Effects of fescue type and sampling date on the ruminal disappearance kinetics of autumn-stockpiled tall fescue

Two tall fescue (Festuca arundinacea Schreb.) forages, one an experimental host plant/endophyte association containing a novel endophyte (HM4) that produces low or nil concentrations of ergot alkaloids, and the other a typical association of Kentucky 31 tall fescue and the wild-type endophyte (Neotyphodium coenophialum; E+), were autumn-stockpiled following late-summer clipping and fertilization with 56 kg/ha of N to assess the nutritive value and ruminal disappearance kinetics of autumn-stockpiled tall fescue forages. Beginning on December 4, 2003, sixteen 361 ± 56.4-kg replacement dairy heifers were stratified by weight and breeding and assigned to one of four 1.6-ha pastures (2 each of E+ and HM4) that were strip-grazed throughout the winter. Pastures were sampled before grazing was initiated (December 4), each time heifers were allowed access to a fresh strip (December 26, January 15, and February 4), and when the study was terminated (February 26). For fiber components, there were no interactions between fescue type and sampling date for either pregrazed or postgrazed forages. Over sampling dates, neutral detergent fiber (NDF; 56.5 to 67.8%), acid detergent fiber (27.7 to 34.9%), hemicellulose (28.8 to 34.0%), cellulose (25.0 to 28.1%), and lignin (3.61 to 10.05%) varied with sampling date, but patterns were almost exclusively curvilinear with time. Ruminal disappearance rate of dry matter (DM) was not affected by any treatment factor (overall mean for both pregrazed and postgrazed forages = 0.050 h⁻¹); similar responses were observed for NDF disappearance (overall mean = 0.048 h⁻¹). Interactions of fescue type and sampling date were observed for both pregrazed and postgrazed forages with respect to effective ruminal disappearance of DM; however, estimates were relatively high for all forages (overall mean = 64.0%). Effective disappearance of NDF was relatively extensive for all forages (overall mean = 55.4% of NDF). Based on the results of this trial, the endophyte status of stockpiled tall fescue forages had little practical effect on forage nutritive value and kinetics of ruminal DM or NDF disappearance. Overall, autumn-stockpiled tall fescue forages would appear to be a legitimate and lower cost alternative to harvested forages, and appear to possess suitable nutritional characteristics for developing dairy heifers in the Ozark Highlands.     

The effect of formulation and amount of potassium fertilizer on macromineral concentration and cation-anion difference in tall fescue

This study investigated the feasibility of altering the dietary cation-anion difference (DCAD) in grass by altering the grass variety and the amount and formulation of K fertilizer application. In experiment 1, treatments were combinations of 2 varieties (Barcel and Hi-Mag) of tall fescue (Festuca arundinacea Schreb); 2 rates of K (0 and 250 kg/ha), supplied as KCl; and 2 rates of Mg (0 and 60 kg/ha), supplied as MgO. In experiment 2, K fertilizer was applied at 0 or 125 kg/ha as KCl or K₂SO₄. There was no difference between HiMag and Barcel tall fescue in the concentrations of Mg, S, and Cl. Application of K fertilizer decreased concentrations of Mg, but the magnitude of the decrease was not consistent across harvests. Conversely, application of Mg fertilizer increased Mg concentrations, but again, the magnitude of the increase was not consistent across harvests. The concentrations of Ca were higher in HiMag than in Barcel tall fescue, with the magnitude of the difference increasing from first to last harvest. Potassium fertilizer decreased Ca concentrations in the first, fourth, and fifth harvests only. Calcium concentration was decreased by a greater magnitude in HiMag tall fescue as a result of Mg fertilization. The HiMag tall fescue contained lower concentrations of K than did Barcel tall fescue in the first, second, and third harvests. Application of K fertilizer increased the K concentration in all 5 harvests but did not affect Na concentrations except in the last harvest. The HiMag tall fescue contained less Na than did Barcel, but the magnitude of the difference was affected by K and Mg fertilization. Application of K fertilizer decreased S concentrations in first-harvest grass, increased concentrations in second-and third-harvest grasses, and had no effect in fourth-or fifth-harvest grasses. Application of Mg fertilizer decreased S concentrations of tall fescue. Application of K fertilizer increased DCAD values for grass harvested from the second through fifth harvests. The increase in DCAD attributable to K fertilizer was less in HiMag than in Barcel tall fescue. Application of K fertilizer as K₂SO₄ increased dry matter yield and S concentrations of HiMag tall fescue, whereas K applied as KCl increased concentrations of K and Cl. There was no effect of fertilizer formulation on Na concentrations. The DCAD was lower in HiMag tall fescue fertilized with K₂SO₄ compared with that fertilized with KCl. This study showed that DCAD of grass can be manipulated by the choice of grass variety, fertilizer formulation, and fertilizer application rate.     

