Nutrient demand interacts with grass particle length to affect digestion responses and chewing activity in dairy cows

Effects of grass particle length on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, digestion and passage kinetics, and chewing activity and the relationship of these effects with preliminary DMI (pDMI) were evaluated using 15 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 18-d treatment periods. During the preliminary period, pDMI of individual cows ranged from 22.6 to 29.8 kg/d (mean=25.8 kg/d) and 3.5% fat-corrected milk yield ranged from 29.2 to 56.9 kg/d (mean=41.9 kg/d). Experimental treatments were diets containing orchardgrass silage chopped to either (a) 19-mm (long) or (b) 10-mm (short) theoretical length of cut as the sole forage. Grass silages contained approximately 46% neutral detergent fiber (NDF); diets contained 50% forage, 23% forage NDF, and 28% total NDF. Preliminary DMI, an index of nutrient demand, was determined during the last 4 d of the preliminary period when cows were fed a common diet and used as a covariate. Main effects of grass particle length and their interaction with pDMI were tested by ANOVA. Grass particle length and its interaction with pDMI did not affect milk yield, milk composition, or rumen pH. Long particle length tended to decrease DMI compared with short particle length, which might have been limited by rumen fill or chewing time, or both. Passage rates of feed fractions did not differ between long and short particle lengths and were not related to level of intake. As pDMI increased, long particles decreased ruminal digestion rate of potentially digestible NDF at a faster rate than short particles. As a result, long particles decreased or tended to decrease rates of ruminal turnover for NDF, organic matter, and dry matter and increased their rumen pools compared with short particles for cows with high pDMI. Long particles increased eating time, which affected cows with high intake to the greatest extent, and total chewing time compared with short particles. As intake increased, ruminal digestion (kg/d) and digestibility (%) of starch decreased, rumen pool size of starch increased, and postruminal digestion and digestibility of starch increased quadratically. When grass silage was the only source of forage in the diet, increasing chop length from 10 to 19 mm tended to decrease DMI but did not negatively affect productivity of cows, which were fed adequate fiber.     

Effects of partially replacing barley silage or barley grain with dried distillers grains with solubles on rumen fermentation and milk production of lactating dairy cows

Dried distillers grains with solubles (DDGS) has been commonly used as a dietary protein source for lactating dairy cows. However, there is a paucity of data evaluating the use of DDGS as a partial replacement of forage or grain. The objective of this study was to determine the effects of partially replacing barley silage or barley grain with corn/wheat-based DDGS on dry matter intake (DMI), chewing activity, rumen fermentation, and milk production. Six ruminally cannulated lactating Holstein cows were used in a replicated 3 × 3 Latin square design with 21-d periods. Cows were fed the control diet (CON: 45% barley silage, 5% alfalfa hay, and 50% concentrate mix), a low forage (LF) diet or a low grain (LG) diet, in which barley silage or barley grain was replaced by DDGS at 20% of dietary dry matter, respectively. All diets were formulated to contain 18% crude protein and fed as total mixed rations. Compared with CON, cows fed the LF diet had greater DMI (26.0 vs. 22.4 kg/d), yields of milk (36.4 vs. 33.0 kg/d), milk protein (1.18 vs. 1.05 kg/d), and milk lactose (1.63 vs. 1.46 kg/d), but milk fat yield was not affected. The LF diet decreased chewing time compared with the CON diet (29.7 vs. 39.1 min/kg of DMI), but did not affect rumen pH and duration of rumen pH below 5.8. Compared with CON, feeding the LG diet tended to increase minimum and maximum rumen pH, but did not affect DMI, milk yield, and milk composition in this study. These results indicate that a partial replacement of barley silage with DDGS can improve the productivity of lactating dairy cows without negatively affecting rumen fermentation and milk fat production. Barley grain can also be partially replaced by DDGS in diets for lactating dairy cows without causing negative effects on productivity.     

Nutrient demand interacts with grass maturity to affect milk fat concentration and digestion responses in dairy cows

Effects of grass maturity on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, digestion and passage kinetics, and chewing activity and the relationship of these effects with preliminary DMI (pDMI) were evaluated using 13 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 18-d treatment periods. During the preliminary period, pDMI of individual cows ranged from 23.5 to 28.2kg/d (mean=26.1kg/d) and 3.5% fat-corrected milk (FCM) yield ranged from 30.8 to 57.2kg/d (mean=43.7kg/d). Experimental treatments were diets containing orchardgrass silage harvested either (1) early-cut, less mature (EC) or (2) late-cut, more mature (LC) as the sole forage. Early- and late-cut orchardgrass contained 44.9 and 54.4% neutral detergent fiber (NDF) and 20.1 and 15.3% crude protein, respectively. Forage:concentrate ratio was 58:42 and 46:54 for EC and LC, respectively; both diets contained approximately 25% forage NDF and 30% total NDF. Preliminary DMI, an index of nutrient demand, was determined during the last 4d of the preliminary period when cows were fed a common diet and used as a covariate. Main effects of grass maturity and their interaction with pDMI were tested by ANOVA. The EC diet decreased milk yield and increased milk fat concentration compared with the LC diet. Grass maturity and its interaction with pDMI did not affect FCM yield, DMI, rumen pH, or microbial efficiency. The EC diet increased rates of ruminal digestion of potentially digestible NDF and passage of indigestible NDF (iNDF) compared with the LC diet. The lower concentration and faster passage rate of iNDF for EC resulted in lower rumen pools of iNDF, total NDF, organic matter, and dry matter for EC than LC. Ruminal passage rates of potentially digestible NDF and starch were related to level of intake (quadratic and linear interactions, respectively) and subsequently affected ruminal digestibility of these nutrients. The EC diet decreased eating, ruminating, and total chewing time per unit of forage NDF intake compared with the LC diet. When grass silage was the only source of forage in the diet, cows supplemented with additional concentrate to account for decreasing protein and increasing fiber concentrations associated with more mature grass had similar feed intake and produced similar FCM yields as cows fed less mature grass.     

