with dietary Bp inclusion. Fecal acetate production showed a quadratic tendency with the lowest concentration (58.9%) of the total short-chain fatty acid in the 12Bp treatment. Inclusion of Bp up to 24% of the diet decreased the fecal butyrate proportion by 27%. The Shannon diversity index was increased from 5.50 to 8.09 with dietary Bp inclusion indicating increased species diversity. Of the 200 most abundant operational taxonomic units, 25 were increased by dietary Bp inclusion, whereas 15 were decreased and 7 were quadratically affected. The second most abundant group was proposed taxon “CF231” of the family Paraprevotellaceae. Although it accounted for only 2.52% of the operational taxonomic units in the CON diet, it was increased by 64% with dietary Bp inclusion. The largest relative change in the abundance was found for the genus Fibrobacter that increased more than 14-fold from 0.04% (CON) to 0.66% (24Bp). In conclusion, feeding molassed sugar beet pulp as partial substitution of corn up to 240 g/kg is a viable alternative that promotes ruminal and hindgut fermentation by supporting physiological pH and bacterial diversity.     

Invited review: Practical feeding management recommendations to mitigate the risk of subacute ruminal acidosis in dairy cattle

Rumen health is of vital importance in ensuring healthy and efficient dairy cattle production. Current feeding programs for cattle recommend concentrate-rich diets to meet the high nutritional needs of cows during lactation and enhance cost-efficiency. These diets, however, can impair rumen health. The term “subacute ruminal acidosis” (SARA) is often used as a synonym for poor rumen health. In this review, we first describe the physiological demands of cattle for dietary physically effective fiber. We also provide background information on the importance of enhancing salivary secretions and short-chain fatty acid absorption across the stratified squamous epithelium of the rumen; thus, preventing the disruption of the ruminal acid–base balance, a process that paves the way for acidification of the rumen. On-farm evaluation of dietary fiber adequacy is challenging for both nutritionists and veterinarians; therefore, this review provides practical recommendations on how to evaluate the physical effectiveness of the diet based on differences in particle size distribution, fiber content, and the type of concentrate fed, both when the latter is part of total mixed ration and when it is supplemented in partial mixed rations. Besides considering the absolute amount of physically effective fiber and starch types in the diet, we highlight the role of several feeding management factors that affect rumen health and should be considered to control and mitigate SARA. Most importantly, transitional feeding to ensure gradual adaptation of the ruminal epithelium and microbiota; monitoring and careful management of particle size distribution; controlling feed sorting, meal size, and meal frequency; and paying special attention to primiparous cows are some of the feeding management tools that can help in sustaining rumen health in high-producing dairy herds. Supplementation of feed additives including yeast products, phytogenic compounds, and buffers may help attenuate SARA, especially during stress periods when the risk of a deficiency of physically effective fiber in the diet is high, such as during early lactation. However, the usage of feed additives cannot fully compensate for suboptimal feeding management.     

Dietary forage concentration affects the feed sorting behavior of lactating dairy cows

The objective of this study was to determine whether the amount of forage in a total mixed ration influences feed sorting by cows and whether the extent of this sorting changes as they adapt to a new diet. Six lactating Holstein cows, individually fed once per day, were provided each of 2 diets in a crossover design (dry matter basis): 1) a higher forage diet (HF; 62.3% forage), and 2) a lower forage diet (LF; 50.7% forage). Dry matter intake, feeding behavior, and sorting activity were monitored for each cow on each diet for 7 d. Fresh feed and orts were sampled daily for each cow and subjected to neutral detergent fiber (NDF) and particle size analysis. The particle size separator contained 2 screens (18 and 9 mm) and a bottom pan, resulting in 3 fractions (long, medium, and short). Sorting activity [for each fraction, NDF and physically effective NDF (peNDF)] was calculated as the actual intake expressed as a percentage of the predicted intake. Overall, sorting activity was greatest on the LF diet, with cows sorting for short particles but against long particles, medium particles, NDF, and peNDF. On the HF diet, cows sorted against long particles, NDF, and peNDF and sorted for short particles. Treatment × day interactions occurred for sorting for short particles and against peNDF, indicating that it took cows 1 d to adjust their sorting behavior to the LF diet. Cows on the LF diet consumed more dry matter but spent less time feeding, which resulted in a greater intake rate compared with cows on the HF diet. These results indicate that cows rapidly adjust their sorting behavior when subjected to a dietary change, and they exhibit more sorting for short particles and against long particles, NDF, and peNDF when fed an LF diet.     