Performance of lactating dairy cows fed tall fescue forage

Two trials were conducted during consecutive summers to compare performance of lactating cows fed four varieties of tall fescue soilage. The first trial was conducted in 1983 and the second in 1984 using 25 midlactation Holsteins. Treatments included endophyte-free Kenhy; 8.1% endophyte-infected Johnstone (a prevarietal release); endophyte-free Kentucky 31; 63% endophyte-infected Kentucky 31; and orchardgrass or alfalfa as controls. In 1983, concentrate was fed twice each day at the rate of 4.1 kg per feeding, and in 1984, 4.5 kg were fed twice daily for first 4 wk and 4.1 kg per feeding thereafter. Intake of Kenhy was higher than all other tall fescue treatments when data for both trials were combined. Means of the high endophyte Kentucky 31 group were lower than all other treatments during both trials for milk yield, dry matter intake, body weight change, and serum prolactin in 1984 while higher for rectal temperature. Improved intake and performance of the cows consuming Kenhy compared with those consuming endophyte-free Kentucky 31 indicated the improved forage quality of this variety. Decreased performance of dairy cows consuming endophyte-infected tall fescue, even at a relatively low infection, was evident.     

Comparisons of in situ dry matter disappearance kinetics of wheat forages harvested by various techniques and evaluated in confined and grazing steers

Ruminal in situ disappearance kinetics of forages are commonly evaluated in confined animals, but there have been relatively few attempts to evaluate disappearance kinetics of forage dry matter (DM) in grazing animals. Our objectives were 1) to evaluate the effects of harvest technique and sampling date on the in situ DM disappearance kinetics and nutritive value of wheat (Triticum aestiuum L.) forage, and 2) to compare the in situ disappearance kinetics of DM for these forages when the experimental steers were housed in confinement with those obtained from steers grazing wheat pasture. Wheat forage was harvested on three dates (March 6, March 27, and April 11, 2000). Sampling techniques evaluated on each date included three clipping techniques (whole plant, random pluck, and top half) and two evaluations of masticates (oven dried at 50 degrees C or lyophilized). There was an interaction of harvest technique and sampling date main effects for crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose, cellulose, lignin, and whole-plant ash. Disappearance kinetics of DM for these 15 forages were then evaluated by the in situ technique using five 393 +/- 54-kg crossbred steers consuming an alfalfa-based (Medicago sativa L.) diet in confinement, and subsequently, in five 448 +/- 49-kg crossbred steers grazing wheat pasture during March 2001. For fractions A, B, and C, potential extent, rate of disappearance (Kd), and effective ruminal degradability, linear regressions of values obtained for steers grazing wheat pasture on those obtained from confined cattle had significant slopes and exhibited high r2 statistics (>0.821). For fractions A and B, and Kd, the slope of these regression lines did not differ from unity, and the intercept did not differ from zero. For fraction C, potential extent of disappearance, and effective ruminal degradability, slopes were all equal to 1.19 and differed from unity. For effective degradability, deviation of the slope from unity can be explained, in part, on the basis of the passage rates used to calculate these values (0.035 and 0.062/h for confined and grazing steers, respectively). From a practical standpoint, the in situ disappearance kinetics of DM for these wheat forages did not appear to be altered substantially by evaluating them in grazing steers.     

Lactation performance of holstein cows fed fescue, orchardgrass, or alfalfa silage

Perennial grasses are increasingly being used as an integral part of nutrient management plans, but fescue (Festuca arundinacea Schreb.) is often overlooked because of perceived intake problems. A 30-d study was conducted to evaluate the lactation performance of cows fed a fescue silage-based total mixed ration (TMR) compared with orchardgrass (Dactylis glomerata L.) and alfalfa (Medicago sativa L.) silage-based TMR, when forages are harvested at recommended neutral detergent fiber (NDF) levels. Holstein cows (body weight [BW] = 627 +/- 66.0 kg, milk yield = 40.9 +/- 6.93 kg/d, parity = 2.6 +/- 1.44, days in milk = 152 +/- 24.5) were randomly assigned to treatment. Statistical design was a randomized complete block with 10 cows per treatment. The 5 treatments consisted of TMR using first-cutting alfalfa, and first- and second-cutting orchardgrass and tall fescue silage. Diets were formulated to provide 0.95% of BW as forage NDF and contained approximately 18% CP and 1.6 mcal/kg. This resulted in diets of about 30% NDF; for a 612-kg cow, approximately 5.8 kg/d of forage NDF was fed. Second-cutting, grass-based TMR had lower intake than alfalfa and first-cutting forage TMR. Cows consuming second-cutting orchardgrass had lower milk production than did cows consuming other forage TMR. Cows fed fescue TMR had higher milk production than those fed orchardgrass. Indigestible residues were higher, and NDF digestibilities were lower, in second-cutting forages vs. first-cutting forages, likely contributing to the differences observed in intake and resulting differences in milk production. Dairy cows consumed the first-cutting fescue TMR readily and performed as well as those on alfalfa or first-cutting, orchardgrass-based TMR in terms of lactation performance, but fescue and orchardgrass rations will require more concentrate in the ration than alfalfa.     

