Experiments were undertaken to validate a method (using adrenaline injection) for determination of the size of cisternal and alveolar compartments in the udder, to use this method to determine the pattern of milk accumulation in the udder over time and to determine the relationship between the size of the alveolar and cisternal compartments and tolerance of once daily milking. Cows received intrajugular injections of adrenaline (3 mg) immediately before milking, to block milk ejection and allow harvesting of the cisternal milk fraction. This was followed by removal of the alveolar fraction 30 min later after intrajugular oxytocin (5 i.u.) injection. Results obtained were similar to those obtained by catheter drainage. The alveolar compartment was 90% full at 16 h post milking while the cisternal compartment filled more slowly and was only 70% full at 24 h post milking. At full capacity (measured at 40 h), the volumes of milk contained in the cisternal and alveolar compartments were similar. In a further experiment involving identical twin cows, it was shown that the greater the degree of filling of the cisternal compartment at 24 h, the lower was the production loss on once daily milking. This suggests that the freedom of the alveoli to drain was an important factor in the production loss on once daily milking. Although there were significant correlations within twin sets for milk yield and the size of udder compartments, the relationship within twin sets for yield loss on once daily milking was not statistically significant.

Forty-two multiparous dairy cows of three different breeds (Holstein, Montbéliarde and Tarentaise) were fed on the same type of forage (natural grassland) preserved in the form of either hay (H) or silage (GS), according to a changeover design (two 4 week periods). The proportion of concentrate in the diet and the energy and nitrogen contents were similar in both treatments. The milk produced by these cows was used for the manufacture of Saint-Nectaire type cheeses, under controlled and identical cheesemaking technological conditions. More cheese was produced with the H treatment milk. The cheeses made with the GS treatment milk were more yellow and tended to be more bitter. The other chemical and sensory characteristics did not differ much between the two treatments. Of the 51 volatile compounds identified, four were in significantly higher proportion in the GS than in the H cheeses. Cheeses produced from Tarentaise cows' milk were more yellow and their pH was higher than those made with the milk of Holstein or Montbéliarde cows. The cheeses from Montbéliarde and Tarentaise cows' milk were firmer, more melting and tastier than those made with the milk of Holstein cows. Although some trends were apparent, there were no significant differences in cheese volatile compounds for different breeds.

Milk was collected from three spring-calving herds, on different daily herbage allowances (DHA) of perennial rye-grass (16, 20 or 24 kg dry matter (DM)/cow for a 17 week period. On five occasions, at weekly intervals in the middle of the period, the three different milks were converted into low-moisture part-skim Mozzarella cheese. Increasing the DHA resulted in significant increases in the concentrations of protein in the cheesemilk (P<0·05) and cheese whey (P<0·02). The moisture-adjusted cheese yield increased significantly (P<0·01) on raising the DHA from 16 to 24 kg grass DM/cow. DHA had no significant effects on any of the gross compositional values of the cheese (although moisture and fat-in-DM levels tended to decrease and increase respectively with increasing DHA). The hardness of the uncooked cheese and functionality of cooked cheese (i.e. melt time, flowability, stretch and viscosity) were not significantly influenced by DHA over the 115 d ripening period at 4°C.

Concurrent falls in milk production and electrical resistance of composite milk were examined in Israeli Holstein cows. The cows were milked three times a day by a system that recorded yield and the lowest electrical resistance in the composite milk from the four glands. The study included two groups: cows that experienced on day 0 a decline in resistance and milk production [ges ]20% from the mean of the previous 9 d (62 cows, case group) and cows that experienced no such episodes over 9 d before and after a fixed day (118 cows, control group). Bacteriological status and somatic cell count (SCC) or California mastitis test scores were assessed on the fixed day in the control group, and on days 0, 1 and 2 in the case group. California mastitis test scores greater than 2 and SCC thresholds of 5×105 cells/ml were used to create two classes of leucocytosis. There was no statistically significant difference between the two groups in frequency distributions of pathogens and their types: in 30% of cows infection was not detected, 33% were infected by major pathogens (95% of which were Staphylococcus aureus), and 53·5% by minor pathogens (80% Micrococcus spp.). Cows in the case group had lower milk production during the 8 d following day 0. Mean electrical resistance was lower in infected cows and particularly in cows infected by Staph. aureus. High leucocytosis was associated with reduced electrical resistance in both groups, and was found in 93% of cows in the case group v. 25% in the control group. The results suggest that falls in electrical resistance of milk and in milk production were not linked to a specific pathogen, and were followed by 3–8 d of reduced milk production and electrical resistance. The study suggests that there are episodic aggravations in mammary health that do not evolve into clinical mastitis but may induce significant losses in milk yield and quality.

