A pre-milking wash disinfectant procedure employing a 2% (w/v) chlorhexidine solution in a detergent base did not reduce the rate of new intramammary infection in a lactating herd challenged with Staphylococcus aureus. Teat-end swabs showed no significant difference in the number of Staph aureus isolated from the teat-ends pre-washed with either water, or water and chlorhexidine. In contrast, disinfecting teats after milking with a solution containing 5000 mg available iodine/1 significantly reduced the staphylococcal population of the teat-ends and the rate of new intramammary infection, compared with teats not disinfected.

Rhythmic motility of teats in lactating cows in vivo was studied by an improved plethysmographic technique. Oxytocin was infused intravenously and drugs were injected into the artery of the filled udder. The β-adrenergic agent, isoprenaline, induced relaxation of the teats whereas the α-adrenergic agents phenylephrine and noradrenaline, elicited contraction. In one animal however, noradrenaline always exerted a biphasic effect. Pre-treatment with propranolol, a β-adrenergic blocking agent, changed the biphasic effect into a purely activating response. Adrenaline, which exhibits both a and β effects, induced relaxation, but after propranolol treatment relaxation was abolished and even converted into contraction of the teat. It seems clear that both α and β adrenoceptors are present in longitudinal smooth muscles of the teats.

Milk losses as intermittent spurts were observed in several cows. Spurts occurred synchronously with rhythmical teat motility in the filled udder during oxytocin infusion. The intensity of milk leakage was increased by isoprenaline and inhibited by noradrenaline, indicating the presence of α and β receptors in teat sphincter muscles. Starting and stopping of milk spurts in correlation with rhythmical teat contractions were studied by audiovisual synchronization of video recording tape. The most common type of spurt began near the middle of the teat's relaxation phase and ended either just before or exactly at the beginning of the contraction phase. Interruption of the spurt is primarily due to closure of the streak canal.

The effects of supplementing a basal diet of grass silage with various oil-enriched mixtures on milk yield and composition, fatty acid composition and the melting characteristics of the milk fats are reported. In the first experiment, various dietary fats (soya oil, tallow and a palm oil/palmitic acid mixture) were fed at a fixed level (10% by weight of the concentrate ration). Soya oil had no effect on the proportion or yield of milk fat, and increased the proportion of low melting material in the milk fat; tallow increased the proportion of milk fat, and had little effect on the melting characteristics of the milk fat; the palm oil/palmitic acid mixture increased both the content and the yield of milk fat, and increased the proportion of high-melting material in the milk fat. In the second experiment, soya oil was fed at 3 levels (10, 15 and 20% by weight of the concentrate ration). No statistically significant effect on the yield of milk or of its constituents was observed; the proportion of low-melting material in the milk fat increased progressively with increasing intake of soya oil.

Feeding lactating cows at a reduced level for a 6-d-period caused blood serum and milk free fatty acids (FFA) to rise. Milk lipolysis developed more slowly and lasted longer than elevation of the level of FFA in blood. In a second experiment protected rape seed oil was given to underfed animals and inhibited the development of rancidity in the milk. Since unsaturated fat reduced lipoprotein lipase activity in the underfed cow, this supplement appears to reduce the effect of underfeeding if it is accepted that a normal response to underfeeding is to improve the efficiency of fat metabolism through increased lipoprotein lipase activity.

The triglyceride compositions of 76 Australian milk fats obtained from 3 factories during a whole year were determined by gas-liquid chromatography. It was shown that all the data fitted the equation

with a S.D. of of 0·7088 where C40, C42 and C44 are the weight percentages of triglycerides with carbon numbers 40, 42 and 44. The triglyceride compositions of 10 samples of milk fat from countries other than Australia were also shown to fit the equation. If the equation is assumed to define pure milk fat, it is shown that as little as 5% of any non-milk fats can be detected with > 99% confidence. The amount of non-milk fat in mixtures of milk and non-milk fats can be quantified to better than ±2% with > 95% confidence. Also, the identity of the non-milk fat can usually be deduced by calculation of its triglyceride composition. Analyses of known mixtures and of chocolate and a table spread comprising butter and vegetable oil showed an agreement between observed and expected results well within the predicted confidence limits.

From bovine mammary secretion during the dry period, the total number of cells was between 1·2 and 5·9 Ǻ 106/ml. A mean of 35% of these cells were classified as lymphocytes and ∼ 85% of them could be isolated by the Ficoll-isopac method. Centrifugation separated 6% of the cells into the fat; 5% of them were lymphocytes. About 47% of the lymphocytes bound Helix pomatia agglutinin, a T-cells marker, while the proportion of Ig-bearing cells was ∼ 28%. The mammary lymphocytes were stimulated by the lectins phytohaemagglutinin, pokeweed mitogen, concanavalin A and by lipopolysaccharide from Salmonella typhimurium. The stimulation indices of mammary lymphocytes were generally lower than those for peripheral blood lymphocytes from the same animals. The background values, i.e. counts/min of lymphocytes incubated without mitogen, were often higher for lymphocytes isolated from mammary secretion than from blood.