Effects of ruminal ammonia and butyrate concentrations on reticuloruminal epithelial blood flow and volatile fatty acid absorption kinetics under washed reticulorumen conditions in lactating dairy cows

The effect of reticuloruminal epithelial blood flow on the absorption of propionate as a volatile fatty acid (VFA) marker in 8 lactating Holstein cows was studied under washed rumen conditions. The cows were surgically prepared with ruminal cannulas and permanent catheters in an artery and mesenteric, right ruminal, and hepatic portal veins. The experiment was designed with 2 groups of cows: 4 cows adapted to high crude protein (CP) and 4 to low CP. All cows were subjected to 3 buffers: butyric, ammonia, and control in a randomized replicated 3 × 3 incomplete Latin square design. The buffers (30 kg) were maintained in a temporarily emptied and washed rumen for 40 min. The initial concentration of VFA was 84.2 mmol/L. Butyrate was increased from 4 to 36 mmol/L in butyric buffer by replacement of acetate, and ammonia (NH₃) was increased from 2.5 to 22.5 mmol/L in ammonia buffer by replacement of NaCl. Increasing amounts of deuterium oxide (D₂O) were added to the buffers as the order of buffer sequence increased (6, 12, and 18 g of D₂O). Ruminal clearance of D₂O was used to estimate epithelial blood flow. To increase accuracy of the epithelial blood flow estimates, data of ruminal liquid marker (Cr-EDTA), and initial and final buffer volumes were fitted to a dynamic simulation model. The model was used to estimate ruminal liquid passages, residual liquid, and water influx (saliva and epithelia water) for each combination of cow and buffer (n = 24). Epithelial blood flow increased 49 ± 11% for butyric buffer compared with control. The ruminal disappearance of propionate (marker VFA) was affected by buffer and followed the same pattern as for epithelial blood flow. The correlation between ruminal disappearance of propionate and epithelial blood flow (r = 0.56) indicates that the removal of propionate can be limited by epithelial blood flow. The ruminal disappearance of propionate increased 30 ± 12% for the butyric compared with ammonia buffer and 12.5 ± 8% when compared with control. The net portal flux of propionate increased 32 ± 6% in butyric compared with control. In conclusion, rumen epithelial blood flow is positively correlated with ruminal disappearance of propionate and affects the kinetics of ruminal VFA absorption.     

Unique interrelationships between fiber composition,water-soluble carbohydrates,and in vitro gas production for fall-grown oat forages

Sixty samples of ‘ForagePlus’ oat were selected from a previous plot study for analysis of in vitro gas production (IVGP) on the basis of 2 factors: (1) high (n = 29) or low (n = 31) neutral detergent fiber (NDF; 62.7 ± 2.61 and 45.1 ± 3.91%, respectively); and (2) the range of water-soluble carbohydrates (WSC) within the high- and low-NDF groups. For the WSC selection factor, concentrations ranged from 4.7 to 13.4% (mean = 7.9 ± 2.06%) and from 3.5 to 19.4% (mean = 9.7 ± 4.57%) within high- and low-NDF forages, respectively. Our objectives were to assess the relationships between IVGP and various agronomic or nutritional characteristics for high- and low-NDF fall-oat forages. Cumulative IVGP was fitted to a single-pool nonlinear regression model: Y = MAX × (1 – e ^{[–K× (t – lag)]}), where Y = cumulative gas produced (mL), MAX = maximum cumulative gas produced with infinite incubation time (mL), K = rate constant, t = incubation time (h), and lag = discrete lag time (h). Generally, cumulative IVGP after 12, 24, 36, or 48 h within high-NDF fall-oat forages was negatively correlated with NDF, hemicellulose, lignin, and ash, but positively correlated with WSC, nonfiber carbohydrate (NFC), and total digestible nutrients (TDN). For low-NDF fall-grown oat forages, IVGP was positively correlated with growth stage, canopy height, WSC, NFC, and TDN; negative correlations were observed with ash and crude protein (CP) but not generally with fiber components. These responses were also reflected in multiple regression analysis for high- and low-NDF forages. After 12, 24, or 36 h of incubation, cumulative IVGP within high-NDF fall-oat forages was explained by complex regression equations utilizing (lignin:NDF)², lignin:NDF, hemicellulose, lignin, and TDN² as independent variables (R² ≥ 0.43). Within low-NDF fall-grown oat forages, cumulative IVGP at these incubation intervals was explained by positive linear relationships with NFC that also exhibited high coefficients of determination (R² ≥ 0.75). Gas production was accelerated at early incubation times within low-NDF forages, specifically in response to large pools of WSC that were most likely to be present as forages approached boot stage by late-fall.     

