Two Cheddar cheeses were analysed for aldehydes and methyl ketones at intervals during the ripening period. One-day-old cheese was found to contain acetaldehyde and acetone, together with traces of butan-2-one and pentan-2-one. As the cheese matured heptan-2-one, nonan-2-one and undecan-2-one appeared, and the concentrations of all these compounds progressively increased.

The distribution and development of bacteria during the maturing of New Zealand Cheddar cheese have been studied using stained sections of cheese. The starter streptococci usually occur singly and in small groups throughout the mass of the cheese, their distribution on a microscopic scale being very irregular. In contrast, the bacteria developing later form discrete microcolonies, most of which are associated with the curd junctions. Instead of adding lactobacilli to milk, smaller numbers may be added to the dry curd before cheddaring or after milling. Some observations on the physical structure of cheese are made.

Observations were made by anoptral phase-contrast microscopy of the effect of various reagents on the state of dispersion of casein micelles in skim-milk and in lactic acid and rennet coagula. Among the hydrogen-bond-breaking reagents, urea at higher (4M) concentration dispersed the casein micelles in skim-milk and in acid and rennet coagula. Sodium salicylate was effective at low (M) concentration. Guanidine hydrochloride at low concentration caused aggregation of the micelles in skim-milk but at high concentration caused dispersion, while at both concentrations it dispersed acid and rennet coagula. Lithium iodide and potassium thiocyanate flocculated the casein in skim-milk, but dispersed it in both types of coagula. Flocculation in skim-milk by these reagents was followed by slow coalescence of the casein.

At substantially lower molar concentrations, sodium dodecyl sulphate, an anionic detergent, which attacks either the hydrophobic bonds or the salt linkages in proteins, dispersed micelles and both types of coagula. Sodium thioglycollate, a disulphide-bond-breaking reagent, had no visible effect on the casein.

In rennet coagulum in which the calcium bridges have been destroyed by the sequestering action of EDTA or in lactic acid coagulum, urea at low concentrations caused a quick and almost complete coalescence of casein. Fibres were formed in the rennet coagulum when the coalesced material, which presumably consists of randomly coiled chains of unfolded casein macromolecules, was subjected to stretching or flowing. Similar chemical and physical conditions would appear to prevail when fibre formation takes place in cheddaring cheese curd.

Rates of flow of milk during milking have been observed on twin and single-born dairy cows with the aid of a device for continuous recording of weight of milk extracted. Each cow has been characterized by a maximum rate arrived at by averaging morning and evening observations on 2 days. Only this maximum rate has been studied.

Repeatability was high (0·8–0·9) whether measured from day to day or from lactation to lactation. Maximum rate of flow was 10–16% higher in second than in first lactations. The range extended from under 2 lb/min to over 7 lb/min.

Lactation yield of milk varied significantly with rate, rising about 50 gal for an increase of 1 lb/min. This relation is reduced or eliminated by taking into account by partial regression analysis either maximum weekly yield or the increase from the second to the peak week of lactation.

Although the higher yielding cows had larger udder areas bounded by the four teats, the regression of 305-day milk yield on rate was not changed much by taking udder area into account. Cows with short teats milked faster and had higher yields than cows with longer teats.

Differences in yield among the four quarters widened slightly between 1 and 3 months of lactation regardless of rate of flow, except possibly in the three slowest milking cows. In these the differences increased three times as much as in the other cows. The wider the inter-quarter differences in yield the less the proportion of milk obtained at the maximum rate.

Heritability of maximum rate of flow derived from observations on paired singleborn cattle and twins was 85%. Field data would probably yield a value of 60–70%. Appropriate selection of breeding stock would effectively alter rate of flow, but there is no reason yet to expect yield of milk to change except perhaps by reducing the incidence of very slow milking cows.

When washed cream was treated with copper and ascorbic acid and held at 2°C for 1–5 days a strong metallic, fish-oil flavour developed. Compounds responsible for the flavour were isolated and identified. Gas chromatographic separation of a flavour concentrate on a silicone oil column gave six characteristic flavour fractions which, in order of elution, were described as painty or drying oil, oily, mushroom, metallic, tallowy and cucumber. The flavours of all fractions were predominantly caused by carbonyl compounds and the oily and metallic fractions were the main contributors to the typical fish-oil flavour. The following compounds were characterized: n-pentanal and pent-2-enal in the painty fraction; n-hexanal, n-heptanal and hex-2-enal in the oily fraction; hept-2-enal and a carbonyl compound with a mushroom odour in the mushroom fraction; a carbonyl compound with a metallic odour in the metallic fraction; n-octanal, n-nonanal, oct-2-enal and hepta-2,4-dienal in the tallowy fraction; and non-2-enal in the cucumber fraction.

