The effect of a switch level of 200 or 400 g/min for automatic cluster removers on milking performance and udder health was measured with 71 first lactation cows in their first 36 weeks of lactation and with 64 older cows in their first 12 weeks of lactation. Early removal of the milking unit decreased machine-on time by 0·5 min, increased average milk flow rate slightly, improved teat condition significantly and reduced the change in teat end thickness during milking of first lactation cows. Early removal of the milking unit did not affect milk yield or composition, and the incidence and prevalence of subclinical mastitis were the same in the two groups. Fewer older cows developed clinical mastitis in the group switched at 400 g/min, but this was not significant. It is concluded that the milking unit can be detached at a milk flow rate of 400 instead of 200 g/min without having a negative influence on milk yield. Machine-on time is shortened and teat condition improved, and udder health does not seem to be affected.

Bacteriology, somatic cell counts (SCO) and N-acetyl-β-glucosaminidase (NAGase) activity determinations were conducted on milk samples collected from does in three dairy herds with caprine arthritis–encephalitis virus (CAEV) infection. In two herds, CAEV-infected does were more likely to have a subclinical bacterial infection of the udder than CAEV-free does (P < 0·05). Does with CAEV but no bacterial udder infection had significantly greater mean SCO and NAGase activity than CAEV-free does without udder infection (P < 0·01). In two herds, changes in milk SCC and NAGase associated with CAEV infection were similar to those produced by coagulase-negative staphylococcal infections. The findings confirm that indirect indicators of bacterial mastitis infection may have reduced specificity in dairy goat herds with CAEV.

British Saanen dairy goats (n = 10) were treated with bromocriptine or vehicle from day 147 of pregnancy to day 4 post partum, a treatment duration of 8·8±1·7 d (mean ± SEM). The periparturient prolactin surge was abolished by this treatment, but there were no significant effects on plasma growth hormone or insulin concentrations. Lactogenesis was delayed in the bromocriptine-treated goats, milk yields being significantly depressed (P < 0·01) for the first week of lactation. Yields had recovered to control values by day 10 when prolactin concentrations were still significantly depressed. Mammary gland biopsies were taken on day 4 post partum from five animals in each group. Using this tissue, no significant differences could be shown in mammary morphology or DNA synthesis, but the RNA:DNA ratio was significantly reduced (P < 0·05). After week 1, there were no significant differences between bromocriptine-treated and control goats in milk yield, milk composition, udder volume, time of peak yield or persistence. The goats given short-term bromocriptine treatment at parturition showed prolonged effects on prolactin secretion, their seasonal prolactin rise being severely blunted (P < 0·001). A normal lactation is therefore not prevented in goats by a delay in lactogenesis, suppression of prolactin at parturition or the resulting prolonged depression of circulating prolactin. Goats in established lactation given bromocriptine for 8 d showed, by contrast, a rapid recovery of plasma prolactin concentrations within 5 d post treatment. Milk yield declined significantly (P < 0·03) compared with pretreatment values during and for 1 week after bromocriptine but then began to recover, with no significant change in vehicle-treated goats.

The functional significance of citrate in the mammary secretion of six sows was investigated during the second stage of lactogenesis (lactogenesis II) and established lactation. The changes in the concentrations of progesterone and lactose in the maternal blood, and lactose, Na and K in the mammary secretion, suggested that lactogenesis II began during the final day of pregnancy. The concentration of citrate in the mammary secretion of the sows during lactogenesis II was high and varied from 5·4 (SEM 0·5) mai at day 0·5 post partum to 6·8 (SEM 0·4) mM at day 1·5 post partum. There was a decline of ˜ 30% in the concentration of citrate in the milk of sows during the first week of lactation. These findings suggest that, in contrast to all other species studied previously, milk citrate is not a harbinger of lactogenesis II in the sow. However, the changes in the concentration of citrate in the mammary secretion of sows may reflect changes in the rate of de novo synthesis of fatty acids that take place in the mammary glands of sows during lactogenesis II and established lactation.

