On the basis of the experimental data provided by Harvey & Walker (1960) and Peterson, Johnson & Price (1949) various mixtures of methyl ketones (mixture K1) and fatty acids (mixture FA) were made up in proportions corresponding approximately to those found in a mature Cheddar cheese (9–10 months old). Only those carbonyl compounds which showed a significant increase in concentration as the cheese matured were included since it was assumed, for these experiments, that these ketones were the key flavour-producing compounds. It was visualized that there might be differences in the uptake of the various ketones by the curd so three additional ketone mixtures (K2, K3, K4), in which the balance of the various constituents had been altered, were also prepared.

1. In an experiment with twenty-four Ayrshire cows, four treatments were compared in a change-over experiment in which each cow completed four periods each of 4 weeks. In all the treatments the cows received daily 4 lb of concentrates and roughage according to their initial live weight. For milk yields above 10 lb the cows received 4 lb of a concentrate mixture per 10 lb of additional milk produced in the previous week in one treatment, and 3 lb in the other three treatments. Two of the treatments with the lower rate of feeding were supplemented with 0·75 lb of sodium acetate daily, given in either one or three doses.

2. Digestion trials were made with the hay and concentrates to aid in the estimation of their starch equivalents. The allowance made for the maintenance requirements of the cows appears to have been close to that recommended by Woodman (1957).

3. On one treatment the cows in fact received 4·29 lb of concentrates/10 lb of milk produced, and gave on average 36·6 lb of milk (35·2 lb of 4% fat-corrected milk) in the last 2 weeks of the experimental period with a daily decline in milk yield of 0·14 lb/day. On the other treatments the cows in fact received 3·48 lb of concentrates/10 lb of milk produced, and averaged 34·4 lb of milk daily with an average daily decline of 0·21 lb/day; this differed significantly from the rate of decline observed with the higher rate of feeding.

4. The addition of 0·75 lb of sodium acetate to the daily diet, in one or three doses, exerted no detectable effect on milk yield or composition, apart from a small effect on the solids-not-fat (S.N.F.) percentage which was of doubtful meaning.

5. At the higher rate of concentrate feeding the S.N.F. content was 0·10% higher than at the lower rate of feeding. This difference and the resulting difference in the yield of S.N.F. (0·21 lb daily) were significant.

An apparatus, which has certain advantages over that designed by Claassens, is described for measuring the combined forces of cohesion and adhesion (‘hesion’). The effects of varying the loading rate are discussed. Heidebroek & Pietsch's theory, which is applicable to adhesion between lubricated metal surfaces, is shown not to hold for butter.

Hesions measured with the new apparatus are compared with the frictional and consistency parameters of Prentice's butter extruder and also with the liquid-fat index. The relationships depended largely on temperature. The majority were significant (P < 0·01). A linear relation was found between Prentice's two parameters, leading to a high correlation coefficient (0·88).

Preliminary experiments are described on the effects of prolonged working and also on the relationship between hesion and weight variations during the printing of butter.

The characteristics are given of a Chaddar cheese defect known as ‘tallowy discoloration’ or ‘white streak’. In the tallowy portions of the cheese the copper content is lower and the iron content higher than in the adjacent normal cheese. The copper probably migrates in cheese following oxidation of the sulphydryl compounds in the tallowy area while the unexpected distribution of iron may be explained by changes that occur during salting of the curd. The proportion of ferrous to ferric iron tends to increase as the cheese matures and tallowy portions of cheese do not contain less ferrous iron than adjacent portions.

The addition of iron salts to cheese milk did not increase the incidence of tallowy discoloration, but the addition of sufficient copper salts reduced it. Although the sulphydryl content of cheese appeared to be related to tallowy discoloration, little evidence of the part it plays was obtained. The oxidation of sulphydryl groups and the formation of peroxides occurred more readily at lower temperatures.

The significance is discussed of ferrous iron in a fat-oxidizing system where copper does not increase oxidation.

Evidence linking a Cheddar cheese defect, known as ‘tallowy discoloration’, with a haematin-catalysed oxidation of the fat is presented. The defect has been produced experimentally by incorporating blood in the cheese-milk. The possibility that excessive amounts of blood in the cheese-milk may be a prime cause of tallowy discoloration is discussed.