Effect of a garlic and citrus extract supplement on performance,rumen fermentation,methane production,and rumen microbiome of dairy cows

The aim of this trial was to determine the effect of a garlic and citrus extract supplement (GCE) on the performance, rumen fermentation, methane emissions, and rumen microbiome of dairy cows. Fourteen multiparous Nordic Red cows in mid-lactation from the research herd of Luke (Jokioinen, Finland) were allocated to 7 blocks in a complete randomized block design based on body weight, days in milk, dry matter intake (DMI), and milk yield. Animals within each block were randomly allocated to a diet with or without GCE. The experimental period for each block of cows (one for each of the control and GCE groups) consisted of 14 d of adaptation followed by 4 d of methane measurements inside the open circuit respiration chambers, with the first day being considered as acclimatization. Data were analyzed using the GLM procedure of SAS (SAS Institute Inc.). Methane production (g/d) and methane intensity (g/kg of energy-corrected milk) were lower by 10.3 and 11.7%, respectively, and methane yield (g/kg of DMI) tended to be lower by 9.7% in cows fed GCE compared with the control. Dry matter intake, milk production, and milk composition were similar between treatments. Rumen pH and total volatile fatty acid concentrations in rumen fluid were similar, whereas GCE tended to increase molar propionate concentration and decrease the molar ratio of acetate to propionate. Supplementation with GCE resulted in greater abundance of Succinivibrionaceae, which was associated with reduced methane. The relative abundance of the strict anaerobic Methanobrevibacter genus was reduced by GCE. The change in microbial community and rumen propionate proportion may explain the decrease in enteric methane emissions. In conclusion, feeding GCE to dairy cows for 18 d modified rumen fermentation and microbiota, leading to reduced methane production and intensity without compromising DMI or milk production in dairy cows. This could be an effective strategy for enteric methane mitigation of dairy cows.     

Nutrient demand interacts with legume particle length to affect digestion responses and rumen pool sizes in dairy cows

Effects of legume particle length on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, and digestion and passage kinetics, and the relationship of these effects with preliminary DMI (pDMI) were evaluated using 13 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 19-d treatment periods. During the preliminary period, pDMI of individual cows ranged from 22.8 to 32.4 kg/d (mean=26.5 kg/d) and 3.5% fat-corrected milk yield ranged from 22.9 to 62.4 kg/d (mean=35.1 kg/d). Experimental treatments were diets containing alfalfa silage chopped to (1) 19 mm (long cut, LC) or (2) 10 mm (short cut, SC) theoretical length of cut as the sole forage. Alfalfa silages contained approximately 43% neutral detergent fiber (NDF); diets contained approximately 47% forage and 20% forage NDF. Preliminary DMI, an index of nutrient demand, was determined during the last 4 d of the preliminary period, when cows were fed a common diet, and used as a covariate. Main effects of legume particle length and their interaction with pDMI were tested by ANOVA. Alfalfa particle length and its interaction with pDMI did not affect milk yield or rumen pH. The LC diet decreased milk fat concentration more per kilogram of pDMI increase than the SC diet and increased yields of milk fat and fat-corrected milk less per kilogram of pDMI increase than the SC diet, resulting in a greater benefit for LC at low pDMI and for SC at high pDMI. The LC diet tended to decrease DMI compared with the SC diet. Ruminal digestion and passage rates of feed fractions did not differ between LC and SC and were not related to level of intake. The LC diet tended to decrease the rate of ruminal turnover for NDF but increased NDF rumen pools at a slower rate than the SC diet as pDMI increased. This indicated that the faster NDF turnover rate did not counterbalance the higher DMI for SC, resulting in larger NDF rumen pools for SC than LC. As pDMI increased, LC increased ruminal digestibility of potentially digestible NDF and total NDF, and SC decreased them, but total-tract digestibilities of potentially digestible NDF, total NDF, organic matter, and dry matter were lower for LC than for SC. Ruminal digestibilities of starch and organic matter interacted quadratically with level of intake. When legume silage was the only source of forage in the diet, increasing chop length from 10 to 19 mm tended to decrease DMI but did not negatively affect productivity of cows.     

