Technical note: In situ ruminal starch disappearance kinetics of hull-less barley,hulled barley,and corn grains

The objective of this study was to compare ruminal starch disappearance rates of hull-less barley, hulled barley, and corn grains. Five different genotypes were used for each of the 2 barley types. In addition, each of these genotypes was grown in 2 different locations and years, resulting 10 independent barley samples for each of the 2 barley grain types. Five different genotypes of corn grain were obtained from a commercial seed company. After being ground to pass through a 4-mm screen of a cutter mill, 3.6 g of each grain was placed into a porous bag, which was then incubated in the rumen of 2 ruminally cannulated cows for 0, 4, 8, 12, 24, and 48 h. Corn grains had greater instant ruminal starch disappearances than barley grains (22.4 and 8.2%, respectively). Instant ruminal starch disappearances did not differ between hulled and hull-less barley grains. Ruminal starch fractional disappearance rates were greatest for hulled barley grains, moderate for hull-less barley grains, and lowest for corn grains (15.3, 13.9, and 7.1%/h, respectively). Ruminal starch half-life was shortest for hulled and hull-less barley grains (4.4 h) and longest for corn grains (6.6 h). Ruminal starch half-life did not differ between hulled barley and hull-less barley grains. In conclusion, using a holistic experimental design and statistical analysis, this study showed that starch from hull-less barley grains has a ruminal half-life similar to that of hulled barley grains and shorter than that of corn grains.     

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.     

Effects of fumarate on ruminal ammonia accumulation and fiber digestion in vitro and nutrient utilization in dairy does

The objective of this study was to evaluate effects of fumarate on ruminal ammonia accumulation and fiber digestion in vitro and on feed intake and nutrient utilization in dairy does. Batch cultures of mixed rumen microorganisms were used to study effects of different concentrations of fumarate on fermentation with various N sources (ammonia as ammonium bicarbonate, casein amino acids, casein peptides, gelatin peptides) and feeds (bermudagrass hay, mixed diet of 60% bermudagrass hay plus 40% concentrate) for 6 and 24 h, respectively. Substrates were grouped into pairs for separate incubations. Monosodium fumarate was added to incubation tubes to achieve final concentrations of 0, 5, and 10 mM fumarate. More ammonia accumulated at the end of incubation with added ammonium bicarbonate. Ammonia concentration was higher for peptide compared with amino acid incubation, and for casein peptide compared with gelatin peptide. Addition of fumarate linearly decreased ammonia for all N sources and for feed substrates. For all substrate types, fumarate treatment increased acetate, propionate, and total volatile fatty acids (VFA), decreased acetate to propionate ratio, and tended to reduce branched-chain VFA. Digestion of feed neutral detergent fiber (NDF) by rumen microorganisms was improved by fumarate along with elevated endoglucanase and xylanase activities. In an animal metabolism experiment, 8 dairy does (4 per treatment) were used in a completely randomized design for 21 d. Does were fed a hay plus concentrate diet without (control) or with fumarate (6 g/head per day) supplementation to determine feed intake, whole-tract nutrient digestibility, and N utilization. Fumarate treatment did not affect weight change or feed intake but increased whole-tract digestion of gross energy, crude protein, and cellulose. Digested N was increased by fumarate supplementation; however, N retention was unaffected. Plasma glucose concentration was elevated with fumarate but urea N concentration remained unchanged. Fumarate addition had significant effects on rumen microbial fermentation by decreasing ammonia and branched-chain VFA, and by increasing acetate and propionate, and NDF digestion. These effects were reflected in the improvement in whole-tract gross energy, crude protein, and cellulose digestion and elevated plasma glucose concentration when dairy does were supplemented with fumarate.     

