Two surveys were done, one in 1943–44 and one in 1958–60, of the seasonal variation in the concentration of vitamin A and carotene in milk fat from 13 different areas in Great Britain. In the 1958–60 survey α-tocopherol and vitamin D were also measured. The main purpose of the second survey was to find out if the marked swing from Shorthorns to Friesians, and the trend towards greater use of carotene-rich foods in winter feeds that occurred in the intervening 15 years, had affected the pattern of vitamin A activity. In addition, monthly samples of butter were obtained in 1958–59 from a single factory in New Zealand during a complete butter-making season (9 months) and were assayed for vitamin A, carotene, α-tocopherol and vitamin D. Three experiments were done to study the effect of breed on the vitamin A and carotene content of milk fat, and in one of them α-tocopherol and vitamin D were also determined.

The seasonal trends for vitamin A and carotene were essentially the same in both surveys. A peak occurred in May after the spring flush of grass and was followed by a decline with a second peak in the autumn, except in 1959 when both the summer and autumn were very dry. Potencies were higher in the south than in the north, where the differences between summer and winter were more marked. In winter, mean vitamin A potencies of 5·8 and 7·7 μg/g fat were found for northern and southern areas, respectively; the corresponding values for β-carotene were 2·0 and 4·5 μg/g fat. Mean summer values were 8·8 and 9·7 μg/g fat for vitamin A and 5·1 and 6·5 μg/g fat for carotene, equivalent to increases of about 52 and 26% and about 155 and 44%, respectively, over winter values. Differences in mean potency between areas are explained by length of grazing season and type of winter feed.

The concentration of vitamin A in the fat was essentially the same for Ayrshires, Friesians, Jerseys and Shorthorns but somewhat lower for Guernseys; that of carotene was higher for the Channel Island breeds, particularly Guernseys, than for the other breeds studied.

Compared with this country, concentrations of carotene were higher and of vitamin A lower in milk fat from New Zealand, probably because of the predominance of Jersey cows in New Zealand herds. The seasonal trends for these vitamins were similar in both countries, but the spring peaks were earlier, the autumn peaks later and the summer declines more pronounced in New Zealand than in this country.

Concentrations of α-tocopherol in British milk fat showed a trend similar to that found for both vitamin A and carotene and were again influenced by feeding practices. Mean values of 23 and 29 μg α-tocopherol/g fat were found in the summer for northern and southern areas, respectively; the corresponding winter values were 15 and 23 μg/g fat. Mean values of about 30 μg/g fat were found, over a 28-month period, for the milk fat of each of the 3 breeds, Ayrshire, Friesian and Jersey. No seasonal trend was observed in the New Zealand samples; the mean value for the 9 months was 32 μg/g fat (range 24–39 μg).

Vitamin D potencies were higher in summer, when there is more sunshine, than in winter. The higher summer values in the northern than in the southern part of the country may have been related to a higher intake of vitamin D in the former from hay and pasture. Summer potencies of 0·44, 0·53 and 0·62 i.u. vitamin D/g fat, respectively, were found for Friesian, Jersey and Ayrshire milk; corresponding winter values were 0·06, 0·08 and 0·9 i.u./g fat. For the New Zealand butters, summerues values were higher than in this country, about 0·7 compared with about 0·4 i.u./g fat; winter values were similar in both countries.

In a survey done in 1943–44 there was no seasonal difference in the riboflavin content of milk from 10 different areas in England and Wales that could have been associated with the change from stall to pasture feeding, and mean values were about 160 μg/100 ml for both the periods November-April and May-October. However, values for the 6 months August-January were higher (about 175 μg) than for the 6 months February-July (about 150 μg). Over a 12 months' period the mean riboflavin contents of Shorthorn and Guernsey milk from the Institute's farm were 142 and 191 μg/100 ml, respectively.

Whole acid casein and α-, β- and γ-caseins were isolated and treated with rennin. Chemical, chromatographical and electrophoretical analyses were done on the caseins and on the products obtained from them after rennin treatment. Three different fractions were obtained which had some specific protective activity for the Ca-sensitive forms of α-, β- and γ-casein, respectively, and which differed in their chemical, chromatographical, and electrophoretical properties.

It is suggested that each casein fraction in milk is associated with its own protective fraction which when released by the action of rennin, allows the casein to clot.

A new method is described for the determination of the free and masked sulphydryl (-SH) groups in heated milk and milk products. The procedure is based on the use of the specific -SH reagent p-chloromercuribenzoate, and utilizes another specific -SH reagent, 5,5' -dithiobis(2-nitrobenzoate), as an indicator producing yellow colours which are matched with the aid of standard glasses in the Lovibond Comparator.

The method was applied to heated skim-milks and a series of commercially prepared milk powders. Measurements were made in particular of the -SH content of UHT-treated milk. The changes in the -SH content of such milks on storage were studied; these changes could not be explained by a reversal of the denaturation of the whey proteins, although evidence was obtained that small amounts of heatdenatured whey protein can revert to the native state.

The possibility of using a skin measurement as an index of potential milkproducing capacity in cattle was re-examined. Skin specimens were obtained by biopsy from 7 dairy herds, and each of 5 anatomical measurements was correlated with (1) milk yield and (2) butterfat percentage.

Only one of the pooled within-herd relationships was statistically significant. This relationship indicated that within the breeds studied, cows with the least hair follicle depth would be expected to give the highest milk yield. It is suggested that a more extensive investigation of this relationship might yield results of practical value in assessing milk-producing capacity and in progeny testing.

