Rumen fermentation in lactating cows selected for milk fat content fed two forage to concentrate ratios with hay or silage

Postbiotics from Saccharomyces cerevisiae fermentation stabilize microbiota in rumen liquid digesta during grain-based subacute ruminal acidosis (SARA) in lactating dairy cows

BACKGROUND

Subacute ruminal acidosis (SARA) is a common metabolic disorder of high yielding dairy cows, and it is associated with dysbiosis of the rumen and gut microbiome and host inflammation. This study evaluated the impact of two postbiotics from Saccharomyces cerevisiae fermentation products (SCFP) on rumen liquid associated microbiota of lactating dairy cows subjected to repeated grain-based SARA challenges. A total of 32 rumen cannulated cows were randomly assigned to 4 treatments from 4 weeks before until 12 weeks after parturition. Treatment groups included a Control diet or diets supplemented with postbiotics (SCFPa, 14 g/d Original XPC; SCFPb-1X, 19 g/d NutriTek; SCFPb-2X, 38 g/d NutriTek, Diamond V, Cedar Rapids, IA, USA). Grain-based SARA challenges were conducted during week 5 (SARA1) and week 8 (SARA2) after parturition by replacing 20% DM of the base total mixed ration (TMR) with pellets containing 50% ground barley and 50% ground wheat. Total DNA from rumen liquid samples was subjected to V3-V4 16S rRNA gene amplicon sequencing. Characteristics of rumen microbiota were compared among treatments and SARA stages.

RESULTS

Both SARA challenges reduced the diversity and richness of rumen liquid microbiota, altered the overall composition (β-diversity), and its predicted functionality including carbohydrates and amino acids metabolic pathways. The SARA challenges also reduced the number of significant associations among different taxa, number of hub taxa and their composition in the microbial co-occurrence networks. Supplementation with SCFP postbiotics, in particular SCFPb-2X, enhanced the robustness of the rumen microbiota. The SCFP supplemented cows had less fluctuation in relative abundances of community members when exposed to SARA challenges. The SCFP supplementation promoted the populations of lactate utilizing and fibrolytic bacteria, including members of Ruminococcaceae and Lachnospiraceae, and also increased the numbers of hub taxa during non-SARA and SARA stages. Supplementation with SCFPb-2X prevented the fluctuations in the abundances of hub taxa that were positively correlated with the acetate concentration, and α- and β-diversity metrics in rumen liquid digesta.

CONCLUSIONS

Induction of SARA challenges reduced microbiota richness and diversity and caused fluctuations in major bacterial phyla in rumen liquid microbiota in lactating dairy cows. Supplementation of SCFP postbiotics could attenuate adverse effects of SARA on rumen liquid microbiota.

Effects of the level and source of dietary physically effective fiber on feed intake, nutrient utilization, heat energy, ruminal fermentation, and milk production by Alpine goats

Thirty-two primiparous and 31 multiparous Alpine goats were used to determine influences of diets varying in level and source of forage on performance in early to mid-lactation for 16 wk. Diets consisted of 40%, 50%, 60%, and 70% forage (designated as 40F, 50F, 60F, and 70F, respectively) with 60F and 70F containing coarsely ground grass hay (primarily orchardgrass) and 40F and 50F containing cottonseed hulls, alfalfa pellets, and coarsely ground wheat hay. Diets contained 15.9% to 16.3% crude protein and 37.8%, 42.1%, 53.5%, and 55.4% neutral detergent fiber (NDF) with 10.0%, 15.8%, 50.1%, and 55.5% particle retention on a 19-mm sieve, and 26.1%, 29.6%, 38.3%, and 40.0% physically effective NDF (peNDF) for 40F, 50F, 60F, and 70F, respectively. Dry matter intake (2.71, 2.75, 1.96, and 1.95 kg/d) and milk yield (2.82, 2.71, 2.23, and 2.10 kg/d for 40F, 50F, 60F, and 70F, respectively) were lower (P < 0.05) for the two diets highest in forage. Digestion of organic matter was similar among diets (P > 0.05), but digestibility of NDF was greater (P < 0.05) for 60F and 70F (57.5%, 58.4%, 68.9%, and 72.2% for 40F, 50F, 60F, and 70F, respectively). Diet affected (P < 0.05) milk fat (3.16%, 3.37%, 2.93%, and 2.97%) and protein concentrations (2.62%, 2.69%, 2.58%, and 2.52% for 40F, 50F, 60F, and 70F, respectively). Milk energy yield was greater (P < 0.05) for the two diets lowest in forage (7.51, 7.45, 5.68, and 5.34 MJ/d), although yield relative to dry matter intake was not affected (P > 0.05) by diet and was lower (P < 0.05) for primiparous vs. multiparous goats (2.71 and 3.09 MJ/kg). Ruminal pH and acetate proportion were greater for 60F and 70F than for the other diets and the proportion of butyrate was lower for the two diets highest in fiber. The mean lengths of time spent ruminating, eating, standing, and lying were not affected (P > 0.05) by diet or parity, but many interactions involving diet, period, hour, and parity were significant (P < 0.05). In conclusion, lactational performance of Alpine goats in early to mid-lactation will be constrained with diets high in forage of moderate quality, peNDF content, and large particle size, which appeared related to limited feed intake.

