Twin-bearing ewes were treated with epidermal growth factor (EGF) to determine its effect on mammogenesis and resultant milk production and composition. The EGF was infused intravenously at a dose rate of O5 mg/d in 300 ml saline between days 117 and 139 of gestation; control animals received placebo infusions of saline. All animals then received continuous infusions of 300 ml/d saline on days 139–144. Following parturition 1–5 d later, ewes were milked by hand for 10 d and thereafter were machine-milked until day 16 of lactation. At this level of treatment, EGF was not detected in the circulation during infusion and feed intake was not affected. All ewes gave birth to healthy twin lambs. There were no effects of EGF on birth weights of lambs, live weights of ewes or lengths of gestation. An EGF immunoreactive material was detected in the mammary secretions of control ewes at a mean concentration of 2 μg/l on day 1 of lactation. Two ewes had detectable levels on day 2, but none was found in the milk thereafter. In the EGF-infused group, concentrations of EGF in colostrum were ñ 10 times higher than in the control ewes on day 1 of lactation and EGF was detected in mammary secretions on day 2 but not in subsequent milk samples. A range of 0·3–0·5% of the EGF infused appeared in mammary secretions over the first 2 d of lactation. No other differences were observed for colostrum composition, subsequent milk yield or composition between the two groups of ewes indicating that mammary gland development and function were unaffected. The levels of EGF observed in the mammary secretions of treated and control ewes indicate that the mammary glands accumulate and store EGF in the pre partum period.

Four goats were studied from the end of their second lactation. One mammary gland of each goat was dried off just prior to the start of the third gestation, whilst the other gland was milked throughout gestation, with no dry period. At the end of gestation the continuously milked gland was significantly smaller than the gland that had been allowed a dry period. However, this difference did not persist beyond parturition and there was no significant difference between the milk yields of the two glands in the next lactation, although the continuously milked gland tended to have the higher yield. At 18 weeks of lactation, mammary parenchyma weight and secretory cell number were significantly greater in the continuously milked gland, but mammary enzyme activities did not differ between the two glands.

Three types of liner (wide bore tapered, wide bore and narrow bore) were compared in a change-over design experiment comprising three 3-d periods and using six lactating Holstein Friesian cows with a wide range in milk flow rate and teat dimensions. Vacuum levels measured within the liner showed a characteristic pattern of three distinct phases: 1, a mouthpiece chamber (MPC) vacuum that fluctuated with vacuum beneath the teat; 2, a stable MPC vacuum that coincided with the period of peak milk flow and 3, a MPC vacuum that fluctuated with pressure changes in the pulsation chamber and coincided with the period of no or reduced flow. Of the three liners examined, the Gascoigne 1030A (wide bore tapered) induced the highest MPC vacuum (29·4 ± 2·23 kPa, mean ± s.e.m), significantly higher (P < 0·01) than the Alfa-Laval 960000–01 wide bore (23·5 ± 2·32), regardless of teat size and milk flow rate. The Alfa-Laval 7275737–01 (narrow bore) gave a significantly lower value (16·5 ± 1·96) than either of the others (P < 0·001). It was not possible to link absolutely raised MPC vacuum to cow discomfort and teat trauma but circumstantial evidence encourages this view. Narrow teats in combination with slow flow rate appeared to exacerbate MPC vacuum and, because milking time for such animals was protracted, teats were exposed for longer periods.

The performances of falling film evaporators used in the New Zealand dairy industry for concentrating skim milk, whole milk and buttermilk were evaluated by determining (1) the kg steam used per kg water evaporated, and (2) the heat transfer coefficient of each pass in the evaporators. A computer program was used to calculate the results. The heat transfer coefficients varied from 0·3 to 3·2 kW/m2 per °C and the steam consumption from 0·4 to 0·09 kg steam/kg evaporation. The viscosity of the feed and the momentum of the vapours passing down the tubes were found to be the main factors controlling the heat transfer coefficient. A correlation between the heat transfer coefficient and these factors is presented. Other factors likely to have an influence on the performance are discussed.