Effect of concentrate level on feeding behavior and rumen and blood parameters in dairy goats: Relationships between behavioral and physiological parameters and effect of between-animal variability

This work aimed first to compare 2 diets differing in their percentage of concentrate [low (LO): 30% concentrate vs. High (HI): 60% concentrate] by measuring simultaneously feeding behavior, rumen parameters, blood and plasma parameters, and milk yield and composition in 8 mid-lactation goats. The second aim was to study the interrelationships between these variables and to analyze the between-animal variability to better understand the between-animal differences in acidosis susceptibility. All of the animals received the 2 diets ad libitum as total mixed ration according to a crossover design of two 4-wk periods. Mean daily DMI was similar between the 2 diets but the variability was higher for the HI than for the LO diet. Goats produced more milk when fed the HI diet compared with the LO diet but with a lower fat:protein ratio (0.81 vs. 0.99). They ate more rapidly the HI than the LO diet but stopped eating sooner after the afternoon feed allowance, and spent less time chewing. The increase in concentrate percentage modified rumen parameters: the pH and acetate:propionate ratio decreased and total VFA, ammonia, and soluble carbohydrate concentrations increased. Hematocrit, plasma NEFA, and blood K and Ca concentrations decreased but glycemia and uremia increased. Other parameters were not modified: milk fat content, blood pH, and bicarbonate and Na concentrations. A large between-animal variability was detected for all the measured parameters, especially for feeding behavior, with important consequences on rumen and blood parameters. This work confirmed the effects of a high percentage of concentrate on feeding behavior, rumen and blood parameters, and milk production, and some known relationships such as the positive link between rumen pH and chewing index. It also pointed out other relationships between parameters seldom measured at the same time, such as rumen redox potential or blood pH and chewing index, or the negative link between blood and rumen pH. When the animals spent a lot of time chewing, they probably produced a lot of saliva that buffered the rumen pH and prevented them from suffering from subacute ruminal acidosis. However, they used part of their blood bicarbonates reserve, which might have induced metabolic acidosis, as rumen and blood pH were inversely related. This could explain why some animals suffer from acidosis and others do not in a herd receiving the same diet, and why some animals seem to suffer more from subacute ruminal acidosis and others from metabolic acidosis.     

Dietary fiber and milk yield, mastication, digestion, and the rate of passage in goats fed alfalfa hay.

Two experiments were conducted to study the effect of intake of fiber on productive performance of high producing dairy goats during early to midlactation. Four dietary treatments were isonitrogenous and consisted of combinations of chopped alfalfa hay and concentrate, yielding 14, 18, 22, and 26% ADF. In Experiment 1, 40 multiparous Alpine does were used in a completely randomized block design. Milk fat content and total chewing time increased, and milk yield tended to decrease, as dietary ADF intake increased. Chewing efficiency [min/(g x kg BW.75)] for DM decreased, whereas that for ADF increased as ADF intake increased. Prediction equations were the following: milk fat yield, g/d = 115.78 - .128 x ADF intake, g/d + .00021 X (ADF intake)2 (r = .55); total chewing time, min/d = 345.33 + .32 x ADF intake, g/d (r = .60). In Experiment 2, 20 does were used in a completely randomized design. Apparent digestibilities of DM and energy decreased as dietary ADF intake increased. Rumen turnover rate and transit time of liquid were affected by ADF intake. Transit time of hay decreased as ADF intake increased. Intake of ADF affected pH and ammonia, acetate, and butyrate concentrations in the rumen. Acetate to propionate ration increased with ADF intake. No apparent trends were observed in whole blood beta-hydroxybutyrate or in plasma NEFA concentrations related to ADF intake. It appeared that DMI and milk fat yield leveled at 22% ADF or 43% NDF. For lactating dairy goats producing more than 3.5 kg/d of milk, calculated fat output reached a plateau when they consumed 587 g/d of ADF and spent 512 min/d chewing.     

Nutrient demand interacts with forage family to affect digestion responses in dairy cows