The aim of this study was to determine whether carbonic anhydrase (CA) activity in goat mammary capillaries is regulated mainly by local or systemic mechanisms. One gland was dried before the contralateral gland, and after parturition only one gland was milked. Biopsies were taken from the mammary glands of three goats at 14 d intervals during involution and the start of the following lactation. A histochemical method was used to visualize sites of CA activity. To follow the involution process, milk (liquid) samples were taken from both teats each week and analysed for pH and composition. The time course of CA activity disappearance and reappearance in the capillaries was related to changes in milk composition and alveolar area. A dense network of capillaries showing membrane-bound staining for CA was found surrounding the alveoli in the lactating gland. CA activity gradually decreased in the drying gland, although the other gland was being milked. After 8 weeks involution the dried gland had a significantly lower number of stained capillaries than the milked gland. Almost no stained capillaries were found during late pregnancy, when both glands were dried and the tissue growth maximal. During lactation milk pH was 6·6±0·3 and this increased to 7·0±0·1 in the course of involution. In the last trimester of pregnancy the pH returned to its lower value, while the mammary gland was devoid of stained capillaries. Therefore, the capillary CA could not have been directly involved in the pH regulation of milk. The CA activity reappeared in the capillaries directly after delivery, but only in the milked gland. Clearly the regulation of CA activity is influenced more by local than by systemic factors and is associated with the metabolic activity of milk secretion.

Colostrum and milk were collected from ten sows at frequent intervals from before farrowing until 9 d after farrowing. Ionized calcium, pH, and total concentrations of citrate, calcium, phosphate and magnesium were measured in whole milk. The diffusible fraction of the mammary secretion was separated by ultrafiltration and was used for the measurement of diffusible citrate, calcium, phosphate and magnesium. The pH before farrowing was 5·7, and increased to 6·5 on day 4 as total calcium and phosphate also increased. Before farrowing, total and diffusible citrate were 7·8 and 7·3 mM respectively, while diffusible phosphate was 11·9 mM, and these concentrations all decreased during the study period. Total magnesium ranged between 3·3 and 4·1 mM, while diffusible magnesium ranged between 2·0 and 3·1 mM. While these concentrations and patterns of change of diffusible calcium and citrate are quite different from those of women's milk during the first week after birth, theoretical physicochemical relationships between diffusible calcium and citrate, and ionized calcium and HPO42− were corroborated by these results. We conclude that diffusible citrate plays an important role in the determination of the concentration of diffusible calcium. However, while citrate may be the major determinant of the total concentration of calcium in women's milk, this is not the case in sows' milk.

The pressure-induced (100–400 MPa) changes in casein micelles from bovine, caprine and ovine milks were investigated by studying the distribution of minerals and proteins after separation of the micellar and serum phases by ultracentrifugation. The results showed that pressurization markedly increased the levels of non-sedimentable casein in the three species, as well as the levels of Ca, P and Mg in the serum, but led to only small increases in the Ca2+ concentration. The dissociation rates of individual caseins corresponded to the ester phosphate contents, in the order κ-casein, β-casein>αs1-casein >αs2-casein. The concentration of non-sedimentable casein was highest in pressurized ovine milk, which also contained higher levels of pressure-liberated serum minerals than the milks from the other two species. In the case of bovine and caprine milks, maximum dissociation from the micelle was found in milks treated at 300 MPa, while in ewes' milk dissociation increased with pressure up to 400 MPa. Denatured β-lactoglobulin (β-lg) was present in the ultracentrifugation pellets of the pressurized milks of the three species, but pressure-denatured β-lg also remained in the soluble fraction. Despite the increases in the content of soluble proteins, all casein and most β-lg were incorporated in the rennet curds of the pressurized milks from the three species.

