Milk conjugated linoleic acid response to fish oil supplementation of diets differing in fatty acid profiles

The objective of this experiment was to examine the effect of feeding fish oil (FO) along with fat sources that varied in their fatty acid compositions (high stearic, high oleic, high linoleic, or high linolenic acids) to determine which combination would lead to maximum conjugated linoleic acid (cis-9,trans-11 CLA) and transvaccenic acid (TVA) concentrations in milk fat. Twelve Holstein cows (eight multiparous and four primiparous cows) at 73 (+/- 32) DIM were used in a 4 x 4 Latin square with 4-wk periods. Treatment diets were 1) 1% FO plus 2% fat source high in stearic acid (HS), 2) 1% FO plus 2% fat from high oleic acid sunflower seeds (HO), 3) 1% FO plus 2% fat from high linoleic acid sunflower seeds (HLO), and 4) 1% FO plus 2% fat from flax seeds (high linolenic; HLN). Diets formulated to contain 18% crude protein were composed of 50% (dry basis) concentrate mix, 25% corn silage, 12.5% alfalfa haylage, and 12.5% alfalfa hay. Milk production (35.8, 36.3, 34.9, and 35.0 kg/d for diets 1 to 4) was similar for all diets. Milk fat percentages (3.14, 2.81, 2.66, and 3.08) and yields (1.13, 1.02, 0.93, and 1.08 kg/d) for diets 1 to 4 were lowest for HLO. Milk protein percentages (3.04, 3.03, 3.10, and 3.08) and dry matter intake (DMI) (25.8, 26.0, 26.2, and 26.2 kg/d) for diets 1 to 4 were similar for all diets. Milk cis-9,trans-11 CLA concentrations (0.70, 1.04, 1.70, and 1.06 g/100 g fatty acids) for diet 1 to 4 and yields (7.7, 10.7, 15.8, and 11.3 g/d) for diets 1 to 4 were greatest with HLO and were least with HS. Milk cis-9,trans-11 CLA concentrations and yields were similar for cows fed the HO and the HLN diets. Similar to milk cis-9,trans-11 CLA, milk TVA concentration (1.64, 2.49, 3.74, and 2.41 g/100 g fatty acids) for diets 1 to 4 was greatest with the HLO diet and least with the HS diet. Feeding a high linoleic acid fat source with fish oil most effectively increased concentrations and yields of milk cis-9,trans-11 CLA and TVA.     

Fatty acid profiles of milk and rumen digesta from cows fed fish oil,extruded soybeans or their blend

Four fistulated primiparous cows (two Holstein and two Brown Swiss) averaging 102 DIM were used in a 4 x 4 Latin square with 3-wk periods to determine the effect of feeding fish oil, extruded soybeans, or their combination on fatty acid profiles of milk and rumen digesta. Experimental diets consisted of: 1) control diet; 2) a diet with 2% (DM basis) added fat from menhaden fish oil; 3) a diet with 2% added fat from extruded soybeans; and 4) a diet with 1% added fat from fish oil and 1% fat from extruded soybeans. All diets consisted of 25% corn silage, 25% alfalfa hay, and 50% concentrate. Milk yields (28.6, 29.7, 29.2, and 28.1 kg/d for control, fish oil, extruded soybeans, and combination diets, respectively) were similar for all fat supplements and control. Milk fat and protein percentages (3.49, 3.08; 3.25, 2.96; 3.47, 3.01; 3.48, 2.99 for diets 1, 2, 3, and 4, respectively) were not affected by fat supplements compared with control. Dry matter intake (23.0, 21.6, 22.7, and 21.6 kg/d) was reduced when diets containing fish oil were fed. Concentrations of conjugated linoleic acid [CLA; cis-9, trans-11 CLA, 0.40, 0.88, 0.87, and 0.80 g/100 g fatty acids (FA)] and transvaccenic acid (TVA, 1.02, 2.34, 2.41, and 2.06 g/100 g of FA) were increased in milk fat by all fat supplements, with no differences in milk CLA and TVA observed among fat supplements. As with milk fat, proportions of ruminal CLA (0.09, 0.26, 0.18, and 0.21 g/100 g of FA) and TVA (2.61, 4.56, 4.61, and 4.39 g/100 g of FA) increased with fat supplements. The effects of fat supplements on ruminal TVA and CLA concentrations were also reflected in rumen FA-salts, free fatty acids, and neutral lipids. The higher TVA to CLA ratio in the rumen compared with milk indicated that fat supplements increased milk CLA concentration mainly by increasing ruminal production of TVA, which also implied the significant role that mammary delta-9 desaturase plays in milk CLA concentrations.     

