Opportunities for varying the composition of cows' milk

MiRNome variations in milk fractions during feed restrictions of different intensities in dairy cows

BACKGROUND

In dairy cows, diet is one factor that can affect their milk production and composition. However, the effect of feed restriction on milk miRNome has not yet been described. Indeed, milk is the body fluid with the highest RNA concentration, which includes numerous microRNA. Its presence in the four different milk fractions, whole milk, fat globules, mammary epithelial cells and extracellular vesicles, is still poorly documented. This study aimed to describe the effects of different feed restrictions on the miRNome composition of different milk fractions.

RESULTS

Two feed restrictions were applied to lactating dairy cows, one of high intensity and one of moderate intensity. 2,896 mature microRNA were identified in the different milk fractions studied, including 1,493 that were already known in the bovine species. Among the 1,096 microRNA that were sufficiently abundant to be informative, the abundance of 1,027 of them varied between fractions: 36 of those were exclusive to one milk fraction. Feed restriction affected the abundance of 155 microRNA, with whole milk and milk extracellular vesicles being the most affected, whereas milk fat globules and exfoliated mammary epithelial cells were little or not affected at all. The high intensity feed restriction led to more microRNA variations in milk than moderate restriction. The target prediction of known microRNA that varied under feed restriction suggested the modification of some key pathways for lactation related to milk fat and protein metabolisms, cell cycle, and stress responses.

CONCLUSIONS

This study highlighted that the miRNome of each milk fraction is specific, with mostly the same microRNA composition but with variations in abundance between fractions. These specific miRNomes were affected differently by feed restrictions, the intensity of which appeared to be a major factor modulating milk miRNomes. These findings offer opportunities for future research on the use of milk miRNA as biomarkers of energy status in dairy cows, which is affected by feed restrictions.

Effect on cow performance and milk fat composition of including full fat soyabeans and rapeseeds in the concentrate mixture for lactating dairy cows

Two experiments were carried out to determine the effect on milk yield, milk composition and composition and physical properties of milk fat of giving full fat soyabeans (FFS) and full fat rapeseeds (FFR) to dairy cows. In both experiments grass silage was provided ad lib. and constituted over 50% of the dry matter (DM) intake of the cows. In experiment 1, cows received 7·25 kg/d of a concentrate mixture containing 240 g/kg of extruded FFS or 7·25 kg/d of a mixture without soyabeans. Cow performance was not significantly affected by the inclusion of FFS but fatty acid composition of the milk fat was greatly altered. The contents of C8:0 to C16:0 were significantly reduced (P < 0·001) while the contents of C18:0, C18:l and C18:2 were significantly increased (P < 0·001). Milk fat produced during feeding on FFS concentrate had a significantly lower content of solid fat at temperatures between 0 and 25 °C compared with milk fat produced when FFS was not given. In experiment 2, cows received concentrate mixtures containing either no whole rapeseed, 150 g/kg of whole unground FFR or 150 g/kg of ground FFR. Milk yield was significantly higher and silage DM intake significantly lower with the ground FFR concentrate compared with the other two diets but milk composition was not significantly different among treatments. FFR inclusion, either ground or unground, reduced diet digestibility. Changes in fatty acid composition of the milk fat were similar to those observed with FFS inclusion but the effect was larger with ground FFR compared with unground FFR. Nuclear magnetic resonance analysis showed a lower solid fat content when the FFR diets were employed with the effect being greatest with ground FFR.

Effects of nutrition and management on the production and composition of milk fat and protein: a review