The effects of depriving cows of pasture, for part or all of a single interval between the morning and evening milkings, on milk yield and composition have been investigated. The yields of milk and solids-not-fat, but not of fat, were reduced. The characteristics of the butterfat obtained at the first 2 milkings following grazing restriction differed markedly from those of cows allowed to graze normally.

The changes observed suggested that the grazing restriction led to a temporary reduction in the supply of volatile fatty acids from the rumen and an increased utilization of fatty acids from body fat by the mammary gland.

A single injection of 100 i.u. ACTH given to milking cows had no statistically significant effect on the yield or composition of the milk. A long-acting preparation of ACTH, when given to cows in single doses of 200 and 400 i.u., depressed milk yield and raised the butterfat content of the milk. There was no significant change in the SNF content of the milk but the SNF content of the milk serum was increased. Three injections of 300 i.u. of long-acting ACTH given at 24-h intervals reduced yields of milk, fat and SNF and increased the fat and SNF contents of the milk.

Small but generally consistent changes occurred in the butterfat characteristics of the milk of all groups treated with ACTH. There was a decrease in the iodine number and refractive index and a rise in the softening point of the fat in all the experiments. The Reichert value of the butterfat was lowered by single or multiple injections of the long-acting preparation. The carotene content of the butterfat was lowered by injections of the long-acting ACTH preparation but the vitamin A content was unaffected.

The early loss of viability of Streptococcus cremoris strain C 13 in Cheddar cheese was investigated. The growth of this strain was markedly inhibited by cheese extracts containing unesterified fatty acids of which oleic acid was the major inhibitory constituent active against the coccus. This acid was found to accumulate in cheese early in the ripening process and may be responsible for the early loss of viability of strain C 13 in cheese.

Early loss of viability of a starter organism in cheese could result in a low peptidase activity by limiting the number of bacterial cells present. The subsequent accumulation of unhydrolysed bitter peptides would produce a bitter flavour.

It was previously found that low concentrations of oleic acid in the growth medium inhibited the growth of Streptococcus cremoris strain C 13. However, a variant of this strain has now been isolated which is capable of growth in relatively high concentrations of oleic acid. This was achieved by the extended incubation of inocula of strain C 13 in milk containing various concentrations of oleic acid.

A method of preventing the action of bacteriophages on starters in cheese milk is described. Direct intramuscular injection of high titre phage preparation into a cow resulted in the appearance in the blood serum and milk of a high concentration of antibody. Even after considerable dilution this antibody is capable of neutralizing the homologous phage and serologically related phages. Methods of concentrating the antibody-containing milk were examined with a view to commercial application of the method in the protection of starter bacteria from phage attack.

The levels of coenzyme A were measured in the milk of normal dairy cows during the first 20 weeks of lactation. Estimations were made on milk samples obtained from some cows in their first lactation and from older cows. The microbiological method described by Brown (1959) for the estimation of bound forms of pantothenic acid was used, but considerable modification of this method was necessary to avoid elevated results due to the stimulatory action of free pantothenic acid on the response of the assay organism. Appreciable amounts of coenzyme A were excreted in the milk of cows in their second or subsequent lactations during the first 12–16 weeks after parturition, peak levels being reached after the end of the 1st week. In comparison, only small amounts of coenzyme A were excreted in the milk of cows in their first lactation. Attempts to detect the presence of phosphopantetheine in milk were unsuccessful.

From a batch of raw milk, evaporated milk was prepared commercially by 3 procedures: A, a normal commercial procedure involving holding the filled cans at a maximum temperature of 113 °C for 15 min; B, with nisin added and holding at a maximum temperature of 105 °C for 15 min; C, with nisin added and holding at a maximum temperature of 113 °C for 3 min. The content of B vitamins in the raw and evaporated milks was measured microbiologically; the nutritive value of the proteins was determined in rat tests.

In milk A, 83% of the vitamin B12, 38% of the vitamin B6 and 20% of the thiamine were destroyed during processing. In milk B, the losses were 67, 30 and 19%, respectively, only the loss of vitamin B12 being significantly lower than in milk A. In milk C, the losses were 67, 23 and 14%, respectively, each of them being significantly lower than in milk A. There was no further loss of thiamine on storage of the milks for 12 months at 4 °C, but at room temperature and at 37 °C further losses occurred in all the milks. Similarly, the vitamin B6 activity of the milks decreased on storage, the loss being greatest at 37 °C, but also detectable at 4 °C. No change in the vitamin B12 content occurred on storage, and no losses of biotin, nicotinic acid, pantothenic acid or riboflavin were detected during manufacture or storage of the evaporated milks.

The biological value and true digestibility of the proteins of the evaporated milks were slightly lower than for the raw milk. Neither nisin treatment nor storage at room temperature for a year affected these characteristics.

A study of casein micelles was made with the electron microscope, using very thin sections cut from micelles embedded in Araldite. The micelles appear to be built up of units that are approximately spherical, about 100 Å in diameter and of about 300000 molecular weight.

The serological identity of group N streptococci was established by Shattock & Mattick (1943), who discovered that Streptococcus lactis and Str. cremoris had a common antigen, which differentiated them from the rest of the Lancefield groups of streptococci. Although phage typing of these organisms has met with some success (Nichols & Hoyle, 1949; Whitehead & Bush, 1957) attempts to type these organisms with rabbit antisera so far have failed (Briggs & Newland, 1953).

The preparation of an immunologically homogeneous β-casein is described, involving several separations by chromatography on diethylaminoethyl cellulose with urea-imidazole buffer at pH 7, followed by Tris buffer at pH 8·2. 30% of the β-casein present in the skim-milk is obtained by this method. β-casein gives a single band in urea-starch gel electrophoresis when it is obtained from the milk of cows homozygous for this character.