Fat globules selected from whole milk according to their size: Different compositions and structure of the biomembrane,revealing sphingomyelin-rich domains

Milk fat globules are unique delivery systems for biologically active molecules in the gastrointestinal tract. However, their properties have not yet been fully investigated. In this study, we performed a comparative analysis of the polar lipid and fatty acid compositions of milk fat globules as a function of their size and investigated the structure of the milk fat globule membrane (MFGM). An optimised process of microfiltration was used to select the small milk fat globule (SMFG; 1.6 μm) fractions and the large milk fat globule (LMFG; 6.6 μm) fractions from the same initial whole milks (4.2 μm). The SMFG-fractions contained significantly (i) higher amounts of polar lipids, 8.9 ± 0.9 vs 2.7 ± 0.3 mg/g fat for LMFG-fractions and 6.3 ± 0.5 mg/g fat for whole milks, (ii) lower relative proportions of phosphatidylcholine and sphingomyelin in the MFGM, (iii) higher amounts of C12:0, C14:0, C16:0, C18:1 trans, C18:2 c9 tr11, and lower amounts of C18:0 and C18:1 c9 than did LMFG-fractions and whole milks. Whatever the size of native milk fat globules, the biophysical characterisation performed in-situ, using confocal laser scanning microscopy, showed heterogeneities in the MFGM. The lateral segregation of sphingomyelin in rigid liquid-ordered domains, surrounded by the fluid matrix of glycerophospholipids in the liquid-disordered phase, was revealed. The heterogeneous distribution of glycolipids and glycoproteins was also observed in the MFGM. A new model for the structure of the MFGM is proposed and discussed. The physical, chemical and biological consequences, (i) of the differences in milk fat globule compositions according to their size and (ii) of the specific structure of the MFGM due to sphingomyelin remain to be elucidated.     

Comparison of analytical and predictive methods for water,protein, fat,sugar, and gross energy in marine mammal milk

Mammalian milks may differ greatly in composition from cow milk, and these differences may affect the performance of analytical methods. High-fat, high-protein milks with a preponderance of oligosaccharides, such as those produced by many marine mammals, present a particular challenge. We compared the performance of several methods against reference procedures using Weddell seal (Leptonychotes weddellii) milk of highly varied composition (by reference methods: 27–63% water, 24–62% fat, 8–12% crude protein, 0.5–1.8% sugar). A microdrying step preparatory to carbon-hydrogen-nitrogen (CHN) gas analysis slightly underestimated water content and had a higher repeatability relative standard deviation (RSD_r) than did reference oven drying at 100°C. Compared with a reference macro-Kjeldahl protein procedure, the CHN (or Dumas) combustion method had a somewhat higher RSD_r (1.56 vs. 0.60%) but correlation between methods was high (0.992), means were not different (CHN: 17.2 ± 0.46% dry matter basis; Kjeldahl 17.3 ± 0.49% dry matter basis), there were no significant proportional or constant errors, and predictive performance was high. A carbon stoichiometric procedure based on CHN analysis failed to adequately predict fat (reference: Röse-Gottlieb method) or total sugar (reference: phenol-sulfuric acid method). Gross energy content, calculated from energetic factors and results from reference methods for fat, protein, and total sugar, accurately predicted gross energy as measured by bomb calorimetry. We conclude that the CHN (Dumas) combustion method and calculation of gross energy are acceptable analytical approaches for marine mammal milk, but fat and sugar require separate analysis by appropriate analytic methods and cannot be adequately estimated by carbon stoichiometry. Some other alternative methods—low-temperature drying for water determination; Bradford, Lowry, and biuret methods for protein; the Folch and the Bligh and Dyer methods for fat; and enzymatic and reducing sugar methods for total sugar—appear likely to produce substantial error in marine mammal milks. It is important that alternative analytical methods be properly validated against a reference method before being used, especially for mammalian milks that differ greatly from cow milk in analyte characteristics and concentrations.     

