For many years, the Milk Marketing Board (MMB) of England and Wales has operated a pricing system related to the compositional quality of milk supplied by the producer and to the month of supply. As milk production has increased and the seasonal pattern altered, a need has arisen to alter the pricing system.

The volume of milk for manufacture has more than doubled since 1970 and now exceeds that taken by the liquid market. The fat and protein elements of milk are of considerably greater value to the manufacturing market than lactose. To match producer payments more closely to market realities, the MMB will, from April 1984, replace the fat and solids-not-fat compositional quality payment scheme with one based on fat, protein and lactose. The proposed prices at 1983/84 levels are: fat, 2.02; protein, 1.77; and lactose, 0.28 pence/1/10 g/kg.

In the last 10 years, the seasonal trough of production has moved from December to August/September. It is still deepening and adds considerably to marketing costs. In an attempt to slow this trend and also provide a disincentive to additional supplies at peak, the MMB is altering its seasonal price adjustments. Milk prices will be increased in August and September and decreased in May and June.

These changes will not affect the total sum of money available to producers, hence most of them will see little difference to their annual income. The exception will be those producers supplying milk of either especially low or high protein and, to a lesser extent, fat content. The change in seasonal adjustments will, however, cause a noticeable disruption in the cash flow to all producers.

The changes in milk composition from the turn of the century to the present date are reviewed and the difficulties that the changes may have given to manufacturers are discussed. Butter manufacture is not affected by changes in milk compositional quality, although the spreadability of butter follows the seasonal changes in the hardness of milk fat. The legal requirements for the composition of cheese are set at levels that have not given any difficulty but the yield of cheese has suffered due to the progressive deterioration in the casein content of milk. There are some specific problems related to the operation of the European Economic Community milk subsidies, although these are more administrative and bureaucratic difficulties than compositional problems. It is concluded that technological advance can cope with any likely change in compositional variability, provided that legislation is not introduced to ensure the perpetuation of traditional methods.

In recent years, the average consumer has become much more aware of the composition of food. Medical opinion, that diets high in fibre and low in fat are likely to result in longer and healthier lives, has provided the food industry with new market sectors and, hence, the need for new product development.

The dairy industry in the United Kingdom has, in the main, been slow to react to this challenge and has left the remainder of the food industry to manipulate the composition of the final product. At one time, the inclusion of 100 g butter per kg margarine was deemed to be a sales advantage but today the consumer believes it is a disadvantage. The cholesterol and saturated fats discussion has obviously been put forward with great fervour by members of the food industry who have sought to gain advantage. The reaction of the dairy industry has been to take a defensive stand rather than to conduct research and promote the nutritional advantage of milk and milk products. This attitude is changing, fortunately, and new dairy products are being developed and marketed aggressively. The belief of the dairy industry, that only new products containing milk ingredients alone would be manufactured, is no longer true and a whole range of new dairy-based products, incorporating varying amounts of other food ingredients, is appearing.

The latest developments in dairy technology are resulting in some new raw materials derived from milk, specially designed for specific uses in the food industry. This paper reviews some of these developments against the background of milk composition, industrial production and market consumption.

Milk composition varies greatly throughout the year, due largely to the effects of the diet of the cow and the stage of lactation. Whilst such variations go unremarked with bottled and cartoned milk, they are of major importance to manufacturers who use milk as a raw material. The most obvious example is when the yield of a dairy product is affected, e.g. in Scotland, the volume of milk required to produce 1 kg butter varies between 21.1 and 23.3 1 at different times of the year.

In addition, however, some of the more subtle changes in milk composition either affect product quality, e.g. the ease with which butter may be spread, or cause processing difficulties, e.g. instability during heating processes. This paper reviews some of our current knowledge on the relationship between milk composition and the properties of some dairy products — butter, whipping cream, Cheddar cheese, ultra-heat treated milk and full-cream evaporated milk. The aim is to identify those milk components that affect each product or process and then enquire how milk composition may be altered to effect improvements — whether at the farm by dietary manipulation or at the creamery by technological adjustment.

