Consumer requirements for milk and milk products have changed dramatically over the last 30 years and will continue to develop. Key drivers of change are explored and opinions given on what will be the impact of these changes in the make up of the population, lifestyles and attitudes on food purchasing and consumption in general and on the dairy sector in particular. The dairy sector has the opportunity to meet many of the requirements of current and future consumers in terms of diversity, healthiness, method of production and value for money. Processors will then have to ensure that they can modify existing products in terms of composition and packaging/presentation to meet the needs of various niches in each consumer product sector. Functional properties will become ever more important for the emerging food-service and food manufacturing sectors. Underpinning the development of all new technologies and methods of production must be a recognition that systems must be environmentally friendly, provide healthy and high quality products and deliver real consumer benefits in terms of taste, value or some other parameter. It is not sufficient for the technology simply to deliver production cost benefits if these are not to be passed on to the consumer - particularly if the technology of doing this is seen as being “unnatural”.

It is also suggested that the industry and its core products already possess a number of key attributes relevant to today's consumer in terms of such parameters as “natural”, “healthy” and “diversity” but that insufficient funds are being expended in communicating these benefits to consumers and opinion formers.

The nutritive value of milk has long been recognised. In the 1920's and 30's several clinical trials explored the influence of a milk supplement on the growth of children. These studies universally showed that milk had a beneficial effect on height gain. The effects of milk on childhood growth were attributed to the impact of the additional dietary calcium on the skeleton, although energy and protein intakes may have been limiting.

Contemporary research on the effects of nutrition on growth has the advantage of being able to focus much more specifically on the strength and mineral mass of the skeleton. Curiosity about the relationship between nutrition and skeletal development has arisen because maximising skeletal development in childhood and adolescence is a recognised preventative strategy against osteoporosis. The effect of additional dietary calcium has been explored in a number of clinical trials of children and teenagers using both supplemental calcium and milk and milk products. The studies have generally shown that the rate of skeletal accrual is greater in the supplemented groups, at least in the short-term. Similarly, clinical trials in post-menopausal women show positive effects of calcium in attenuating bone loss and fracture risk.

While calcium has been the main nutrient of interest in relation to milk and milk products and their effects on bone growth there is also the possibility that other nutrients which are found in milk may be important. Energy and protein modulate bone growth and micronutrients such as zinc may also have an effect. The form of calcium salt may also be important. It has been proposed that the calcium phosphate in milk may have different mechanistic effects on bone compared to other calcium salts.

While these studies show that milk and milk products may decrease the risk of osteoporosis through their effects on growth, recent epidemiological evidence may point to negative influences of childhood growth on later human health. Cancer mortality rates seem to be associated with nutritional conditions which encourage growth in childhood, while the opposite is true for risk of cardiovascular disease.

Milk and milk products have also been vilified because of their fat content and the link between fat, particularly saturated fatty acids, and coronary heart disease. The classical diet heart hypothesis centres on the relationship between saturated fatty acids, blood cholesterol and risk of coronary heart disease. This classic diet hypothesis has formed the basis of dietary recommendations to reduce the incidence of coronary heart disease. Dietary change in the direction of reduced consumption of saturated fatty acids, particularly changes in the consumption of milk and milk products has been a bastion of UK dietary recommendations. However, there is debate as to the efficacy of such an approach as a method to reduce deaths from coronary heart disease.

Milk protein and lactose may cause adverse reactions in a small proportion of the population. However, exact figures for the prevalence of cow's milk allergy and lactose maldigestion are difficult to estimate.

Milk and dairy products are major components of the human diet in Western countries, providing about 30% of dietary proteins and lipids. The current annual production of milk is 560 x 106 tonnes, of which 85, 11, 2 and 2% are bovine, buffalo, caprine and ovine, respectively. Although some raw milk is still consumed, the vast majority of milk is processed to at least some extent. Liquid milk is a major food item in all developed dairying countries, representing 30% of total milk production. The remainder is processed into one of several thousand products, making dairy products the most diverse and flexible group of food products. The flexibility of milk as a raw material resides in the chemical and physico-chemical properties of its constituents, many of which are unique. The principal constituents of milk can be modified by enzymatic, chemical and/or physical methods, permitting the production of new products. However, the concentrations and properties of milk constituents are variable and hence the processability of milk and the properties of dairy products are inconsistent, although much of this variability can be eliminated by employing modern technology, which exploits certain features of milk constituents. Today, most milk is processed in very large, highly mechanised and automated factories, where consistency in processing properties is essential. The resulting products are distributed through large wholesale and retail outlets, where consistency is, again, paramount. Finally, today's consumers expect consistency. The consistency expected by the processor, distributor and consumer can be achieved only if the properties of milk constituents are understood at the molecular level.