Effects of physically effective fiber on digestive processes and milk fat content in early lactating dairy cows fed total mixed rations

Data from recent research studies were analyzed quantitatively, and the random effect of experiment was assessed to define the physiological responses of dairy cows in early lactation to intake of physically effective neutral detergent fiber (peNDF). All studies were conducted with lactating Holstein cows (84.8 ± 3.54 days in milk) in Latin square designs, and feeds were offered ad libitum as total mixed rations (TMR). The peNDF was estimated by 2 measurement techniques, the NDF content of TMR multiplied by amount of dry matter (DM) retained on a 1.18-mm screen (peNDF_{> 1.18}) and NDF content of TMR multiplied by the proportion of DM retained by 19- and 8-mm Penn State Particle Separator screens (peNDF_{> 8}). Other factors, including concentrations of NDF, forage NDF, non-fiber carbohydrates, the amount of digestible organic matter of forages (FDOM), and the intake of ruminally degradable starch (RDSI) from grain in the diet were also investigated. The studied animal response variables included feed intake, ruminal fermentation, chewing activity, fiber digestibility, and milk production and composition. The ruminal pH (day mean) in this study ranged from 5.30 to 6.59. Using peNDF_{> 1.18} approach, the requirements for physically effective fiber in high-yielding dairy cows fed TMR in an ad libitum intake were estimated to be about 19% of ration DM or 4.1 kg/d or 0.6 kg/100 kg of body weight to maintain a ruminal pH of about 6.0. When peNDF was measured as peNDF_{> 8}, ruminal pH responded in a quadratic fashion but the confidence of estimation was lower (R² = 0.27) compared with the peNDF_{> 1.18} approach (R² = 0.67). Results of these data analyses showed that peNDF_{> 1.18} provided a satisfactory estimation of the mean ruminal pH (R² = 0.67) and NDF digestibility (R² = 0.56). Furthermore, peNDF_{> 1.18} was poorly, although positively, correlated to daily chewing (R² = 0.17), and rumination (R² = 0.24) activity. On the other hand, results from these analyses showed that milk parameters are less sensitive to the effects of dietary peNDF than other variables, such as ruminal pH, chewing activity, and fiber digestibility. Dietary FDOM correlated positively (moderately) to ruminal pH (R² = 0.24), daily chewing (R² = 0.23), and rumination (R² = 0.29) activity, whereas the daily RDSI from grain correlated negatively to ruminal pH (R² = 0.55) and positively to total volatile fatty acids (R² = 0.27). Inclusion of FDOM and RDSI from grain along with peNDF_{> 1.18} in the models that predict rumen pH further improved the accuracy of prediction. This approach appeared to further complement the concept of peNDF that does not account for differences in ruminal fermentability of feeds.     

Hot topic: Enhancing omega-3 fatty acids in milk fat of dairy cows by using stearidonic acid-enriched soybean oil from genetically modified soybeans

Very long chain n-3 fatty acids such as eicosapentaenoic acid (EPA; 20:5n-3) are important in human cardiac health and the prevention of chronic diseases, but food sources are limited. Stearidonic acid (SDA; 18:4n-3) is an n-3 fatty acid that humans are able to convert to EPA. In utilizing SDA-enhanced soybean oil (SBO) derived from genetically modified soybeans, our objectives were to examine the potential to increase the n-3 fatty acid content of milk fat and to determine the efficiency of SDA uptake from the digestive tract and transfer to milk fat. Three multiparous, rumen-fistulated Holstein cows were assigned randomly in a 3 × 3 Latin square design to the following treatments: 1) control (no oil infusion); 2) abomasal infusion of SDA-enhanced SBO (SDA-abo); and 3) ruminal infusion of SDA-enhanced SBO (SDA-rum). The SDA-enhanced SBO contained 27.1% SDA, 10.4% α-linolenic acid, and 7.2% γ-linolenic acid. Oil infusions provided 57 g/d of SDA with equal amounts of oil infused into either the rumen or abomasum at 6-h intervals over a 7-d infusion period. Cow numbers were limited and no treatment differences were detected for DMI or milk production (22.9 ± 0.5 kg/d and 32.3 ± 0.9 kg/d, respectively; least squares means ± SE), milk protein percentage and yield (3.24 ± 0.04% and 1.03 ± 0.02 kg/d), or lactose percentage and yield (4.88 ± 0.05% and 1.55 ± 0.05 kg/d). Treatment also had no effect on milk fat yield (1.36 ± 0.03 kg/d), but milk fat percentage was lower for the SDA-rum treatment (4.04 ± 0.04% vs. 4.30 ± 0.04% for control and 4.41 ± 0.05% for SDA-abo). The SDA-abo treatment increased n-3 fatty acids to 3.9% of total milk fatty acids, a value more than 5-fold greater than that for the control. Expressed as a percentage of total milk fatty acids, values (least squares means ± SE) for the SDA-abo treatment were 1.55 ± 0.03% for α-linolenic acid (18:3n-3), 1.86 ± 0.02 for SDA, 0.23 ± <0.01 for eicosatetraenoic acid (20:4n-3), and 0.18 ± 0.01 for EPA. Transfer efficiency of SDA to milk fat represented 39.3% (range = 36.8 to 41.9%) of the abomasally infused SDA and 47.3% (range = 45.0 to 49.6%) when the n-3 fatty acids downstream from SDA were included. In contrast, transfer of ruminally infused SDA to milk fat averaged only 1.7% (range = 1.3 to 2.1%), indicating extensive rumen biohydrogenation. Overall, results demonstrate the potential to use SDA-enhanced SBO from genetically modified soybeans combined with proper ruminal protection to achieve impressive increases in the milk fat content of SDA and other n-3 fatty acids that are beneficial for human health.     