It is believed that all the evidence indicates that, despite difficulties due to restrictive legislation, the answer must lie at the creamery. The farmer should concentrate on producing desirable milk solids at the lowest possible cost and leave the technologist to do the fine tuning that leads to improved products.

The broad principles of animal breeding are outlined and the ‘normal-probability curve’ is used to illustrate how progress should be made in improving the genetic merit of dairy cattle. The importance of genetically correlated responses is discussed, together with the need to test progeny. The way in which genetic improvement accumulates in dairy cattle is described and the need to use high-production sires with reliable proofs is stressed. Present and proposed milk-quality payment schemes require that selection should be based on the yield of recorded solids as the best indicator of total solids. As cattle breeding involves a long time-scale, it is not always possible to take into account short-term changes in the value of milk constituents. The effect of changing values upon the ranking of bulls is small and, for the foreseeable future, the use of the weight of recorded solids, i.e. the weight of fat plus the weight of protein, as the selection factor, is likely to maximize progress. The relationship between functional type and herd life is examined. It is concluded that there is no obvious relationship between type and herd life; yield is the dominant factor in determining the length of time an animal remains in the herd. Any breeding programme should therefore place maximum emphasis on production.

The effects of breed, stage of lactation, age and seasonality on the compositional quality of milk are discussed. The Jersey breed has the highest fat and protein contents, 51.9 and 38.5 g/kg milk, respectively, followed by the Guernsey breed, with 46.4 and 36.3 g/kg milk. The British Holstein has the lowest fat and protein contents, at 37.3 and 32.0 g/kg milk, respectively, whilst the Ayrshire is intermediate between the Channel Island and the Friesian and Holstein breeds. The range of fat within a breed may be over 20 g/kg milk. The variation in protein content is less than this value but may be over 10 g/kg milk. Lactose values vary less than those for fat and protein. Mean lactose values are 45.5 g/kg, with a range from 41.0 to 50.0 g/kg milk.

The protein content of milk is high in early lactation, falls rapidly to reach a minimum at approximately 6 weeks after calving, increases slowly to 6 months after calving and then increases rapidly to the end of lactation. The fat content of milk is also high in early lactation and falls to a minimum between the 6th and 10th weeks of lactation. It then rises in a manner similar to protein. Converse changes occur with lactose: the content is low in colostrum and increases to twice its initial value within the 1st week. It remains steady until the 5th or 6th week of lactation, after which it declines slowly and then more rapidly towards the end of lactation.

The fall in the fat content of milk from the 1st to the 5th lactation is progressive and of the order of 2 g/kg milk. Solids-not-fat content declines by approximately 4 g/kg. This fall in solids-not-fat is largely a fall in lactose; the change in protein content is small. In Friesian herds, a decrease in average lactose content from 46.9 to 44.7 g/kg milk from 1st to 3rd lactation and over has been observed.

The average fat content of bulk milk in England and Wales is highest in October and November and lowest in May and June. The protein content of milk falls to a low level in March, rises rapidly during April and May and shows a slight fall in July, followed by an increase until October, when a progressive fall occurs during the winter months. The lactose content of milk does not vary as much as protein, with values being 0.5 g/kg higher in June and 0.8 g/kg lower in September than the overall average.

Decreasing the proportion of long forage in mixed diets from 400 to 100 g/kg at constant digestible energy intakes reduces milk fat content by approximately 5 g/kg for every 100 g/kg decrease in hay. This response varies widely and a safe minimum diet composition to maintain approximately 40 g fat/kg milk from Friesian cows in mid-lactation is approximately 450 g long forage/kg or 220 g acid-detergent fibre/kg dry matter. This, however, would reduce milk yields. With barley-based concentrates, milk yield increases as the proportion of hay in the diet is reduced, with the result that the reduction in the yield of fat is less than the fall in its concentration. Milk fat content is higher when ground maize, which is a slowly fermented starch source, or fodder beet or fibrous by-products replace rapidly fermented starch sources such as barley in low-roughage diets. Milk yield, however, is lower. Supplementary fats and oils generally increase milk yield but their effects on milk fat content and yield vary widely.

