It is now some 6 years since the appearance in this series of a Review of Bacteriology and Mycology applied to Dairying (1) with sections on milk control, detergents and disinfectants, and pasteurization. Nearly 12 years have elapsed since a complete Review (2) including all the sections listed above was published in the Journal of Dairy Research; some attempt has been made to deal with the more important work going back to these Reviews.

An improved milk-flow recording instrument is described which is completely controlled by the milking operations in an experimental dairy and which automatically indicates the end of milking in terms of a predetermined rate of milk flow. The instrument makes possible the recording of milk-ejection curves without changing the milking routine or requiring an additional operator in the milking shed.

The pulsator mechanism of the double-action milking machine causes the rhythmical expansion and collapse of the rubber teat-cup liner during milking by alternately applying a partial vacuum (usually 13–15 in. Hg) and admitting atmospheric air to the space between the rubber liner and the teat-cup shell. The inside of the liner is subjected to continuous partial vacuum.

The accumulation of fat in a rubber liner occurs mainly in two regions, the mouthpiece and the portion of the barrel in contact with the teat. It is suggested that the mouthpiece is attacked by body fats and udder salves mainly, whereas the barrel absorbs milkfats from milk trapped between the rubber and teat. The accumulation of fat increases linearly with the number of milkings performed.

The loss of milking efficiency is connected with the stiffness of the rubber compound, and this latter property decreases linearly with the number of milkings. The length of service of a liner on the farm is shown to be largely dependent on the individual farmer and his standards of efficiency and cleanliness.

The presence of fat in rubber leads to an enhanced rate of oxidation and consequent loss of physical properties. This has been confirmed in practice. An increase in the tension of a liner increases the rate of swelling and the souring of milk on rubber gives a similar result. The use of detergents has no direct deleterious effect on the physical properties of rubber. They are not effective in removing fat from below the surface layers. The occurrence of ozone-cracking of parts of milk liners or tubing, which are under tension, is discussed and the use of waxes in the compound as a remedy is described.

1. Using the capillary technique previously described, examination has been made of various factors in relation to the reactivation of raw milk phosphatase. Of these, ageing of the raw milk was found to affect considerably the level of reactivation, this increasing as the bacteriological quality of the milk deteriorated.

2. It has been found that absence of air and the presence of reducing conditions in the raw milk increases the reactivation obtained.

3. The influence of reducing conditions on the reactivation of a bacterial phosphatase has been demonstrated.

During the course of some earlier work (not yet published) on the physical properties and the quality of butter, the writer noticed that occasionally a sample was encountered which appeared to be very slightly rancid after only 3 weeks' storage in a cold store. These samples were observed to have a low electrical resistance, and to be of inferior texture, usually exhibiting some free moisture droplets when freshly cut. It appeared likely that there might be some definite relation between the resistance, the texture, and the keeping quality of butter. At the time of these experiments, however, the phenomenon only occurred with a few samples of one type of blended butter. The present note describes an experiment designed to explore the possibility that the relationship might be more general, and apply to other types of butter.

1. A study has been presented of the machine milking rate of 141 cows recorded in 326 lactations.

2. The coefficients of variation between cows of various measures of machine milking rate are usually in the range 30–40%, whilst the within-cow variations are of the order of 8–11%.

3. The differences between the milking rates of cows in a single herd are given, together with the distribution of these differences.

4. Milking rate declines as lactation advances, the decline being greater for fast milking cows.

5. Lactation decline in milking rate is related independently to change in milk yield and to interval since calving.

Chemical factors reputed to promote fishiness in butter were studied. Attempts were made to reproduce fishiness in experimental churnings of butter by deliberately applying factors reputed to cause the defect, viz. low pH, high salt content, lack of pasteurization, traces of copper, borates—singly and in combination.

Supplementation of a typical Danish winter ration with 2 g. of DL-α-tocopherol acetate per cow per day did not result in an increased yield of milk or milk-fat. The keeping quality of the butter was practically uninfluenced or possibly slightly reduced by the supplementation. The supplementation caused a rise in the tocopherol content of the butter from 10 to 12µg./g. in the unsupplemented group to 23–26/µg./g. in the supplemented group. After the experimental period the amount of total tocopherol in the butter decreased rapidly. It increased again when the cows went to pasture.

Butter-fat obtained from the unsupplemented group with 9·6–13·2µg. tocopherol/g. and from the supplemented group with 27·3–31·2µg. tocopherol/g. did not produce encephalomalacia in chicks when incorporated at a level of 30% instead of lard in a suitable test diet, but the amount of tocopherol present, especially in the butter-fat from the unsupplemented group, was not sufficient to prevent white striation of breast muscles in chicks under the same conditions.

A general preliminary description is given of a uniformity trial with twin cattle, the object of which was to study sources of variation within pairs by comparing one-egg and two-egg twins with pairs of contemporary half-sibs. Problems relating to equality of treatment and accuracy of diagnosis are discussed.

1. Results from a uniformity trial with fifteen pairs each of one-egg and two-egg twins and pairs of half-sibs are described.

2. Intra-pair variance in age at the first observed heat was less for the one-egg than for the other pairs but not significantly so. The slowest growing pairs showed delay in onset of heat.

3. 71·8% of the intervals between heats shown by unserved heifers were 17–27 days in length. No genetic variation and no individuality could be detected in either this character or the number of services per conception.

4. The variance in the gestation period was less within the one-egg than within the other pairs but not significantly so.

The preparation of crystalline rennin previously described (1) was somewhat long and inconvenient, but the knowledge gained about the properties of the crystals suggested that a simpler method might be successful. Since then Møgensen (2) has shown that the mere precipitation of commercial rennet with saturated sodium chloride gives a product with proteolytic properties resembling those of the crystalline material, and with enhanced milk-clotting activity per unit of dry weight. Some years previously, Hankinson (3) had also achieved considerable purification by these means. The results of an attempt to discover a simple method of crystallization are described below.

1. Iodinated casein or L-thyroxine, under the conditions of this experiment, had no adverse effect on the general health of a dual purpose (Red Poll) or a dairy breed (Ayrshire) of cattle.

2. The treatment did not increase the total milk or butter-fat production.

3. The treated animals did significantly better than the controls in one lactation only and in the following variables only: (a) daily milk yield adjusted for pre-treatment differences—Red Polls, lact. 1; (b) milk yield for duration of treatment adjusted for pre-treatment differences—Red Polls, lact. 1.