Size distribution of fat globules in human colostrum, breast milk, and infant formula

Only a few results are available on the size of human milk fat globules (MFG), despite its significance regarding fat digestion in the infant, and no data are available at <24 h postpartum (PP). We measured the MFG size distribution in colostrum and transitional human milk in comparison with fat globules of mature milk and infant formula. Colostrum and transitional milk samples from 18 mothers were collected regularly during 4 d PP and compared with mature milk samples of 17 different mothers and 4 infant formulas. The size distribution was measured by laser light scattering. For further characterization, the ζ-potential of some mature MFG was measured by laser Doppler electrophoresis. The MFG diameter decreased sigmoidally in the first days. At <12 h PP, the mode diameter was 8.9 ± 1.0 μm vs 2.8 ±0.3 μm at 96 h PP. Thus, the surface area of MFG increased from 1.1 ±0.3 to 5.4 ±0.7 m²/g between colostrum and transitional milk. In mature milk, the MFG diameter was 4 μm on average and increased with advancing lactation, whereas the droplets in infant formula measured 0.4 μm. The ζ potential of mature MFG was −7.8 ± 0.1 mV. The fat globules are larger in early colostrum than in transitional and mature human milk and in contrast with the small-sized fat droplets in infant formula. Human MFG also have a low negative surface charge compared with bovine globules. These structural differences can be of nutritional significance for the infant.     

Polar lipids,sphingomyelin and long-chain unsaturated fatty acids from the milk fat globule membrane are increased in milks produced by cows fed fresh pasture based diet during spring

Milk lipids are an interesting source of bioactive molecules with functional and nutritional properties. Although the composition of milk lipids is of utmost importance for food processing and human consumption, it is far from being fully known. The objective of this study was to perform a comparative analysis of the chemical composition of lipids from bovine milks produced in French Brittany during spring (fresh pasture based diet) and winter (corn silage based diet). The polar lipid content and relative proportions of the glycerophospholipids and sphingomyelin were determined using HPLC/ELSD. The fatty acid composition of total lipids and polar lipids was determined using GC. The milks collected in spring contained i) a lower amount of total lipids: 39.7 ± 0.8 g/kg vs 41.7 ± 0.5 g/kg in winter, ii) a higher amount of polar lipids: 138 ± 11 vs 112 ± 8 mg/kg milk; 3.5 ± 0.3 vs 2.7 ± 0.4 mg/g fat, which was related to a smaller size of fat globules, and iii) a higher amount of sphingomyelin, 32 mg/kg milk vs 25 mg/kg milk in winter. Interestingly, the polar lipids from the milk fat globule membrane contained a higher concentration of unsaturated fatty acids in spring (C18:1 n − 9, C18:2 n − 6, C18:3 n − 3 and long-chain n − 3 fatty acids). Milk from cows fed a fresh pasture-based diet during spring is an interesting source of dietary long chain polyunsaturated fatty acids for human consumption.     

Comparative fat digestibility of goat,camel, cow and buffalo milk

The differences in the milk fat digestion from milk of different species using an in vitro digestion model were investigated. Milk samples were collected from healthy lactating goats, camels, cows and buffalos. The in vitro digestion of milk fat was carried out at pH 7.5 to mimic pancreatic lipase activity in the small intestine leading to fatty acid release from fat globules. It was found that the amount of free fatty acids released per unit volume of the milk sample decreased in the following order: goat camel > cow > buffalo. The differences in the structure of fat globules during the digestion were characterised using confocal laser scanning microscopy. The information generated provided important insights into the factors that influence the activity of lipases during lipid digestion and improve understanding of in vivo fat digestion by pancreatic lipase.     

Dietary molasses increases ruminal pH and enhances ruminal biohydrogenation during milk fat depression

