Suckling following mechanical milking is common practice in organic dairy production systems and in developing countries. The objective of the experimental work was to assess the effect of suckling and suckling frequency following mechanical milking on milk yield, milk composition and somatic cell count. Two experiments were completed using multiparous dairy cows allocated at 3 days post partum to their respective treatment groups. In experiment one, twenty–four multiparous dairy cows were allocated to one of two treatments for 305 days; 12 cows not suckled (NS) and 12 cows, which were suckled twice daily following mechanical milking (S2). Daily milk yield was significantly greater (P<0.05) in suckled cows, NS 8.0, S2 8.9 (sem 0.18) kg/d. Milk fat content was significantly lower (P<0.05) in suckled cows (NS 32.0, S2 30.7 (sem 0.56) g/kg). However, milk protein was not significantly different in suckled cows, NS 29.2, S2 27.6 (sem 10.79) g/kg compared with non suckled cows. Somatic cell count was significantly lower (P<0.05) in suckled cows NS 106, S2 85 (sem 2.85) 000/ml, compared with non suckled cows. In experiment two, thirty-eight cows were allocated one of two treatments for 120 days; 19 cows not suckled (NS) and 19 cows, which were suckled once daily following the afternoon milking (S1). Suckling took place for fifteen minutes daily following machine milking only. The calves were weaned at 6 months of age. Total daily milk yield was significantly greater (P<0.05) in suckled cows, NS 11.7, S1 12.5 (sem 0.04) (kg/d) compared with non suckled cows. The milk fat and protein content were not significantly different in suckled and non suckled cows. Milk fat content NS 33.4, S1 32.9 (sem 0.14) g/kg and milk protein content NS 29.8, S1 30.0 (sem 0.07) g/kg. In conclusion, suckled cows had significantly higher milk yields. Cows suckled twice daily had significantly lower milk fat content. Suckling did not affect milk protein content. Suckling cows twice daily significantly reduced SCC.

Dietary manipulation of milk fat content and/or fatty acid composition is becoming a feasible, and for certain niche–markets, attractive means of boosting the nutritive value and acceptability of milk and its secondary products. However it is not yet possible to indicate equivalent ways of manipulating milk protein content and/or composition. This paper will consider current knowledge on milk protein biosynthesis and the opportunities for nutritional manipulation. Recent infusion studies which have linked changes in mammary amino acid metabolism with changes in milk protein content will be examined in an attempt to elucidate key features of the metabolic regulation of the dairy cow which need to be addressed if the British consumer is to have the choice of higher protein (possibly designer protein) milk products. This review will (in part) utilise data from a joint project at the Rowett Institute and Reading University funded by a consortium comprising government (MAFF, BBSRC and SOAEFD) and agribusiness (MDC, Purina Mills and Hendrix).

Milk fat consists of approximately 960-980 g of triacylglycerol, 20-25 g of 1,2-diacylglycerol, 10 g of phospholipid, 5g of cholesterol and very small quantities of free fatty acids and monoacylglycerol per kg. There are three stages in milk fat biosynthesis: the accumulation of fatty acids in the mammary cells through de-novo synthesis or absorption from the blood stream, triacylglycerol construction and fat globule assembly and secretion. Fatty acids in mammary secretory cells arise from two sources. Those having between 4 and 14 carbon atoms are synthesised de-novo in the mammary gland whereas those with 18 carbon atoms are of dietary origin and are absorbed from the blood stream. Palmitic acid (16 carbon atoms) is supplied almost equally from the diet and de-novo synthesis. In ruminants the principal sources of carbon for fatty acid synthesis are acetic acid and b-hydroxybutyrate.

