In each of 5 cows, 2 quarters which had been regularly milked throughout the whole of pregnancy produced less milk in the next lactation than the other 2 quarters which had a normal dry period. The concentrations of the individual constituents in the milk of all 4 quarters of each cow were similar. The effect appears to be due to factors located within the individual quarter of the mammary gland rather than to factors such as the hormonal background or plane of nutrition which affect the whole animal.

After the suspension of milking for 2 weeks in 2 ‘experimental’ quarters of each of 4 Friesian cows, there was a reduction in the yield of milk from these quarters. Although subsequently there was a marked recovery, for the remainder of the lactation the yield was lower than that of the corresponding control quarters in which milking had not been suspended. Throughout the next lactation, in all 4 cows, the experimental quarters produced more milk than the corresponding control quarters. At the first milking after the suspension, there were marked increases in the concentrations of sodium and chloride and decreases in those of lactose and potassium in the milk obtained. Within 8 weeks, the composition recovered, and for the remainder of the experiment the composition of the milk from the control quarters was similar to that from the experimental quarters of each cow.

Phospholipid was isolated from milk, butter, and washed-cream serum by solvent extraction followed by simple counter-current distribution and thin-layer chromatography. Iodine values from fresh samples, determined by a micro-Wijs technique, ranged, for the cephalin fraction, from 70 to 86, for the lecithin fraction from 44 to 55, and for the sphingomyelin fraction from 36 to 44. In washed-cream serum, oxidation with copper and ascorbic acid led to reduction in extractable phosphorus, decreased chromatographic mobility of phospholipid and significant falls in the iodine values of the 3 phospholipid fractions. In milk, slight reductions in phospholipid iodine values were observed following copper-catalysed oxidation but they were not consistently significant. Iodine values of butter phospholipids remained unchanged even after gross oxidative quality deterioration.

Penicillin G at a dose level of 1 and 5 million units infused in a quick release base or an aqueous solution into quarters of cows after the last milking of the lactation persisted in infused quarters for about 4 days. From 1 h after infusion penicillin was detected in the venous blood and from 2 h after infusion in non-infused quarters.

Heat sterilization of milk destroyed about 50% of its folic acid activity, and subsequent exposure of the milk to sunlight caused a progressive further loss. This loss of folate, as of vitamin B12, was a consequence of the oxidative destruction of the milk's ascorbic acid, and was largely prevented by thorough exclusion of oxygen from the milk during heat processing and subsequent storage. With thiamine, riboflavin, nicotinic acid, vitamin B6 and biotin, stability towards heating and during exposure to sunlight was affected little, if at all, by the oxygen tension in the milk.

Results of studies on the operation of the Milko-tester Mark II for the estimation of fat in both herd and individual milks are presented. Milko-tester readings were compared to the means of duplicate Gerber results.

It was found that, for 894 herd milks, a direct Milko-tester reading (G = M) had a standard error of estimate of ±0·071, whereas regression equation (G = 1·02 M −0·075) derived for the same data gave ±0·070. For 1133 individual milks, the equation (G = 1·03 M − 0·186) also had an accuracy of ±0·070, while the direct Milko-tester reading gave ±0·107. However, a simple subtraction of 0·077 from each Milko-tester value (i.e. G = M−0·077) for individual milks reduced the standard error to ±0·071.

It is concluded that the Milko-tester is satisfactory for herd milks, particularly for milks up to 3.8 % fat. For individual milks a special regression relationship is necessary to achieve comparable accuracy.

The effect of equal and unequal milking intervals (12 + 12, 10 + 14 and 8 + 16h) was investigated in milch ewes. The treatments were applied to 9 ewes using a double 3 × 3 Latin square. The daily production of milk and fat was unaffected by the changes in milking interval.

The sensitivities of isolates of bovine staphylococci, corynebacteria and streptococci to various antibiotics were determined. The growth of various strains of Staphylococcus aureus was inhibited by the following range of concentrations of antibiotic: cloxacillin, 0·07 to 0·6 μg/ml; penicillin G, 0·018 to > 250 μg/ml; streptomycin, 1·25 to > 250 µg/ml; novobiocin, 0·15 to 25 μg/ml; chlortetracycline, 0·6 to 10 µg/ml. The concentrations of cloxacillin required to inhibit growth were between 0·15 and 1·25 μg/ml for strains of Streptococcus agalactiae; 0·07 to 0·3 μg/ml for strains of Streptococcus dysgalactiae and 0·15 to 0·6 μg/ml for strains of Streptococcus uberis.

