The effects of supplementing cows' diets with protein and energy on milk composition and the composition and yield of Cheddar cheese were investigated. This research addresses the problems of seasonal reduction in the capacity of cheese curds to expel moisture as observed in parts of south-eastern Australia. Milk was collected from cows offered a basal diet of silage and hay supplemented with different sources and levels of dietary protein and energy. The protein supplements were sunflower, canola, cottonseed meal and lupin, and the energy supplements were maize grain, oats, wheat and barley. This milk was used to manufacture Cheddar cheese on a pilot scale. Cheese moisture content was dependent on the source and level of dietary protein and energy. Milk from cows offered the lupin protein supplements and wheat energy supplements consistently produced cheese with a lower moisture content and moisture in fat-free matter. Milk from these supplemented diets had increased casein concentrations and higher proportions of αs2-casein than milk from the poor quality control diet. Cheese yield was directly related to the total casein concentration of milk, but was not influenced by differences in casein composition. Supplementing the cows' diets increased the inorganic P, Mg and Ca concentrations in milk. A low inorganic P concentration in milk from cows offered the control diet was caused by a low intake of dietary P. These findings showed that changes in the mineral and casein composition of milk, associated with diet, could influence the composition of Cheddar cheese.

The effects of supplementing a basal diet of silage and hay with increasing amounts of harvested spring pasture, or with lupin and wheat, on the composition of milk and the consequent effects on cheese composition and yield were investigated in an indoor feeding study. Milk was collected from five groups of eight cows in mid lactation offered different diets and manufactured into Cheddar cheese on a pilot scale. Milk from cows given the lupin–wheat (LW) and the high pasture level (HP) diets produced low moisture cheese. Cheese produced with milk from cows given the control diet was high in moisture content compared with that made with milk from cows offered the LW diet. Cheese yields from the milk of cows offered the HP and LW diets were greater than from the milk of cows on the control diet, and were associated with the higher casein concentrations of these milks. Casein number was higher in milk from diets supplemented with pasture but was not an indicator of the functional properties of milk that affected cheese moisture. The proportion of β-casein in milk from cows offered the HP diet was higher and that of γ-casein lower than in milk from cows given the LW supplement, although cheese moisture content was similar with both diets. Milk from cows offered the HP diet had a greater inorganic P concentration than that from cows given the LW diet, although the dietary intake of P was higher for the LW diet. The significance of the effect of dietary P intake on the concentration of inorganic P in milk and hence its suitability for cheesemaking was apparent when dietary P intake was low, as shown in milk produced by cows offered the control diet.

Applied dairy research is characterized by experiments for which financial and physical constraints permit only a small number of experimental units. With few units it is difficult to replicate treatments, and without replication experimental error cannot be estimated. The statistical analysis and interpretation of such experiments is problematic. However, if there have been several such experiments it may be possible to perform a combined analysis. Nine unreplicated experiments comparing effects of diet on the composition of cows' milk and on cheese characteristics were jointly analysed as an incomplete block design. This analysis method was contrasted with analyses of individual experiments. For cheese moisture, the key outcome measurement, the assessment of statistical significance concurred for the two methods in 13 out of 21 comparisons of treatments with the control. Sources of error variation allowed for under the two methods were delineated. The combined analysis paradigm provided stronger inference and a wider interpretation of results than could be achieved using analyses for individual experiments. Unequal replication of treatments and unequal concurrence of treatments within experiments over the series gave rise to a wide range of SED. The challenge of presenting results with unequal SED was addressed graphically using error bars. Attention to series design, in particular the apportioning of replication and treatment concurrence across the series of experiments, was shown to ameliorate presentation difficulties and, more importantly, to yield higher precision at no extra cost.

The respiratory burst activity, measured as H2O2 production, of isolated bovine polymorphonuclear leucocytes (PMN) was evaluated during experimentally induced Escherichia coli mastitis by means of flow cytometry in cells activated by phorbol 12-myristate 13-acetate (PMA) and in unstimulated cells. As expected, a significantly reduced respiratory burst activity was observed in PMA-activated PMN 18 h after intramammary inoculation with Escherichia coli. At this time only 75% of the PMA-activated PMN showed a respiratory burst, but with a higher intensity than that measured before and later after infection with Esch. coli. In addition, an increase in the respiratory burst activity was observed in unstimulated blood PMN during a short period at 18 h after infection, when up to 30% of the unstimulated PMN had a respiratory burst activity. The increase in the respiratory burst intensity of PMA-activated PMN and the spontaneously augmented production of reduced oxygen species by the unstimulated PMN during infection with Esch. coli might indicate the production of a natural stimulator of burst activity in circulation, most probably originating from the inflamed udder.