The composition and functional properties of cow’s milk are of considerable importance to the dairy farmer, manufacturer, and consumer. Broadly, there are 3 options for altering the composition and/or functional properties of milk: cow nutrition and management, cow genetics, and dairy manufacturing technologies. This review considers the effects of nutrition and management on the composition and production of milk fat and protein, and the relevance of these effects to the feeding systems used in the Australian dairy industry. Dairy cows on herbage-based diets derive fatty acids for milk fat synthesis from the diet/rumen microorganisms (400–450 g/kg), from adipose tissues (<100 g/kg), and from de novo synthesis in the mammary gland (about 500 g/kg). However, the relative contributions of these sources of fatty acids to milk fat production are highly dependent upon feed intake, diet composition, and stage of lactation. Feed intake, the amount of starch relative to fibre, the amount and composition of long chain fatty acids in the diet, and energy balance are particularly important. Significant differences in these factors exist between pasture-based dairy production systems and those based on total mixed ration, leading to differences in milk fat composition between the two. High intakes of starch are associated with higher levels of de novo synthesis of fat in the mammary gland, resulting in milk fat with a higher concentration of saturated fatty acids. In contrast, higher intakes of polyunsaturated fatty acids from pasture and/or lipid supplements result in higher concentrations of unsaturated fatty acids, particularly oleate, trans-vaccenate, and conjugated linoleic acid (CLA) in milk fat. A decline in milk fat concentration associated with increased feeding with starch-based concentrates can be attributed to changes in the ratios of lipogenic to glucogenic volatile fatty acids produced in the rumen. Milk fat depression, however, is likely the result of increased rates of production of long chain fatty acids containing a trans-10 double bond in the rumen, in particular trans-10 18 : 1 and trans-10-cis-12 18 : 2 in response to diets that contain a high concentration of polyunsaturated fatty acids and/or starch. Low rumen fluid pH can also be a factor. The concentration and composition of protein in milk are largely unresponsive to variation in nutrition and management. Exceptions to this are the effects of very low intakes of metabolisable energy (ME) and/or metabolisable protein (MP) on the concentration of total protein in milk, and the effects of feeding with supplements that contain organic Se on the concentration of Se, as selenoprotein, in milk. In general, the first limitation for the synthesis of milk protein in Australian dairy production systems is availability of ME since pasture usually provides an excess of MP. However, low concentrations of protein in milk produced in Queensland and Western Australia, associated with seasonal variations in the nutritional value of herbage, may be a response to low intakes of both ME and MP. Stage of lactation is important in determining milk protein concentration, but has little influence on protein composition. The exception to this is in very late lactation where stage of lactation and low ME intake can interact to reduce the casein fraction and increase the whey fraction in milk and, consequently, reduce the yield of cheese per unit of milk. Milk and dairy products could also provide significant amounts of Se, as selenoproteins, in human diets. Feeding organic Se supplements to dairy cows grazing pastures that are low in Se may also benefit cow health. Research into targetted feeding strategies that make use of feed supplements including oil seeds, vegetable and fish oils, and organic Se supplements would increase the management options available to dairy farmers for the production of milks that differ in their composition. Given appropriate market signals, milk could be produced with lower concentrations of fat or higher levels of unsaturated fats, including CLA, and/or high concentrations of selenoproteins. This has the potential to allow the farmer to find a higher value market for milk and improve the competitiveness of the dairy manufacturer by enabling better matching of the supply of dairy products to the demands of the market.

Fatty acid and triglyceride composition of milk fat from lactating Holstein cows in response to supplemental canola oil

The objective was to determine the influence of dietary lipid on total and sn-2 fatty acid composition and triglyceride structure of milk fat in lactating Holstein cows. Five primiparous Holstein cows surgically fitted with ruminal and duodenal cannulas were used in a 4 x 5 incomplete Latin square. All cows received a basal diet. Treatments consisted of a basal diet with no supplemental canola oil (control), basal diet with canola oil added to the concentrate portion of the diet to provide 1.6% fat, basal diet with 330 g of canola oil infused directly into the rumen, and basal diet with 330 g of canola oil infused directly into the abomasum. Canola oil treatments decreased palmitic acid and increased oleic acid content of milk fat compared with the control. Stearate was higher when canola oil was rumen available compared with control and abomasal infusion. Abomasal infusion increased linoleic and linoleic acids in milk fat compared with the other treatments. The sn-2 fatty acid composition reflected total fatty acid composition. All canola oil treatments reduced palmitic acid and increased oleic acid content at the sn-2 position. Changes in sn-2 composition reflect specificity of the acyl transferases and substrate concentration. Triglyceride composition reported as carbon number was altered by canola oil. Triglycerides in carbon number C50, C52, and C54 were increased while C32, C34, and C36 were decreased.

Feed and animal factors influencing milk fat composition

Genetic selection for increased milk fat percentage leads to increased proportions of short-chain fatty acids in milk fat and decreased proportions of long-chain fatty acids. Milk fat composition is strongly influenced by stage of lactation; proportion of short chains (de novo synthesis) is low initially and increases until at least 8 to 10 wk into lactation. Milk fat composition is changed more by the amount and composition of dietary fat than any other dietary component. Seasonal and regional differences in milk fat composition are measurable, most likely because of local differences in feed supplies. Milk fat composition can be modified readily by changing the feeding regimen. The most significant changes in milk fat quality relate to rheological (melting) properties, which influence numerous aspects of character and quality of manufactured dairy products. Dietary fat fed to change milk fat composition may also influence contents of protein, urea, citrate, and soluble calcium in milk and influence oxidative stability and flavor. It is important for both dairy nutritionists and dairy food chemists to understand the consequences of feeding programs on milk quality.

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.