Feeding high-concentrate diets has the potential to cause milk fat depression, but several studies have suggested that dietary sugar can increase milk fat yield. Two experiments were conducted to evaluate the ability of dietary molasses to prevent milk fat depression in the presence of a 65% concentrate diet. In trial 1, molasses replaced corn grain at 0, 2.5, or 5% of diet dry matter in diets fed to 12 second-lactation Holstein cows (134 ± 37 d in milk) in a 3 × 3 Latin square design. Trial 1 demonstrated that replacing up to 5% of dietary dry matter from corn with molasses had positive effects on de novo fatty acid synthesis, increasing the yield of short- and medium-chain fatty acids during diet-induced milk fat depression. Increasing inclusion rate of molasses increased milk fat concentration, but decreased milk yield and milk protein yield. Trial 2 used 7 ruminally cannulated, multiparous, late-lactation Holstein cows (220 ± 18 d in milk) to evaluate effects of dietary molasses on ruminal parameters and milk composition, and also to assess whether increased metabolizable protein supply would alter these responses. Cows were randomly assigned to a dietary treatment sequence in a crossover split plot design with 0 and 5% molasses diets. Dietary treatments were fed for 28 d, with 16 d for diet adaptation, and the final 12 d for 2 abomasal infusion periods in a crossover arrangement. Abomasal infusions of water or AA (5 g of l-Met/d + 15 g of l-Lys-HCl/d + 5 g of l-His-HCl-H₂O/d) were administered 3 times daily for 5 d, with 2 d between infusion periods. Administration of AA had no effect on concentration or yield of any milk components. Addition of molasses increased milk fat concentration (2.71 vs. 2.94 ± 0.21%), but had no effect on yields of milk fat or protein. Dietary molasses decreased total volatile fatty acid concentration (141 vs. 133 ± 4.6 mM), decreased the molar proportion of propionate, and increased the molar proportion of butyrate in ruminal fluid. Molasses also increased ruminal pH (5.73 vs. 5.87 ± 0.06), decreased the yield of trans-10 C18:1, and increased the yield of trans-11 C18:1 in milk fat. These data provide evidence that molasses may promote mammary de novo fatty acid synthesis in cows fed high-energy rations by moderating ruminal pH and altering ruminal fatty acid biohydrogenation pathways.     

Effect of lactation stage and energy status on milk fat composition of Holstein-Friesian cows

The effects of lactation stage, negative energy balance (NEB), and milk fat depression (MFD) were estimated on detailed milk fat composition in primiparous Holstein-Friesian cows. One morning milk sample was collected from each of 1,933 cows from 398 commercial Dutch herds in winter 2005. Milk fat composition was measured using gas chromatography, and fat and protein percentage were measured using infrared spectrometry. Each fatty acid changed 0.5 to 1 phenotypic standard deviation over lactation, except odd-chain C5:0 to C15:0, branched-chain fatty acids, and trans-10, cis-12 conjugated linoleic acid (CLA). The greatest change was an increase from 31.2 to 33.3% (wt/wt) for C16:0 from d 80 to 150 of lactation. Energy status was estimated for each cow as the deviation from each average lactation fat-to-protein ratio (FPdev). A high FPdev (>0.12) indicated NEB. Negative energy balance was associated with an increase in C16:0 (0.696 ± 0.178) and C18:0 (0.467 ± 0.093), which suggested mobilization of body fat reserves. Furthermore, NEB was associated with a decrease in odd-chain C5:0 to C15:0 (−0.084 ± 0.020), which might reflect a reduced allocation of C3 components to milk fat synthesis. A low FPdev indicated MFD (<−0.12) and was associated with a decrease in C16:0 (−0.681 ± 0.255) and C18:0 (−0.128 ± 0.135) and an increase in total unsaturated fatty acids (0.523 ± 0.227). The study showed that both lactation stage and energy balance significantly contribute to variation in milk fat composition and alter the activity of different fatty acid pathways.     

Buffalo milk fat globules and their biological membrane: in situ structural investigations

Milk fat globules and their surrounding biological membrane (the MFGM) are not well understood despite the importance of these milk components in human nutrition and the role of fat globules in determining the properties of dairy products. The objectives of this study were to investigate these unique colloidal assemblies and the microstructure of the MFGM in buffalo milk, which is the second largest global source of dairy products. In-situ structural investigations were performed at room temperature using confocal microscopy with multiple fluorescent probes (Nile Red, Rh-DOPE, the lectin WGA-488). Microscopic observations showed cytoplasmic crescents around fat globules and the heterogeneous distribution of glycosylated molecules and polar lipids with the occurrence of lipid domains. The lipid domains in the buffalo MFGM appear to form by the segregation of lipids with a high phase transition temperature (e.g. sphingomyelin and saturated phosphatidylcholine molecular species) and cholesterol resulting in a gel phase or a Lo phase forming circular domains. The structure of the buffalo MFGM results from a non-random mixing of components, consistent with observations for other species. Structural heterogeneities of the MFGM could affect the processability of buffalo fat globules and the bioavailability of milk lipids.     

