Effect of silage type and concentrate level on conjugated linoleic acids, trans-C18:1 isomers and fat content in milk from dairy cows

The objective of the study was to examine how the fatty acid composition of milk especially concentrations of conjugated linoleic acids (CLA) and trans-C18:1 isomers and milk fat percentage were affected by silage type and concentrate level. Forty dairy cows were blocked and randomly assigned to one of four diets in a 2 x 2 factorial arrangement of treatments and a six week experimental period. Treatments were total mixed rations with maize (M) or grass (G) silage differing in polyunsaturated fatty acid (PUFA) profile and starch content, combined with a high (H) or a low (L) level of concentrate (with or without grain). Treatments had no significant effect on milk, protein and lactose yield, but energy corrected milk yield, milk fat percentage and fat yield was lower and protein percentage higher for maize compared with grass silage diets. Overall, maize silage diets resulted in higher concentrations of CLA isomers compared with grass silage diets, but there was a significant interaction between silage type and concentrate level for concentrations of cis9,trans11-CLA; trans10,cis12-CLA; trans11-C18:1 and trans10-C18:1. A high level of concentrate increased trans10,cis12-CLA and trans10-C18:1 and reduced cis9,trans11-CLA and trans11-C18:1 when maize but not grass silage was provided. The results suggest that high levels of concentrate (grain) do not significantly alter the pattern of PUFA biohydrogenation in the rumen, the concentration of CLA and trans-C18:1 isomers in milk or cause milk fat depression unless combined with forage naturally high in starch and C18:2n-6 such as maize silage.     

Butters rich either in trans-10-C18:1 or in trans-11-C18:1 plus cis-9, trans-11 CLA differentially affect plasma lipids and aortic fatty streak in experimental atherosclerosis in rabbits

Dairy fat contains high amounts of saturated fatty acids (FA), which are associated with cardiovascular disease (CVD) risk. Manipulation of dairy cows nutrition allows to decrease the saturated FA content of milk fat, and is associated with increases either in conjugated linoleic acid (CLA) and trans-11-C18:1 contents, or in trans-10-C18:1 content. CLA putatively exhibits beneficial properties on CVD risk, whereas trans FA are suspected to be detrimental. The present study compared the effects of a trans-10-C18:1-rich butter (T10 butter), a trans-11-C18:1+CLA-rich butter (T11-CLA butter) and a standard butter (S butter) on lipid parameters linked to the CVD risk and fatty streaks. Thirty-six White New Zealand rabbits were fed one of the three butters (12% of the diet, plus 0.2% cholesterol) for 6 (experiment 1) or 12 (experiment 2) weeks. Liver lipids, plasma lipids and lipoprotein concentrations (experiments 1 and 2) and aortic lipid deposition (experiment 2) were determined. The T10 butter increased VLDL-cholesterol compared with the two others, and total and LDL-cholesterol compared with the T11-CLA butter ( P < 0.05). The T10 butter also increased non-HDL/HDL ratio and aortic lipid deposition compared with the T11-CLA butter ( P < 0.05). The T11-CLA butter non-significantly reduced aortic lipid deposition compared with the S butter, and decreased HDL-cholesterol and increased liver triacyglycerols compared with the two other butters (< 0.05). These results suggest that, compared with the S butter, the T10 butter had detrimental effects on plasma lipid and lipoprotein metabolism in rabbits, whereas the T11-CLA butter was neutral or tended to reduce the aortic lipid deposition.     

