Deflector shields were inserted in the teatcup to prevent ‘impacts’ against the teat end, and their effect on the rate of new udder infections was studied on 15 commercial dairy farms in Britain and 16 in Australia. Small metal shields were fitted between the liner barrel and short milk tube of 2 teatcups in each cluster in a milking installation so that all cows in a herd always had the same 2 quarters shielded. Half-udder comparisons were made using 1039 cows in the British herds and 1268 in the Australian herds. Herds were quarter-sampled for cytological and bacteriological examination when shields were fitted at the start of the experiment and again after 6 months. The shield effects were similar in the 2 experiments. The combined results from the 31 farms showed that 10·5% fewer quarters became infected when protected by shields (P < 0·05). In the 1287 cows that had no infected quarters at the start of the trial, 15% fewer quarters became infected when protected by shields (P < 0·01). The shield effect was mainly confined to hind quarters in which 23% fewer shielded quarters became infected (P < 0·001). The small reduction of 2% in forequarters was not significant. In the 16 herds in which post-milking disinfection of teats was practised, shielded quarters had 23·5% fewer new infections than unshielded quarters (P < 0·01). In 6 British herds milked in installations classed as non-standard, shielded quarters had almost 50% fewer new infections than the unshielded quarters (0·05 < P < 0·10). The results provide evidence of a milking machine effect, at varying levels of intensity, to increase new infection rates on all or most farms. Control of this machine effect could lead to substantial reduction in new infections in some herds and a modest reduction in most.

The teats of 18 cows were externally exposed to infection with mastitis organisms by dipping them daily for 1 or 2 weeks in a mixed suspension of Streptococcus dysgalactiae and Str. uberis at the start, the middle or the end of the dry period. The teat sinuses of quarters which remained uninfected after external exposure at the beginning or the middle of the dry period were then infused with the same strains of streptococci. Of the 9 quarters infected following external exposure 8 occurred in animals exposed at the start and one in the middle of the dry period. Thirty-six new infections occurred after infusion of bacteria into the teat sinuses of 38 quarters. In a further trial with 10 cows, Staphylococcus aureus and Str. zooepidemicus were inoculated into the distal 3 mm of the streak canals of 5 cows immediately after drying-off and into those of 5 cows which had been dry for 28 weeks. Animals were slaughtered 48 h later and infection determined by teat puncture. Five infections occurred in cows which were at the start of the dry period and only one in the cows dry for 28 weeks. It is suggested that these differences in the rates of new infection between the early dry period and a very extended dry period are due to differences in the ease with which bacteria can penetrate the teat canal. At the later stage bacterial growth through the teat canal appeared to be inhibited.

An iodine teat skin disinfectant tested in lactating cows over a range of concentrations, 100 to 10 000 mg available iodine/1 (mg avI/l) was found bactericidally effective against Staphylococcus aureus when containing 1000 mg avI/l or greater. Against Streptococcus dysgalactiae 5000 mg avI/l or greater was bactericidally effective.

The addition of glycerine to a disinfectant containing 5000 or 1000 mg avI/l at levels of 225 ml/1 and 105 ml/1, respectively, resulted in a reduction in bactericidal efficacy of the disinfectant. Emulsified paraffin added at concentrations of between 50 and 500 ml/1 had no effect on the efficacy of the 5000 mg avI/l disinfectant, but the addition of 200 ml/1 emulsified paraffin to a 1000 mg avI/l disinfectant significantly reduced its efficiency. Iodine disinfectants containing emulsified paraffin phase separated rapidly during storage, and the bactericidal efficacy of the phases differed significantly and diminished with time.

Use of an iodine teat dip containing 5000 mg available iodine/l (mg avI/l) resulted in a significant reduction in the number of new Staphylococcus aureus infections in a lactating herd, while no significant reduction was found with a disinfectant containing only 1000 mg avI/l. When Streptococcus dysgalactiae was used as the challenge organism, the rate of new infection was extremely low, and no reduction in levels of new infection were found with either disinfectant. The pathogenicity of the Str. dysgalactiae strain was high, as 60 % of the quarters becoming infected produced clinical symptoms.

Teat dipping of lactating cows with either 1000 or 5000 mg available iodine/; (mg avI/;) solution and thoroughly washing and drying of the teats before sampling resulted in levels of 70 and 99 µg avI per quarter per milking respectively. Without any pre-milking udder preparation prior to sampling the levels of iodine recorded were 143 and 291 µg avI per quarter per milking respectively. Some systemic transfer of iodine from the teat skin to the milk was observed, but the bulk of iodine residue in milk was of direct teat skin origin.

Differential counts of electron microscope sections of cell pellets isolated from bovine udder secretions showed that no secretory epithelial cells and very few ductal epithelial cells were present at any stage. The predominant cell type was the macrophage in dry and lactating cows or the polymorphonuclear leucocyte (PMNL) in colostrum. Lymphocytes were also present but no plasma cells were found. The macrophages took up polystyrene latex particles (as did the PMNL) and adhered toglass in culture. Neither macrophage-nor PMNL-rich cell suspensions produced any increase in free fatty acid levels when incubated with fresh milk.