The amido black and orange G methods for protein estimation in milk were investigated. The quantity of dye required for complete precipitation of a given quantity of milk protein was determined.

Dye samples of various degrees of purity all gave a linear relation between protein and dye precipitation, as determined by optical density, but with the less pure samples slightly less dye was bound per unit weight of protein.

Amido black, though reacting with protein in the same molar ratio as orange G, gave a much more sensitive optical indication of protein content.

In milks of individual cows there was a relatively constant relationship between dye values and Kjeldahl protein from 3 to 4 days after calving until 3 to 4 weeks before the end of lactation. Late lactation milks gave about 5% higher dye values than did normal milks of the same protein content.

The relation of dye precipitation to Kjeldahl nitrogen was the same for casein as for total nitrogen in normal milks.

Forty-four strains of tributyrolytic group D streptococci isolated from Cheddar cheese were identified by physiological, biochemical and serological tests. They were also independently grouped using two-way paper chromatography in which patterns of ninhydrin positive spots were developed from 10% acetic acid extracts of the bacteria. The groupings obtained by the chromatographic and conventional techniques were then compared. Strains of Str. durans were well differentiated by chromatography from the other species of group D streptococci examined, but with the remainder less clear differentiation was obtained.

Since grassland conservation crops are normally bulky fibrous feeds and often limit the appetite and nutrient intake of dairy cows, a feeding trial was made in which a basal ration of hay and grass silage was compared with similar rations containing roots. Three rations were compared in a 12–week winter feeding trial using twelve Ayrshire cows. Ration A consisted of 8 lb of hay and 65 lb of grass silage daily, whilst rations B and C contained 30 and 60 lb of fodder-beet, respectively, in addition. With all three rations concentrates were given at 3½ lb per 10 lb of milk. The total weights of dry matter consumed per day were 29·1, 32·5 and 35·4 lb, respectively, for rations A, B and C and were significantly different. For every 1 lb of additional fodder-beet dry matter eaten the decline in the amount of basal feeds consumed was 0·45 lb. The largest effect was on the silage which fell from 10·8 lb of silage dry matter per day for ration A to 8·8 lb for ration B and 6·8 lb for ration C.

The weight of starch equivalent (S.E.) given per day increased significantly from 18·1 lb for treatment A to 22·2 lb for treatment C, whilst at the same time the total weight of crude fibre and lignin eaten decreased significantly in the rations containing fodder-beet.

The mean daily milk yields for rations A, B and C were 37·4, 39·2 and 38·5 lb, respectively, with a response of 0·9 lb milk per 1 lb of extra S.E. given between rations A and B but no further response between rations B and C. The fat percentages of the milk were not significantly different for the three rations whereas the solidsnot-fat (S.N.F.) varied significantly from 8·58% for ration A to 8·77% for ration C— a response of 0·05% S.N.F. for each additional 1 lb of S.E. The change in the S.N.F. was mainly in the protein fraction of the milk. The cows were significantly heavier when on ration C than when on ration A.

The effect of feeding roots on the appetite of the cow and on the resulting milk quality, and the problems of growing roots on intensively managed grassland farms are briefly discussed.

In experiments to determine the effect of feeding changes on milk yield and composition, udder disease or injury may easily invalidate the results, particularly those for milk composition. It is suggested that regular examination of the milk from each quarter of the udder would allow a diseased or injured quarter to be recognized and a true value for the effect of the feeding treatment to be obtained from the composition of the milk from at least two healthy quarters. Examples to illustrate the suggestion are given.

Interesterification of milk fats resulted in increased softening points, hardness and high melting glycerides (HMG). Increasing the content of trans-unsaturated acyl groups in milk fat resulted in increased softening points and hardness. While the increased solid fat content after interesterification occurred mostly at the higher measuring temperatures, the increase due to isomerization occurred mainly at the lower measuring temperatures. However, in both cases hardness was increased at all measuring temperatures. These results indicate that glyceride structure and trans-unsaturated acyl content influence the physical properties of the solidified fat.