Effects of supplementation of maize silage diets with extruded linseed, vitamin E and plant extracts rich in polyphenols, and morning v. evening milking on milk fatty acid profiles in Holstein and Montbéliarde cows

The aim of this study was to evaluate the effects on dairy performance and milk fatty acid (FA) composition of (i) supplementation with extruded linseed (EL), (ii) supplementation with synthetic or natural antioxidants, namely vitamin E and plant extracts rich in polyphenols (PERP), (iii) cow breed (Holstein v. Montbéliarde) and (iv) time of milking (morning v. evening). After a 3-week pre-experimental period 24 lactating cows (12 Holstein and 12 Montbéliarde) were divided up into four groups of six cows: the first group received a daily control diet (diet C) based on maize silage. The second group received the same diet supplemented with EL (diet EL, fat level approximately 5% of dietary dry matter (DM)). The third group received the EL diet plus 375 IU/kg diet DM of vitamin E (diet ELE). The fourth group received the ELE diet plus 10 g/kg diet DM of a PERP mixture (diet ELEP). Compared with the diet C, feeding EL-rich diets led to lower concentrations of total saturated FA (SFA) and higher concentrations of stearic and oleic acids, each trans and cis isomer of 18:1 (except c12-18:1), non-conjugated isomers of 18:2, some isomers (c9t11-, c9c11- and t11t13-) of conjugated linoleic acid (CLA), and 18:3n-3. The vitamin E supplementation had no effect on milk yield, milk fat or protein percentage and only moderate effects on milk concentrations of FA (increase in 16:0, decreases in 18:0 and t6/7/8-18:1). The addition of PERP to vitamin E did not modify milk yield or composition and slightly altered milk FA composition (decrease in total saturated FA (SFA) and increase in monounsaturated FA (MUFA)). The minor effects of vitamin E may be partly linked to the fact that no milk fat depression occurred with the EL diet. During both periods the Holstein cows had higher milk production, milk fat and protein yields, and milk percentages of 4:0 and 18:3n-3, and lower percentages of odd-branched chain FA (OBCFA) than the Montbéliarde cows. During the experimental period the Holstein cows had lower percentages of total cis 18:1, and c9,c11-CLA, and higher percentages of 6:0, 8:0, t12-, t16/c14- and t13/14-18:1, and 18:2n-6 than Montbéliarde cows because of several significant interactions between breed and diet. Also, the total SFA percentage was higher for morning than for evening milkings, whereas those of MUFA, total cis 18:1, OBCFA and 18:2n-6 were lower. Extruded linseed supplementation had higher effect on milk FA composition than antioxidants, breed or time of milking.     

Complete stereospecific determination of conjugated linoleic acids in triacylglycerol of milk-fat

We analyzed two kinds of dairy fat differing in their contents of cis9, trans11-conjugated linoleic acid (cis9,trans 11-CLA or rumenic acid), and determined the positional distribution of this CLA-isomer within the three sn- positions of the triacylglycerol. In the high rumenic acid fat (HR), the CLA-isomers amounted to 2.1% of total fatty acids, and 0.8% in the low rumenic acid fat (LR). Over 90% of the total CLA-isomers were in the form of rumenic acid, with an identical isomeric CLA distribution in both fats. The two fats differed mainly with regards to their contents in palmitic acid, alpha-linolenic acid, and isomers of trans-C 18:1. Conversely, our stereospecific determination indicates that the positional distribution of rumenic acid is preserved among both types of fat, and is more specific for the sn-3 position of the triacylglycerol (54 to 64% of the total rumenic acid). Such a positional distribution is believed to be nutritionally relevant.     

Influence of roughage/concentrate ratio and linseed oil on the concentration of trans-fatty acids and conjugated linoleic acid in duodenal chyme and milk fat of late lactating cows

The objective of the study was to investigate the influence of two roughage-to-concentrate ratios, with or without linseed oil supplementation, on the flow of fatty acids in the intestinal chyme and the secretion in milk fat in late lactating cows. Seven late lactating cows fitted with cannulae in the dorsal rumen and simple T-shaped cannulae in the proximal duodenum were randomly assigned to four experimental periods applying an incomplete replicated 2 x 2 Latin square design. The rations consisted of meadow hay and a concentrate mixture given in a ratio of 70:30 or 30:70 on dry matter basis. The basal rations were fed without or with 200 g linseed oil daily. After three weeks of adaptation, samples from the duodenal chyme were taken to study the flow of fatty acids. Additionally, milk samples were analysed for their milk fat composition. Decreasing roughage/concentrate ratio and linseed oil supplementation significantly increased the flow of monounsaturated fatty acids (MUFA), trans-fatty acids (tFA) and conjugated linoleic acids (CLA) in the duodenum. Furthermore, linseed oil increased the flow of saturated fatty acids (SFA) in the duodenum. Higher concentrate portion (H 30) and linseed oil supplementation significantly decreased the milk fat content. SFA were lower (p < 0.05) and MUFA were higher (p < 0.05) in milk fat after linseed oil supplementation; H 30 resulted in more polyunsaturated fatty acids (PUFA, p < 0.05) in the milk. Linseed oil supplementation significantly increased tFA and CLA in milk fat. The higher CLA content in milk fat as compared to that in the digesta suggests that a substantial endogenous synthesis of CLA in the mammary gland tissue through A9-desaturase took place. Between 21% and 48% of duodenal t11-C(18:1) were converted into c9, t11-CLA in milk fat.     