Feeding fish meal and extruded soybeans enhances the conjugated linoleic acid (CLA) content of milk

Twelve multiparous Holstein cows averaging 65 (33 to 122) DIM were used in a 4 x 4 Latin square for 4-wk periods to determine whether feeding fish oil as fish meal would stimulate increased amounts of milk conjugated linoleic acid (cis-9, trans-11 C18:2; CLA) and transvaccenic acid (trans-11 C18:1; TVA) when the cows were fed extruded soybeans to supply additional linoleic acid. Treatment diets were 1) control; 2) 0.5% fish oil from fish meal; 3) 2.5% soybean oil from extruded soybeans; and 4) 0.5% fish oil from fish meal and 2% soybean oil from extruded soybeans. Diets were formulated to contain 18% crude protein and were composed (dry basis) of 50% concentrate mix, 25% corn silage, and 25% alfalfa hay. Intake of DM was not affected by diet. Milk production was increased by diets 2, 3, and 4 compared with diet 1 (control). Milk fat and milk protein percentages decreased with diets 3 and 4. Milk fat yield was not affected by treatments, but yield of milk protein was increased with supplemental fish meal and extruded soybeans or their blend. When diets 2, 3, or 4 were fed, concentrations of cis-9, trans-11 CLA in milk fat increased by 0.4-, 1.4-, and 3.2-fold, and TVA concentrations in milk fat increased by 0.4-, 1.8-, and 3.5-fold compared with the control milk fat. Increases in TVA and cis-9, trans-11 CLA were 91 to 109% greater when a blend of fish meal and extruded soybeans was fed than the additive effect of fish meal and extruded soybeans. This suggested that fish oil increased the production of CLA and TVA from other dietary sources of linoleic acid such as extruded soybeans.     

Flavor and stability of pasteurized milk with elevated levels of conjugated linoleic acid and vaccenic acid

The objectives of this study were to determine if flavor differences between 2% fat pasteurized milks with and without naturally enhanced vaccenic acid (VA) and cis-9, trans-11 conjugated linoleic acids (CLA) levels could be detected over the commercial shelf life of the product and to determine if milk with elevated VA and cis-9, trans-11 CLA levels was more susceptible to development of light-induced oxidative flavor defects. Cows were fed a control diet or the same ration supplemented with 2% soybean oil and 1% fish oil (CLA diet). The milk, standardized to 2% fat, was pasteurized, homogenized, and stored in plastic containers at 4 degrees C. Oxidation was induced by exposing half of the containers to light. Testing was conducted at 1, 7, and 14 d postpasteurization. Average cis-9, trans-11 CLA content of the milks from the control and CLA diet groups was 0.52 and 4.74 g/100 g of fatty acids, respectively (8-fold increase). Average VA content of the milk from the control and CLA diet groups was 1.43 and 12.06 g/100 g of fatty acids, respectively (7.5-fold increase). Together, VA plus CLA represented almost 17% of the total milk fatty acids. There was no effect of light exposure on fatty acid composition initially or over the 14-d storage period. Although VA, cis-9, trans-11 CLA, and degree of unsaturation were significantly elevated in the milk from the CLA diet group, untrained panelists were unable to detect flavor differences initially or over time in 15 of 16 triangle test evaluations. Similarly, sensory results indicated no difference in susceptibility to the development of oxidized off-flavors between the milk from the control and CLA diet groups, even when oxidation was induced by light exposure.     

trans-10, cis-12 conjugated linoleic acid decreases lipogenic rates and expression of genes involved in milk lipid synthesis in dairy cows

Feeding conjugated linoleic acid (CLA) reduces milk fat synthesis in lactating dairy cows, and the effect has been shown to be specific for the trans-10, cis-12 CLA isomer. Our objectives were to examine potential mechanisms by which trans-10, cis-12 CLA inhibits milk fat synthesis. Multiparous Holstein cows (n = 4) in late lactation were used in a balanced 2 x 2 crossover design. Treatments consisted of a 5 d abomasal infusion of either skim milk (control) or purified trans-10, cis-12 CLA (13.6 g/d) emulsified in skim milk. On d 5 of infusion, mammary gland biopsies were performed and a portion of the tissue analyzed for mRNA expression of acetyl CoA carboxylase, fatty acid synthetase, delta 9-desaturase, lipoprotein lipase, fatty acid binding protein, glycerol phosphate acyltransferase and acylglycerol phosphate acyltransferase. Lipogenic capacity was evaluated with another portion of the tissue. Infusion of trans-10, cis-12 CLA decreased milk fat content and yield 42 and 48%, respectively and increased the trans-10, cis-12 CLA content in milk fat from < 0.1 to 4.9 mg/g. Reductions in milk fat content of C4 to C16 fatty acids contributed 63% to the total decrease in milk fat yield (molar basis). Analysis of the ratios of specific fatty acid pairs indicated trans-10, cis-12 CLA also shifted fatty acid composition in a manner consistent with a reduction in delta 9-desaturase. Mammary explant incubations with radiolabeled acetate established that lipogenic capacity was decreased 82% and acetate oxidation to CO2 was reduced 61% when cows received trans-10, cis-12 CLA. Infusing trans-10, cis-12 CLA also decreased the mRNA expression of all measured enzymes by 39 to 54%. Overall, data demonstrated the mechanism by which trans-10, cis-12 CLA inhibits milk fat synthesis includes decreasing expression of genes that encode for enzyme involved in circulating fatty acid uptake and transport, de novo fatty acid synthesis, desaturation of fatty acids and triglyceride synthesis.     

