From 6 weeks before calving to the end of lactation 2 groups of 8 cows were fed a ration incorporating a dairy nut containing 29 g/kg urea or an isocaloric isonitrogenous nut containing fish-meal and groundnut. During the 18 weeks after calving, concentrates were fed to appetite. 305-d yields of milk (7023 and 5796 kg) and lactose (345.7 and 273.4 kg) were significantly lower in the urea-fed cows (P < 0·05). Intakes of dry matter, metabolizable energy and digestible crude protein were similar in both groups until 18 weeks after calving when feeding according to yield commenced, but by 6 weeks after calving the urea-fed cows lost only 5% of their immediate post-calving weight compared with 7% in the controls. There was no evidence of ammonia toxicity in the urea-fed cows. Blood glucose concentrations were similar in both groups, but higher serum urea concentrations in the urea-fed cows suggested that there was poor utilization of ingested N. A model proposed by Roy et al. (1977) has been used to calculate the requirements of rumen-degradable protein and undegraded protein (UDP) of the 2 groups from their energy intakes and milk yields. Between 4 and 11 weeks post-calving, dietary requirement for UDP closely matched intake of UDP. It is concluded that UDP intake was a major factor in determining the peak milk yield. Mechanisms by which the degradability of the dietary protein might influence milk yield are discussed.

Dynamic responses of the teat end, measured as changes in external diameter and milk flow-rate, due to step changes in pressure, uniformly applied to the whole teat, are presented. The experiment involved a front and a rear teat of each of 6 Holstein–Friesian cows. The measured variables were: (1) step change in pressure, (2) milk flow-rate, (3) step change in external teat end diameter, (4) rise times of pressure and teat end diameter changes, (5) fall times of pressure and teat end diameter changes, and (6) delay times between pressure and teat end diameter changes both at start of rise and of fall times. A statistical analysis showed that front teats expanded more than rear teats (P < 0·05). Several other findings of importance to any system of milk removal through the streak canal of the teat are discussed.

A frequency response of the cow's teat has been determined by applying sinusoidal changes in vacuum level to the teat. Twelve frequencies were applied ranging from 0.06 to 12 Hz. The responses investigated were the external teat end diameter and the teat milk flow-rate. The measured variables were: (1) frequency of applied pressure and teat end diameter, (2) peak-to-peak pressure and teat end diameter, (3) average vacuum level and teat end diameter, (4) time delay between maxima of vacuum level and teat end diameter, (5) time delay between minima of vacuum level and teat end diameter, and (6) teat milk flow-rate. The results showed that within the range of the investigation milk flow-rates were lower between 0.8 and 2.5 Hz than at frequencies both below and above this range. A statistical analysis of the flow rate and teat end diameter data supports the common practice of applying the same frequency to both front and rear teats during milking. Other findings show good agreement with results reported previously on dynamic responses of the teat to step changes in pressure.

The lactose synthetase activity of homogenates and particulate fractions prepared from the udders of goats killed at various stages of pregnancy were determined. Both components of the enzyme, galactosyltransferase and α-lactalbumin, became detectable about half way through the gestation period, at the time when rapid proliferation of mammary epithelial tissue commences. Throughout the second half of pregnancy the udder possessed a high level of lactose synthetase activity though the lactose content of the tissue did not increase. These findings are discussed in relation to the endocrine control of lactogenesis in the goat and possible mechanisms for the induction of milk production at parturition.

Milk-ejection activity was determined in the blood plasma of ewes during normal milking and during milking when adrenaline was injected intravenously before or after udder stimulation. It was found that administration of adrenaline either before or after udder washing, decreased the oxytocin concentration and milk yield but increased the yield by hand-stripping. Adrenaline also retards the average time for peak oxytocin concentration. These results and the use of a β-receptor blocker to inhibit the effect of adrenaline at the myoepithelial cell level indicate that in ewes adrenaline can prevent the release of oxytocin from neurohypophysis.

Two lactating mammary glands excised from 2 goats were perfused for several hours in the presence of [U-14C; 2,3-3H]-L-valine and received adequate quantities of glucose, acetate and amino acids. In the synthesized milk 96 and 89% respectively of the casein valine was derived from free plasma valine. Valine was extensively catabolized by mammary tissue, resulting in a considerable 14CO2 production and in the incorporation of 14C into milk citric acid and to a lesser extent into casein aspartic acid and glutamic acid. About 30% of the valine molecules which were taken up by the mammary gland were oxidized to CO2 and 70% were incorporated in casein as valine residues. About 10% of the plasma valine molecules were reversibly transaminated during one passage through the udder. An important amount of radioactivity of plasma was present in unknown metabolites. Only 7% of this activity was localized in isobutyrate. The radioactivity of total milk fat was very low. Mainly iso-14:0, iso-16:0 and 15:0 were labelled.

