A milk-related model system, 2 mM-trilinolein in 0·1 M-piperazine-N, N′-bis-2-ethanesulphonic acid buffer, pH 6·8, stabilized by lysophosphatidylcholine was used to assess the effect of milk proteins on lipid oxidation in emulsion, catalysed by Cu2+ ions. In some experiments the trilinolein was replaced by sunflower oil (2 g 1-1). Oxidation at 25°C was assessed by measurement of the rate of O2-utilization and by the thiobarbituric acid assay. The features, relevance and reliability of the model are described in terms of the observed effects in the absence and presence of added protein. Casein was antioxidative at concentrations relevant to those in bovine milk, human milk, infant milk formulations and ‘high linoleic acid’ milk. Whole whey protein was a less effective inhibitor of lipid oxidation at similar concentrations. Purified α-lactalbumin was also marginally antioxidative, and its effect was independent of the molar Cu2+: protein ratio between 1:1 and 3:1.

1. Two Shorthorn cows with rumen fistulas were used to investigate the effect of diets high in concentrates and low in hay on the physical and biochemical processes of the reticulo-rumen.

2. During the initial control period of the investigation the cows received daily 16 lb. hay and 20 lb. concentrates (flaked maize 50%, weatings 35%, decorticated ground-nut cake 15%) and during the final control period 18 lb. hay and 10 lb. concentrates. There were three intervening experimental periods, in each of which the cows received 2 lb. hay daily. In the first experimental period they received, in addition to the hay, 24 lb. concentrates; in the second, 20 lb. concentrates and 5 lb. of dried delignified straw pulp in a finely macerated form; and in the third, 20 lb. concentrates. The experiment lasted 27 weeks.

3. In the experimental periods the mean milk-fat percentage remained below 2·0 for 10 weeks, whereas the mean value for the control periods was about 3·5. Addition of the straw pulp to the diet low in hay brought about no recovery in milk-fat percentage. It is calculated that in the two cows the losses in the yield of fat were 62·2 and 51·2% in the first experimental period and 62·5 and 58·7% in the second. In the experimental periods there were increases in the milk solids-not-fat percentage amounting in the two cows to upwards of 0·75 and 0·40 respectively. The composition of the butterfat was influenced by the diets low in hay, the main changes being a marked fall in the Reichert value, and a rise in the iodine value.

4. Digestibility trials showed that in the initial control period and the first and second experimental periods the mean daily intake of digestible crudefibrewas 2·6,0·6 and 3·0 lb. respectively. A tentative estimate of the extent of digestion in the reticulo-rumen, based on the lignin-ratio method, showed that a marked depression in values for the digestibility of the cellulosic constituents of the diet given during the first experimental period took place in the reticulo-rumen. In all experimental periods, even the first, the digestion of starch in the reticulo-rumen was virtually complete, only traces passing undigested to the remainder of the gut. In these three periods the mean daily intake of ether extract remained at 0·4·0·5 lb.

Microfiltration and ultrafiltration were used to manufacture skim milks with an increased or reduced concentration of whey proteins, while keeping the casein and milk salts concentrations constant. The skim milks were heated on a pilot-scale UHT plant at 80, 90 and 120 °C. The heat-induced denaturation and aggregation of β-lactoglobulin (β-lg), α-lactalbumin (α-la) and bovine serum albumin (BSA) were quantified by polyacrylamide gel electrophoresis. Apparent rate constants and reaction orders were calculated for β-lg, α-la and BSA denaturation. Rates of β-lg, α-la and BSA denaturation increased with increasing whey protein concentration. The rate of α-la and BSA denaturation was affected to a greater extent than β-lg by the change in whey protein concentration. After heating at 120 °C for 160 s, the concentration of β-lg and α-la associated with the casein micelles increased as the initial concentration of whey proteins increased.

The non-protein nitrogen (NPN) of samples of Parmigiano-Reggiano cheese ripened for 6 and 15 months was fractionated by ion-exchange chromatography on a Cu2+-Chelex column to separate oligopeptides from free amino acids. Peptide components were isolated by reversed-phase HPLC and identified by fast atom bombardment–mass spectrometry (FAB–MS). Only the NPN fraction of 6 month old cheese samples contained enough peptides to be further characterized. On the basis of FAB–MS spectral results, 39 oligopeptides were identified, the main components being phosphopeptides. Two sets of both intact and partly dephosphorylated peptides, accounting for a total of 19 phosphopeptides, were formed by the hydrolysis of β–casein and belonged to regions 1–20 and 6–28 of β–casein. The formation and potential role of these peptides in cheese is discussed.