Feeding soyhulls to high-yielding dairy cows increased milk production, but not milking frequency, in an automatic milking system

To attract a cow into an automatic milking system (AMS), a certain amount of concentrate pellets is provided while the cow is being milked. If the milking frequency in an AMS is increased, the intake of concentrate pellets might increase accordingly. Replacing conventional starchy pellets with nonstarchy pellets increased milk yield, milk fat, and milk protein and decreased body weight. The hypothesis was that a nonroughage by-product rich in digestible neutral detergent fiber, such as soyhulls and gluten feed, could replace starchy grain in pellets fed in an AMS. Sixty cows were paired by age, milk yield, and days in milk, and were fed a basic mixture ad libitum [16.2 ± 0.35 (mean ± SE) kg of dry matter intake/d per cow] plus a pelleted additive (6 to 14 kg of dry matter/d per cow) that was consumed in the AMS and in a concentrate self-feeder, which could only be entered after passing through the AMS. The 2 feeding regimens differed only in the composition of the pelleted additives: the control group contained 52.9% starchy grain, whereas the experimental group contained 25% starchy grain, plus soyhulls and gluten feed as replacement for part of the grain. Wheat bran in the control ration, a source of fiber with low digestibility, was replaced with more digestible soyhulls and gluten. During the first 60 d in milk, a cow received 10 to 12 kg of concentrate pellets. After 60 DIM, concentrate feed was allocated by milk production: ≤25 kg/d of milk entitled a cow to 2 kg/d of concentrate feed; >25 kg/d of milk entitled a cow to receive 1 kg/d of additional concentrate feed per 5 kg/d of additional milk production, and >60 kg/d of milk entitled a cow to receive 9 kg of concentrate. The concentrate feed was split between the AMS and concentrate self-feeder. The 2 diets resulted in similar frequencies of voluntary milking (3.12 ± 0.03 to 2.65 ± 0.03 visits/d per cow vs. 3.16 ± 0.00 to 2.60 ± 0.01 visits/d per cow). Average milk yields were higher in the experimental group (42.7 ± 0.76 to 39.09 ± 0.33 kg/d per cow vs. 39.69 ± 0.68 to 37.54 ± 0.40 kg/d per cow) and percentages of milk protein (3.02 ± 0.06 to 3.12 ± 0.05% vs. 3.07 ± 0.04 to 3.20 ± 0.04%) and milk fat (3.42 ± 0.17 to 3.44 ± 0.08% vs. 3.38 ± 0.13 to 3.55 ± 0.06%) were similar in the 2 groups. The results suggest that the proposed pellets high in digestible neutral detergent fiber can be allocated via the AMS to selected high-yielding cows without a negative effect on appetite, milk yield, or milk composition while maintaining a high milking frequency.     

Potentials to differentiate milk composition by different feeding strategies

To investigate the effect of the dietary intake of the cow on milk composition, bulk-tank milk was collected on 5 occasions from conventional (n = 15) and organic (n = 10) farms in Denmark and on 4 occasions from low-input nonorganic farms in the United Kingdom, along with management and production parameters. Production of milk based on feeding a high intake of cereals, pasture, and grass silage resulted in milk with a high concentration of α-linolenic acid (9.4 ± 0.2 mg/kg of fatty acids), polyunsaturated fatty acids (3.66 ± 0.07 mg/kg of fatty acids), and natural stereoisomer of α-tocopherol (RRR-α-tocopherol, 18.6 ± 0.5 mg/kg of milk fat). A milk production system using a high proportion of maize silage, by-products, and commercial concentrate mix was associated with milk with high concentrations of linoleic acid (LA; 19.7 ± 0.4 g/kg of fatty acids), monounsaturated fatty acids (27.5 ± 0.3 mg/kg of fatty acids), and a high ratio between LA and α-linolenic acid (4.7 ± 0.2). Comparing these 2 production systems with a very extensive nonorganic milk production system relying on pasture as almost the sole feed (95 ± 4% dry matter intake), it was found that the concentrations of conjugated LA (cis-9,trans-11; 17.5 ± 0.7 g/kg of fatty acids), trans-11-vaccenic acid (37 ± 2 g/kg of fatty acids), and monounsaturated fatty acids (30.4 ± 0.6 g/kg of fatty acids) were higher in the extensively produced milk together with the concentration of antioxidants; total α-tocopherol (32.0 ± 0.8 mg/kg of milk fat), RRR-α-tocopherol (30.2 ± 0.8 mg/kg of milk fat), and β-carotene (9.3 ± 0.5 mg/kg of milk fat) compared with the organic and conventional milk. Moreover, the concentration of LA (9.2 ± 0.7 g/kg of fatty acids) in milk from the extensive milk production system was found to approach the recommended unity ratio between n-6 and n-3, although extensive milk production also resulted in a lower daily milk yield.     