From butterfat with tallowy and painty flavours, the same range of carbonyl compounds was obtained as from fishy flavoured butterfat or washed cream. They consisted of the C5–10 n-alkanals, the C5–10 alk-2-enals, hepta-2, 4-dienal and a compound with a metallic flavour. Heptan-2-one, present only in small amounts in washed cream, was also isolated. Three factors distinguished the tallowy and painty from the fish-oil flavoured butterfat. There was a relative increase in n-heptanal, n-octanal, n-nonanal, heptan-2-one, hept-2-enal and non-2-enal in the tallowy butterfat and a relative increase in n-pentanal and the C5–10 alk-2-enals in the painty butterfat. Secondly, the ‘metallic’ compound was present in such small relative amounts in both the tallowy and painty flavoured butterfats as to have no effect on the flavour. Thirdly, the total weight of volatile carbonyl compounds was about 10 times greater in the tallowy and 100 times greater in the painty butterfat than in the fish-oil flavoured butterfat.

A study was made of the effect of various sampling intervals on the accuracy of estimating lactation milk yield, fat yield, solids-not-fat (S.N.F) yield, fat percentage and S.N.F. percentage. The basic data consisited of daily milk, fat and S.N.F. yields for eighteen lactations made by twelve Dairy Shorthorn cows. Estimates of the lactation yields and quality were obtained using sampling intervals of 7, 14, 28, 42, 56 and 63 days, and were expressed as differences from the actual values. Only in the case of milk yield was there any effective bias in the estimates. This bias increased with increasing sampling interval.

The distributions of differences between estimated and actual values are presented. The error of estimation increased with increasing sampling interval. Keeping in mind the comparatively small-sized sample used in the investigation, the results are discussed in the light of the purposes for which records are kept.

It has been shown that iodine present as iodide in milk can be quantitatively removed by passing the milk through a column of an anion-exchange resin in the chloride form. Any residual iodine is present as non-ionic species which are not removed by the resin.

This technique was used to determine the non-ionic iodine in milk at various times after the oral administration of a single dose of 131I to dairy cows and also during a multiple-dose experiment. Non-ionic131I was present in milk 6 h after its administration and the fraction in this form varied considerably in milk from different cows, ranging from 1·2 to 14·5% of the total 131I content. The chemical form of the nonionic iodine was not investigated.

Removal of colloidal phosphate leads to changes in the propertics of milk of which the increased viscosity and greatly increased sensitivity to calcium salts, and the apparently diminished degree of mutual integration of the various casein fractions are the most striking. Re-introduction of colloidal phosphate restores incompletely and only in certain instances the original properties of the milk.

These observations are interpreted as favouring the conception of chemical links between colloidal phosphate and casein in milk.

Two experiments are described in which spring-calved Ayrshire cows were fed supplementary food when grazing good, leafy pasture.

In the first experiment 6 lb of a mixture of three parts bruised oats and one part flaked maize was fed daily to three groups of five cows. One group received the supplement from 1 July until 30 October, and the other two groups from 1 August and 1 September respectively. A control group received no supplement.

In no month was there any statistical difference in daily milk yield between supplemented and unsupplemented groups of cows. The group fed from 1 July gave the highest total milk yield in the period June to October, but with a return of only 1 gal of milk from 34 lb of meal.

The length of the lactation was not significantly affected by the treatment.

In the second experiment, three groups of four cows on a 9-week change-over trial (4 May-5 July) grazed herbage containing an average of only 17·6% dry matter and 3·8% crude fibre. On the three treatments the cows ate pasture only, pasture plus 1·6 lb hay/day and pasture plus 5·7 lb of meal/day. The meal consisted of four parts by weight of undecorticated cotton cake, four of bruised oats and three of locust beans.

Milk yield was significantly increased from 41·8 lb on the all-grass ration to 43·2 lb/day on the meal treatment but the hay did not affect milk yield.

The fat content of the milk was significantly increased from 3·77 to 3·91% on the hay treatment, whereas the solids-not-fat content of the milk was not significantly affected by any of the treatments.

At the present-day prices of the feeds and with cows on good leafy pasture it was clearly uneconomic to feed the meal supplements.

Three groups of eight Friesian cows, four of high and four of low milk yield, were given during the last month of the winter-feeding period rations that provided respectively low, normal and high planes of energy nutrition, at approximately 75,100 and 130% of the Woodman standards for starch equivalent (S.E.). They were then all changed to the grazing of good, spring pasture, without supplementary food. The changes with grazing in solids-not-fat (S.N.F.) content and yield of milk were markedly influenced by the previous level of winter feeding. After 15–18 days of grazing the mean changes in S.N.F. percentage were +0·33, +0·11 and –0·12 for the low, normal and high energy groups, and the corresponding changes in milk yield were +7·70, +2·13 and –0·68 lb per cow per day. The changes in S.N.F. reflected mainly changes in protein content, and to these casein, β-lacto-globulin and α-lactalbumin all contributed. Small, differential changes were found in the fat and lactose contents of the milk. The effects of the level of initial milk yield of the cow on the various responses to grazing are recorded.

These observations support the view that when a rise in S.N.F. with spring grazing occurs it probably results from an improvement in the plane of energy nutrition. There appears to be no need to postulate a special effect of any specific herbage constituent.