Whey protein concentrate (WPC) solutions containing 10, 30, 60 and 120 g dry powder/kg were heated at 75°C and whey protein aggregation was studied by following the changes in the distribution of β-lactoglobulin, α-lactalbumin and bovine serum albumin, using one dimensional and two dimensional PAGE. The one dimensional PAGE results showed that a minimal quantity of large aggregates was formed when 10 g WPC/kg solutions were heated at 75°C for up to 16 min whereas appreciable quantities were formed when 30, 60 and 120 g WPC/kg solutions were similarly treated. The two dimensional PAGE analysis showed that some disulphide-linked β-lactoglobulin dimers were present in heated 10 g WPC/kg solution, but very little was present in heated 120 g WPC/kg solution. By contrast, SDS was able to dissociate monomeric protein from high molecular mass aggregates in heated WPC solution of 120 g/kg but not in 10 g WPC/kg solution heated for 30 min. The rates of loss of native-like and SDS-monomeric β-lactoglobulin, α-lactalbumin and bovine serum albumin during heating increased as the WPC concentration was increased from 10 to 120 g/kg. In 120 g WPC/kg solution heated at 75°C, the amounts of SDS-monomeric β-lactoglobulin in each sample were greater than the quantities of native-like protein. However, in WPC solutions of 10, 30 and 60 g/kg, the differences between the amounts of native-like and SDS-monomeric proteins were slight. The loss of the native-like or SDS-monomeric proteins was consistent with a first or second order reaction. In each case, the apparent reaction rate constant appeared to be concentration-dependent, suggesting a change of aggregation mechanism in the more concentrated solutions. Overall, these results indicate that in addition to disulphide-linked aggregates, hydrophobic aggregates involving β-lactoglobulin, α-lactalbumin and bovine serum albumin were formed in heated WPC solution at high protein concentration, as suggested by model studies using binary mixtures of these proteins.

Growth factors are thought to play a decisive role in the course of inflammatory processes. The aim of the present study was to characterize a potential interrelationship between the concentrations of insulin-like growth factor-1 (IGF-1), basic fibroblast growth factor (bFGF) and somatic cell count (SCC) in normal milk, and to investigate the presence of these growth factors in mammary secretions of cows suffering from clinical and subclinical mastitis. Quarter secretions of cows with spontaneous acute clinical mastitis and of cows with subclinical mastitis were analysed radioimmunologically for their concentrations of IGF-1 and bFGF. During two relocation trials with normally lactating Brown Swiss cows, dramatic changes in milk somatic cell count were obtained following a short-term change (5 d) of location and housing system. The animals were relocated from their familiar loose housing system with concrete slatted floor to a separate stanchion barn with long stalls and straw bedding, and vice versa. The concentration profile of IGF-1, but not of bFGF, corresponded well with SCC during the relocation trials, the positive correlation between the characteristics being highly significant, as determined by regression analysis (r=0·60; P<0·001). The results provide evidence that significant changes in SCC and growth factor content may be caused by environmental factors other than infection. The concentrations of both IGF-1 and bFGF were greatly elevated in secretions of quarters affected by acute clinical mastitis compared with the corresponding clinically healthy quarters. Subclinically affected quarters with high SCC, as compared with non-affected quarters with low SCC, also had elevated milk IGF-1, but unchanged bFGF. Measuring of growth factor profiles in milk may have value in the near future in monitoring the state of udder health in addition to SCC.

Analysis of the concentrations of free amino acids in milk during growth of Lactococcus lactis subsp. lactis revealed a biphasic pattern of change during the logarithmic phase. During the first period there was little overall change in the total concentration of amino acids in the medium. The second phase was characterized by increased net liberation of free amino acids. There were also qualitative differences in the amino acids that were taken up and utilized during each period. The concentrations of Val, Leu and Ile decreased only during the early phase, while those of Ser, Arg, Thr and Met decreased only during the second phase. Gly and Ala were utilized throughout logarithmic growth. Gly uptake appeared to be greater during the second period and accounted for the largest proportion of free amino acid utilization at this time. It is possible that the biphasic nature of amino acid nutrition was due to increased consumption in late log phase of peptides derived from milk proteins by proteolysis. Increased activity of the arginine deiminase pathway during late log phase was inferred from increased utilization of Arg and liberation of citrulline and ornithine.

