Experiments were designed to determine the cisternal milk during machine milking in unfamiliar surroundings, which has previously been shown to inhibit milking-related oxytocin (OT) release and milk ejection. The first experiment was performed with 22 cows in early, mid and late lactation. After cisternal milk was removed, 10 i.u. OT were twice injected intravenously to remove the remaining milk. Total milk yield, cisternal milk yield, cisternal milk fraction (17 and 12% in early and late lactation) and the milk yield obtained in response to the first OT injection significantly decreased from early to late lactation. Cisternal milk yield was similar in front and rear udder halves. However, owing to higher total yield, the cisternal milk fraction was lower in rear than in front halves. Cisternal milk yield and cisternal milk fraction were smaller in primiparous than in older cows. In a further experiment milk distribution in the bovine udder was evaluated after preceding teat stimulation and milk ejection. Teats of 12 cows were manually stimulated for 1 min at 15, 60 or 120 min before milking. Total milk yield was not significantly different with or without teat stimulation. However, cisternal milk yield and fraction were significantly higher in teat stimulated cows than in unstimulated controls but were similar whether cows were stimulated 15, 60 or 120 min before milking.

In two separate experiments, the effects of pulsationless milking and milking vacuum on the rate of keratin removal from the teat canal were determined. Sixteen cows were milked with or without pulsation for either a single milking or for eight milkings. Milking without pulsation removed 10% of keratin present before milking, significantly less than milking with pulsation, which removed 32%. After eight milkings (4 d) without pulsation, up to 20% more keratin had accumulated within the teat canal but the rate of keratin regeneration reduced significantly upon return to pulsation milking. In a second experiment, ten cows were milked at 45 or 55 kPa and with or without pulsation. Only the absence of pulsation significantly reduced keratin loss during milking. Keratin loss during milking appears to be controlled by liner compression rather than by the rate of milk flowing through the teat canal. Pulsationless milking may increase penetrability of the teat canal to bacteria by reducing the natural rate of keratin removal during milking and reducing the rate of keratin regeneration.

Teat orifice hyperkeratosis, a commonly observed condition in dairy cows, has been considered a consequence of machine milking and the degree of hyperkeratosis may be increased by a poor milking system. A fully illustrated technique is described which uses a scoring system from 0 for a perfect orifice to 5 for an orifice significantly enlarged with extensively protruding fronds of teat duct keratin. A range of scores found in 25 commercial dairy herds is presented. The scores have been averaged for each cow and the markedly skewed distribution corrected by a square root transformation. This scoring procedure allows comparative measures of hyperkeratosis within and between herds. An 8-fold difference (0·17–1·31) in herd average score was found. Within all herds the score increased with lactational age of the animals and peaked, for any lactation, some 3–4 months post partum, declining as the animals dried off. There was no significant relationship between mean somatic cell count and degree of hyperkeratosis at the herd level. This implies that such chronic pathological changes are unlikely to be related to the level of intramammary infection. It appeared that some hyperkeratosis is an obvious and probably natural response to milking and occurs in a significant proportion of animals in all herds although often only to a slight degree. Much more hyperkeratosis may be a measure of the performance and management of the herd. The genetic influence is unknown. Higher yielding cows will score higher as they milk for longer, but generally high scores may reflect consistent and possibly considerable overmilking. Hyperkeratosis may be an indicator of the quality of management and show the level of attention being paid to the welfare of the herd.

The distribution of albendazole (ABZ) and its main metabolites albendazole sulphoxide (ABZSO), albendazole sulphone (ABZS02) and albendazole 2-aminosulphone (NH2ABZSO2) were investigated in bulk milk and milk products after administration of a single oral dose of the drug (12·5 mg/kg) to 80 Laticauda sheep. An analytical method was developed for this investigation from an existing procedure used for the determination of these compounds in plasma and digesta samples. No traces of the parent compound or NH2ABZSO2 were found in milk or milk products, with the exception of the milk collected 36 h after treatment in which 89 μg NH2ABZSO2/kg was detected. Results indicated that ABZ was rapidly oxidized to ABZSO and then to ABZSO2. These metabolites were found at high levels (1–4 mg/kg) in milk collected within 24 h after treatment. Products derived from such milk also contained high concentrations of the two oxidized metabolites, including up to 5 mg ABZSO/kg in Pecorino cheese. Only small quantities of these two metabolites were found in milk collected during the second day after treatment (range 50–500 μg/kg). They were no longer detectable in milk, collected during the third day after dosing, nor were they found in products made from such milk. These findings confirm that the two polar metabolites ABZSO and ABZSO2 were efficiently excreted from the body. Considering that the established maximum residue limit for ovine milk is 100 μg/kg for ABZ plus its metabolites, our results confirmed the appropriateness of the currently prescribed withdrawal time (3 d) after the use of ABZ in lactating sheep. However, considerable levels of ABZSO were detected in milk collected within 24 h after treatment as well as in products and by-products derived from such milk. Owing to the known toxicity of the ABZSO, we stress the need for careful control to ensure adherence to the prescribed withdrawal time.