Effects of fat source and dietary sodium bicarbonate plus straw on the conjugated linoleic acid content of milk of dairy cows

The effects of fat source (0.7 kg of fatty acids from extruded soybeans or palmitic acid), of sodium bicarbonate (0.3 kg) plus straw (1 kg) and the interaction of these treatments on the content of conjugated linoleic acid (CLA) in the milk of dairy cows were examined. During nine weeks a group of 10 cows received a ration with palmitic acid and bicarbonate plus straw (ration PAB). During three periods of three weeks a second group of 10 cows received successively a ration with extruded soybeans and bicarbonate plus straw (ration ESB), a ration with palmitic acid without bicarbonate or straw (ration PA), and a ration with extruded soybeans without bicarbonate or straw (ration ES). Rations ES and ESB increased the content of polyunsaturated fatty acids in milk, but decreased milk fat content, compared to rations PAB and PA. Ration ESB led to the greatest milk CLA content, by a synergy between the high amount of dietary fat, and the action of bicarbonate plus straw, favouring trans11 isomers of CLA and C18:1, presumably via a ruminal pH near neutrality. Ration ES favoured trans10 isomers, not desaturated in the mammary gland, so that the milk CLA content was lower than with ration ESB, and resulted in the lowest milk fat content. In conclusion, a ration supplemented with both extruded soybeans and bicarbonate plus straw, was an efficient way to increase the CLA content in the milk of dairy cows.     

The role of Delta(9)-desaturase in the production of cis-9, trans-11 CLA

Biomedical studies with animal models have demonstrated that cis-9, trans-11 conjugated linoleic acid (CLA), the predominant isomer found in milk fat from dairy cows, has anticarcinogenic effects. We recently demonstrated endogenous synthesis of cis-9, trans-11 CLA from ruminally derived trans-11 C18:1 by Delta(9)-desaturase in lactating dairy cows. The present study further examined endogenous synthesis of cis-9, trans-11 CLA and quantified its importance by increasing substrate supply using partially hydrogenated vegetable oil (PHVO) as a source of trans-11 C18:1 and blocking endogenous synthesis using sterculic oil (SO) as a source of cyclopropene fatty acids which specifically inhibit Delta(9)-desaturase. Four cows were abomasally infused with 1) control, 2) PHVO, 3) SO, and 4) PHVO+SO in a 4 x 4 Latin square design. With infusion of PHVO, cis-9, trans-11 CLA was increased by 17% in milk fat. Consistent with inhibition of desaturase, SO treatments increased milk fat ratios for the fatty acid pairs effected by Delta(9)-desaturase, C14:0/cis-9 C14:1, C16:0/cis-9 C16:1, and C18:0/cis-9 C18:1. The role of endogenous synthesis of CLA was evident from the 60-65% reduction in cis-9, trans-11 CLA which occurred in milk fat with SO treatments. cis-9 C14:1 originates from desaturation of C14:0 by Delta(9)-desaturase and can be used to estimate the extent of SO inhibition of Delta(9)-desaturase. When this correction factor was applied, endogenous synthesis was estimated to account for 78% of the total cis-9, trans-11 CLA in milk fat. Thus, endogenous synthesis was the major source of cis-9, trans-11 CLA in milk fat of lactating cows.     