Lipid composition and structural characteristics of bovine,caprine and human milk fat globules

Milk fat is widely accepted to be the major nutrient in human milk. Commercial infant formulas are usually based on mammalian milk such as bovine or caprine milk, but the differences in milk fat globules (MFGs) between human, bovine and caprine milk remain unclear. We showed that saturated fatty acid content was higher in bovine and caprine MFGs (>60%) than in human MFG (<40%), but that content of the unsaturated fatty acids C18:2 in human MFG was >7 times higher than in bovine and caprine MFGs. The cholesterol content of human milk was ∼20% higher than that of bovine and caprine milk. Triacylglycerol molecular species and polar lipids also differed between bovine, caprine and human MFGs. Confocal laser scanning microscopy images of MFGs revealed that the shape of the liquid-ordered domains varied by species.     

Hot topic: Enhancing omega-3 fatty acids in milk fat of dairy cows by using stearidonic acid-enriched soybean oil from genetically modified soybeans

Very long chain n-3 fatty acids such as eicosapentaenoic acid (EPA; 20:5n-3) are important in human cardiac health and the prevention of chronic diseases, but food sources are limited. Stearidonic acid (SDA; 18:4n-3) is an n-3 fatty acid that humans are able to convert to EPA. In utilizing SDA-enhanced soybean oil (SBO) derived from genetically modified soybeans, our objectives were to examine the potential to increase the n-3 fatty acid content of milk fat and to determine the efficiency of SDA uptake from the digestive tract and transfer to milk fat. Three multiparous, rumen-fistulated Holstein cows were assigned randomly in a 3 × 3 Latin square design to the following treatments: 1) control (no oil infusion); 2) abomasal infusion of SDA-enhanced SBO (SDA-abo); and 3) ruminal infusion of SDA-enhanced SBO (SDA-rum). The SDA-enhanced SBO contained 27.1% SDA, 10.4% α-linolenic acid, and 7.2% γ-linolenic acid. Oil infusions provided 57 g/d of SDA with equal amounts of oil infused into either the rumen or abomasum at 6-h intervals over a 7-d infusion period. Cow numbers were limited and no treatment differences were detected for DMI or milk production (22.9 ± 0.5 kg/d and 32.3 ± 0.9 kg/d, respectively; least squares means ± SE), milk protein percentage and yield (3.24 ± 0.04% and 1.03 ± 0.02 kg/d), or lactose percentage and yield (4.88 ± 0.05% and 1.55 ± 0.05 kg/d). Treatment also had no effect on milk fat yield (1.36 ± 0.03 kg/d), but milk fat percentage was lower for the SDA-rum treatment (4.04 ± 0.04% vs. 4.30 ± 0.04% for control and 4.41 ± 0.05% for SDA-abo). The SDA-abo treatment increased n-3 fatty acids to 3.9% of total milk fatty acids, a value more than 5-fold greater than that for the control. Expressed as a percentage of total milk fatty acids, values (least squares means ± SE) for the SDA-abo treatment were 1.55 ± 0.03% for α-linolenic acid (18:3n-3), 1.86 ± 0.02 for SDA, 0.23 ± <0.01 for eicosatetraenoic acid (20:4n-3), and 0.18 ± 0.01 for EPA. Transfer efficiency of SDA to milk fat represented 39.3% (range = 36.8 to 41.9%) of the abomasally infused SDA and 47.3% (range = 45.0 to 49.6%) when the n-3 fatty acids downstream from SDA were included. In contrast, transfer of ruminally infused SDA to milk fat averaged only 1.7% (range = 1.3 to 2.1%), indicating extensive rumen biohydrogenation. Overall, results demonstrate the potential to use SDA-enhanced SBO from genetically modified soybeans combined with proper ruminal protection to achieve impressive increases in the milk fat content of SDA and other n-3 fatty acids that are beneficial for human health.     

