Mammary cistern anatomy derived from ultrasound measurement, milk ejection in response to exogenous oxytocin and oxytocin release and milking characteristics with and without manual prestimulation in early (months 2–4) and late (months 5–8) lactation were investigated in Lacaune and Ostfriesian dairy ewes. Vertical ultrasound cisternal cross sections of the cisternal cavities did not differ in the two breeds, whereas the cisternal area fraction located lower than the exit into the teat channel was larger in Ostfriesian than in Lacaune sheep. The cisternal area enlarged within 1 min in response to i.v. oxytocin injection, indicating milk ejection. During milking, oxytocin concentrations in Lacaune generally increased dramatically within 0·5 min from the start of prestimulation or milking, whereas only slight or no oxytocin release was detected during milking without prestimulation in Ostfriesian ewes. Prestimulation induced oxytocin release in Ostfriesian sheep within 1–2 min after the start of milking, indicating delayed response to stimulation. Two peaked milk flow curves were observed when oxytocin release and milk ejection occurred only after removal of cisternal milk. This type of milk flow was more frequent in Ostfriesian than in Lacaune ewes and was reduced in both breeds by prestimulation, while the frequency of one peaked milk flow curves increased. During the course of lactation, milk yield, main milk fraction and milk flow rates decreased, while stripping yield was almost unchanged. Although milk yield was similar in both breeds, milk flow was lower and stripping yield was higher in Ostfriesian than in Lacaune ewes. We conclude that milk ejection in ewes occurred in response to elevated oxytocin concentrations. In Ostfriesian ewes reduced and delayed oxytocin response to teat stimulation resulted in milk ejection only during stripping. Therefore, and probably because a larger volume of the cistern was located below the teat exit in the Ostfriesian breed, stripping yield was higher in Ostfriesian than in Lacaune sheep.

The effects of a daily supplement of 300 ml fish oil and 20 g rumen-protected methionine, alone or in combination, were investigated in mid-lactation cows receiving a maize silage-based diet ad lib. Fish oil significantly decreased feed intake, increased milk yield, decreased protein and casein concentrations, and especially fat concentration (by 13·1 g/kg) and output. Fat concentration decreased more in primiparous than in multiparous cows. Methionine supplementation increased protein and casein concentrations and outputs. No significant interaction between oil and methionine supplementation was found on milk composition. Treatments did not modify live weight or body condition changes, or lactose and non-casein nitrogenous compounds in milk. Oil plus methionine supplementation made it possible to decrease milk fat content without changing protein content.

Dairy cows fitted with ruminal, duodenal and ileal cannulas were utilized to investigate the effects of feeding with Ca soaps (CaS) of palm fatty acids (FA) and rapeseed FA. Diets compared were control diet based on maize silage and concentrate, and two diets with 40 g CaS of palm oil FA or rapeseed oil FA/kg diet, replacing part of the concentrates of the control diet. Total digestibilities of dry matter, fibre and fat, and ruminal fermentation were not significantly altered by giving CaS; the extent of ruminal biohydrogenation of total unsaturated C18 FA was significantly reduced by both CaS diets. Apparent intestinal digestibility of FA was not different among diets, although the amount of FA absorbed with the CaS diets was twice that with the control diet. No difference among diets was observed for milk production, or fat and protein contents. Giving CaS diets decreased the proportions of 4[ratio ]0 to 14[ratio ]0 FA in milk fat, and increased cis-18[ratio ]1n−9, compared with control diet. The rapeseed diet lowered the content of 16[ratio ]0, and increased the contents of 18[ratio ]0 and trans-18[ratio ]1n−7. CaS diets did not result in a marked increase of polyunsaturated FA content in milk fat. Butter from cows fed on the CaS diets contained more liquid fat at 6 and 14°C than butter from the cows fed on the control diet. Incorporating CaS, particularly those from rapeseed, in dairy cows' diets increased C18 FA in milk and improved butter spreadability.

The distribution pattern of myoepithelial cells in the bovine mammary gland was investigated by an immunohistochemical technique, using monoclonal antibodies against cytokeratins 5, 6 and 18 and cytokeratins 8 and 14 and against α-smooth-muscle actin filaments. Myoepithelial cells were shown to be present as a continuous basal cell layer in the intralobular ducts, as discontinuous cell rows in the basal cell layer of the interlobular ducts, and as single cells dispersed in the basal cell layer of the quarter cisterns, while they were apparently absent in the teat cisterns. Unlike the case with myoepithelial cells of the human breast, anti-cytokeratin 14 was less specific as a marker of bovine myoepithelial cells than was anti-α-smooth-muscle actin.