Short communication: milk fat response to low doses of tran-10, cis-12 conjugated linoleic acid (CLA)

Trans-10, cis-12 conjugated linoleic acid (CLA) is a potent inhibitor of milk fat synthesis. We examined the effect of low doses of trans-10, cis-12 CLA using Holstein cows in a 4 x 4 Latin square design. Milk yield and milk protein were unaffected, but abomasal infusion of 1.25, 2.5, and 5.0 g/d of trans-10, cis-12 CLA reduced milk fat yield by 7, 16, and 29%, respectively. When combined with previous data, the reduction in milk fat yield was curvilinear, relating to both quantity infused and milk fat content of trans-10, cis-12 CLA (R2 = 0.99 and 0.96, respectively). Further, changes in milk fatty acid composition indicated the mechanism involved inhibition of de novo fatty acid synthesis and the utilization of circulating fatty acids.     

Effects of dietary supplementation of rumen-protected conjugated linoleic acid in dairy cows during established lactation

Short-term studies (< 5 d) involving abomasal infusion of a mixture of CLA isomers or pure trans-10, cis-12 CLA have demonstrated that supplements of conjugated linoleic acids (CLA) reduce milk fat synthesis during established lactation in dairy cows. Our objective was to assess longer term effects of supplementation during established lactation using a dietary supplement of rumen-protected CLA. Thirty Holstein cows were blocked by parity and received a dietary fat supplement of either Ca-salts of palm oil fatty acids (control) or a mixture of Ca-salts of palm oil fatty acids plus Ca-salts of CLA (CLA treatment). Supplements provided about 90 g/d of fatty acids and were topdressed on the TMR. The CLA supplement provided 30.4 g/d of CLA in which the predominant isomers were: trans-8, cis-10 (9.2%), cis-9, trans-11 (25.1%), trans-10, cis-12 (28.9%), and cis-11, trans-13 (16.1%). All cows were pregnant; treatments were initiated on d 79 of pregnancy (approximately 200 d prepartum) and continued for 140 d until dry off. Twenty-three cows completed the study; those receiving CLA supplement had a lower milk fat test (2.90 versus 3.80%) and a 23% reduction in milk fat yield (927 versus 1201 g/d). Intake of DM, milk yield, and the yield and content of true protein and lactose in milk were unaffected by treatment. Milk fat analysis indicated that the CLA supplement reduced the secretion of fatty acids of all chain lengths. However, effects were proportionally greater on short and medium chain fatty acids, thereby causing a shift in the milk fatty acid composition to a greater content of longer-chain fatty acids. Changes in body weight gain, body condition score, and net energy balance were not significant and imply no differences in cows fed the CLA supplement in replenishment of body reserves in late lactation. Likewise, maintenance of pregnancy, gestation length, and calf birth weight were unaffected by treatment. Overall, feeding a dietary supplement of rumen-protected CLA to pregnant cows over the last 140 d of the lactation cycle resulted in a marked reduction in milk fat content and yield, and a shift in milk fatty acid composition, but other milk components, DMI, maintenance of pregnancy, and cow well-being were unaffected.     

Effect of dose of calcium salts of conjugated linoleic acid (CLA) on percentage and fatty acid content of milk fat in midlactation holstein cows