NSP酶对大麦体外消化的影响

大麦体外消化试验结果揭示，添加NSP酶（GXC）使大麦中干物质、粗蛋白、粗灰分、无氮浸出物、粗脂肪和粗纤维的消化率分别提高了18．13％、20．27％、15．99％、16．42％、和26．93％和30．02％；大麦中各种氨基酸体外消化率显著提高，幅度为11．83％－61．39％；添加NSP酶使大麦胚乳细胞壁在体外完全降解；消化过滤液中葡萄糖和总氨基酸含量分别提高了17．58％和10．26％；而粘度降低了4．51％。     

Isolation of grass cell walls as neutral detergent fibre increases their fermentability for rumen micro‐organisms

Cell wall isolated from grasses as neutral detergent fibre (NDF) is fermented more readily than cell wall in the unfractionated forage by rumen organisms in vitro. In several experiments with Heteropogon contortus and Astrebla squarrosa the NDF digestibility at 48 h for the isolated cell wall was 8–18 units higher than for the unfractionated forage, with most of the difference appearing in the first 24 h of fermentation. Similar in vitro increases were obtained for Sorghum sp, wheat hay, bagasse and Lolium perenne and less so for Panicum maximum. The difference was not significant for Chloris gayana, nor for the tropical legumes Stylosanthes hamata, Clitoria ternatea and Lablab purpureus. For those grasses in which the above effect was statistically significant there was a significant relationship between NDF content of the unfractionated grass (x) and the ratio of NDF digestibility of isolated NDF to that of the unfractionated grass, as described by y=0.018x (P<0.01). For H contortus, kinetic analysis of gas produced from 0 to 48 h of in vitro incubation with rumen microbes showed an increased (from 0.016 to 0.020 h ⁻¹, P<0.001) rate of production from the slowly‐digested pool. Spear grass NDF incubated in the rumen in polyester bags had a higher NDF loss than unfractionated forage between 9 and 24 h and the difference was maintained after 24 h. Treatments in which amorphous silica was precipitated within NDF or leached from a grass substrate indicated that the enhanced rate in grasses was not due to removal of biogenic silica by the neutral detergent treatment. © 1999 Society of Chemical Industry     

Inhibition of amylases present in ruminal particle‐associated micro‐organisms

The effect of different substances potentially inhibitory of ruminal amylase activity in sheep was assessed using biochemical and electrophoretic assays. Most amylase activity was detected in the particle‐associated fraction (70%) of the ruminal contents (which was selected for the assays) in comparison with the bacterial (21%) and extracellular (9%) fractions. Salts of divalent ions such as Sn²⁺, Hg²⁺, Cu²⁺ and Zn²⁺ produced 90, 82, 65 and 44% inhibition of amylase activity respectively when assayed at a relative concentration of 5 × 10^?3 mol l^?1. Organic acids such as tannic, formic, ascorbic and benzoic acid produced 79, 48, 43 and 37% inhibition respectively, whereas chelators such as EDTA, EGTA and 1,10‐phenanthroline produced an inhibition ranging from 32 to 37%. Substrate SDS‐PAGE zymograms allowed the identification of different amylase‐active bands in ruminal extracts, showing a wide range of relative molecular masses (from 36 to more than 100 kDa). Such zymograms also confirmed the effect of some inhibitors. The reversibility of the inhibitory effect of some of the assayed substances was assessed. ZnSO₄ was the most persistent inhibitory substance even at low concentrations and, owing to its low toxicity, appears to be an adequate substance to reduce the high in vitro ruminal degradation of starch. Implications for the process of enzymatic digestion of starch are discussed. © 2002 Society of Chemical Industry     

In vitro digestion of fresh alfalfa under different conditions of ruminal pH

BACKGROUND: Relatively low ruminal pH values have been frequently registered in dairy cows grazing alfalfa, which can be involved in reducing feed digestion. An in vitro experiment was carried out to study the effect of ruminal pH (6.4, 6.1, 5.8 and 5.5) on the digestion of fresh alfalfa. RESULTS: Decreasing the pH, in vitro gas production (ivGP) decreased (P < 0.05). The lowest ivGP was registered at pH 5.5 and it was product of a higher lag time and a lower digestion rate. Dry matter disappearance (DMD) was not affected by pH at 48 h (P > 0.05). Neutral detergent disappearance (NDFD) at 48 h decreased below pH 6.1. The NDFD was reduced by 62% at pH 5.5 with respect to results at pH 6.4 and 6.1 (where the highest DMD and NDFD were observed). CONCLUSION: As expected, low rumen pH decreased alfalfa digestion. However, limits to ruminal digestion activity differed from those usually proposed for TMR diets. It is apparent that different relationships between rumen pH and NDFD exist when cows graze fresh alfalfa or grasses. Moreover, our results suggest the convenience to complement the data obtained through ivGP, DMD and NDFD. While ivGP and DMD seem to be more useful at early digestion times, NDFD may be a good predictor of final digestion. Copyright © 2009 Society of Chemical Industry     

