1. A record has been made of the volume of the trade in surplus calves in Great Britain for the period 1940–50; it has averaged one and a quarter million calves each year. The highest numbers sold in any year occurred in 1946 (Fig. 1).

2. The seasonality of calf sales showing an annual increasing volume of autumn calves (with October the peak month) is a reflexion of the development of dairying and of the priority for winter milk (Fig. 2A and Fig. 3, Sheets 1 and 2).

3. Of the total calves 46.7% were classified as bobbies and 50.8% as veals. The small remainder consisted of stirkies (other strong calves), casualties and those unfit for human consumption (Table 1).

4. Nearly 63% of the veals were 3rd quality and only about 12% of the 1st quality.

5. The seasonality of veal deliveries showed a maximum proportion in June (with a correspondingly lower proportion of bobbies in that month). The maximum numbers however correspond with the maximum gross deliveries in October (Fig. 2B).

6. There has been an annual deterioration in the quality of the surplus calves as indicated by: (a) the lower proportions of veals in the total during each year, (b) the higher proportions of 3rd quality veals in the total veals each year, and (c) the reduction in the monthly proportions of 1st quality veals.

7. An attempt has been made to relate the calf sales to calf births and populations of under 1-year-old cattle and of total cows.

8. It is estimated that the calf crop as a percentage of the total cows has improved since 1940, and for the last 8 years it has averaged 92%.

The difficulty of keeping herds free from Strep. agalactiae for long periods has been demonstrated in five herds. In one sense, however, these herds were not representative of the majority of herds for they were relatively large and under the same management. Furthermore, if one herd became infected with the streptococcus, there was a real risk of the infection spreading to all herds via the hands of the relief milker, particularly if hand stripping was practised and no special precautions were taken by the relief milker.

There is no doubt that herds under the same management should take stringent precautions against the spread of infection between herds.

The presence of fat in milking machine liners is probably the chief cause of their deterioration. The primary effect of the fat is to cause softening and swelling of the rubber and greasiness of its surface; the secondary effect is to increase greatly the rate of oxidation. The primary effect may be reversed by removing the fat by solvent extraction or prolonged treatment with cold caustic soda; the secondary effect is irreversible.

Although the fat is derived chiefly from milk, rubber absorbs fat only slowly from liquid milk. Thus it is likely that most of the absorption is from milk residues remaining on liners between milkings, under conditions which favour the breaking of the natural emulsion. Such conditions would include drying, souring or other bacterial activity, and the presence of traces of detergents which act as protein denaturing agents.

Thus, if the widely recommended technique of cold or tepid rinsing is properly practised (8), fat absorption is kept to a minimum, and the life of liners will be prolonged. Under such conditions the absorption of fat from the cow's skin will be more important and methods of removal, or of prevention, such as the use of fat-resistant rubber may be advantageous.

1. Twelve Shorthorn cows were used for an investigation into the effect of diets low in roughage and high in concentrates on the fat content of milk.

2. An experiment was conducted with initial and final control periods. During the control periods all the cows received daily 17 to 21 lb. of hay, 30 lb. of mangolds and 4 lb. of a balanced concentrate mixture per 10 lb. of milk. In the period of experimental treatment, lasting 4 weeks, a control group of four cows remained on this diet. Two other similar groups received daily only 6 and 2 lb. of hay, but this was supplemented with 9 lb. of a concentrate mixture low in fibre and protein. The same allowances of mangolds and of concentrates for production were given to these as to the control group.

3. The mean fat content of milk produced in the last 2 weeks of the period of experimental treatment by cows receiving the diets low in roughage was 0·49 % (group receiving 6 lb. of hay) and 0·59% (group receiving 2 lb. of hay) below that produced by the cows receiving the control diet, these differences being statistically significant. In the group receiving daily 6 lb. of hay the drop in fat content was accompanied by an increase in the yield of milk and there was only a small fall in the yield of milk fat, but in the group receiving daily 2 lb. of hay there was a significant fall in the yield of fat. The latter fall represented a loss of 18·9% of the fat as compared with the control group. The fat content of the milk and the yield of milk rapidly returned to normal when the cows reverted to 18 lb. of hay per day.

4. The butterfat produced by the cows receiving diets low in roughage had a higher iodine value and lower softening point than that from the control cows. The fat from the group receiving daily 2 lb. of hay, but not that from the group receiving 6 lb. of hay, had a distinctly lower Reichert value than fat from the control group. The treatments caused no change in the saponification value.

5. The level of solids-not-fat in the milk was not affected by reduction in the roughage intake.

Of 161 cultures of aerobic sporeformers isolated from raw and pasteurized milk 96 were found to be B. cereus, 27 B. mycoides, 17 B. subtilis, 11 B. sphaericus, 3 B. megatherium, 2 B. pumilus, 1 B. firmus and 4 were unidentified strains.