Dietary lipids and forages interactions on cow and goat milk fatty acid composition and sensory properties

This review summarises the known effects of dietary factors on bovine and caprine milk fatty acid composition, as well as the regulation of cow and goat mammary lipid secretion. Special attention is given to fatty acids that could play a role for human health, such as saturated fatty acids, oleic acid, n-6- or n-3-C18 to C22 polyunsaturated fatty acids, trans isomers of C18:1 and C18:2, and isomers of conjugated linoleic acid (CLA). The main dietary factors taken into account are the nature of forages, including pasture, the forage:concentrate ratio and diet starch content, and the supplementation of dairy rations with crude or processed vegetable oils or oilseeds, and vitamin E. A particular emphasis is given to studies on interactions between these dietary factors, which show that there is a considerable plasticity of ruminant milk fatty acid composition. Despite the existence of several studies on the effects of dietary factors on the sensorial quality of milk and dairy products, there is a need to evaluate more deeply how the different feeding strategies could change the nutritional, sensorial and technological aspects of milk fat quality.     

Metabolic and health effects of isomeric fatty acids

PURPOSE OF REVIEW: Isomeric fatty acids have the same number of carbon and hydrogen atoms, but may have distinct metabolic and health effects. Two well-known examples of isomeric fatty acids are cis and trans monounsaturated fatty acids, and conjugated isomers of linoleic acid (CLA). The purpose of this review is to summarize recent findings from human studies on the metabolic and health effects of these two classes of isomeric fatty acids. RECENT FINDINGS: Apart from an unfavorable effect on serum lipoproteins, trans monounsaturated fatty acids from hydrogenated oils may increase plasma markers for a low-grade inflammatory state. From epidemiological studies, however, it is not possible to conclude if effects of ruminant and industrial trans fatty acids on cardiovascular risk are different. In contrast to in-vitro and animal studies, there are no indications that in humans the two most common CLA isomers (cis9,trans11-CLA and trans10,cis12-CLA) affect body composition differently. Longer-term supplementation, however, may slightly decrease body fat mass without apparent effects on plasma markers for glucose and lipid metabolism. Other studies have even reported adverse effects of CLA supplementation on insulin resistance and lipid peroxidation. SUMMARY: Evidence is increasing that trans monounsaturated fatty acids from hydrogenated oils increase plasma markers of low-grade chronic inflammation. From epidemiological studies, however, it is not clear if effects of ruminant and industrial trans fatty acids on cardiovascular risk are different. Effects of CLA on body composition remain controversial and more research is needed before the widely available CLA supplements should be advocated as an adjunct to control body weight.     

Feeding heat-oxidized oil to dairy cows affects milk fat nutritional quality

Heating oil and oilseeds results in oxidation products that affect ruminal biohydrogenation of polyunsaturated fatty acids, altering milk fatty acids profile, and could be transferred to milk. An experiment was conducted to investigate the effects of oil heating on rumen and milk fatty acids profile and the transfer of oxidation products to milk. Sunflower oil was heated at 150°C for 15 h and given to lactating dairy cows in a 2×2 arrangement: two groups of two cows, equipped with a ruminal cannula and receiving two diets (containing either heated or unheated oil) during two experimental periods. Oil heating generated hydroperoxides and/or hydroxyacids and aldehydes, in particular trans-2,trans-4-decadienal. In milk, heated oil only significantly decreased trans-11-C18:1 and cis-9,trans-11-CLA percentage compared to non-heated oil, and slightly increased cis-9,cis-12-C18:2 percentage, which was probably linked to an inhibition of the ruminal Δ12 isomerase by oxidative products in the rumen. However, feeding highly oxidized oil did not result in the appearance of hydroperoxides or hydroxyacids in milk and did not increase milk aldehydes content.     