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 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.     

Short communication: Effect of subacute ruminal acidosis on in situ fiber digestion in lactating dairy cows

Subacute ruminal acidosis (SARA) was induced by replacing 25% of the total mixed ration intake [dry matter (DM) basis] with pellets consisting of 50% wheat and 50% barley. This reduced dietary forage content (DM basis) from 39.7 to 29.8% and increased the dietary concentrate content from 60.3 to 70.2%. Induction of SARA reduced the 24- and 48-h in situ neutral detergent fiber (NDF) degradabilities of grass hay numerically from 31.5% to 24.6% (P = 0.29) and from 51.3% to 36.9% (P < 0.05), respectively. The 24- and 48-h in situ NDF degradabilities of legume hay were reduced from 35.3 to 26.3% (P < 0.05) and from 49.0 to 35.8% (P < 0.05), respectively. The 24- and 48-h in situ NDF degradabilities of corn silage were reduced from 44.0 to 37.2% (P < 0.05) and from 56.1 to 44.8% (P < 0.05), respectively. This study suggests that induction of SARA by excess feeding of wheat/barley pellets reduces the rumen digestion of NDF from grass hay, legume hay, and corn silage.     

Effect of dietary physically effective fiber on ruminal fermentation and the fatty acid profile of milk in dairy goats

The objective of this experiment was to characterize the relationship among rumen fermentation variables, milk fatty acid profile, and dietary physically effective neutral detergent fiber (peNDF) content in a study that controlled for the potential confounding effects of dissimilar dry matter intake among treatments. Ten multiparous Xinong Saanen dairy goats were divided into 2 groups with 2 ruminally cannulated goats per group. Goats in each group were assigned to 1 of 2 dietary treatments (high and low peNDF) according to a 2 × 2 crossover design with 2 periods. The peNDF content of alfalfa hay (proportion of neutral detergent fiber retained on an 8.0-mm screen) was 42.1% for the high-peNDF and 14.5% for the low-peNDF group. To ensure similar dry matter intake, each morning the amount of alfalfa hay consumed on the prior day by the high-peNDF group was determined (amount offered minus morning refusals), and this was the amount of hay offered to the low-peNDF group that day. Each adaptation period consisted of 21 d, followed by a 9-d sampling period. Dry matter intake and milk production and composition were similar between treatments. Milk energy efficiency increased with low dietary peNDF. Duration of pH below 5.60 was longer for goats fed the low-peNDF ration compared with the high-peNDF ration (4.08 vs. 0.41 h/d); however, mean rumen pH (6.05 vs. 6.13) was not different between treatments. Reducing dietary peNDF increased rumen total volatile fatty acids (114.6 vs. 95.1 mM) and decreased chewing time (404 vs. 673 min/d), but did not affect the ratios of acetate, propionate, and butyrate. The relative abundance of Fibrobacter succinogenes and Ruminococcus flavefaciens increased with reduced dietary peNDF, but Ruminococcus albus proportions were not influenced by treatment. Reducing dietary peNDF decreased the proportion of iso C14:0, iso C15:0, and trans-11 C18:1 in milk fat, whereas the iso C17:0 and trans-10 C18:1 increased. This study demonstrated that low dietary peNDF in dairy goats increases rumen volatile fatty acids, reduces chewing time, and is correlated to the amount of F. succinogenes and R. flavefaciens.     