Elevated concentrate-to-forage ratio in dairy cow rations is associated with a shift in the diameter of milk fat globules and remodeling of their membranes

We examined the effects of concentrate-to-forage ratio in dairy cow rations on milk-fat composition, with a specific focus on the structure of milk fat globules (MFG). Twenty-four Holstein cows, 153 d in milk, were assigned to 2 dietary treatments in a crossover design study. Treatments were (1) high-concentrate (65%), low-forage (35%; HCLF) diet and (2) low-concentrate (35%), high-forage (65%; LCHF) diet. The mean diameter of the MFG; plasma concentrations of insulin, glucose, and nonesterified fatty acids (FA); and the composition and concentrations of milk FA and polar lipids were determined. Concentrations of insulin were 56% higher, and those of nonesterified FA 46% lower, in the HCLF than in the LCHF diet. The milk yield was 8.5 kg/d higher and yields of fat, protein, and lactose were 180, 350, and 403 g/d higher, respectively, in the HCLF versus LCHF diet. Milk FA composition differed between treatments, with 1.5 and 1.0 percentage units higher saturated and polyunsaturated FA concentrations, respectively, in the HCLF versus LCHF diet. Mean MFG diameter tended to be smaller (0.2 μm) in the HCLF diet than in the LCHF diet, associated with increased daily phospholipids yield (34%), lower phosphatidylserine and higher phosphatidylcholine concentrations. In conclusion, the decreased milk and fat yields in the LCHF diet were associated with remodeling of the MFG membrane and with the secretion of larger MFG. Membrane remodeling of the mammary epithelium membranes seems to play a role in regulating MFG size.     

Effect of supplementing myristic acid in dairy cow rations on ruminal methanogenesis and fatty acid profile in milk

The objective of this study was to evaluate the effects of supplementing myristic acid in dairy cow rations on ruminal methanogenesis and the fatty acid profile in milk. Twelve multiparous Holstein dairy cows (710 ± 17.3 kg of live weight; 290 ± 41.9 d in milk) housed in a tie-stall facility were used in the study. The cows were paired by parity and days in milk and allocated to 1 of 2 treatments: 1) the regular milking cow total mixed ration (control diet), and 2) the regular milking cow total mixed ration supplemented with 5% myristic acid on a dry matter basis (MA diet). The cows were fed and milked twice daily (feeding, 0830 and 1300 h; milking, 0500 and 1500 h). The experiment was conducted as a completely randomized design and consisted of a 7-d pretrial period when cows were fed the control diet to obtain baseline measurements, a 10-d dietary adaptation period, and a 1-d, 8-h measurement period. The MA diet reduced methane (CH₄) production by 36% (608.2 vs. 390.6 ± 56.46 L/d, control vs. MA diet, respectively) and milk fat percentage by 2.4% (4.2 vs. 4.1 ± 0.006%, control vs. MA diet, respectively). The MA diet increased 14:0 in milk by 139% and cis-9 14:1 by 195%. There was a correlation (r = −0.58) between the 14:0 content in milk and CH₄ production and cis-9 14:1 and CH₄ production (r = −0.47). Myristic acid had no effect on the contents of CLA or trans-10 18:1 and trans-11 18:1 isomers in milk. These results suggest that MA could be used to inhibit the activities of methanogens in ruminant animals without altering the conjugated linoleic acid and trans-18:1 fatty acid profile in milk.     

Composition of milk fat from cows selected for milk fat globule size and offered either fresh pasture or a corn silage-based diet

