Linoleic Acid In Milk Research Articles

Effects of extruded linseed supplementation on n-3 fatty acids and conjugated linoleic acid in milk and cheese from ewes

The objective of this study was to assess the effects of dietary supplementation of extruded linseed on animal performance and fatty acid (FA) profile of ewe milk for the production of n-3 FA- and conjugated linoleic acid-enriched cheeses. A Manchega ewe flock (300 animals) receiving a 60:40 forage:concentrate diet was divided into 3 groups supplemented with 0, 6, and 12g of extruded linseed/100g of dry matter for the control, low, and high extruded linseed diets, respectively. Bulk and individual milk samples from 5 dairy ewes per group were monitored at 7, 14, 28, 45, and 60 d following supplementation. Manchego cheeses were made with bulk milk from the 3 treatment groups. Milk yield increased in dairy ewes receiving extruded linseed. Milk protein, fat, and total solids contents were not affected by linseed supplementation. Milk contents of α-linolenic acid increased from 0.36 with the control diet to 1.91% total FA with the high extruded linseed diet. Similarly, cis-9 trans-11 C18:2 rose from 0.73 to 2.33% and its precursor in the mammary gland, trans-11 C18:1, increased from 1.55 to 5.76% of total FA. This pattern occurred with no significant modification of the levels of trans-10 C18:1 and trans-10 cis-12 C18:2 FA. Furthermore, the high extruded linseed diet reduced C12:0 (−30%), C14:0 (−15%) and C16:0 (−28%), thus significantly diminishing the atherogenicity index of milk. The response to linseed supplementation was persistently maintained during the entire study. Acceptability attributes of n-3-enriched versus control cheeses ripened for 3 mo were not affected. Therefore, extruded linseed supplementation seems a plausible strategy to improve animal performance and nutritional quality of dairy lipids in milk and cheese from ewes.

Case Study

A 100-cow dairy herd was investigated for chronic milk fat depression. Implementation of traditional measures to reduce the impact of altered rumen fermentation by increasing physically effective fiber intake only partially alleviated the problem. A field study was then performed to quantify the effect of reducing polyunsaturated fatty acid intake on milk fat and milk fatty acid profile. A total of 22 cows randomly selected in the herd were enrolled in the study. Dietary intake of linoleic acid was decreased from 0.609 lb (277 g) to 0.519 lb (236 g) per cow per day by modifying the ration. The effect of ration reformulation was analyzed in linear regression models using repeated measures within cows. Milk production, milk composition, and milk fatty acid profile data were considered the outcomes. Ration reformulation was associated with an increase of 0.3 percentage points of milk fat (P<0.01) and a concomitant decrease of trans-10, cis-12 conjugated linoleic acid in milk (P<0.001). Results from this case study indicate a small reduction of polyunsaturated fatty acid intake may mitigate milk fat depression in dairy cows.

