Individual milk fatty acids are potential predictors of enteric methane emissions from dairy cows fed a wide range of diets: Approach by meta-analysis

There is a need to quantify methane (CH₄) emissions with alternative methods. For the past decade, milk fatty acids (MFA) could be used as proxies to predict CH₄ emissions from dairy cows because of potential common rumen biochemical pathways. However, equations have been developed based on a narrow range of diets and with limited data. The objectives of this study were to (1) construct a set of empirical models based on individual data of CH₄ emissions and MFA from a large number of lactating dairy cows fed a wide range of diets; (2) further increase the models' level of complexity (from farm to research level) with additional independent variables such as dietary chemical composition (organic matter, neutral detergent fiber, crude protein, starch, and ether extract), dairy performance (milk yield and composition), and animal characteristics (days in milk or body weight); and (3) evaluate the performance of the developed models on independent data sets including measurements from individual animals or average measurements of groups of animals. Prediction equations based only on MFA [C10:0, iso C17:0 + trans-9 C16:1,cis-11 C18:1, and trans-11,cis-15 C18:2 for CH₄ production (g/d); iso C16:0, cis-11 C18:1, trans-10 C18:1, and cis-9,cis-12 C18:2 for CH₄ yield (g/kg of dry matter intake, DMI); and iso C16:0, cis-15 C18:1, and trans-10 + trans-11 C18:1 for CH₄ intensity (g/kg of milk)] had a root mean squared error of 65.1 g/d, 2.8 g/kg of DMI, and 2.9 g/kg of milk, respectively, whereas complex equations that additionally used DMI, dietary neutral detergent fiber, ether extract, days in milk, and body weight had a lower root mean squared error of 46.6 g/d, 2.6 g/kg of DMI, and 2.7 g/kg of milk, respectively). External evaluation with individual or mean data not used for equation development led to variable results. When evaluations were performed using individual cow data from an external data set, accurate predictions of CH₄ production (g/d) were obtained using simple equations based on MFA. Better performance was observed on external evaluation with individual data for the simple equation of CH₄ production (g/d, based on MFA), whereas better performance was observed on external evaluation mean data for the simple equation of CH₄ yield (g/kg of DMI). The performance of evaluation of the models is dependent on the domain of validity of the evaluation data sets used (individual or mean).     

Milk fatty acids in dairy cows fed whole crude linseed, extruded linseed, or linseed oil, and their relationship with methane output

This experiment studied the effect of 3 different physical forms of linseed fatty acids (FA) on cow dairy performance, milk FA secretion and composition, and their relationship with methane output. Eight multiparous, lactating Holstein cows were assigned to 1 of 4 dietary treatments in a replicated 4 × 4 Latin square design: a control diet (C) based on corn silage (59%) and concentrate (35%), and the same diet supplemented with whole crude linseed (CLS), extruded linseed (ELS), or linseed oil (LSO) at the same FA level (5% of dietary dry matter). Each experimental period lasted 4 wk. Dry matter intake was not modified with CLS but was lowered with both ELS and LSO (−3.1 and −5.1 kg/d, respectively) compared with C. Milk yield and milk fat content were similar for LSO and ELS but lower than for C and CLS (19.9 vs. 22.3 kg/d and 33.8 vs. 43.2 g/kg, on average, respectively). Compared with diet C, CLS changed the concentrations of a small number of FA; the main effects were decreases in 8:0 to 16:0 and increases in 18:0 and cis-9 18:1. Compared with diet C (and CLS in most cases), LSO appreciably changed the concentrations of almost all the FA measured; the main effects were decreases in FA from 4:0 to 16:0 and increases in 18:0, trans-11 16:1, all cis and trans 18:1 (except trans-11 18:1), and nonconjugated trans 18:2 isomers. The effect of ELS was either intermediate between those of CLS and LSO or similar to LSO with a few significant exceptions: increases in 17:0 iso; 18:3n-3; trans-11 18:1; cis-9, trans-11 conjugated linoleic acid; and trans-11, trans-13 conjugated linoleic acid and a smaller increase in cis-9 18:1. The most positive correlations (r = 0.87 to 0.91) between milk FA concentrations and methane output were observed for saturated FA from 6:0 to 16:0 and for 10:1, and the most negative correlations (r = −0.86 to −0.90) were observed for trans-16+cis-14 18:1; cis-9, trans-13 18:2; trans-11 16:1; and trans-12 18:1. Thus, milk FA profile can be considered a potential indicator of in vivo methane output in ruminants.     