The objective of this study was to examine the synthesis and composition of milk produced by dairy cows that secrete either small milk fat globules (SMFG) or large milk fat globules (LMFG), and to study their response to diets known to alter milk composition. Four groups of 3 multiparous dairy cows were assigned to 2 isoenergetic feeding treatments: a corn silage treatment supplemented with soybean meal, and fresh pasture supplemented with cereal concentrate. The 4 groups comprised 2 groups of 3 dairy cows that produced SMFG (3.44 μm) and 2 groups of 3 dairy cows that produced LMFG (4.53 μm). The SMFG dairy cows produced higher yields of milk, protein, and calcium. Nevertheless, their milk had lower fat and protein contents. Both SMFG and LMFG cows secreted similar amounts of milk fat; therefore, higher globule membrane contents in milk fat were observed in SMFG cows. Higher calcium mineralization of the casein micelles in SMFG cows suggests that it may be possible to improve cheese-making properties even if the lower protein content may lead to lower cheese yields. The SMFG cows secrete milk fat with a higher concentration of monounsaturated fatty acids and a lower concentration of short-chain fatty acids. They also have a higher C18:1/C18:0 ratio than LMFG cows. This suggests that SMFG cows have more significant fatty acid elongation and desaturation. The pasture treatment led to an increase in milk and protein yields because of increased energy intake. It also resulted in lower milk fat yield and fat and protein contents. The pasture treatment led to a decrease in milk fat globule size and, as expected, an increase in monounsaturated and polyunsaturated fatty acid contents. However, it induced a decrease in the protein content, and in calcium mineralization of casein micelles, which suggests that this type of milk would be less suitable for making cheese. This study also shows that there is no correlation between the cows, based on milk fat globule size and diet. These results open up possibilities for improving milk fat quality based on milk fat globule size, and composition. The mechanisms involved in milk fat globule secretion are still to be determined.     

Transfer of dietary zinc and fat to milk--evaluation of milk fat quality, milk fat precursors, and mastitis indicators

The present study demonstrated that the zinc concentration in bovine milk and blood plasma is significantly affected by the intake of saturated fat supplements. Sixteen Holstein cows were used in a 4 × 4 Latin square design with 4 periods of 12 d, and 4 dietary treatments were conducted. A total mixed ration based on corn silage, grass-clover silages, and pelleted sugar beet pulp was used on all treatments. A high de novo milk fat diet was formulated by adding rapeseed meal and molasses in the total mixed ration [39 mg of Zn/kg of dry matter (DM)], and a low de novo diet by adding saturated fat, fat-rich rapeseed cake, and corn (34 mg of Zn/kg of DM). Dietary Zn levels were increased by addition of ZnO to 83 and 80 mg of Zn/kg of DM. Treatments did not affect daily DM intake, or yield of energy-corrected milk, milk fat, or milk protein. The high de novo diet significantly increased milk fat percentage and milk content of fatty acids with chain length from C6 to C16, and decreased content of C18 and C18:1. Treatments did not influence milk free fatty acids at 4°C at 0 or 28 h after milking. The average diameter of milk fat globules was significantly greater in milk from cows offered low de novo diets. Furthermore, the low de novo diet significantly increased the concentration of nonesterified fatty acids and d-β-hydroxybutyrate in blood plasma, the latter was also increased in milk. Treatments did not affect the enzyme activity of lactate dehydrogenase and N-acetyl-β-d-glucosaminidase in milk or the activity of isocitrate dehydrogenase and malate dehydrogenase in blood plasma. The low de novo diet significantly increased plasma Zn and milk Zn content, whereas dietary Zn level did not in itself influence these parameters. This indicates that the transfer of fat from diet to milk might facilitate transfer of Zn from diet to milk.     

Effects of trans-10, cis-12 conjugated linoleic acid on ovine milk fat synthesis and cheese properties