The lactational variation in milk protein composition and renneting properties and their relationship to the cow's body condition at calving were investigated in 39 Danish Holstein first lactation cows fed on a well balanced standard diet. All milk characteristics measured were significantly affected by stage of lactation (P<0·01). Casein as a proportion of total milk nitrogen reached a maximum in mid lactation. The proportion of αs- and κ-casein in total casein decreased and the proportion of β-casein increased systematically during lactation while the proportion of γ-casein was lowest in mid lactation. The α-lactalbumin content of milk and its proportion of total whey proteins decreased during lactation. Renneting time was highest and curd firmness lowest in mid lactation. These results appeared to reflect a low degree of proteolysis in late-lactation milks compared with several other investigations, probably because of the good nutritional state of the cows. The body condition at calving affected proteolysis and the renneting properties of milk. A good body condition increased the content of whey protein in total milk nitrogen and of γ-casein in total caseins (P<0·05); in addition, curd firmness was improved (P<0·01) and aggregation time was reduced (P<0·05). We suggest that these effects were related to the fat metabolism and energy status of the cows during lactation. The interrelationships between the milk characteristics were evaluated by factor analysis to support the interpretation.

Capillary electrophoresis using a hydrophilically coated capillary and a low pH buffer containing urea has been used to follow the proteolytic action of plasmin and chymosin on isolated casein fractions, whole casein and individual milk samples selected on the basis of their genetic variants. Several of the main casein breakdown products were identified. These included, among others, γ1-casein (CN) A1, γ1-CN A2, γ1-CN B, γ1-CN C, γ2-CN A, γ1-CN A3, γ2-CN B, γ3-CN A and γ3-CN B, as well as proteose peptones, arising from the action of plasmin on the different genetic variants of β-CN. αs1-I-CN and αs1-CN f(1-23) from αs1-CN, and para-κ-CN and caseinomacropeptide from κ-CN produced by chymosin action were also separated. The knowledge of their migration times provided information on the extent and origin of casein hydrolysis in both milk and cheese, as found in samples of proteolysed milk or fresh cheese.

A rapid procedure for isolating genomic DNA from milk samples has been devised, based on the use of Chelex resin. By using this protocol, genomic DNA was extracted from milk samples from 15 cows and 15 goats. The suitability of these DNA preparations as a template for performing the polymerase chain reaction (PCR) was tested by amplifying three different loci of the bovine genome: exon 4 of the κ-casein gene and the INRA5 and INRA23 microsatellites, together with two others: exon 19 of the αs1-casein gene and exon 2 and part of intron 2 of the DRB gene of the caprine genome. No amplification products could be obtained from any samples at 30 cycles. In contrast, at 45 cycles the number of amplified samples ranged from 86 to 100% and at 65 cycles all the DNA targets were amplified, indicating that the number of cycles was a critical factor to be optimized for obtaining the desired PCR target. These results suggest that this method may be a useful tool for analysing genetic polymorphism at the DNA level by PCR and relating it to milk composition and other traits of economic interest.

Recent findings suggest a protective role for folates in the reduction of neural tube defects and possibly also coronary heart disease and cancer. Consequently, an increase in the daily intake of folates is warranted, which emphasizes the need for quantitative as well as qualitative measurements of dietary folates. Milk plays an important part in the food chain in many Western countries today. Several studies suggest that folate-binding proteins might have an impact on folate absorption and therefore their concentrations are also important. The mean concentration of the predominant form of folate, 5-methyltetrahydrofolate (5-CH3THF), was determined using HPLC in thirteen selected dairy products; skim milk powder, two pasteurized milks, UHT milk, two fermented milks, three whey products and four different cheeses. All results were corrected for recovery by spiking the samples with 5-CH3THF. Effects of storage of dairy products on 5-CH3THF concentrations were also investigated; generally small and insignificant fluctuations were found, except for hard cheese, in which 5-CH3THF decreased significantly. There was a significant seasonal variation in the folate concentration of pasteurized milk which peaked in the summer months. The concentrations of folate-binding protein in skim milk powder and pasteurized milk analysed using an enzyme-linked immunosorbent assay were similar. UHT milk and fermented milk, both of which are processed at temperatures >90°C, contained significantly lower concentrations of folate-binding protein.

The susceptibility to penicillin-G of Staphylococcus aureus strains that cause mastitis was tested in milk and in Iso-sensitest broth (ISB). The minimal inhibitory concentrations (MIC) of β-lactamase-positive strains in milk were 10–100-fold those in ISB, whereas the MIC of β-lactamase-negative strains in milk were some 10-fold those in ISB; β-lactamase production was induced by milk in β-lactamase-positive strains. Much of the increase in resistance to penicillin-G caused by milk can be attributed to milk fat globules; the increase in resistance was related to the binding capacity of the bacteria to milk fat globules as well as to capsule formation by the bacteria. It appears that the binding of the staphylococci to the fat globules and bacterial capsule formation resulted in a biofilm type of growth. In this case, the staphylococci behaved differently from the planktonic type of growth in artificial broth medium in which antibiotic susceptibility testing is usually carried out.

A total of 50 isolates of Bacillus spp. and one reference strain were investigated for their growth at 6·5°C for 10 d, 30°C for 3 d and 40°C for 2 d. The results obtained differentiated three physiological groups: one clearly psychrotrophic (able to grow at 6·5°C in 10 d, but not at 40°C in 2 d), one intermediate in psychrotrophy (it grew at both 40 and 6·5°C) and one mesophilic (capable of growth at 30 and 40°C, but not at 6·5°C). The proportion of strains in the second group was higher among isolates of B. cereus than for other Bacillus spp. However, the proportion of real mesophilic strains was lower for B. cereus isolates. Psychrotrophic B. cereus grew better at both 6·5 and 30°C than other psychrotrophic Bacillus spp. Using eight strains, a correlation between differential growth at mesophilic temperatures (count at 30°C minus count at 40°C) and a standard psychrotrophic count at 6·5°C for 10 d (r=0·95) was obtained in mixed cultures when the psychrotrophic flora count was [les ]1 log (cfu/ml) lower than the mesophilic count.