Alteration of milk fat concentration is achieved by changimore spreadable butter. Monounsaturated fatty acids in the diet have been shown to have beneficial effects on the plasma lipoprotein indicators of coronary heart disease risk. From a human nutrition point of view it could be beneficial to incorporate the long chain omega-3 fatty acids, eicosapentanoic (EPA, C20:5) and docosahexanoic (C22:6) acids, into milk fat. The principal source of these fatty acids is fish oil but research to date indicates that their transfer into milk fat is inefficient. Conjugated linoleic acid (CLA) is a collective term describing one or more positional and geometric isomers of linoleic acid (cis-9, cis-12 C18:2). CLA has been shown to have anticarcinogenic activity, antiatherogenic activity, an ability to reduce the catabolic effects of immune stimulation and an ability to enhance growth promotion and reduce body fat. It is present in ruminant milk and meat as a result of biohydrogenation in the rumen where it is an intermediate. Its concentration in bovine milk fat is influenced by dietary factors such as pasture feeding and supplementation with full fat oilseeds. Two other components of bovine milk fat which have been shown to have anticarcinogenic properties are butyric acid and sphingomyelin and their concentration warrants further study. It is likely that research will continue into means of manipulating both the content and composition of milk fat but ultimately the adoption of any of the strategies in practice is likely to depend on strong economic or consumer imperatives.ng either the level of de-novo synthesis in the mammary gland or the supply of long chain fatty acids in the diet. Dietary factors that affect the supply of acetic acid from the rumen for de-novo synthesis include fibre quantity and quality, forage to concentrate ratio, buffer inclusion, concentrate composition and concentrate feeding frequency. The effects of fat supplements on fat concentration are variable. In general, feeding rumen protected fat increases milk fat concentration whereas moderate amounts of unprotected unsaturated fat tend to decrease it.

Most nutritional manipulation has been directed at increasing the proportion of unsaturated fatty acids in milk fat in order to enhance its appeal to the consumer and to produce a softer fat. A more spreadable butter could be produced from such fat thus overcoming a major criticism of conventional butter.

If unsaturated fatty acids are fed to ruminants in an unprotected form rumen microbial digestion can be impaired and the unsaturated fatty acids are extensively saturated in the rumen. One strategy to overcome this is to include unsaturated fatty acids in a form protected from microbial digestion in the rumen. This resulted in the production of polyunsaturated milk fat from which a low melting point butter was produced. This product was predisposed to oxidative deterioration. More recently whole oilseeds have been fed to dairy cows. The unsaturated 18-carbon fatty acids in these seeds are hydrogenated in the rumen but the activity of a D-9 desaturase in the mammary gland and to a lesser extent the intestine converts the stearic acid (C18:0) to the monounsaturated fatty acid, oleic acid (C18:1). Milk fat rich in oleic acid is softer than conventional milk fat allowing the manufacture of a more spreadable butter. Monounsaturated fatty acids in the diet have been shown to have beneficial effects on the plasma lipoprotein indicators of coronary heart disease risk.

From a human nutrition point of view it could be beneficial to incorporate the long chain omega-3 fatty acids, eicosapentanoic (EPA, C20:5) and docosahexanoic (C22:6) acids, into milk fat. The principal source of these fatty acids is fish oil but research to date indicates that their transfer into milk fat is inefficient. Conjugated linoleic acid (CLA) is a collective term describing one or more positional and geometric isomers of linoleic acid (cis-9, cis-12 C18:2). CLA has been shown to have anticarcinogenic activity, antiatherogenic activity, an ability to reduce the catabolic effects of immune stimulation and an ability to enhance growth promotion and reduce body fat. It is present in ruminant milk and meat as a result of biohydrogenation in the rumen where it is an intermediate. Its concentration in bovine milk fat is influenced by dietary factors such as pasture feeding and supplementation with full fat oilseeds. Two other components of bovine milk fat which have been shown to have anticarcinogenic properties are butyric acid and sphingomyelin and their concentration warrants further study.

It is likely that research will continue into means of manipulating both the content and composition of milk fat but ultimately the adoption of any of the strategies in practice is likely to depend on strong economic or consumer imperative.

This review considers the control of milk composition by endocrine factors and local mechanisms operating within the udder, and the impact of management systems and the environment on these control systems. Much less is known about control of milk composition than yield, although one can propose that prolactin is more concerned with control of lactose and protein secretion whilst growth hormone has a bigger role to play in fat secretion. Molecular biological approaches have the potential to increase understanding and, in the distant but foreseeable future, to manipulate milk composition on a commercial scale. The feedback inhibitor of lactation (FIL), which is responsible for local control of milk yield, has equal effects on lactose, fat and protein secretion, so changes in milking frequency do not alter gross milk composition. During the course of lactation the processing properties of milk gradually deteriorate as a consequence of proteolytic degradation of caseins, but new research shows that this can largely be prevented by milking thrice–daily. This has significant implications for future milking strategies such as robotic milking and extended lactation.