Increasing conjugated linoleic acid (CLA) content of milk fat from lactating dairy cattle has become a research interest due to the possible health benefits afforded humans consuming CLA. Dietary supplementation of CLA to lactating dairy cows is one potential method by which CLA content of milk and dairy products may be enhanced. Feeding CLA in calcium salt form could potentially deliver CLA to the lower digestive tract through prevention of biohydrogenation by rumen microbes. Milk fat depression (MFD) occurs when cows receive CLA-60, a commercially available CLA source containing numerous CLA isomers, abomasally. Our objectives were to determine the quantity of CLA as calcium salts required to elicit maximal MFD and to evaluate the effects of CLA supplementation on fatty acid composition of milk fat. Five Holstein cows at approximately 93 DIM were utilized in a 5 x 5 balanced Latin square crossover design. Periods were 14-d in length with a 5-d treatment phase and 9-d rest phase. Treatments were 5-d supplementation of 0, 12.5, 25, 50, and 100 g of CLA-60 in calcium salt form. Milk samples were collected on d 5 of CLA supplementation and analyzed for composition and fatty acid profile. Regression analysis of milk fat data suggested that MFD was not maximized over the dose levels investigated, despite delivery of 34.5 g of trans-10, cis-12 CLA in the 100-g dose of CLA. Supplementation with 50 and 100 g of CLA per day resulted in a reduction of milk fat percent of 29 and 34%, respectively. Trend analysis indicated a linear decrease in the milk fat content of caprylic, capric, and lauric acids as the dose of CLA increased. Milk fat content of cis-9, trans-11, and trans-10, cis-12 CLA increased at an increasing rate as dose increased.     

Conjugated linoleic acid (CLA) effects on pups growth, milk composition and lipogenic enzymes in lactating rats

Conjugated linoleic acid (CLA) has a range of biological properties, including effects on lipid metabolism, milk and body composition in animals. This study investigated the effects of dietary CLA on lactating rats and development of the suckling pups. Dams were fed either a control diet or the same diet supplemented with 25 g/kg of a fat supplement containing 540 g CLA/kg (final concentration of 13.5 g CLA/kg diet) from parturition to the 15th day post-partum. The CLA mixture used in this study contained the following isomers (per 100 g): cis-9, trans-11 (24 g); cis-10, trans-12 (35 g); cis-8, trans-10 (15 g); cis-11, trans-13 (17 g) and others (9 g). On d 15 post partum, CLA supplementation reduced milk fat content by 33% and pup growth by 21%. The milk fatty acid profile, with decreased content of short and medium chain acids, suggests CLA inhibition was more pronounced for de novo lipid synthesis. Consistent with these results, activities of fatty acid synthase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were reduced by CLA treatment in the mammary gland and liver. In contrast, the activity of NADP-malate dehydrogenase was unchanged.     

Conjugated linoleic acid increases in milk when cows fed fish meal and extruded soybeans for an extended period of time

The objective of this study was to determine the effect of feeding a conjugated linoleic acid (CLA) stimulating diet for an extended period of time on milk cis-9, trans-11 CLA and vaccenic acid (VA) concentrations. Twenty cows (16 Holstein and 4 Brown Swiss) were divided into 2 groups (n = 10 per treatment) for a 10-wk study. Cows in group 1 were fed a traditional corn-soybean-basal diet (control), while those in group 2 were fed a blend of 0.5% fish oil from fish meal and 2% soybean oil from extruded soybeans (FMESB) to achieve higher milk fat cis-9, trans-11 CLA and VA. Diets were formulated to contain 18% CP and were composed (dry matter basis) of 50% concentrate mix, 25% corn silage, and 25% alfalfa hay. Dry matter intake was not affected by diet. Milk production increased in cows fed the FMESB diet. Milk fat and milk protein percentages decreased with the FMESB diet; however, milk fat and protein yields were not affected by treatments. Milk fat cis-9, trans-11 CLA and VA concentration (g/100 of fatty acids) and yield (g/d) were 2.5-fold greater for cows fed the FMESB diet over the 10 wk of fat supplementation. For cows fed the FMESB diet, contents of milk fat cis-9, trans-11 CLA and VA gradually increased from the first week of fat supplementation, reached the highest concentrations in wk 3, then gradually decreased during wk 4 and 5 and then remained relatively constant until wk 10. The concentration of cis-9, trans-11 CLA and VA from the control diet was relatively constant over the 10 wk of fat supplementation. Concentrations of cis-9, trans-11 CLA and VA in milk fat can be increased within a week by feeding a blend of fish meal and extruded soybeans, and that increase remains relatively constant after wk 5 of fat supplementation.     

The effect of dietary inclusion of olive tree leaves and grape marc on the content of conjugated linoleic acid and vaccenic acid in the milk of dairy sheep and goats