Feeding Soybean Oil to Dairy Goats Increases Conjugated Linoleic Acid in Milk

A total of 24 Murciano-Granadina dairy goats milked once daily throughout lactation were used to study the effects of including soybean oil (SBO) in the diet on lactational performance and milk fatty acid (FA) content, particularly conjugated linoleic acid (CLA) and trans-vaccenic acid (trans-11 C18:1, TVA). Three weeks after parturition, goats were allocated to 2 balanced groups according to lactation number, body weight, and daily milk yield, and were kept in separate pens. The experiment consisted of a 2-period (28 d each) crossover with 2 dietary treatments: control and SBO (6% as fed in the concentrate). Goats were fed dehydrated fescue (ad libitum), alfalfa pellets (0.5 kg/d), and concentrate (1 kg/d) to which the SBO was or was not added. Forage was fed in the pens, and concentrate was fed individually in 2 equal portions at milking (0900h) and in the afternoon (1700h). Final SBO content in the consumed SBO diet was 2.5% (dry matter basis). Diets were isonitrogenous (17.4% crude protein), but their total FA content varied from 2.2% (control) to 4.6% (SBO). There was no effect of SBO on dry matter intake, milk yield, energy-corrected milk, body weight, or body condition score. Compared with the control diet, feeding SBO increased milk fat content (4.57 vs. 5.24%) and yield as well as total solids content. Soybean oil had no effect on milk crude and true protein contents, but it reduced milk casein content (2.48 vs. 2.34%). Short- and medium-chain FA decreased by feeding SBO, whereas long-chain FA increased. Feeding preformed linoleic acid through SBO increased milk concentrations of linoleic, oleic, and stearic FA but reduced levels of linolenic and palmitic FA. As a consequence, feeding SBO decreased the saturated-to-unsaturated FA ratio and the atherogenicity index. Compared with the control treatment, milk contents of cis-9, trans-11 CLA (0.68 vs. 2.03%) and TVA (2.04 vs. 6.41%) in the SBO treatment increased by approximately 200%. In conclusion, feeding a moderate dose of SBO to dairy goats was a useful way to increase milk fat, CLA, and TVA contents in milk and to reduce the atherogenicity index without negative effects on intake, milk yield, and protein content.

Dietary manipulations to increase the concentration of conjugated linoleic acid in milk

Ten Holstein cows between 8 and 12 weeks in lactation were used to investigate the effect of feeding full-fat soybean, full-fat sunflower, and a Ca-soap source (Profat) on the conjugated linoleic acid (CLA) content of milk. Cows were fed the experimental fat sources in the dosage of 500 g crude fat daily. The results indicated that milk CLA content increased in relation to the linoleic acid concentration of experimental fat supplements, namely full-fat sunflower increased the most and Profat increased the least the CLA concentration in milk. The strength of the correlation was r=0.62 between the linoleic acid concentration in feed and the CLA content in milk. The strength of correlation increased to r=0.69 when both linoleic acid and linolenic acid concentration of feed were used in the calculation. Considering milk production and the daily production of CLA in milk, the following equation described the relationship between the linoleic acid content of fat supplements and CLA concentration in milk: x=167....

Effectiveness of Oils Rich in Linoleic and Linolenic Acids to Enhance Conjugated Linoleic Acid in Milk from Dairy Cows

Forty Holstein dairy cows were used to determine the effectiveness of linoleic or linolenic-rich oils to enhance C18:2cis-9, trans-11 conjugated linoleic acid (CLA) and C18:1trans-11 (vaccenic acid; VA) in milk. The experimental design was a complete randomized design for 9 wk with measurements made during the last 6 wk. Cows were fed a basal diet containing 59% forage (control) or a basal diet supplemented with either 4% soybean oil (SO), 4% flaxseed oil (FO), or 2% soybean oil plus 2% flaxseed oil (SFO) on a dry matter basis. Total fatty acids in the diet were 3.27, 7.47, 7.61, and 7.50 g/100g in control, SO, FO, and SFO diets, respectively. Feed intake, energy-corrected milk (ECM) yield, and ECM produced/kg of feed intake were similar among treatments. The proportions of VA were increased by 318, 105, and 206% in milk fat from cows in the SO, FO, and SFO groups compared with cows in the control group. Similar increases in C18:2cis-9, trans-11 CLA were 273, 150, and 183% in SO, FO, and SFO treatments, respectively. Under similar feeding conditions, oils rich in linoleic acid (soybean oil) were more effective in enhancing VA and C18:2cis-9, trans-11 CLA in milk fat than oils containing linolenic acid (flaxseed oil) in dairy cows fed high-forage diets (59% forage). The effects of mixing linoleic and linolenic acids (50:50) on enhancing VA and C18:2cis-9, trans-11 CLA were additive, but not greater than when fed separately. Increasing the proportion of healthy fatty acids (VA and CLA) by feeding soybean or flaxseed oil would result in milk with higher nutritive and therapeutic value.