The effect of dietary fiber level on milk fat concentration and fatty acid profile of cows fed diets containing low levels of polyunsaturated fatty acids

The objective of this study was to investigate the effect of dietary fiber level on milk fat concentration, yield, and fatty acid (FA) profile of cows fed diets low in polyunsaturated fatty acid (PUFA). Six rumen-fistulated Holstein dairy cows (639 ± 51 kg of body weight) were used in the study. Cows were randomly assigned to 1 of 2 dietary treatments, a high fiber (HF; % of dry matter, 40% corn silage, 27% alfalfa silage, 7% alfalfa hay, 18% protein supplement, 4% ground corn, and 4% wheat bran) or a low fiber (LF; % of dry matter, 31% corn silage, 20% alfalfa silage, 5% alfalfa hay, 15% protein supplement, 19% ground wheat, and 10% ground barley) total mixed ration. The diets contained similar levels of PUFA. The experiment was conducted over a period of 4 wk. Ruminal pH was continuously recorded and milk samples were collected 3 times a week. Milk yield and dry matter intake were recorded daily. The rumen fluid in cows receiving the LF diet was below pH 5.6 for a longer duration than in cows receiving the HF diet (357 vs. 103 min/d). Neither diet nor diet by week interaction had an effect on milk yield (kg/d), milk fat concentration and yield, or milk protein concentration and yield. During wk 4, milk fat concentration and milk fat yield were high and not different between treatments (4.30% and 1.36 kg/d for the HF treatment and 4.31% and 1.33 kg/d for the LF treatment, respectively). Cows receiving the LF diet had greater milk concentrations (g/100 g of FA) of 7:0; 9:0; 10:0; 11:0; 12:0; 12:1; 13:0; 15:0; linoleic acid; FA <C16; and PUFA; and lower concentrations of iso 15:0; 18:0; trans-9 18:1; cis-9, trans-11 conjugated linoleic acid (CLA); trans-9, cis-12 18:2; 20:0; and cis-9 20:1 compared with cows receiving the HF diet. Milk concentrations (g/100 g of FA) of total trans 18:1; trans-10 18:1; trans-11 18:1; trans-10, cis-12 CLA, and trans-9, cis-11 CLA were not different between treatments. The study demonstrated that cows fed a diet low in fiber and low in PUFA may exhibit subacute ruminal acidosis and moderate changes to milk fatty acid profile but without concomitant milk fat depression. The changes in FA profile may be useful for the diagnosis of SARA even in the absence of milk fat depression.     

Milk saturated fatty acids,odd- and branched-chain fatty acids,and isomers of C18:1, C18:2, and C18:3n-3 according to their duodenal flows in dairy cows: A meta-analysis approach

We sought to establish predictive response models of milk fatty acid (FA) yields or concentrations from their respective duodenal flow, rumen digestive parameters, or diet characteristics in dairy cows, with a special focus on cis and trans isomers of C18:1, C18:2, odd- and branched FA, and mammary de novo synthesized FA. This meta-analysis was carried out using data from trials with nature of forage, percentage of concentrate, supplementation of diets with vegetable oils or seeds, and marine products' animal fats as experimental factors. The data set included 34 published papers representing 50 experiments with 142 treatments. Increasing duodenal C18 FA flow induced a quadratic increase in milk total C18 yield and a linear decrease in milk C4:0 to C14:0 concentration. Intra-experimental predictive response models of individual milk cis C18:1 isomers (Δ 11 to 15 position) from their respective duodenal flows had coefficients of determination (R²) ranging from 0.74 to 0.99, with root mean square error varying from 0.19 to 0.96 g/d, 0.02 to 0.10% of total FA, and 0.03 to 0.29% of C18 FA. Models predicting milk trans C18:1 isomer yields or concentrations had R² greater than 0.90 (except for trans-4 and trans-10 C18:1) with root mean square error varying from less than 0.1 to 5.2 g/d. Linear regressions for C18:2n-6, trans-10,cis-12 CLA, and trans-11,trans-13 CLA were calculated according to their respective duodenal flows. Quadratic models of milk C18:3n-3 yield or concentration from its duodenal flow had R² values above 0.97. Models of amounts desaturated from C18:0 into cis-9 C18:1 and trans-11 C18:1 into cis-9,trans-11 CLA indicated that the contribution of C18:0 and trans-11 C18:1 desaturation to respective cis-9 C18:1 and cis-9,trans-11 CLA yields in milk fat was 83.8% (±0.75) and 86.8% (±2.8). Furthermore, when cows were fed marine products, our results could indicate a lower mammary uptake of C18:0 and trans-11 C18:1 in proportion to their respective duodenal flow, with no associated change in mammary Δ⁹-desaturase activity. Yields or concentrations of C15:0, C17:0, iso-C15:0, iso-C17:0, anteiso-C15:0, and anteiso-C17:0 were dependent on their respective duodenal flow or concentration at duodenum, but synthesis of these FA from C3 units for linear-chain odd FA, and from C2 units for branched-chain FA was suggested, respectively. Several milk C18 FA concentrations were closely related to their duodenal concentrations with slopes of the linear models close to the bisector; this could reflect a priority for the use of these duodenal C18 FA by the mammary gland to favor their high concentration in plasma triglycerides and nonesterified FA, which are preferentially taken up by the mammary gland.     