Effects of forage family on dry matter intake (DMI), milk production, ruminal pool sizes, digestion and passage kinetics, and chewing activity and the relationship of these effects with preliminary DMI (pDMI), an index of nutrient demand, were evaluated using 13 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 18-d treatment periods. During the preliminary period, pDMI of individual cows ranged from 19.6 to 29.5 kg/d (mean=25.9 kg/d) and 3.5% fat-corrected milk yield ranged from 24.3 to 60.3 kg/d (mean=42.1 kg/d). Experimental treatments were diets containing either a) alfalfa silage (AL) or b) orchardgrass silage (OG) as the sole forage. Alfalfa and orchardgrass contained 42.3 and 58.2% neutral detergent fiber (NDF) and 22.5 and 11.4% crude protein, respectively. Forage:concentrate ratios were 60:40 and 43:57 for AL and OG, respectively; both diets contained approximately 25% forage NDF and 30% total NDF. Preliminary DMI was determined during the last 4 d of the preliminary period when cows were fed a common diet and used as a covariate. Main effects of forage family and their interaction with pDMI were tested by ANOVA. Forage family and its interaction with pDMI did not affect feed intake, milk yield, or milk composition. The AL diet increased indigestible NDF (iNDF) intake and decreased potentially digestible NDF (pdNDF) intake compared with OG. The AL diet increased ruminal pH, digestion rates of pdNDF and starch, and passage rates of pdNDF and iNDF compared with OG, which affected ruminal digestibility. Passage rate of iNDF was related to pDMI; AL increased iNDF passage rate and OG decreased it as pDMI increased. The AL diet decreased ruminal pool sizes of pdNDF, starch, organic matter, dry matter, and rumen digesta wet weight and volume compared with OG. The AL diet decreased ruminating time per unit of forage NDF consumed compared with OG, indicating that alfalfa provided less physically effective fiber than orchardgrass. The AL diet, but not OG, increased ammonia N, nonammonia nonmicrobial N, and nonammonia N fluxes as pDMI increased. Efficiency of microbial protein synthesis was positively related to pdNDF passage rate for OG, but not AL. The faster rates of digestion and passage for AL compared with OG decreased rumen pool size but did not increase feed intake for cows consuming AL. Digestion responses to forage family were affected by nutrient demand of cows.     

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.     

Effects of feeding a high-fiber byproduct feedstuff as a substitute for barley grain on rumen fermentation and productivity of dairy cows in early lactation

The objective of the study was to evaluate effects of partial substitution of dietary grain with wheat dried distillers grains with solubles (DDGS) on dry matter intake (DMI), sorting behavior, rumen fermentation, apparent total-tract nutrient digestibility, plasma metabolites, and milk production of dairy cows in early lactation. Sixty-one Holstein cows, including 13 ruminally cannulated cows, were blocked by parity and calving date and assigned to 1 of 2 experimental diets immediately after calving until 12 wk in lactation. The control (CON) diet contained 43% barley silage, 17.3% dry-rolled barley grain, and 39.7% concentrate mix on a dry matter basis, and wheat DDGS replaced dry-rolled barley grain in the DDGS diet. Dietary starch content was 29.2 and 19.1% for CON and DDGS diets, respectively. Despite the 10-percentage-unit difference in dietary starch content, cows fed the DDGS diet did not increase ruminal pH. A significant treatment by parity interaction was observed for DMI; feeding the DDGS diet decreased DMI of multiparous cows compared with CON (20.1 vs. 21.3 kg/d) but increased that of primiparous cows (16.2 vs. 14.7 kg/d). Although milk yield was not affected by treatment, cows fed the DDGS diet had lower apparent total-tract digestibility of starch compared with CON (81.9 vs. 91.2%) and tended to have higher plasma concentrations of nonesterified fatty acids (173 vs. 143 mEq/L). High-fiber byproduct feedstuffs such as wheat DDGS can be used as a partial substitute for grains in diets of dairy cows in early lactation but the substitution may not mitigate rumen acidosis problems and may decrease energy intake of multiparous cows in early lactation.     

Effects of abomasally infused rumen fluid from corn-challenged donor cows on production,metabolism, and inflammatory biomarkers in healthy recipient cows

Subacute rumen acidosis may cause postruminal intestinal barrier dysfunction, but this does not appear to be due to increased hindgut fermentation. Alternatively, intestinal hyperpermeability may be explained by the plethora of potentially harmful substances (e.g., ethanol, endotoxin, and amines) produced in the rumen during subacute rumen acidosis, which are difficult to isolate in traditional in vivo experiments. Therefore, objectives were to evaluate whether abomasal infusion of acidotic rumen fluid collected from donor (Donor) cows elicits systemic inflammation or alters metabolism or production in healthy recipients. Ten rumen-cannulated lactating dairy cows [249 ± 63 d in milk; 753 ± 32 kg of body weight (BW)] were randomly assigned to 1 of 2 abomasal infusion treatments: (1) healthy rumen fluid (HF; 5 L/h; n = 5) or (2) acidotic rumen fluid (AF; 5 L/h; n = 5) infused. Eight rumen-cannulated cows [4 dry, 4 lactating (lactating = 391 ± 220 d in milk); 760 ± 70 kg of BW] were used as Donor cows. All 18 cows were acclimated to a high-fiber diet (46% neutral detergent fiber; 14% starch) during an 11-d prefeeding period during which rumen fluid was collected for the eventual infusion into HF cows. During period (P) 1 (5 d), baseline data were obtained and on d 5 Donor were corn-challenged (2.75% BW ground corn after 16 h of 75% feed restriction). Cows were fasted until 36 h relative to rumen acidosis induction (RAI), and data were collected through 96 h RAI. At 12 h RAI, an additional 0.50% BW of ground corn was added, and acidotic fluid collections began (7 L/Donor every 2 h; 6 M HCl was added to collected fluid until pH was between 5.0 and 5.2). On d 1 of P2 (4 d), HF/AF cows were abomasally infused with their respective treatments for 16 h, and data were collected for 96 h relative to the first infusion. Data were analyzed in SAS (SAS Institute Inc.) using PROC MIXED. Following the corn challenge in the Donor cows, rumen pH only mildly decreased at nadir (pH = 5.64 at 8 h RAI) and remained above the desired threshold for both acute (5.2) and subacute (5.6) acidosis. In contrast, fecal and blood pH markedly decreased to acidotic levels (nadir = 4.65 and 7.28 at 36 and 30 h RAI, respectively), and fecal pH remained below 5 from 22 to 36 h RAI. In Donor cows, dry matter intake remained decreased through d 4 (36% relative to baseline) and serum amyloid A and lipopolysaccharide-binding protein markedly increased by 48 h RAI in Donor cows (30- and 3-fold, respectively). In cows that received the abomasal infusions, fecal pH decreased in AF from 6 to 12 h relative to the first infusion (7.07 vs. 6.33) compared with HF; however, milk yield, dry matter intake, energy-corrected milk, rectal temperature, serum amyloid A, and lipopolysaccharide-binding protein were unaffected. Overall, the corn challenge did not cause subacute rumen acidosis but markedly decreased fecal and blood pH and stimulated a delayed inflammatory response in the Donor cows. Abomasal infusion of rumen fluid from corn-challenged Donor cows decreased fecal pH but did not cause inflammation, nor did it create an immune-activated phenotype in recipient cows.     

