Meat fats in nutrition

This article reviews the fat content and fatty acid composition of meats in the human diet and discusses nutritional facts related to meat, meat products and other meat-containing foods as sources of dietary fats. Meat is an increasingly important source of high-value animal protein worldwide. Meat fat comprises mostly monounsaturated and saturated fatty acids, with oleic (C18:1), palmitic (C16:0), and stearic acid (C18:0) being the most ubiquitous. Meat and meat products are considerable sources of cholesterol in the diet. In most industrialized countries, a high meat intake contributes to a higher than recommended total and saturated fat and cholesterol intake. Another concern is that meat may replace sources of other important nutrients in the diet. Therefore, the advice to consumers is to prefer lean meats and low-fat meat products and use meat in moderation only.     

Infusion of long-chain fatty acids varying in saturation and chain length into the abomasum of lactating dairy cows.

Free long-chain fatty acids were infused into the abomasum of lactating dairy cows to determine postruminal effects on feed intake, production and composition of milk, nutrient digestibilities, and metabolites in blood. Four Holstein cows averaging 120 DIM and fitted with ruminal cannulas were used in a 4 x 4 Latin square design with 14-d periods. Treatments were abomasal infusions of 1) control, 168 g/d of meat solubles (carrier for fatty acids), 2) control plus 450 g/d of mostly saturated fatty acids (C16:C18 = .75), 3) control plus 450 g/d of a mixture of saturated and unsaturated fatty acids (C16:C18 = .40), and 4) control plus 450 g/d of mostly unsaturated fatty acids (C16:C18 = .11). Production of milk and milk components, DMI, and intake of digestible energy decreased linearly as unsaturation and chain length of infused fatty acids increased. Percentages of fat, CP, and SNF in milk and total tract apparent digestibilities of DM, OM, ADF, NDF, energy, and fatty acids were not affected significantly by treatments. Infusing fatty acids decreased proportions and yields of short- and medium-chain fatty acids and increased proportions and yields of unsaturated C18 fatty acids in milk fat. Increasing unsaturation and chain length of infused fatty acids linearly decreased proportion and yield of palmitic acid but increased proportions and yields of polyunsaturated C18 fatty acids in milk fat. Infusing fatty acids increased concentrations of NEFA and cholesterol in blood plasma. The profile of fatty acids reaching the intestine may be an important determinant of responses to supplemental fats fed to lactating dairy cows.     

Effects of age on fatty acid composition of the hump and abdomen depot fats of the Arabian camel (Camelus dromedarius)

This study aimed to quantify concentrations of fatty acids in the hump and abdomen fats of three different age groups of camel. Hump and abdomen fats were extracted from eight each of one-humped camels (Camelus dromedarius) of three age groups: group 1 (<1 year old), group 2 (1-3 years old) and group 3 (>3 years old). The fatty acid methyl ester concentrations of these fats were determined by gas-liquid chromatography (GLC). The percentage of fat in the hump (H) and abdomen (A) fats was significantly (P<0.05) lower for group 1 (H 92.0% and A 94.3%) than for group 2 (H 97.4% and A 97.2%) and group 3 (H 97.6% and A 97.5%), on a dry matter basis. Hump and abdomen fats from the three different groups had similar fatty acid patterns with more saturated than unsaturated fatty acids. The saturated fatty acids in the hump fats accounted for 58.3, 67.6, and 63.0% of the total fatty acids for groups 1, 2 and 3, respectively; group 1 had significantly (P<0.05) lower saturated and higher unsaturated fatty acid concentrations than group 2. The iodine numbers were significantly (P<0.05) higher in group 1 than either group 2 or 3. Palmitic acid (C16:0) was the major fatty acid in hump fat with 32.06, 32.90 and 34.37%, followed by oleic acid (C18:1) 33.65, 21.66 and 28.91.0% and stearic acid (C18:0) 18.85, 24.13 and 20.74% for groups 1, 2 and 3, respectively. Group 1 had significantly higher (P<0.05) oleic acid and lower stearic acid concentrations than group 2. The melting point of both hump and abdomen fats varied between the age groups. This study indicated that age has an effect on the fatty acid composition and the melting point of hump and abdomen fats in one-humped Arabian camels.     