Olive tree leaves (OTL) and grape marc (GM) are by-products with high linolenic (LNA) and linoleic (LA) acid content, respectively, which can be used as dietary ingredients to increase the cis-9 trans-11 conjugated linoleic acid (CLA) content of milk fat in sheep and goats. An experiment was conducted with 16 Friesian ewes and 16 Alpine goats to study the effect of OTL and GM inclusion in sheep and goat diets on their milk fatty acid profile, with emphasis on cis-9, trans-11 CLA and vaccenic acid (VA). Ewes and the goats were fed the control (C) diets from parturition to the 90 days in milk (DIM) and then both groups were divided into two sub-groups (treatments). The control groups of both species continued to be fed the C diets, whereas the treated groups were gradually switched over a 2-week period (DIM=91-105) from the C diets to that of treatment 1, which contained air-dried OTL. These OTL diets were fed ad libitum for 1 month (DIM=106-135). After that period, the same treated groups, after 2 weeks of gradual adaptation (DIM=136-150), were switched to treatment 2, which contained air-dried GM. The GM diets were fed ad libitum for 1 month (151-180 DIM). Concentrations of polyunsaturated fatty acids (PUFA) and mono-unsaturated fatty acids increased significantly in milk fat of sheep fed OTL v. C. For goats, only the PUFA in milk fat was increased by feeding OTL compared with C. Relative to C, GM increased significantly the concentration of PUFA only in milk fat of sheep. OTL and GM diets increased the cis-9, trans-11 CLA and VA content in milk fat, compared with C, only in sheep. GM caused a sharp increase in 18:0 only in sheep milk fat, while the OTL diet increased significantly the 18:0 in milk fat of goats. GM and OTL diets also had opposite effects on the 18:1/18:0 ratio of sheep milk fat. In conclusion, OTL and GM, when included in sheep diets altered the milk fatty acid profile with a pronounced increase in cis-9, trans-11 CLA and VA contents. The results show that the response of sheep and goats to OTL and GM diets was different, suggesting a species difference that needs further investigation.     

Dose response of milk fat to intravenous administration of the trans-10, cis-12 isomer of conjugated linoleic acid

Intravenous infusion of conjugated linoleic acid (CLA) was evaluated as a simpler method than abomasal infusion and the feeding of calcium salts to examine milk fat depression. The objectives were to determine the dose-dependent response of milk fat and plasma metabolites to intravenous administration of the trans-10, cis-12 isomer of CLA, an isomer identified to possess an inhibitory effect on milk fat synthesis. Four multiparous Holstein cows averaging 123 +/- 30 d in milk were randomly assigned to treatments in a 4 x 4 Latin square design. Catheters were inserted into the jugular vein for infusions and blood sampling. Treatments consisted of intravenous infusions of 0, 2, 4, and 6 g/d CLA (> 95% trans-10, cis-12 CLA). Infusates contained 72 g/d of a parenteral solution, saline, and CLA to 90 ml. Periods were of 5 d duration with a 7 d wash out. Milk was sampled at each milking and analyzed for fat, protein, and fatty acids. Blood samples were obtained on the last day of each period. Dry matter intake (22.4 +/- 2.4 kg/d), milk yield (28.5 +/- 3.3 kg/d), and protein percent (3.26 +/- 0.08%) of cows were not affected by treatment. However, milk fat percentage was reduced linearly with increasing doses of CLA. Milk fat percentage was 4.17, 3.53, 3.29, and 2.92% on d 5 for treatments 0, 2, 4, and 6 g/d CLA, respectively. Concentrations (4.2 mg/g of fat) of cis-9, trans-11 CLA in milk fat were not affected by treatment. However, an increase in the trans-10, cis-12 CLA content of milk fat was observed. Milk fat contained 0.00, 0.02, 0.06, and 0.10 mg of trans-10, cis-12 CLA per g of fat (SEM = 0.065) for treatments 0, 2, 4, and 6 g/d CLA, respectively. Plasma NEFA concentration increased linearly with the dose of the trans-10, cis-12 CLA. Intravenous infusion of the trans-10, cis-12 isomer of CLA depressed milk fat in a linear manner over the range of infusion studied and, therefore, is an alternative to abomasal infusion.     

Effect of a supplement containing trans-10,cis-12 conjugated linoleic acid on the performance of dairy ewes fed 2 levels of metabolizable protein and at a restricted energy intake

Trans-10,cis-12 conjugated linoleic acid (CLA) inhibits milk fat synthesis in dairy ewes, but the effects under varying dietary metabolizable protein (MP) levels when energy-limited diets are fed have not been examined. The objectives of the study were to evaluate the response of lactating dairy ewes to CLA supplementation when fed diets limited in metabolizable energy (ME) and with either a low or high MP content. Twelve multiparous ewes in early lactation were randomly allocated to 1 of 4 dietary treatments: a high MP (110% of daily MP requirement) or low MP (93% of daily MP requirement) diet unsupplemented or supplemented with a lipid-encapsulated CLA to provide 2.4 g/d of trans-10,cis-12 CLA, in each of 4 periods of 25 d each in a 4×4 Latin square design. All diets were restricted to supply each ewe with 4.6 Mcal of ME/d (equivalent to 75% of ME requirement). Supplementation with CLA decreased milk fat percentage and yield by 33% and 24%, respectively, and increased milk, milk protein, and lactose yields by 16, 13, and 17%, respectively. Feeding the high MP diet increased the yields of milk, fat, protein, and lactose by 18, 15, 19, and 16%, respectively. Milk fat content of trans-10,cis-12 CLA (g/100g) was 0.09 and <0.01 for the CLA-supplemented and unsupplemented ewes, respectively. Ewes supplemented with CLA had a reduced yield (mmol/d) of fatty acids of C16, although the effect was greatest for C16. Plasma urea concentrations were lowest in ewes supplemented with CLA compared with those unsupplemented (6.5 vs. 7.4 mmol/L, respectively) and receiving low compared with high MP diets (5.6 vs. 8.3 mmol/L, respectively). In conclusion, dairy ewes fed energy-limited diets and supplemented with CLA repartitioned nutrients to increase yields of milk, protein, and lactose, with the response to CLA supplementation and additional MP intake being additive.     