This communication will describe:

• The chemical and physico-chemical properties of the principal constituents of milk, i.e. lactose, lipids, proteins and salts,

• Variations in milk composition and in the properties of its constituents and the influence of dairy husbandry practices thereon,

• Exploitation and significance of the chemical and physico-chemical properties of milk constituents in the production and properties of the principal groups of dairy foods, i.e. liquid milk products, cheese, butter, fermented milks, functional milk proteins and lactose.

• Process modifications which may be used to overcome variations in the properties of milk constituents.

Mycobacterium paratuberculosis is the known cause of Johne's disease in cattle and has been implicated as a cause of Crohn's disease in humans. Concern has been expressed that the organism, which is excreted in milk and faeces of infected cattle, may be transmitted via pasteurised milk. This is largely from work that has shown an unacceptable risk of survival of the organism when it is present in raw milk at numbers exceeding 102 cfu/ml. Three possible reasons for this apparent heat resistance were investigated viz. use of a milk heating menstruum, presence of a heat resistant sub–population, and the tendency of the organism to form clumps. Heat resistance studies using a combined acid–fast/viability stain, and a comparison of the relative heat sensitivities of clumped and de-clumped M. paratuberculosis cells provided circumstantial evidence that it is the organism's tendency to form clumps which confers the apparent heat resistance. This work casts doubt on the efficacy of current commercial pasteurisation heat treatments (72°C/15s) for the inactivation of M. paratuberculosis. This would be of concern if a link between M. paratuberculosis and Crohn's disease is eventually established.

The chemical composition and processing characteristics of milks from spring and autumn calving herds were investigated to establish if an autumn/winter milk supply would overcome the variation in composition and quality which is characteristic of a seasonal milk supply. Three herds of 26 cows were established with mean calving dates of 22 February, 28 September and a 50:50 combination of both. The experimental period was from 5 August to 22 December. Bulk milks were collected separately from each of the three herds at one consecutive am and pm milking each week. Spring and autumn milks were also bulked in proportions of 70:30, 50:50 and 30:70, respectively. All milks were analysed for gross composition, protein fractions, renneting properties (rennet coagulation time [RCT], rate of curd aggregation [K20] and curd firmness [A60]), free fatty acids (FFA) and somatic cell count (SCC). Total protein and casein of spring milk were reduced (P<0.001) from 38.1 and 28.7 g/kg, respectively in the period 14 October-24 November to 33.8 and 25.9 g/kg in the period 25 November-22 December. This was accompanied by a deterioration (minimum P<0.01) in RCT from 21.7 to 33.3 min, in K20 from 8.2 to 15.2 min and in A60 from 43.8 to 30.8 mm. Autumn milk had higher fat (P<0.01) and lactose (P<0.001) concentrations, lower FFA levels (P<0.001), improved (P<0.001) RCT, K20 and A60 values compared to spring milk in the period 25 November-22 December. During this period, the 70:30 milk had improved RCT (P<0.01) and K20 (P<0.05) values and reduced (P<0.01) FFA levels compared to spring milk. It is concluded that the composition and processing characteristics of spring milk deteriorated after 275 days in milk. Changes in total protein and casein were closely associated with changes in renneting properties. Blending of autumn milk with spring milk improved the processing characteristics of the mix compared to those of spring milk. Thus, the introduction of early lactation autumn milk at the end of the spring lactation would maintain good milk processability and allow continuous product manufacture.