Effect of duodenal infusion of trans10,cis12-CLA on milk performance and milk fatty acid profile in dairy goats fed high or low concentrate diet in combination with rolled canola seed

The effect of t10,c12-C18:2 on milk production, and fatty acid (FA) profile of milk fat was studied in 8 goats infused duodenally with t10,c12-C18:2 (2 g.10 h-1) during 3 days, followed by a 2-day infusion of skim milk (SM). The goats were assigned to 4 diets in a factorial arrangement constituted by low (L = 45%) or high (H = 65% of the diet DM) percentage of concentrate without (CS0) or with (CS20) rolled canola seed (20% of the concentrate DM). Milk samples were collected before (basal), and during the t10,c12-C18:2 and SM infusions. The t10,c12-C18:2 in milk fat increased from undetectable basal values to an average of 0.39% of total FA in the 3rd day of t10,c12-C18:2 infusion. DMI, milk yield, and the contents and yield of milk fat, protein, and lactose were similar between basal and the t10,c12-C18:2 infusion. The concentration of saturated FA with 4 to 16C did not change during the t10,c12-C18:2 infusion, whereas C18:0 increased, particularly in the milk fat of the CS20 group. The t10,c12-C18:2 infusion increased the t10- and t11-C18:1 (except a reduction in t11-C18:1 for the H-CS20 group), and it decreased the c9,t11-C18:2 in milk fat, particularly for the H-CS20 group. The t10,c12-C18:2 infusion reduced the c9,t11-C18:2/t11-C18:1 ratio, particularly for the CS0 group. The results indicate that mammary lipogenesis in dairy goats was not decreased by t10,c12-C18:2, however, the desaturation of long chain FA appeared to be equally affected as in dairy cows. This reduction in the desaturase index of milk fat could have been a direct effect of t10,c12-C18:2, or mediated via an increase in t10-C18:1.     

Trans fatty acids in hydrogenated fat inhibited the synthesis of the polyunsaturated fatty acids in the phospholipid of arterial cells

Our hypothesis that the trans fatty acids in hydrogenated fat inhibited the synthesis of polyunsaturated fatty acids in the phospholipid of arterial cells was tested with five groups each with six pregnant porcine fed from d 35 of gestation and during lactation. The basal diet contained 2% corn oil (control). The other four diets included the control + 10% butter or 10% hydrogenated fat plus two levels of Mg. Plasma, milk and aortic phospholipid fatty acids, phospholipid composition and calcium content of the aorta from the piglets were determined. At 48 +/- 2 d of age, the aorta phospholipid of piglets from porcine fed hydrogenated fat contained a significantly higher concentration of linoleic acid, less arachidonic acid, and less long chain polyunsaturated fatty acid (PUFA) than did piglets from porcine fed either butterfat or the control diet. Mg had no effect. These changes in composition in piglets from porcine fed hydrogenated fat indicate that trans fat inhibits the metabolic conversion of linoleic acid to arachidonic acid and to other n-6 PUFA. The aortic calcium content data showed a significant interaction of calcium concentration with age. We concluded: 1) that dietary trans fat perturbed essential fatty acid (EFA) metabolism which led to changes in the phospholipid fatty acid composition in the aorta, the target tissue of atherogenesis, 2) this inhibition of EFA to PUFA by the isomeric fatty acids in hydrogenated fat is a risk factor in the development of coronary heart disease.     

Dietary trans fatty acids modulate erythrocyte membrane fatty acyl composition and insulin binding in monkeys

The substitution of trans- for half of the cis-monounsaturated fatty acids in the diet of Macaca fasicularis monkeys resulted in alterations in erythrocyte fatty acid composition and insulin receptor properties but not in membrane fluidity. Both cis and trans diets contained 10% fat and similar fatty acid compositions, except that approximately 50% of the cis-octadecenoate (c-18:1) in the cis diet was replaced with trans-octadecenoate isomers (t-18:1) in the trans diet. Compared with the cis diet, the trans diet resulted in the incorporation of approximately 11% t-18:1, an approximately 50% decrease in c-18:1, an approximately 16% decrease in total saturated fatty acids, and an approximately 20% increase in 18:2(n-6) in erythrocyte membrane lipids. The increase in 18:2(n-6) may reflect on homeostatic mechanisms designed to maintain overall membrane fluidity, as no diet-related changes in fluidity were observed with diphenylhexatriene steady state fluorescence polarization. Values observed for insulin binding and insulin receptor number were higher and binding affinity was lower in monkeys fed the cis diet. In the absence of an effect on overall membrane fluidity, altered receptor activity suggests that insulin receptor activity is dynamic, requiring specific fluid membrane subdomains or highly specific fatty acid-protein interactions.     