Conjugated linoleic acid increases in milk from cows fed condensed corn distillers solubles and fish oil

Twelve lactating Holstein cows were randomly assigned to 1 of 4 experimental diets in a replicated 4 × 4 Latin square design with 4-wk periods to ascertain the lactational response to feeding fish oil (FO), condensed corn distillers solubles (CDS) as a source of extra linoleic acid, or both. Diets contained either no FO or 0.5% FO and either no CDS or 10% CDS in a 2 × 2 factorial arrangement of treatments. Diets were fed as total mixed rations for ad libitum consumption. The forage to concentrate ratio was 55:45 on a dry matter basis for all diets and the diets contained 16.2% crude protein. The ether extract concentrations were 2.86, 3.22, 4.77, and 5.02% for control, FO, CDS, and FOCDS diets, respectively. Inclusion of FO or CDS or both had no effect on dry matter intake, feed efficiency, body weight, and body condition scores compared with diets without FO and CDS, respectively. Yields of milk (33.3 kg/d), energy-corrected milk, protein, lactose, and milk urea N were similar for all diets. Feeding FO and CDS decreased milk fat percentages (3.85, 3.39, 3.33, and 3.12%) and yields compared with diets without FO and CDS. Proportions of trans-11 C18:1 (vaccenic acid), cis-9 trans-11 conjugated linoleic acid (CLA; 0.52, 0.90, 1.11, and 1.52 g/100 g of fatty acids), and trans-10 cis-12 CLA (0.07, 0.14, 0.13, and 0.16 g/100 g of fatty acids) in milk fat were increased by FO and CDS. No interactions were observed between FO and CDS on cis-9 trans-11 CLA although vaccenic acid tended to be higher with the interaction. The addition of CDS to diets increased trans-10 C18:1. Greater ratios of vaccenic acid to cis-9 trans-11 CLA in plasma than in milk fat indicate tissue synthesis of cis-9 trans-11 CLA in the mammary gland from vaccenic acid in cows fed FO or CDS. Feeding fish oil at 0.5% of diet dry matter with a C18:2 n-6 rich source such as CDS increased the milk CLA content but decreased milk fat percentages.     

Endogenous synthesis of cis-9, trans-11 conjugated linoleic acid in dairy cows fed fresh pasture

New Zealand Holstein-Friesian cows (n = 4) were used to quantify the importance of endogenous synthesis of cis-9, trans-11 conjugated linoleic acid (CLA) via Delta(9)-desaturase in cows fed a fresh pasture diet. The experiment was a 4 x 4 Latin square design with treatments arranged in a 2 x 2 factorial. Treatments lasted 4 d and were pasture only, pasture plus sterculic oil, pasture plus sunflower oil, and pasture plus sunflower oil plus sterculic oil. Abomasal infusion of sterculic oil inhibited Delta(9)-desaturase and decreased the concentration of cis-9, trans-11 CLA in milk fat by 70%. Using the changes in cis-9 10:1, cis-9 12:1 and cis-9 14:1 to correct for incomplete inhibition of Delta(9)-desaturase, a minimum estimate of 91% of cis-9, trans-11 CLA in milk fat was produced endogenously in cows fed fresh pasture. Dietary supplementation of a pasture diet with sunflower oil increased the proportion of long chain fatty acids in milk fat; however, the increase in vaccenic acid concentration was small (18%) and there was no increase in cis-9, trans-11 CLA concentration. Overall, results show that endogenous synthesis is responsible for more than 91% of the cis-9, trans-11 CLA secreted in milk fat of cows fed fresh pasture. However, the failure of plant oil supplements to increase the concentration of cis-9, trans-11 CLA in milk fat from pasture-fed cows requires further investigation.     