Supplementing total mixed rations with pasture increase the content of conjugated linoleic acid in milk

Forty-five Holsteins cows in early to mid-lactation were used to evaluate the milk fatty acid composition of three feeding systems that combined pasture and total mixed ration (TMR) in a 19-week experiment. The three treatments were: (1) pasture plus concentrate (PC), (2) pasture plus TMR (PTMR), and (3) TMR. The content of short- and medium-chain fatty acids (FA) decreased from 11.3 to 9.0 g/100 g of FA and from 40.5 to 36.5 g/100 g, respectively, from the TMR to the PC treatment. The content of long-chain FA increased from 47.7 to 53.8 g/100 g as the amount of pasture dry matter (DM) intake increased from the TMR to the PC treatment. The content of saturated FA was lower (55.5 g/100 g versus 60.1 g/100 g) and the content of unsaturated FA was higher (43.9 g/100 g versus 38.6 g/100 g) in the PC treatment versus the PTMR and TMR treatments. As the amount of pasture DM intake increased from the TMR to the PC treatment, the content of conjugated linoleic acid (CLA) increased from 0.59 to 1.21 g/100 g, resulting in a 42 and 105% increase for the PC treatment compared to the PTMR and TMR treatments, respectively. The increase in CLA content in milk with inclusion of pasture was primarily associated with a higher intake of C18:3 and a higher delivery of trans11 C18:1 to the mammary gland.

Milk production and milk composition of dairy cows fed Lac100® or whole flaxseed

Cows were fed whole flaxseed or calcium salts of soybean oil as a fat source. Cows fed flaxseed had lower (P < 0.01) milk yield and higher (P < 0.01) percentages of fat and protein than cows fed calcium salts. Feeding whole flaxseed and calcium salts of soybean oil increased, respectively, the concentrations of alpha-linolenic acid and conjugated linoleic acid in milk. Key words: Flaxseed, fatty acids, fat supplement

Factors Affecting Conjugated Linoleic Acid Content in Milk and Meat

Conjugated linoleic acid (CLA) has been recently studied mainly because of its potential in protecting against cancer, atherogenesis, and diabetes. Conjugated linoleic acid (CLA) is a collective term for a series of conjugated dienoic positional and geometrical isomers of linoleic acid, which are found in relative abundance in milk and tissue fat of ruminants compared with other foods. The cis-9, trans-11 isomer is the principle dietary form of CLA found in ruminant products and is produced by partial ruminal biohydrogenation of linoleic acid or by endogenous synthesis in the tissues themselves. The CLA content in milk and meat is affected by several factors, such as animal's breed, age, diet, and management factors related to feed supplements affecting the diet. Conjugated linoleic acid in milk or meat has been shown to be a stable compound under normal cooking and storage conditions. Total CLA content in milk or dairy products ranges from 0.34 to 1.07% of total fat. Total CLA content in raw or processed beef ranges from 0.12 to 0.68% of total fat. It is currently estimated that the average adult consumes only one third to one half of the amount of CLA that has been shown to reduce cancer in animal studies. For this reason, increasing the CLA contents of milk and meat has the potential to raise the nutritive and therapeutic values of dairy products and meat.

Effects of Dietary Sources of Vegetable Oils on Performance of High-Yielding Lactating Cows and Conjugated Linoleic Acids in Milk