Effects of harvest date and grass species on silage cell wall components and lactation performance of dairy cows

This study evaluated the effect of harvest date and forage species on the concentration of hydroxycinnamic acids in silage and its relationship to dairy cow performance. Tall fescue and timothy were harvested at a regular date on June 27 and July 8, respectively, or at a late date on July 8 and 25, respectively, in the first regrowth. Forage was treated with a salt-based additive and ensiled in hard-pressed round bales. Forty-seven lactating dairy cows were used in a block design. Cows received 1 of 4 treatments: (1) tall fescue harvested at regular date (RTF), (2) timothy harvested at regular date (RTI), (3) tall fescue harvested at late date (LTF), and (4) timothy harvested at late date (LTI). Diets were formulated to have the same forage-to-concentrate ratio (46:54 on a dry matter basis). Harvesting at late date increased fiber components, but only for timothy, where LTI contained greater neutral detergent fiber, acid detergent fiber, and acid detergent lignin concentrations than the other silages. Concentrations of hydroxycinnamic acids were affected by forage species, where concentrations of esterified ferulic acid and p-coumaric acid were greater for tall fescue silages than for timothy silages. Cows fed the RTI diet showed the greatest intakes of dry matter, organic matter, and crude protein. Feeding diets containing timothy silages increased milk yield and energy-corrected milk yield compared with tall fescue diets when averaged over harvest dates. Cows fed the RTI diet had greater milk protein yield than cows fed the RTF and LTF diets, and milk lactose yield was greater for cows fed diets containing timothy silage compared with tall fescue silage when averaged over harvest dates. Cows fed the LTF diet showed greater urinary N excretion compared with the LTI diet, but RTI showed the lowest urinary N and urea N excretions when calculated as percent of N intake. Cows fed diets containing timothy silage excreted more uric acid than cows fed tall fescue diets. Allantoin excretion was greater for cows eating the RTI and LTI diets compared with cows eating the RTF diet. Cows fed the RTI diet had a greater estimated microbial N flow and a greater excretion of hippuric acid than the RTF and LTF groups. In conclusion, besides the effect of harvest date on increasing the fiber components of timothy, concentrations of hydroxycinnamic acids were mainly affected by forage species; consequently, milk production was only affected by forage species. This indicates that hydroxycinnamic acids, such as ferulic acid, which cross-links to glucuronoarabinoxylans, was a major factor regulating milk production of cows fed tall fescue- and timothy silage-based diets, where lower hydroxycinnamic acid concentrations were responsible for greater milk yield.     

Effects of feeding wheat or corn-wheat dried distillers grains with solubles in low- or high-crude protein diets on ruminal function,omasal nutrient flows,urea-N recycling,and performance in cows

A study was conducted to determine the effects of including either wheat-based (W-DDGS) or corn-wheat blend (B-DDGS) dried distillers grains with solubles as the major protein source in low- or high-crude protein (CP) diets fed to dairy cows on ruminal function, microbial protein synthesis, omasal nutrient flows, urea-N recycling, and milk production. Eight lactating Holstein cows (768.5 ± 57.7 kg of body weight; 109.5 ± 40.0 d in milk) were used in a replicated 4 × 4 Latin square design with 28-d periods (18 d of dietary adaptation and 10 d of measurements) and a 2 × 2 factorial arrangement of dietary treatments. Four cows in one Latin square were ruminally cannulated for the measurement of ruminal fermentation characteristics, microbial protein synthesis, urea-N recycling kinetics, and omasal nutrient flow. The treatment factors were type of distillers co-product (W-DDGS vs. B-DDGS) and dietary CP content [15.2 vs. 17.3%; dry matter (DM) basis]. The B-DDGS was produced from a mixture of 15% wheat and 85% corn grain. All diets were formulated to contain 10% W-DDGS or B-DDGS on a DM basis. No diet effect was observed on DM intake. Yields of milk, fat, protein, and lactose, and plasma urea-N and milk urea-N concentrations were lower in cows fed the low-CP compared with those fed the high-CP diet. Although feeding B-DDGS tended to reduce ruminal ammonia-N (NH₃-N) concentration compared with feeding W-DDGS (9.3 vs. 10.5 mg/dL), no differences were observed in plasma urea-N and milk urea-N concentrations. Additionally, dietary inclusion of B-DDGS compared with W-DDGS did not affect rumen-degradable protein supply, omasal flows of total N, microbial nonammonia N (NAN), rumen-undegradable protein, and total NAN, or urea-N recycling kinetics and milk production. However, cows fed the low-CP diet had lower N intake, rumen-degradable protein supply, ruminal NH₃-N concentration, and omasal flows of N, microbial NAN, and total NAN compared with those fed the high-CP diet. Feeding the low-CP compared with the high-CP diet also resulted in lower endogenous urea-N production, urea-N recycled to the gastrointestinal tract, and urea-N excretion in urine. In summary, our results indicate that both W-DDGS and B-DDGS can be included as the major protein sources in dairy cow diets without compromising nutrient supply and production performance. However, feeding the low-CP diet lowered omasal flows of microbial protein and metabolizable protein, which, in turn, resulted in lower milk production compared with feeding the high-CP diet.     