Increasing the intake of high-concentrate diets of fixed composition increases the yield of milk but reduces its fat content. Increasing the number of meals per 24 h reduces this milk fat depression without affecting milk yield. Thus, advice on milk fat production must take account of the level of intake, the pattern of feeding and the diet composition.

In most situations, the avoidance of low milk fat content requires control of rumen fermentation to prevent high proportions of propionic acid. However, with frequent feeding during the 24 h, high propionic acid in the rumen has less effect on milk fat. It appears that high plasma insulin concentration is the main factor reducing milk fat production.

The release of insulin is stimulated by the peaks of propionate, which are produced after large meals of concentrates but not by the steady supply of propionate associated with frequent feeding.

Available knowledge can permit wide variation in milk fat production by dietary manipulation with reasonable accuracy but the future aim should be for more direct intervention at metabolic control points.

This paper reviews the effects of feeding on milk protein production. It deals, first, with the chemical composition of the milk proteins and the extent to which the composition is influenced by diet, the synthesis of proteins in the mammary gland and the effects of variations in the supply of amino acids and of the energy-yielding nutrients that are absorbed from the gastrointestinal tract. There is then an examination of the impact of changes in dietary energy and protein supply on the content and yield of protein in milk and specific consideration of particular features of ration formulation, including supplementary energy concentrate foods, supplementary lipids and amount and type of supplementary protein foods. Finally, it is argued that the effects of diet on milk protein production are evaluated best simply in terms of milk protein yield; some of the pitfalls of interpreting information on milk protein content in practice are pointed out.

It is concluded that the yield of milk protein is determined by the dietary supply of energy-yielding constituents and protein but that presently employed systems for ration formulation do not provide a satisfactory means of interrelating milk protein yield and the intake of nutrients in the cow's diet.

In most experiments in which the influence of forage to concentrate ratios on milk quality have been examined, the composition of the forage has been incidental to the purpose of the trial. Legumes have resulted in higher yields of milk than grasses of similar digestibility. However, these increases were a reflexion of higher outputs of protein and lactose, since the feeding of legumes resulted in lower contents of milk fat. Changes in the digestibility of forage have shown considerable variability in response, in terms of the concentration of milk solids. However, an increase in digestibility of forage has not resulted in decreases in the yield of fat and, further, the yield of protein has been increased.

There is no indication that there is a requirement for ‘long hay’ to maintain milk quality and that a reduction in the chop length of silage has any influence on milk composition. However, the fine grinding of grass, which was the sole forage component of the diet, has caused a marked decrease in milk fat content. This effect was not apparent when finely ground and pelleted dried grass was used as a supplement but only in ad libitum feeding regimes.

Attempts to increase the content of milk fat in May and June by the supplementation of grazed grass with small quantities of hay have had little influence on milk yield and fat content. A much greater effect was observed when grazing was restricted and silage offered ad libitum overnight. The increase in fat content may be overcome by a reduction in milk and protein yield.

In general, the changes in milk composition have been small and this is likely to be a result of the high proportion of forage in the diets examined. The quantification of response in yield and content of fat and protein to changes in forage composition requires a change in approach. More emphasis should be given to the examination of the interaction between level or type of concentrate and the composition of the forage. Further, these trials should be accompanied by experiments to examine the effects of the dietary changes on the end products of digestion.

