The conductivity of raw and homogenized milks was measured using apparatus capable of high precision. The effect of fat content was examined and found to conform to the established behaviour for a polydisperse suspension of nonconductors in a homogeneous conducting medium. Homogenization of the milk over a range of pressures was found to have no measurable effect on the conductivity.

A routine method giving accurate results was required for the determination of the glyceride content of eluate fractions obtained in the silicic acid chromatography of lipid mixtures. The technique of determining glyceride glycerol by saponification, oxidation of the liberated glycerol to formaldehyde, reaction of the formaldehyde with chromotropic acid and measurement of the resulting chromogen at 570 mμ has been investigated. Procedures based on this principle have appeared in the literature but none of these has been found to be entirely satisfactory. Accordingly, a modification of the method has been developed that is capable of giving results of a high degree of accuracy.

Details are given of a histochemical technique suitable for the detection of alkaline phosphatase in cheese.

Lactoperoxidase activity has been measured in whey form fresh milk and from milk cultured with Str. cremoris or Str. lactis. It was found that with benzidine as hydrogen donor, the optimum H2O2 concentration in whey from fresh milk was 10–4M, whereas in whey from cultured milk it was greater than 10–2M. The lactic acid streptococci appeared to modify lactoperoxidase. The modified form of the enzyme resembled lactoperoxidase in its absorption spectrum, its inhibition by fluoride and cyanide, its chromatographic behaviour on IRC50 resin and its activation energy of heat denaturation, but differed in its heat and pH stability, and its optimum hydrogen peroxide concentration for reaction with benzidine or o-dianisidine.

Details are given of the method used in this laboratory for the preparation of k-casein. The recovery is about 25% and the material has a purity, estimated from electrophoretic patterns, of about 90% with β-casein as the main contaminant. Higher temperatures and lower ion concentration caused precipitation of k-casein in the presence of calcium ions, 0·1m-acetate buffer at pH 6·5 being sufficient to stabilize a 0·5% solution in the presence of 0·01–0·2m-CaCl2 at 20 and 30°C but not at all calcium concentrations at 40°C. It was also found that solutions of para-k-casein did not aggregate in the presence of concentrations of electrolytes above about 0·25m.

The rate of release of non-protein nitrogen and decline in viscosity during the enzymic stage of gel formation in solutions of k-casein and rennin had similar apparent first order constants (0·087 ± 0·03 min—1 and 0·086 ± 0·021 min—1, respectively, at 25°C). A gel could be formed by rennin action in a solution containing as little as 6·25mg of the protein per litre. In the non-enzymic stage of gelling of k-casein solutions the calculated activation energy over the range of 20–40°C was much lower than that obtained from the non-enzymic stage of milk coagulation.

The ‘metallic compound’ previously reported as an important cause of off-flavour in oxidized dairy products has been identified as oct-l-en-3-one. The compound was found to have a flavour threshold value of one part in 109 in butterfat and one part in 1010 in water. This compound was also isolated from oxidized safflower oil.

A study was made of the effect of various factors which may influence the calcium content of milk. The basic data consisted of the calcium content of 20840 samples of individual milks, taken once a month, during the course of 2300 lactations of Montbeliarde cows. For each lactation, a weighted average figure for the calcium concentration was calculated, taking into account the milk quantities recorded on each sampling day. The calcium content has been expressed in g/kg of milk.

The stage of lactation caused significant variations in calcium content mainly during the first month and the last three months. Expressed as percentages of the arithmetic mean for the whole lactation period, these variations were always within the limits —4 to +8% (Fig. 1).

The season of calving did not greatly affect the weighted lactational average content of calcium but caused some important changes in the average value with advancing lactation (Fig. 2). The minimum values were always observed in July, whatever the month of calving (Fig. 3).

The age of the cow, as well as the age at first calving (Table 1), had very small effects on the calcium content.

Four hays were compared in a 20-week winter feeding trial using eight Ayrshire cows. The hays consisted of either ryegrass (variety S 24) or cocksfoot (S 37), and each grass was cut either on 23–25 May (cut 1) or 3 weeks later on 13–15 June (cut 2). The ryegrass cut 1 hay (R1) had the highest content of digestible dry matter, the cocksfoot cut 2 hay (C2) had the lowest content. The ryegrass cut 2 hay (R2) and cocksfoot cut 1 hay (Cl) had intermediate values. On all the treatments the cows were offered 19 lb of hay daily plus concentrates at the rate of 3½ lb/10 lb of milk.

The consumption of concentrate dry matter was almost identical on the four treatments and averaged 10·1 lb per cow per day but the intake of C2 was slightly, but significantly, below that of the other three hays. On average the hays contributed 62% of the total daily intake of dry matter. The total weight of starch equivalent (S.E.) eaten per day increased from 13·6 lb on the C2 treatment to 15·2 lb on the R1 treatment.

The mean daily milk yields on the four hay treatments were: Rl, 32·1 lb; R2, 29·9 lb; C1, 30·5 lb and C2, 26·9 lb. On average the milk yields from cut 1 hays were significantly higher than the yields from cut 2 hays, and the yields from the ryegrass were significantly higher than the corresponding yields from the cocksfoot. The differences in milk composition between treatments were small. The fat percentage of the milk on C2 was higher than that with the other three hays, and with the higher yielding cows the solids-not-fat (S.N.F.) and crude protein percentages were significantly higher on R1 than on the other hays.

It is concluded that the nutritional value of ryegrass hay is superior to that of cocksfoot hay for milk production.

From an analysis of the milking rate data of 200 cows it has been shown that for individual cows the yields of milk obtained in the second minute of milking give a good prediction of their maximum milking rates.