Heat-induced association of β-lactoglobulin (β-lg) and casein micelles, mainly at 85–90 °C, was studied by means of preparative ultracentrifugation, using [3H]-labelled β-lg. Qualitative aspects were studied by gel electrophoresis and electron microscopy. In this association, the formation of intermolecular S–S bonds between β-lg and κ-casein plays a role, but hydrophobic bonds are also involved.

After heating mixtures containing 25 g/kg casein and 4 g/kg β-lg at 90 °C for 20 min, the amount of β-lg sedimented with the casein micelles by ultracentrifugation decreased by approximately 30% when the milk salt buffer system was reduced to 0·25 of its normal concentration; it decreased by about 20% when the pH was increased from 6·8 to 7·3 and increased by 15% when the pH was reduced from 6·8 to 5·8. When the β-lg concentration was decreased from 4 to 2 g/kg, the amount of sedimented β-lg decreased by 25% after heating at 90 °C for 6 min. After heating in milk salt buffer, the amount of sedimented β-lg was 15% higher than after heating in a salt solution which contained neither Ca nor citrate ions.

Although α-lactalbumin (α-la) is involved in the heat-association of β-lg and casein micelles, no influence of α-la on the amount of associated β-lg was found. In addition to the heat-association product of β-lg and whole casein micelles, an association product consisting mainly of β-lg and κ-casein was also formed. This product was observed by electron microscopy as noodle-like particles. The size of these particles depended on the β-lg/κ-casein ratio.

An examination has been made of the heat stability characteristics of skim-milk concentrate prepared by ultrafiltration (UF). Concentrate prepared by UF was found to be more stable than that prepared by conventional evaporation. In contrast to conventional concentrate, the heat stability of UF concentrate was not appreciably affected by forewarming or addition of permitted stabilizers, but the effect of addition of urea was generally the same for both UF and conventional concentrates; an increase in heat stability was obtained if the milk total solids level was less than 14%. As with conventional concentrate, addition of simple aldehydes induced large increases in the heat stability of UF concentrate. It is suggested that a novel range of sterile milk products could be prepared from UF concentrates. Because of the high protein and low lactose contents of these concentrates, the products might be nutritionally more attractive than those prepared from conventional concentrates.

The turbidity increase on storage of milk dialysate was shown to be due to Ca phosphate precipitation. The rate of precipitation at 40 °C could be decreased by shortening the duration of dialysis or by the addition of small amounts of EDTA. The dialysate was stabilized against Ca phosphate precipitation by the addition of the whey protein fraction of milk. Individual whey proteins varied in their stabilizing ability: α-lactalbumin was found to be more effective than β-lactoglobulin which gave approximately the same effect as an immunoglobulin fraction. BSA and lysozyme had a destabilizing effect and ovalbumin possessed a slight stabilizing ability.

Dialysed whey and dialysed ultracentrifugate from skim-milk were found to be satisfactory dilution media for light scattering studies on bovine casein micelles at 20 °C. Both milk dialysate and milk ultracentrifugate were only useful at fairly low levels of dilution and even then only for short periods of time. Whey, pH-adjusted to that of the original milk, was found to be an unsuitable diluent medium. Most of the instability of casein micelles to dilution could be attributed to some form of Ca phosphate precipitation or Ca phosphate–casein micelle aggregation.

A method has been developed for quantitative determination of para-κ-casein, involving spectrophotometric scanning of stained protein bands following polyacrylamide gel electrophoresis. The rate of hydrolysis of κ-casein in skim-milk at pH 6·6 and 30 °C was compared with that in EDTA-treated skim-milk under the same conditions. This showed that at the visually observed clotting time, at least 90% of the total κ-casein in milk had been hydrolysed. The time course of the reaction was consistent with all the κ-casein molecules being hydrolysed with the same efficiency. The results strongly suggest that essentially all of the κ-casein in milk is equally accessible to rennet action. This is consistent with the casein micelle being porous, or having all the κ-casein on the surface.

Casein micelles in milk-salts solution adsorbed charged detergents and highly-charged polypeptides strongly, neutral detergents less strongly and low molecular-weight amines weakly. A tetra-amine was adsorbed more strongly than a tri-amine. The extent of adsorption of proteins tended to rise as the molecular weight increased. Glycerol and lactate were adsorbed to a limited extent but dextran and α-ketoglutarate were not adsorbed at all. Proline was partly adsorbed, indicating that hydrophobic binding sites were available, and caused some disruption of the casein micelles. Additives were bound to approximately the same extent by casein micelles and rennet coagula. The proportions adsorbed were constant over at least 10-fold ranges of concentration. Additives which increased the rennet clotting time (RCT) acted by binding Ca2+. Most additives decreased the RCT, the extent increasing with the amount adsorbed and the positive charge on the additive. The greatest reduction in RCT was observed with those additives which had positively-charged and hydrophobic moieties and bound most strongly to casein micelles. Of the additives tested, only sodium dodecyl sulphate affected the enzymic action of rennet. The reduction in RCT may have resulted from the neutralization of the negative charge of the micelles or enhancement of their hydrophobicity, favouring hydrophobic interactions between the particles.

