A study of the hydrolysis of β-casein-B by crystalline rennin or rennet extract at pH 6·5, using a disk electrophoresis technique, showed that 3 bonds in β-casein are appreciably more sensitive than the others to rennin proteolysis, and that these bonds are probably located near the C-terminus of the protein. The most susceptible bond is hydrolysed, at 10°C, about 200 times faster than any other bond, whilst at 37°C it is hydrolysed 60 times faster. A study of the hydrolysis of this bond showed that its rate of hydrolysis at 37°C and pH 6·5 is decreased by either increased ionic strength or increased calcium ion concentration at constant ionic strength. Conformational changes in the substrate are probably responsible for these effects.

The viscosity and adhesive strength of casein from the milk of 6 individual cows were determined on samples collected regularly over a period of 21 months. Three of the cows calved in autumn and 3 in spring. The viscosity of the casein from 5 of the cows showed a decline during lactation that was independent of the date of calving. It was therefore concluded that the decline in casein viscosity may be attributed to lactational rather than seasonal effects.

The effects of diets high in concentrates and low in roughage on the yield of milk and milk constituents were studied in 32 cows and heifers throughout lactation. A high level of concentrates in the ration caused an increase in milk yield, a decrease in fat percentage but not in total fat yield, and an increase in protein production.

Milk produced under such feeding conditions is capable of yielding greater quantities of curd than would be expected from its fat content, and should be evaluated accordingly. Feed requirements of the cows should be assessed not solely on the basis of the fat content of their milk but also in accordance with the protein content.

TWO levels of roughage, 3 FU (feed units) and 5 FU daily, were fed to Israeli?–Friesian cows and heifers receiving either a normal (Normal) or a high-energy (High) diet.

Milk yield and composition were examined for 12 weeks following parturition. The animals receiving 5 FU of roughage daily showed a higher milk yield during the first 8 weeks. With the Normal diet the amount of roughage had no effect on milk composition. With the High diet, milk yield was higher than with the Normal, and a depression in fat percentage was observed in the milk of cows and heifers receiving 3 FU daily. No corresponding fall in milk protein percentage was observed – the cows of this group (High-3 FU roughage) showing, in fact, a rise in protein percentage. No differences in milk total solids were found. With these high-energy low-roughage diets no correlation was apparent between milk fat and protein percentages.

Bloat in identical twin lactating cattle grazing clover-rich pastures was controlled by twice-daily drenching with 7 ml ‘ Pluronic’ L 64 in water. The drench did not alter milk composition and there was no significant difference in milk production between control and treated groups. A significant (P <0·05) linear relationship between bloat protection and butterfat production was found between twin sets. Drenching increased milk production in high-bloating cows but slightly depressed production in low-bloating animals.

An experiment lasting 4 years has been carried out with 4 groups (3 test and a control) of 10 sheep. Non-protein nitrogen (NPN) (as urea, ammonium sulphate or a mixture of the two) replaced 25% of the dietary nitrogen in the first 2 years and 50% in the second 2 years. The yields of milk, protein and fat were generally depressed in the test groups but not all of the differences reached significance. In the group receiving ammonium sulphate, the milk fat percentage was higher than in the control group in all years and the protein percentage was higher in the last 2 years. Contrary to results elsewhere, the yield of lactose was depressed in all test groups. In the urea group, the content of minerals and of calcium in the milk was significantly less than in the control groups. The total amount of NPN and its components (ammonia, urea and creatine) in milk were not affected by the substitution of NPN in the rations.

(1) Lactating Large White sows were given an intravenous infusion of [U-14C]glucose (3 sows), or of triglycerides containing [1-14C]palmitic acid (1 sow) or [1-14C]stearic acid (1 sow).

(2) The contribution of labelled plasma constituents to the synthesis of milk citrate, lactose, triglyceride glycerol, individual amino acids of the milk proteins and individual fatty acids of the triglyceride fraction was estimated by the ‘transfer quotient’ method. For the glucose infusions the mean values for the transfer quotients were: lactose, 70%; citrate, 42%; glyceride glycerol, 38%; protein, 3%; laurate, 6%; myristate, 12%; palmitate, 6%; palmitoleate, 4% and stearate, 2%. Palmitic acid of the plasma triglycerides made similar contributions of about 60% to the palmitic and palmitoleic acids of milk fat, whereas stearic acid made a major contribution (71 %) to the stearic acid of milk fat but a smaller contribution (42%) to oleic acid.