The fouling of an inorganic microfiltration membrane with an average pore diameter of 0·2 μm obtained in static conditions with milk, acidified milk and acid coagulum was examined using scanning electron microscopy. The structure and porosity of external fouling related to the pH of the milk accounts for the performance and efficiency obtained in microfiltration. Electrophoretic analysis of permeate, characterized by lack of casein, shows that the deposit plays a fundamental role in mass transfer through filter layers. Variations in the physicochemical properties of casein as a function of pH at 50 °C were used to account for the development of the structure of fouling, which comprised three main states: (i) dense deposit of juxtaposed micelles, (ii) loose network formed by chains made up of bonded protein aggregate, (iii) irregular protein aggregate leading to high-porosity deposits. The presence of a protein film strongly adsorbed on the membrane layer of alumina particles is demonstrated.

The functioning of an inorganic microfiltration membrane (Membralox-SCT) with an average pore diameter of 0·8 μm, used for processing milk, acidified milk and lactic coagulum, was studied using dynamic and static conditions. Milk processing (pH 6·62) gave acceptable rates of protein retention but at low flow rates. Study of the effect of operating parameters during microfiltration of coagulum led to determination of optimal operating conditions leading to satisfactory performance and adequate retention rate. The results are explained using a model of the formation and development of internal and external fouling of a mineral membrane. Observations using scanning electron microscopy related to the pH of milk were used to verify the model by showing that internal fouling occurred only when the pH was higher than 5·50. This internal fouling was closely linked with the physicochemical state of milk proteins. Indeed, the fouling particles visualized at the alumina grains of the membrane support changed progressively from individual micelles (pH 6·62) to a chain or clustered structure (pH 5·60). Electrophoretic study confirmed this observation and showed that casein was present in milk permeates (pH 6·62) but not in coagulum permeates (pH 4·40).

Recombined concentrated milks (18% SNF, 8% fat) at their natural pH and at pH values in the range 6·28–6·68, made with powders subjected to different preheat conditions (high heat (85°C, 30 min), indirect UHT (120°C, 2 min) and direct UHT (120°C, 2 min)), were sterilized at 120°C for 13 min. The heat stabilities of recombined concentrated milks were dependent on preheat treatment. Ca2+ activity and pH of sterilized recombined concentrated milks, measured l h after sterilization, were lower than those of corresponding unsterilized recombined concentrated milks. The magnitude of the decreases in Ca2+ activity and pH induced on sterilization were dependent on the pH of the unsterilized recombined concentrated milk but were not markedly influenced by the type of preheat treatment applied during powder manufacture. The results suggest that differences in heat stability of high heat, indirect UHT and direct UHT powders are unlikely to be due to Ca2+ activity.

A turbidimetric method, based on light reflection, was used to study acid coagulation of reconstituted skim milk at low temperature. Capillary viscosimetry, gelograph and laser granulometer techniques were also employed. Acidification of milk was produced by hydrolysis of glucono-δ-lactone. The general shape of the turbidimetric signal as a function of pH or time can be divided into three stages: a lag phase followed by a significant decrease and then a final rise. Two factors have a great influence on the development of milk turbidity, pH and temperature. Dynamic viscosity measurements can be related to the turbidimetric signal while laser granulometrie measurements cannot be correlated with changes in turbidity: the micelle size distribution remains constant until the first signs of gelation. As previous work showed, dynamic viscosity diminishes with acidification until a particular pH is reached (pH 5·9 at 15°C and pH 5·75 at 20°C). We have related this latter period to the turbidimetric lag phase. As milk turbidity became lower than its initial value (pH 5·75 at 15°C and pH 5·55 at 20°C), dynamic viscosity increased significantly. The release of material from micelles (β-casein and Ca) could explain this phenomenon. In the same way, further increase of turbidity at a particular pH value (pH 5·3 at both 15 and 20°C) coulcl be partly due to the reincorporation of soluble casein monomers in the micelle framework. As the onset of gelation was approached, turbidity still increased as a result of gel network formation.

Bovine milk Hydrophobic fraction of proteose-peptone was prepared by hydrophobic interaction fast protein liquid chromatography. This method has several advantages such as high rapidity, simple good reproducibility and less denaturation. The proteose-peptone was eluted from a TSK-Phenyl-5PW column with a 1 M-0 M ionic strength gradient of NaH2PO4, pH 6·8, using a 6 ml/min flow rate for 56 min. The quantity of protein injected was 62·5 mg; however, it could be increased up to 100 mg. The elution order was β-CN-4P < BSA (1·6% of total N) < β-CN-5P < β-CN-1P. The hydrophobic fraction was obtained in pure water at the end of the gradient (17·3% of total N). A proteose-peptone cartograph was achieved by bidimensional electrophoresis. This hydrophobic fraction represented three principal zones of Mr 30000–28000, 19000 and 11000, which were respectively composed of 13, 4 and 2 principal spots distributed between 4·9 and 6·1 isoelectric points (IP). These spots corresponded to glycoproteins. ·7, 5·0 and 5·1 IP which migrated to Mr 18000 while β-CN-1P was identified as Mr 9000 in two spots of 5·1 and 5·3 IP.