The characteristics of the transport systems of L-alanine in lactating mouse mammary gland and their regulation by lactogenic hormones have been studied. L-alanine uptake was mediated by three Na+-dependent and one Na+- independent systems. The 2-(methylamino)isobutyric acid-sensitive component of Na+-dependent uptake exhibited the usual characteristics of system A. Cl− dependency has been established for system A. The other two Na+-dependent systems, which we have named BCl−-dependent and BCl−-independent, are described for the first time. These are systems with broad specificity and were distinguished on the basis of inhibition analysis, Cl− dependency and the effect of preloading mammary tissue with amino acids. The Na+-independent route was identified as system L, which operates independent of Cl−. The A, L and BCl−-independent transport systems were upregulated in pregnant mouse mammary tissue cultured in vitro in the presence of lactogenic hormones (insulin plus cortisol plus prolactin). Insulin alone also upregulated systems A and L to some extent in pregnant mouse mammary tissue. BCl−-dependent activity was not detected in pregnant mouse mammary tissue and was not induced by lactogenic hormones in vitro.

A methanol extract of green tea was fractionated on Sephadex LH-20. The compounds eluted were identified by thin layer chromatography as catechin–epicatechin, gallocatechin, epigallocatechin, epicatechin gallate and epigallocatechin gallate. When added to milk at 2·0 g/l, these polyphenols, apart from the catechin–epicatechin mixture, increased the heat stability of skim milk, particularly in the region of the minimum (pH 6·8–7·1). When added at 0·4 g/l, green tea polyphenols also increased the heat stability of concentrated milk. The effects of other phenolic compounds on the heat stability of milk were also examined. Chlorogenic acid, guaiacol, thymol, vanillin, butylene hydroxyanisole, propyl gallate and butylene hydroxytoluene did not affect the heat stability of milk or concentrated milk. Quinic acid markedly reduced the heat stability of skim milk. Pyrogallol, catechol, tannic acid, ellagic acid, phloroglucinol and gallate converted a type A heat coagulation time–pH profile to a type B profile. Ferulic acid and vanillic acid increased heat stability in the region of the maximum, with little effect on the minimum, and stability did not recover at pH values on the alkaline side of the minimum. Caffeic acid increased the heat stability of milk while the related non-phenolic compounds 2,5-dimethoxycinnamic acid and 3,4-dimethoxycinnamic acid had no effect.

The effects of sheep αs1-casein CC, CD and DD genotypes on milk composition and cheese yield were studied. Processed bulk milk was collected from three groups of 15 ewes, carrying αs1- casein CC, CD and DD genotypes. CC milk was higher in casein content than CD or DD milk (+3·5 and +8·6% respectively), and had a higher protein[ratio ]fat ratio and a smaller casein micelle diameter. In addition, DD milk had a significantly lower αs1-casein content. The main differences were in curd formation: CC milk had better renneting properties. Cheesemaking trials, carried out in a pilot plant, showed that CC milk had better cheesemaking characteristics than DD milk, while CD milk was intermediate. Both 1 d old and fully ripened cheeses had different fat[ratio ]dry matter ratios and αs1-I-casein electrophoretic mobilities: these were lower for DD cheese. As a consequence, these genotypes could be considered as markers of milk and/or cheese quality.