Feeding oleamide to lactating Jersey cows 1. Effects on lactation performance and milk fatty acid composition

Oleamide was previously reported to resist ruminal biohydrogenation and elevate milk oleic acid concentration when fed to lactating Holstein cows. To determine if Jersey cows responded similarly to oleamide, four lactating Jersey cows (mean 417 kg of body weight and 64 days in milk) were fed four diets in a 4x4 Latin square with 2-wk periods. Diets were total mixed ration containing 47% corn silage and 53% concentrate (dry matter basis) and were supplemented with no added fat (control), or with 3.5% added fat from either higholeic canola oil, a commercial source of oleamide, or oleamide synthesized from oleic acid and urea. The canola oil supplement had no effect on milk yield or composition. Compared to canola oil, the oleamide supplements reduced milk yield, dry matter intake, and milk fat and protein contents. Milk oleic acid concentration increased from 17.4% of total fatty acids for the control diet to 22.1% for the canola oil diet. Both oleamides further increased milk oleic acid to 30.0 and 27.1% of total fatty acids for the commercial and synthesized oleamides, respectively. Milk palmitic acid was reduced and stearic acid was increased by all fat supplements but more so by the oleamides than by the canola oil. Consistent with previous reports that fatty acyl amides resist ruminal biohydrogenation, feeding oleamide to Jersey cows in this study increased milk oleic acid concentration but had negative effects on feed intake and milk yield.     

Fatty acid composition of ewe milk as affected by solar radiation and high ambient temperature

Forty lactating Comisana ewes were either exposed to or protected from solar radiation and fed either in the morning or afternoon during summer in a Mediterranean climate. Individual milk samples were taken on days 7, 21 and 42 of the study period to determine fatty acid composition by gas chromatography. Exposure to solar radiation resulted in higher proportions of short-chain and saturated fatty acids in milk, primarily because of increased contents of caproic, capric, lauric, myristic and stearic acids (by 3-18%), and decreased contents of oleic, linoleic and linolenic acids (by 2-9%). As a consequence, the long to short chain and the unsaturated to saturated fatty acid ratios were significantly higher by 4 and 13% respectively in the milk of the protected ewes compared with that of the exposed animals. Provision of shade also led to an increase in the 18:0+18:1 to 16:0 ratio, and to a decrease in the 12:0 + 14:0 + 16:0 fatty acid group, which are regarded as reliable indexes of the nutritional property of dietary fat in reducing cholesterol levels in human plasma. Feeding time had little impact on milk fat. Our findings suggest that high ambient temperature may markedly modify the lipid composition of ewe milk and that provision of shade, but not feeding management, can improve the milk fatty acid profile in dairy sheep raised in hot climates.     

Effect of added dietary fat and bovine somatotropin on the performance and metabolism of lactating dairy cows

Four early lactation Holstein cows (44 to 105 d postpartum) were used in a 4 X 4 Latin square experiment in a 2 X 2 factorial arrangement of treatments to study effects of added dietary fat and/or bovine somatotropin on performance and metabolism. Treatments were: 1) control diet plus placebo injection; 2) 5% added dietary fat (hydrolyzed blend of animal and vegetable fat) + placebo injection; 3) control diet + 50 IU bovine somatotropin/d; and 4) 5% added dietary fat + 50 IU bovine somatotropin/d. Dietary fat reduced dry matter intake (21.6 vs. 22.7 kg/d) and elevated plasma triglycerides (34.7 vs. 29.2 mg/100 ml). Injection of somatotropin lowered blood urea nitrogen, increased plasma free fatty acids, and increased plasma somatotropin. Milk production, milk fat percent, and 4% FCM production were increased by the injection of somatotropin. Milk protein percent was decreased (3.30 vs. 3.44%) with added fat and tended to be lower with somatotropin. The percentage of short-chain fatty acids (C6 to C14) in milk fat decreased with added fat while the percentage of stearic and oleic acids in milk fat increased. Production responses for fat plus somatotropin and somatotropin treatments were similar. Under the conditions of this study, the addition of dietary fat with injection of somatotropin had little effect on production parameters compared with that found with somatotropin alone.     