Long-chain fatty acid metabolism in dairy cows: a meta-analysis of milk fatty acid yield in relation to duodenal flows and de novo synthesis

This study is a meta-analysis of the response of milk long-chain fatty acid (FA) yield and composition to lipid supply, based on published experiments reporting duodenal FA flows or duodenal lipid infusions and milk FA composition (i.e., 39 experiments reporting 139 experimental treatments). Analysis of these data underlined the interdependence between milk yields of C18 and short- and medium-chain (C4 to C16) FA. Lipid supplementation (producing an increase in duodenal C18 flow) decreased linearly milk C4 to C16 yield (−0.26 g of C4 to C16 produced per gram of duodenal C18 flow increase) and increased quadratically milk C18 yield. When these 2 effects increased the percentage of C18 in milk FA up to a threshold value (around 52% of total FA), then milk C18 yield was limited by C4 to C16 yield, decreasing the C18 transfer efficiency from duodenum to milk with high-lipid diets. Moreover, for a given duodenal C18 flow, a decrease in milk C4 to C16 yield induced a decrease in milk C18 yield. Despite high variations in C18 transfer efficiency between duodenum and milk, for a given experimental condition, the percentages of C18 FA in milk total C18 could be predicted from their percentages in duodenal C18, and the percentages at the duodenum and in milk were very similar when mammary desaturation was taken into account (i.e., considering the sums of substrates and products of mammary desaturase). The estimated amounts of 18:0, trans-11-, and trans-13-18:1 desaturated by the mammary gland were a linear function of their mammary uptake, and mammary desaturation was responsible for 80, 95, and 81%, respectively, of the yield of their products (i.e., cis-9-18:1; cis-9, trans-11-, and cis-9, trans-13-18:2). Thus, mammary FA desaturation capacity did not seem to be a limiting factor in the experimental conditions published so far.     

Effect of unsaturated fatty acids and triglycerides from soybeans on milk fat synthesis and biohydrogenation intermediates in dairy cattle

Increased rumen unsaturated fatty acid (FA) load is a risk factor for milk fat depression. This study evaluated if increasing the amount of unsaturated FA in the diet as triglycerides or free FA affected feed intake, yield of milk and milk components, and feed efficiency. Eighteen Holstein cows (132 ± 75 d in milk) were used in a replicated 3 × 3 Latin square design. Treatments were a control (CON) diet, or 1 of 2 unsaturated FA (UFA) treatments supplemented with either soybean oil (FA present as triglycerides; TAG treatment) or soybean FA distillate (FA present as free FA; FFA treatment). The soybean oil contained a higher concentration of cis-9 C18:1 (26.0 vs. 11.8 g/100 g of FA) and lower concentrations of C16:0 (9.6 vs. 15.0 g/100 g of FA) and cis-9,cis-12 C18:2 (50.5 vs. 59.1 g/100 g of FA) than the soybean FA distillate. The soybean oil and soybean FA distillate were included in the diet at 2% dry matter (DM) to replace soyhulls in the CON diet. Treatment periods were 21 d, with the final 4 d used for sample and data collection. The corn silage- and alfalfa silage-based diets contained 23% forage neutral detergent fiber and 17% crude protein. Total dietary FA were 2.6, 4.2, and 4.3% of diet DM for CON, FFA, and TAG treatments, respectively. Total FA intake was increased 57% for UFA treatments and was similar between FFA and TAG. The intakes of individual FA were similar, with the exception of a 24 g/d lower intake of C16:0 and a 64 g/d greater intake of cis-9 C18:1 for the TAG compared with the FFA treatment. Compared with CON, the UFA treatments decreased DM intake (1.0 kg/d) but increased milk yield (2.2 kg/d) and milk lactose concentration and yield. The UFA treatments reduced milk fat concentration, averaging 3.30, 3.18, and 3.11% for CON, FFA, and TAG treatments, respectively. Yield of milk fat, milk protein, and 3.5% fat-corrected milk remained unchanged when comparing CON with the UFA treatments. No differences existed in the yield of milk or milk components between the FFA and TAG treatments. The UFA treatments increased feed efficiency (energy-corrected milk/DM intake), averaging 1.42, 1.53, and 1.48 for CON, FFA, and TAG treatments, respectively. Although milk fat yield was not affected, the UFA treatments decreased the yield of de novo (<16-carbon) synthesized FA (40 g/d) and increased the yield of preformed (>16-carbon) FA (134 g/d). Yield of FA from both sources (16-carbon FA) was reduced by the UFA treatments but to a different extent for FFA versus TAG (72 vs. 100 g/d). An increase was detected in the concentration of trans-10 C18:1 and a trend for an increase in trans-10,cis-12 C18:2 and trans-9,cis-11 C18:2 for the UFA treatments compared with CON. Under the dietary conditions tested, UFA treatments supplemented at 2% diet DM as either soybean FA distillate or soybean oil increased milk yield but did not effectively cause a reduction in milk fat yield, with preformed FA replacing de novo synthesized FA in milk fat. Further research is required to determine if the response to changes in dietary free and esterified FA concentrations is different in diets that differ in their risk for milk fat depression.     

Influence of a supplement containing conjugated linoleic acid on dairy performance,milk fatty acid composition,and adipose tissue reactivity to lipolytic challenge in mid-lactation goats