Colostrum and milk samples from 60 Holstein–Friesian cows were analysed for concentrations and yields of immunoglobulin G (IgG), β-lactoglobulin (β-lg), α-lactalbumin (α-la) and serum albumin (BSA) throughout the first 16 milkings post partum (8 d of lactation) using a single radial immunodiffusion assay. Concentrations (mg/ml, means±SD) at first milking were IgG 59·8±28·5, β-lg 14·3±4·6, α-la 2·04±0·6, BSA 1·21±0·44. Large variations were recorded for IgG concentrations (15·3–176·2 mg/ml) and yields (0·2–925 g). Cows in their first lactation produced significantly lower concentrations and yields of colostral IgG than cows in later lactations. A colostral yield of IgG below the 100 g required to prevent calf hypo-γ-globulinaemia was found in 18·3% of the cows. The concentrations of IgG, β-lg and BSA dropped abruptly in subsequent milkings and α-la concentration decreased slowly. The mean IgG concentration was <2 mg/ml after eight milkings and <1 mg/ml after fifteen milkings. However, IgG concentration did not differ significantly, at the 1% level, during milkings 11–15. The results were tabulated to make it possible to calculate the excess of whey proteins that would be obtained if early milks were illegally added to the milk supply.

Recombinant human αs1-casein expressed in Escherichia coli was purified and digested with trypsin in an attempt to find peptides with angiotensin-I-converting enzyme (ACE) inhibitory activity. Three novel ACE inhibitory peptides, A-II, B-II and C, were isolated and their amino acid sequences identified as Tyr–Pro–Glu–Arg (residues 8–11), Tyr–Tyr–Pro–Gln–Ile–Met–Gln–Tyr (residues 136–143) and Asn–Asn–Val–Met–Leu–Gln–Trp (residues 164–170) respectively. ACE inhibitory activities were measured for the corresponding synthetic peptides, and the ACE IC50 (the amount of peptide causing 50% inhibition of ACE activity) values of A-II, B-II and C estimated to be 132·5, 24·8 and 41·0 μmol/l respectively. Peptides A-II and C were resistant to further digestion by pepsin, whereas peptide B-II was hydrolysed. All three peptides were resistant to digestion by chymotrypsin. These ACE inhibitory peptides may prove useful for oral administration in the treatment of hypertension.

A chemiluminescent method for determining xanthine oxidase (XOD) activity was developed and applied to the assay of milk enzyme activity using a photomultiplier luminometer. Various kinds of milk and cream samples were analysed for XOD content. In pasteurized milk, XOD activity depended on the fat content and in UHT milk it disappeared owing to the heat treatment. Milk sample preparation was very simple, requiring only homogenization at 40°C followed by a 1[ratio ]10 dilution with UHT (‘XOD-free’) milk. The assay was carried out at 25°C. The response obtained from XOD standard solutions in milk was linear from 0·1 to 500 enzyme units (U) l−1, but for the actual milk samples values ranged only from 1 to 135 U l−1. The detection limit at 2 SD was 0·1 U l−1 in milk, while in buffer it was 100 times lower. The intra-assay and interassay CV for XOD activity in milk were 6–12%.

Mammary infections caused by Staphylococcus aureus are still one of the most serious problems in dairy farms all over the world (Sischo et al. 1993), and the epidemiology of the infection has not yet been completely elucidated (Aarestrup et al. 1995). Any effective modern approach to this disease must therefore be based on more comprehensive epidemiological studies, conducted with valid microbiological typing tools.

A technique for use in epidemiological studies should identify many types, and should be inexpensive, quick and easy to perform, but above all reproducible. Among the available methods, phage typing has up to now been widely and successfully used in differentiating strains of Staph. aureus isolated from cattle with mastitis (Mackie et al. 1987; Fox et al. 1991), but it has some limitations, being a technically demanding method subject to considerable experimental as well as biological variation (Maslow et al. 1993). Moreover, in some studies the number of strains that could not be typed with available bacteriophage panels has been high (Carroll & Francis, 1985; Farah et al. 1988).

Alternative methods have been investigated, and of these molecular techniques have been the most intensely studied (Aarestrup et al. 1995). In studies of human infections caused by Staph. aureus, analysis of the so-called X region of protein A gene polymorphism has been a useful epidemiological marker (Frénay et al. 1994). This gene is ∼2150 bp and harbours some functionally distinct regions: an FC-binding region, the so-called X region and, at the C terminus, a sequence required for cell wall attachment (Guss et al. 1984; Frénay et al. 1994). The X region polymorphism depends on the presence, within the region itself, of a varying number of 24 bp repeats, highlighted by the amplification of this highly polymorphic DNA region and its subsequent restriction fragment length polymorphism (RFLP) analysis (Frénay et al. 1994).