The corynebacteria were generally sensitive to the penicillins (ampicillin, penicillin G, phenethicillin and cloxacillin), but showed least sensitivity to cloxacillin which had a similar activity to that of chlortetracycline, neomycin and oleandomycin. Chloramphenicol and streptomycin were less active than the penicillins and novobiocin showed little activity against Corynebacterium ulcerans.

A clear relationship was confirmed between the sensitivity of staphylococci to cloxacillin and penicillin G. Some indication was found of an association between the sensitivity of staphylococci to cloxacillin and the success of cloxacillin intramammary therapy in the non-lactating udder. There was no evidence of a change in the sensitivity of Staph. aureus following exposure to cloxacillin in the non-lactating udder.

Concentration of milk results in a considerable increase in retention of fat by the rennet curd formed under conditions of disturbance. The fat retention property is not conferred by concentration per se but by some effect, probably involving surface phenomena, associated with the process.

Changes in composition of the fat globule membrane due to incorporation of milk protein accompany the improvement in fat retention. It is suggested that casein bound firmly to the globule during the concentration process, forms strong links with the coagulated micelles of the curd.

When κ-casein from buffalo's milk was treated with carboxypeptidase A (EC 3. 4. 2. 1),4 amino acids, valine, threonine, serine and alanine were released from the protein in a manner consistent with the view that they originate in the C-terminal sequence of a single peptide chain. The amounts produced suggest a minimum molecular weight for buffalo κ-casein of approximately 17000, in agreement with the value calculated from the phosphorous content on the basis of the presence of 2 phosphorus atoms/molecule. A comparison is made with the C-terminal sequence reported for bovine κ-casein.

Comparisons were made of the flavour, free fatty acids and bacterial flora of commercial cheese made at different factories and experimental cheese made under aseptic conditions: (i) with δ-gluconic acid lactone instead of starter, (ii) with starter only, (iii) with starter and added floras derived from the curd of the commercial cheeses (reference flora cheeses).

Comparison of the bacterial flora of commercial and reference flora cheeses showed that replication of organisms was better with some reference floras than with others. In all the cheeses the lactobacilli increased in numbers during maturation, whilst other groups of organisms died out.

The amount of acetic acid present was influenced by the starter and by the lactobacilli. Single-strain starters produced some acetic acid, most of which was lost in the whey; commercial starters produced considerably more, due to the presence in them of Streptococcus diacetilactis. Later in maturation lactobacilli increased the acetic acid content, a greater increase being observed with homo-than with heterofermentative strains.

The initial levels of butyric and higher fatty acids in the milk varied with source of the milk and with the season, summer milk having higher levels than winter milk. During cheese-making a slight increase of these acids occurred in every cheese made with starter and a further small increase occurred during ripening. However, there was no increase in the content of these acids in the cheese made with δ-gluconic acid lactone, indicating that lactic acid bacteria were weakly hydrolysing the milk fat.

Flavour trials showed that Cheddar flavour was present not only in the reference flora and commercial cheese, but also in the cheese made with starter only. Different starters produced different intensities of flavour; one strain produced an intense fruity off-flavour. Cheeses made with δ-gluconic acid lactone were devoid of cheese flavour.

Possible mechanisms are considered for the formation of a metallic flavour component, oct-1-en-3-one, in a vacuum-packed butterfat-antioxidant-synergist mixture, and in washed cream and butter with free access to atmospheric oxygen. The oct-1-en-3-one is likely to be derived from linoleic or arachidonic acids, or both. A complex of reactions linking oxygen, catalysts, substrate, radicals, and antioxidants is discussed. Pathways for the production of intermediates giving rise to oct-1-en-3-one are suggested for systems with free and with limited access to oxygen. These mechanisms would involve secondary oxidations with formation of polyfunctional monomers and would be competing for oxygen with those giving rise to polymers. The reasons why they compete to a significant extent are discussed in relation to the detailed environmental conditions including lipid reactivity, effective oxygen pressure in situ, steric effects at phase boundaries and the role of acidity and of ionic intermediates.