Modeling the adequacy of dietary fiber in dairy cows based on the responses of ruminal pH and milk fat production to composition of the diet

The main objective of this study was to develop practical models to assess and predict the adequacy of dietary fiber in high-yielding dairy cows. We used quantitative methods to analyze relevant research data and critically evaluate and determine the responses of ruminal pH and production performance to different variables including physical, chemical, and starch-degrading characteristics of the diet. Further, extensive data were used to model the magnitude of ruminal pH fluctuations and determine the threshold for the development of subacute ruminal acidosis (SARA). Results of this study showed that to minimize the risk of SARA, the following events should be avoided: 1) a daily mean ruminal pH lower than 6.16, and 2) a time period in which ruminal pH is <5.8 for more than 5.24 h/d. As the content of physically effective neutral detergent fiber (peNDF) or the ratio between peNDF and rumen-degradable starch from grains in the diet increased up to 31.2 ± 1.6% [dry matter (DM) basis] or 1.45 ± 0.22, respectively, so did the daily mean ruminal pH, for which a asymptotic plateau was reached at a pH of 6.20 to 6.27. This study also showed that digestibility of fiber in the total tract depends on ruminal pH and outflow rate of digesta from reticulorumen; thereby both variables explained 62% of the variation of fiber digestibility. Feeding diets with peNDF content up to 31.9 ± 1.97% (DM basis) slightly decreased DM intake and actual milk yield; however, 3.5% fat-corrected milk and milk fat yield were increased, resulting in greater milk energy efficiency. In conclusion, a level of about 30 to 33% peNDF in the diet may be considered generally optimal for minimizing the risk of SARA without impairing important production responses in high-yielding dairy cows. In terms of improvement of the accuracy to assessing dietary fiber adequacy, it is suggested that the content of peNDF required to stabilize ruminal pH and maintain milk fat content without compromising milk energy efficiency can be arranged based on grain or starch sources included in the diet, on feed intake level, and on days in milk of the cows.     

The effects of subacute ruminal acidosis on sodium bicarbonate-supplemented water intake for lactating dairy cows

Four multiparous ruminally fistulated Holstein dairy cows were used in an 8-wk experiment utilizing a repeated measures block design to determine the effects of subacute ruminal acidosis (SARA) on supplemented water intake. Animals were subjected to SARA, which was induced by replacing 25% of the ad libitum intake of the total mixed ration (dry matter basis) with 50:50 wheat:barley pellets utilizing a grain challenge model. Cows had free choice from 2 water bowls. One bowl contained water with sodium bicarbonate (SB) supplemented at 2.5 g/L. The other bowl contained unsupplemented water. Ruminal pH was monitored continuously during the trial using indwelling pH probes. The induction of SARA reduced daily mean ruminal pH and increased the duration when ruminal pH was below 6. The total mixed ration intake by the cows decreased during the SARA periods. The overall preference for SB-supplemented water did not change, as the preference ratio was similar during the control and SARA periods. During the period of greatest ruminal pH depression, total water intake was higher during the SARA periods than during the control periods. During SARA, there was no difference in the preference of a SB water source to unsupplemented water. During the period of day with the most severe ruminal pH depression, the lactating dairy cows subjected to SARA increased their total water intake.     

Particle size and endosperm type of dry corn grain altered duodenal flow of B vitamins in lactating dairy cows

The objective of the experiment was to determine if factors such as endosperm type (floury vs. vitreous) and particle size (fine vs. medium) of dry corn grain, known to affect starch digestibility in the rumen, modify apparent ruminal synthesis and duodenal flow of B vitamins in lactating dairy cows. Eight lactating multiparous Holstein cows equipped with rumen and duodenal cannulas were assigned randomly to a treatment sequence according to a 2 × 2 factorial arrangement in duplicate 4 × 4 Latin square design experiment. Duration of each experimental period was 21 d. When expressed per unit of dry matter intake (DMI), floury treatments increased duodenal flow and apparent ruminal synthesis of niacin and folates but tended to increase apparent degradation of thiamin in the rumen. Duodenal flow of thiamin, riboflavin, niacin, folates, and vitamin B₁₂, expressed per unit of DMI, decreased with an increase in particle size. Similarly, apparent degradation of thiamin and riboflavin was greater and apparent synthesis of niacin, folates, and vitamin B₁₂ was reduced when cows were fed coarser dry corn grain particles. Neither endosperm type nor particle size had an effect on duodenal flow and apparent ruminal synthesis of vitamin B₆. Apparent ruminal syntheses, expressed per unit of DMI, of all studied B vitamins but thiamin were negatively correlated with apparent ruminal digestibility of neutral detergent fiber. Duodenal flow of microbial N was positively correlated with apparent ruminal synthesis of riboflavin, niacin, vitamin B₆, and folates. Under the conditions of the present experiment, except for thiamin, the effects of factors increasing starch digestibility of dry corn grain in the rumen on the amounts of B vitamins available for absorption by the dairy cow seem to be mediated through differences on ruminal digestibility of neutral detergent fiber and, to a lesser extent, on duodenal microbial N flow.     