Severity of ruminal acidosis in primiparous holstein cows during the periparturient period

The objectives of this study were: 1) to determine the effect of providing additional prepartum concentrate on the occurrence and severity of ruminal acidosis (RA) and lactational performance during the periparturient period in primiparous cows; and 2) to characterize the occurrence and severity of RA during the periparturient period. We hypothesized that providing additional concentrate prepartum would reduce postpartum RA. Fourteen ruminally cannulated Holstein heifers were paired by expected calving date and body condition score. The heifers were assigned to 1 of 2 prepartum feeding regimens: 1) a control treatment consisting of a far-off diet (forage:concentrate, F:C = 80:20) fed from d −60 to d −25 and a close-up diet (F:C = 54:46) fed from d −24 until parturition; or 2) a high-concentrate (HC) feeding program consisting of 4 prepartum diets, HC-1 (F:C = 68:32) fed from d −60 to d −43, HC-2 (F:C = 60:40) fed from d −42 to d −25, HC-3 (F:C = 52:48) fed from d −24 to d −13, and HC-4 (F:C = 46:54) fed from d −12 until parturition. All cows received the same lactation diet postpartum. Ruminal pH was measured continuously from d −5 to d +5, and for 3 consecutive days starting on d +17 ± 1.2, d +37 ± 1.4, and d +58 ± 1.5 relative to parturition using an indwelling ruminal pH system. Ruminal acidosis was considered to occur when ruminal pH was <5.8 (total RA). Ruminal acidosis was further partitioned into: 1) mild RA (5.8 > ruminal pH > 5.5), 2) moderate RA (5.5 > ruminal pH > 5.2), and 3) acute RA (ruminal pH < 5.2). Feeding additional concentrate prepartum did not reduce postpartum RA. In fact, cows fed the HC treatment had more daily episodes of acute RA than cows fed the control treatment. Day relative to parturition affected the occurrence and severity of RA; RA increased following parturition and was sustained thereafter. The DM intake during the last 5 d of gestation was lower for cows fed the HC treatment compared with cows fed the control treatment, but lactational performance was not affected. We conclude that, under the conditions imposed, feeding additional concentrate prepartum does not reduce postpartum RA. Furthermore, the incidence and severity of RA increases immediately postpartum, emphasizing the need to develop and implement feeding strategies that reduce this risk.     

Effect of pregrazing herbage mass and pasture allowance on the lactation performance of Holstein-Friesian dairy cows

The objective of this study was to investigate the effect of pregrazing herbage mass (HM) and pasture allowance (PA) on the grazing management and lactation performance of spring-calving dairy cows. Sixty-eight Holstein-Friesian dairy cows (mean calving date, February 6) were randomly assigned across 4 treatments (n = 17) in a 2 × 2 factorial arrangement. The 4 treatments consisted of 2 pregrazing HM (>4 cm) and 2 PA (>4 cm): 1,700 kg of dry matter (DM)/ha (medium, M) or 2,200 kg of DM/ha (high, H), and 16 or 20 kg of pasture DM/cow per day. The experimental period lasted 30 wk. The experimental area was divided into 4 farmlets, with 1 farmlet per treatment. Mean HM throughout the experimental period was 1,767 kg of DM/ha (M HM) compared with 2,358 kg of DM/ha (H HM). Offering an M HM sward resulted in significantly greater milk protein yield (+31.7 g/d) and lower mean body weight (−12.8 kg). The body condition score change was significantly smaller (−0.21) with the M HM treatments compared with the H HM treatment (−0.34). Milk solids output per hectare was 6% greater on the M HM treatments compared with the H HM treatments. Increasing PA significantly increased milk (+0.9 kg/d), solids-corrected milk (+0.7 kg/d), protein (+43.9 g/d), and lactose (+52.7 g/d) yields. Mean body weight was also significantly greater for cows offered 20 kg of PA (+11.4 kg/cow). It was concluded that in rotational grazing systems, adapting the concept of grazing M HM pastures (1,700 kg of DM/ha) will result in increased sward quality and increased milk solids output per hectare. At medium levels of pregrazing HM, offering animals 20 kg of DM PA will result in increased milk yield per cow.     

Intake and performance of lactating cows grazing diverse forage mixtures

Twenty multiparous Holstein cows in midlactation grazed pastures of 4 forage mixtures in a 12-wk study repeated during 2 grazing seasons to determine if forage mixture complexity affected intake and productivity of lactating dairy cows. The forage mixtures were 1) orchardgrass plus white clover [2 species (SP)]; 2) orchardgrass, white clover, and chicory (3SP); 3) orchardgrass, tall fescue, perennial ryegrass, red clover, birdsfoot trefoil, and chicory (6SP); and 4) 6SP mixture plus white clover, alfalfa, and Kentucky bluegrass (9SP). Total herbage intake was similar among forage mixtures, averaging 12.0 kg/d across all forage mixtures and years. Milk production and composition were not affected by forage mixture or year, and averaged 34.6 kg/d, 3.4%, and 2.8% for milk production, milk fat percentage, and milk protein percentage, respectively. The conjugated linoleic acid content of milk fat was higher for cows that grazed the 3SP, 6SP, and 9SP mixtures than from cows that grazed the 2SP mixture (1.02 vs. 0.87 g of conjugated linoleic acid/100 g of fatty acids, respectively). Blood glucose, blood urea nitrogen, and nonesterified fatty acids were not affected by forage mixture and averaged 69.2 mg/dL, 13.4 mg/dL, and 277.5 μEq/L, respectively. The results of this study indicate that altering the forage mixture in pastures did not affect dry matter intake, milk production, or blood metabolite profiles of lactating cows. The use of complex mixtures of forages in grazing systems should not affect dairy cow performance.     