The objective of this work was to evaluate the effect of the supplementation of conjugated linoleic acid (CLA; 4.5 g of cis-9,trans-11 C18:2 and 4.5 g of trans-10,cis-12 C18:2) on milk performance, milk fatty acid (FA) composition, and adipose tissue reactivity in dairy goats fed a high-concentrate diet based on corn silage. Twenty-four multiparous dairy goats in early to mid lactation were used in a 10-wk trial, with a 3-wk adaptation to the experimental total mixed ration that contained corn silage (35%, dry matter basis), beet pulp (20%), barley (15%), and a commercial concentrate (30%). Goats were randomly allocated to 2 experimental groups and they were fed 45 g/d of a lipid supplement (either CLA or Ca salts of palm oil added on top of the total mixed ration). Individual milk production and composition were recorded weekly, and milk FA composition was analyzed in wk 2, 5, and 6. In the last week of the trial, an isoproterenol challenge was performed for 12 goats before morning feeding. The CLA supplementation had no effect on dry matter intake (DMI), body weight (BW), milk yield, milk protein content, and lactose yield and content, but it significantly decreased milk fat yield and content by 18 and 15%, respectively. The decrease in milk fat yield was related to a lower secretion of FA synthesized de novo, of the medium-chain FA, and to a lesser extent of the long-chain FA that are taken up from the peripheral circulation. The CLA supplementation decreased the proportion of the sum of C16:0 and C16:1 and the sum of total cis C18:1, and it increased the proportions of the sum of long-chain (C >16) and the sum of iso FA without modification of the total trans C18:1 and the sum of FA synthesized de novo (C <16). During the first 25 min relative to isoproterenol injection, the maximal concentrations, the increases above basal concentration, the changes in area under the curve, and the total area under the curve for glucose and nonesterified FA were not affected by CLA treatment. In conclusion, CLA supplementation associated with a high-concentrate diet based on corn silage resulted in decreased milk fat yield, increased net energy balance, and it did not affect the sensitivity of the adipose tissue to lipolytic challenge in lactating goats.     

Effects of monensin and dietary soybean oil on milk fat percentage and milk fatty acid profile in lactating dairy cows

The objective of this study was to investigate the effect of monensin (MN) and dietary soybean oil (SBO) on milk fat percentage and milk fatty acid (FA) profile. The study was conducted as a randomized complete block design with a 2 × 3 factorial treatment arrangement using 72 lactating multiparous Holstein dairy cows (138 ± 24 d in milk). Treatments were [dry matter (DM) basis] as follows: 1) control total mixed ration (TMR, no MN) with no supplemental SBO; 2) MN-treated TMR (22 g of MN/kg of DM) with no supplemental SBO; 3) control TMR including 1.7% SBO; 4) MN-treated TMR including 1.7% SBO; 5) control TMR including 3.4% SBO; and 6) MN-treated TMR including 3.4% SBO. The TMR (% of DM; corn silage, 31.6%; haylage, 21.2%; hay, 4.2%; high-moisture corn, 18.8%; soy hulls, 3.3%; and protein supplement, 20.9%) was offered ad libitum. The experiment consisted of a 2-wk baseline, a 3-wk adaptation, and a 2-wk collection period. Monensin, SBO, and their interaction linearly reduced milk fat percentage. Cows receiving SBO with no added MN (treatments 3 and 5) had 4.5 and 14.2% decreases in milk fat percentage, respectively. Cows receiving SBO with added MN (treatments 4 and 6) had 16.5 and 35.1% decreases in milk fat percentage, respectively. However, the interaction effect of MN and SBO on fat yield was not significant. Monensin reduced milk fat yield by 6.6%. Soybean oil linearly reduced milk fat yield and protein percentage and linearly increased milk yield and milk protein yield. Monensin and SBO reduced 4% fat-corrected milk and had no effect on DM intake. Monensin interacted with SBO to linearly increase milk fat concentration (g/100 g of FA) of total trans-18:1 in milk fat including trans-6 to 8, trans-9, trans-10, trans-11, trans-12 18:1 and the concentration of total conjugated linoleic acid isomers including cis-9, trans-11 18:2; trans-9, cis-11 18:2; and trans-10, cis-12 18:2. Also, the interaction increased milk concentration of polyunsaturated fatty acids. Monensin and SBO linearly reduced, with no significant interaction, milk concentration (g/100 g of FA) of short- and medium-chain fatty acids (<C16). Soybean oil reduced total saturated FA and increased total monounsaturated FA. These results suggest that monensin reduces milk fat percentage and this effect is accentuated when SBO is added to the ration.     

Effects of corn silage particle length and forage:concentrate ratio on milk fatty acid composition in dairy cows fed supplemental flaxseed

This study aimed to evaluate the effects of length of chop of corn silage and forage:concentrate ratio (F:C) on performance and milk fatty acid profiles in dairy cows supplemented with flaxseed. Our hypothesis was that decreasing forage particle length and F:C ratio would increase unsaturated fatty acid flow to the small intestine and subsequent transfer of these unsaturated fatty acids into milk. Eight Holstein cows (648.1 ± 71.5 kg body weight; 109.6 ± 43.6 days in milk) were used in a replicated 4 × 4 Latin square design with 21-d periods and a 2 × 2 factorial arrangement of dietary treatments. Dietary factors were: 1) F:C ratios (dry matter basis) of 55:45 and 45:55; and 2) corn silage particle lengths of 9.52 and 19.05 mm. All experimental cows received 1 kg of flaxseed to substitute for 1 kg of a rolled barley grain-based concentrate daily. Diets were fed twice daily as a total mixed ration. Corn silage particle length and F:C ratio had no effect on dry matter intake, milk yield, and milk composition; however, feeding short cut corn silage depressed milk protein yield. Significant particle size × F:C ratio interactions were observed for milk fat proportions of C_16:0, C_18:1cis-9, and C_18:2cis-9, trans-11 (a conjugated linoleic acid isomer). At short corn silage particle size, decreasing F:C ratio depressed milk fat proportion of C_16:0. Conversely, feeding short corn silage at high F:C ratio increased the proportion of C_18:1cis-9 and C_18:2cis-9, trans-11 in milk fat. The milk fat proportion of C_18:2trans-10, cis-12, a conjugated linoleic acid isomer that is associated with milk fat depression, was not affected by dietary treatment. Our results show that corn silage particle length and F:C ratio influence milk fatty acid profiles in dairy cows fed supplemental flaxseed as a source of polyunsaturated fatty acids.     