Human epidemic (MRSA) and non-epidemic methicillin-resistant Staph. aureus (non-MRSA) strains, which both cause infections but have completely different infection patterns, have been successfully distinguished by analysis of this polymorphism (Frénay et al. 1994). However, protein A has been identified in only 93% of Staph. aureus strains isolated from bovine intramammary infections (Poutrel & Ducelliez, 1979; Johne & Jarp, 1988).

The aim of the present study was to determine whether the gene for protein A of Staph. aureus (Spa) was present in Staph. aureus strains isolated from cases of subclinical bovine mastitis. This was carried out using the polymerase chain reaction (PCR), as suggested by Frénay et al. (1994). In addition, we have investigated the genetic polymorphism related to the X region of the gene, by means of PCR amplification and subsequent RFLP analysis. Finally we verified the stability of this region after in vitro subculture.

A number of endemic diseases of dairy cattle cause significant losses to the dairy industry in the mainland UK (England, Scotland and Wales), both in terms of the reductions in output levels or wastage of resources incurred and the resource costs of disease prevention and treatment (Esslemont & Spincer, 1993; Esslemont & Kossaibati, 1996). Various studies have estimated the costs associated with different diseases (Bennett, 1992). However, these studies use different methods of assessment, relate to different populations at risk, refer to different points in time and utilize different ways of measuring disease and valuations of the effects of disease on production. Thus, it is difficult to use these studies for any comparative assessment of the magnitude of output losses and resource wastage incurred as a result of different diseases. Such information is useful in exploring both the economic consequences of diseases and the potential benefits of research on improved disease control (Howe, 1991; McInerney, 1996).

This paper presents analyses of the impacts on production of five endemic diseases and conditions of dairy cattle in mainland UK: bovine viral diarrhoea (BVD), fasciolosis, lameness, leptospirosis and mastitis (including summer mastitis). These analyses follow from a preliminary economic study of the impacts on livestock production of some 30 non-notifiable diseases and conditions of farm animals (Bennett et al. 1997). The study was funded by the Ministry of Agriculture, Fisheries and Food in the UK, with the (eventual) aim of providing information to policy makers that might help them to reach decisions on allocating funds to research into livestock diseases. Full details of the analyses are available from the website address given at the end of this paper.

Lipid oxidation in milk and dairy products is a chain reaction initiated by formation of free radicals (Richardson & Korycka-Dahl, 1983). Thanks to intensive studies on both model systems and actual food, the autocatalytic process, including the formation of secondary lipid oxidation products from the lipid hydroperoxides formed initially, is fairly well understood. However, actually predicting the rate at which the first free radicals leading to spontaneous oxidation are formed in milk from different cows awaits the development of new analytical methods with higher specificity and sensitivity (Nicholson, 1993; Barrefors et al. 1995). Such methods would also be valuable for predicting the stability and shelf life of dried dairy products, which are determined by oxidative phenomena. Electron spin resonance (ESR) spectrometry has the potential for detecting the early events in lipid oxidation, as it is the only spectrometric method that will directly detect the unpaired electron characteristic of the free radical and it is, moreover, a highly sensitive method (Brudvig, 1995). ESR spectrometry has recently been shown to provide quantitative information on the level of free radicals in milk powder that correlates with the level of secondary oxidation products developed upon reconstitution and that also correlates with subsequent sensory evaluation (Nielsen et al. 1997; Stapelfeldt et al. 1997a, b, c). However, in order to explore further the potential of this method for raw milk, it was considered valuable to measure the tendency of milk to form free radicals in relation to its level of α-tocopherol, the most important lipophilic chain-breaking antioxidant (cf. Kamal-Eldin & Appelqvist, 1996).