Effects of California chaparral plants on in vitro ruminal fermentation of forage and concentrate diet

BACKGROUND: The combustible nature of chaparral plants has been attributed to the presence of secondary compounds such as phenolic acids, flavonoids and essential oils, among others. However, the implication of the antimicrobial properties of secondary compounds of chaparral in modulating rumen microbial metabolism has not been determined. The effects of 11 chaparral plants on rumen microbial fermentation were assessed in an in vitro batch culture fermentation fed a barley silage:barley grain‐based low concentrate (LC) and high concentrate (HC) diets. RESULTS: With LC, gas production [g dry matter (DM) incubated] and DM disappearance (DMD) were unaffected by Adenostoma fasciculatum, Ceanothus cuneatus, Baccharis pilularis or Eriodictyon californicum, but all plants except C. cuneatus decreased (P < 0.05) CH₄ production. With HC diet, all species except A. fasciculatum decreased (P < 0.01) total gas produced. Total volatile fatty acids (VFA) produced, molar proportions of acetate, propionate and butyrate, and the acetate:propionate (A:P) ratio were unaffected by chaparral addition to both HC and LC diets. Increased concentrations of A. fasciculatum and E. californicum decreased (linear; P < 0.05) fermentability and productions of CH₄ and NH₃‐N. CONCLUSION: Among all chaparral species investigated A. fasciculatum and E. californicum added as 10% of LC diet showed some potential to exert beneficial effects on rumen microbial fermentation. © Her Majesty the Queen in Right of Canada 2012     

Effects of simulated gastric and intestinal digestion on chitooligosaccharides in two in vitro models

Chitooligosaccharides (COS) with different degree of polymerisation (DP) have different physiological activities such as anti-tumour and anti-hyperlipidemia activities. However, the digestive process might lead to the change of DP of COS as well as cause the change of physiological activities in vivo. In this study, two in vitro digestion models (static and dynamic) were used to investigate digestion behaviours of COS and the influencing factors during digestion with or without food matrix. The results showed that COS with DP 2–5 were indigestible and COS with DP 6–10 degraded with time during gastric and intestinal digestion. Pepsin, pancreatin and lipase were the main factors leading to degradation. Food matrix could protect COS with DP 6–10 from degradation during gastric digestion. However, the degradation of COS with DP 6–10 accelerated and the degradation of COS with DP 5 occurred during intestinal digestion with food matrix due to pancreatin, lipase and bile salt.     

In vitro degradation of 10 mono‐ and sesquiterpenes of plant origin by caprine rumen micro‐organisms

The extent of disappearance of 10 mono‐ and sesquiterpenes in presence of mixed rumen micro‐organisms has been measured in 24‐h batch cultures. The molecules that were tested are frequently found in the plants consumed by ruminants in highland pastures (limonene, β‐myrcene, β‐ocimene, α‐pinene, sabinene, γ‐terpinene and thymol) or are potential markers of the diet (camphene, β‐caryophyllene and α‐copaene). All terpenes were tested at 2 µL mL^?1, except α‐copaene and thymol, which were tested at 0.9 µL mL^?1 and 2 mg mL^?1, respectively. Camphene and thymol were not degraded to a significant extent. The disappearance of part of β‐caryophyllene, (?)‐limonene and γ‐terpinene could not be attributed to the direct action of rumen micro‐organisms but rather than to an effect of the extracellular medium. In contrast, a third group of one sesquiterpene (α‐copaene) and four monoterpenes (myrcene, β‐ocimene, α‐pinene and sabinene) was extensively degraded by rumen micro‐organisms, at rates of 1.6, 4.5, 3.5, 4.8 and 5.4 µmol mL^?1 inoculum day^?1, respectively. The preliminary exposure of rumen micro‐organisms to a specific blend of essential oils compounds, containing mainly thymol, guajacol and limonene, increased the extent of disappearance of γ‐terpinene only. Copyright © 2007 Society of Chemical Industry     