Rumen biohydrogenation-derived fatty acids in milk fat from grazing dairy cows supplemented with rapeseed, sunflower, or linseed oils

The effects of supplementation with rapeseed, sunflower, and linseed oils (0.5 kg/d; good sources of oleic, linoleic, and linolenic acids, respectively) on milk responses and milk fat fatty acid (FA) profile, with special emphasis on rumen-derived biohydrogenation intermediates (BI), were evaluated in a replicated 4 × 4 Latin square study using 16 grazing dairy cows. The dietary treatments were 1) control diet: 20-h access to grazing pasture supplemented with 5 kg/d of corn-based concentrate mixture (96% corn; CC); 2) RO diet: 20-h access to grazing supplemented with 4.5 kg/d of CC and 0.5 kg of rapeseed oil; 3) SO diet: 20-h access to grazing supplemented with 4.5 kg/d of CC and 0.5 kg of sunflower oil; and 4) LO diet: 20-h access to grazing supplemented with 4.5 kg/d of CC and 0.5 kg of linseed oil. Milk fatty acids were converted to methyl esters and analyzed by gas-liquid chromatography and silver-ion HPLC. Dietary treatments had no effect on milk production or on milk protein content and milk protein production. Supplementation with rapeseed and sunflower oils lowered milk fat content and milk fat production, but linseed oil had no effect. Inclusion of dietary vegetable oils promoted lower concentrations of short-chain (including 4:0) and medium-chain FA (including odd- and branched-chain FA) and 18:3n-3, and higher concentrations of C₁₈ FA (including stearic and oleic acids). The BI concentration was higher with the dietary inclusion of vegetable oils, although the magnitude of the concentration and its pattern differed between oils. The RO treatment resulted in moderate increases in BI, including trans 18:1 isomers and 18:2 trans-7,cis-9, but failed to increase 18:1 trans-11 and 18:2 cis-9,trans-11. Sunflower oil supplementation resulted in the highest concentrations of the 18:1 trans-10, 18:1 cis-12, and 18:2 trans-10,trans-12 isomers. Concentrations of 18:1 trans-11 and 18:2 cis-9,trans-11 were higher than with the control and RO treatments but were similar to the LO treatment. Concentration of BI in milk fat was maximal with LO, having the highest concentrations of some 18:1 isomers (i.e., trans-13/14, trans-15, cis-15, cis-16), most of the nonconjugated 18:2 isomers (i.e., trans-11,trans-15, trans-11,cis-15, cis-9,cis-15, and cis-12,cis-15), and conjugated 18:2 isomers (i.e., trans-11,cis-13, cis-12,trans-14, trans-11,trans-13, trans-12,trans-14, and trans-9,trans-11), and all conjugated 18:3 isomers. The LO treatment induced the highest amount and diversity of BI without decreasing milk fat concentration, as the RO and SO treatments had, suggesting that the BI associated with 18:3n-3 intake may not be the major contributors to inhibition of mammary milk fat synthesis.     

Effects of different forage:concentrate ratios in dairy ewe diets supplemented with sunflower oil on animal performance and milk fatty acid profile

The aim of this study was to evaluate the effect of different forage:concentrate (FC) ratios in dairy ewe diets supplemented with sunflower oil (SO) on animal performance and milk fatty acid (FA) profile, particularly focusing on trans C18:1 FA and conjugated linoleic acid (CLA). Sixty lactating Assaf ewes were randomly assigned to 6 treatments in a 3 × 2 factorial arrangement: 3 FC ratios (30:70, 50:50, and 70:30) and 2 levels of SO addition (0 and 20 g/kg of dry matter). Both the diet FC ratio and SO supplementation affected milk yield, but differences between treatments were small. Although the proportion of concentrate induced limited changes in milk FA profile, dietary SO significantly decreased saturated FA and enhanced total CLA. Furthermore, the incorporation of SO in ewe diets decreased the atherogenicity index value by about 25% and doubled the contents of potentially healthy FA such as trans-11 C18:1 and cis-9,trans-11 CLA. However, the inclusion of SO in a high-concentrate diet (30:70) could switch linoleic acid biohydrogenation pathways, resulting in a significant increase in trans-10 C18:1, trans-9,cis-11 C18:2, and trans-10,cis-12 C18:2 milk fat percentages.     