The effect of Staphylococcus aureus on detachment of bovine mammary epithelial cells in culture was examined. Mammary epithelial cells became detached from fresh monolayers following a 3 h incubation in the presence of Staph. aureus M60. Two different procedures indicated that cell detachment coincided with the S-phase of the cell cycle. The roles of proteinases, toxins and Ca availability in inducing cell detachment were examined. Addition of the proteinase inhibitor phenyl-methylsulphonyl fluoride (1 mM) to the culture medium prevented cell detachment. Addition of a combination of purified staphylococcal proteinases XVI and XVII-B to the culture medium of mammary epithelial cells induced cell detachment in the absence of Staph. aureus. Cell detachment may be caused by a staphylococcal proteinase. However, addition of Ca (10 mM) to the culture medium abolished Staph. aureus-induced cell detachment, despite the fact that proteinase activity was still apparently present. Isogenic mutants of Staph. aureus M60, expressing either ± or β toxins but not both, induced cell detachment, but to a lesser extent than the wild type. Thus, Ca and toxins play some role during cell detachment. Clones established from detached cells that were washed and replated showed the same susceptibility to Staph. aureus-induced cell detachment as the parental cells. This indicated that there is no subclone of mammary epithelial cells more sensitive to this effect.

Mineral acid casein (MAC) curd was subjected to a range of ionic strength, pH and temperature conditions to explore their effects on curd water-holding capacity, particularly the reversibility of shrinkage. The shrinkage of MAC curd on whey removal during the washing stage of casein manufacture could be attributed almost completely to the reduction in ionic strength and not specifically to either calcium or lactose removal. This shrinkage on whey removal during washing could not be reversed by adding whey back to the curd to attain the original ionic environment. In this sense it was irreversible. The pH during formation of MAC curd was more important than later pH adjustments in controlling curd water-holding capacity. The effect of a high precipitation pH in creating a tough, compact curd could not be reversed by subsequently decreasing the pH. However, the effect of a low precipitation pH in creating a soft, open curd could be partly reversed by subsequently increasing the pH. MAC curd shrank by 45% when the temperature was increased from 20 to 80°C. This temperature-dependent shrinkage was virtually fully reversible on cooling. It is suggested that the water-holding capacity of casein curd is governed largely by hydrophobic interactions and that once such interactions have occurred they cannot easily be disrupted by small changes in either pH or ionic strength.

Milk fat globule membranes (MFGM) were isolated from milk from cows injected intraperitoneally with dl-α-tocopherol acetate. The fatty acid composition and content, and the contents of tocopherols, retinol and β-carotene were determined and compared with the composition and content in the original cream sample. Intraperitoneal injection of 10 g dl-α-tocopherol acetate elevated the α-tocopherol content in the milk fat from 13–30 to 50–70 εg α-tocopherol/g milk fat 2–3 d after injection. The increase depended on the α-tocopherol status of the cow prior to injection. The concentrations of retinol and β-carotene in the milk fat were unchanged after the α-tocopherol injections. MFGM fatty acids made up 18–27 g/kg total fatty acids in the milk fat. However, the proportions of monounsaturated and polyunsaturated fatty acids were higher in MFGM than in total milk fat, while the proportion of saturated fatty acids was lower in MFGM (P < 0·001). Thus, the longchain polyunsaturated fatty acids in MFGM constituted ∼ 40–70 g/kg total milk fat. α-Tocopherol was the only fat-soluble vitamin detected in MFGM; γ-tocopherol, retinol and β-carotene were detected only in the cream. A significant relationship between α-tocopherol contents in cream and MFGM was found: (α-tocopherol in MFGM fatty acids) =–1652 × (1/ln(α-tocopherol in cream fatty acids)3)+ 97 (r = 0·857, P < 0·001) when the contents of α-tocopherol were expressed as εg/g fatty acid. According to this equation the upper limit for incorporation of α-tocopherol into MFGM is 97±5 εg/g MFGM fatty acids. Thus, under normal farming conditions the α-tocopherol content will be highest in MFGM. However, in cream with an α-tocopherol concentration < 15 εg/g cream fatty acids the concentration in MFGM will be lower and furthermore will decrease rapidly. The possible importance of this relationship in relation to the oxidation of milk fat is discussed.

The milk whey protein β-lactoglobulin has been isolated from ovine milk, purified and crystallized in a form suitable for X-ray crystallography. The crystals, which diffract to 1·9 Å resolution, belong to the trigonal space group P3121 with unit cell lengths a = b = 99·8 Å, c = 67·7 Å and unique angle γ = 120·0°. Although there have been many crystal forms reported for bovine β-lactoglobulin, none has been reported with these unit cell parameters. A preliminary native data set has been collected and a molecular replacement solution obtained, using the structure of dimeric bovine β-lactoglobulin as the search model. The importance of the ovine structure in relation to that of the bovine is discussed.