Growth and proteolytic activity of Lactococcus lactis strains were investigated in milks subjected to different heat treatments. Only 13·7% of the strains were of proteolytic phenotype. Proteinase-positive (Prt+) strains exhibited a proteolytic activity that increased when the level of heat treatment was reduced and grew to a higher level than proteinase-negative (Prt−) strains in low-heat-treated milk. When grown in autoclaved reconstituted skim milk, both Prt− and Prt+ strains had the same specific growth rate. Total DNA from four Prt+ and eleven Prt− strains was extracted and used for polymerase chain reaction amplification of fragments belonging to genes encoding for cell wall proteinase. Specific amplification products were displayed by all the Prt+ strains, and by the Prt− strain Lc. lactis subsp. lactis NWC 125. Reverse transcriptase-polymerase chain reaction was performed to detect the transcript of the proteinase genes. In addition to the Prt+ strains, the experiment also detected the specific transcript in Lc. lactis subsp. lactis NWC 125, suggesting that other structural or functional deficiencies occurred in this strain.

In Swiss-type cheese such as Emmental, proteolysis is one of the major phenomena occurring during ripening. Among the proteolytic agents involved in cheese ripening, the free enzymes originally present in milk and those arising from bacterial autolysis can act directly on the casein network. In order to understand the contribution of the bacterial enzymes and especially those arising from the thermophilic starters, the juice of an Emmental cheese entering the warm room was extracted by pressure, then sterilized by filtration and incubated at 24°C for 20 d under anaerobiosis. At different times, the peptides and free amino acids were determined in the sterile cheese juice. In parallel, in order to gather information about the nature of the enzymes present, the sterile juice was also incubated with β-naphthylamide derivatives as substrates. We have demonstrated a continuous increase in free NH2 groups and in free amino acids throughout the 20 d incubation time. The main peptidase activity was due to aminopeptidase(s) and X-prolyldipeptidyl aminopeptidase(s) whose activities were recovered after non-denaturing polyacrylamide gel electrophoresis. Most of the enzymes found in the juice would have their origin in thermophilic starters. As they are generally intracellularly located, their release could be explained by the autolysis of these starters. Finally, the main free amino acids released in the juice (Pro, Glu, Ala, Val, Leu and Lys) corresponded to those previously found in Emmental cheese, suggesting that the enzymes detected in this study participate significantly in peptide degradation during ripening.

The effect of yogurt on the inhibition of colon tumours induced by 1,2-dimethylhydrazine in BALB/c mice has been studied, and the hypothesis examined that yogurt induces a great reduction in the inflammatory immune response and inhibits tumour growth. Mice were assigned to five experimental groups: a control group fed with a conventional balanced diet, and four other test groups that received yogurt supplements for 2, 5, 7 or 10 consecutive days. At the end of each feeding period, mice were given subcutaneous injections of 1,2-dimethylhydrazine (20 mg/kg) once a week for 8 weeks. After tumour induction, yogurt was given again for 2, 5, 7 or 10 consecutive days each 10 d for 20 weeks. By week 20, 70% of the animals in the control group had developed colorectal tumours. From week 8, there was a considerable infiltration of mononuclear cells into the lamina propria of the large intestine. There was an increase in the number of IgG-producing cells and a slight increase in the IgA-secreting cells, and of CD8+ but not CD4+ T lymphocytes, a high level of β-glucuronidase activity in the intestinal fluid and leucocytosis with neutrophilia in the blood. However, in the test groups given yogurt tumour growth was inhibited, the effect being more evident with 7 or 10 d treatment. The inflammatory immune response as measured by the characteristics we assessed was also reduced, with an increase in the IgA-secreting cells and in CD4+ T lymphocytes. The blood count was similar to that of normal animals and no colorectal tumours were observed in week 20. We suggest that one of the mechanisms by which yogurt exerts antitumour activity is through its immunomodulator activity, by reducing the inflammatory immune response, which was markedly increased when the carcinogen was administered.