Recombined milks manufactured from milk powders made from milk produced by b-lactoglobulin (b-LG) AA phenotype cows were not suitable for processing into ultra-heat-treated (UHT) milk products as these milks rapidly fouled heat exchanger surfaces when compared with standard mixed b-LG variant milk. Recombined milks manufactured from powders from b-LG BB phenotype milk generally gave low fouling rates upon UHT treatment and in some cases gave almost negligible fouling of UHT heat exchanger surfaces. Fresh milk from b-LG AA phenotype cows fouled evaporator preheaters more rapidly than standard milk, whereas fresh milk produced from b-LG BB phenotype cows fouled evaporator preheaters less rapidly than standard milk. Recombined milks manufactured from powders made with milk from k-casein (k-CN) BB phenotype cows fouled heat exchanger surfaces more rapidly than recombined milks manufactured from powders from milk from k-CN AA phenotype cows.

Cost–price models were developed to describe milk collection, manufacture and marketing of standardised fluid milk, butter, cheese, casein, and milk powders. Market constraints were modelled by fixing fluid milk demand to 10% or 70% of milk production. Milks representative of New Zealand Holstein-Friesian (HF) and Jersey (J) breeds, and novel technologies were considered. The true value of each milk was assessed from its own processing performance on the basis of fat, protein, lactose and volume considerations. Average milk was worth £0.193/kg when a significant fluid market exists, reducing to £0.112/kg when most milk was manufactured into concentrated dairy products for sale on the world market. Milk from different breeds varied in true value. On a per kilogram basis, HF milk was less valuable than J milk.

Single and multiple component payment systems were quantified for various subsets of milk components and used to obtain predicted values of a range of milks for comparison to their true values. Values of milks that differ in composition from average milk tend to have predicted values that deviate from their true value. The extent of such bias varies depending upon the payment system considered. For example, volume-based payment over-valued HF milk and penalised J milk. Other payment systems undervalued HF milk and over–valued J milk.

Payment systems should be fair, discourage unfavourable changes in composition and provide opportunities for shifts towards the production of more valuable milk. The marketing mix and the choice of payment system have major impact on the potential for economic benefits to the producer from modifying the composition of milk. Payment systems need careful, thorough investigation in concert with market research and studies into breeding and other management opportunities for modifying milk composition.

A value-based payment system can encourage producers to alter the composition of their milk in order to increase revenue.

Genetic improvement is constrained by the long-term and cumulate nature of genetic improvement, by the economic rewards for making genetic change and by the variances and covariances among traits of interest. Genetic change is cumulate, so that small annual changes make substantial differences over time. This cumulate nature of genetic improvement dictates the importance of identifying long-term goals driven by robust economic signals and then adhering to them. The economic rewards for genetic improvement will ultimately determine the uptake and therefore the success of any breeding program. In developed countries the value of milk can be divided between the weight of water, fat and protein produced. Water generally has a negative value due the cost of handling, removal and disposal. Fat and protein have varying values depending on the market, but both will always have underlying positive values. Genetic variances and covariances among the aggregate composition traits, water, fat and protein, are such that simultaneous increase in the yield of all three is considerably easier than improvement of just one, or improvement of one while decreasing others. Selection for simultaneous increase of fat and protein percentage will also be successful, but at the price of not increasing fat and protein yield nearly as rapidly as when selecting directly on yield traits. In virtually all developed countries, the optimum selection goal will be for some combination of increased fat and protein yield that may lead to a gradual increase in the protein to fat ratio. Genetic polymorphisms in several protein genes have been associated with yield and with milk processing properties, but are unlikely to play more than a minor role in overall selection. There is some evidence of genetic variation in milk fat composition, but the level of variation and economic incentives for change mean that selection for milk fat composition is not worthwhile. Thus, with the exception of very slow changes in the water to fat to protein yield ratio, genetic improvement does not seem a particularly suitable route for altering milk composition.

Two partially balanced change-over design experiments were undertaken to examine the effects of concentrate energy source on milk yield and composition of lactating diary cows offered a diverse range of grass silages. A total of nine silages differing in fermentation digestibility and intake characteristics were produced in experiments 1 and 2. Silage dry matter (DM) concentration ranged from 170 to 473 g/kg, ammonia nitrogen ranged from 58 to 356 g/kg nitrogen, digestible organic matter in the DM ranged from 551 to 724 g/kg and silage DM intake potential ranged from 57 to 103.8 g/kg w0.75 respectively. In experiment 1, 5 concentrates were formulated to contain similar concentrations of crude protein (CP), effective rumen degradable protein (ERDP), metabolizable energy (ME) and digestible undegradable protein (DUP) while three concentrates were formulated in experiment 2 to contain similar concentrations of CP, ME and DUP. The concentrates were prepared using barley, wheat, sugar beet pulp and citrus pulp as energy sources and formulated to achieve a wide range of starch concentrations. Starch concentrations ranged from 50 to 384 g/kg DM and 22 to 273 g/kg DM in experiments 1 and 2 respectively. There were no concentrate energy source by silage type interactions for silage intake, milk yield and composition. It is concluded that increasing starch intake resulted in positive and negative linear relationships for milk protein (P<0.001, R2 = 0.96) and fat (P<0.001, R2 = 0.85) concentrations respectively. Concentrate energy source had no effect on silage DM intake or milk yield.