Proteomic characterization and comparison of milk fat globule membrane proteins of Saanen goat milk from 3 habitats in China using SWATH-MS technique

Saanen goats are among the major dairy goats in China. In present study, variation of milk fat globule membrane proteins profile of Saanen goat milk caused by geographic location was investigated using sequential window acquisition of all theoretical fragment ions data-independent acquisition mass spectrometry based proteomic approach. A total of 1,001 proteins were quantified in goat milk collected from 3 habitats of China [Guangdong (GD); Inner Mongolia (IM); Shannxi (SX)]. Most of the proteins were found to act cellular process of biological process, cell of cellular component, binding of molecular function after Gene Ontology annotation and metabolic of pathway indicated by Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Differentially expressed proteins (DEP) for GD versus IM, GD versus SX, IM versus SX were identified to be 81, 91, and 44, respectively. Gene Ontology enrichment analysis showed that the greatest DEP for 3 groups (GD vs. IM, GD vs. SX, IM vs. SX) were cellular process, cellular process and organonitrogen compound biosynthetic process/immune system process for biological process. For cellular component, the largest number of DEP for 3 comparison groups were organelle, organelle and organelle/intracellular. For molecular function, DEP of the 3 comparison groups were expressed most in structural molecule activity, binding and anion binding, respectively. Pathways with the majority of DEP were ribosome, systemic lupus erythematosus and primary immunodeficiency/systemic lupus erythematosus/amoebiasis/PI3K-Akt signaling pathway for GD versus IM, GD versus SX and IM versus SX, severally. Protein-protein interaction network analysis showed that DEP interacted most were 40S ribosomal protein S5, fibronectin and Cytochrome b-c1 complex subunit 2, mitochondrial for GD versus IM, GD versus SX and IM versus SX, separately. Data may give useful information for goat milk selection and milk authenticity in China.

The impact of environmental and nutritional stresses on milk fat synthesis in dairy cows

Stress reduces milk and milk components synthesis and increases maintenance requirements of cows. The major stress-related alterations involve enhanced secretion of glucocorticoids and increased sympathetic nervous system activity, which results in biochemical and physiologic changes. In dairy cows exposed to social (ie housing conditions, overstocking, regrouping, feed delivery), physiological (ie initiation of lactation and parturition), or physical (ie heat or cold stress) stressors, responses involve alterations in energy balance and nutrient partitioning. The capacity of the animal to synthesize milk fat largely depends on the availability of substrates for lipid synthesis from the diet, ruminal fermentation or adipose tissue stores, all of which can be altered under stress conditions. Indeed, milk fat concentration is particularly responsive to diet and environment modifications, where a wide range of nutritional and non-nutritional factors influence milk fat output. Milk fat synthesis is an energy demanding process, and extremely sensitive to stress factors during lactation and the involvement of multiple organs. Recent studies examining social, physical, and physiological stressors have provided important insights into how differences in milk yield and milk components may be associated with biological responses to stress factors in dairy cows. This review focuses primarily on the role of stress sources and indicators to which the dairy cow is exposed in regulating milk fat synthesis. We will review the role of nutritional and non-nutritional factors on milk fat synthesis in dairy cows under stress conditions.

Effects of Dietary Energy Levels on Rumen Fermentation, Gastrointestinal Tract Histology, and Bacterial Community Diversity in Fattening Male Hu Lambs

This study investigated rumen fermentation and histological and microbial diversity in male Hu lamb fed diets with different metabolizable energy (ME) levels (MEA, 9.17 MJ/kg, MEB, 10.00 MJ/kg, and MEC, 10.82 MJ/kg). Thirty-six male Hu lambs were randomly allotted to three treatments, and the feeding trial lasted for 67 days. Rumen fermentation results suggest that the iso-valerate had a significant effect on dietary energy level. The papillary height (PH) of rumen was the highest in the MEB group, the crypt depth (CD) was significantly increased in the duodenum and jejunum, and the villus height (VH)-to-CD ratio (VH/CD) was significantly decreased in the duodenum by increasing dietary energy levels; the VH, villus width (VW), and VH/CD also had significant differences in the ileum. 16S rRNA sequencing results showed that the operational taxonomic units (OTUs) number, the ACE, and Chao1 indices were linearly decreased by increasing dietary energy level; 24 phyla including 124 genera were identified, and the relative abundance of Papillibacter and Quinella linearly decreased by increasing the dietary energy level. Compared to MEA and MEB groups, the relative abundance of unidentified_Veillonellaceae and Anaerovibrio was significantly increased in the MEC group at the genus level. The relative abundance of the carbohydrate metabolism pathway predicted by Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) was linearly increased by increasing the dietary energy levels. Three metabolic pathways identified in Kyoto Encyclopedia of Genes and Genomes (KEGG) level 3 were significantly influenced as the dietary energy level increased. In summary, these results demonstrated that the dietary energy levels affected the rumen fermentation parameters, morphological structures of the gastrointestinal tract (GIT), and the composition and function of rumen microflora in male Hu sheep.

Can We Observe Expected Behaviors at Large and Individual Scales for Feed Efficiency-Related Traits Predicted Partly from Milk Mid-Infrared Spectra?