Effects of physically effective fiber on intake, chewing activity, and ruminal acidosis for dairy cows fed diets based on corn silage

A study was conducted to investigate the effects of physically effective (pe) neutral detergent fiber (NDF) content of dairy cow diets containing corn silage as the sole forage type on feed intake, meal patterns, chewing activity, and rumen pH. The experiment was designed as a replicated 3 × 3 Latin square using 6 lactating dairy cows with ruminal cannulas. Diets were chemically similar but varied in peNDF content (high, medium, and low) by altering corn silage particle length. The physical effectiveness factors for the long (original), medium (rechopped once), and fine (rechopped twice) silages were determined using the Penn State Particle Separator and were 0.84, 0.73, and 0.67, respectively. The peNDF contents of the diets were 11.5, 10.3, and 8.9%, for the high, medium, and low diets, respectively. Increased forage particle length increased intake of peNDF but did not affect intake of DM or NDF. Number of chews (chews/d) and chewing time, including eating and ruminating time, were linearly increased with increasing dietary peNDF. Meal patterns were generally similar for all treatments, except that number of meals was quadratically increased with increasing dietary peNDF. Mean ruminal pH, area between the curve and a horizontal line at pH 5.8 or 5.5, and time that pH was below 5.8 or 5.5 were not affected by peNDF content. Dietary peNDF content was moderately correlated to number of chews during eating (r = 0.41) and to total chewing time (r = 0.37). The present study demonstrates that increasing the peNDF content of diets increased chewing time, but increased chewing time did not necessarily reduce ruminal acidosis. Models that predict rumen pH should include both peNDF and fermentable OM intake. Dietary particle size, expressed as peNDF, was a reliable indicator of chewing activity.     

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.     

Effect of feed sorting on chewing behavior, production, and rumen fermentation in lactating dairy cows

Ration sorting is thought to allow cows to eat different rations throughout the day, causing fluctuations in rumen fermentation patterns that can be detrimental to production and possibly animal health. The objective of this experiment was to study the effects of varying total mixed ration (TMR) particle size on sorting behavior of lactating dairy cows and to evaluate effects on chewing behavior, milk yield, milk components, and rumen fermentation. Eight multiparous, Holstein cows (90 ± 32 d in milk; 4 rumen cannulated) were randomly assigned to replicated 4 × 4 Latin squares. Cows were fed diets that varied in the chop length of dry grass hay. The diet consisted of 29.4% corn silage, 22.9% ground corn, 17.6% alfalfa haylage, and 11.8% dry grass hay on a dry matter basis. The percentage of hay particles >26.9 mm was 4.2, 34.1, 60.4, and 77.6% for the short (S), medium (M), long (L), and extra long (XL) hays, respectively. This resulted in the TMR of each diet having 1.5 (S), 6.5 (M), 8.6 (L), and 11.7% (XL) of particles >26.9 mm. Daily ruminating time [19.3, 19.2, 22.4, and 21.3 min/kg of dry matter intake (DMI) for S, M, L, and XL] and eating time (13.9, 14.6, 17.2, and 16.1 min/kg of DMI for S, M, L, and XL) increased linearly as TMR particle size increased. Daily DMI decreased linearly as TMR particle size increased and was 26.9 (S), 27.0 (M), 24.1 (L), and 25.1 (XL) kg/d. No differences were found in rumen volatile fatty acids and NH₃, and only slight changes were found in rumen pH. Milk production and milk components were also similar among diets. Despite large differences in particle size among these diets and certain chewing and ruminating differences, no changes in rumen fermentation, milk production, or milk components were found in this study.