Conjugated linoleic acid (CLA) is a naturally occurring anticarcinogen found in dairy products which is produced in the rumen as an intermediate in the biohydrogenation of polyunsaturated fatty acids by the bacteria Butyrivibrio fibrivsolvens. An experiment was conducted to examine the changes in CLA concentration in bovine milk throughout the year. 338 milk samples were taken from the University of Nottingham's commercial dairy herd between December 1997 and March 1999. All animals followed the same dietary regime throughout the study. Samples were analysed for fat and CLA content. Morning and evening samples were pooled to calculate daily fat and CLA concentrations and yields. There was a small variation in milk yield (P<0.05) whereas CLA content and yield varied considerably (P<0.001) throughout the year (CLA = 0.91 to 2.81 mg/g of fat). The highest concentrations were found during the summer months when the cows were mainly eating fresh grass as opposed to conserved forages. Fat content and yield followed by the month were the predominant factors affecting CLA output. Results indicate that, if required, CLA in milk could be increased through suitable dietary management practices.

The Committee on Medical Aspects of Food Policy report Nutritional Aspects of Cardiovascular Disease recommended increased dietary intakes of the long chain polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid to help protect against cardiovascular disease. There is some evidence that a-linolenic acid can be elongated and desaturated by mammalian enzyme systems to produce small amounts of eicosapentaenoic and docosahexaenoic acids. Whole linseeds are rich in a–linolenic acid, and it has been suggested that feeding this oilseed to dairy cows may result in higher levels of the long chain polyunsaturated fatty acids in bovine milk. To examine this hypothesis, the effect of feeding whole ground linseed and xylose treated whole ground linseed on the performance and milk composition of dairy cows was investigated.

Either form of whole linseed reduced dry matter intakes and milk protein concentration. The xylose treated whole linseed increased milk yield, but neither linseed source changed milk fat concentration. Levels of milk a-linolenic acid increased to 1.2 g/100 g fatty acid when whole ground linseed was fed, and to 1.5 g/100 g fatty acid with the xylose treated linseed compared with 0.7 g/100 g fatty acid for cows fed the control diet. The efficiency of incorporation of additional dietary a-linolenic acid into milk fat was estimated to be 1.6 and 3.4% for the whole ground and xylose treated whole ground linseed respectively. Feeding whole ground linseed increased the proportion of a-linolenic acid in milk fat, but there was no evidence of eicosapentaenoic and docosahexaenoic acids in milk fat, suggesting that if any elongation and desaturation of a-linolenic acid occurs in dairy cows, none is transferred to milk.

Human nutritionists have identified that dietary myristic and palmitic fatty acids are major risk factors in cardiovascular disease. Bovine milk fat is particularly rich in these fatty acids as they can be produced de novo in the mammary gland from by-products of fibre fermentation in the rumen. However, increased dietary levels of C18 fatty acids has been shown to reduce the concentration of myristic and palmitic acids in milk fat. Supplying dietary oil from whole oilseeds treated with xylose, may reduce rumen biohydrogenation of polyunsaturated fatty acids and further decrease the saturated fatty acid content of milk. In this study, the effect of feeding whole ground soya beans, whole ground soya beans treated with xylose and whole ground rape seed on dairy cow performance and milk composition was investigated. All three oilseeds reduced dry matter intakes and milk protein concentration. Both the xylose treated whole ground soya beans and the whole ground rape seed increased milk yield, but the whole rape reduced milk fat content. Levels of linoleic acid in milk fat increased when whole soya was fed, whereas oleic acid concentration was highest when whole rape was included in the diet. Concentrations of myristic and palmitic acids in milk fat were lower when any whole ground oilseed was fed, but the reduction was greatest with whole ground rape which reduced the myristic plus palmitic acid content of milk fat to 25 g/100 g fatty acid, compared with 47 g/100 g milk fatty acid in the milk from cows fed a standard low oil diet. These results suggest that feeding specific sources of dietary oil can dramatically reduce levels of myristic and palmitic acids in milk fat, and that different oilseeds have different effects on milk fat concentration.