Flavour, aroma and appearance of milks fermented with commercially available kefir grains were compared with similar characteristics of heat treated (90 ΰC/30 min) milks that had been fermented with aroma producing starters in addition to the kefir grains. The starters used were either a mixture of Streptococcus lactis subsp. diacetilactis and Leuconostoc cremoris (lactic culture) or of Str. thermophilus and Lactobacillus bulgaricus (yogurt culture).

Two methods of fermentation were investigated involving removal of the grains followed by (i) a second fermentation of the kefir with the aroma-producing organisms and (ii) combining the kefir with aroma-producing organisms for use as a starter to ferment a further sample of heat-treated milk. Products were assessed by a taste panel and marked for acceptability. Addition of lactic or yogurt cultures resulted in products with increased mean scores for aroma and more acceptable flavours.

Genes in the sterol regulatory element-binding protein-1 (SREBP1) pathway play a central role in regulation of milk fat synthesis, especially the de-novo synthesis of saturated fatty acids. SCD, a SREBP-responsive gene, is the key enzyme in the synthesis of monounsaturated fatty acids in the mammary gland. In the present study, we discovered SNP in candidate genes associated with this signalling pathway and SCD to identify genetic markers that can be used for genetic and metabolically directed selection in cattle. We resequenced six candidate genes in the SREBP1 pathway (SREBP1, SCAP, INSIG1, INSIG2, MBTPS1, MBTPS2) and two genes for SCD (SCD1 and SCD5) and discovered 47 Tag SNP that were used in a marker-trait association study. Milk and blood samples were collected from Holstein cows in their 1st or 2nd parity at 100–150 days of lactation. Individual fatty acids from C4 to C20, saturated fatty acid (SFA) content, monounsaturated fatty acid content, polyunsaturated fatty acid content and desaturase indexes were measured and used to perform the asociation analysis. Polymorphisms in the SCD5 and INSIG2 genes were the most representative markers associated with SFA/unsaturated fatty acid (UFA) ratio in milk. The analysis of desaturation activity determined that markers in the SCD1 and SCD5 genes showed the most significant effects. DGAT1 K232A marker was included in the study to examine the effect of this marker on the variation of milk fatty acids in our Holstein population. The percentage of variance explained by DGAT1 in the analysis was only 6% of SFA/UFA ratio. Milk fat depression was observed in one of the dairy herds and in this particular dairy one SNP in the SREBP1 gene (rs41912290) accounted for 40% of the phenotypic variance. Our results provide detailed SNP information for key genes in the SREBP1 signalling pathway and SCD that can be used to change milk fat composition by marker-assisted breeding to meet consumer demands regarding human health, as well as furthering understanding of technological aspects of cows' milk.

Milk is an important protein source in human diets, providing around 32 g protein/l (for bovine milk, which constitutes some 85% of global consumption). The most abundant milk proteins are α-lactalbumin, β-lactoglobulin, αs-casein, β-casein, and κ-casein. Besides their nutritional value, milk proteins play a crucial role in the processing properties of milk, such as solubility, water bonding, heat stability, renneting and foaming, among others. In addition, and most importantly for this review, these proteins are the main source of bioactive components in milk. Due to the wide range of proposed beneficial effects on human health, milk proteins are considered as potential ingredients for the production of health-promoting functional foods. However, most of the evidence for bioactive effects comes from in vitro studies, and there is a need for further research to fully evaluate the true potential of milk-derived bioactive factors. Animal genetics and animal nutrition play an important role in the relative proportions of milk proteins and could be used to manipulate the concentration of specific bioactive peptides in milk from ruminants. Unfortunately, only a few studies in the literature have focused on changes in milk bioactive peptides associated to animal genetics and animal nutrition. The knowledge described in the present review may set the basis for further research and for the development of new dairy products with healthy and beneficial properties for humans.