PRODUCTION OF LOW-FAT FRANKFURTERS WITH VEGETABLE OILS FOLLOWING THE DIETARY GUIDELINES FOR FATTY ACIDS

Low-fat frankfurters (10% fat) were produced with vegetable oils following the dietary guidelines for fatty acids as suggested in the currently recommended diet (CRD) by the American Heart Association, the Grundy diet (GD) and the Mediterranean diet (MD). MD-frankfurters, produced with olive oil (31.82%) and soybean oil (17.51%), had the highest (P<0.05) ratio of monousaturated fatty acids (MUFA)/saturated fatty acids (SFA) minus stearic. CRD-frankfurters, produced mainly with cottonseed oil (40.70%) and soybean oil (6.90%), had the highest (P<0.05) content of polyunsaturated fatty acids (PUFA). GD-frankfurters, produced with cottonseed oil (34.04%) and olive oil (15.19%), had the highest (P<0.05) ratio of (C18:2 n-6)/(C18:3 n-3). Compared to high-fat frankfurters (27% all animal fat), low-fat frankfurters had lower (P<0.05) stearic acid and trans ω-9 oleic acid, higher (P<0.05) content of total PUFA, higher (P<0.05) ratio of (C18:2+C 18:3)/SFA minus stearic acid, and lower cholesterol content (52.60%-59.11%), were darker, redder and more yellow, firmer and less juicy, but had similar overall acceptabily.     

Conjugated linoleic acid and vaccenic acid in rumen, plasma, and milk of cows fed fish oil and fats differing in saturation of 18 carbon fatty acids

The objective of this study was to examine the effect of feeding fish oil (FO) along with fat sources that varied in saturation of 18 carbon fatty acids (high stearic, high oleic, high linoleic, or high linolenic acids) on rumen, plasma, and milk fatty acid profiles. Four primiparous Holstein cows at 85 d in milk (+/- 40) were assigned to 4 x 4 Latin squares with 4-wk periods. Treatment diets were 1) 1% FO plus 2% commercial fat 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 were formulated to contain 18% crude protein and were composed of 50% (dry basis) concentrate mix, 25% corn silage, 12.5% alfalfa silage, and 12.5% alfalfa hay. Milk production, milk protein percentages and yields, and dry matter intake were similar across diets. Milk fat concentrations and yields were least for HO and HLO diets. The proportion of milk cis-9, trans-11 conjugated linoleic acid (CLA; 0.71, 0.99, 1.71, and 1.12 g/100 g fatty acids, respectively), and vaccenic acid (TVA; 1.85, 2.60, 4.14, and 2.16 g/100 g fatty acids, respectively) were greatest with the HLO diet. The proportions of ruminal cis-9, trans-11 CLA (0.09, 0.16, 0.18, and 0.16 g/100 g fatty acids, respectively) were similar for the HO, HLO, and HLN diets and all were higher than for the HS diet. The proportions of TVA (2.85, 4.36, 8.69, and 4.64 g/100 g fatty acids, respectively) increased with the HO, HLO, and HLN diets compared with the HS diets, and the increase was greatest with the HLO diet. The effects of fat supplements on ruminal TVA concentrations were also reflected in plasma triglycerides, (2.75, 4.64, 8.77, and 5.42 g/100 g fatty acids, respectively); however, there were no differences in the proportion of cis-9, trans-11 CLA (0.06, 0.07, 0.06, and 0.07 g/100 g fatty acids, respectively). This study further supports the significant role for mammary delta-9 desaturase in milk cis-9, trans-11 CLA production.     

Addition of protected and unprotected fish oil to diets for dairy cows. I. Effects on the yield,composition and taste of milk

Thirty Holstein cows in mid-lactation (158+/-20 DIM) were given a total mixed ration based on grass silage, maize silage and rolled barley. After a preliminary period of 1 week, this diet was supplemented with nothing (control), unprotected fish oil (3.7% of dry matter, DM), or two levels of glutaraldehyde-protected microcapsules of fish oil (1.5% and 3.0% of DM, respectively). Unprotected and protected supplements contained, respectively, 74% and 58% of DM as lipids. Cows given the unprotected supplement reduced their feed intake by > 25%. Consequently, these cows lost body weight and produced less milk. DM intake, body weight, and milk yield were unaffected by protected fish oil. Fish oil reduced both milk fat and protein percentages, and decreased the proportion of short-chain fatty acids, stearic, and oleic acids in milk fat. Milk trans C18:1 fatty acids increased in cows given both unprotected and protected fish oil. Milk fat content of very-long-chain n3 polyunsaturated fatty acids, including C20:5 and C22:6, increased with fish oil in the diet. Accordingly, the peroxide index increased and a taste panel was able to detect unusual taste in milk from cows consuming the higher level of protected fish oil and disliked the milk from cows given unprotected fish oil. In conclusion, when lactating cows consumed fish oil, milk concentration of long-chain n3 fatty acids increased and mammary de novo synthesis of fatty acids decreased, but milk yield and milk protein content were reduced, and the milk was more susceptible to oxidation and its taste was adversely affected.     