Various species of coagulase-negative staphylococci (C-NS) are reported to be common in milk and on the teat skin of domestic ruminants. The commonest C-NS species in mastitic milk of cows varies between reports, with Staphylococcus simulans (Jarp, 1991) in one and Staph. hyicus in another (Watts & Washburn, 1991). The teat skin of heifers may be colonized by Staph. xylosus or Staph. chromogenes, while Staph. chromogenes and Staph. warneri are reported as frequent isolates from teat canals and secretion (Boddie & Nickerson, 1986; White et al. 1989). Staph. haemolyticus was isolated frequently from the nares, the teat skin and the milk of goats (Valle et al. 1991), although others reported Staph. xylosus (Bedidi-Madani et al. 1992) or Staph. epidermidis and Staph. capitis (Kalogridou-Vassiliadou, 1991) as the most predominant C-NS in goats' milk. Staph. simulans has been found experimentally to be pathogenic for the mammary gland of meat ewes (Fthenakis & Jones, 1990), but little is known about the prevalence of this species in ewes' milk collected from cases of naturally occurring subclinical mastitis (SCM). The aim of the present investigation was the identification of the commonest C-NS species in ewes' milk collected from field cases of SCM or predominating in the ewes' environment.

The enterococci have traditionally been used as indicators of faecal contamination because they are common inhabitants of the human and animal intestinal tract. In addition, some strains are well documented as opportunistic pathogens, and have been implicated in endocarditis, infant diarrhoea and other conditions. However, other strains are widespread in foods, particularly in milk and dairy products, where they are considered desirable microflora. In fact, through their proteolytic and lipolytic abilities, they play an important role in cheese ripening, contributing to the development of the organoleptic properties characteristic of certain cheeses (Villani et al. 1993).

Production of antimicrobial substances is one of the mechanisms by which microorganisms can exert a probiotic effect in a host. In this context, a significant number of bacteriocin-producing enterococci of dairy origin have been isolated in recent years (Giraffa, 1995). Production of these antimicrobial peptides or proteins is a common phenotype among lactic acid bacteria, and this is the application of enterococcal bacteriocins of special interest in dairy systems. Firstly, they show activity against a broad spectrum of spoilage and pathogenic organisms of concern in dairy industries, such as Listeria monocytogenes. Secondly, they are inactivated by human gastric enzymes but not by some enzymes that, like rennet, are frequently used in dairy plants. Finally, their marked heat stability enables them to be used in a wide variety of dairy products (Giraffa, 1995).

The genes that encode the biosynthesis of some enterocins or enterococcins, such as enterocin AS-48 (Martínez-Bueno et al. 1994), have been sequenced, allowing their rapid detection by molecular biology techniques such as the polymerase chain reaction (PCR) (Joosten et al. 1997). Enterococcal bacteriocins that have been genetically characterized have been shown to be plasmid-encoded (Clewell, 1993).

In this paper, we report a simple method for the isolation of plasmid DNA from dairy enterococci, using a combination of lysozyme and glass beads (Frère, 1994; Reinkemeier et al. 1996) to achieve cell lysis. Plasmid DNA was used in dot-blot and Southern hybridization analyses to identify enterocin AS-48-encoding dairy enterococci by using a specific PCR-generated probe. In addition, a more rapid detection method based on colony hybridization was also developed.

Kefir is a traditional fermented milk originating many centuries ago in the Caucasian mountains. It is produced by fermentative activity of ‘kefir grains’ consisting mainly of lactococci, lactobacilli and yeasts in a protein–polysaccharide matrix. The grains contain a relatively stable and specific balance of microorganisms which exist in a complex symbiotic relationship. The grains grow in the process of kefir making only from pre-existing grains (Saloff-Coste, 1996). When kefir grains are allowed to grow in milk, microorganisms are shed from the grains into milk where they continue to multiply with the production of acid, flavour and physicochemical changes.