(3) The results are compared with corresponding values for the goat and the cow.

Samples of commercially processed ultra-high-temperature (UHT) milk were stored at 4, 20, 30 and 37°C for up to 2 years or until gelation occurred.

The stability of the proteins to ethanol, calcium ions and rennet decreased with time of storage. However, preliminary autoclaving of the UHT milk induced a high degree of stability.

The extent of protein decomposition that had occurred in the UHT milk samples depended on the time and temperature of storage. There was negligible decomposition when the samples had been autoclaved before storage at 4 and 20°C. Storage at 37°C led to significant decomposition.

UHT milk samples gelled after being stored for 13 months at 4, 20 and 30°C, but not at 37°C. The autoclaved milk was still fluid after being stored for 2 years at these temperatures.

The time of onset of gelation did not depend on the degree of protein breakdown, and it seemed therefore that proteolysis was not the primary cause of gelation on storage.

It was concluded that the proteins in UHT milk underwent several changes on storage that were apparently independent of each other and led ultimately to coagulation of the milk. These changes included proteolysis, and a progressive loss of stability under conditions that favoured aggregation of the casein micelles.

The concentrations of lactose, potassium, sodium, chloride and citric acid were determined in milks of cows, sows, ewes and goats. For cows, sows and ewes trends with lactation are reported and for all species correlations between constituents in milks secreted in mid-lactation are given. The results are discussed in relation to the secretion of water-soluble constituents in milk.

The interaction of β-lactoglobulin and κ-casein at high temperature was studied polarimetrically. The rate of interaction was related to the genetic variant of β-lactoglobulin present. β-Lactoglobulin B, whose thermodenaturation was faster than that of A variant, interacted more rapidly with κ-casein than did the A variant. Velocity sedimentation studies indicated that characteristics of the complex were determined more by the β-lactoglobulin than by the κ-casein. The presence of κ-casein during the thermodenaturation of β-lactoglobulin appeared to prevent the aggregation of β-lactoglobulin from proceeding to completion, the κ-casein complexing with intermediate species and restricting the aggregation process.

The contribution that the computer has made in the interpretation and analysis of a metabolic profile test, which is designed to monitor the metabolic health of a dairy herd and assess the adequacy of dietary intake for production, is described. The test is based on an assessment of blood chemistry for any number of variates, which constitute the metabolic profile, measured for randomly selected cows from 3 groups of a herd: dry cows, cows giving intermediate quantities of milk and cows giving high daily yields. The computer program is designed to give an objective and comprehensive assessment of the test in an easily interpretable form based on a pictorial form of print-out. The profile is displayed as a ‘histogram’ presented as standard deviations from the normal base-line, and for each variable a scatter diagram is included presenting the individual variates plotted against the particular animal's daily milk yield.

Three experiments were conducted to determine the effect of feeding polyunsaturated fish oils to dairy cows receiving rations of high, medium or low roughage content. In the rumen, the decreases in the proportion of acetic acid and increases in propionic acid induced by the oils became greater as the amount of oil given was increased but the magnitude of the response to any dose depended upon the composition of the basal diet. The effects on volatile fatty acids (VFA) proportions of small amounts of the oils (125–150 ml/day) were greatest with the low-roughage rations. With large doses of oil (375–450 ml/day) the responses were variable but it is concluded that, in general, changes in VFA proportions are least with low-roughage rations.

The fat content of milk was more sensitive to dietary oil supplementation than were the rumen VFA proportions. When the unsaturated oils were given there was a decrease in milk fat percentage and an increase in the proportion of unsaturated fatty acids in the fat; there was also increased incorporation of fatty acids with more than 18 carbon atoms in the milk fat. The metabolism in the rumen tended to become adapted to the feeding of 150 ml/day of oil, the VFA pattern returning during the second and third week of supplementation to that observed before the addition of oil.