Phenotypes related to feed efficiency were predicted from records easily acquired by breeding organizations. A total of 461,036 and 354,148 records were collected from the first and second parity Holstein cows. Equations were applied to the milk mid-infrared spectra to predict the main milk components and coupled with animal characteristics to predict the body weight (pBW). Dry matter intake (pDMI) was predicted from pBW using the National Research Council (NRC) equation. The consumption index (pIC) was estimated from pDMI and fat, and protein corrected milk. All traits were modeled using single trait test-day models. Descriptive statistics were within the expected range. Milk yield, pDMI, and pBW were phenotypically positively related (r ranged from 0.08 to 0.64). As expected, pIC was phenotypically negatively correlated with milk yield (-0.77 and -0.80 for the first and second lactation) and slightly positively correlated with pBW (0.16 and 0.07 for the first and second lactation). Later, parity cows seemed to have a better feed efficiency as they had a lower pIC. Although the prediction accuracy was moderate, the observed behaviors of studied traits by year, stage of lactation, and parity were in agreement with the literature. Moreover, as a genetic component was highlighted (heritability around 0.18), it would be interesting to realize a genetic evaluation of these traits and compare the obtained breeding values with the ones estimated for sires having daughters with reference feed efficiency records.

Effects of replacement of late-harvested grass silage and barley with early-harvested silage on ruminal digestion efficiency in lactating dairy cows

The objective of this experiment was to quantify the effects of graded replacement of late-harvested grass silage and barley with early-harvested silage on nutrient digestion and rumen fermentation. Four experimental diets were fed to 4 multiparous rumen-cannulated Nordic Red cows in 4 × 4 Latin square design with 21-d periods. Dietary treatments consisted of late-cut grass silage (LS) and rolled barley, which was gradually replaced with early-cut grass silage [ES; 0, 33, 67, and 100% of the forage component (ES + LS) of the diet]. With increased proportion of ES in the diet, the proportion of barley decreased from 47.2 to 26.6% on a dry matter basis. Early- and late-cut silages were harvested at 2-wk intervals (predicted concentrations of metabolizable energy 11.0 and 9.7 MJ/kg of dry matter). The 4 diets were formulated to support the same milk production. Nutrient flows were quantified using omasal sampling technique applying the triple-marker method (Cr, Yb, and indigestible neutral detergent fiber) and ¹⁵N as a microbial marker. Feed intake decreased with graded replacement of LS and barley with ES, but milk production was not influenced by diet. Digestibility of nutrients improved with graded addition of ES in the diet with the greatest difference observed in digestibility of neutral detergent fiber (NDF) and potentially digestible NDF (pdNDF). The results suggested that improved cell wall digestibility with graded level of ES in the diet was partly related to higher intrinsic digestibility of ES than LS, and partly due to negative associative effects with an increased proportion of LS and barley in the diet. Efficiency of microbial N synthesis was not influenced by the diet, but ruminal protein degradability increased with ES in the diet. Rumen fermentation pattern was not affected by the diet despite large difference in the profile of dietary carbohydrates. Rumen pool size of NDF and pdNDF, and ruminal turnover time of NDF decreased with graded addition of ES in the diet, whereas digestion rate of pdNDF improved. The results of this study indicate that increased CH₄ yield in a parallel production study with graded addition of ES in the diet were more related to greater ruminal and total digestibility of organic matter than to the changes in rumen fermentation pattern.

Innate immune responses to metabolic stress can be detected in rumen fluids

Many production diseases of dairy cows are related to digestive troubles. The rumen subacute acidosis is the most relevant one, albeit not easily recognized. Recent studies suggest that forestomachs can perform regulatory actions at both regional and systemic levels, since forestomach walls express immune receptors and cytokines, and the rumen liquor is infiltrated by leukocytes. Therefore, the rumen fluid could be conveniently collected for investigating metabolic production diseases. Thus, we investigated the origin of the leukocytes of the rumen fluid and demonstrated that they partly derive from saliva. Next, we carried out a field survey of innate immunity in rumen fluids of 128 cows from 12 dairy farms, along with clinical inspections, assessment of milk yield, rumen pH, volatile fatty acids (VFA) and major inflammo-metabolic parameters. Significant statistical correlations were found between immune markers in rumen fluids and biochemical parameters. A significant negative correlation was found in rumen between CD45 gene expression (leukocyte infiltration) and pH level. B cells were the most frequent mononuclear leukocyte population in the rumen liquor and their infiltration was negatively affected by low ruminal pH and high concentrations of VFA. Moreover, total Ig and IgM in rumen fluids were negatively correlated with ruminal pH and positively correlated with uremia. Our data suggest that forestomach immune responses could be directed to "dangers" arising within the forestomach environment. The immune markers could integrate consolidated diagnostic parameters (e.g. rumen pH) and contribute to robust, early diagnosis of tricky digestive troubles of cattle.