超声-微波协同萃取野樱莓原花青素及体外模拟消化抗氧化活性研究

为研究野樱莓原花青素在模拟体外胃肠消化过程中抗氧化活性的变化。采用超声-微波协同萃取法提取原花青素并探讨了乙醇体积分数、提取时间、液料比和提取温度对原花青素提取率的影响。结果表明,超声-微波协同萃取野樱莓原花青素的最佳工艺条件为乙醇体积分数为60%,提取时间40min,液料比为20∶1mL/g,提取温度为50℃,在此条件下野樱莓原花青素提取率为5.77%±1.01%。模拟体外消化表明野樱莓原花青素消化产物具有较强的抗氧化活性。在模拟口腔唾液消化15min时,野樱莓原花青素的·OH和O₂^-·自由基清除能力达到最强,而O₂^-·在模拟唾液消化过程中无明显变化。在模拟胃液消化1h时·OH和O₂^-·自由基清除率最强,DPPH·自由基清除率在模拟胃液消化2h时达到最强;在模拟小肠消化4h时,野樱莓原花青素的·OH和O₂^-·自由基清除率最强,DPPH·自由基清除率在消化6h时最强。     

超声-微波协同萃取野樱莓原花青素及体外模拟消化抗氧化活性研究

为研究野樱莓原花青素在模拟体外胃肠消化过程中抗氧化活性的变化。采用超声-微波协同萃取法提取原花青素并探讨了乙醇体积分数、提取时间、液料比和提取温度对原花青素提取率的影响。结果表明,超声-微波协同萃取野樱莓原花青素的最佳工艺条件为乙醇体积分数为60%,提取时间40min,液料比为20∶1mL/g,提取温度为50℃,在此条件下野樱莓原花青素提取率为5.77%±1.01%。模拟体外消化表明野樱莓原花青素消化产物具有较强的抗氧化活性。在模拟口腔唾液消化15min时,野樱莓原花青素的·OH和O₂^-·自由基清除能力达到最强,而O₂^-·在模拟唾液消化过程中无明显变化。在模拟胃液消化1h时·OH和O₂^-·自由基清除率最强,DPPH·自由基清除率在模拟胃液消化2h时达到最强;在模拟小肠消化4h时,野樱莓原花青素的·OH和O₂^-·自由基清除率最强,DPPH·自由基清除率在消化6h时最强。     

Ruminal digestion and fermentation of high-producing dairy cows with three different feeding systems combining pasture and total mixed rations

Six multiparous Holstein cows fitted with rumen cannulas were used to study the effect of three feeding systems combining pasture and total mixed rations (TMR) on ruminal digestion in a 21-wk repeated measures experiment. The three treatments were: 1) pasture plus concentrate (PC), 2) pasture plus partial TMR (pTMR), and 3) TMR (nonpasture). Ruminal NH3-N concentration was lower on both the pTMR and TMR treatments (10.2 +/- 0.5 mg/dL) than on the PC treatment (19.9 +/- 0.5 mg/dL). Ruminal pH was not affected by treatments and averaged 5.87. Neither total volatile fatty acid concentration (137.5 mmol/L) nor individual volatile fatty acid proportions (63.1,20.6, and 12.0 mol/ 100 mol for acetate, propionate, and butyrate, respectively) differed among treatments. The pTMR treatment reduced the total potentially degradable fraction of dry matter (85.5 vs. 82.3%) and the potentially digestible fraction of neutral detergent fiber (82.1 vs. 74.9%) of pasture compared to the PC treatment. Ruminal NH3-N losses were reduced when combining pasture and TMR; however this combination decreased the ruminal digestion of pasture, indicating the presence of associative effects in the rumen.     