In the autumn of 1997 a butter manufacturer in Northern Ireland was approached by their principal buyer and asked to consider how the store's own brand creamery butter product could be improved in order to compete with the new spreadable butters and spreads arriving in the marketplace. In succeeding months, meetings between groups representing the dairy processing industry, animal production specialists, food scientists and animal feed manufacturers set in motion a major project aimed at managing the transfer of scientific technology into a commercial operation. Each group within the project had their own objectives and the level of risk associated with their involvement varied between the groups. However, it was undoubtedly the interaction between groups that was the most significant factor in the overall success of the project in producing a naturally spreadable creamery butter which has received extremely favourable consumer feedback.

Improving milk protein concentration at farm level can add fifty pounds per cow to milk sales annually. The benefit for processors is an increase in protein supply by ten percent and improved milk processability. The farm changes needed to improve milk protein content can also lead to a reduction in milk production costs of at least fifty pounds per cow. The objective of the Kerry Agribusiness/Teagasc “Focus on Profit” project was to adopt current technology in relation to improving milk protein at farm level to enable farmers to improve their income. Specifically to improve milk value by 0.85 p/litre by increasing milk protein content from 32 g/kg, the Kerry average for 1994, to 34 g/kg by the year end 2000. Thirty five farmers were selected to represent each category of milk supplier to Kerry Agribusiness in relation to scale of production, size of holding, soil type, farm management practices and farm location. Herds were milk recorded. Milk volume, protein and butterfat concentration, production costs, farm characteristics and management practices were monitored. Current information/technology from research on improving milk protein content and reducing costs was communicated to monitor farms by means of farm visits, farm walks, demonstrations, discussion groups, clinics, seminars, newsletters, booklet, press articles and the radio by advisors and research personnel from Kerry Agribusiness, Teagasc, Munster Cattle Breeding Society, Department of Agriculture and New Zealand. From 1994, milk protein concentration has increased by 1.1 g/kg from 31.7 to 32.8, butterfat concentration has increased by 2.4 g/kg from 35.2 to 37.6 g/kg and milk value has increased by 0.97 p/litre from 20.23 to 21.20 p/litre. The best improvement in milk protein was observed during January, February and March — 0.27 g/kg, 0.36 g/kg and 0.24 g/kg respectively. Twelve monitor farmers had protein content in their milk greater than 32.0 g/kg in 1994. This increased to 33 farmers by 1998 of which 14 had milk protein content greater than 33.0 g/kg. Thirty two (91%) of monitor farmers improved milk protein by over 0.1 g/kg, six increased milk protein by over 2.0 g/kg. Milk costs were reduced by 0.7 p/litre by monitor farmers when 1995 was compared to 1998. This reduction was 1.74 p/litre from 4.66 p/litre to 2.92 p/litre when 1995 was compared with 1997. By applying current information/technology, Kerry Agribusiness monitor farmers increased milk protein content and reduced milk production costs.