Effect of feeding long or short wheat hay v. wheat silage in the ration of lactating cows on intake, milk production and digestibility

The objective of this study was to evaluate in lactating cows the effect of either chopping or ensiling of wheat roughage on: intake, digestibility, lactation performance and animal behavior. Three groups of 14 lactating cows each, were fed total mixed rations (TMRs) based on either long wheat hay (HL), short wheat hay (HS) or wheat silage (SI), as the sole roughage source (30% of TMR dry matter (DM)). Parameters examined: sorting behavior, DM intake, milk yield and composition, rumination, recumbence, average daily rumen pH, digesta passage rate, and in-vivo digestibility. Performance data was summarized by day and analyzed using a proc-mixed model. The content of physically effective neutral detergent fiber (peNDF) was similar in the HL and SI and lower in the HS, resulting in similar differences among the three corresponding TMRs. In vitro DM digestibility of wheat silage was higher than that of the two hays (65.6% v. 62.8%) resulting in higher in vitro DM digestibility of the SI-TMR compared with the hay-based TMRs (79.3 v. 77.0%). HS-TMR was better than HL- or SI-TMRs at preventing feed sorting by cows after 12 or 24 h eating of the diets. Cows fed HS-TMR consumed more DM and NDF but less peNDF than the other two groups. Average daily rumen pH was similar in the three groups, but daily rumination time was highest in the cows fed HS-TMR. Rumen retention time was longest in cows fed HL-TMR. DM digestibility in cows fed SI-TMR was higher than that of HS and HL groups (65.2%, 61.8% and 62.4%, respectively), but NDF digestibility was similar in the three treatments. The highest intake of digestible DM was observed in cows fed SI-TMR, HS cows were intermediate and HL cows were the lowest. Consequently, cows fed SI-TMR had higher yields of milk, 4% fat corrected milk and energy-corrected milk (47.1, 42.9 and 43.2 kg/day, respectively) than cows fed HS-TMR (45.7, 41.0 and 41.0 kg/day, respectively) or HL-TMR (44.1, 40.3 and 40.3 kg/day, respectively). Net energy production (NEL+M+gain) per kg DM intake was highest in the SI-TMR, lowest in the HS-TMR and intermediate in the HL-TMR (1.52, 1.40 and 1.45, respectively). Animal welfare, as expressed in daily recumbence time and BW gain was similar in the SI and HS groups and higher than the HL cows.

Effect of forage to concentrate ratio with sorghum silage as a source of forage on rumen fermentation, N balance, and purine derivative excretion in limit-fed dairy heifers

Sorghum silage has been shown to be a good alternative to corn silage for dairy cows; however, studies regarding heifers are insufficiently explored. Therefore, the objective of this study was to evaluate effects of changing forage to concentrate ratio (FOR:CON) in diets based on sorghum silage on N digestibility, rumen fermentation, N balance, C excretion, and microbial N yield in limit-fed dairy heifers. A split-plot 4×4 Latin square design with 19-d periods (15 d of adaptation and 4 d of sampling) was conducted with 8 rumen cannulated dairy heifers (age 13.7±0.6mo and weight 364.8±17.6kg). Heifers were fed sorghum silage-based diets with 4 FOR:CON (85:15, 75:25, 65:35, and 55:45) balanced for similar metabolizable energy intake per unit of body weight and crude protein concentration. Diets were fed to allow 900 to 1,000g/d body weight gain and were fed once daily. Total collection of feces and urine was completed on d 15 to 19 to determine N, C, urea N, allantoin, uric acid, and creatinine excretion. Rumen contents were sampled on d 19 at 0, 1.5, 3, 4.5, 6, 9, 13, 17, 21, and 23h after feeding to measure pH, volatile fatty acid (VFA), ammonia-N, and free AA concentrations. The pH decreased linearly while ammonia-N and free AA levels increased linearly with decreasing FOR:CON of diets. Although mean total VFA did not differ among treatment diets, molar proportions of VFA did. Acetate proportion decreased while propionate and butyrate increased with decreasing FOR:CON. Intake of N and urea N excretion decreased with decreasing forage proportion in diets while total N excretion, apparent N digestibility, and N retention were not different. Intake of C and excretion in feces (g/d) decreased linearly with decreasing FOR:CON in diets. Creatinine, allantoin, and uric acid excretion were not affected by FOR:CON; however, microbial N yield tended to increase linearly with greater concentrate in diets. Heifers limit fed diets based on sorghum silage demonstrated the effect of available ammonia-N and readily fermentable carbohydrates with subsequent effects on nutrient utilization when different FOR:CON were applied. Based on the presented results, FOR:CON 65:35 had the most suitable balance of available ammonia-N and readily fermentable carbohydrates for the most optimal results.

Effect of wheat hay particle size and replacement of wheat hay with wheat silage on rumen pH, rumination and digestibility in ruminally cannulated non-lactating cows