In 2 experiments, chloroform was introduced into the rumen of lactating goats given a mixture of 40% chopped hay and 60% barley-based concentrates. The effects on food intake, apparent digestibility, rumen fermentation and the yield and composition of milk were measured. In expts 1 and 2 food intake was reduced by 7% and less than 1% respectively. There were no significant effects on apparent digestibility in expt 1, but there were significant increases in the apparent digestibility of the dry matter and organic matter in expt 2. The results of in vitro determinations suggested that the loss of energy in combustible gas was reduced by 52 and by 25% in expts 1 and 2 respectively. As a result of these changes, the metabolizability of the dietary energy was increased by 2·1 and 4·8% respectively. In both experiments, the total volatile fatty acid concentration in the rumen was reduced when chloroform was added and there were changes in the molar proportions of the individual fatty acids, principally a reduction in acetic acid and an increase in propionic acid. Milk yield was not affected, but the fat content of the milk was reduced and, in expt 1, the protein content was increased.

The increase in unesterified fatty acid content of unpasteurized bulk milk in storage at 4 °C in the presence of known effectors of bovine milk lipoprotein lipase originating from bovine serum was studied. Bovine serum and high density lipoprotein (HDL) caused an increase in developed unesterified fatty acid levels whilst lipoprotein-free serum, apo-HDL, all individual apo-HDL tested, and the unfractionated C-peptide fraction were without lipolytic effect. In the presence of HDL-lipids, 2 C-peptides stimulated considerable lipolysis, as did the combination of HDL-lipid with unfractionated C-peptides. These characteristics of unesterified fatty acid development could be duplicated in milk whose endogenous lipolytic activity had been destroyed by heat treatment (75 °C for 5 min) and then restored by addition of purified bovine milk lipoprotein lipase. Radioactively labelled glycerol trioleate in milk was not hydrolysed in the same way as milk fat on the addition of serum liproproteins.

Casein composition in Friesian herd milks was examined by quantitative column chromatography on hydroxyapatite. Whole casein was resolved into 5 fractions: (1) γ-casein + para-κ-casein; (2) κ-casein + unidentified chymosin-resistant components; (3) unidentified minor protein; (4) β-casein; (5) αs1,0- + minor αs-caseins. Protein in fractions 1, 2, 4, 5 was measured by ultraviolet spectrometry, using appropriate specific absorption coefficients. The quantitative contribution of chymosin-resistant components to the κ-casein fraction was measured by a method involving hydroxyapatite chromatography of chymosin-treated whole casein. Compositional analysis was carried out throughout a lactation cycle on a total of 24 casein samples from the milks of a winter/spring calving and autumn-calving herd. Average composition (expressed as % total casein), which was similar for both herds, was 48·7% αs-, 33·8% β-, 4·9% γ-, 9·5% κ- and 3·2% unidentified components. Lactational effects on composition were also similar for both herds and were most pronounced in late lactation where increases were recorded in γ-casein and unidentified components, and decreases in β- and αs-caseins. Fluctuations in κ-casein proportions were small and slightly higher values were obtained in early and late lactation. Casein composition also appeared to be affected to some extent by season, as shown by differences in the proportions of αs-caseins and unidentified components between mid-lactation milks from the 2 herds. Compositional variations resulted partly from the action of milk proteinase on β-casein and also, apparently, from differences in relative rates of protein biosynthesis.

The content and composition of protein in milk samples from creameries in south-west Scotland were determined over a period of 12 months. The composition of the whole casein was expressed in terms of αsl-, β-, κ-, αs2- and γ-caseins, and that of the total milk serum protein in terms of β-lactoglobulins (β-lg), α-lactalbumins, bovine serum albumin, and a mixture of immunoglobulins, proteose-peptone component 3 and lactoferrin (IPL). Concentrations of the individual caseins varied appreciably and for most, concentration was closely correlated with and showed the same seasonal pattern as total casein concentration. Concentrations of the milk serum proteins also varied but only those of β-lg and the IPL fraction were closely correlated with that of total milk serum protein and seasonal trends were not marked. Relative amounts of the individual proteins, on the other hand, showed smaller variations and so throughout the experimental period the milks contained a protein complex of comparatively constant composition. Because of this comparative constancy it would appear that seasonal variations in milk properties in south-west Scotland are unlikely to be determined to a major extent by milk protein composition, but could be more affected by protein concentration.