The traditional method of kefir making is currently by adding kefir grains directly as starter to milk that has been pasteurized and cooled to 20–25°C. After a period of fermentation lasting ∼24 h, the grains are removed by filtration and the beverage is ready for consumption (Saloff-Coste, 1996). Kefir from which the grains have been removed may be used as starter. However, this fermented milk cannot be used for subsequent inoculations to make an acceptable product, because the original balance of microorganisms has been disrupted (Kroger, 1993).

The complex microbiological composition of kefir grains explains why it is difficult to obtain starter with the optimal and constant composition necessary for a regular production of kefir of standard quality (Koroleva, 1988a). Studies have been undertaken to establish cultivation conditions[ratio ]grain[ratio ]milk ratio, cultivation temperature, period of time and conditions prior to separation of grains from the fermented milk, shaking conditions for agitation of milk with the grains in the course of fermentation, washing of kefir grains and so on. All these factors influence the microflora of the kefir starter and fermented milk. There are no rules about household manufacture of kefir. Different reports indicate a wide range of grain[ratio ]milk ratios for kefir making. Bottazzi & Bianchi (1980), Marshall & Cole (1985), Merin & Rosenthal (1986), Mann (1989), Hosono et al. (1990) and Kroger (1993) employed 20–50 g/l while Koroleva (1988a) employed 20–100 g kefir grain/l and Marshall et al. (1984) and Neve (1992) 50–100 g/l. Rea et al. (1996) used 1 g kefir grain/l as starter and 200 g starter in the form of kefir grains is recommended by Hansen for the fermentation of 1 l milk (Marshall & Cole, 1985). A critical control point in kefir manufacture to obtain a product with constant quality is the standardization of the kefir grain[ratio ]milk ratio. Koroleva (1988b) claimed that it is better to use kefir grains as starter for kefir production and, at the same time, to decrease the amount of inoculum.

The purpose of this study was to evaluate the effects of changes in the kefir grain[ratio ]milk ratio (quantity of kefir grains inoculated into the milk) on microflora composition, acidity, apparent viscosity and carbon dioxide content of fermented milk.

During the last two decades the traditional subjective appraisal of the body fat stores in farm animals, made by eye and touch, has been rationalized by the introduction of numerical systems of rating specific anatomical points.

Palpation of the lumbar vertebrae, the pin and hook bones (tail head) (Lowman et al. 1973), and, occasionally, width behind the shoulders (Treacher et al. 1986) provides an assessment of the fatness of the animal. This is calibrated from standard photographic charts, in the use of which the operator is trained. Body condition scoring (CS) by this method has been widely developed for dairy cows (Earle, 1976; Mulvany, 1977; MacCarthy, 1978; Scott & Smeaton, 1980; Wildman et al. 1982; Aalseth et al. 1983; Anon. 1986; Garcia Paloma, 1990).

The actual numerical scales have varied among systems. Thus over the range from very thin to very fat cows the scale is 1, 2…7, 8 (Earle, 1976) and 0½, 1,…4½, 5 (Mulvany, 1977), for example. CS is thus a discrete variate with a limited number of readings. Several authors have sought to decrease the division size, for example 1, 1 1/3; 1 2/3;…4 2/3, 5 (Ducker et al. 1985a, see also Dewhurst et al. 1996) and by using the means of the separate values obtained by two operators judging CS independently (W. H. Broster, V. J. Broster, A. J. Clements, J. W. Siviter and T. Smith, unpublished results). In this review CS will be stated in the units given by Mulvany (1977), to which other ranges have been scaled. Inspection of CS data has usually been conducted by analysis of variance, but also by the Mann–Whitney signed rank test (Moorby et al. 1996).

Evans (1978) and Nicoll (1981) studied the variation in recording CS. Both investigators concluded that a system of observation by two independent assessors per recording occasion is advantageous and that revision training is necessary to maintain operator standardization. Of total variance in CS, some 60–70% was found attributable to ‘between-animal’ differences, <5% to assessor variation and <10% to animal×assessor variation. Croxton & Stollard (1976) found good repeatability of CS measurements ‘between’ and ‘within’ operators. It is regrettable that few reports of experimentation give full details of method of and number of operators engaged in body score recording.