Feeding micronized and extruded flaxseed to dairy cows: effects on blood parameters and milk fatty acid composition

Four lactating Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square design to determine the effects of feeding micronized and extruded flaxseed on milk composition and blood profile in late lactation. Four diets were formulated: a control (C) diet with no flaxseed, a raw flaxseed (RF) diet, a micronized flaxseed (MF) diet, and an extruded flaxseed (EF) diet. Flaxseed diets contained 12.6% flax-seed (dry matter basis). Experimental periods consisted of 21 d of diet adaptation and 7 d of data collection. Feeding flaxseed reduced milk yield and energy-corrected milk by 1.8 and 1.4 kg/d, respectively. Yields of milk protein and casein were also lower for cows fed flaxseed diets than for those fed the C diet. Milk yield (1.6 kg/d) and milk fat percentage (0.4 percentage unit) were lower for cows fed EF than those fed MF. Plasma cholesterol and nonesterified fatty acid concentrations were higher for cows fed flaxseed diets relative to those fed the C diet. Flaxseed supplementation decreased plasma concentrations of medium-chain (MCFA) and saturated (SFA) fatty acids and increased concentrations of long-chain (LCFA) and monounsaturated fatty acids. Feeding flaxseed reduced the concentrations of short-chain fatty acids (SCFA), MCFA, and SFA in milk fat. Consequently, concentrations of LCFA and unsaturated fatty acids were higher for cows fed flaxseed diets than for those fed the C diet. Flaxseed supplementation increased average concentrations of C(18:3) and conjugated linoleic acid by 152 and 68%, respectively. Micronization increased C(18:3) level, and extrusion reduced concentrations of SCFA and SFA in milk. It was concluded that feeding raw or heated flaxseed to dairy cows alters blood and milk fatty acid composition. Feeding extruded flaxseed relative to raw or micronized flaxseed had negative effects on milk yield and milk composition.     

Determination of Milk Fat Adulteration with Vegetable Oils and Animal Fats by Gas Chromatographic Analysis

This study assessed the potential application of gas chromatography (GC) in detecting milk fat (MF) adulteration with vegetable oils and animal fats and of characterizing samples by fat source. One hundred percent pure MF was adulterated with different vegetable oils and animal fats at various concentrations (0%, 10%, 30%, 50%, 70%, and 90%). GC was used to obtain the fatty acid (FA) profiles, triacylglycerol (TG) contents, and cholesterol contents. The pure MF and the adulterated MF samples were discriminated based on the total concentrations of saturated FAs and on the 2 major FAs (oleic acid [C18:1n9c] and linoleic acid [C18:2n6c], TGs [C52 and C54], and cholesterol contents using statistical analysis to compared difference. These bio‐markers enabled the detection of as low as 10% adulteration of non‐MF into 100% pure MF. The study demonstrated the high potential of GC to rapidly detect MF adulteration with vegetable and animal fats, and discriminate among commercial butter and milk products according to the fat source. These data can be potentially useful in detecting foreign fats in these butter products. Furthermore, it is important to consider that several individual samples should be analyzed before coming to a conclusion about MF authenticity.     

常用动、植物食用油中脂肪酸组成的分析

以氢氧化钾/甲醇碱催化法对食用油样品进行甲酯化衍生化预处理,采用气相色谱-质谱联用技术,对采自西安、咸阳市的16种食用植物油和4种动物油(猪油、牛油、羊油和鸡油)中的脂肪酸组成进行测定,并对其所含各类脂肪酸的比例关系进行详细地分析,以确定不同类型食用油的营养特征。结果显示,各类食用油所含的主要脂肪酸成分是棕榈酸、硬脂酸、油酸、11-十八碳烯酸、亚油酸、亚麻酸、花生单烯酸以及芥酸等;不同类型的食用油脂中,饱和、单不饱和、多不饱和脂肪酸之比值差异极大,而且多不饱和脂肪酸中n-6脂肪酸与n-3脂肪酸之比值差别也很大。     

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.     

Effect of feed on the composition of milk fat.