DGAT1 underlies large genetic variation in milk-fat composition of dairy cows

Dietary fat may play a role in the aetiology of many chronic diseases. Milk and milk-derived foods contribute substantially to dietary fat, but have a fat composition that is not optimal for human health. We measured the fat composition of milk samples in 1918 Dutch Holstein Friesian cows in their first lactation and estimated genetic parameters for fatty acids. Substantial genetic variation in milk-fat composition was found: heritabilities were high for short- and medium-chain fatty acids (C4:0-C16:0) and moderate for long-chain fatty acids (saturated and unsaturated C18). We genotyped 1762 cows for the DGAT1 K232A polymorphism, which is known to affect milk-fat percentage, to study the effect of the polymorphism on milk-fat composition. We found that the DGAT1 K232A polymorphism has a clear influence on milk-fat composition. The DGAT1 allele that encodes lysine (K) at position 232 (232K) is associated with more saturated fat; a larger fraction of C16:0; and smaller fractions of C14:0, unsaturated C18 and conjugated linoleic acid (P < 0.001). We conclude that selective breeding can make a significant contribution to change the fat composition of cow's milk.     

Milk fat depression and energy balance in stall-fed dairy goats supplemented with increasing doses of conjugated linoleic acid methyl esters

Feeding dietary supplements containing trans-10, cis-12-conjugated linoleic acid (t10,c12-CLA) has been shown to induce milk fat depression in cows, ewes and goats. However, the magnitude of the response is apparently less pronounced in lactating goats. The objective of this study was to evaluate the effects of increasing doses of CLA methyl esters (CLA-ME) on milk production, composition and fatty-acid profile of dairy goats. Eight Toggenburg goats were separated in two groups (four primiparous and four multiparous) and received the following dietary treatments in a 4×4 Latin Square design: CLA0: 45 g/day of calcium salts of fatty acids (CSFA); CLA15; 30 g/day of CSFA+15 g/day of CLA-ME; CLA30: 15 g/day of CSFA+30 g/day of CLA-ME; and CLA45: 45 g/day of CLA-ME. The CLA-ME supplement (Luta-CLA 60) contained 29.9% of t10,c12-CLA; therefore, the dietary treatments provided 0, 4.48, 8.97 and 13.45 g/day of t10,c12-CLA, respectively. Feed intake, milk production, concentration and secretion of milk protein and lactose, body condition score and body weight were unaffected by the dietary treatments. Milk fat secretion was reduced by 14.9%, 30.8% and 40.5%, whereas milk fat concentration was decreased by 17.2%, 33.1% and 40.7% in response to CLA15, CLA30 and CLA45, respectively. Secretions of both de novo synthesized and preformed fatty acids were progressively reduced as the CLA dose increased, but the magnitude of the inhibition was greater for the former. There was a linear reduction in most milk fat desaturase indexes (14:1/14:0, 16:1/16:0, 17:1/17:0 and 18:1/18:0). Milk fat t10,c12-CLA concentration and secretion increased with the CLA dose, and its apparent transfer efficiency from diet to milk was 1.18%, 1.17% and 1.21% for CLA15, CLA30 and CLA45 treatments, respectively. The estimated energy balance was linearly improved in goats fed CLA.     