This study examined the effects on intake, diurnal rumen pH changes, rumination and digestibility of feeding ruminally cannulated non-lactating cows in a Latin square design (four cows×four periods) with four total mixed rations (TMRs) typical for lactating cows. TMRs were based on: long wheat hay or short wheat hay, wheat silage or wheat silage+1.5% NaHCO3 buffer, as the sole roughage source (30% of TMR dry matter (DM)). The level of physically effective NDF remaining above the 8 mm screen (peNDF) was similar in the long hay and silage-based TMRs (9.45% to 9.64% of DM) and lower in the short hay TMR (7.47% of DM). The four TMRs were offered individually at 95% of ad libitum intake to avoid orts within 24 h. Cows fed long hay consumed less DM than the short hay and silage groups (9.6 v. 10.5 and 10.8 kg/day, respectively) and sorted against large hay particles at 12 h post-feeding. Under the limitations of this study (non-lactating cows fed at restricted intake) short hay TMR prevented sorting within 12 h post-feeding, encouraged rumination per kg peNDF ingested, and had higher average rumen pH (6.24), whereas preventing sub acute ruminal acidosis (SARA, defined as pH<5.8 for at least 5 h/day). In contrast, the long hay and silage-based groups were under SARA. In vitro methane production of rumen fluid was higher in the hay-fed cows than in their silage-fed counterparts, and in all treatments lower at 1 h pre-feeding than at 6 h post-feeding. In vivo DM and NDF digestibility were similar for the short hay and silage TMRs, and higher than those of the long hay TMR. Under the conditions of this study, addition of 1.5% buffer to the wheat silage TMR had no effect on intake, rumen pH, creation of SARA and digestibility.

Effects of Forage:Concentrate Ratio on Growth Performance, Ruminal Fermentation and Blood Metabolites in Housing-feeding Yaks

The objective of this study was to determine the effect of forage: concentrate ratio (F:C) on growth performance, ruminal fermentation and blood metabolites of housing-feeding yaks. Thirty-two Maiwa male yaks (initial body weight = 207.99±3.31 kg) were randomly assigned to four dietary treatments (8 yaks per treatment). Experimental diets were: A, B, C, D which contained 70:30, 60:40, 50:50 and 40:60 F:C ratios, respectively. Dry matter intake and average daily gain in yaks fed the C and D diets were greater (p<0.05) than yaks fed the A and B diets. No differences were found in ruminal NH₃-N, total volatile fatty acids, acetate, butyrate, valerate, and isovalerate concentrations. The propionate concentration was increased (p<0.05) in the C and D groups compared with the A and B diets. In contrast, the acetate to propionate ratio was decreased and was lowest (p<0.05) in the C group relative to the A and B diets, but was similar with the D group. For blood metabolites, no differences were found in serum concentrations of urea-N, albumin, triglyceride, cholesterol, low density lipoprotein, alanine aminotransferase, and aspartate aminotransferase (p>0.05) among treatments. Treatment C had a higher concentration of total protein and high density lipoprotein (p<0.05) than A and B groups. In addition, there was a trend that the globulin concentration of A group was lower than other treatments (p = 0.079). Results from this study suggest that increasing the level of concentrate from 30% to 50% exerted a positive effect on growth performance, rumen fermentation and blood metabolites in yaks.

Using a novel macro in vitro technique to estimate differences in absorption rates of volatile fatty acids in the rumen

A novel macro in vitro system was used to test the theory that rumen proportions of acetate, propionate and butyrate are not representative of their respective net production rates. Whole rumen content (10-16 kg) from two cows was mixed with a bicarbonate buffer and incubated separately in two 40-l in vitro vessels for 3 h. A total of six experimental periods were used. In this study, a total of six cows were used and fed 1/8 of the daily ration by hand every 3 h. To obtain differences in rumen volatile fatty acids (VFA) composition, 1 l of acetate (416 mm), propionate (108 mm), butyrate (79 mm), lactic acid (300 mm) or nothing was infused during 24 h into the rumen before collection of representative samples of rumen contents. Infusions of acids were then continued during the in vitro incubations in exact proportion to the digesta removed from the rumen. In Periods 1 and 2, the cows were alternatively infused with acetate or nothing. In Periods 3 and 4, the infusions consisted of propionate or butyrate and in Periods 5 and 6 of lactate or nothing. Nine liquid samples were obtained between 3 and 180 min after the start of incubation and analysed for concentrations of VFA. Changes in proportions of individual VFA were estimated by linear regression. No differences in VFA proportions were observed in the absence of infusion (p> 0.5) over time, but when individual VFA were infused, their respective proportions increased. This was interpreted as the result of a decreased in vitro fermentation rate of digesta substrates compared with that in the rumen. Lactate infusion increased butyrate proportion in vitro. It is concluded that this study could not provide any evidence that ruminal VFA proportions are unrepresentative of the proportions of net production.

Effects of dairy cow diet forage proportion on duodenal nutrient supply and urinary purine derivative excretion

Four mature Holstein-Friesian dairy cows were used in a 4 x 4 Latin square change-over design experiment made up of four 4-wk periods to investigate the relationship between microbial protein flow to the duodenum and excretion of purine derivatives (PD) in the urine. Four dietary treatments based on ad libitum access to ryegrass silage were offered, with a standard dairy concentrate included at different forage:concentrate (F:C) ratios, calculated on a dry matter basis: 80:20, 65:35, 50:50, and 35:65. Feed intakes increased as the proportion of concentrate in the diet increased, despite a concurrent decrease in silage intake. Increased feed intake led to increased nutrient flow to the duodenum. Milk yields increased as the diet F:C ratio decreased, with cows offered the 35:65 diet yielding nearly 8 kg/d more milk than cows offered the 80:20 diet; the concentrations of milk fat decreased and milk protein increased with a decreasing F:C ratio. Purine derivative excretion in the urine increased with an increasing proportion of concentrate in the diet, and there was a strong linear relationship between total PD excretion (allantoin and uric acid) and microbial N flow to the duodenum: microbial N (g/d) = 19.9 + 0.689 x total PD (mmol/d); R = 0.887. This strengthens the case for using PD excretion as a noninvasive marker of microbial protein flow from the rumen in dairy cows.