Lactation depends on milk secretion and the storage of the accumulating milk, followed by milk ejection and effective milk removal during milking. Environmental and disease factors may affect each of these stages independently and, thus, alter the milk composition. With normal milking intervals, the secretion of each of the milk constituents is continuous and linear with time. Subsequently, changes in milk composition occur during storage in the udder, mainly through the free movement of water between milk and blood and as a consequence of maintaining their osmotic equilibrium. The changes in composition are greatest in infected glands. The composition of milk varies in different parts of the udder: the fat content is much lower in the milk in the udder and teat sinuses. Following milk ejection, 10 to 20% of the milk is retained and cannot be removed by milking; the fat content of this residual milk will usually exceed 150 g/kg. The dynamics of these changes are complex and, whilst they may bring about large alterations in the composition of the milk obtained at individual milkings, their effect over longer periods is small. Thus, although incomplete milking, changing the milking intervals and increasing the frequency of milking will cause large fluctuations in the composition of milk at individual milkings, their longer-term effects are minor. The main effect of high levels of udder disease will be to reduce the lactose content but the serum protein level will increase and changes will occur in the concentrations of potassium, sodium and chloride ions. The design of milking equipment and the hygiene during farm storage of milk may materially alter the quality of milk for processing, because of lipolysis.

Proposed changes in milk pricing to be introduced on 1 April 1984 will make milk fat payments 53% of total milk returns. Current breed averages indicate that Jersey returns will show the greatest improvement at £40 per cow but will still be £100 lower than Friesian returns. Additionally, the higher calf and barren cow values enhance the Friesian, although this can be offset if Jerseys achieve a 50% increase in longevity compared with Friesians.

The proposed seasonal differentials give a milk price variation around the mean of 29%, compared with the present 13%. However, in 1969/70, the variation was 36%. Milk values by month of calving on the new proposals vary by a maximum of £87 at a yield of 5000 1. August to October calving gives the highest and February to May the lowest milk income after seasonal adjustment.

Farm examples show that block-calving herds have seasonal quality trends that will be highlighted by contemporary payment. In the past, arithmetic averages have put block-calving herds into higher-quality classes than was warranted. Contemporary payment penalizes lapses in quality immediately. Conversely, improvements will be immediately rewarded. Summer-milk producers will have a dramatic decrease in their traditional cash flow in May and June. Comparison of weekly sample results and monthly averages with the same period last year, and with the England and Wales monthly average, enables economic corrective management steps to be taken.

The cost of computerized out-of-parlour feeders depends on herd size. Justification of their cost can be based on changes in milk sales by volume and/or compositional quality.

The changes in the payment scheme proposed by the Milk Marketing Board from 1 April 1984 cover a number of issues relating to compositional quality, seasonality of pricing and the monthly distribution of production. Although the changes in total must be financially self-balancing on a national basis, the effect on individual farms may be significant.

A computer program has been used on the records from a number of farms to investigate the effect of the changes, separately and together, on annual and monthly income from milk. The effects on three herds were as follows.

Herd 1 was a Jersey herd that showed an overall increase in income per cow, due mainly to the higher price of protein. Herds with a high protein to lactose ratio in the milk will stand to gain from the new price of protein.

Herd 2 was a Friesian/Holstein herd with a low protein and low milk fat content in the milk. The herd was also calving seasonally and had a low output of milk during August and September. A substantial decrease in income of approximately £29 per cow was due principally to the low protein to lactose ratio but also to the low fat content and the seasonal pattern of milk production on the farm.

Concerns by the consumer over the relationships between diet and health are growing and there is increased recognition that the diseases of contemporary society can only be combatted by preventive measures. Dietary change is advocated in programmes designed to reduce the incidence of obesity, coronary heart disease and cancer. Recommendations relating to fat are particularly pertinent, with suggestions to reduce total fat consumption from approximately 40% of the energy to nearer 30% and to concentrate efforts on sources high in saturated fatty acids. This means less fat from animal sources, including milk. An immediate adoption of these recommendations is unlikely but increased media coverage is stimulating interest. Evidence from overseas indicates trends away from full-fat towards skimmed and semi-skimmed milks. In Britain, such products are not universally available and demand for milk is declining. However, dairies are increasing production of fat-reduced milks, particularly for supermarkets, and many consumers select these products in the interest of better health. The consequences for the milk producer may be predicted. An increased demand for fat-reduced rather than full-fat milk, coincident with a reduced demand for butter, will result in an accelerating reduction in the demand for milk fat. Under the new payments scheme, the prices paid for fat, protein and lactose must be influenced by market forces. Therefore, there is a strong possibility that, within the foreseeable future, the value of fat, relative to that of protein, is likely to fall. This would have profound implications for milk production and relevant research and development.