A study was undertaken of the heat exchange possible in a milk powder plant consisting of milk treatment, a four-effect evaporator fitted with a thermovapour recompressor and a spray drier fitted with a fluidized bed secondary drier. The study utilized the techniques of process integration analysis and grand composite curve matching. Of particular interest was the optimum utilization of vapours within the evaporator. It was shown that with a minor redesign of the evaporator, and utilization of some vapour in the milk treatment section of the plant, a 6% reduction in total energy consumption of the milk powder plant was possible. If heat exchange between inlet and outlet air of the spray drier was not considered practical, preheating spray drier air with vapour from the evaporator resulted in a 10% reduction in energy consumption. Other minor heat exchange possibilities were also revealed. It was concluded that the use of vapour from the evaporator, and increased steam consumption in the evaporator, may lead in some designs to decreased plant thermal energy consumption overall. As well as the process integration study, formulae are presented for calculating the change in thermal economy of an evaporator when vapour is extracted for use in other sections of the plant. The use of process integration studies needs to be given consideration in overall design of energy-intensive dairy plant.

Proteolysis during storage of UHT skim and whole milks processed by either direct or indirect systems has been studied. All the proteolysis indices determined (measurement of free amino groups, PAGE of caseins and PAGE and reversed-phase HPLC of the fraction soluble at pH 4·6) revealed greater proteolytic degradation during storage of skim milks compared with that of whole milks subjected to the same UHT treatments. Increased activities of both native milk proteinase and proteinases of bacterial origin were observed in skim UHT milks. The different behaviour of UHT skim and whole milks on storage would have to be taken into account in establishing the process conditions.

Rheological properties of whey protein concentrate (WPG) solutions were studied in steady shear, using a Bohlin VOR Rheometer, as a function of concentration, temperature, shear rate, shearing time, pH, salt type, salt concentration and solution age. At 22 °C and pH 7, the WPC solutions exhibited Newtonian behaviour up to a concentration of 10% total solids, pseudoplastic behaviour between 10 and 30% and time-dependent shear thinning at 35% and above. The apparent viscosity of solutions at 22 °C and pH 7 was linearly related to concentration up to 8%. The effect of temperature on apparent viscosity in the range 5–60 °C was closely described by the Arrhenius equation. The viscosities of WPC solutions were independent of solution age in the pH range 4–8 at all concentrations up to and including 20%, the precise pH range narrowing as concentration increased. At pH values above or below this range apparent viscosity became dependent on both pH and solution age, the age effect becoming more marked at higher WPC concentrations. Apparent viscosity at pH 7 increased markedly with both CaCl2 concentration and solution age at concentrations above 0·6 M-CaCl2, the age effect in this case increasing with CaCl2 concentration. In contrast, NaCl concentrations of up to 0·8 M-NaCl had little effect on apparent viscosity. The rheological behaviour of WPC solutions changed from time-independent to time-dependent shear thinning at high concentration, at extreme pH values, at high CaCl2 concentration (after ageing) and on heating to above ∼ 60 °C. This change is considered to be caused by the formation of structure in solutions; a 40% solution (at 22 °C and pH 6·75) exhibited classic thixotropic behaviour in a step–shear rate experiment.