A partially balanced changeover design experiment was undertaken to evaluate the effects of level of fish oil inclusion in the diet on milk fat concentration and composition when offered to 50 lactating dairy cows in early lactation, which were offered either 5 or 10 kg concentrates/cow/day. Concentrates were formulated to contain similar concentrations of crude protein (CP), effective rumen degradable protein (ERDP) digestible undegradable protein and starch and to provide 0 (T0), 150 (T150), 300 (T300) or 450 (T450) g fish oil/cow/day or 300 g (T300B) fish oil/cow/day from a commercial fish oil premix. All animals were offered 5 kg treatment concentrate in two equal feeds through the in-parlour feeder at each milking. Additionally, cows offered the higher level of concentrates received a further 5 kg of T0 concentrate in two equal feeds per day through out-of-parlour feeders. Increasing the level of fish oil increased milk yield (P<0.01) and decreased the concentrations of fat (P<0.001) and protein (P<0.001). Increasing the level of fish oil decreased the concentrations of C6:0, C8:0, C10:0, C16:0, C14:0 and C18:0 and increased the concentrations of C18:1t, C20:0, C20:1, C20:4w6, C18:2c, C23:0, C20:5w3 and C18:2t. Relative to T300, T300B significantly decreased the concentrations of C20:4w6, but did not alter any of the other fatty acids. The transfer from feed to milk of EPA and DHA averaged 0.61 and 0.19 respectively across the three levels of fish oil supplementation. For T300 the efficiency of transfer of EPA was higher while the efficiency of transfer of DHA was lower to that for T300B. It is concluded that increasing fish oil supplementation decreased milk fat concentration by up to 15 g/kg. Also feeding fish oil is an efficient method of increasing EPA in the human diet through transfer into milk.

Conjugated linoleic acid (cis-9, trans-11-C18:2; CLA) in milk arises as a result of microbial biohydrogenation of dietary linoleic and linolenic acids in the rumen (Kepler and Tove, 1967). Milk fat CLA concentrations were significantly (P<0.05) higher when cows were fed silage supplemented with pulp’n brew (a mixture of brewers grains, a by-product of the brewing industry, and sugar beet pulp in dry matter proportions of 0.65:0.35), compared with silage alone (Trial 1). Intake of spring grass resulted in a 2.1–fold increase in milk fat CLA concentrations over cows receiving autumn grass. Throughout lactation in Trial 2, spring calving cows produced higher milk fat CLA concentrations (from 0.5-2.7 g/100 g fatty acid methyl esters (FAME)) than autumn calving cows (0.3-1.7 g/100 g FAME); the former having spent 80% and the latter 50% of lactation on pasture. The CLA content was higher in late lactation milk compared with early lactation milk in both herds. There were no significant differences in milk yields or milk constituent yields between the herds. Manufacturing milk obtained between March and September was analyzed for milk fatty acid composition and the data correlated with grass growth throughout the season. Significant positive correlations were obtained between grass growth rates and concentrations of CLA and linolenic acid in milk fat. The data indicate that seasonal variation in milk fat CLA concentrations may be attributed to variation in pasture growth rates.

One hundred and thirteen Holstein Friesian heifers (PIN (95) £88 s.d. 11.1) were used in a study to determine the effect of rearing regime, in terms of diet offered and target calving weight, on milk production in high genetic merit heifers. Eighty of the heifers were supplied from 11 commercial farms, the remainder were supplied from the herd at the Agricultural Research Institute of Northern Ireland. The heifers commenced the experiment at 7 weeks of age when they were allocated on the basis of source, live weight and genetic merit to one of four rearing regimes. The target weights at calving were 540 kg (Treatment 1) and 620 kg (treatments 2, 3 and 4). Treatments 1 heifers were offered grass silage-based diets during the winter and grass–based diets during the summer. Treatment 2 heifers were offered the same forage base along with additional concentrate supplementation. Treatment 3 heifers were offered a straw/concentrate diet during the winter and grass-based diets during the summer. Treatment 4 heifers received the same diets as treatment 3, apart from the first summer period when they were housed and offered a straw/concentrate diet. The heifers were mated at 14 months of age and were returned to the 11 farms one month prior to calving. Heifers reared on treatment 1 weighed less had a lower withers height (P<0.001) and were of a lower condition score (P<0.001) before calving than heifers reared on the other treatments. During early lactation (3 months post-calving) heifers reared on treatment 1 lost less weight and condition score than the heifers reared on treatments 2, 3 and 4. Over the winter housing period (mean 140 days) the average milk yield was lower for heifers reared on treatment 1 compared with heifers reared on treatments 2 (P<0.05), 3 (P=0.08) and 4 (P<0.05). Milk protein content was higher in animals reared on treatment 1 compared with treatment 2 (P<0.01), 3 (P<0.05) and 4 (P=0.12). Overall milk fat plus protein yield was lower for heifers reared on treatment 1 compared with treatments 2 (P<0.05), 3 (P=0.06) and 4 (P<0.05).