Nine organisms were isolated from separate pasteurized milk samples after they had been incubated at 6 °C for 5 d (European Union preincubated count, PIC), four from high count samples (> 5 x 106 cfu/ml) and five from low count samples (< 103 cfu/ml). When the organisms were harvested without overt stress being applied and subjected to a simulated PIC using UHT whole milk, all except one isolate gave comparatively high (> 106 cfu/ml) counts. The imposition of a heat stress at 50 °C prior to a simulated PIC resulted in a segregation of the isolates into those giving high and those giving low counts, which reflected the PIC values of the milk samples from which they were originally isolated. When the isolates were subjected to a cold stress (25 to 4 °C) and inoculated into nutrient broth at 4 °C, the high count isolates were found to have significantly (P < 0·05) shorter lag phases than the low count isolates.

Listeria monocytogenes and List. innocua were isolated from commercial soft ripened and blue-veined cheeses manufactured in France, mainly from Brie cheese made from unpasteurized milk. Five isolates were List. monocytogenes serotype 1/2 and two were List. innocua. Examination of Bleu d'Auvergne cheese with the cryoscanning electron microscope showed that many conidia spores were present in the blue veins in close contact with the cheese surface. There were few conidia spores in the Brie, mostly on the outside of the cheese but not in contact with the surface. High concentrations of free dodecanoic (lauric) acid (1·77–2·50 g/kg cheese) and tetradecanoic (myristic) acid (2·54–6·38 g/kg cheese) were found in the veins of the blue cheese, but concentrations in the white regions were much lower. Free lauric and myristic acids were not detected in the Brie cheeses. There was no difference in the overall fatty acid composition of the fat in the surface ripened and blue-veined cheeses, although higher concentrations of free medium-chain fatty acids were found in a blue cheese compared with a surface ripened cheese. The pH and fat content were higher in regions with obvious fungal growth, the blue veins of Fourme d'Ambert and the rind of Brie. Free lauric acid dissolved in butteroil inhibited multiplication in broth at pH 7·0 of a test strain of List. monocytogenes isolated from Bleu d'Auvergne. Some inhibition was seen with hexanoic, octanoic, decanoic and tetradecanoic acids. We suggest that the presence of localized concentrations of free medium-chain fatty acids (dissolved in the fat) in the blue veins of blue mould ripened cheese could act as natural preservatives and inhibit the growth of listerias in conditions where (if present), one would otherwise expect them to grow.

Plain yogurts (set type) fermented by three different starter cultures were subjected to different heat treatments (20 s at 72, 80 or 100 ·C, or 30 min at 60, 70, 80 or 100 ·C). DNA was extracted from each yogurt and analysed by agarose gel electrophoresis, by species-specific hybridization and by primer-specific polymerase chain reaction (PCR). Obvious degradation of DNA could be observed after heating at 80 ·C for 30 min and at 100 ·C for 20 s and 30 min. Identification of Lactobacillus delbrueckii using a species-specific hybridization fragment could be carried out in yogurt treated at 100 ·C for 20 s or for 30 min at lower temperatures. After treatment for 30 min at 100 ·C identification by hybridization was no longer possible. However, under the same conditions identification of starter microorganisms was still possible by primer-specific PCR, and this was demonstrated as an example for Streptococcus thermophilus.

During chill storage, cholesterol oxidation in feta cheese produced from bovine butteroil bleached at high temperature was compared with cholesterol oxidation in feta cheese produced from non-bleached butteroil. The bleaching was performed at two different temperatures, 265 and 280 °C, and the oil was bleached for 2·4, 3·8 or 4·3 min; a reference feta cheese was produced without bleaching. All cheeses were stored in brine at 4 °C, and cholesterol oxidation was measured during a storage period of 5 months. For the first 11 weeks of storage, the concentration of cholesterol oxides was comparable for the bleached feta cheeses, but on longer storage the concentration of oxysterols was highest in feta cheeses produced from the butteroil bleached at 280 °C. The bleaching temperature rather than the bleaching time affected cholesterol oxidation, which was minimal in the non-bleached reference cheese throughout the storage period compared with the bleached feta cheeses. 7-Ketocholesterol was found to be the dominant oxysterol in the feta cheeses at the end of the storage, comprising ∼ 50% of the total cholesterol oxides. In feta cheeses based on butteroil bleached at 265 °C, the concentration of 7-ketocholesterol ranged from 3·7 to 4·9 µg/g lipid at the end of the storage period, and in feta cheese based on butteroil bleached at 280 °C the concentration was 10·4–13·1 µg/g lipid. In the reference feta cheese the concentration of 7-ketocholesterol was 1·2 /µg/g lipid. There was no difference in yellowness, measured by tristimulus colorimetry as the Hunter b characteristic, of the feta cheeses bleached at 265 and 280 °C, and a small scale bleaching experiment with butteroil showed that it was possible to secure complete bleaching at temperatures down to 220 °C. We suggest that bleaching of butteroil for feta production should be performed at temperatures as low as possible in order to prevent cholesterol oxidation.