Results are given of the examination for blood of 3214 milk samples from 935 cheese factory supplies. Over 75% of the milks contained less than 2·5 ppm. blood. Excessive blood was due to factors largely controllable by an efficient farmer, and so may be used as an indicator of poor dairy herd management and shed hygiene. No evidence could be obtained that the concentrations of blood likely to be found in commercial milk have any adverse effect on the keeping quality of whole milk or butter.

Approximately 30% of the nitrogen of κ-casein was soluble at pH 4·7 after the protein had been treated with rennin at pH 7 while approximately 10% was soluble in 12% trichloroacetic acid (TCA). The material soluble in 12% TCA appeared at a slower rate initially than did the nitrogen soluble at pH 4·7 but as the reaction proceeded it was released more rapidly.

Treating κ-casein with urea, or repeated precipitation of the protein at pH 4·7, caused the formation of material insoluble at pH 7, apparently para-κ-casein. Both treatments appeared to free the same soluble fraction as does rennin acting in low concentration or for a short time.

Low concentrations of rennin (0·07 μg/ml) released only part of the available soluble nitrogen from 2% solutions of whole casein at pH 7. Heating the reaction mixture appeared to restore the casein complex, the restoration being less complete the longer the reaction had proceeded.

It is suggested that κ-casein is not a single protein but a complex, and that the action of rennin is first to open the secondary bonds responsible for the stability of this complex.

A series of precipitation zones appears when proteolytic enzymes diffuse through an agar gel containing 1% whole casein and 10–20 mM-calcium chloride. As the enzyme diffuses through the gel the casein stability changes giving first a precipitate which subsequently redissolves followed by a second precipitate which also redissolves. The first or outermost zone of precipitation occurs at the periphery of the area of the diffused enzyme. Using a high enzyme concentration all four zones, two of precipitation and two of subsequent clearing, are visible in about 24 h. The proportion of the total nitrogen which occurs as non-protein nitrogen (N.P.N.) in the first or outermost precipitation zone is similar to that found after the first stage of rennet action on casein solutions.

A chemical, cytological and bacteriological examination of the milk from each quarter of a cow suffering from subclinical mastitis, but giving 5–6 gal of milk per day, was made at weekly intervals during the first 84 days after parturition. The infection, caused by micrococcal and staphylococcal bacteria, resisted repeated treatments with various antibiotics administered via the teat canals and also intramuscularly, although in vitro the bacteria were susceptible to all the antibiotics used. The cow was slaughtered and a histological examination made of the udder in an attempt to establish the cause of the continuing infection and to assess the extent of tissue damage. Two quarters each contained large abscesses in the upper level of the udder and these could have acted as reservoirs of infection; no cause was established for the other two quarters and it can only be assumed that reinfection occurred from the two abscessed quarters.

The amount of active lesions in the lobules of all the quarters was small, 1–6%, but half or more of all the lobules were involuted, although only a minority appeared to have involuted as a result of infection. In the two abscessed quarters there was extensive damage to the duct system, 23 and 31% showing lesions.

When the milk contained an abnormally large number of cells the chemical composition was also abnormal, containing less lactose (and hence less solids-not-fat) and having a nitrogen distribution in which there was more blood serum albumin and globulin and less casein than usual. Cell content and chemical composition were better indicators of tissue damage than the presence of mastitis organisms. It is estimated that the solids-not-fat content of the milk of the whole udder as a result of the infections was considerably lower than it would otherwise have been (8·0 instead of 8·8%) and that the daily loss in milk yield was about 9 lb.

Results are reported of an experiment made under commercial conditions on the effect of the level of meal fed in conjunction with an unrestricted supply of whey on the performance and carcass quality of pigs.

All the pigs received the same meal mixture and had continuous access to an unrestricted supply of whey. The four treatments were: (1) 3 lb meal per pig per day reduced to 2 lb at 13 weeks of age; (2) 3 lb meal per pig per day throughout; (3) 2½ lb meal per pig per day throughout; and (4) as (1) but the daily allowance of meal increased to 2½ lb/pig at 20 weeks of age. There were five pens of nine group-fed pigs on each treatment, involving a total of 180 pigs. The pigs were on experiment from 8–9 weeks of age to bacon weight. Comprehensive carcass measurements were made on all the pigs.

Mean differences in rate of growth, efficiency of food utilization and carcass quality between the four groups of pigs were small and were not statistically significant. The significant differences in the proportions of meal and of whey consumed by the pigs on the different treatments during the growing period are discussed in relation to relative prices of the two foods. It is concluded that where unrestricted whey feeding is to be used, the feeding system employed in treatment 3 could be recommended in most of the environmental and economic situations likely to be encountered in practice.

The superior performance of the pigs in the experiment compared with that in earlier trials is discussed in relation to the stock improvement work and concurrent improvements in housing and management carried out during the intervening years on the Cow and Gate farm in Dorset where the experiments were conducted.