Skim milks were prepared from skim milk powder at several concentrations between 10 and 25% total solids and portions were pH-adjusted to between pH 6·3 and 7·1 and heated at 120°C. After ultracentrifugation (88000 g for 90 min), the supernatants were analysed using gel electrophoresis to determine the concentrations of β-lactoglobulin, α-lactalbumin and κ-casein. The dissociation of κ-casein from the micelles was dependent on both the pH and the total solids content of milk before heating. Both higher pH (in the range 6·5–7·l) and higher concentration increased the extent of dissociation. A further series of samples were heated for 2–11 min at 120°C at pH 6·55. κ-Casein dissociation increased with concentration and with heating time. It was concluded that as the milk increased in concentration, the pH at which micellar κ-casein dissociated on heating was lowered.

A total of 555 milk samples was collected from 53 Holstein cows for 1 year. Samples were analysed for N-acetyl neuraminic acid (NANA) content, κ-casein content and somatic cell count. The extent of glycosylation of κ-casein was estimated through the NANA content of κ-casein in each milk sample. The overall mean value for the NANA content was 63·6 ± 20 μg/mg of κ-casein with a range of 23–166 μg/mg. Least squares analysis showed significant (P < 0·01) effects of parity, test day, stage of lactation, phenotype for κ-casein, somatic cell count, and cow within phenotype. The NANA content of κ-casein decreased with increasing parity number and increased significantly when somatic cell count was above 200000 cells/ml. After reaching a minimum value between 2 and 3 months after calving, the NANA content of κ-casein increased during the later part of the lactation. NANA content was higher in the milk of cows phenotyped AB for κ-casein than for cows phenotyped for κ-casein AA, thus suggesting that B variant is more efficiently glycosylated than A variant.

Preparations of total human casein and its individual fractions were isolated for production of specific polyclonal antibodies. Immunization procedures used differed in the schedule for antigen administration, antigen concentrations, degree of additional purification, and modification of the size of molecules. Immunoprecipitation techniques failed to provide an unambiguous proof of the presence of antibodies to human milk caseins in antisera even after immunization of animals phylogenetically considerably different from man. Immunoblotting, however, allowed antibodies to β-casein to be identified and compared with available monoclonal antibodies.

The psychrotrophic bacterial flora of milk was examined after aseptic hand milking. A total of 409 strains were tentatively characterized and classified into 17 groups by a reduced set of tests and cluster analysis. Lipolytic organisms (53·7%) exceeded proteolytic organisms (29·6%), and a reported predominance of oxidase-positive organisms (54·5%) was not found. Gram-negatives were mainly Entero-bacteriaceae, Flavobacterium, Acinetobacter and Pseudomonas. In the Gram-positive groups Micrococcaceae were the most abundant (44·4%) followed by coryneforms (16·3%). Only two of seven commonly used disinfectants acted differently with Gram-positive and Gram-negative organisms (P < 0·01), although in general Gram-positives were more resistant than Gram-negatives.

Several strains of Lactococcus lactis subsp. lactis, Lactobacillus casei and Lactobacillus plantarum isolated from traditional goats' cheese have been studied for titratable acidity, proteolysis in milk and enzymic activities. Aminopeptidasc activities were measured with whole cells and cells permeabilized with Triton X-100. Caseinolytic activity was investigated using electrophoresis in polyacrylamide gel with sodium dodecyl sulphate. Lc. lactis subsp. lactis had a level of proteolytic activity in skim milk greater than that of Lb. casei, while this activity in Lb. plantarum was very low. Alanine aminopeptidase activity was almost non-existent for all strains tested, while lysine aminopeptidase activity appeared to be of fundamentally intracellular origin. Leucine aminopeptidase activity was also greater in cells that had been permeabilized than in whole cells for Lb. casei and Lb. plantarum. Lc. lactis subsp. lactis leucine aminopeptidase activity was greater in whole cells. No significant hydrolysis of casein was found with Lb. casei I FPL 725 and Lb. plantarum IFPL 722 permeabilized with Triton X-100 after 24 h incubation with whole bovine casein.