Effect of replacing calcium salts of palm oil distillate with incremental amounts of conventional or high oleic acid milled rapeseed on milk fatty acid composition in cows fed maize silage-based diets

Based on potential benefits to human health, there is increasing interest in altering the composition of ruminant-derived foods. Including rapeseeds in the dairy cow diet is an effective strategy for replacing medium-chain saturated fatty acids (SFA) with cis-monounsaturated fatty acids (MUFA) in bovine milk, but there is limited information on the optimum level of supplementation. Decreases in SFA due to plant oils are also accompanied by increases in milk trans fatty acid (FA) content and it is possible that high oleic acid rapeseeds may result in a higher enrichment of cis-9 18:1 and lower increases in trans FAs in milk compared with conventional varieties. Seven multiparous lactating Holstein-Friesian cows were allocated to one of seven treatments in an incomplete Latin square design with five 28-day experimental periods, to evaluate the effect of replacing calcium salts of palm oil distillate (CPO; 41 g/kg diet dry matter, DM) with 128, 168 or 207 g/kg diet DM of conventional (COR) or a high oleic acid (HOR) rapeseed fed as a supplement milled with wheat. Rapeseed variety and inclusion level had no effect (P > 0.05) on DM intake, milk yield and composition. Both rapeseed varieties decreased linearly (P < 0.001) milk fat SFA content, which was partially compensated for by a linear increase (P < 0.001) in cis-9 18:1 concentration. Reductions in milk SFA were also associated with increases (P < 0.05) in trans 18:1 and total trans FA content, with no difference (P > 0.05) between rapeseed varieties. Replacing CPO in the diet with milled rapeseeds had no effect (P > 0.05) on total milk conjugated linoleic acid (CLA) concentration. Relative to a COR, inclusion of a high oleic acid variant in the diet increased (P = 0.01) the ratio of trans-MUFA : trans-polyunsaturated fatty acids in milk that may have implications with respect to cardiovascular disease risk in humans. In conclusion, data indicated that replacing CPO with milled rapeseeds at levels up to 1150 g oil/day could be used as a nutritional strategy to lower milk SFA content without inducing adverse effects on DM intake and milk production. HOR reduced milk fat SFA content to a greater extent than a conventional variety, but did not minimise associated increases in trans FA concentrations. However, the high oleic acid variant did alter the relative abundance of specific trans 18:1, CLA and trans 18:2 isomers compared with conventional rapeseeds.     

Response of milk fat concentration and yield to nutrient supply in dairy cows

Dietary changes alter dairy cow milk fat concentration (MFC) and yield (MFY) through modifications in the supply of nutrients, which act as precursors or inhibitors of mammary fat synthesis. The current models used to formulate dairy cow diets cannot predict changes in milk fat. The knowledge of the effects of the nutrients on milk fat would help to progress toward this prediction. To this end, we quantified and compared the milk fat responses to variations in the supply of seven nutrients derived from digestion: volatile fatty acids, glucose, proteins, long-chain fatty acids (LCFA) and t10,c12-conjugated linoleic acid (CLA). A database was compiled from studies involving digestive infusions of these nutrients in dairy cows. It included 147 comparisons between a nutrient infusion and a control treatment. The nutrient infusions were limited to the range of physiological variations to mimic nutrient changes after dietary modifications. We established models for the response of MFC, MFY and milk fatty acid (FA) composition to the supply of each nutrient. MFC and MFY responses to the nutrients were significant and linear, except for the MFC response to glucose that was curvilinear. The nutrients differed in their effects on MFC and MFY: acetate, butyrate and LCFA increased MFC and MFY, whereas propionate, glucose and t10,c12-CLA decreased them. Protein infusions increased MFY and decreased MFC because of an increase in milk yield. The effects of numerous interfering factors related to animals, diets or experimental conditions were tested on the residuals of the response models. The responses of milk FA percentages are also provided. When adjusted to the in vivo variations in the nutrients observed after dietary changes, the effects of the different nutrients were moderate. Finally, this study showed that several of these nutrients could contribute to the changes in milk fat production and composition observed after dietary changes. This is a first step toward predicting milk fat response to changes in nutrient supply.     