In this method, the curd, formed in a beaker, was retained after cutting by means of a wire grid placed on top of it. This enabled the whey to be poured off easily at timed intervals for measurement of its volume. The method gave results reproducible within 1·5%. Increasing the amount of rennet added to the milk increased the rate of syneresis of the curd slightly. Adding CaCl2 to the milk, raising the temperature and decreasing the pH, all increased the rate of syneresis. Addition of fat, as cream, to skim-milk decreased the rate of syneresis proportionally. The rate of syneresis was decreased if the milk was concentrated by ultrafiltration and increased if the milk was diluted with permeate. In all instances the early stages of syneresis followed first-order kinetics, the rate depending on the amount of whey remaining within the curd. The later stages of syneresis appeared to depend on hydrophobic forces. Probably, the increasing aggregation of the casein within the curd caused the whey to be squeezed out.

Six lactating dairy cows were used in a three period, part balanced changeover design experiment to investigate the effects of forage digestibility and concentrate composition on the efficiency of nutrient utilization in lactating dairy cows. Six treatments comprising three forage regimens and two concentrate types (starch υ. fibre) were examined in a 3 × 2 factorial design. The three forage regimens were high digestibility grass silage offered ad lib. (HA) or restricted to 6·5 kg dry matter/d (HR) and a low digestibility grass silage offered ad lib. (LA). Within each forage regimen animals were offered 10 kg·d of supplements containing either high-starch or high-fibre concentrations. Experimental periods lasted 28 d with a 10 d recording period, during which animal performance, ration digestibility and nitrogen and energy utilization were measured. Respiratory exchange measurements were made over a 72 h period using indirect open-circuit calorimetry. Throughout the experiment, there were no significant forage × concentrate interactions in any of the intake, production or nutrient utilization results. Milk yield was significantly influenced by forage regimen (24·1, 21·7 and 21·9 kg/d for HA, HR and LA respectively) and concentrate type (21·6 and 23·5 kg/d for high-starch and high-fibre respectively). Concentrate type also significantly influenced milk protein concentration (32·8 and 30·9 g/kg for high-starch and high-fibre respectively). Forage regimen significantly influenced the efficiency of utilization of metabolizable energy (ME) for milk production (κ1) with values of 0·62, 0·64 and 0·59 for HA, HR and LA respectively. Concentrate type had no significant effect on ME intake, heat production or κ1, although animals receiving the high-fibre concentrates synthesized proportionately 0·11 more milk energy per unit of available energy (ME intake – heat production) than those receiving the high-starch concentrates. Interpolation of the values obtained with the two high digestibility forage regimens indicated that at similar ME intakes there was a trend towards a higher κ1 with the diet based on high digestibility silage, and this was in line with the higher metabolizability of the overall diet with this silage.

Heat-induced gelation, an important functional property of β-lactoglobulin, was studied by measuring the rheological properties of both the A and B variants of the protein during and after heat treatment within a range of pH, temperature and concentration. Gel electrophoresis was used to determine the extent of denaturation and disulphide bond crosslinking of some samples. Both variants formed gel networks on heating at temperatures > 75 °C, and under most conditions the storage modulus (G′) of βlactoglobulin A gels was higher than the G′ of β-lactoglobulin B gels, in particular after cooling to 25 °C. A minimum protein concentration of 50 g/1 was required for gel formation at pH 7·0 in 0·1 M-NaCl by both variants at 80 °C. Increasing the protein concentration above 50 g/1 increased G′, the extent of increase being much greater for the A variant than the B variant. G′ of variant A gels was not much influenced by pH whereas G′ of variant B gels decreased slightly from pH 3 to pH 6 and increased between pH 6 and pH 9. When mixtures of the two variants were gelled G′ increased at the temperature of heating (80 °C) and after cooling (25 °C) as the relative quantity of variant A was increased. Comparisons of the loss of discrete protein bands from electrophoretic gels (native-PAGE, SDS-PAGE and SDS-PAGE of reduced samples) showed that heating β-lactoglobulin solutions of 100 g/1 at pH 7 in 0·1 M-NaCl and at 75, 80 and 85 °C caused a faster loss of both native and SDS-soluble β-lactoglobulin A than of β-lactoglobulin B. It was concluded that the loss of native β-lactoglobulin structure from these solutions during heating was faster than the formation of disulphidelinked aggregates, which was faster than gel formation for both β-lactoglobulin A and β-lactoglobulin B, and that each of these reactions was faster for β-lactoglobulin A than for β-lactoglobulin B. This contrasts with conclusions drawn from some previous studies and may arise from the differences in protein concentration between the present study (∼ 100 g/1) and the previous ones (< ∼ 10 g/1).