Conjugated linoleic acids (CLA) are potent anticarcinogens secreted into the milk of ruminants. The present study was carried out to detect the post–ruminal effects of a duodenally infused commercial CLA product on milk–fat synthesis and fatty acid pattern in lactating cows. Four Holstein cows, fistulated with duodenal cannulae, were infused with 200 g of a CLA mixture daily into the duodenum over a period of 5 days (period II), while no application of CLA acted as controls in period I and III. In contrast to the marginal effect of the CLA application on milk yield, an obvious decrease of milk fat content of 40% was measured. The fat yield decreased during the infusion period to about half of the control period, whereas protein and lactose content in milk was not significantly influenced. The CLA percentage of milk fat increased sevenfold during infusion of the CLA supplement. The data demonstrate that duodenal infusion of CLA inhibits the milk fat synthesis, resulting in the decrease of milk fat content and fat yield. It can be concluded, that CLA supplements increase the CLA concentration in milk fat, which probably has to be rumen protected for oral administration.

The experiment was designed to investigate the effect of increasing the concentration of Cu2+ in the diet of the lactating dairy cow with a view to stimulating the activity of the mammary gland △9–desaturase enzyme system to increase the C18:1/18:0 ratio in the milk fat.

In a preliminary study, two lactating dairy cows were provided with ground rapeseed/maizebased concentrates containing either a normal or a high concentration of supplementary Cu2+, the animal offered the normal concentration supplement was also provided with an oral CuSO4 solution drench so that both animals received an equal daily supply of Cu2+. Daily blood samples were collected from the cows and total plasma Cu2+ concentration was determined. A blood plasma lipid analysis was also carried out. In a second study, eight lactating dairy cows were provided with a silage and concentrate diet. The lipid portion of the concentrates was provided by either ground or unground rapeseed while the Cu2+ in the mineral supplement of the unground rapeseed-based concentrate was manipulated to provide one of the following three concentrations of Cu2+ in the concentrate (mg/kg DM); <10, 50 or 100. The subsequent milk fat was analysed for fatty acid composition.

Presentation of an increased concentration of Cu2+ to the cow was more efficiently absorbed when provided in the concentrate mix than when provided as a CuSO4 solution in an oral drench. Increased dietary Cu2+ in the concentrates was successful at increasing the concentration of plasma Cu2+ from a normal concentration of 80–100 mg/cm3 to over 200 mg/cm3. An increased concentration of Cu2+ in the blood of the cows in the first experiment resulted in a significant increase (P<0·05) in the C18:1 content of the plasma lipid, possibly through the increased activity of the intestinal △9–desaturase enzyme system.

The composition of the milk, including the fatty acid composition of the milk fat, from the second experiment was unaffected by the concentration of Cu2+ in the diet of the dairy cows within the concentration range of <10 to 35 mg/kg DM per day.

A study was conducted to assess the effects of rapid wilting of grass prior to ensiling on milk composition in lactating dairy cattle across a range of silage harvests. The effects of wilting on the response to bacterial inoculation were also examined. Experiments 1 and 2 were of 2 x 2 factorial design based on the factors wilting (unwilted and wilted treatments) and inoculant (control and inoculant treatments). The inoculants each had Lactobacillus plantarum plus other bacterial species. Experiments 1 and 2 had 3 and 8 harvests respectively and the corresponding feeding experiments were balanced changeover designs with 3 and 8 periods respectively. The feeding periods were of 8 and 3 weeks duration in Experiments 1 and 2 respectively and during each period each silage was fed ad libitum together with a concentrate supplement to 12 cows.

The durations of the wilting periods ranged from 24 to 48 h in each experiment and the mean initial and final dry matter contents of the grass were 200; 317 g/kg and 176; 316 g/kg for Experiments 1 and 2 respectively.