Effects of incremental amounts of extruded linseed on the milk fatty acid composition of dairy cows receiving hay or corn silage

The effect of supplementation of increasing amounts of extruded linseed in diets based on hay (H; experiment 1) or corn silage (CS; experiment 2) was investigated in regard to dairy performance and the milk fatty acid (FA) composition. In each experiment, 4 lactating multiparous Holstein cows were used in a 4 × 4 Latin square design (28-d periods). The cows were fed a diet (50:50 and 40:60 concentrate:forage ratio for experiments 1 and 2, respectively; dry matter basis) without supplementation (H0 or CS0) or supplemented with 5% (H5 or CS5), 10% (H10 or CS10), or 15% (H15 or CS15) of extruded linseed. Regardless of the forage type, diet supplementation with increasing amounts of extruded linseed had no effect on the dry matter intake, milk yield, or protein content or yield. In contrast, the milk fat content decreased progressively from H0 to H10 diets, and then decreased strongly with the H15 diet in response to increasing amounts of extruded linseed. For CS diets, the milk fat content initially decreased from CS0 to CS10, but then increased with the CS15 diet. For the H diets, the milk saturated FA decreased (−24.1 g/100 g of FA) linearly with increasing amounts of extruded linseed, whereas the milk monounsaturated FA (+19.0 g/100 g), polyunsaturated FA (+4.9 g/100 g), and total trans FA (+14.7 g/100 g) increased linearly. For the CS diets, the extent of the changes in the milk FA composition was generally lower than for the H diets. Milk 12:0 to 16:0 decreased in a similar manner in the 2 experiments with increasing amounts of extruded linseed intake, whereas 18:0 and cis-9 18:1 increased. The response of total trans 18:1 was slightly higher for the CS than H diets. The milk trans-10 18:1 content increased more with the CS than the H diets. The milk cis-9,trans-11 conjugated linoleic acid response to increasing amounts of extruded linseed intake was linear and curvilinear for the H diets, whereas it was only linear for the CS diets. The milk 18:3n-3 percentage increased in a similar logarithmic manner in the 2 experiments. It was concluded that the milk FA composition can be altered by extruded linseed supplementation with increasing concentrations of potentially health-beneficial FA (i.e., oleic acid, 18:3n-3, cis-9,trans-11 conjugated linoleic acid, and odd- and branched-chain FA) and decreasing concentrations of saturated FA. Extruded linseed supplementation increased the milk trans FA percentage.     

Effect of supplementation of grazing dairy ewes with a cereal concentrate on animal performance and milk fatty acid profile

This work was conducted to investigate the effect of supplementing grazing ewes on pasture with a cereal concentrate on the milk fatty acid (FA) profile. Ninety Assaf ewes in mid lactation were distributed in 9 lots of 10 animals each and allocated to 3 feeding regimens: 1) pasture—ewes were only allowed to graze pasture (an irrigated sward of Lolium perenne, Trifolium pratense, and Dactylis glomerata); 2) PS—grazing ewes were supplemented with oat grain (700 g/animal and day); and 3) TMR—ewes were fed ad libitum a total mixed ration (TMR; 80:20 concentrate/forage ratio). Milk yield and composition were recorded for 5 wk. The highest milk yield was observed in ewes receiving the TMR and the lowest in grazing ewes supplemented with oat grain. Productions of milk fat, protein, and total solids showed the lowest values in treatment PS. The atherogenicity index, which comprises C12:0, C14:0, and C16:0, in PS milk fat was no different from that observed in milk from animals on pasture (1.53 for pasture, 1.54 for PS, and 3.22 for TMR). Oat grain supplementation generated higher amounts of C18:0 and cis-9 C18:1 in milk fat than the pasture-only diet, but significantly decreased the levels of α-linolenic acid and most of intermediates of the process of biohydrogenation of this FA. Cis-9 trans-11 C18:2 and trans-11 C18:1, its precursor for endogenous synthesis in the mammary gland, were lower in PS (0.58 and 1.59 g/100 g of total FA) than in TMR (0.72 and 1.92 g/100 g of total FA) and very different from the results observed in grazing ewes receiving no supplement (1.21 and 3.88 g/100 g of total FA). Furthermore, the lowest levels of trans-10 C18:1 and trans-10 cis-12 C18:2 were detected in the milk fat of ewes fed pasture. It is concluded that, when pasture quality and availability do not limit dairy production, supplementation of grazing ewes with oat grain compromised the milk FA profile without any significant positive effect on milk production.     

Milk fatty acid profile and dairy sheep performance in response to diet supplementation with sunflower oil plus incremental levels of marine algae