This study was conducted to examine the effects of dietary supplementation with vegetable oils on performance of high-yielding lactating cows and conjugated linoleic acid (CLA) content in milk fat. Twelve lactating Holstein cows in early lactation (30 to 45 d postpartum) were used in a triple 4×4 Latin square design. In each period, the cows in each group were fed the same basal diet and received one of the following treatments: 1) control (without oil), 2) 500g of cottonseed oil, 3) 500g of soybean oil, and 4) 500g of corn oil. Each experimental period lasted for 3 wk, with the first 2 wk used for adaptation to the diet. Supplementation with vegetable oils tended to increase milk yield, with the highest milk yield in the cottonseed oil group (35.0 kg/d), compared with the control (34.4 kg/d). Milk fat percentage was decreased, but there were few effects on percentage and yield of milk protein as well as milk fat yield. The cows fed added soybean oil produced milk with the highest content of trans-11C18:1 (23.8 mg/g of fat), which was twice that of the control (12.6 mg/g of fat). Content of cis-9, trans-11 CLA in milk fat increased from 3.5 mg/g in the control to 6.0, 7.1, and 10.3 mg/g for the cows fed oils from cottonseed, corn, and soybean, respectively. A significant linear relationship existed between trans-11C18:1 and cis-9, trans-11 CLA. Supplementation with oils doubled the content of total fatty acids in blood plasma, with little difference between different vegetable oil sources. Octadecenoic acid content was significantly higher in blood plasma of animals fed added oils from cottonseed and soybean than those fed with corn oil and control. The plasma trans-11C18:1 content was significantly higher in the oil-added animals than in control. Supplementation of vegetable oils tended to improve milk production of lactating cows, and the CLA content in milk fat was significantly increased. Soybean oil seemed to be the optimal source to increase CLA production.

Seasonal Differences Of The Nutrient Content Of The Milk Of The Cows Of Fulani Pastoralist In Northern Nigeria

The Fulani are semi-nomadic pastoralist who inhabited western Sahel from Mauritania and Senegal across Mali, Burkina Faso, the Republic of Niger and Northern Nigeria to Chad. Their culture is centred around cattle and dairy products contribute substantially to the diets of Fulani children and adults. Having found in previous study that the milk fat of lactating Fulani women contained relatively low proportions of critical n-3 fatty acid docosahexaenoic acid and the essential fatty-acid, linoleic acid, we were interested in the general issue of the nutrient quality of the milk of Fulani cows and specifically in the question of the essential fatty acid and n-3 and n-6 polyunsaturated fatty acid content of the milk fat they produce. Since the pasture upon which Fulani cattle graze varies markedly between the two main seasons in the western Sahel, namely the cold-dry season (November-April) and the rainy season (May-September) we collected milk samples from seven cows during April and from another four cows during the month of August and analyzed these milk specimens for their content of fatty acids, amino acids, and minerals and trace elements. We found significant season-dependent differences in the linoleic acid content of the milk lipid fraction; the proportion of linoleic acid in milk produced during the cold-dry season was 2.19% whereas that of cow milk during the rainy season was 0.65% (p

Manipulating the Dietary Cation-Anion Difference via Drenching to Early-Lactation Dairy Cows Grazing Pasture

Diets offered to grazing dairy cows can vary considerably in their dietary cation-anion difference (DCAD) and are often well in excess of what has been considered optimal. The effects of a range of DCAD on the health and production of pasture-based dairy cows in early lactation was examined in a randomized block design. Four groups of 8 cows were offered a generous allowance of pasture (45±6 kg/d of dry matter (DM) per cow) for 35 d and achieved mean pasture intakes of approximately 17 kg/d of DM per cow. Cows were drenched twice daily with varying combinations of mineral compounds to alter the DCAD. Dietary cation-anion difference ranged from +23 to +88 mEq/100g of DM. A linear increase in blood pH and HCO3− concentration and blood base excess, and a curvilinear increase in the pH of urine with increasing DCAD indicated a nonrespiratory effect of DCAD on metabolic acid-base balance. Plasma concentrations of Mg, K, and Cl declined as DCAD increased, whereas Na concentration increased. Urinary excretion of Ca decreased linearly as DCAD increased, although the data suggest that the decline may be curvilinear. These results in conjunction with the increased concentrations of ionized Ca suggest that intestinal absorption of Ca or bone resorption, or both, increased as DCAD declined. Dry matter intake, as measured using indigestible markers, was not significantly affected by DCAD. However, the linear increase in the yield of linolenic acid, vaccenic acid, and cis-9, trans-11 conjugated linoleic acid in milk, as DCAD increased is consistent with a positive effect of DCAD on DM intake. Increasing DCAD did not significantly affect milk yield or milk protein, but the concentration and yield of milk fat linearly increased with increasing DCAD. The increased milk fat yield was predominantly a result of increased de novo synthesis in the mammary epithelial cells, although an increase in the yield of preformed fatty acids also occurred. Milk production results suggest that DCAD for optimal production on pasture diets may be higher than the +20 mEq/100g of DM previously identified for total mixed rations.