Conjugated linoleic acid and other beneficial fatty acids in milk fat from cows fed soybean meal, fish meal, or both

Twelve multiparous Holstein cows at 48 +/- 8 DIM were used in a 4 x 4 Latin square with 21-d periods to determine the effect of replacing soybean meal with fish meal on feed intake, milk yield, and milk composition. Fish meal substituted for soybean meal on an isonitrogenous basis at 0, 25, 50, and 100% of supplemental protein. Total mixed diets were (DM basis) 25% corn silage, 25% alfalfa hay, and 50% concentrate mix. Intake of DM (27.9, 27.8, 26.1, and 25.8 kg/d for diets 1 to 4, respectively) was similar for all diets. Milk yield (37.5, 37.8, 37.2, and 37.7 kg/d) was not affected by diets. Milk protein percentages (3.23, 3.24, 3.31, and 3.35) increased with 100% fish meal supplementation and tended to be higher with 50% fish meal supplementation compared with 100% soybean meal diet. Milk fat percentages (3.18, 2.99, 3.04, and 2.87) and yield were lower with the 100% fish meal than with the 100% soybean meal diet. Concentration of n-3 fatty acids in milk fat (0.54, 0.56, 0.63, and 0.72 g/100 g fatty acids) increased as the proportion of fish meal in the diet increased. Concentrations of c9,t11 conjugated linoleic acid (CLA; 0.39, 0.44, 0.46, and 0.72 g/100 g fatty acids) and transvaccenic acid (TVA; 1.09, 1.19, 1.28, and 1.54 g/100 g of fatty acids) were higher with the 100% fish meal diet than with the 100% soybean meal diet. A total replacement of soybean meal with fish meal in the diet of lactating cows increased milk protein percentages and the beneficial fatty acids (CLA, TVA, and n-3 FA) in milk fat.     

Increasing amounts of conjugated linoleic acid progressively reduces milk fat synthesis immediately postpartum

Mixed conjugated linoleic acid (CLA) isomers decrease milk fat synthesis during established lactation, but their ability to cause milk fat depression (MFD) immediately postpartum remains unclear. Multiparous Holstein cows (n = 19) were randomly assigned to 1 of 4 doses of rumen-protected (RP) CLA supplements (0, 200, 400, and 600 g/d); each dose provided equal amounts of fatty acids by replacing and balancing treatments with an RP supplement of palm fatty acid distallate. Doses provided a total of 468 g fatty acids/d and 0, 62, 125, or 187 g of mixed CLA isomers/d, respectively. The CLA supplement contained a variety of CLA isomers: 5.4% trans-8, cis-10; 6.3% cis-9, trans-11; 7.9% trans-10, cis-12; and 8.2% cis-11, trans-13 CLA. Each group received treatments from approximately -10 to 21 d relative to calving. To improve palatability and ensure complete consumption, doses were mixed with equal amounts of steam-flaked corn and dried molasses; one-half the supplement was fed at 0600 h, and the remaining supplement was fed at 1800 h. Milk yield and individual feed intake were recorded daily, and milk samples were obtained from each cow every 2nd day (at both milkings) starting on d 1 postpartum. There were no differences in dry matter intake (17.1 kg/d), milk yield (34.2 kg/d), protein content (3.74%), lactose content (4.61%), or yield of milk protein or lactose. The CLA supplementation decreased overall milk fat content in a dose-responsive manner (4.57, 3.97, 3.32, and 3.10, respectively), and milk fat yield displayed the same progressive decline. The dose-dependent decrease in milk fat content was evident during wk 1 and became highly significant during wk 2 and 3. The milk fat yield response pattern was similar, and by d 21, the highest RP-CLA supplement decreased milk fat content and yield by 49 and 56%, respectively. These data clearly indicate RP-CLA can markedly (40 to 50%) induce MFD immediately postpartum without negatively affecting other production parameters.     