Typical broken cream followed by rapid sweet curdling of sterile milk was produced by 36 of 39 strains of B. cereus and 5 strains of B. mycoides examined. Three strains of B. cereus failed to produce broken cream. These 3 strains were atypical in that they failed to produce lecithinase, unlike the remaining 93 strains isolated during this study. Other species of aerobic sporing bacilli tested, including 17 strains of B. subtilis, 10 of B. sphaericus, 2 of B. megatherium, 2 of B. pumilus and 1 of B. firmus, all failed to produce broken cream and in fact produced no visual change in milk within 48 hr. at 22° C.

Under the conditions of our experiments, 48 out of 60 samples of fresh farm milk and 12 out of 14 samples of freshly bottled pasteurized milk developed broken cream within 18 hr. at 22° C. followed by sweet curdling within a further 24 hr. Strains of B. cereus or B. mycoides were isolated from all samples showing broken cream, but only 3 atypical strains of B. cereus were isolated from the 14 samples which did not develop the fault.

It seems that the production of broken cream is in some way associated with the production of lecithinase by B. cereus and B. mycoides. This view is supported by the fact that three non-lecithinase producing strains of B. cereus were also unable to produce broken cream. However, attempts to reproduce the fault by adding a concentrated culture filtrate to sterile milk or cream were unsuccessful.

Because of the widespread distribution of spores of B. cereus and B. mycoides in both raw and pasteurized milk, the absolute prevention of broken cream does not seem possible, but preliminary observations suggest that maintenance of milk at 5° C. or lower from the time of pasteurization until delivery to the consumer may sufficiently delay the onset of the fault to obviate the difficulty in practice except in very hot weather in households where insufficient care is taken to keep milk cool.

The keeping quality of various mixtures, made up of raw milk and skim milk-powder in varying proportions, has been studied. It has been found that the keeping quality of unpasteurized samples containing milk powder was slightly better than that of raw milk. The keeping quality of the pasteurized mixtures was satisfactory during the time of storage for 40 hr. at 23 and 18° C. and for 60 hr. at 10° C.

1. The results of experiments on the changes with temperature in the relative viscosity and viscosity of whole milk have been considered.

2. Some inconsistencies have been traced and amendments proposed.

3. It has been suggested that values for the relative viscosity and viscosity of whole milk cannot usefully be regarded as independent of the experimental circumstances in which the observations were obtained.

4. Empirical curves have been calculated for the viscosity-temperature relations, in forms convenient for practical use in circumstances similar to those of the experiments examined.

A method for the determination of lactose in milk based on clarification with dialysed iron and oxidation of the filtrate with alkaline ferricyanide solution, followed by titration with sulphato-ceric acid, is proposed. It is simple, rapid and well adapted to the routine estimation of lactose in milk or to the determination of small quantities of lactose. The conditions of the reactions and comparison of results with other methods are discussed.

1. The coefficient of variation of lactation milk yield was approximately 25% for all age groups. That for lactation milk-fat percentage approximately 10% and that for lactation solids-not-fat percentage only 3%. The last two coefficients tended to increase with the age of the cow.

2. Lactation milk yield was least with first calvers and rose to a maximum for sixth calvers. Milk quality was highest with first calvers.

3. No tendency to vary with the season of calving could be found for any lactation record of any age group.

4. During the first years of the herd's existence there was a small negative correlation between lactation milk yield and lactation milk-fat percentage. This has disappeared in more recent years.

5. There was no correlation between lactation milk yield and lactation solids-not-fat percentage.

6. There was a small (r = +0·40 approximately) positive correlation between lactation milk-fat percentage and lactation solids-not-fat percentage.

Curves are presented showing the trends in the solids-not-fat fractions of milk during the course of normal lactation periods.

The trends may vary with pregnancy, age of the cow, and the mean level of the solids-not-fat.

Seasonal changes in the solids-not-fat content of milk occur only from April to May when the level rises, from May to July when the level falls and from August to September when the level rises again.

These changes are thought to be due to changes in feeding practice.

It has been shown that a statistically significant decline in the level of solids-not-fat in milk from Dairy Shorthorn first calvers occurred in the months of January, February, March, April and August. The period of the survey was the 12 years from 1935 to 1946.

1. Reasons for the seasonal variations in the vitamin A potency of New Zealand butterfat have been investigated. Adequate carotene for the production of butterfat of maximum potency has been shown to be present in New Zealand pasture throughout the year, but during the summer period this carotene is relatively non-available to dairy cows.

2. In experiments with monozygotic twins grazing average summer pasture it has been shown that a supplement of 1 g. of tocopherol per day increased both carotene and vitamin A levels in the milk fat, the total vitamin A potency being raised from a typical midsummer minimum of 34 i.u./g. fat to a value approaching the maximum late winterspring level of about 50 i.u./g. This maximum level was unaffected by increasing the tocopherol supplement to 3 g. per day or by supplying 300 mg. of carotene in a readily available form in addition to the 3 g. tocopherol.

3. Supplementing the summer pasture with 300 mg. of carotene in oil without tocopherol was without effect on the potency of the fat, supporting the conclusion that the carotene intake was already adequate.

4. A significant correlation was found to exist between vitamin A potency and tocopherol content of New Zealand butterfat.

5. It is suggested that the low vitamin A potencies may be associated with the high percentage of clover in the summer pastures.