Effects of Saccharomyces cerevisiae-based direct-fed microbial and exogenous enzyme products on enteric methane emission and productivity in lactating dairy cows

The objective of this experiment was to investigate the effects of a Saccharomyces cerevisiae-based direct-fed microbial product (SDM) and an exogenous enzyme product (ENZ) on enteric methane emission, milk yield and composition, total-tract digestibility of nutrients, ruminal fermentation, and nitrogen excretion and secretion in lactating dairy cows. Eighteen Holstein cows were used in a 3 × 3 Latin square design experiment with three 28-d periods. Treatments were (1) control (no additive), (2) 28 g of SDM/d per cow, or (3) 10 g of ENZ/d per cow. Treatments were top-dressed at the time of feeding. The basal diet consisted of (dry matter basis) 60% forage and 40% concentrates and contained 16.5% crude protein and 32.0% neutral detergent fiber. Treatments had no effect on enteric methane production, yield (methane per kg of dry matter intake, DMI), or intensity (methane per kg of energy-corrected milk yield). Carbon dioxide production was similar among treatments. Compared with control, SDM increased milk yield by 2 kg/d without affecting DMI or feed efficiency. Supplementation of the diet with ENZ did not affect DMI, milk yield, or feed efficiency. Concentrations and yields of milk fat, true protein, and lactose, and energy-corrected milk yield were not different among treatments. Neither SDM nor ENZ had an effect on total-tract digestibility of nutrients or nitrogen excretion and secretion. Concentration of total volatile fatty acids (VFA) in ruminal fluid was increased by both SDM and ENZ, and rumen pH was decreased by SDM compared with the control. At levels similar to the control DMI, the increased concentration of VFA in ruminal fluid of cows receiving SDM suggests an increased postruminal supply of energy and may partly explain the increased milk yield with that treatment. However, it is important to note that milk composition and energy-corrected milk yield were not affected by treatment.     

The effect of calcareous marine algae,with or without marine magnesium oxide,and sodium bicarbonate on rumen pH and milk production in mid-lactation dairy cows

Two experiments were carried out to evaluate different dietary buffers and their influence on (1) rumen pH in dairy cows and (2) milk production in dairy cows. The supplements included were calcareous marine algae (CMA; Lithothamnion calcareum), with or without marine magnesium oxide (MM; precipitated magnesia derived from seawater), and sodium bicarbonate (SB). Dietary treatments in experiment 1 consisted of the control [32.9% starch and sugar, and 19.9% neutral detergent fiber from forage per kg of dry matter (DM)] including no dietary buffer (CON); the control plus 0.45% DM CMA (CMA); the control plus 0.45% DM CMA and 0.11% DM MM (CMA+MM); the control plus 0.9% DM SB (SB). Diets were formulated to a dry matter intake (DMI) of 18 kg per cow/d. Dietary treatments in experiment 2 also consisted of CON (28.3% starch and sugar, and 23% neutral detergent fiber from forage per kg of DM), CMA, CMA+MM, and SB and were formulated to achieve identical intakes of experimental ingredients (80 g of CMA, 80 g of CMA plus 20 g MM, and 160 g of SB per cow/d) with a DMI of 22.6 kg per cow/d. Experiment 1 used 4 rumen-cannulated dairy cows in a 4 × 4 Latin square design. Rumen pH was measured over five 2-h periods, following feeding, using rumen pH probes. In experiment 2, 52 multiparous and 4 primiparous cows (62.7 ± 3.4 d in milk) were assigned to 4 experimental treatments for 80 d. Both CMA treatments maintained a greater mean rumen pH than the CON during 4 of the 5 periods following feeding and the CON had a greater number of hours below rumen pH 5.5 compared with all other treatments. Dry matter intakes tended to be higher on the SB compared with CON. The CMA treatment increased the production of milk fat and protein yield (kg/d) compared with all other treatments. Both CMA and CMA+MM increased milk fat yield compared with CON but were similar to each other and SB. Protein yield was highest in the CMA treatment compared with CON, CMA+MM, and SB. All 3 buffer treatments increased milk fat concentration compared with CON but did not differ from each other. The SB treatment reduced milk protein concentration and milk production efficiency, energy-corrected milk per kilogram of DMI. Results indicate that the addition of CMA can benefit milk fat and protein production when included in diets based on typical feedstuffs of the northern European region. The use of CMA when compared with SB, in such diets, can increase milk protein production and milk production efficiency.     

