Seven changeover experiments were conducted to examine the effect of giving restricted amounts of concentrates on the voluntary intake of different roughages by non-lactating dairy cows. The addition of up to 6 kg concentrates daily to the diet of cows receiving roughage ad lib. caused little change in the intake of hay and a small increase in the intake of barley straw. Larger amounts of concentrates of 6 and 8 kg daily reduced hay intake by between 0·2 and 0·4 kg dry matter/kg concentrate dry matter given. When concentrates were given to the cows the rate of decline in intake of hay tended to be greatest with the hays of highest digestibility. The daily addition of up to 8 kg concentrates to the diet of cows offered silage ad lib. caused only small depressions in the intake of silage. The results are discussed in relation to recent work on this subject with cattle and sheep.

Two experiments were conducted with non-lactating cows to examine the effect of adding concentrates to a diet of hay on the rate of disappearance of digesta from the alimentary tract. The addition of large amounts of concentrates to the diet of cows offered hay ad lib. decreased the voluntary intake of hay, increased slightly the digestibility of the organic matter and decreased markedly the digestibility of the crude fibre of the diet. Also, the addition of concentrates increased the mean time of retention of stained hay residues in the alimentary tract and increased the time/kg hay the cows spent ruminating. At the end of a meal the amount of digesta in the reticulo-rumen of the cows offered hay ad lib. with restricted amounts of concentrates was about the same as that found when offered hay ad lib. as the only food. The results are discussed in relation to the regulation of the voluntary intake of hay by the cow.

Dry butterfat occasionally develops a greenish colour when stored for at least 1½ years at −12°C whereas samples of the same fat kept for 2 years at +2 or +15°C do not show this colour defect. Spectrophotometrical measurements have shown that the defect is accompanied by a chemical change of the carotene. Its absorption maxima are shifted towards the shorter wavelengths, and a new absorption is observed at 400–410, 430–435 and 450–460 mm. The possible involvement of oxidation products of carotene, such as isomeric diepoxides or furanoid oxides is discussed. The colour defect can be observed before any change in flavour is noticed.

The C1,2,5–8 n-alkan-1-ols were identified from oxidized butter prepared from cream treated with cupric chloride and ascorbic acid. The six n-alkan-1-ols occurred in approximately equimolar amounts and in concentrations of approximately 1 μmole/kg, the same order of magnitude as that of the C6–9 n-alkanals. The amounts increased rapidly during the first 4 weeks of storage, but only slowly during the succeeding 4–20 weeks. Only insignificant amounts of the C3–8 alkanols formed in the untreated samples. It is suggested that C1–8 alkanols are formed by the oxidation of unsaturated fatty acids according to the theory of Farmer, Koch & Sutton (1943) from primary alkoxy radicals resulting from the decomposition of lipid hydroperoxides.

Lactose could not be detected in the urine of non-lactating cows but was invariably found, though usually in low concentration, in the urine of lactating cows; the highest values were observed with cows of high lactation number. Towards the end of an extended milking interval of 39 h, the lactose concentration in the blood and the excretion of lactose in urine increased markedly, but on milking there was a rapid return to original values. Lactosuria was observed in pregnant cows from about 20 days before parturition, and at parturition there was a temporary, marked increase in the excretion of lactose in urine.

Milk was analysed from twin Saanen goats. In one of the goats one mammary gland was transplanted to the neck. The milk yields and fat content from each gland were recorded and the composition of the fat examined using gas-liquid chromatography. The yield and fat content of the milk from all the glands fell within the normal range. With the operated goat, the milk from the transplanted gland differed little in fatty acid composition from that from the non-transplanted gland. Milk from either gland differed little in this respect from milk from the normal goat.

A technique for determining the concentration of leucocytes in cow's milk is described which is more rapid and accurate as well as much less tedious than conventional microscope methods. The leucocytes are isolated from the fat globules of comparable size by a novel centrifuging procedure. Sizing of the leucocytes with a Coulter electronic counter shows that their volumes range from about 45 to 1770 µm3 but a partially overlapping distribution of other particulate matter prevents the accurate determination of the total number of cells present. The numbers counted in truncated leucocyte distributions, however, correlate linearly with total cell counts determined with an improved microscope method up to 6 × 106 cells/ml of milk.

Van den Hamer & Elias (1958) described a method of estimating D(–) lactic acid using lactic dehydrogenase and a Warburg technique. The enzyme was obtained as an acetone preparation of Escherichia coli grown on a medium containing lactate as energy source.

A subjective test for the determination of the stability of milk protein to heat is described. In the test, the time required for particles of coagulated protein to become visible throughout a 2·5-ml sample of separated milk maintained at 135°C in a glass tube rocking at 8 c/min is taken as a measure of stability. The precision of the test was such that single determinations were generally adequate.

Coagulation time decreased by about 12% as rocking speed was increased over the range 4–12 c/min and increased by a factor of about 3 for a decrease in heating temperature of 10 degC over the range 140–105 °C; with some milks the Q10 °C value increased to 5–8 a temperature decreased. As sample volume was increased over the range 1–3 ml coagulation time increased, especially With milks whose coagulation was poor (initial clots small). This volume effect appeared to be a consequence of the accompanying decrease in the proportion of headspace oxygen to volume of milk.

The effect on heat stability as measured by coagulation time, of storing separated milk at 20, 4 and −20 °C has been examined. Milk with a good coagulation (initial clots large) could be stored for at least 30 h at 20 °C, 1 week at 4 °C and 1 month at −20 °C with no significant change in coagulation time. With milks giving a poor coagulation (initial clots small), a common occurrence during storage at 20 °C was a marked progressive increase in coagulation time; the rate of increase was reduced by storage at 4 °C. The increase in coagulation time of these labile milks, which are usually obtained from cows with subclinical mastitis, may occur to the same extent in darkness as in light, may be enhanced by exposure to light or may occur only when the milk is exposed to light. From these results, together with others reported by Davies & White (1966) and White & Davies (1966) it is concluded that, in studying heat stability, milks giving a good coagulation should be regarded as in a different class from milks giving a poor coagulation.

An objective test has been developed to help in assessing the value, as a method for determining the heat stability of milk, of the subjective test described by Davies & White (1966a). The objective test showed that coagulation time, as determined by the subjective test, is a reasonably accurate measure of the induction period that precedes the onset of initial rapid coagulation, but that coagulation proceeds in 2 different ways depending primarily on whether the coagulation of the milk is good (initial clots large) or poor (initial clots small). The latter finding confirms the view that in studying heat stability these 2 categories of milk should be examined separately.