The changes in the yield and composition of the mammary gland secretion in the first 16 days of the dry period have been investigated in 6 cows. The quantity of secretion, lactose, potassium, casein, α-lactalbumin, β-lactoglobulin and fat present in the gland decreased rapidly. A decrease was also observed for sodium, chloride, residual albumin and proteose-peptone + globulin but was much less marked. Changes in composition were qualitatively similar to those normally occurring at the end of lactation but they were much more pronounced. Within 8 days after drying-off the concentrations in the secretion of sodium, chloride and potassium were similar to those of blood. There were differences between, animals in the rate at which the changes developed. As the secretory activity of the gland ceased, the constituents of the mammary gland secretion appeared to be resorbed.

The changes in yield and composition of mammary gland secretion throughout the whole of the dry period have been investigated in 6 cows. The yields of lactose, potassium, fat and casein decreased to very low values for the greater part of the dry period but then increased slightly just before parturition. Similar trends were observed for sodium and chloride but they were much less marked. During the middle of the dry period the concentrations of sodium, potassium and chloride tended towards those of blood serum while the concentrations of fat and lactose decreased to < 1%.

The measurement by gas chromatography of pregnanediol in the urine of normal and ketosed cows in the first 3 months of lactation is described. Mean pregnanediol levels, corrected for recovery losses, are reported for 3 groups of cows, namely: normal lactating cows 30·7 μg/1 urine; experimentally induced ketosed cows 22·3 μg/1 urine; and primary spontaneously ketosed cows, 31·4 μg/1 urine. No significant differences between the 3 groups of animals were found.

Immunological methods have been used to test samples of urine from 5 cows for the presence of milk proteins. None could be detected when the cows were milked twice daily at the usual intervals, but during an extended milking interval α-lactalbumin was found in the urine of all 5 cows and β-lactoglobulin in the urine of 2 cows. The urine of one cow during and after a milking interval of 39 h contained 1·63 g α-lactalbumin, 1·12 g β-lactoglobulin and a small amount of casein. One of the factors affecting the transfer of these milk constituents from the udder to the urine appears to be their molecular weight.

A study of the production of L(+) and D(−) lactic acid in cultures of DL forming lactic acid bacteria has shown that they can be divided into 2 groups. The first includes the thermobacteria and Pediococcus cerevisiae in which the percentage of L(+) lactic acid is high initially but decreases as the cultures grow. The second includes Lactobacillus plantarum and the heterofermentative lactobacilli and in cultures of these species the percentage of L(+) acid changes little during growth and is generally below 50% of the total.

In a strain of Lactobacillus acidophilus it has been found that if the pH is kept constant during growth the proportion of L(+) lactic acid decreased. However, when acid production stopped the proportion of total acid which is the L(+) isomer is greater than the proportion at the same stage of development in cultures where the pH was not adjusted. Cells harvested from young cultures formed more L(+) acid than cells harvested from older cultures.

There is some evidence that the composition of the medium can affect the ratio of L(+):D(−) lactic acid.

In suitable media the relationship between the citrate content and the acetoin formed by the growth of Streptococcus lactis var. diacetilactis NCDO 1007 is linear. An assay method for citrate is described which is based on this relationship. It has been used to assay the residual citrate in cultures of lactic acid bacteria and, therefore, to assess the ability of these bacteria to dissimilate citrate. Some suitable media for the test are described.

A series of experiments has been carried out in order to develop antibiotic preparations which, when infused into the udder at drying-off, eliminate established infection and prevent new infection from occurring in the dry period. It has been shown that the persistence of antibiotic in the dry udder is affected by the solubility of the antibiotic salt, the quantity of antibiotic infused and the base in which it is formulated. Whereas 0.2 g cloxacillin as the sodium salt infused in a 3% aluminium monostearate in mineral oil base after the last milking of lactation persisted for less than 1 week, 0.5 and 1.0 g cloxacillin in the form of the benzathine salt, in a similar base, usually persisted for 3 weeks.

Secretions removed from the udders of dry cows inhibited the growth of Bacillus subtilis and Sarcina lutea but not 2 strains of staphylococci.

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.

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.

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.

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.