Forage intake, ruminal dry matter disappearance, and ruminal blood volatile fatty acids for steers in 18 and 32 degrees C temperatures

Six steers with rumen cannulas and exteriorized carotid arteries were fed chopped alfalfa, orchardgrass, or tall fescue hay in ambient temperatures (18 and 32 degrees C) using a factorial arrangement of forage and temperature with repeated measurements. Arterial blood, venous blood, and rumen fluid were sampled for VFA at 0, 2, 4, and 7 h after forage was offered. Rate of digestion of plant cell wall was determined by in vitro methods. Rate of ingesta and particulate passage was determined by 144Ce marker. Volatile fatty acid concentrations in blood plasma and rumen fluid were not related to forage voluntary intake. Voluntary forage intake was related to calculated ruminal disappearance of cell wall (r2 of .94). Elevated ambient temperature, 32 degrees C, depressed voluntary forage intake but did not increase ruminal or blood VFA concentrations.     

Quantifying ruminal digestion of organic matter and neutral detergent fiber using the omasal sampling technique in cattle—A meta-analysis

A data set from 32 studies (122 diets) was used to evaluate the accuracy and precision of the omasal sampling technique by investigating the relationships between ruminal and total digestion of neutral detergent fiber (NDF), between intake and apparent and true ruminal digestion of organic matter (OM), and between omasal NAN flow and milk protein yield. A mixed model regression analysis with random study effect was used to evaluate the relationships. The data were obtained when feeding North American diets (n = 36) based on alfalfa silage, corn silage, and corn grain and North European diets (n = 86) comprising grass silage supplemented with barley-based concentrates. In all studies, digesta flow was quantified using a triple-marker approach. Standard deviations of ruminal NDF and true OM digestibility were smaller than typically reported in duodenal sampling studies using only chromic oxide as a flow marker. The relationship between total and ruminal NDF digestion was consistent, indicating little variation in the proportion of total-tract NDF digestion that occurred in the rumen. Furthermore, the slope of this regression indicated that 94.7% (±2.7%) of total NDF digestion occurred in the rumen. The slopes of mixed model regression equations between OM intake and amount digested indicated that 42% (±2.4%) and 74% (±3.1%) of OM was apparently and truly digested in the rumen, respectively. The contribution of the rumen to total-tract apparent OM digestion was 62% (±2.6%). The close relationship between omasal flow of nonammonia crude protein and milk protein yield (with adjusted residual mean squared error = 31 g) provided further confidence in the reliability of omasal flow measurements.     

Corn silage hybrid type and quality of alfalfa hay affect dietary nitrogen utilization by early lactating dairy cows

This experiment was conducted to determine the effects of corn silage (CS) hybrids and quality of alfalfa hay (AH) in high-forage dairy diets on N utilization, ruminal fermentation, and lactational performance by early-lactating dairy cows. Eight multiparous Holstein cows were used in a duplicated 4 × 4 Latin square experiment with a 2 × 2 factorial arrangement of dietary treatments. The 8 cows (average days in milk = 23 ± 11.2) were surgically fitted with ruminal cannula, and the 2 squares were conducted simultaneously. Within square, cows were randomly assigned to a sequence of 4 diets: conventional CS (CCS) or brown midrib CS (BMR) was combined with fair-quality AH [FAH: 46.7% neutral detergent fiber (NDF) and 18.4% crude protein (CP)] or high-quality AH (HAH: 39.2% NDF and 20.7% CP) to form 4 treatments: CCS with FAH, CCS with HAH, BMR with FAH, and BMR with HAH. Diets were isonitrogenous across treatments, averaging 15.9% CP. Each period lasted a total of 21 d, with 14 d for treatment adaptation and 7 d for data collection and sampling. Intake of DM and milk yield did not differ in response to CS hybrids or AH quality. Although feeding BMR-based diets decreased urinary N output by 24%, it did not affect fecal N output. Feeding HAH decreased urinary N output by 15% but increased fecal N output by 20%. Nitrogen efficiency [milk N (g/d)/intake N (g/d)] tended to increase for BMR treatments. Ruminal ammonia-N concentration was lower for cows fed BMR-based diets than for those fed CCS-based diets but was not affected by quality of AH. Feeding BMR-based diets or HAH decreased milk urea N concentration by 23 or 15%, respectively, compared with CCS-based diets or FAH. Total volatile fatty acid concentration increased with HAH but was not influenced by CS hybrids. Feeding BMR-based diets decreased urinary N-to-fecal N ratio (UN:FN), and it was further reduced by feeding HAH. Although cows fed the BMR-based diets tended to increase milk N-to-manure N ratio, the quality of AH did not affect the ratio. The lower ratio of UN:FN with a higher ratio of milk N-to-manure N ratio for the BMR-based diets indicates that feeding BMR may reduce manure ammonia-N by reducing excretion of urinary N and increasing secretion of milk N per unit of manure N excreted.     