Use of principal component analysis to investigate the origin of heptadecenoic and conjugated linoleic acids in milk.

The aim of this paper was the application of principal component analysis (PCA) 1) to elucidate mutual metabolic relationships between milk fatty acids (FA) and 2) to illustrate the origin of milk FA, in particular C17:1 and cis-9,trans-11 conjugated linoleic acid. Data were combined from 3 experiments with lactating Holstein-Friesian cows offered diets based on grass or legume silage and concentrates. Loading plots of PCA based on milk FA concentrations showed 4 groups of milk FA, having similar precursors or metabolic pathways in the rumen and/or mammary gland: medium-chain saturated FA, de novo synthesized from acetate and beta-hydroxybutyrate; monoenoic milk FA, products of delta9-desaturase activity in the mammary gland; odd chain FA of rumen microbial origin and C18:0, n-6 C18:2, and n-3 C18:3 of dietary origin or the result of rumen biohydrogenation. Loading plots of PCA based on both milk and duodenal FA concentrations as well as on milk FA yields and duodenal FA flows further illustrated the importance of postabsorptive synthesis of the milk medium chain saturated and monoenoic FA and the direct absorption from the blood stream of odd chain FA, C18:0, n-6 C18:2, and n-3 C18:3. In all loading plots, milk oleic acid (C18:1) appeared intermediate between clusters of 18-carbon FA and monoenoic FA, illustrating its dual (dietary and endogenous production) origin. Milk C17:1 was suggested to be a desaturation product of C17:0, in common with other milk monoenoic FA. Finally, the PCA technique, based on milk FA patterns of one experiment, was applied to investigate factors determining cis-9,trans-11 conjugated linoleic acid concentrations in milk. Within the range of diets and cows studied here, we showed changes in cis-9,trans-11 conjugated linoleic acid to be mainly dependent on vaccenic acid supply and to a lesser extent on variation in desaturase activity.

Fish Oil and Extruded Soybeans Fed in Combination Increase Conjugated Linoleic Acids in Milk of Dairy Cows More Than When Fed Separately

Eight multiparous Holstein and four multiparous Brown Swiss (78±43 DIM) cows were used in a 4 x 4 Latin square with 28-d periods to evaluate if feeding fish oil with a source of linoleic acid (extruded soybeans) would stimulate additional amounts of conjugated linoleic acid in milk. Four treatments consisted of a control diet with a 50:50 ratio of forage to concentrate (DM basis), a control diet with 2% added fat from either menhaden fish oil or extruded soybeans, or a combination of fish oil and extruded soybeans each adding 1% fat. DM intake (24.3, 21.6, 24.5, and 22.5 kg/d, for control, fish oil, extruded soybeans, and combination diets, respectively), milk production (32.1, 29.1, 34.6, and 31.1 kg/d), and milk fat content (3.51, 2.79, 3.27, and 3.14%) were lower for cows that consumed either fish oil-containing diet, especially the 2% fish oil diet. The proportion of n-3 fatty acids in milk fat increased similarly among all three fat-supplemented diets. Concentrations of transvaccenic acid (1.00, 4.16, 2.17, and 3.51 g/100g of fatty acids) and cis-9, trans-11 conjugated linoleic acid (0.60, 2.03, 1.16, and 1.82 g/100g of fatty acids) in milk fat increased more with fish oil than with extruded soybeans. When fed the combination diet, these fatty acids were approximately 50% higher than expected for Holsteins, whereas concentrations were similar for Brown Swiss compared with feeding each fat source separately. These data indicated that fish oil modifies ruminal or systemic functions, stimulating increased conversion of linoleic acid into transvaccenic and conjugated linoleic acids.