Ten different types of milk, arranged in 3 sets, were observed to be pseudoplastic fluids with linear behaviour at high shear rates in a coaxial cylinder rheometer; at low rates of shear all the samples could be considered sufficiently Newtonian and a Höppler viscometer was used for their study. Dynamic viscosity coefficients of skimmilk, half-and-half milk, whole milk and their concentrates up to about 30% total solids were determined every 5°C between 0 and 80°C. For every milk type a quadratic equation relating t to log η was obtained. At a given temperature the concentration dependence of η for the 3 milk sets was expressed by a single relation of the same mathematical model as in the previous case. A general expression was derived to enable η to be calculated at any temperature (0–80°C), and for any concentration (0–30% total solids) whatever the fat to solids-not-fat ratio (0·01–0·4). A nomogram was also constructed for the immediate computation of η without any practical loss of accuracy.

The numbers and types of non-starter lactic acid bacteria, lipolytic bacteria and group D streptococci in cheese milks and corresponding Cheddar cheeses have been studied and their relationship to cheese flavour discussed. Different milks, heat-treatments and starters were used, and their association with flavour investigated. The pH and fat, salt and moisture contents of the cheeses were also determined.

The non-starter lactic acid flora consisted mainly of Lactobacillus casei, L. plantarum, L. brevis, L. buchnerii, Pediococcus spp. and Leuconostoc spp. Lactobacillus casei was nearly always present in the milks and cheeses, predominating in most of the cheeses, particularly in those made from milk which received the most severe of the three heat-treatments tested (160°F for 17 sec). Leuconostocs were not found in any of the cheeses. Other species sometimes occurred in approximately equal numbers to L. casei, particularly in cheeses manufactured from the milder heattreated milks. Cheeses made from milk receiving the highest heat-treatment contained fewest bacteria and scored lowest for flavour. The average flavour scores increased as the number of species contributing to the non-starter lactic acid flora at the time of tasting increased.

The lipolytic organisms capable of hydrolysing butterfat consisted mainly of Gram-positive cocci, predominantly Staphylococcus saprophyticus. The group D streptococci occurred infrequently, Streptococcus faecium being the most commonly occurring species.

A definite correlation was found to exist between the starters used and the flavour of the cheeses. The pH of the cheeses was associated with the flavour, but the fat, moisture and salt contents of the cheeses showed no definite effect.

The influence of storage time and temperature on the distribution of individual milk proteins between the micellar and soluble phases has been examined. Storage at 4 or 7 °C is accompanied by a dissociation of micellar caseins, particularly β-casein, into the soluble phase during the first 48 h, but on further storage there is a partial reversal of this process. At higher storage temperatures (10–20 °C) the contents of all the individual caseins in the soluble phase decrease throughout storage. During cheese–making, losses of fat and curd fines in whey were greater with increased soluble phase casein and clotting times were prolonged. Curd structure was weaker, curds were more moist and slightly lower cheese yields were obtained in stored milks with elevated soluble–phase casein. When milks were stored for up to 3 d at 4 °C cheese gradings were virtually unaffected by storage, but higher temperatures (10–15 °C) led to cheeses being downgraded, largely for body and texture defects but also for flavour after 3 d.

Attempts to reverse the pattern of casein dissociation and to minimize the detrimental effects of milk storage on subsequent cheese-making showed that a heat treatment of 30 min at 60 °C was the most beneficial.

The udder health of a research herd of between 160 and 220 Friesian cows run on a commercial basis has been monitored closely, including detailed bacteriological study, over 5 years. The five point mastitis control plan had been in use for several years prior to this study and was continued with minor alterations to the management of the plan, more detailed bacteriological monitoring and increased encouragement to apply it. It has proved possible to make a substantial improvement in the udder health of the herd. The percentage of infected cows fell from 21·9 to 12·0 and the percentage of infected quarters from 7·3 to 3·3. The main benefit has been a drastic reduction in the rate of clinical and subclinical mastitis caused by coagulase-positive staphylococci. However the total incidence of clinical mastitis did not change substantially, averaging around 30 cases/100 cows per year. This was largely because environmental mastitis organisms were responsible for 65 % of all clinical cases. The results showed marked differences in the patterns of infection due to the environmental mastitis pathogens, Gram-negative bacteria and aesculin-hydrolysing streptococci, suggesting different mechanisms of invasion of the gland.