Effect of milk allowance on concentrate intake, ruminal environment, and ruminal development in milk-fed Holstein calves

The aim of the present experiment was to test the hypothesis that a barley-based concentrate would induce an acidic ruminal environment in young calves and that increased milk allowance would alleviate this condition. Eight Holstein calves ruminally cannulated at d 7 ± 1 of age were used to study the effect of variation in barley-based starter concentrate intake induced by 4 different milk allowances (3.10, 4.84, 6.60, and 8.34 kg of milk replacer/d; 123 g of dry matter/kg of milk) on the ruminal environment, blood variables, and fore-stomach development from wk 2 to 5 of age. Twelve ruminal fluid samples were collected during a weekly 24-h sampling in 4 consecutive weeks. Blood samples were collected by venipuncture between 1200 and 1300 h on ruminal sampling days. Rumen papillae development and visceral organ mass were recorded at slaughter. A linear treatment × week effect was observed for concentrate intake, with the calves fed the lowest milk allowance having the fastest increase in concentrate intake whereby these calves reached the same ME intake in wk 5 compared with calves with the highest milk allowance. Effects on ruminal variables were dominated by week of sampling, with minor differences among treatments. Ruminal pH was below 5.5 for 5 to 13 h/d and all calves with concentrate intake above 20 g of dry matter/d were observed to have a daily ruminal pH minimum at pH 5.5 or lower. The ruminal concentration of total volatile fatty acids (VFA) increased from 71 to 133 ± 9 mmol/L in wk 2 to 5 and was characterized by a relatively high molar proportion of propionate, increasing from 34 to 40 mol/100 mol of VFA in wk 2 to 5. In addition, the presence of ethanol and propanol as well as numerous VFA esters points to a ruminal environment with a relatively high hydrogen pressure. Plasma glucose and insulin responded to the highest milk allowance in wk 2 to 4. Plasma VFA and ketone bodies increased with the lowest milk allowance in wk 4 to 5. At slaughter, empty wet weights of the rumen + reticulum and omasum as well as mass of digesta in these compartments were found to decrease linearly and perirenal fat was found to increase linearly with milk allowance, indicating that the milk allowance changed the body composition of the calves. Lengths of ruminal papillae in the atrium and ventral ruminal sac were not affected by treatment. We concluded that the ruminal environment of young calves fed a barley-based starter concentrate was characterized by a low ruminal pH and high VFA concentration regardless of the milk allowance.     

Effects of rumen acid load from feed and forage particle size on ruminal pH and dry matter intake in the lactating dairy cow

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

Ruminal degradability of dry matter,crude protein,and amino acids in soybean meal,canola meal,corn, and wheat dried distillers grains

Different protein sources, such as canola meal (CM) or dried distillers grains (DDG), are currently used in dairy rations to replace soybean meal (SBM). However, little data exists comparing their rumen degradation in a single study. Therefore, the objective of this study was to compare the ruminal degradation of dry matter (DM), crude protein (CP), and AA of SBM, CM, high-protein corn DDG (HPDDG), and wheat DDG plus solubles (WDDGS). In situ studies were conducted with 4 rumen-fistulated lactating Holstein cows fed a diet containing 38% grass hay and 62% corn-based concentrate. Each protein source was incubated in the rumen of each cow in nylon bags for 0, 2, 4, 8, 16, 24, and 48 h to determine DM and CP rumen degradation kinetics, whereas additional bags were also incubated for 16 h to evaluate AA ruminal disappearance. Rumen DM and CP degradability was calculated from rumen-undegraded residues corrected or not for small particle loss. Data were fitted to an exponential model to estimate degradation parameters and effective degradability (ED) was calculated with a passage rate of 0.074 h⁻¹. The WDDGS and SBM had higher uncorrected ED (DM = 75.0 and 72.6%; CP = 84.8 and 66.0%, respectively) than CM and HPDDG (DM = 57.2 and 55.5%; CP = 59.3 and 48.2%, respectively), due to higher soluble fraction in WDDGS and a combination of higher potentially degradable fraction and rate of degradation in SBM. Correction for small particle loss from bags, higher for WDDGS than for the other protein sources, decreased estimated ED but did not alter feed ranking. The ruminal disappearance of AA after 16 h of incubation reflected the overall pattern of CP degradation between protein supplements, but the ruminal disappearance of individual AA differed between protein supplements. Overall, these results indicate that, in the current study, (1) SBM and WDDGS were more degradable in the rumen than CM and HPDDG, and (2) that small particle loss correction is relevant but does not alter this ranking.