The milk composition responses in five feeding trials were as follows.

1. A study of silage quality showed that the fat content was lower (39.9 v. 43.1 g/kg, s.e. of difference 1.00) and the protein content was higher (35.0 v. 33.7 g/kg, s.e. of difference 0.48) with silage cut three times per season compared with silage cut twice per season.

2. Silage offered as a buffer food overnight in the early part of the grazing season reduced milk yield (18.9 v. 19.9 kg/day, s.e. of difference 0.26) and increased fat content (39.4 v. 35.6 g/kg, s.e. of difference 0.50) when compared with grazing only. Silage offered in the late grazing season did not affect milk yield but increased fat content(44.1 v. 41.3 g/kg, s.e. of difference 0.94). There was no significant effect on protein content.

3. A concentrate containing 18 g crude protein/kg was offered at rates of 0.30, 0.375 and 0.45 kg/kg milk plus silage ad libitum. The fat contents were 38.0, 38.6 and 36.1 g/kg and the protein contents 30.3, 31.2 and 32.1 g/kg, respectively.

4. In two experiments comparing flat-rate concentrate feeding with feeding according to yield, no significant differences were found in milk yield, fat and protein contents.

5. In a study of body condition at calving, cows calving at score 2 had milk fat contents similar to cows calving at score 3 but there were differences in the fatty acid composition of the milks. The cows calving at score 2 produced milk with a higher protein content than those at score 3 (32.8 v. 30.7 g/kg, s.e. of difference 0.85).

A dual approach is required to diagnose the cause or causes of the production of herd milk of inferior compositional quality. By studying the results of the analysis of a milk sample in conjunction with accurate information obtained at the farm, it is frequently possible to trace the origin of the problem and, hence, give reliable advice to overcome it. Simple flow diagrams are available as an aid to the Adviser and the diagrams for milk fat, protein and lactose are illustrated.

Case histories are available to illustrate the approach used and indicate the effects of advice on milk production and compositional quality. When diagnosis is difficult, a more detailed investigation is necessary. This might involve the sampling and analysis of foods and the analysis of samples of milk from individual cows. The use of automated infra red spectrophotometric instruments for milk analysis and the processing of results using computers, enable large numbers of samples to be dealt with expeditiously and at low cost.

Forty-eight autumn-calving cows were fed individually during the winter period. Twenty-four cows were offered a complete diet and 24 cows were given the same dietary ingredients as in the complete diet but offered separately. The complete diet was an integral mix of ingredients in the proportion of 500 g silage dry matter (DM) and 500 g compound DM/kg. The compound offered to the cows receiving the separate ingredients was adjusted so that the total compound offered was similar on both feeding treatments. Cows offered the complete diet had a greater intake than those on the separate ingredients, with intakes of 21.4 and 19.1 kg DM/day (s.e. 0.50, P < 0.001) in the first 10 weeks of lactation; and also over the first 18 weeks of lactation, with intakes of 20.1 and 18.6 kg DM/day, respectively (s.e. 0.84, P < 0.01). The extra DM intake was largely silage. Milk yields on both treatments were similar at 31.0 1/day during the winter and there was no significant difference in live-weight gain between the treatments, with values of 22.0 and 19.8 kg on the complete and separate treatments, respectively (s.e. 9.03, NS). Milk fat content was markedly higher with the complete diet at 35.1 g/kg, compared with 31.0 g/kg on the separate treatment (s.e. 0.13, P < 0.001). At current prices, the cost of the extra silage DM on the complete treatment was 10.5 p/day and the improved value of the milk was 15.5 p/day. Another experiment showed no consistent effect on milk fat content when sodium bicarbonate was included in a complete diet. A casual observation on the commercial part of the herd at Bridgets indicated that, when 2 kg of liquid molasses replaced 2 kg of energy from cereal sources in a complete diet, milk protein content in early lactation was raised.