The influence of storage time and temperature on the distribution of individual milk proteins between the micellar and soluble phases has been examined. Storage at 4 or 7 °C is accompanied by a dissociation of micellar caseins, particularly β-casein, into the soluble phase during the first 48 h, but on further storage there is a partial reversal of this process. At higher storage temperatures (10–20 °C) the contents of all the individual caseins in the soluble phase decrease throughout storage. During cheese–making, losses of fat and curd fines in whey were greater with increased soluble phase casein and clotting times were prolonged. Curd structure was weaker, curds were more moist and slightly lower cheese yields were obtained in stored milks with elevated soluble–phase casein. When milks were stored for up to 3 d at 4 °C cheese gradings were virtually unaffected by storage, but higher temperatures (10–15 °C) led to cheeses being downgraded, largely for body and texture defects but also for flavour after 3 d.

Attempts to reverse the pattern of casein dissociation and to minimize the detrimental effects of milk storage on subsequent cheese-making showed that a heat treatment of 30 min at 60 °C was the most beneficial.

In assessing the performance of milk for cheese-making, the influence of a number of factors in addition to cold storage time and temperature of the milk on the equilibria between the soluble and micellar phases and on cheese-making parameters has now been examined. An important factor was pH and although not apparent in fresh unstored milk, after storage at 4 °C there was a minimum in the soluble casein concentration at about pH 6·6, largely due to variations in β-casein concentration. As expected, addition of Ca reduced soluble casein concentrations while treatment with EDTA caused increases, and in most cases the cyclic pattern of casein dissociation from the micellar phase followed by a partial reassociation was again observed during storage at 4 °C over a 3-d period. Addition of low levels of urea (up to 75 mg/100 ml milk) led to some dissociation of all casein components, Ca and phosphate into the soluble phase while treatment of milk with urease caused small decreases. Additions of purified casein components to milk were accompanied by only small alterations to the composition of the soluble phase and added casein was largely incorporated into the micellar phase. In spite of this, most added casein was not recovered in curds, and cheese yields were not greatly enhanced by quite considerable additions of caseins to the milk. The effects of pH adjustment, addition of Ca, EDTA, urea, cyanate, purified αs1-, β- or κ-casein and urease treatment on rennet clotting time, curd strength, curd moisture and cheese yield are presented.

The effects of increased somatic cell count, whether caused by infection or by experimental infusion of bacterial endotoxin, on the distribution in milk of caseins between the micellar and soluble forms were investigated. The relationship of somatic cell count to some cheese-making parameters was also studied. With quite modestly elevated cell counts (2–3 × 106/ml) increases of up to 37% in total casein in the soluble phase were observed, most of which was contributed by β-casein, while κ- and αs1-caseins increased only slightly. With storage at 4°C, the concentrations of all the caseins, Ca and phosphate in the soluble phase increased substantially during the first 48 h, but this was followed by a slight decline on further storage. Rennet clotting time, losses of fat in whey, curd moisture, and losses in curd yield and rigidity were all greater the higher the somatic count. Clear differences were detectable in these parameters between milks of very low cell count (e.g. 5 × 104 cells/ml) and milks with counts more typical of those found in bulk supplies (e.g. about 5 × 105 cells/ml). If these findings can be reproduced in commercial practice even a modest reduction in bulk milk somatic cell counts might be expected to bring definite benefits.

The reactions between 6 strains of mesophilic lactic streptococci and their respective phages were studied quantitatively. Of 30 nonhomologous reactions, the bacteria were fully sensitive in 4 and restricted the phages in 23. A mathematical model was developed that was used to identify at least 4 and probably 5 modification restriction (M/R) systems of which up to 3 were found in the same strain. The model was based on 24 measured values and correctly predicted the values of 5 others. One of the 3 negative reactions was shown to be due to a restriction beyond the limit of detection, a second was due to lysogeny or lack of adsorption, but was shown to have the predicted value when the homologous phage was modified on the host of the challenging phage. In the last reaction a measurable restriction was predicted, but could not be proven by means of a modified phage. These results suggest M/R to be one of the main defenses of the lactic streptococci against their phages. They explain why host range is not a useful criterion in the classification of phages and suggest a rational approach to the definition of a starter rotation.

The effect of ripening cow'milk cream (40% fat) with 4 strains of lactic acid bacteria on the quality of ghee, an Indian product resembling clarified butterfat, was studied by measuring changes in titratable acidity, pH, volatile acids and diacetyl content due to Streptococcus lactis, Str. lactis subsp. diacetylactis (Str. diacetylactis), Str. thermophilus and Lactobacillus bulgaricus in cream prior to conversion into ghee. L. bulgaricus produced the maximum titratable acidity (1·25% lactic acid) followed by Str. diacetylactis (0·80 % lactic acid) after 72 h. Str. diacetylactis produced the highest level of diacetyl (28 ppm), after 48 h. L. bulgaricus produced no detectable diacetyl. Both of these strains produced the maximum amount of volatile acids (2·2–3·5 ml), after 72 h. The flavour and keeping quality of ghee were improved by Str. diacetylactis and Str. lactis whilst Str. thermophilus and L. bulgaricus had no effect.