The effect of concentrate supplementation on nutrient flow to the omasum in dairy cows receiving freshly cut grass

An experiment was carried out to determine the effect of increasing the amount of grain-based concentrate (0, 3, or 6 kg/d) on nutrient flow to the omasum, rumen fermentation pattern, milk yield, and nutrient use of dairy cows. Harvested timothy-meadow fescue grass was fed individually 3 times daily to 6 rumen-cannulated Holstein-Friesian cows in a duplicated 3 x 3 Latin square experiment. Grass was offered as 6 equal meals daily, and concentrates were fed as 2 equal meals daily. Nitrogen, microbial N, and neutral detergent fiber (NDF) flow from the rumen were measured using an omasal sampling technique in combination with a triple marker method [CoEDTA, Yb, and indigestible NDF (INDF) as markers]. Concentrate supplementation linearly decreased ruminal pH, N degradability, ammonia N concentration, and molar proportion of acetate and increased the molar proportion of butyrate. Supplementation of grass with concentrates linearly increased dry matter intake (DMI), microbial N synthesis, N, and NDF flow to the omasum, and ruminal and total tract NDF digestibility decreased linearly. Decreases in NDF digestibility in response to concentrates was primarily related to a decrease in the rate of digestion. Increased DMI overcame the negative effects of concentrate on NDF digestion, resulting in a linear increase in total metabolizable energy intake and milk production. Physical constraints were found not to limit grass DMI. Concentrate supplementation increased the apparent use of dietary N for milk production because of a reduction in N intake, rather than thorough improvements in N capture in the rumen.     

Effect of dietary roughage level on chewing activity,ruminal pH,and saliva secretion in lactating Holstein cows

Increasing dietary roughage level is a commonly used strategy to prevent subacute ruminal acidosis. We hypothesized that high-roughage diets could promote chewing activity, saliva secretion, and hence more alkaline to buffer rumen pH. To verify the hypothesis, 12 multiparous Holstein cows in mid lactation were randomly allocated to 4 treatments in a triplicated 4 × 4 Latin square experiment with one cow in each treatment surgically fitted with a ruminal cannula. Treatments were diets containing 40, 50, 60, or 70% of roughage on a DM basis. Increasing dietary roughage level decreased DM, CP, OM, starch, and NE_L intake, increased ADF intake, and decreased milk yield linearly. Intake of NDF was quite stable across treatments and ranged from 7.8 to 8.1 kg/d per cow. Daily eating time increased linearly with increased roughage level. The increase in eating time was due to increased eating time per meal but not number of meals per day, which was stable and ranged from 8.3 to 8.5 meals per day across treatments. Increasing dietary roughage level had no effect on ruminating time (min/d), the number of ruminating periods (rumination periods per d), and chewing time per ruminating period (min/ruminating period). Ruminating time per kilogram of NDF intake and total chewing time per kilogram of ADF intake were similar across treatments (57.4 and 183.8 min/kg, respectively). Increasing dietary roughage level linearly increased daily total chewing time; linearly elevated the mean, maximum, and minimum ruminal pH; and linearly decreased total VFA concentration and molar proportion of propionate in ruminal fluid. Saliva secretion during eating was increased, the secretion during rumination was unaffected, but the secretion during resting tended to decrease with increased dietary roughage level. As a result, total saliva secretion was not affected by treatments. In conclusion, the results of the present study did not support the concept that high-roughage diets elevated ruminal pH through increased salivary recycling of buffering substrates.     