Effects of feeding forage soybean silage on milk production, nutrient digestion, and ruminal fermentation of lactating dairy cows

The objective of this study was to determine the feeding value of forage soybean silage (SS) for dairy cows relative to a fourth-cut alfalfa silage (AS). Forage soybean was harvested at full pod stage. Two isonitrogenous diets were formulated with a 48:52 forage:concentrate ratio. Soybean silage and AS constituted 72% of the forage in each diet, with corn silage constituting the remaining 28%. Twenty Holsteins cows in early lactation were used in a switchback design. Four lactating Holsteins cows fitted with ruminal cannulas were used to determine the effects of dietary treatments on ruminal fermentation parameters and in vivo total tract nutrient utilization. Relative to AS, SS contained 15, 28, and 25% more neutral detergent fiber, acid detergent fiber, and crude protein, respectively. Dry matter intake (23.5 vs. 25.1 kg/d) and milk yield (35.5 vs. 37.2 kg/d) were lower for cows fed SS than for those fed AS. However, energy-corrected milk and milk efficiency were similar for both dietary treatments. Milk protein, lactose, and total solids concentrations were not influenced by dietary treatments (average 3.0, 4.7, and 12.6%, respectively). However, cows fed SS produced milk with greater milk fat (3.8 vs. 3.6%) and milk urea nitrogen concentrations (15.6 vs. 14.3 mg/dL) compared with cows fed AS. Ruminal pH was lower, whereas ruminal NH3-N concentration was greater in cows fed SS than in cows fed AS. Total tract digestibilities of dry matter, crude protein, and neutral detergent fiber were not influenced by silage type. We concluded that forage SS, when compared with AS, had a negative impact on feed intake and milk yield, whereas energy-corrected milk, milk efficiency, and total tract nutrient digestion were similar.

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 x 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.

Subacute rumen acidosis in lactating cows: an investigation in intensive Italian dairy herds

Subacute rumen acidosis (SARA) represents one of the most important metabolic disorders in intensive dairy farms that affects rumen fermentations, animal welfare, productivity and farm profitability. The aim of the present study was to study the occurrence of SARA in intensive Italian dairy herds and to determine the relationship between diet composition, ruminal pH and short chain fatty acids (SCFA) concentration. Ten commercial dairy herds were investigated; twelve cows in each herd were selected randomly among animal without clinical signs of disease, with good body condition and between 5 and 60 day-in-milk (DIM), to perform rumenocentesis and obtain rumen fluid. Ruminal pH was determined immediately after sampling and concentration of SCFA in ruminal fluid was determined on samples after storage. An other objective of this research was to study in detail the effects of rumenocentesis on animal health: this study could confirm the extreme validity of this technique as ruminal sampling. Results were subject to anova and correlation analysis using SIGMA STAT 2.03. The results indicated the presence of SARA in three herds (more than 33% cows with rumen pH < 5.5), a critical situation (more than 33% cows with rumen pH < 5.8) in five farms and a normal rumen pH condition in two herds. In particular, dairy herds show on average SCFA concentration of 150, 145, 123 mmol/l for low pH, critical pH and normal pH herds respectively. There were not significant differences among diet composition even if herds with SARA showed a light discordance between initially chemistry composition and residual feed. In the affected herds it was not possible to understand the exact causes of SARA. Animal management seems to be one of the most important factors in developing SARA including total mixed ration preparation.

The effects of anAspergillus oryzaeextract containing alpha-amylase activity on ruminal fermentation and milk production in lactating Holstein cows

The effects of anAspergillus oryzaeextract containing alpha-amylase activity (Amaize™, Alltech Inc., Nicholasville, KY) were examinedin vivoandin vitro. A lactating cow study employed 20 intact and four ruminally fistulated Holstein cows in a replicated 4 × 4 Latin-square design to examine the effects of four concentrations of dietary Amaize™ extract on milk production and composition, ruminal fermentation and serum metabolite concentrations. The treatment diets contained 0, 240, 480 or 720 alpha-amylase dextrinizing units (DU) per kg of total mixed ration (TMR) (dry-matter basis). The supplemental alpha-amylase increased the yields of milk (P= 0·02), fat (P= 0·02) and protein (P= 0·06) quadratically. The maximum milk yield was obtained when 240 DU per kg of TMR were offered. Ruminalin situstarch disappearance was not affected by alpha-amylase supplementation in lactating cows or ruminally cannulated steers. Supplemental alpha-amylase extract reduced the molar proportion of propionate in the rumen of steers (P= 0·08) and lactating cows (P= 0·04), and in rumen-simulating cultures (P= 0·04). The supplement also increased the molar proportions of acetate (P= 0·06) and butyrate (P= 0·05), and the serum beta-hydroxybutyrate (P= 0·01) and non-esterified fatty acid (P= 0·03) concentrations in lactating cows. The improvements in milk production appear to be a consequence of the effects of alpha-amylase on ruminal fermentation and the potential changes in nutrient metabolism that result from them. We conclude that supplemental alpha-amylase may be given to modify ruminal fermentation and improve milk and component yield in lactating Holstein cattle.