Researchers attending the Wisconsin Milk Board 1988 Milk Fat Roundtable indicated that the ideal nutritional milk fat would contain 10% polyunsaturated fatty acids, 8% saturated fatty acids, and 82% monounsaturated fatty acids. This cannot be accomplished by modifying diets of lactating cows. Monounsaturated fatty acid (C18:1) content can be increased by 50 to 80% and may approach 50% of milk fatty acids by feeding lipids rich in 18-carbon fatty acids. Because of ruminal hydrogenation and intestinal and mammary desaturase activity, degree of unsaturation of dietary 18-carbon fatty acids is not critical in influencing milk fat C18:1. Feeding low roughage diets increases the proportion of C18:1 in milk fat, and effects of feeding low roughage diets and lipid may be additive. Palmitic acid (C16:0) content of milk fat can be reduced by 20 to 40% unless the supplemented lipid is rich in C16:0. Milk fat alteration is dependent on the level of lipid supplementation. Limited evidence indicates frequency of lipid feeding and physical form of oil (free oil vs. oilseed), and heat treatment of oilseeds has relatively little influence on modification of milk fat. Significant changes in milk fat composition can be achieved on farm via nutritional modifications.     

Evaluation of cooling strategies for pumping of milk - impact of fatty acid composition on free fatty acid levels

Cooling strategies for pumping of raw milk were evaluated. Milk was pumped for 450 s at 31 degrees C, or pumped after cooling to 4 degrees C and subsequently subjected to various incubation times. Two types of milk were used; i.e. milk from cows fed a diet high in saturated fat supplements resulting in significantly larger milk fat globules than the other type of milk which comes from cows fed a low-fat diet that stimulates high de novo fat synthesis. The content of liquid fat was determined by low-field 1H NMR, which showed that milk from cows given the saturated fat diet also contained less liquid fat at both 4 degrees and 31 degrees C than the other type of milk. This can be ascribed to the differences in the fatty acid composition of the milk as a result of the fatty acid composition of the diets. After pumping of the milk at 31 degrees C, measurement of fat globule size distribution revealed a significant coalescence of milk fat globules in the milk obtained from the saturated fat diet due to pumping. Pumping at 4 degrees C or pumping the other type of milk did not result in coalescence of milk fat globules. Formation of free fatty acids increased significantly in both types of milk by pumping at 31 degrees C. Cooling the milk to 4 degrees C immediately before pumping inhibited an increased content of free fatty acids. However, when the milk was incubated at 4 degrees C for 60 min after cooling and then subjected to pumping, a significant increase in the formation of free fatty acids was observed in both types of milk. It is suggested that this increase in free fatty acids is caused by transition of polymorphic crystal forms or higher level of attached lipoprotein lipases to the milk fat globule before pumping.     

Influences of anatomical location and muscle quality on porcine lipid composition

Carcasses of sixty Lacombe and Lacombe cross swine fed the same high concentrate ration were selected to equally represent three muscle quality groups (pale soft exudative (PSE), normal and dark firm dry (DFD)). These carcasses were utilised to supply back and belly fat samples for the evaluation of the influences of muscle quality and anatomical location on fatty acid composition. Back fat samples had lower percentages of palmitic (C16:0) and stearic (C18:0) acids, long (≥ C18), and short (≤ C16) chain saturated fatty acids and total saturated fatty acids and higher percentages of oleic (C18:1) and linoleic (C18:2) acids, polyunsaturated fatty acids and total unsaturated fatty acids than belly fat samples. They also had a higher unsaturated fatty acid to saturated fatty acid ratio than belly fat samples. Carcasses with DFD hams and loins had lower percentages of palmitoleic (C16:1) and linoleic (C18:2) acids and polyunsaturated fatty acids in their back fat than those with PSE hams and loins. They also had higher (P < 0·05) percentages of myristic (C14: 0) and stearic (C18:0) acids and long chain saturated fatty acids (≥ C18) and lower percentages (P < 0·05) of palmitic (C16:0) and palmitoleic (C16:1) acids in their back fat than carcasses with normal hams and loins. Moreover, they had lower (P < 0·05) percentages of palmitoleic (C16:1) and linoleic (C18:2) acids and poly-unsaturated fatty acids in their belly fat than carcasses with normal and PSE hams and loins. The fact that the lipid composition of carcasses differed significantly among muscle quality groups is of considerable importance, since it implies that factors (stress) producing differences in muscle quality may also significantly influence the fatty acid composition-and thereby the physical properties of carcass lipids.     