This paper describes the steps that were taken to increase the productivity of a commercial cheese company by genetically altering the milk composition. These steps included validation of the effect of b–lactoglobulin polymorphism on casein production and cheese yield under typical New Zealand pastoral farming conditions, manufacture and ripening of cheese from single variant milks, selection of a suitable company to trial breeding for a single variant, development of a suitable payment scheme to reflect the additional value of the higher casein milk, development of a testing regime to support the payment system and getting buy–in from the company. These steps have all been taken, and the company has pursued the recommended breeding strategy for 3 years, purchased instrumentation and elected to move to the new testing and payment scheme for the current dairy season.

The papers presented at this Conference have highlighted the many exciting and challenging developments occurring in relation to milk composition within the production, processing and retail sectors. Historically, review papers considering future issues in relation to milk composition have focussed on opportunities to manipulate milk constituent composition. However, the overriding issue at present, in relation to milk composition in the broadest sense, concerns consumer perception of milk and dairy products. This is particularly the case with respect to : food safety; human health and; the naturalness and wholesomeness of milk and milk products. Food safety has become a key issue for consumers given current concerns over BSE, Escherichia coli 0157, antibiotic residues and dioxin contamination. Consequently, quality assurance schemes and traceability of supply from “farm to plate” have, or will become, essential features of the liquid milk/dairy product sector.

Consumer concerns regarding effects of consumption of milk/dairy products on human health have historically centred on the highly publicised link between fat consumption, particularly saturated fat, and coronary heart disease. However, more recently the less well publicised beneficial effects of milk/dairy product consumption on human health are now being recognised. These include the importance of milk and cheese as calcium sources for bone growth, which can reduce the risk of osteoporosis in later life, the positive effect of milk consumption on dental health (particularly when substituted for high–sugar soft drinks in young children) and anticarcinogenic and antiatherogenic effects mediated through the conjugated linoleic acid (CLA), butyric acid and sphingomyelin components within milk and dairy products. Increased emphasis on generic advertising of milk is essential to highlight these positive features to opinion–formers and consumers, especially when contrasted with the advertising budgets associated with competing products.

Major shifts in consumer consumption patterns have occurred in the last 30 years, with increased demand for low fat products, ready meals etc. and this has led to changes in milk processors’ requirements as assessed in terms of raw milk composition and properties. Alongside this, technological advances at the production level have facilitated opportunities to accelerate the rate of genetic change in the dairy herd and to modify/adapt feeding systems to better meet processor requirements. Further opportunities exist to increase fat plus protein yield whilst improving the protein :fat ratio through genetic improvement, but opportunities for genetic improvement in the composition of protein and fat fractions appear more limited. Alteration of protein, and particularly milk fat composition (e.g. enhanced unsaturated fatty acid and CLA contents) can be much more readily attained by modifying the diet of the dairy cow, and large scale projects using this approach are already delivering improved products to the consumer. One of the most excitingareas in terms of use of milk as a raw material relates to the production of both natural and induced bioactive components. In future, the mammary gland of the dairy cow may well be viewed as a bioreactor with the potential to synthesise large quantities of high value proteins. Use of transgenics, whilst potentially facilitating production of high value therapeutic or food ingredient components, is likely to be limited by consumer resistance to genetically modified dairy cows.

Development of niche markets for tailor–made milks and milk products (including organic produce), achieved through dietary manipulation, will require increased vertical integration between animal feed suppliers, milk producers, milk processors and food retailers. Increasing consideration in the future will also have to be given to the potential change in milk composition/processing characteristics mediated through changes in production systems, such as seasonality of calving, use of extended lactations and adoption of new milking systems e.g. robotic milking. Finally, the concept of naturalness and wholesomeness of milk and dairy products is also a major consideration for the consumer. We must be careful in adopting new technologies, whether at the level of on farm production e.g. animal breeding and feeding, or at the processing level e.g. food irradiation and high pressure processing, to ensure that the attributes of naturalness and wholesomeness of milk and milk products are retained.