The concentrations of seven types of microorganism in the milk produced by farms using high quality milking procedures were monitored monthly. The most commonly encountered bacterium was Pseudomonas, whose concentration varied greatly between samples, but lactococci, lactobacilli and yeasts were also present at more stable concentrations. Staphylococcus aureus and β-glucuronidase-positive Escherichia coli were occasionally detected. Listeria monocytogenes was found in the samples from only one farm, while Yersinia enterocolitica was never detected. There were seasonal variations in the concentrations of lactobacilli and yeasts over the 2 years monitored. The changes in certain bacteria (Lactococcus, Lactobacillus) on any given farm were very similar from one year to the next. The microbiological characteristics of the milk from the farms examined seemed to be fairly constant. The profiles of some bacteria used for cheesemaking were relatively stable over time. It thus seems that the milk provided by different producers could be typed.

The effects of ruminant whey and its purified fractions on neutrophil chemotaxis and superoxide production in sheep were studied. Both colostral whey and milk whey were found to inhibit chemotaxis regardless of whether they were autologous or homologous, but the inhibitory effects were abolished by washing neutrophils with culture medium before their use in the chemotaxis assay. Colostral whey and milk whey also inhibited the chemotactic activity of zymosan-activated serum. Whey fractions of various degrees of purity such as lactoferrin, lacto-peroxidase, lactoferrin–lactoperoxidase, α-lactalbumin, bovine serum albumin and whey protein concentrate were then studied. While none of these proteins showed any effects on chemotaxis, lactoferrin–lactoperoxidase and whey protein concentrate were found to have an enhancing effect on superoxide production in a dose-dependent manner. Our results provide information on the modulatory role of ruminant milk proteins in inflammatory responses and warrant future investigation.

Hydrophobic and hydrophilic peptides in the water-soluble fraction of 20 batches of Hispanico cheese made from pasteurized and raw milk were determined by reversed-phase HPLC, with detection at 214 and 280 nm. Cheese flavour characteristics were evaluated by a sensory panel, and regressions of bitterness scores on levels of hydrophobic and hydrophilic peptides and their ratio were calculated. The best fitting relationship for pasteurized milk cheese was the linear regression of mean panel bitterness scores on hydrophobic peptides at 280 nm (r2=0·791). The determination coefficient for the regression of hydrophobic peptides at 280 nm on panellist bitterness scores (r2=0·356) was lower, owing to individual differences in the perceived intensity of bitterness. In the case of raw milk cheese, the respective determination coefficients were 0·203 for panel scores and 0·034 for individual panellist scores.

There is considerable interest in the relationship between milk protein polymorphism and cheesemaking properties of milk (e.g. Jakob & Puhan, 1992, 1995; Jakob, 1993). For example, the B variant of κ-casein is associated with firmer cheese curds, shorter renneting times, a smaller average micelle size, higher milk casein and κ-casein concentrations and lower whey protein concentrations (Jakob, 1994; Horne et al. 1995).

Parmigiano Reggiano is a hard, cooked cheese produced in specific areas of Northern Italy. The raw material is obtained by mixing the partly skimmed evening milk and whole morning milk. The mixture is then heated to 22°C, and natural whey starter is added at 28–30 g/l after 1–2 min, bringing the pH of the mixture to 6·2–6·3. After coagulation, which takes ∼15 min and occurs at 32–33°C owing to the addition of calf rennet powder, the curd is broken up for 2–4 min, cut into fragments and cooked at a temperature raised gradually to 42–44°C and then more quickly to 55–56°C over 10–15 min. The curd is left undisturbed, covered by the whey, for 40–60 min, then removed and placed inside a circular wooden mould. The cheese is held at ∼20°C for 3 d during which it is turned at frequent intervals to facilitate complete whey drainage. The cheese, which now has its typical shape and size, is then salted by immersion in brine (260–280 g NaCl/l at 16–17°C) for 20–24 d. During this period the cheese absorbs 15–18 g NaCl/kg and its weight decreases by 4%. During the subsequent period of ripening (12–24 months) in store rooms at 16–18°C and 85% moisture, the cheese is frequently turned. At the end of ripening the cheese is cylindrical in shape, with a slightly convex side, 0·22–0·24 m high, 0·40–0·45 m diam. weighs 35–36 kg, has 320–330 g fat/kg dry matter and a minutely granulated internal structure with small holes formed by the activity of some heterofermentative lactic acid bacteria.

Butyric acid fermentation in brine salted, semi-soft and hard cheeses (late blowing) can create considerable loss of product. Clostridium tyrobutyricum, a Gram-positive, sporeforming, anaerobic bacterium, has been identified as the causative agent (Klijn et al. 1995).