A survey of lipid composition of Khoa samples in relation to possible adulteration

The fatty acid composition of Khoa a heat‐desiccated milk product was determined and compared with those obtained with cow milk, buffalo milk and toned milk. Fatty acid methyl esters were analysed by capillary gas chromatography (GC). Among the Khoa samples analysed, 57% showed fatty acid composition characteristic of milk fat. The ratio of major saturated fatty acids to unsaturated fatty acids (S/U) including 18:1 transfatty acids was calculated for all the fats. The GC profiles of 43% Khoa samples showed the composition of fatty acids not conforming to milk fats. The Khoa samples adulterated with nonmilk fats were further confirmed by cholesterol and triglyceride estimation.     

Effect of naked oats in the dairy cow's diet on the oxidative stability of the milk fat

Oxidative stability of milk fats from cows offered naked oats- and barley-based diets were compared in shelf-life tests using the Schaal Oven Test at 63°C, and determination of peroxide and thiobarbituric acid values. Milk fat from cows offered the diet containing naked oats, although containing a higher proportion of monounsaturated fatty acids, had a significantly longer oxidation induction period (13 days) than milk fat from cows offered the control (barley-based) diet (9 days). However, sensory testing of the milk fats indicated that a perceptible odour difference was apparent between stored (63°C) and unstored milk fats after 3 days of storage irrespective of the diet fed. It is possible that the odours perceived may have originated from the cows' diets or from hydrolytic rancidity reactions. The difficulties of relating chemical and sensory testing of the oxidative deterioration of milk fat or butter are underlined. © 1998 SCI.     

Invited review: Palmitic and stearic acid metabolism in lactating dairy cows

Energy is the most limiting nutritional component in diets for high-producing dairy cows. Palmitic (C16:0) and stearic (C18:0) acids have unique and specific functions in lactating dairy cows beyond a ubiquitous energy source. This review delineates their metabolism and usage in lactating dairy cows from diet to milk production. Palmitic acid is the fatty acid (FA) found in the greatest quantity in milk fat. Dietary sources of C16:0 generally increase milk fat yield and are used as an energy source for milk production and replenishing body weight loss during periods of negative energy balance. Stearic acid is the most abundant FA available to the dairy cow and is used to a greater extent for milk production and energy balance than C16:0. However, C18:0 is also intimately involved in milk fat production. Quantifying the transfer of each FA from diet into milk fat is complicated by de novo synthesis of C16:0 and desaturation of C18:0 to oleic acid in the mammary gland. In addition, incorporation of both FA into milk fat appears to be limited by the cow’s requirement to maintain fluidity of milk, which requires a balance between saturated and unsaturated FA. Oleic acid is the second most abundant FA in milk fat and likely the main unsaturated FA involved in regulating fluidity of milk. Because the mammary gland can desaturate C18:0 to oleic acid, C18:0 appears to have a more prominent role in milk production than C16:0. To understand metabolism and utilization of these FA in lactating dairy cows, we reviewed production and milk fat synthesis studies. Additional and longer lactation studies on feeding both FA to lactating dairy cows are required to better delineate their roles in optimizing milk production and milk FA composition and yield.     

Phospholipids and fat secretion by cows on normal and low fiber diets: lactational trends.

Daily yields of milk, milk fat, phospholipids, and fatty acids were measured weekly during lactations of two groups of cows on a normal and restricted roughage diet. Milk yield was higher in normal cows during the initial 15 wk of lactation. Fat production decreased and was consistently lower in milk from cows on restricted roughage (from 1.2 to .4 in normal and from .8 to .3 kg/day for restricted). Phospholipid secretion decreased from an average 7 g to 3 g/day in both groups. The concentration of phospholipid in both milks fluctuated during lactation (20 to 30 mg/100 ml milk), but in milks from restricted cows it tended to increase with progress of lactation. Milk lipids from cows on restricted diets had higher phospholipid to fat ratio, (1.0 to 1.5 compared to .5 to .6 g phospholipid/100 g fat for milk from normal cows). Composition of the phospholipid classes changed slightly during lactation. Phosplatidylinositol changed most, increasing from 4 to 10 and 6 to 8% in normal and restricted milks, respectively. Fatty acids of short and medium chain lengths (C6 to C14) followed a typical quadratic regression in normal milks increasing from 10 to 30% of the total fatty acids during the first 25 wk of lactation. In restricted milk these fatty acids were already high (25%) within 2 wk and followed a linear regression with lactation. Both palmitic and stearic acid were lower in milk from restricted cows while oleic and linoleic acid were higher particularly after 10 wk of lactation.