Three hundred and fifty-one lactating dairy cows, which were between 40 and 100 d post-calving, were selected from cows sampled during metabolic profile testing of 21 herds. Blood samples were analysed for packed cell volume (PCV), blood glucose and haemoglobin, and serum urea-N, albumin, total protein, inorganic phosphate, Ca, Mg, Na, K, Cu and Fe. After adjusting for herd and date of sampling and each cow's age, stage of lactation, milk yield and interval from calving to first service, concentrations of albumin and K (P < 0·01) and PCV (P < 0·05) were inversely related and concentrations of globulin (derived as the difference between total protein and albumin) directly related (P < 0·05) to the number of services required for conception. Conception rates to first service were inversely related to lactation number but not to milk yield on day of sampling.

Using fistulated calves, the influence of the age, type of dietary protein and weaning on the secretion of chymosin and pepsin by the abomasum were studied. The abomasum secreted both chymosin and pepsin when the animals were fed milk. Chymosin secretion appeared to be independent of the age of the animals, whereas a slow increase in pepsin secretion was observed as the calves aged. Several preruminant animals were fed either a skim-milk diet or a milt substitute in which proteins were provided by fish, soya or whey concentrates. Each of these 3 milk substitutes led to a decrease in chymosin secretion without modification of pepsin secretion. Chymosin secretion was partly restored when the calves were again given a skim-milk diet. At weaning, chymosin secretion dropped abruptly, but the pepsin level was not affected. These results indicate that milk (most probably its casein fraction) is responsible for the activation of chymosin secretion.

Diagnosis of microbial infections in the udders of cows in commercial dairy farms for large experiments cannot be without error. Limitations of sampling method and routine prevent collection of the necessary information for sure diagnosis. However, with an organized method of repeated bacteriological examinations using consistent and proven methods of aseptic sampling the errors were shown to be very low. A method based on bacteriological tests on aseptic milk samples was used in 32 herds (approximately 2000 cows) for a 3-year period. This is described and examined in terms of other criteria to validate its use in experimental work. With this method it was not difficult to differentiate between those quarters which regularly shed pathogens and those which did not. Other evidence indicated that it was reasonable to assume that this classification accurately distinguished between infected and uninfected quarters. The errors using this method were quite small: when measuring the state of infection of all quarters in the herds the errors did not exceed 1 %. Some small modifications to the method described are suggested to improve further its diagnostic accuracy.

The efficacy of 18 disinfectant teat dips was tested on teats artificially contaminated with a milk suspension of Staphylococcus aureus. A solution of Na hypochlorite with 40 g/l available chlorine was significantly more bactericidal than one containing 1 g/l available chlorine and than most other disinfectants tested. The method was not able to distinguish differences in efficacy between solutions containing 40 g/l and 10 g/l available chlorine nor between these and some of the iodophors containing 5 g/l available iodine. The addition of 190–416 g/l (15–33 % v/v) glycerol significantly reduced the bactericidal properties of 3 iodophors (5 g/l available iodine), but soluble lanolin at approximately 20 g/l did not appear to lower the efficiency of NaOCl (45 g/l available chlorine) or of an iodophor (5 g/l available iodine).

Six adult West African dwarf does, about 2½ years old and weighing from 24 to 29 kg, were kept for 18 weeks/lactation, and for 2 lactation periods in all. During these periods the does were hand-milked twice daily and the daily samples were bulked for each animal for subsequent analysis. Milk yields for the period were low. Colostrum was characterized by a high content of total solids of 19·2%, fat 8·3%, total protein 5·1% and a gross energy of 517 kJ/100 g milk, but a low lactose content of 4·9%. The composition tended to approach that of mature goat milk between the second and third d after parturition. The mature goat's milk contained higher mean percentages of fat (6·9) and lactose (6·3) than any temperate breeds of goats and indigenous dairy cattle, but their protein (3·9%) and total ash (0·8%) contents were comparable with any temperate breeds of goats. The percentage protein, lactose, fat and total solids declined slightly with advance in lactation and there was a steady fall in milk yield which was statistically significant (P < 0·01).

When whole caseins from cow and Italian buffalo (Bubalus arnee) were fractionated by chromatography on a column of hydroxyapatite they behaved in a similar manner. κ-Casein was eluted with 5 mM phosphate buffer, pH 6·8, containing 0·2 M-KCI, 4·5 M-urea and 2 mM-2-mercaptoethanol, but β- and αs-caseins were retained and could be eluted successively by a linear gradient from 5 mM to 250 mMphosphate buffer. Buffalo κ-casein preparations, obtained from bulk milk or from milks of individual animals by chromatography on hydroxyapatite, produced identical electrophoretic patterns at pH 8·6. By further fractionation of these κ-caseins on DEAE-cellulose, in each case, at least 7 components were purified; they had different electrophoretic mobilities but were all sensitive towards chymosin. The major fraction migrated like component 1 of bovine κ-casein B.