The interaction of lactoferrin from human and bovine milk with the human promonocytic cell line U937 has been studied. Both human and bovine Fe-lactoferrins bound to the cells. Binding of bovine lactoferrin was inhibited by excess bovine lactoferrin but not by human lactoferrin, suggesting that the binding mechanisms for the two proteins are different. Binding of human but not bovine lactoferrin was inhibited by bovine lactoperoxidase, while a 20-fold excess of human IgA inhibited binding of human but not bovine lactoferrin. Human and bovine α-lactalbumins, bovine β-lactoglobulin, and human lysozyme had no effect on binding of lactoferrin from either species. Samples of bovine Fe- and apolactoferrin in capillary tubes were exposed to temperatures of 72 °C for 20 s, 85 °C for 20 min or 137 °C for 8 s. All the heated samples inhibited binding of native Fe- and apolactoferrin, though to a lesser extent than the native proteins. Both heated and native lactoferrins enhanced [3H]thymidine incorporation by U937 cells, except for Fe-lactoferrin heated at 85 °C for 20 min, which was inhibitory. These results suggest that heat treatment of lactoferrin under conditions used for industrial processing does not greatly affect its ability to interact with and stimulate monocytic cells, and that other milk proteins in general do not interfere with lactoferrin–monocyte interactions. It may thus be feasible to incorporate biologically active lactoferrin into infant formulas.

A total of 204 psychrotrophic isolates from raw ewes' milk (hand and machine milked) were identified by conventional methods. In addition, a numerical taxonomic study was conducted on 180 of these isolates and 19 reference strains. Three of the isolates were yeasts. Using identification schemes, 54 isolates were assigned to genera of Gram-negative aerobic rods (Pseudomonas, Acinetobacter, Flavobacterium, Moraxella and Psychrobacter), 48 were Enterobacteriaceae (Entero-bacter, Hafnia, Klebsiella, Citrobacter and Serratia) and one was identified as Aeromonas hydrophila. The 98 Gram-positive isolates were identified as Enterococcus, Streptococcus, Leuconostoc, Lactococcus, Bacillus, Staphylococcus, Micrococcus, Aureobacterium, Kurthia and Microbacterium. At the 82% similarity level (SSM), 18 clusters were formed. Cluster I included 34 strains of Lactococcus, Streptococcus and Leuconostoc. Most of the 35 strains in cluster II were Enterococcus. Clusters III and IV were identified as Kurthia and Microbacterium respectively. Cluster V was identified as Aureobacterium and cluster VI consisted of coagulase-negative staphylococci. Gram-negative isolates formed 12 clusters: Aeromonas (one cluster), Enterobacteriaceae (two clusters), Flavobacterium (two clusters), Pseudomonas and Psychrobacter immobilis (three clusters) and Acinetobacter (four clusters). Non-motile variants of Ps. fragi were found. Enterococcus and Enterobacteriaceae did not have significant spoilage properties. As expected, Gram-negative aerobic rods were proteolytic and/or lipolytic even at low temperature. Contamination with certain types of psychrotrophs (Gram-negative aerobic rods and enterococci) seemed to be associated with the milking method. The isolate of Aes. hydrophila had properties associated with virulence.

After treatment with mitomycin C, 12 of the 120 strains of the French Collection of Lactic Acid Bacteria (CNRZ) belonging to the species Streptococcus salivarius subsp. thermophilus were found to be inducible and lysogenic. The corresponding temperate phages were multiplied on indicator strains and further characterized. It is noteworthy that some of the indicators were themselves lysogenic. The temperate phages belonged to Bradley's group B, or to the Siphoviridae family of the International Committee on Taxonomy of Viruses. Seven of them were shared among the two protein profiles previously established for virulent phages of Str. salivarius subsp. thermophilus. Seven different DNA restriction profiles were found for ten native temperate phages examined just after mitomycin C induction. Genome sizes varied from 40 to 45 kb and were classified into four related homology groups by DNA cross-hybridization, but there was no clear-cut relationship with the protein clusters previously shown. DNA homology with representatives of virulent phages was also found. The DNA restriction profiles of seven native temperate phages, examined just after mitomycin C induction of the lysogenic hosts, were noticeably different from those of the corresponding phages once they had been propagated on lysogenic indicators. Moreover, the host range of the latter phages was extended to a greater number of sensitive strains. The possible role of lysogenic strains of Str. salivarius subsp. thermophilus in the occurrence of phage outbreaks affecting this dairy streptococcal species is discussed.