Transfer of omega-3 linolenic acid and linoleic acid to milk fat from flaxseed or Linola protected with formaldehyde

Four Holstein cows were randomly assigned to four treatments in a 4 × 4 Latin square design. The primary objective of this study was to measure the transfer and increased level of omega-3 fatty acid C18:3 in milk by feeding sup plemental protected fat from flax and, second, to measure the transfer and increase in level of C18:2 by feeding supplemental protected fat from linola. The four dietary treatments were total mixed rations (TMR) plus i) control-no added fat, ii) high levels of protected Linola containing high linoleic acid content, iii) low level of protected flax containing high linoleic acid content and iv) high levels of protected flax containing high linolenic acid content. Linola is a variety of Solin containing approximately 74% linoleic acid, which was developed from flax. These supplements were added to the diet as a top dress and provided 454 g fat (high level) from the protected Linola product, 187 g fat (low level) from the protected flax product and 410 g fat (high level) from the protected flax product. Treatments had no effect on feed intake, milk yield or milk content of fat, protein or solids not fat. Medium chain fatty acids, C12:0 to C16:0, were significantly lower (P < 0.05) in the milk of cows fed supplemental fat. Milk stearic acid (C18:0) was significantly greater in the milk fat from cows fed Linola vs. control, but was unaffected by other dietary treatments. Milk linoleic acid (C18:2) was significantly higher at 10.3% in the milk of cows fed the protected Linola vs. the control at 4.8%. Linolenic acid (C18:3) was not affected by feeding Linola, but was significantly greater in the milk of cows fed the high level of protected flax (6.4% vs. 0.8% in the control). This represents an eightfold increase, while the low level of protected flax diet increased C18:3 by 3.9-fold in milk fat. Supplementing dairy cow diets with a formaldehyde-treated flax product at acceptable levels of fat for high producing cows results in a milk fat high in omega-3-linolenic acid. Key words: Flaxseed, cow, milk, fatty acids, linoleic acid, linolenic acid

Composition and Flavor of Milk and Butter from Cows Fed Fish Oil, Extruded Soybeans, or Their Combination

Milk was collected from eight multiparous Holstein and four multiparous Brown Swiss cows that were distributed into four groups and arranged in a randomized complete block design with four 4-wk periods. The four treatments included a control diet of a 50:50 ratio of forage-to-concentrate; a fish oil diet of the control diet with 2% (on dry matter basis) added fat from menhaden fish oil; a fish oil with extruded soybean diet of the control diet with 1% (on dry matter basis) added fat from menhaden fish oil and 1% (on dry matter basis) added fat from extruded soybeans; and an extruded soybean diet of the control diet with 2% (on dry matter basis) added fat from extruded soybeans. Milk from cows fed control, fish oil, fish oil with extruded soybean, and extruded soybean diets contained 3.31, 2.58, 2.94, and 3.47% fat, respectively. Concentrations of conjugated linoleic acid in milk were highest in the fish oil (2.30 g/100g of fatty acids) and fish oil with extruded soybean (2.17 g/100g of fatty acids) diets compared with the control (0.56 g/100g fatty acids) diet. Milk, cream, butter, and buttermilk from the fish oil, fish oil with extruded soybean, and extruded soybean diets had higher concentrations of transvaccenic acid and unsaturated fatty acids compared with the controls. Butter made from the extruded soybean diet was softest compared with all treatments. An experienced sensory panel found no flavor differences in milks or butters.