In an attempt to develop strategies for enhancing the nutritional value of sheep milk fat, dairy ewe diet was supplemented with 3 incremental levels of marine algae (MA), in combination with sunflower oil, to evaluate the effects of these marine lipids on milk fatty acid (FA) profile and animal performance. Fifty Assaf ewes in mid lactation were distributed in 10 lots of 5 animals each and allocated to 5 treatments (2 lots per treatment): no lipid supplementation (control) or supplementation with 25 g of sunflower oil/kg of DM plus 0 (SO), 8 (SOMA₁), 16 (SOMA₂), or 24 (SOMA₃) g of MA (56.7% ether extract)/kg of DM. Milk production and composition, including FA profile, were analyzed on d 0, 3, 7, 14, 21, and 28 of treatment. Neither intake nor milk yield were significantly affected by lipid addition, but all MA supplements decreased milk fat content from d 14 onward, reaching a 30% reduction after 28 d on SOMA₃. This milk fat depression might be related not only to the joint action of some putative fat synthesis inhibitors, such as trans-9,cis-11 C18:2 and probably trans-10 C18:1, but also to the limited ability of the mammary gland to maintain a desirable milk fat fluidity, that would have been caused by the noticeable increase in trans-C18:1 together with the lowered availability of stearic acid for oleic acid synthesis through Δ⁹-desaturase. Furthermore, all lipid supplements, and mainly MA, reduced the secretion of de novo FA (C6:0-C14:0) without increasing the yield of preformed FA (>C16). Supplementation with sunflower oil plus MA resulted in larger increases in cis-9,trans-11 C18:2 than those observed with sunflower oil alone, achieving a mean content as high as 3.22% of total FA and representing a more than 7-fold increase compared with the control. Vaccenic acid (trans-11 C18:1) was also significantly enhanced (on average +794% in SOMA treatments), as was C22:6 n-3 (DHA) content, although the transfer efficiency of the latter, from the diets to the milk, was very low (5%). However, the highest levels of MA inclusion (SOMA₂ and SOMA₃) reduced the milk n-6:n-3 ratio, but MA supplements caused an important increase in trans-10 C18:1, which would rule out the possibility that this milk has a healthier fat profile before determining the specific role of each individual FA and ensuring that this trans-FA is at least innocuous in relation to cardiovascular disease risk.     

Altering the ratio of dietary C16:0 and cis-9 C18:1 interacts with production level in dairy cows: Effects on production responses and energy partitioning

The objective of our study was to evaluate the effects of altering the dietary ratio of palmitic (C16:0) and oleic (cis-9 C18:1) acids on nutrient digestibility, energy partitioning, and production responses of lactating dairy cows. Cows were blocked by milk yield and assigned to 3 groups (12 cows per group) in a main plot: low (45.2 ± 1.7 kg/d), medium (53.0 ± 1.6 kg/d), and high (60.0 ± 1.9 kg/d). Within each production group, a truncated Latin square arrangement of fatty acid (FA) treatments was used in 2 consecutive 35-d periods. The FA treatments supplemented at 1.5% of diet dry matter were (1) 80:10 (80% C16:0 + 10% cis-9 C18:1), (2) 73:17 (73% C16:0 + 17% cis-9 C18:1), (3) 66:24 (66% C16:0 + 24% cis-9 C18:1), and (4) 60:30 (60% C16:0 + 30% cis-9 C18:1). Treatment × production group interactions were observed for yields of milk, fat-corrected milk, energy-corrected milk, milk fat, milk protein, and milk lactose and energy partitioned to milk. Increasing cis-9 C18:1 in FA treatments reduced fat-corrected milk, energy-corrected milk, and milk energy output in low-producing cows but increased these in high-producing cows. Increasing cis-9 C18:1 in FA treatments did not affect milk yield, milk protein yield, and milk lactose yield in low- and medium-producing cows but increased these in high-producing cows. Regardless of production level, there was no effect of treatments on dry matter intake; however, increasing cis-9 C18:1 in FA treatments increased body weight change and body condition score change. Increasing cis-9 C18:1 in FA treatments increased total FA digestibility due to a linear increase in 16- and 18-carbon FA digestibilities. Interactions between FA treatments and production level were observed for the yield of milk fat and milk FA sources. In low-producing cows, increasing cis-9 C18:1 in FA treatments decreased milk fat yield due to a decrease in de novo and mixed milk FA without changes in preformed milk FA. In contrast, in high-producing cows, increasing cis-9 C18:1 in FA treatments increased milk fat yield due to an increase in de novo and preformed milk FA. Our results indicate that high-producing dairy cows (averaging 60 kg/d) responded better to a fat supplement containing more cis-9 C18:1, whereas low-producing cows (averaging 45 kg/d) responded better to a supplement containing more C16:0.     

Effect of dietary antioxidant and increasing corn oil inclusion on milk fat yield and fatty acid composition in dairy cattle

The objective of this study was to examine the effect of a dietary synthetic antioxidant on feed intake, yields of milk and milk components and milk fatty acids (FA), in combination with increasing concentrations of dietary corn oil to provide increasing rumen unsaturated fatty acid load (RUFAL) challenges. Twenty-six Holstein cows (177 ± 57 d in milk; mean ± standard deviation) were assigned to treatment in a randomized complete block design. Treatments were a control diet (CON; n = 13 cows) or the same diet supplemented with a synthetic antioxidant (AOX; 6.1 g/d; dry blend of ethoxyquin and propyl gallate, Novus International Inc., St. Charles, MO; n = 13 cows). In period 1 (21 d), no supplemental corn oil was fed; in periods 2, 3, and 4 (14 d each), corn oil was supplemented at 0.7, 1.4, and 2.8% of the diet [dry matter (DM) basis] to incrementally increase RUFAL. For all variables measured, no significant interactions were detected between treatment and period, indicating no differences between the CON and AOX treatments at all levels of oil inclusion. Intake of DM was lower for AOX compared with CON but AOX had no effect on milk yield or milk fat concentration and yield. Milk protein yield and feed efficiency (energy-corrected milk/DM intake) tended to be greater for AOX compared with CON. Increasing dietary corn oil concentration (RUFAL) decreased DM intake, milk yield, milk fat concentration and yield, and feed efficiency. The AOX treatment increased the concentration and yield of 16-carbon milk FA, with no effect on de novo (<16 carbon) or preformed (>16 carbon) milk FA. Milk FA concentration of trans-10 C18:1, trans-10,cis-12 C18:2, and trans-9,cis-11 C18:2 were unaffected by AOX but increased with increasing RUFAL. In conclusion, supplementation with AOX did not overcome the dietary-induced milk fat depression caused by increased RUFAL.     