Meta-analysis of the influence of Saccharomyces cerevisiae supplementation on ruminal parameters and milk production of ruminants

The effects of yeast supplementation on intake, production, and rumen fermentation characteristics have been widely studied, but results are inconsistent between different studies. A quantitative meta-analysis was applied to 110 papers, 157 experiments, and 376 treatments dealing with yeast supplementation in ruminants. The objective was first to highlight the major quantitative effects of live yeast supplementation on intake, rumen fermentation, and milk production, and second, to identify major differences in experimental conditions between studies that can affect the response to treatment. Some of these experimental conditions are referred to as interfering factors. Yeast supplementation increased rumen pH (+0.03 on average) and rumen volatile fatty acid concentration (+2.17 mM on average), tended to decrease rumen lactic acid concentration (−0.9 mM on average), and had no influence on acetate-to-propionate ratio. Total-tract organic matter digestibility was also increased by yeast supplementation (+0.8% on average). Yeast supplementation increased dry matter intake (DMI; +0.44 g/kg of body weight; BW), milk yield (+1.2 g/kg of BW), and tended to increase milk fat content (+0.05%), but had no influence on milk protein content. Dose effects of yeast supplementation, expressed as log₁₀ [1+(cfu per 100 kg of BW)], globally confirmed the qualitative effects observed in the first analysis. The positive effect of yeast supplementation on rumen pH increased with the percentage of concentrate in the diet and with the DMI level. It was negatively correlated with the level of dietary neutral detergent fiber (NDF). The positive effect of yeast supplementation on rumen volatile fatty acid concentration increased with DMI and crude protein levels. The positive effect of yeast supplementation on organic matter digestibility increased with the percentage of concentrate and NDF in the diet. The negative effect of yeast supplementation on lactic acid concentration tended to decrease when the DMI level and the percentage of concentrate in the diet increased. The effects of interfering factors were globally similar when either dose effect or qualitative effect of yeast was taken into account. Although rumen fermentation efficiency per se was not measured, these results suggest an improvement in rumen fermentation by yeast supplementation. This effect could, however, be modulated by several different factors such as DMI, percentage of concentrate or NDF in the diet, or species.     

The effect of corn silage particle size and cottonseed hulls on cows in early lactation

The objective of this study was to evaluate the effects of reducing forage particle length (FPL) and the inclusion of cottonseed hulls (CSH) on intake, digestibility, chewing activity, and milk production of cows in early lactation. Sixteen multiparous cows averaging 17 +/- 3 d in milk and 677 +/- 58 kg BW were assigned to one of four 4 x 4 Latin squares. One square contained ruminally cannulated cows to evaluate effects of treatment on rumen fermentation and function. During each of the 23-d periods, cows were offered one of four total mixed rations that differed in particle length (long or short corn silage) and CSH inclusion rate (0 or 8% DM). Dietary treatments were: long no CSH (LGNH), long with CSH (LGH), short no CSH (SHNH), and short with CSH (SHH). Total physically effective NDF content, measured as percentage of NDF greater than 1.18 mm, was similar across diets, but mean particle length decreased with reducing FPL and inclusion of CSH. Dry matter intake was not significantly affected by FPL but was significantly increased with the inclusion of CSH. Decreasing FPL and the inclusion of CSH significantly increased neutral detergent fiber intake. Total chewing activity expressed as minutes per day was unaffected by FPL and the inclusion of CSH. Both eating and ruminating efficiency expressed as minutes per kilogram of neutral detergent fiber intake increased with increasing FPL and decreased with the inclusion of CSH. Milk production did not differ across treatments, but the inclusion of CSH significantly increased percent and yield of milk protein. Reducing FPL tended to reduce percentage milk fat but not yield. Mean ruminal pH was not affected by FPL but was highest on diets containing CSH, even though no treatment effects were observed on total VFA, acetate, or propionate concentration. These resuits indicate that corn silage FPL is a poor predictor of total chewing time and rumen pH but is useful in understanding factors affecting feeding behavior. In addition, the inclusion of CSH, resulted in increased rumination and mean rumen pH even though effects on VFA concentration were not observed.     

Pelleted beet pulp substituted for high-moisture corn: 1. Effects on feed intake, chewing behavior, and milk production of lactating dairy cows

The effects of increasing concentrations of dried, pelleted beet pulp substituted for high-moisture corn on intake, milk production, and chewing behavior were evaluated using eight ruminally and duodenally cannulated multiparous Holstein cows in a duplicated 4 x 4 Latin square design with 21-d periods. Cows were 79 +/- 17 (mean +/- SD) d in milk at the beginning of the experiment. Experimental diets with 40% forage (corn silage and alfalfa silage) and 60% concentrate contained 0, 6.1, 12.1, or 24.3% beet pulp substituted for high-moisture corn on a dry matter basis. Diet concentrations of neutral detergent fiber (NDF) and starch were 24.3 and 34.6% (0% beet pulp), 26.2 and 30.5% (6% beet pulp), 28.0 and 26.5% (12% beet pulp), and 31.6 and 18.4% (24% beet pulp), respectively. Increasing beet pulp in the diet caused a linear decrease in dry matter intake (DMI). Time spent eating per day and per kilogram of DMI increased, and sorting against NDF tended to increase, with added beet pulp. Substituting beet pulp for corn caused a quadratic response in milk fat yield, with the highest yield for the 6% beet pulp treatment. A tendency was detected for a similar quadratic response in 3.5% fat-corrected milk yield. Lower plasma insulin concentration may have resulted in lower body condition gain for cows fed diets with higher beet pulp concentration. Partial substitution of pelleted beet pulp for high-moisture corn decreased intake but also may have permitted greater fat-corrected milk yield.     