Whole milk from cows was concentrated 2-fold by reverse osmosis in a small pilot scale apparatus. All the main constituents of the milk were retained in the concentrate.

The experiment showed that protein was a major cause of blocking of the membrane. Laboratory trials were therefore made on the ultrafiltration of milk to remove the protein with the aim of developing a 2-stage process for the concentration of milk by ultrafiltration followed by reverse osmosis with subsequent recombination of the concentrates from the 2 operations. The rates of both processes and the retentions of the constituents of milk by the membranes were measured.

Thirty-six lactating cows were used in a 3×2 factorial design experiment to study the effects of level of energy and fibre intake on milk yield and composition over an 8-week experimental period. Three levels of fibre intake — 1g of crude fibre per 25, 17·5 and 10 kcal of estimated metabolizable energy (ME) requirements — were given in diets supplying both 80 and 100% of energy requirements. The level of energy intake significantly affected milk yield, milk energy output and the percentage solids-not-fat (SNF) and protein in the milk. The effects of fibre intake on both milk yield and milk energy output were marked but not significant. Fibre intake had a significant curvilinear effect on both the SNF and protein in the milk with the highest fibre intake resulting in a significant decrease in both fractions. A significant linear decrease was obtained in the lactose fraction as the fibre intake increased.

The total volatile fatty acid (VFA) level in the rumen was significantly affected by both energy and fibre intake. The level of energy intake only significantly affected the proportion of propionic acid. Fibre intake significantly affected the proportion of both acetic and butyric acids resulting in mean proportions of acetic acid of 66, 70 and 72 at the low, medium and high fibre intakes. The correlations between the rumen acids and lactation efficiencies are also presented.

Multiple regression analysis within each fibre level has been used to partition the ME available for production between that used for milk energy output and liveweight change. The results showed efficiencies of utilization of ME for milk output of 66, 65 and 56 on the low, medium and high fibre diets respectively.

Nitrogen balance data are presented.

When the pH of milk was varied within the range 7·1 to 6·3 by addition of acid or alkali or through bacterial action, the reflectance of the milk after subsequent ultra-heat-treatment (UHT) was at a maximum of about pH 6·70. Below this value the reflectance dropped rapidly with decrease in pH. The cause of this decrease was the development of increasing amounts of sediment in the product. At pH 6·4–6·5, at least 90% of the casein and 40% of the whey proteins had been precipitated. The addition of 0·1% sodium di-hydrogen phosphate or 0·1% sodium citrate to the raw milk prevented the formation of the sediment. The role of calcium appeared important as small additions of calcium chloride or EDTA altered the patterns of sediment formation and reflectance with changing pH. Addition of 0·3% EDTA prevented sediment formation as the pH dropped.

The distribution of protein nitrogen was determined in milk treated by an experimental ultra-high-temperature (UHT) plant, operating alternatively as an indirect or as a direct heating plant.

The extent of denaturation of β-lactoglobulin can be used to assess the relative severity of UHT heat treatments; this criterion was used to compare the indirect and direct arrangements of the plant with each other and with other published results.

The time-temperature profiles of the plant were used to calculate the expected extent of denaturation of β-lactoglobulin during treatment of the milk. The results of the calculations are in fair agreement with the analytical results.

The protein, phospholipid and neutral lipid composition of a deoxycholatesoluble fraction (DOCM) from bovine milk fat globule membrane (FGM) was determined, at intervals during lactation, in 3 cows maintained at a constant level of food intake. It was suggested that the appearance of free fat in washed cream during the first 2 days post partum was related to membrane stability in colostral secretion. Differences between the cows in DOCM yield (mg/100 g cream lipid) and composition were greatest during the first 25 days post partum. DOCM yield increased markedly as lactation proceeded in one animal, and this was thought to be due to a decrease in globule size. Variation in DOCM composition was principally due to an alteration in neutral lipid content. There were few differences, however, between the quantities of phospholipid and protein in DOCM for all 3 animals, and similarly the percentage composition of the major DOCM phospholipids varied little, phosphatidyl choline being the predominant phospholipid.