Experiments were made to determine the effects on yield and butterfat percentage of three times a day milking and of inefficient milking using cows whose milk secretion rates had been shown to be unaffected by the milk accumulation involved. The milking treatments were applied to half-udders of the same cow to ensure that there was no difference between each pair of experimental units in the amount of oxytocic hormone released by the pituitary gland.

Milking three times a day compared with twice a day over a 39-day period resulted in an increase of 12% in both milk and butterfat yields. Increasing the residual milk by 1 lb in each half-udder for a 39-day period caused a 15% decrease in both milk and butterfat yields. It was concluded that since the cause of these findings could be neither the direct effect of differences in milk accumulation nor the effect of different amounts of oxytocic hormone, some local cell effect was involved, activated either by differences in the amount of residual milk or by long-term effects of differences in milk accumulation.

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.

Five hundred and sixty-nine individual cow milk samples from forty-five cows in a single herd were analyzed for fat by the Gerber method, and solids-not-fat by a standard gravimetric method and by the two commonly used British hydrometric techniques. Three hundred and four of the samples were analyzed also for lactose, protein and ash. Large differences between the total solids values obtained by the hydrometric and gravimetric methods were recorded. The magnitude of the differences from the gravimetric values varied with the season of the year and the stage of lactation. The main factor affecting the differences was the protein content of the milk, and equations for the calculation of total solids content incorporating a protein correction factor are given for use if the protein content be known. The hydrometric methods are considered to be of limited use when applied to milks of individual cows.

Comparable cheeses were made using single strains of Streptococcus cremoris and Str. lactis as starters. The three Str. lactis strains imparted a characteristic rather abnormal flavour to the cheese, whereas the three strains of Str. cremoris all gave cheeses of normal flavour. The abnormal flavour caused by the lactis cultures increased in intensity as ripening proceeded, and differed slightly from strain to strain.

Bacteriophage usually developed slightly in the whey and in the curd during the manufacturing process, but never to such a degree as to delay acid production unduly. The extent of phage development did not have a significant influence on cheese flavour.

All the lactis strains survived in much larger numbers in the cheese than the cremoris strains. The simplest explanation of the data is that the ‘lactis’ flavour was a direct effect, due to flavour substances produced by the Str. lactis cells present in the young cheese.

The crystal habit of milk fat is determined by the cooling procedure employed and is changed markedly by interesterification (randomization) of the fat. X-ray diffraction analysis indicated that slowly cooled milk fat occurs in both beta prime and beta modifications, whereas in rapidly cooled milk fat, evidence for the beta prime modification only was obtained. The long spacing was greatly increased by interesterification, especially when the fat was slowly cooled. The presence or absence of certain high melting glyceride fractions greatly influenced solid fat content, softening point and hardness of milk fat.

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.

Using an experimental method of half-udder comparisons the effects on the amount of residual milk of varying milking intervals, the duration of milking, and the delay between the stimulation of milk ejection and the start of milking were measured. Yield of residual milk was not related to the length of milking intervals within the range of 4–16 h but the butterfat content was directly related to the length of the interval. Neither the yield nor the butterfat content of residual milk was affected by a change in the duration of milking of 1 min. A delay between the stimulation of ejection and the start of milking of 6–8 min resulted in increasing the yield of residual milk by about 1 lb.

It is suggested that these results indicate that milk ejection is sufficiently persistent that residual milk is unlikely to be affected by delays between stimulation of milking and the start of milking until they exceed 4–6 min.

Two levels of steaming-up and two levels of concentrate feeding after calving were compared in a feeding trial extending over a complete lactation using sixteen autumn-calving Ayrshire cows in each of 2 years. On the high and low levels of steaming-up 3·3 and 1·6 cwt of concentrates respectively were fed per cow in the 5 weeks before calving. On the high and low levels of concentrate feeding after calving the concentrates were fed at rates of 4·1 and 2·2 lb per 10 lb of milk respectively from the third day after calving until spring grazing began. The total weight of concentrates fed after calving was 25·8 cwt per cow on the high treatment and 12·1 cwt on the low treatment. All the cows grazed good pasture in the autumn and the following spring and had a ration of 9–11 lb of hay and 50–90 lb of grass silage per day during the winter feeding period. During this period the estimated mean intakes of starch equivalent on the high and low concentrate treatments were 17 and 13 lb/day, which were equivalent to 122 and 103% of Woodman's standards respectively.

Milk yield, milk quality, length of lactation and live weight were not affected by the difference between the steaming-up treatments, and no interaction between steaming-up and post-calving treatments was found. Average milk yields in the first 70 and 140 days after calving and in the complete lactations were all higher on the high post-calving concentrate treatment than on the low treatment, and the response per 1 lb additional starch equivalent fed was 1·05 lb milk. The fat content of the milk was similar on all treatments whereas the S.N.F. content increased from 8·64% on the low treatment to 8·82% on the high treatment, giving a response of 0·045% S.N.F. per 1 lb of additional starch equivalent.

Larger losses in live weight occurred on the low treatment in the first 10 weeks after calving than on the high treatment, but in both groups the weights were almost identical after 45 weeks.