Effect of the amount of concentrate offered in an automated milking system on dry matter intake,milk yield,milk composition,ruminal digestion,and behavior of primiparous Holstein cows fed isocaloric diets

The objective of this study was to determine if the quantity of concentrate provided in an automated milking system (AMS) affects dry matter intake (DMI), attendance to the AMS, milk and milk component yield, feeding behavior, cow activity, and ruminal fermentation of lactating dairy cows fed isocaloric diets. Eight ruminally cannulated primiparous Holstein cows were used in a replicated 4 × 4 Latin square design with 28-d periods. Cows were housed in a freestall facility with a guided-traffic (feed-first) flow barn design. Treatments included 0.5, 2.0, 3.5, or 5.0 kg/d of dry matter of pellet in the AMS with an equivalent reduction of the same pellet in the partial mixed ration (PMR). Days 21 to 24 of each treatment period were used for DMI, milking performance (visits, yield, and composition), behavior, and ruminal pH determination, and d 25 to 28 were used for ruminal short-chain fatty acid and ammonia concentrations as well as total-tract digestibility. As imposed, consumption of AMS pellet linearly increased, equating to 0.50, 2.00, 3.49, and 4.93 kg of dry matter/d for the 0.5, 2.0, 3.5, and 5.0 kg/d treatments, respectively. Correspondingly, the standard deviation in AMS pellet intake among days linearly increased from 0.06 to 0.85 kg of dry matter/d as the quantity of concentrate in the AMS increased from 0.5 to 5.0 kg. The PMR DMI decreased linearly with increasing AMS concentrate allocation, but total DMI (PMR + AMS) was not affected (25.3 kg/d). As the AMS concentrate allocation increased, the selection against particles retained on an 18-mm sieve linearly increased and selection against particles retained on the pan decreased. Milking frequency (3.22 milkings/d), milk yield (37.5 kg/d), milk fat yield (1.43 kg/d), and milk protein yield (1.22 kg/d) were not affected; however, milk urea nitrogen concentration decreased linearly with increasing AMS concentrate. Ruminal pH averaged 6.18 and was not affected by AMS concentrate. Total ruminal short-chain fatty acid concentration was greatest when 3.5 kg of concentrate was allocated in the AMS and ruminal ammonia decreased linearly with increasing AMS concentrate. Time spent lying, the number of lying bouts, and average bout duration were not affected by treatment. These data indicate that increasing the quantity of concentrate in the AMS increases daily variability in AMS concentrate intake while decreasing PMR intake without affecting voluntary visits to the AMS and milk or milk component yield. As such, under isocaloric dietary settings, increasing the supply of pellet in the AMS is not likely to affect voluntary visits to the AMS, milk and milk component yields, or ruminal fermentation.     

Nutrient demand interacts with legume maturity to affect rumen pool sizes in dairy cows

Effects of legume maturity on dry matter intake (DMI), milk production, ruminal fermentation and pool sizes, and digestion and passage kinetics, and the relationship of these effects with preliminary DMI (pDMI) were evaluated using 16 ruminally and duodenally cannulated Holstein cows in a crossover design with a 14-d preliminary period and two 17-d treatment periods. During the preliminary period, the pDMI of individual cows ranged from 22.9 to 30.0 kg/d (mean=25.9 kg/d) and the 3.5% fat-corrected milk yield ranged from 34.1 to 68.2 kg/d (mean=43.7 kg/d). Experimental treatments were diets containing alfalfa silage harvested either a) early-cut, less mature (EC) or b) late-cut, more mature (LC) as the sole forage. Early- and late-cut alfalfa contained 40.8 and 53.1% neutral detergent fiber (NDF) and 23.7 and 18.1% crude protein, respectively. Forage:concentrate ratios were 53:47 and 42:58 for EC and LC, respectively; both diets contained approximately 22% forage NDF and 27% total NDF. Preliminary DMI, an index of nutrient demand, was determined during the last 4d of the preliminary period when cows were fed a common diet and used as a covariate. Main effects of alfalfa maturity and their interaction with pDMI were tested by ANOVA. Alfalfa maturity and its interaction with pDMI did not affect milk yield but EC increased DMI compared with LC; thus, EC had lower efficiency of milk production than LC. The EC diet decreased milk fat concentration more per kilogram of pDMI increase than the LC diet, but milk fat yield was not affected. The lower concentration and faster passage rate of indigestible NDF for EC resulted in lower rumen pools of indigestible NDF, total NDF, and dry matter than did LC, which EC increased at a slower rate than did LC as pDMI increased. The EC diet decreased starch intake and increased ruminal pH compared with the LC diet. The rate of ruminal starch digestion was related to level of intake, but this did not affect ruminal or postruminal starch digestion. Total-tract digestibility of NDF, organic matter, and dry matter was higher for EC than LC. Microbial efficiency tended to be related to pDMI and the response differed by treatment. When alfalfa silage was the only source of forage in the diet, cows supplemented with additional concentrate to account for decreased protein and increased fiber concentrations associated with LC produced similar fat-corrected milk yields with greater efficiency than cows fed EC.