Effects of Two Different Feeding Strategies During Dry-Off on Metabolism in High-Yielding Dairy Cows

The objectives of this study were to investigate different feeding strategies of high-yielding dairy cows during dry-off. With a 12- to 13-mo calving interval and increasing milk yield, metabolic and health problems during the dry-off period will increase. Twenty-two dairy primiparous and multiparous cows were randomly assigned to 2 feeding treatments. One group was fed straw ad libitum (straw), and the other group was fed silage (4 kg/d of dry matter) daily and straw ad libitum (silage). At the dry-off point (d 0), the cows had an average milk yield of 17.1 +/- 0.8 kg/d. All cows were milked in the morning on d 3 and 5 during the dry-off period. Rumen fluid was analyzed for volatile fatty acids (VFA), pH, NH3-N, and protozoa were counted from samples collected at d -3, 4, and 17. Total VFA concentration decreased at dry-off in both treatments and the drop was most pronounced among cows fed straw. Rumen pH increased significantly in both groups, and cows fed straw had significantly higher pH during dry-off. Ammonia N in rumen decreased significantly at dry-off and there was a tendency to lowered NH(3)-N in cows fed straw at dry-off. The plasma concentration of nonesterified fatty acids was markedly elevated during the dry-off period among cows in the straw treatment group, but was less pronounced among the cows fed silage with straw. The glucose level in plasma was not significantly affected during the dry-off period, and the insulin concentration was markedly reduced in both treatment groups. Plasma leptin concentration was lower in the lactating state than in the dry period. Both the beta-hydroxybutyrate and urea concentrations in plasma were significantly reduced during dry-off. Our results indicate that dry-off markedly affected the metabolism in the blood and in the rumen of the cows, and that the cows offered only straw during the dry-off were most affected.

Nitrogen Balance, Microbial Protein Production, and Milk Production in Dairy Cows Fed Fodder Beets and Potatoes, or Barley

Fourteen multiparous midlactation dairy cows were used in a change-over experiment with 3 periods and 3 diets to evaluate the effects of fodder beets and potatoes on N metabolism, microbial protein production, and milk production. A basal ration of alfalfa/grass silage offered ad libitum, 1 kg of grass hay and 1 kg of heat-treated rapeseed cake was supplemented with 5 kg DM of either rolled barley/raw potatoes 80:20 (BAP), fodder beets/raw potatoes 80:20 (BEP) or rolled barley (BA). Urine and feces were collected quantitatively from 8 cows and ruminal samplings, and evacuations were performed on 4 cannulated cows. Intake and production did not differ between BAP and BA, but the BEP diet lowered intake of both silage and total ration by 0.9 kg DM. Daily yield of energy-corrected milk (ECM) was decreased by 1.7 and 2.3 kg compared with BAP and BA, respectively. Milk urea concentration was 1 mM lower with the BEP diet. The proportion of feed N recovered in milk was 20 to 21% for all diets. With the BEP diet, urinary N amount and proportion were reduced correspondingly to the lower total N intake. Fecal N amount remained unchanged, and hence nitrogen apparent digestibility decreased by 5 percentage units with the BEP diet. Microbial protein production, assessed by allantoin excretion, tended to be highest with the BAP diet. Acetate proportion of VFA was lowered by the BEP diet, while proportions of propionate and butyrate both tended to increase. Different fermentation patterns, probably related to differences in rumen microbiota, could explain why changes in energetic efficiency and milk composition reported in the literature did not occur in the actual experiment when roots replaced barley. Compared with barley, roots appeared to have a greater negative effect on silage intake in conjunction with a prewilted silage with high intake potential allowed ad libitum and this decreased milk production by a magnitude corresponding to the lower intake of ME.

Subacute Ruminal Acidosis (SARA): a Review

Subacute ruminal acidosis (SARA) is likely to arise when an easily palatable, high-energy diet meets a ruminal environment not adapted to this type of substrate. Increase of short-chained fatty acids (SCFA) will occur. Eventually, this may result in a transient nadir of ruminal pH below 5.5. Two situations are likely to represent the risk of SARA. First, fresh lactating cows are confronted with a diet considerably differing from that in the dry-period. A diet change carried out too rapidly or without proper transition management will put the animals at risk. Secondly, further in lactation, inaccurate calculation of dry-matter-intake (DMI) leading to wrong roughage/concentrate ratio, an inadequate content of structure within the diet or mistakes in preparing of total mixed rations may produce SARA. The consequences of SARA are diverse and complex. Laminitis is regularly connected to SARA and the negative impact of organic acids on the ruminal wall may lead to parakeratosis enabling translocation of pathogens into the bloodstream provoking inflammation and abscessation throughout the ruminant body. Moreover, milk-fat depression (MFD) can be related to SARA. In order to achieve a proper diagnosis, SARA has to be understood as a herd-management problem. A screening of the herd for SARA by means of a rumenocentesis, performed on a sample-group, preferably 12 individuals, may reveal the presence of SARA. The herd screening should include the risk group suspected, preferably. The prevention of SARA applies to the principles of ruminant feeding. Careful transition management from the dry to the lactation period and control of fibre-content and ration quality should be more yielding than the use of buffers or antibiotic drugs.