The recent increased use of out-of-parlour feeders for dairy cows has occurred for two main reasons: (1) convenience, including ease of rationing and saving labour; and (2) claims made for beneficial responses in milk yield and/or milk composition. The suggestions concerning improvements in milk composition arise from the effects of the increased frequency of concentrate feeding on certain rumen parameters. There is a reduced fluctuation in those parameters, with a maintenance of ruminai acetate production, which gives beneficial effects on milk fat production. Evidence from the literature indicates that an increased frequency of concentrate feeding does not increase the proportion of milk fat (on a weight basis) but merely rectifies a decrease in milk fat caused by a high concentrate to forage ratio. In trials conducted over 2 years, two groups of cows were offered equal amounts of concentrates from either a controlled out-of-parlour concentrate feeder to provide frequent feeding (O), or twice daily in the parlour (P). Group O out-yielded group P (25.1 v. 23.9, s.e. of difference 0.32** and 27.1 v. 25.4, s.e. of difference 0.56** kg milk/day) in years 1 and 2, respectively. The milk fat content (g/kg) for group O was consistently lower than for group P (36.5 v. 38.1, s.e. of difference 0.91, P = 0.10; 39.8 v. 42.6, s.e. of difference 1.47, P = 0.15) but the difference was not significant. The solids-not-fat content (g/kg) was significantly higher for group O in year 1 (89.9 v. 89.1, s.e. of difference 0.18***) but similar for the two groups in year 2 (90.9 v. 90.9, s.e. of difference 0.60, NS). Overall, the yields of milk fat on the two treatments were similar but the yields of all other milk constituents were increased significantly with out-of-parlour feeding.

To achieve high yields of total solids in a dairy herd requires the implementation of appropriate breeding and feeding strategies. The Edinburgh School of Agriculture's Langhill herd, which consists of 200 cows, embarked on a long-term breeding programme in the early 1970s to demonstrate to what extent genetic improvement might be achieved within a herd, using selection methods available to commercial dairy farmers. The specific selection objective was yield of total solids, with artificial insemination (AI) sires being chosen on their improved contemporary comparison for fat plus protein production and females being selected on their genetic index for the same traits. To measure genetic change, a genetic control population was established. Thus, a section of the herd, currently 25 animals but increasing to 20% of the total herd, are bred from a panel of 50 AI sires selected randomly from the 1976 Milk Marketing Board and Scottish Milk Marketing Board Dairy Bull Progeny Testing Schemes. The herd is given complete diets during the winter housing period, September to May, and grazed on a paddock system in the summer months. The average 305-day yield in the selected herd in 1983 was 6924 kg at 41.8 g fat and 34.2 g protein/kg. This yield shows an increase from the 1977 yield of 5732 kg at 38.7 g fat and 32.5 g protein/kg. Current first-lactation yields average 6107 kg at 42.5 g fat and 33.9 g protein/kg. The food intake of a section of the herd is recorded and initial results suggest that cows producing high yields of solids are more efficient than cows producing lower yields.

Fifty herds with the highest annual average mastitis cell counts in England and Wales were compared with 50 herds with the lowest cell counts. The milk-quality test results of these herds for milk fat, protein and lactose contents, and total bacterial count (TBC), over the 6 winter months, October 1982 to March 1983, were examined.

The herds with high cell counts had an arithmetic mean of 2.50 × 109 cells/1 and the herds with the low cell counts had 0.117 × 109 cells/1. The milk-quality test results were: milk fat, 39.8 and 40.0 g/kg; protein, 33.2 and31.5 g/kg; lactose, 42.8 and 46.9 g/kg; and TBC, 139 and 12.0 × 106/1 for the herds with the high and low cell counts, respectively. There were highly significant differences in protein and lactose contents and in TBC. When the average monthly results were compared, these differences were statistically significant in all months. On average, lactose was 9% lower and protein 5% higher in the herds with the high cell counts when compared with the herds with the low cell counts.