In an indoor feeding trial with three sets of monozygotic twin cows during late spring the effects of H1 short rotation ryegrass and white clover as feeds for the cows on the characteristics and the carotene and vitamin A contents of the butterfat were compared. The butterfat from the cows fed ryegrass had a lower iodine value and refractive index, higher Reichert and saponification values, and lower carotene and vitamin A contents than the butterfat from the cows fed clover. The carotene and vitamin A contents of the blood of the cows fed ryegrass were also lower than those of the cows fed clover

In a subsequent outdoor feeding trial with four sets of monozygotic twins the feeding of pure H1 short rotation ryegrass or of perennial ryegrass was compared with the feeding of mixed pastures containing a high but varying proportion of clover. The results for the spring and early summer months were similar in direction but smaller in magnitude than those from the indoor feeding trial. In the result for the autumn months there was a reversal of the relationship for the characteristics and the carotene and vitamin A contents of the butterfat and for the carotenoid contents of the blood.

It is suggested that the lack of consistency between the spring and autumn results could have been due to differences in the stage of growth of the ryegrass fed and that butterfat characteristics may be influenced more by the stage of maturity than by the botanical composition of the pasture.

In two outdoor feeding trials with monozygotic twin cows during the spring and early summer months the effects of mature and immature H1 short rotation ryegrass on the composition of the butterfat produced and on the carotene and vitamin A contents of the butterfat and the blood were compared. In both trials the characteristics investigated were markedly affected by the stage of maturity of the grass. The butterfat from cows receiving immature ryegrass was more unsaturated and had higher carotene and vitamin A contents than that from cows receiving mature ryegrass. The blood of cows fed immature ryegrass also contained more carotene than the blood of cows fed mature ryegrass.

It is suggested that variation in the stage of maturity of New Zealand dairy pastures throughout the year is an important factor contributing to the seasonal variations in the characteristics and the carotene and vitamin A contents of commercial butterfat. The influence of stage of maturity is probably associated with the quantity and nature of the pasture lipids.

The lipid content of short rotation ryegrass at two stages of growth was followed at weekly intervals for several months in two spring-early summer seasons. Short succulent ryegrass consisting entirely of leaf tissue contained more lipid (mean, 8·1% of the dry weight) than mature ryegrass which contained appreciable stalk (mean, 5·1% of the dry weight). The lipid from the new growth contained fatty acids with appreciably higher proportions of linolenic acid, which was balanced mainly by lower proportions of linoleic and palmitic acids.

When monozygotic twin milking cows were grazed on the short rotation ryegrass grown to two stages of maturity, it was found that the fatty acid composition of the milk fat from the two groups was different. The milk fat of cows grazed on the new growth contained higher proportions of oleic acid and other C18 acids, whilst the proportions of myristic and palmitic acids were lower. The total proportions of the short-chain fatty acids were not greatly different, although in the group on new growth butyric acid was present in higher proportions and hexanoic and octanoic acids in lower proportions. The higher unsaturation of the fatty acids in the milk fat of this group of cows may be related to the higher levels of unsaturated fatty acids in the young ryegrass diet and to the extent to which these unsaturated fatty acids are hydrogenated in the rumen.

When k-casein was treated with rennin at neutral pH all the sialic acid contained in the protein was found in the glycopeptide released by the enzyme. From the known molecular weight of the glycopeptide and its proportion in k -casein, a molecular weight of the order of 50000 was calculated for the protein

The bulked milk from a flock of Awassi sheep was analysed in two successive seasons. In the second season a wider range of analyses of samples taken from the time the first few ewes came into milk until almost the end of the production season (minimum and maximum numbers in milk 8 and 199) gave the following average values: specific gravity, 1·0366; titratable acidity, 0·217%; pH, 6·65; fat, 6·88%; protein, 6·18%; lactose, 5·75%; solids-not-fat, 12·99%; ash, 0·928%; CaO, 0·29%; p2O5, 0·32%; CaO in ash, 31·5%; P2O5 in ash, 34·3%.

The results are compared with the published compositional figures for sheep's and cow's milks.

The numbers and types of non-starter lactic acid bacteria, lipolytic bacteria and group D streptococci in cheese milks and corresponding Cheddar cheeses have been studied and their relationship to cheese flavour discussed. Different milks, heat-treatments and starters were used, and their association with flavour investigated. The pH and fat, salt and moisture contents of the cheeses were also determined.

The non-starter lactic acid flora consisted mainly of Lactobacillus casei, L. plantarum, L. brevis, L. buchnerii, Pediococcus spp. and Leuconostoc spp. Lactobacillus casei was nearly always present in the milks and cheeses, predominating in most of the cheeses, particularly in those made from milk which received the most severe of the three heat-treatments tested (160°F for 17 sec). Leuconostocs were not found in any of the cheeses. Other species sometimes occurred in approximately equal numbers to L. casei, particularly in cheeses manufactured from the milder heattreated milks. Cheeses made from milk receiving the highest heat-treatment contained fewest bacteria and scored lowest for flavour. The average flavour scores increased as the number of species contributing to the non-starter lactic acid flora at the time of tasting increased.

The lipolytic organisms capable of hydrolysing butterfat consisted mainly of Gram-positive cocci, predominantly Staphylococcus saprophyticus. The group D streptococci occurred infrequently, Streptococcus faecium being the most commonly occurring species.

A definite correlation was found to exist between the starters used and the flavour of the cheeses. The pH of the cheeses was associated with the flavour, but the fat, moisture and salt contents of the cheeses showed no definite effect.

A method is described for the preparation of k -casein and for its purification by chromatography on DEAE cellulose. The conditions of preparation have been chosen so as to avoid drastic alteration of the k -casein and permit the isolation in relatively pure form of one-half to two-thirds of the amount theoretically available.