Strategies for increasing energy density of dry cow diets

The objective of this trial was to compare the effects of increasing dietary energy density from 1.51 to 1.65 Mcal/kg of dry matter (DM) by replacing forage with concentrate or by further increasing concentrate via the substitution of corn silage and alfalfa silage by a mixture of straw, starch, and soybean meal. Our hypothesis was that the latter diet would be more glucogenic while increasing rumen fill and be potentially desirable for transition cows. Nine far-off dry cows (greater than 3 wk before parturition at the end of the trial) were fed three diets: low energy diet, [LE, 1.51 Mcal/kg of DM, 14.0% crude protein (CP) and 35% nonfiber carbohydrates (NFC)], high energy diet, (HE, 1.65 Mcal/kg of DM, 13.9% CP and 39.5% NFC) and high energy diet, where a portion of alfalfa and corn silage was replaced by straw, soybean meal, and cornstarch (HES, 1.65 Mcal/kg of DM, 13.5% CP and 40.5% NFC). The experiment was a replicated 3 x 3 Latin square design with 21-d periods. Six cows from two squares were used to examine kinetics of DM disappearance from nylon bags suspended in the rumen. Two contrasts of interest were: LE versus HE, HES (effects of energy density) and HE versus HES (method of increasing energy density). Increasing energy density increased the potentially degradable (B) and decreased the undergradable (C) DM fractions of the diets. Because HES had greater B and a faster rate of degradation of fraction B (k), effective rumen degradable DM (ERDDM) was higher in HES compared to HE. Cows fed high energy diets had greater DM intake. No differences in DM intake were observed between HE and HES. Rumen volume or DM pool sizes were not affected by treatment. High energy diets increased total ruminal fluid volatile fatty acid concentration compared with LE. Propionate concentration was higher in cows fed high energy diets compared with cows fed LE. The partial replacement of alfalfa and corn silage by straw, soybean meal, and cornstarch further increased propionate concentration. The greatest increase in serum insulin concentration following feeding was observed in cows fed HE. Cows consuming high energy diets had lower plasma nonesterified fatty acids (NEFA) before and after feeding. The HES diet was less effective in decreasing plasma NEFA concentration after feeding compared to HE. In conclusion, increasing diet energy density of far-off dry cows positively affected DMI, ruminal propionate, serum insulin, and plasma NEFA. Increasing energy density with a blend of feeds that represent extremes in rates of carbohydrate fermentation may be a strategy to provide greater amounts of glucogenic precursors. Applicability of this strategy should be examined in transition cows.

Influence of carbohydrate source and buffer on rumen fermentation characteristics, milk yield, and milk composition in late-lactation Holstein cows

The effects of concentrate-to-forage ratio and buffer on rumen fermentation and production parameters were examined in four rumen-cannulated cows (240 +/- 18 d in milk) fed a total mixed ration ad libitum in a 4 x 4 Latin square design. The treatments were a 50:50 concentrate to forage ratio with [1.2% of dry matter, (DM)] and without (0% of DM) buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. Rumen pH declined in response to increased concentrate but was not influenced by buffer. In the absence of the buffer, rumen acetate declined and propionate was elevated at the higher level of concentrate inclusion. The milk fat concentration was lower for cows fed the high concentrate diet without buffer; however, the addition of buffer to the diet prevented the milk fat depression. Milk fat depression was associated with elevated trans-C18:1 fatty acids in milk, which provides additional support for an inhibitory effect of these fatty acids on mammary fat synthesis. We concluded that the potential of nutrition as a tool to alter milk composition is greater in later lactation as these animals are better able to cope with the negative effects of high grain diets, and the treatment response is greater than in early lactation.

Effects of forage source and amount of concentrate on rumen and intestinal digestion of nutrients in late-lactation cows

The objectives of this study were to determine the effects of dietary forage source with two concentrate concentrations on dry matter (DM) intake, rumen fill, ruminal and intestinal digestibility of nutrients, and duodenal N fractions in lactating cows. Four rumen and duodenal cannulated Holstein cows in late lactation were used in 4 x 4 Latin square design experiment with 21-d periods. Diets were 1) 65% first-cut alfalfa silage and 35% concentrate, 2) 50% alfalfa and 50% concentrate, 3) 65% bromegrass silage and 35% concentrate, and 4) 50% bromegrass and 50% concentrate. Dry matter intake was not affected by forage source but tended to be (P = 0.08) higher for cows fed diets with 50% concentrate. Rumen fill was greater (P < 0.01) for cows fed bromegrass compared with those fed alfalfa silage. Ruminal and intestinal digestion of DM was not affected by dietary forage source or concentrate level. Total N intake was greater for cows fed alfalfa-based diets, reflecting the higher crude protein content of alfalfa. However, total N flow at the duodenum was not affected by either forage source or concentrate in the diet. Although forage source influenced the site of digestion of some nutrients no significant effects on total tract digestibilities were observed.