Trans-10, cis-12 conjugated linoleic acid (CLA) reduces milk fat synthesis in sheep in a manner similar to that seen in dairy cows, but its effects on cheese yield and flavor are unknown. Additionally, when dietary energy supply is restricted, CLA can increase milk and milk protein yield, which may alter cheese yield and eating quality. The objectives of the study were to examine the effects of supplementing ewe diets with a rumen-protected source of CLA at a high and low dietary energy intake on milk fat and protein synthesis and on cheese yield and eating quality. Sixteen multiparous ewes were randomly allocated to 1 of 4 dietary treatments: a high (6.7 Mcal of metabolizable energy/d) or low (5.0 Mcal of metabolizable energy/d) feeding level that was either unsupplemented or supplemented with 25 g/d of a lipid-encapsulated CLA (to provide 2.4 g/d of CLA) in each of 4 periods of 21 d duration in a 4 × 4 Latin square design. There was no effect of treatment on milk yield (g/d), but milk fat percentage and milk fat yield were reduced by 23 and 20%, respectively, in ewes supplemented with CLA. Milk fatty acid concentration (g/100 g) of chain length <C₁₆ was decreased and >C₁₆ was increased in milk and cheese following CLA supplementation, whereas decreasing the feeding level increased fatty acids ≥C₁₆. Milk fat contents of CLA were 0.01 and 0.12 g/100 g of fatty acids for the unsupplemented and CLA-supplemented treatments, respectively, whereas cis-9, trans-11 CLA was unaffected by CLA supplementation. There was no main effect of treatment on cheese yield, which was 0.11 ± 0.001 kg of cheese/kg of milk, but cheese yield was highest, at 0.12 ± 0.001 kg/kg, when made from milk of ewes fed the high feeding level + unsupplemented treatment. Cheese made from the milk of ewes supplemented with CLA, compared with the unsupplemented diet, was rated (scale 0 to 10) higher in the creaminess (2.1 vs. 1.4; SEM 0.15) and less oily (0.8 vs. 1.3; SEM 0.17) attributes, and was preferred overall (4.5 vs. 3.9; SEM 0.21). Cheese produced from sheep on the high vs. low feed level was rated less yellow (2.8 vs. 4.2; SEM 0.11), less salty (1.9 vs. 2.3; SEM 0.15), and more sour (1.5 vs. 1.1; SEM 0.13). We concluded that the effect of feeding level on animal performance and cheese characteristics was small, whereas supplementing the diets of ewes with a ruminally protected CLA source reduced milk fat yield, did not affect cheese yield, and beneficially altered the flavor characteristics of the cheese.     

Evaluation of nutritional quality of fat obtained from different breeds of cow and buffalo with respect to fatty acids and in vitro digestibility

A comparative fatty acid analysis of raw milk and during in vitro digestion of milk from different breeds of cow (Gir, Sahiwal, Tharparkar, and Karan fries) and buffalo (Murrah) maintained under similar feeding regimes was conducted. Saturated fatty acids were higher in Murrah and Karan Fries, whereas monounsaturated fatty acids were higher in Gir, Sahiwal and Tharparkar. Based on the fatty acid profile, atherogenic, thrombogenic index and hypercholesterolemic saturated fatty acids were lower, and desired fatty acids were higher in milk from indigenous breeds than in crossbred and Murrah. The size of milk fat globules was also lower in indigenous cattle breeds, which has allowed for faster in vitro digestibility of milk fat.     

Short communication: Effect of antioxidant supplementation on milk production,milk fat synthesis,and milk fatty acids in dairy cows when fed a diet designed to cause milk fat depression

This study evaluated the effect of a blend of synthetic antioxidants on the yield of milk and milk components and milk fatty acid composition in dairy cows fed a diet designed to cause milk fat depression (MFD). We hypothesized that supplementing a synthetic antioxidant to diets with a high rumen unsaturated fatty acid load (RUFAL) would decrease the severity of MFD. Sixteen lactating Holstein cows (163 ± 47 d in milk), in a crossover design with two 21-d periods, were fed a corn silage and grass silage-based diet containing 15% distillers grains. The diet contained 34% neutral detergent fiber, 18% crude protein, 26% starch, and 4.3% total fatty acids (dry matter basis). Cows were fed the diet without supplementation (control; CON) or supplemented with 0.02% (dry matter basis) of a synthetic antioxidant (AOX; Agrado Plus, Novus International Inc., St. Charles, MO). Dry matter intake and milk yields were recorded daily. Milk samples were collected at the start of the study for baseline values and the end of each period (d 20–21) and analyzed for milk components and fatty acid composition. Dry matter intake and milk yield were unaffected by treatment and averaged 25.9 and 50.2 kg/d, respectively. Similarly, we observed no effect of treatment on yields of fat, protein, lactose, 3.5% fat-corrected milk, energy-corrected milk, feed efficiency, body weight, or body condition score. Milk fat concentration and yield were both reduced by the high RUFAL diets. We observed a tendency for AOX to increase the concentration of milk fat and decrease the concentration of milk protein. Yields of de novo and preformed fatty acids were not affected by treatment, although we detected a trend for a slight increase in the yield of 16-carbon fatty acid for AOX compared with CON. Treatment had only minor effects on individual milk fatty acids, except for the concentration and yield of linoleic acid, which were over 90% higher for AOX compared with CON. In conclusion, milk fat concentration and yield were reduced by a high RUFAL diet containing 15% distillers grains; however, supplementation with AOX did not overcome the MFD induced by this diet.