Bovine milk systems were analysed for adenosine 5′-triphosphate (ATP) using the luciferase-ATP reaction in a liquid scintillation counter. Approximately 0·2 µmol ATP/1 milk serum were evident both in whole milks and the corresponding skim-milks. ATP was not detectable in skim-milk ultrafiltrates. These findings indicated that ATP was present in a non-dialysable portion of skim-milk. Centri-fugation of whole milks from individual cows at 5500 g for 15 min at 10°C yielded skim-milks essentially devoid of somatic cells and bacteria. However, the ATP in the skim-milks decreased by less than 20% compared with the whole milks indicating that the calcium phosphate-citrate (CPC)–caseinate micelles were the source of the ATP. ATP was not detectable in colloidal phosphate-free milk, from which CPC had been removed, confirming that the ATP was sequestered in the constituent CPC. Likewise, the occurrence of significant amounts of Mg, another potent stabilizer of amorphous calcium phosphate (ACP) in other biological systems, was confirmed in the colloidal phosphate of milk. From 0·13 to 0·31 µmole ATP/1 (mean, 0·23) was found in the 9 milk samples studied. The discovery of small but appreciable levels of ATP in the CPC of milk provides further evidence for the analogy previously shown to exist between the CPC complex of milk and the ACP which accumulates in mitochondria. The latter has been postulated to provide an essential precursor for crystalline bone salts to form in ordered calcification processes. The implications of these findings in the biosynthesis of milk are briefly discussed.

The 4 major caseins, A1, A2, B1, B2, from rat milk have been isolated and analysed. From molecular weight determination, amino acid and phosphorus analyses and N-terminal sequence determination, A1 and A2 are concluded to possess similar peptide chains as do B1 and B2, with the individual fractions within each of these 2 groups differing only in their sialic acid content.

Mol. wts of approximately 22000 and 38000 were found for A1–A2 and B1–B2 respectively. The amino acid sequence of the first 13 residues of A1–A2 has been partly established. Components A1 and A2 appeared to be homologous with bovine β-casein, whereas B1 and B2 were different from any known casein, especially in their molecular weight.

Two stages of gelling by the milk-clotting enzymes chymosin and pepsin were studied at different milk protein concentrations, using milk retentates. In each case, enzymic velocity versus protein concentration described a standard hyperbola. According to the experimental conditions such as pH and type of enzyme, which changed the enzyme concentration used, either the quasi-linear part of the hyperbola was observed, or the velocity hardly increased and tended to a limiting value. Gelling occurred with a lower degree of proteolysis of κ-casein when the protein concentration increased but a minimum proteolysis (1% of total nitrogenous matter content) was required for aggregation to take place. Gelling time varied with the protein concentration, the pH and the enzyme concentration. The final degree of proteolysis of κ-casein was the same whatever the substrate concentration used.

Binding isotherms for the calcium ion–αsl-casein system have been measured, as functions of ionic strength, temperature, and pH, and the isotherms have been analysed in terms of binding constants modified by substitution effects. The results demonstrate that the strength of binding is increased with increasing temperature and decreased by increasing ionic strength or decreasing pH, all of which may be explained semi-quantitatively. Parallel studies on the precipitability of the αsl-casein–Ca2+ complexes showed that there is considerable variation in the extent of calcium binding required to initiate precipitation of the protein, and in the calcium concentration necessary to achieve the required extent of ligand binding.

Hydrophobic surface areas of αs1- and κ-casein polymers and αs1-casein: κ-casein complex were estimated by the salting-out technique using various salts according to the theory of Melander & Horvath (1977). Calculated hydrophobic surface areas of αs1, κ-casein polymers and αs1-casein: κ-casein complex were 1976, 3571 and 2989 Å2 respectively. Assuming that κ-casein polymer dissociated into 4 particles in complex formation and that 1 mole of αs1-casein: κ-casein complex was produced from 2 mole of αs1-casein polymer and one of these dissociated κ-casein particles, the hydrophobic surface area of αs1-casein: κ-casein complex was less than those of 2 mole of αs1-casein polymer plus a quarter κ-casein polymer. On the other hand, the net charge of αs1-casein: κ-casein complex was nearly equal to that of 2 mole of αs1-casein polymer plus a quarter of κ-casein polymer. From these results, it was concluded that the complex formation of αs1- and κ-casein polymers was hydrophobic and that electrostatic interaction did not participate in complex formation.

For 17 phages active against Streptococcus cremoris, Str. lactis and Str. lactis subsp. diacetylactis, the killing efficiency of pasteurization (log No/N) at 72°C for 15 s in skim-milk showed large variations from > 6 to 0; the efficienty of killing during spray-drying ranged from 3.7 to 0.2 and phages survived well storage of milk powder at room temperature. Destruction in a heat exchanger was found to be greater than that calculated from biphasic curves obtained by heating phages in sealed ampoules. No relationship was established between lytic classification of phages and their heat resistance.

The production of a range of single-strain cheese starter concentrates by diffusion culture and some of their subsequent properties are described. Five strains of Streptococcus cremoris and 4 strains of Str. lactis were grown to concentrations of above 1.0 × 1011 cells/ml, these concentrates all being of satisfactory cheese-making potential. Ammonium lactate accumulation in the system appeared to be the limiting factor to growth, although some strains were more tolerant than others. A continuous harvesting experiment demonstrated that the equipment was potentially capable of this mode of concentrate production. A cheese-making trial was carried out with concentrates produced by diffusion culture; a higher proportion of extra and upper selected cheese was obtained than from control cheese produced with conventionally propagated commercial mixed starters.