Isoelectric focusing in thin-layer polyacrylamide gel has been applied successfully to the characterization and identification of calf rennet and its substitutes. The use of acidic pH gradients (pH range 2·5–6) allows the identification of calf and microbial rennets and bovine and pig pepsins.

A new, very rapid and sensitive zymogram technique has been developed by overlaying the gel with a highly porous, transparent cellulose acetate film impregnated with casein.

The enzymes chymosin, bovine pepsin A and bovine pepsin B in 40 commercial rennets were assayed by rocket immunoelectrophoresis, using monospecific antibody preparations against the 3 enzymes. Concentrations found were chymosin, 0–1208 mg/l; bovine pepsin A, 359–3818 mg/l; bovine pepsin B, 0–320 mg/l. Bovine pepsin B was found to be a minor enzymic component in bovine rennets, representing maximally 2·9 % of the milk-clotting activity or 9·7 % of the weight of the enzymes. The sensitivity for the quantification of the 3 enzymes was 0·5–1·0 mg/l. The coefficient of variation was 3·7 %. The sum of the immunochemical data converted into milk-clotting activities was in good agreement with the directly observed milk-clotting activity, indicating that there was no immunochemical overestimation due to the presence of non-enzymic active antigens. A high correlation was found between the enzymic composition determined immunochemically and by activity ratio assay.

The coagulation of caseins is considered in the light of a polyfunctional condensation model for protein. This model was originally developed to explain aspects of the polymerization behaviour of small molecules, but it is shown here that it can be used to explain certain aspects of the polymerization of caseins, particularly the Ca2+-induced association of αs-casein and the heat-induced coagulation of casein in whole milk.

The theory of branching processes is used to present a unified kinetic model for the heat induced coagulation of milk. Nitrogen depletion curves for the overall reaction are fitted to a theoretical curve to demonstrate that the reaction is a single process and that the idea of a lag phase up to the coagulation time, followed by the aggregation reaction proper, is an unnecessary complication. Coagulation times as a function of temperature are then used to determine the activation energy of the reaction; the average value of 126 kJ/mol agrees with that found from analysis of the post-coagulation reaction.

Water vapour adsorption and desorption properties of spray- and roller-dried milk baby foods were determined by a dynamic method at 25, 35 and 45°C. The equilibrium moisture content increased with increase in relative humidity and decrease in temperature; values for the spray-dried milk baby food were higher than those for the roller-dried product. The desorption and adsorption isotherms exhibited hysteresis. The desorption isotherms were of sigmoid shape: the adsorption isotherms were of similar shape except for a region of discontinuity. The relative humidity at which this discontinuity occurred depended on the temperature at which sorption was determined. Monomolecular moisture contents and latent heat ratios are reported.

Thermal conductivities of creams of about 20, 30 and 40 % fat were measured at several temperatures between 5 and 75 °C. Because of the meagre data on cream, special attention was given to the prediction of conductivity using different mathematical models. An equation was derived for the thermal conductivity of cream as a function of temperature and volume fraction of the fat phase.

The stability of homogenized ultra-heat-treated (UHT) aseptically-packed cream of 18 % fat content when added to hot coffee was indirectly monitored in 10 batches of cream, stored for 10 weeks at different temperatures. A tendency to coagulate under standard conditions (instability) is known as feathering. Stability was determined by a procedure in which acetate buffer instead of coffee solution was used as the test solution. The distribution of components between the fat and aqueous phases of the stored cream was also monitored. Feathering score (stability) decreased during storage but was not accompanied by any increase in non-protein nitrogen levels. The amount of casein and Ca in the fat phase of the cream increased with time and was inversely related to feathering score. Some batches of cream contained 0·1 % Na2CO3 and 0·1 %Na citrate as stabilizers and these additions were found to improve feathering scores early in the storage period. Initially, the fat phase of these creams contained less casein and Ca than those without the additives, but after 10 weeks the differences in feathering score and in casein and Ca distribution, between the 2 types of cream diminished. Examination by electron microscopy showed that casein micelles were associated with fat globules, apparently linking several globules together, which was less in the creams containing additives, but after 10 weeks the appearance of all creams was similar. Electrophoretic separation of the fat globule membrane (FGM) proteins by SDS-polyacrylamide-gel electrophoresis showed that casein was the principal protein component, but that β-lactoglobulin and native FGM proteins were aslo present.

A small process analyser employing the pulsed nuclear magnetic resonance technique has been used to determine both water and fat contents of milk powder and cottage cheese samples. The procedures used for establishing and eliminating cross-interferences in these analyses are described. For milk powders, water and fat contents in the ranges 1–5 and 0·5–25 % respectively were determined with standard deviations of 0·20 % water and 0·64 % fat. Cottage cheese samples with water and fat contents in the ranges 77–81 and 2–7 % respectively were determined with standard deviations of 0·30 % water and 0·16 % fat.