We have reported previously on the kinetics of thermal inactivation at 80–120°C of the extracellular proteinase from Pseudomonas fluorescens 22F (Schokker & van Boekel, 1997, 1999b). During these studies, we noted some inactivation during the heating up and cooling periods, but allowed for this by calculating the residual activity as a fraction of the activity after the heating up period of 2 min followed by cooling to 0°C. However, it may be of interest to evaluate the extent of inactivation during these heating up and cooling periods. If the temperature dependence of the reaction rate behaves according to Eyring's theory, inactivation would, of course, be slower than at the final heating temperature. However, during the heating and cooling of the enzyme solution, the temperature also passes the region in which autoproteolysis occurs (Schokker & van Boekel, 1998a). Prolonged residence time in the critical zone for autoproteolysis may cause increased inactivation, as has been demonstrated in electrophoresis experiments for proteinases from other Ps. fluorescens strains (Barach & Adams, 1977; Richardson, 1981; Diermayr et al. 1987). Consequently, the inactivation during the first few minutes would be dependent on factors influencing both autoproteolytic and thermal inactivation.

In most of our heating experiments (Schokker & van Boekel, 1997, 1999b), inactivation during heating up was relatively rapid compared with inactivation at the final heating temperature, leading to a biphasic inactivation curve. This was also found for proteinases from many other Ps. fluorescens strains. In some studies the inactivation during heating up was not taken into account when analysing the kinetics of thermal inactivation (Patel et al. 1983; Yan et al. 1985; Fairbairn & Law, 1986), which led to misinterpretation of the mechanism or the kinetic values. Others explained the biphasic inactivation curve by autoproteolysis (Barach & Adams, 1977; Richardson, 1981; Stepaniak & Fox, 1983; Kroll & Klostermeyer, 1984; Diermayr et al. 1987), or stabilization by Ca2+ of a small portion of the proteinase to heat inactivation (Stepaniak & Fox, 1983; Azcona et al. 1988).

In this paper we discuss the influence of protein, enzyme purification and Ca2+ activity on inactivation during the heating up and cooling periods. The aim of this study was to determine, using kinetic modelling, whether the inactivation during heating up and cooling periods could be explained by autoproteolysis and thermal inactivation, or whether other mechanisms are involved in the strong initial inactivation.

Dr M. Elisabeth Sharpe, who died last year, was Editor of the Journal of Dairy Research from 1975 to 1989. During this period she devoted her considerable energies and talent to putting the Journal on a sound financial footing and expanding its contributions from authors in the developing world. Becky, as she was known to her friends and colleagues, was highly successful in both these goals and the Journal continues to build upon her success to this day.

Her editorship was the culmination of a notable scientific career, full of achievement and friendships. Born in 1916 in Barnsley, Yorkshire, Becky Sharpe completed her BSc degree at University College London in 1937 and went on to a year of postgraduate study in microbiology at the University of Manchester. She then joined the staff of the National Institute for Research in Dairying, Shinfield, an Agricultural Research Council Institute and a part of the University of Reading. She left in 1942 for a 4 year stint with The Boots Company in Nottingham and returned to Shinfield for a 30 year period of exemplary research in dairy microbiology in the Department of Bacteriology.

The Department had a tremendous group of researchers and was a really exciting place for many of us to start our careers working with people like Becky Sharpe, Bruno Reiter, Frank Neave and Christina Cousins. Becky interacted with many of us over her career, and her research resulted in hundreds of publications and contributions to the scientific literature on the microbiology and microflora of milk and dairy products. She is probably best remembered for her work on staphylococci, micrococci and the lactobacilli. Often she pioneered the development of new techniques for the growth, isolation and identification of these Gram-positive organisms. She was especially pleased with her work as a contributor and editor for Bergey's Manual of Systematic Bacteriology, which continued after retirement. She received her PhD from the University of Reading in 1951 and a DSc degree from the University of London in 1973.

On a more personal note, the author remembers Becky as a generous and stimulating scientific colleague. She was always willing to listen to the ideas of a young and inexperienced scientist and offer help and advice. She was highly respected and well known in the world of dairy microbiology, and many outstanding microbiologists either worked with her or trained under her. Her laboratory was a favoured stop for researchers from across the globe.

After retiring from active research in 1976 she remained very active in scientific circles. Her Editorship of the Journal was a major commitment, but she was also an active participant in scientific society activities, particularly as a fellow of the Institute of Biology. Her numerous scientific contributions, and the health and international flavour of the Journal speak to her professional accomplishments. Her friendship and help will be fondly remembered and missed by all of those fortunate enough to have worked with her.