Selection of barley grain affects ruminal fermentation, starch digestibility, and productivity of lactating dairy cows

The objective of this study was to evaluate the effects of 2 lots of barley grain cultivars differing in expected ruminal starch degradation on dry matter (DM) intake, ruminal fermentation, ruminal and total tract digestibility, and milk production of dairy cows when provided at 2 concentrations in the diet. Four primiparous ruminally cannulated (123 ± 69 d in milk; mean ± SD) and 4 multiparous ruminally and duodenally cannulated (46 ± 14 d in milk) cows were used in a 4 × 4 Latin Square design with a 2 × 2 factorial arrangement of treatments with 16-d periods. Primiparous and multiparous cows were assigned to different squares. Treatments were 2 dietary starch concentrations (30 vs. 23% of dietary DM) and 2 lots of barley grain cultivars (Xena vs. Dillon) differing in expected ruminal starch degradation. Xena had higher starch concentration (58.7 vs. 50.0%) and greater in vitro 6-h starch digestibility (78.0 vs. 73.5%) compared with Dillon. All experimental diets were formulated to supply 18.3% crude protein and 20.0% forage neutral detergent fiber. Dry matter intake and milk yield were not affected by treatment. Milk fat concentration (3.55 vs. 3.29%) was greater for cows fed Dillon compared with Xena, but was not affected by dietary starch concentration. Ruminal starch digestion was greater for cows fed high-starch diets compared with those fed low-starch diets (4.55 vs. 2.49 kg/d), and tended to be greater for cows fed Xena compared with those fed Dillon (3.85 vs. 3.19 kg/d). Ruminal acetate concentration was lower, and propionate concentration was greater, for cows fed Xena or high-starch diets compared with cows fed Dillon or low-starch diets, respectively. Furthermore, cows fed Xena or high-starch diets had longer duration that ruminal pH was below 5.8 (6.6 vs. 4.0 and 6.4 vs. 4.2 h/d) and greater total tract starch digestibility (94.3 vs. 93.0 and 94.3 vs. 93.0%) compared with cows fed Dillon or low-starch diets, respectively. These results demonstrate that selection of barley grain can affect milk fat production and rumen fermentation to an extent at least as great as changes in dietary starch concentration.     

玉米淀粉-脂质复合物对曲奇饼干体外消化和血糖生成指数的影响

目的 探究玉米淀粉-脂质复合物的结构和消化特性以及对曲奇饼干的体外消化特性与血糖生成指数的影响。方法 利用水热法制备了制备不同脂质(包括饱和脂肪酸与不饱和脂肪酸)与玉米直链淀粉的复合物, 通过傅里叶红外光谱仪(fourier transform infrared spectroscopy, FT-IR)与X-射线衍射(X-ray diffractometer, XRD)探究了淀粉分子短程和长程有序性。结果 研究表明, 淀粉-脂质复合物的形成使快消化淀粉含量显著降低, 慢消化淀粉和抗性淀粉含量显著增加。水热法制备中通过疏水相互作用得到的淀粉-脂质复合物利用氢键链接使其结构更加稳定, 体外消化速率呈降低趋势。其中玉米淀粉-卵磷脂复合物、玉米淀粉-硬脂酸复合物与玉米淀粉-肉豆蔻酸复合物为 V+B 型晶体结构, 玉米淀粉-大豆油复合物与玉米淀粉-玉米油复合物的晶型结构未发生改变。在五种淀粉-脂质复合物中, 玉米淀粉-卵磷脂复合物的水解率最低, 水解指数预估血糖指数分别为44.65%、64.22%, 所对应的曲奇饼干的水解指数与预估血糖指数也最低, 分别为51.68%、68.08%。结论 表明玉米淀粉-卵磷脂复合物适合作为新型淀粉-脂质复合物用于开发具有低血糖指数的饼干食品。     

Effect of inhibitor concentration and end-product accumulation on estimates of ruminal in vitro protein degradation