Investigation of long-chain polyunsaturated fatty acid metabolism in lactating women by means of stable isotope techniques.

Long-chain polyunsaturated fatty acids are important components of human milk that seem to influence infant development. After oral administration of U-13C-labeled linoleic acid to a lactating woman the recovery of tracer in milk linoleic acid was 6.4%, whereas tracer recovery in dihomo-gamma-linolenic acid (DGLA) was 0.3% and in arachidonic acid (AA), <0.01%. Some 14.9% of linoleic acid intake was converted to breath-CO2. In combination with data on dietary intake and quantitative milk output, we estimate that 23% of milk linoleic acid, 7% of milk dihomo-gamma-linolenic acids and 0.5% of milk arachidonic acid were contributed by direct endogenous conversion and transfer from dietary linoleic acid. These findings lead us to conclude that long-chain polyunsaturated fatty acids for human milk synthesis are produced in the body, but either a relatively low percentage is contributed under these dietary conditions, or there are large body pools for intermediate storage of these fatty acids that are utilized for secretion into milk.

Effects of Fat Source and Copper on Unsaturation of Blood and Milk Triacylglycerol Fatty Acids in Holstein and Jersey Cows

Fatty acid composition of plasma triacylglycerides and milk fat was analyzed from Holstein and Jersey cows with control or depleted copper status and fed roasted whole soybeans or tallow. Conjugated linoleic acid in plasma was higher in Jersey cows. Dietary fat source influenced the proportions of all fatty acids in plasma and in milk, except for conjugated linoleic acid in milk. Feeding soybeans increased plasma C14:1, C18:0, C18:2, and conjugated linoleic acid, and decreased C14:0, C16:0, C16:1, and cis- and trans-C18:1 compared with feeding tallow. Low copper diets decreased C18:0 and increased cis- and trans-C18:1, and conjugated linoleic acid in plasma. A fat source × copper status interaction occurred for cis-C18:1 in plasma. Proportions of C4:0 to C14:0 were higher, and cis16:1, cis- and trans-C18:1, and conjugated linoleic acid were lower in milk fat of Jersey compared with Holstein cows. Generally, the effects of copper depletion were less apparent in milk than in plasma. Copper depletion increased C4:0, trans-C18:1, and conjugated linoleic acid, and decreased C16:1 in milk. Feeding whole soybeans increased C4:0 to C14:0, C18:0, C18:2, and C18:3, and decreased C14:1, C16:0, C16:1, and cis- and trans-C18:1 in milk. Breed × fat interactions occurred for C4:0, C14:1, C16:1, and conjugated linoleic acid in milk. Copper status × fat source interaction occurred for trans-C18:1. The breed × copper status interaction was apparent in milk fat for C16:1 and C18:0 and conjugated linoleic acid in milk. Both C18:0 and trans-C18:1 were desaturated by mammary tissue; however, whereas desaturation of C18:0 was linear, desaturation of trans-C18:1 reached a plateau that could have been caused by presence of the trans-10 isomer, which is not desaturated and was not separated from trans-11C18:1 in our analysis. Comparison of the plasma triacylglycerol fatty acid profile with the milk fat profile was useful to interpret separate events of biohydrogenation in the rumen and desaturation by the mammary gland.

Milk Fat Composition of Holstein and Jersey Cows with Control or Depleted Copper Status and Fed Whole Soybeans or Tallow