Production of conjugated fatty acids by lactic acid bacteria

Conjugated fatty acids have attracted much attention as a novel type of biologically beneficial functional lipid. Some isomers of conjugated linoleic acid (CLA) reduce carcinogenesis, atherosclerosis, and body fat. Considering the use of CLA for medicinal and nutraceutical purposes, a safe isomer-selective process is required. The introduction of biological reactions for CLA production could be an answer. We screened microbial reactions useful for CLA production, and found several unique reactions in lactic acid bacteria. Lactic acid bacteria produced CLA from linoleic acid. The produced CLA comprised a mixture of cis-9,trans-11-octadecadienoic acid (18:2) and trans-9,trans-11-18:2. Lactobacillus plantarum AKU 1009a was selected as a potential CLA producer. Using washed cells of L. plantarum AKU 1009a as a catalyst, CLA production from linoleic acid reached 40 mg/ml under the optimized conditions. The CLA-producing reaction was found to consist of two successive reactions, i.e., hydration of linoleic acid to 10-hydroxy-12-octadecenoic acid and dehydrating isomerization of the hydroxy fatty acid to CLA. On the basis of these results, the transformation of hydroxy fatty acids by lactic acid bacteria was investigated. Lactic acid bacteria transformed ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) to CLA (a mixture of cis-9,trans-11-18:2 and trans-9,trans-11-18:2). Castor oil, which is rich in the triacylglycerol form of ricinoleic acid, was also found to act as a substrate for CLA production by lactic acid bacteria with the aid of lipase-catalyzed triacylglycerol hydrolysis. L. plantarum AKU 1009a produced conjugated trienoic fatty acids from alpha- and gamma-linolenic acid. The trienoic fatty acids produced from alpha-linolenic acid were identified as cis-9,trans-11,cis-15-octadecatrienoic acid (18:3) and trans-9,trans-11,cis-15-18:3. Those produced from gamma-linolenic were cis-6,cis-9,trans-11-18:3 and cis-6,trans-9,trans-11-18:3. The conjugated trienoic fatty acids produced from alpha- and gamma-linolenic acid were further saturated by L. plantarum AKU 1009a to trans-10,cis-15-18:2 and cis-6,trans-10-18:2, respectively.     

Changes in milk fat in response to dietary supplementation with calcium salts of trans-18:1 or conjugated linoleic fatty acids in lactating dairy cows

Milk fat was investigated in lactating dairy cows fed diets supplemented with Ca salts of trans fatty acids (Ca-tFA) or Ca salts of conjugated linoleic acids (Ca-CLA). Forty-five Holstein cows (115 days in milk) were fed a control diet (51% forage; dry matter basis) supplemented with 400 g of EnerG II (Ca salts of palm oil fatty acids) for 2 wk; subsequently, 5 groups of 9 cows each were assigned for 4 wk to the control diet or diets containing 100 g of Ca-CLA or 100, 200, or 400 g of Ca-tFA in a randomized block design. Treatments had no effect on dry matter intake, milk production, protein, lactose, or somatic cell count. Milk fat percentage was reduced from 3.39% in controls to 3.30, 3.04, and 2.98%, respectively, by the Ca-tFA diets and to 2.54% by the Ca-CLA diet. Milk fat yield (1.24 kg/d in controls) was decreased by 60, 130, and 190 g/d with increasing dose of Ca-tFA and by 290 g/d with the Ca-CLA supplement. Consistent with increased endogenous synthesis of cis-9-containing CLA from precursors provided by the Ca-tFA diets, total CLA were similar in milk of cows fed Ca-CLA or Ca-tFA. Compared with controls, the Ca-CLA diet increased trans-10, cis-12-18:2 yield in milk, without altering levels of trans-18:1 isomers. In contrast, yields of most trans-18:1 isomers were elevated in milk of cows fed Ca-tFA diets, whereas yields of trans-10, cis-12-18:2 remained similar to control values. We conclude that milk fat depression can occur without an increase in trans-10, cis-12-18:2 in milk and that other components, perhaps the trans-10-18:1 isomer, may be involved.     

Analysis of variation in cis-9, trans-11 conjugated linoleic acid (CLA) in milk fat of dairy cows

Conjugated linoleic acid (CLA) is a fatty acid with numerous putative health benefits and is a natural component of ruminant-derived food products. An intermediate in rumen biohydrogenation is cis-9, trans-11 CLA, the major CLA isomer in milk fat. However, the major source of cis-9, trans-11 CLA in milk is endogenous synthesis by delta 9-desaturase conversion of trans-11 C18:1, another rumen biohydrogenation intermediate. The desaturase indices serve as a proxy for delta 9-desaturase activity and are calculated from the ratios of fatty acid pairs that represent product/substrate for this enzyme. This study analyzed individual animal variation in milk fat content of cis-9, trans-11 CLA and in desaturase indices in milk fat. Thirty lactating Holstein cows were allocated to one of three treatment groups: one received a standard total mixed ration, one received a diet that produced an elevated milk fat content of CLA, and a third treatment group was alternated between these diets at 3-wk intervals over the 12-wk study. There was a two- to threefold variation among individuals on the same diet for both milk fat content of CLA and desaturase indices in milk fat. This hierarchy was maintained to a large extent over the 12-wk study even in the variable treatment group that alternated between the two diets. Within the variable diet treatment, some animals consistently had a substantial response in milk fat content of CLA to dietary shifts, whereas other cows had little or no response. We conclude that while diet is a major determinant of the CLA content in milk fat, individual animal differences also have a substantial effect. The variation among individuals includes differences related to both rumen biohydrogenation and delta 9-desaturase activity in the mammary gland.