Fatty acid profile of yak milk from the Qinghai-Tibetan Plateau in different seasons and for different parities

Yaks are the most important grazing livestock for milk production on the Qinghai-Tibetan plateau because these animals are adapted to the high elevations and extremes of cold and can graze throughout the year. In the present study, 30 yaks were selected and the fatty acid (FA) profile of yak milk at different seasons and parities was investigated using gas chromatography. The concentrations of cis-9 C18:1, cis-11 C18:1, cis-9,trans-11 C18:2, and C18:3 n-3 in yak milk were higher in summer (25.26, 1.50, 1.46, and 0.33 g/100 g of total FA, respectively) than in winter (22.17, 0.77, 1.27, and 0.28 g/100 g of total FA, respectively). The contents of monounsaturated and polyunsaturated FA in milk fat of multiparous (parities 2 to 5) yaks (31.61 and 4.20 g/100 g of total FA, respectively) were higher than those in primiparous yaks (29.61 and 3.80 g/100 g of total FA, respectively). These results suggest (1) that the potential exists to improve the FA composition of yak milk by developing local supplement resources during the winter and (2) that multiparous yaks have a more favorable FA profile than primiparous yaks.     

A comparison between Holstein-Friesian and Jersey dairy cows and their F1 hybrid on milk fatty acid composition under grazing conditions

The objective of this study was to investigate the effect of 2 breeds, Holstein and Jersey, and their F₁ hybrid (Jersey × Holstein) on milk fatty acid (FA) concentrations under grazing conditions, especially conjugated linoleic acid (CLA) and n-3 polyunsaturated fatty acids because of their importance to human health. Eighty-one cows (27 per breed grouping) were allocated a predominantly perennial ryegrass pasture. Samples were collected over 2 periods (June and July). Breed affected dry matter intake and milk production and composition. Holstein cows had the highest dry matter intake (18.4 ± 0.40 kg of DM/d) and milk production (21.1 ± 0.53 kg of DM/d). Holstein and Jersey × Holstein cows had similar 4% fat corrected milk, fat yield, and protein yield; with the exception of fat yield, these were all higher than for Jersey cows. Milk fat concentration was highest for Jersey cows and lowest for Holstein cows, with the hybrid cows intermediate. Total FA and linolenic acid intake (1.09 ± 0.023 and 0.58 ± 0.012 kg/d, respectively) were highest for Holstein cows. In terms of milk FA, Holstein cows had higher contents of C14:1, cis-9 C18:1 and linoleic acid. In turn, Jersey and Jersey × Holstein cows had higher content of C16:0. Milk concentrations of neither the cis-9,trans-11 isomer of CLA nor its precursor, vaccenic acid, were affected by breed. Nevertheless, large variation between individual animals within breed grouping was observed for CLA and estimated Δ⁹-desaturase activity. There was some evidence for a negative heterotic effect on milk concentration of CLA, with the F₁ hybrid cows having lower concentrations compared with the mid parent average. Plasma FA profile did not accurately reflect differences in milk FA composition. In conclusion, there was little evidence for either breed or beneficial heterotic effects on milk FA content with human health-promoting potential, though significant within-breed, interanimal variation was observed.     

Addition of olive oil to dairy ewe diets: effect on milk fatty acid profile and animal performance

The effects of ruminant diet supplementation with linoleic or different polyunsaturated fatty acids (FA) have been well documented. Less abundant information, however, exists on the effects of incorporating monounsaturated FA, such as oleic acid, on lipid metabolism or animal performance. The purpose of this work was to assess the effects of feeding dairy ewes a diet supplemented with high levels of olive oil (OO) on milk yield and composition, paying particular attention to the FA profile. Twenty-four Assaf ewes were fed ad libitum with 2 diets, control or supplemented with 6% OO (2 lots of 6 animals per diet) for 4 wk. Milk yield and composition and dry matter intake were recorded weekly. Milk FA composition was determined by gas chromatography and conjugated linoleic acid profile by silver ion HPLC. Milk yield increased in ewes receiving OO, with no differences in dry matter intake. The OO diet decreased the milk protein percentage but increased the milk fat, protein, and total solids yield. Medium-chain saturated FA (C10:0 to C16:0) content was reduced with OO supplementation, whereas C18:0 and cis-9 C18:1 content increased. Leaving aside trans-11, most trans C18:1 isomers, mainly trans-10, increased in supplemented ewes. The main conjugated linoleic acid isomer (cis-9, trans-11 C18:2) decreased with OO supplementation, whereas trans-7, cis-9 and trans-9, cis-11 C18:2 exhibited a remarkable increase. These results support the argument that the supplementation of ewe diets with high levels of OO does not have any detrimental effects on animal performance but substantially modifies the FA profile.