We studied effects of breed, dietary fat source, and dietary copper intake as factors known to influence unsaturation of milk fat and its potential for development of spontaneous oxidized flavor in milk. Twelve Holstein and 12 Jersey cows were allotted to three blocks with four cows of each breed. Cows within breed were allotted randomly within blocks and fed control or copperdepleting diets for 2 mo to achieve stable or depleted liver copper stores. Cows then were fed tallow or roasted whole soybeans in a two-period switchback (5 wk per period); during the last week of each period additional vitamin E (2000 IU/d) was added. Copper depletion for 2 mo decreased concentrations of copper in liver. Feed intake and milk yield were influenced only by breed. The proportions of C4:0 to C14:0 and C18:0 in milk fat were higher, whereas C16:1 and cis-C18:1 were lower in Jersey cows. Feeding soybeans increased C4:0 to C14:0, C18:0, C18:2, and C18:3 in milk, and decreased C14:1, C16:0, C16:1, trans-C18:1, and cis-C18:1. Depleted copper status increased conjugated linoleic acid in milk. Several breed x fat source interactions for individual milk fatty acids occurred. Feeding soybeans decreased plasma concentrations of copper and zinc, and increased concentrations of α-tocopherol in plasma and milk. The concentration of zinc was higher in milk of Jersey cows. Depleted copper status tended to increase copper concentration in plasma and decreased copper in milk. Fat source did not influence plasma copper concentration when status was adequate, but plasma copper concentration was higher when tallow was fed to cows with depleted copper status. Supplementing vitamin E increased concentration of α-tocopherol in plasma and milk and decreased concentration of zinc in milk. Factors influencing the potential for oxidized flavor development in milk can be manipulated by changing the diet of the cow.

Effect of Intake of Pasture on Concentrations of Conjugated Linoleic Acid in Milk of Lactating Cows

We examined the effect of intake of fresh pasture on concentrations of conjugated linoleic acid in milk fat. Sixteen Holstein cows were paired and divided into either the control group or the grazing group. The study involved initial, transition, and final periods. During the initial period, all cows consumed a total mixed diet. Cows in the control group were fed the total mixed diet throughout the study, and cows in the grazing group were gradually adjusted to a diet consisting of intensively managed pasture. Performance of cows in the grazing group was significantly reduced from that of cows in the control group during the final period (dry matter intake, 19% less; milk yield, 29.6 vs. 44.1 kg/d; and live weight, 40kg less). During the initial period, when both groups were consuming a total mixed diet, concentrations of conjugated linoleic acid in milk fat were similar (X = 5.1 mg/g of milk fat). As the grazing group was gradually adjusted to pasture, concentrations of conjugated linoleic acid in milk gradually increased. During the final period, when cows in the grazing group were consuming a diet consisting of pasture only, conjugated linoleic acid concentrations in the milk fat were doubled (10.9 vs. 4.6 mg/g of milk fat). Furthermore, results showed the individual consistency of the milk fat content of conjugated linoleic acid over time but also demonstrated substantial variation among individual cows within treatment groups. Overall, this study indicated that the concentration of conjugated linoleic acid in milk fat is enhanced by dietary intake of fresh pasture.

Selenium Content and Glutathione Peroxidase Activity of Milk from Vegetarian and Nonvegetarian Women

The concentration of selenium (Se) in milk samples obtained from 26 lacto-ovo-vegetarian (vegetarian) women was significantly greater (22.2 +/- 0.8 ng/ml) than from 12 nonvegetarian women (16.8 +/- 1.3). Mean GSH-Px activity (EC 1.11.1.9) in milk from vegetarians was 146% of that in milk from nonvegetarians. A significant correlation between GSH-Px activity and Se concentration was observed (r = 0.76). Likewise a significant correlation was observed between milk linoleic acid content and GSH-Px activity (r = 0.68). In undialyzed samples from vegetarian women, most of the increased content of Se was found in fractions containing proteins of 100 kdaltons (kD) or more. The high glutathione peroxidase activity in milk from vegetarians was associated with selenoproteins in the 90 to 100 kD range. A distinct 40 kD Se peak was also detected in milk from vegetarians. There was no difference in Se intake between the two groups of women. Therefore, although data from the present study show that both the quantity and distribution of Se in human milk can be modified by the maternal diet, the increased Se content and GSH-Px activity in milk from vegetarians cannot be explained by an increased Se intake.