Effects of varying the concentrations of hydrazine sulfate (HS) and chloramphenicol (CAP), inhibitors of microbial-N uptake and protein synthesis, on rates of protein degradation estimated from net appearance of NH3 and total amino acids (TAA) were studied in a ruminal in vitro fermentation system. Without inhibitors, recoveries of N added as NH3 and TAA were 4 and 6% after 4-h incubations, and apparent degradation rates estimated from release of NH3 and TAA for casein, solvent soybean meal (SSBM), and expeller soybean meal (ESBM) approached 0. Increasing inhibitor concentrations from the standard amounts of 1 mM HS plus 30 mg of CAP/L to 2 mM HS plus 90 mg of CAP/ L gave rise to numerically greater N recoveries and degradation rates, but these differences were not statistically significant. Compared with the standard inhibitor concentrations, use of 2 mM HS, without CAP, yielded similar recoveries and rates, but 30 or 90 mg of CAP/L, without HS, was not satisfactory. Versus that with 1 mM HS plus 30 mg of CAP/L, media containing 2 mM HS plus 90 mg of CAP/L gave increased TAA recoveries and higher rates for casein, but not SSBM, in the presence of added starch. Faster degradation rates were obtained for casein, but slower rates for SSBM and ESBM, in Sweden versus Wisconsin using inocula from cows fed different diets but with similar CP and energy contents. Differences in microbial catabolism of peptides may account for differences in degradation rates observed between Sweden and Wisconsin. Adding NH3 plus free and peptide-bound amino acids to the inoculum reduced apparent degradation rates, possibly via end-product inhibition. Analysis of data from multiple time-point incubations indicated that casein degradation followed simple, first-order kinetics, while a biexponential model fitted degradation patterns for both SSBM and ESBM.     

Effects of cinnamon leaf, oregano and sweet orange essential oils on fermentation and aerobic stability of barley silage

BACKGROUND: Silage additives are marketed with the primary aim of improving the fermentation and/or aerobic stability of silage. The objective of this study was to evaluate the impact of three different essential oils (EOs; cinnamon leaf (CIN), oregano (ORE) and sweet orange (SO)) on the fermentation characteristics and stability of barley silage. Chopped whole‐plant barley (Hordem vulgare L.) forage was ensiled either untreated (0 mg kg^?1 dry matter (DM)) or treated with CIN, ORE or SO (37.5, 75 and 120 mg kg^?1 DM). RESULTS: Moulds were not detected in any treatments, including the control, after 7 days of air exposure. All EOs at a concentration of 120 mg kg^?1 silage DM decreased (P = 0.001) yeast populations in comparison with the control during air exposure. Net gas, methane and ammonia concentrations in vitro did not differ among treatments. Changes in volatile fatty acid concentrations were small, and in situ data showed no changes in DM and neutral detergent fibre digestion rates for CIN, ORE or SO at concentrations up to 120 mg kg^?1 DM. CONCLUSION: The findings from this study show that a concentration of 120 mg EO kg^?1 DM decreased yeast counts during aerobic stability tests. However, all EO treatments had minimal effects on data from in vitro and in situ incubations. Copyright © 2011 Crown in the right of Canada. Published by JohnWiley & Sons, Ltd     

Effects of fatty acid supplements on ruminal and total tract nutrient digestion in lactating dairy cows

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on ruminal digestion kinetics, and ruminal and postruminal nutrient digestion. Eight early lactation ruminally and duodenally cannulated cows (77 ± 12 days in milk, mean ± SD) were used in a replicated 4 × 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from supplemented saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). All rations contained identical forage and concentrate components including 37.2% forage and 13.5% cottonseed. Saturated FS linearly decreased ruminal digestibility of dry matter and organic matter and linearly decreased ruminal neutral detergent fiber (NDF) digestibility. The reduction in ruminal NDF digestibility was because of a linear decrease in digestion rate and a linear increase in passage rate of potentially digestible NDF with increasing saturated FS. Total tract digestibility of NDF was not different between treatments because of compensatory postruminal digestion. Ruminal fatty acid and C18 fatty acid digestibility tended to increase linearly with increasing unsaturated FS, and postruminal C18 fatty acid digestibility decreased with increasing saturated FS. Saturated FS linearly decreased ruminal organic matter digestibility and decreased intestinal long-chain fatty acid digestibility, although differences in fatty acid digestibility may be partially explained by fatty acid intake.