Component PP3 is a phosphorylated glycoprotein with an apparent molecular mass of 28 kDa isolated from the proteose peptone fraction of bovine milk. The function of the protein is not known. The primary structure has been determined and shown to contain 135 amino acid residues (EMBL accession no. P80195). It was phosphorylated at Ser29, Ser34, Ser38, Ser40 and Ser46. Two O-linked carbohydrate groups were found at Thr16 and Thr86, while one N-linked carbohydrate group was present at Asn77. Thr16 was only ∼ 50% glycosylated. The amino sugar detected by the amino acid analyser at Thr86 was mainly galactosamine but a small amount of glucosamine was also present. The amino sugars found in the carbohydrate group linked to Asn77 were both glucosamine and galactosamine. A fragment of PP3 has been isolated from milk and shown to correspond to residues 54–135. This fragment was probably generated by plasmin hydrolysing the Arg53–Ser54 bond.

Activation of the antibacterial lactoperoxidase system in milk, i.e. increasing the thiocyanate concentration to 0·25 mM and adding an equimolar amount of H2O2, results in a substantial reduction of the bacterial flora and prevents the multiplication of psychrotrophic bacteria for up to 5 d. This treatment has no effect on the physico-chemical properties of milk and does not lead to the accumulation of resistant bacteria. The practical application of the lactoperoxidase system in prolonging the storage period of raw milk at low temperatures is discussed.

Heating raw milk at 80 °C for 2·5–20 min was found to result in compositional changes in the milk fat globule membrane (MFGM). The yield of protein material increased with the duration of heating, owing to incorporation of skim milk proteins, predominantly β-lactoglobulin, into the membrane. Lipid components of the MFGM were also affected, with losses of triacylglycerols on heating.

1. An analysis has been made of production records and body measurements of dairy cattle from farms and special progeny testing stations in Denmark.

2. Heritability estimates of various measurements of body size and also of gross efficiency of food conversion were all in the neighbourhood of 0·50. Body weight was more closely correlated with girth than with height.

3. Milk yield had a very high correlation, both phenotypic and genetic, with gross efficiency. This was shown on theoretical grounds to be a necessary result of any standard system of feeding.

4. Correlations between production characteristics and body measurements were slight. There was some suggestion that selection for yield would increase skeletal size but decrease fleshing.

5. The best index on which to select for efficiency of food conversion under these conditions would be the yield divided by the height.

The effects of κ-casein genetic variants, lactation number, pH and casein content on the renneting properties of individual milks were studied. Rennet coagulation time (RCT) and curd firmness were determined with the aid of a lactodynamograph and the results statistically analysed. Renneting properties were strongly related to κ-casein variants and lactation number, with κ-casein B and higher lactation numbers giving shorter RCT and increased curd firmness, the effects on curd firmness being more pronounced. The effect of κ-casein variant on RCT could be eliminated by reducing pH and adding CaCl2 to the milk samples. The effect on curd firmness was not altered by this treatment, however. The results show that the renneting properties of individual milks are to a considerable degree genetically controlled.

High pressure (HP) treatment affects many constituents of milk (for reviews see Huppertz et al. 2002; Needs, 2002); particular in the properties of casein micelles in HP-treated milk differ considerably from their counterparts in untreated milk. In milk treated at 100–200 MPa, average casein micelle size differs little from that of untreated milk (Needs et al. 2000a; Huppertz et al. 2004a; Regnault et al. 2004; Anema et al. 2005), but micelle size in milk treated at 250 MPa for [ges ]15 min is considerably higher than in untreated milk, probably due to HP-induced aggregation of casein micelles (Huppertz et al. 2004a,b; Regnault et al. 2004); after treatment at 300–800 MPa, micelle size is ~50% lower than that in untreated milk (Needs et al. 2000a; Huppertz et al. 2004a,b; Anema et al. 2005). HP-induced changes in average casein micelle size are irreversible on subsequent storage, except for the increase in micelle size after treatment at 250 MPa (Huppertz et al. 2004a).