Stearoyl-CoA desaturase 1 genotype and stage of lactation influences milk fatty acid composition of Canadian Holstein cows

Single nucleotide polymorphisms in the coding region of the bovine stearoyl-CoA desaturase 1 gene have been predicted to result in p.293A (alanine at amino acid 293) and p.293V (valine at amino acid 293) alleles at the stearoyl-CoA desaturase1 locus. The objectives of this study were to evaluate the extent to which genotypes at the stearoyl-CoA desaturase 1 locus and stage of lactation influence milk fatty acid composition in Canadian Holstein cows. Cows with the p.293AA genotype had higher C10 index, C12 index and C14 index and higher concentrations of C10:1 (10 carbon fatty acid with one double bond), C12:1 (12 carbon fatty acid with one double bond) and myristoleic acid (C14:1) compared with the p.293AV or p.293VV cows. Cows had higher C18 index and total index, and lower C10 index, C12 index, C14 index and CLA index during early lactation compared with the subsequent lactation stages. Early lactation was also characterized by higher concentrations of oleic acid (C18:1 cis -9), vaccenic acid (C18:1 trans -11), linoleic acid (C18:2), monounsaturated fatty acids and total polyunsaturated fatty acids, and lower concentrations of capric acid (C10:0), C10:1, lauric acid (C12:0), C12:1, myristic acid (C14:0), myristoleic acid (C14:1), palmitic acid (C16:0) and total saturated fatty acids compared with the subsequent lactation stages. Neither the stearoyl-CoA desaturase 1 genotype nor the stage of lactation had an influence on conjugated linoleic acid concentrations in milk.     

一株产共轭亚油酸瘤胃细菌Streptococcus infantarius RB111的筛选与鉴定

从内蒙古鄂尔多斯山羊瘤胃中分离筛选到1株产共轭亚油酸的瘤胃细菌RB111,该菌株的cis9,trans11-CLA和trans10,cis12-CLA总产量为269.2 mg/L,其中cis9,trans11-CLA占52.64%,trans10,cis12-CLA占47.36%。对菌株RB111进行了形态学观察、生理生化鉴定、脂肪酸组成分析以及16S rRNA基因序列分析。16S rRNA基因序列分析结果表明该菌株与婴儿链球菌(Streptococcus infantarius)的模式菌株NCDO 599的序列相似性为99%,该菌株的形态特征及生理生化特性与文献报道的Streptococcus infantarius一致。脂肪酸组成分析结果显示,菌株RB111的细胞脂肪酸主要成分是C16:0、C18:1ω9c和C18:0,3种脂肪酸占脂肪酸总量的60.64%。综合以上结果,菌株RB111被鉴定为婴儿链球菌Streptococcus infantarius。     

Effect of replacing calcium salts of palm oil distillate with extruded linseeds on milk fatty acid composition in Jersey and Holstein cows

Clinical and biomedical studies have provided evidence for the critical role of n-3 fatty acids on the reduction of chronic disease risk in humans, including cardiovascular disease. In the current experiment, the potential to enhance milk n-3 content in two breeds with inherent genetic differences in mammary lipogenesis and de novo fatty acid synthesis was examined using extruded linseeds. Six lactating cows (three Holstein and three Jersey) were used in a two-treatment switchback design with 3 × 21-day experimental periods to evaluate the effect of iso-energetic replacement of calcium salts of palm oil distillate (CPO) in the diet (34 g/kg dry matter (DM)) with 100 g/kg DM extruded linseeds (LIN). For both breeds, replacing CPO with LIN had no effect (P > 0.05) on DM intake or milk yield, but reduced (P < 0.05) milk fat and protein yield (on average, from 760 to 706 and 573 to 552 g/day, respectively). Relative to CPO, the LIN treatment reduced (P < 0.01) total saturated fatty acid content and enhanced (P < 0.001) 18:3n-3 in milk, whereas breed by diet interactions were significant for milk fat 16:0, total trans fatty acid and conjugated linoleic acid concentrations. Increases in 18:3n-3 intake derived from LIN in the diet were transferred into milk with a mean marginal transfer efficiency of 1.8%. Proportionate changes in milk fatty acid composition were greater in the Jersey, highlighting the importance of diet-genotype interactions on mammary lipogenesis. More extensive studies are required to determine the role of genotype on milk fat composition responses to oilseeds in the diet.