The proteolytic specificity of chymosin (EC 3.4.23.4) on bovine αs1-casein at 30°C in phosphate buffer, pH 6·5 and at pH 5·2 in the presence of 5% (w/v) NaCl was investigated. Peptides (pH 4·6-soluble) were isolated by reversed-phase HPLC and identified from their amino acid sequence; the identity of some peptides was confirmed by mass spectrometry and/or amino acid composition. The small peptides produced at pH 6·5 were Arg1–Phe23, Phe24–Phe28, Phe24–Leu40(?), Phe150–Phe153, Phe150–Leu156, Tyr154–Tyr159, Tyr154–Trp164, Asp157–Trp164 and Tyr165–Trp199. The same peptides, except Tyr154–Trp164, were produced at pH 5·2 in the presence of NaCl and, in addition, the peptides Arg1–Leu11, Phe24–Phe32, Lys102–Leu142, Ala143-Leu149 and Tyr165-Phe179. The rates of production of individual peptides differed under the two conditions studied but Arg1-Phe23 and Tyr165–Trp199 were the first and second peptides produced under both conditions. Pathways are proposed to interpret the proteolysis of αs1-casein in solution under the conditions of this study.

Comparing the primary sequences of bovine and ovine milk proteins, some short peptide fragments are cow-specific, in particular the 141–148 fragment of bovine αs1-casein, which is deleted in its ovine counterpart. The 140–149 peptide was chemically synthesized on a solid phase matrix and directly used as an immunogen to produce polyclonal monospecific antibodies in rabbits. These antibodies recognized this fragment both on the peptidyl resin and in the native protein. They appeared to be monospecific, since no antigen–antibody complex was formed with homologous ovine or caprine proteins. Subsequently, a competitive enzyme-linked immuno-sorbent assay was successfully developed for the detection of defined amounts of cows' milk in sheep's milk from 0·125 to 64% (v/v) and in cheese from 0·5 to 25% (v/v) that was not influenced by heat treatment of milk or the degree of ripening of cheese.

Listeria monocytogenes survived and, under most conditions, multiplied when inoculated directly into the cheese milk of laboratory made Camembert cheeses. The rate and extent of growth was reduced at lower storage temperatures. Significantly higher rates of growth occurred at the surface compared with the centre of the cheeses, and these were probably associated with increased pH and proteolysis at the cheese surface due to the mould ripening process. Similar results were obtained with Camembert cheeses surface inoculated after manufacture. There was also temperature-dependent growth of List, monocytogenes on a range of inoculated commercially manufactured soft cheeses. Significant growth occurred in Cambazola, French and English Brie, blue and white Lymeswold, French Camembert and Brie with garlic. Little if any growth occurred in blue and white Stilton, Mycella, Chaume and full fat soft cheese with garlic and herbs at the temperatures examined.

Sixteen rennet casein samples and the corresponding sixteen cheese analogues made from these caseins were obtained from a local processor. Following storage at 4°C for 6 months, pH 4·6-soluble N contents of the cheese analogues increased, while αs- and β-casein contents, elastic moduli and apparent relaxation times decreased. The β-casein and pH 4·6-soluble N contents of the 6 month old products were significantly correlated, both were significantly correlated with the plasmin (EC 3.4.21.7) contents of the corresponding rennet caseins from which the analogues were made and all three were significantly correlated with the rheological properties of the stored analogues. Of the compositional characteristics, only percent moisture in non-fat substance and percent fat in dry matter were significantly correlated (P < 0·05) with any of the proteolytic or rheological properties. The sixteen cheese analogues were also assayed at one time, when they ranged in age from 1 to 35 weeks, and highly significant interrelationships between plasmin activity, proteolysis and rheological properties were established. The results indicate that the plasmin content of rennet caseins had a significant influence on the proteolytic and rheological changes that occurred during storage of cheese analogues made from these caseins.