Details are given of a method, based on the peroxidase activity of the sedimented erythrocytes, that is suitable for the quantitative estimation of blood in milk.

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.

Three strains of micrococci and two of pediococci were individually tested for effect on Cheddar cheese flavour by their addition to cheese milk. Only one of the micrococcal strains had a significant effect on flavour. In twenty-eight of the thirty-three trials with this strain the flavour of the experimental cheeses was appreciably better than that of the corresponding control cheeses; in the other five trials the experimental and control cheeses were similar in flavour.

This micrococcus did not grow appreciably during manufacture or ripening of the cheese, the peak number being present in the curd at the time of pressing. The count fell to less than 30% of the peak number after 1 week, and to less than 0·5% after 5 weeks.

The ways in which the micrococcus may have influenced the flavour of the cheese are discussed and attention is drawn to the possibility that bacterial action in the milk and the young cheese may play an important part in flavour development.

An apparatus and procedure for the laboratory investigation of some of the factors which control milk deposits on heat exchange surfaces is described. The use of the method has been illustrated by applying it to determine how the amount of deposit varies with the acidity of the heated milk.

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.

Fat and carotene oxidation in Cheddar cheese may give rise to bleached areas surrounding slits in the cheese and to a tallowy flavour. It was shown that direct contact of the fat with atmospheric oxygen was essential for oxidation to occur, and examination of cheeses showed that slits running from the rind into the interior provided this contact. Factors enhancing slit formation such as gas production by bacteria and mechanical shock to the cheese were shown to increase the incidence of tallowy discoloration. Factors which tended to exclude oxygen such as waxing the cheese surface, wrapping the cheese in plastic film or sealing in a tin were shown to reduce the incidence of the fault or eliminate it.

Accelerating factors were shown to be low cheese storage temperature, excess moisture in the cheese and possibly low salt content. Various factors which may be relevant to a commercial cure for discoloration are also discussed.

Two experiments concerned with the testing of plant material for oestrogenic activity, utilizing vaginal reactions and uterine weight changes in immature ovariectomized mice are reported.

In the first experiment the effects of varying the feeding period of an oestrogenic diet, containing 20% of freeze-dried red clover, and of varying the interval between the last feeding of this diet and slaughter were investigated. In general, uterine weight increased linearly with increased period of feeding and decreased linearly with delay in slaughtering. A feeding period of 4 days was satisfactory for comparisons based on uterine weight. If vaginal reactions were also to be utilized a feeding period of not less than 6 days was desirable.

In the second experiment the dose-response relationships of diethylstilboestrol, genistein and oestrogenic red clover were investigated. All materials were incorporated in the diet of mice, and the level of plant material was kept at 20% of the mixed feed by adding inactive plant material where necessary. In general, either diethylstilboestrol or genistein could form a satisfactory standard for biological estimation of oestrogenic activity in red clover. Relative potencies based on uterine weight response and occurrence of vaginal opening and oestrus-type vaginal smears are given.

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.

Unwrapped samples of salted sweet-cream butter were stored in darkness at 1°C for 6–8 weeks over silica gel, water, isotonic salt solutions, and in free air. Moisture and fat peroxide gradients from the surfaces to the interior of the stored samples were measured in thin sections obtained by a simple macrotome technique. The surface oxidized at the same rate as the rest of the butter and its rate of oxidation was not affected by moderate drying or moisture uptake. With severe surface drying, especially when induced by silica gel, fat oxidation was inhibited, while moisture uptake by the more heavily salted butters promoted surface oxidation.

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.

Friesian cows averaging about 30 lb of milk daily, were used for nitrogen balance experiments of the change-over type, in which 3·0–3·5 lb of two mixtures of molasses and urea were added to basal diets low in protein, but containing a high proportion of starch and lower carbohydrates, and ample energy for the amount of milk produced. The molasses mixtures contained 9–10% urea, about 2% H3PO4 and were added either alone or with 7% ethyl alcohol.

In the first experiment, with three cows, the intake of digestible crude protein from the basal diet was about 90% of the recommended allowance and the utilization of urea nitrogen was poor. In the second experiment, with four cows, the intake of digestible crude protein with the basal diet was about 40% of the recommended allowance and the utilization of the nitrogen of urea and of additional groundnut meal was almost complete.

Owing to the way in which the experiments developed the addition of alcohol to the mixture of molasses and urea could not be expected in the present work to increase the utilization of the nitrogen of urea even if it does have that effect under other circumstances. When added to the basal diet very low in nitrogen, the nitrogen of both urea and groundnut meal was used mainly to prevent the withdrawal of nitrogen from body reserves, but partly for a small increase in milk yield.

Under the special conditions of this experiment, which were very favourable for the utilization of non-protein nitrogen, the allowances of digestible crude protein recommended by Woodman (1957) for maintenance of cows weighing 1250 lb (0·73 lb) and 1340 lb (0·82 lb) and giving about 30 lb of milk daily (0·6 lb/10 lb milk) did not appear to be excessive.