In Experiment 1 the butterfat, protein and lactose concentrations (g/kg) from the unwilted and wilted silages were 45.1 and 47.2 (s.e. 0.23, P<0.001), 33.7 and 35.6 (s.e. 0.11, P<0.001) and 48.9 and 48.7 (s.e. 0.08, P<0.05) respectively. In Experiment 2 the corresponding values (g/kg) were 45.2 and 46.4 (s.e. 0.23, P<0.05), 32.3 and 33.2 (s.e. 0.13, P<0.05) and 48.9 and 49.1 (s.e. 0.06, P>0.05) respectively. Inoculation had no significant effects on milk composition with either unwilted or wilted silage except for a reduction in protein content in Experiment 1, with values (g/kg) of 34.8 and 35.4 (s.e. 0.11, P<0.05) for control and inoculant treated silage respectively.

It is concluded that wilting produced statistically significant increases in the concentrations of butterfat and protein in milk and that inoculants had little effect on milk composition in this study.

A technology transfer project has been set up to demonstrate management techniques to help raise the weighted average annual milk protein concentration to 36 g/kg in a cost effective manner using feeding, breeding and management techniques over a period of five years. A herd of autumn calving Holstein/Friesian cows was selected for the project on the basis of performance records and a number of commercial farms were selected for demonstration and benchmarking purposes. Methods which have been employed to improve milk protein include the use of extended grazing, improvements in silage quality, the use of specifically formulated concentrate supplements and the development of a breeding strategy designed to improve milk protein. Herd performance currently stands at 34.2 g/kg milk protein. Improvements in protein content to date have coincided with improvements in silage quality, the early introduction of grazed grass and the use of a specifically formulated concentrate. To date heifers entering the herd have not improved milk protein content. However, this appears to have been a result of the breeding policy adopted prior to the start of the project. Farmers have been able to develop their own competencies and management skills through project features on the Internet, in press articles, during visits to Greenmount College and through John Thompson and Sons Technical Department.

The freezing point of bovine milk is known to vary between narrow limits. However, some variation is possible, because of the osmotic relationship between blood and milk. The extent of variation in freezing points of cow's milk was studied. For one year, freezing points were determined in individual milk samples from a high producing herd. Differences (P<0.05) were found between evening and morning milk yield and freezing points. A ‘lactation curve’ for freezing points was fitted and showed some similarity with milk yield curves. Stage of lactation explained part of the variation of freezing points of cow's milk.

The objective of this study was to measure the effects of varying doses of atropine on the concentration and composition of milk protein and on blood α-amino N levels. Four treatments were administered to each of 12 cows over 12 days in a replicated Latin square experiment. There were at least 2 days between each of 4 treatment days. Treatments were: control (C; saline); low dose (L; 30mg atropine/kg LWT); medium dose (M; 40mg atropine/kg LWT); and 2 x low dose (2L). All treatments were administered via subcutaneous injection immediately after the morning milking; the second dose of the 2L treatment was given two hours later. Milk was sampled from each cow at the morning milking (time 0 h). Cows were then milked again 2, 6 and 10 h after treatment, and milk samples again collected. Blood samples were drawn from the coccygeal vein of each cow after each milking. Atropine decreased milk secretion at 6 h for the 2L treatment and 10 h for all treatments. Atropine reduced concentrations of milk protein and casein at 2 h and 6 h, but not at 10 h. Concentrations of whey proteins and of α-casein were depressed by atropine only at 6 h post-treatment, while a reduction in α-lactalbumin due to atropine was observed at 6 and 10 h post-treatment. In contrast, atropine increased concentrations of IgG and BSA at 6 h and 10 h post-treatment. Atropine also increased the ratio of casein:total protein at 6 h after injection. There was no difference between the effects of the low and medium doses of atropine, but the double low dose induced effects which were greater than for the single doses. Effects of a single dose of atropine were greatest for most milk proteins at 6 h post treatment; thus this would be the most useful milk sampling time for future experiments. Atropine did not significantly affect α-amino N concentrations in whole blood, although there was a trend for a reduction for all treatments at 2 h after treatment. Atropine may be useful for reducing milk protein concentrations and circulating levels of certain blood amino acids to base levels, during studies designed to elucidate the effects of perturbations in the blood amino acid profile on milk protein composition.