The effects of high rates of infusion of essential amino acids on amino acid uptake by the isolated perfused guinea-pig mammary gland were studied. Infusion of methionine, tyrosine, phenylalanine, histidine and tryptophan (designated group 1) resulted in significant increases in the uptakes of tyrosine, phenylalanine and histidine. Methionine, tryptophan and other essential amino acids were not significantly affected. Infusion of threonine, valine, isoleucine, leucine, lysine and arginine (designated group 2) resulted in significant increases in uptake of all these amino acids. Group 1 amino acid uptake was not significantly affected. Infusion of all the essential amino acids (i.e. groups 1 and 2 together) resulted in significant increases in all their uptakes. Using as index ‘the predicted rate of protein synthesis’, infusion of group 1 and 2 together led to an apparent 27% increase in protein synthesis. The above results are discussed in relation to the control of milk protein synthesis by limiting essential amino acids.

When individual essential amino acids were omitted for periods of 40–100 min from the infusate substrate solution in isolated perfused guinea-pig mammary gland experiments, uptake of methionine, tyrosine, phenylalanine, histidine and tryptophan (group 1) was significantly depressed by a mean of 49·8%, whereas the remaining essential amino acids (group 2) showed no significant decrease in uptake. During depletion periods oxidation of [14C\amino acids was increased. The possible significance of the differences in absorption between the 2 groups of amino acids is discussed.

Pancreatic lipase deacylation was used to study the variation in distribution of the fatty acids at position sn-2 of milk fat triglycerides of a series of butters and of the milk obtained from a cow on a restricted feeding regimen. Selected samples were analysed for stereospecific distribution of their triglyceride fatty acids which were found to be esterified in a non-random manner. The percentage of a fatty acid at position sn-3 generally decreased with increase in the chain length of the acid; the reverse occurred at position sn-1. There was no major variation in the stereospecific distribution of fatty acids throughout the year; the variation that did occur was exhibited mainly by the medium chain length acids. Variation was greater at positions sn-1 and sn-3 than at position sn-2 and when the proportion of an acid varied at position sn-1 it usually varied at position sn-3 in the reverse manner.

For the milk samples it was found that change in triglyceride fatty acid composition was not associated with random increases or decreases of fatty acids at the 3 stereospecific positions. With changing triglyceride fatty acid composition (6:0, 8:0, 10:0, 12:0, 14:0, and 16:0 decreasing and 18:1 increasing) the percentage of 6:0, 8:0, 10:0, 12:0, 14:0 and 16:0 acids at position sn-3 decreased while the percentage of 18:0 and 18:1 acids increased. These changes were compensated for by changes in the opposite direction at positions sn-1 and sn-2.

The heat denaturation of Fe-saturated lactoferrin (If) and Fe-free lactoferrin (apo-lf) was studied using the methods of micro-complement fixation and fluorescence. It was established that the change in conformation of apo-lf, induced by iron binding, conferred a higher heat stability to the molecule: the changes were observed at temperatures above 40 °C for apo-lf and above 60 °C for If. The Fe-binding ability of the protein was partially independent of the degree of denaturation. Fluorescence analyses indicated that tryptophan residues were probably not directly involved in the metal binding. There was no evidence of antibodies interfering with the binding sites.

Quantitative polyacrylamide gel electrophoresis has been used to measure residual native whey proteins remaining after heat treatment of skim-milk and cheese whey in a kinetic study. The denaturation of α-lactalbumin (α-la) appeared to be first order, but was probably a second-order reaction displaying pseudo first-order kinetics. The denaturation of both β-lactoglobulin A and B (β-lgA and β-lgB) followed second-order kinetics while that of serum albumin was more complex, and could equally well be described as first or second order. Equations are given relating log k1 (in s-1) to temperature for α-la denaturation in skim-milk between 70 and 95 °C and between 100 and 150 °C. Similarly, equations relating log k2 (in lg-1s-1) to temperature are given for ²-lgA in skim-milk between 100 and 150 °C, and for ²-lgB between 95 and 150 °C. The relative heat stability of ²-lgA and ²-lgB was found to vary.

Below 95 °C ²-lgA appeared slightly more thermostable than ²-lgB in skim-milk, and the same was observed in cheese whey below 100 °C. Above these temperatures ²-lgB appeared more stable than ²-lgA.

Denaturation of ²-lgB was only slightly more rapid in skim-milk than in whey at temperatures below 95 °C, but was significantly slower at higher temperatures.

Measurements of residual native protein remaining after heat treatment of cheese whey have been made using quantitative polyacrylamide gel electrophoresis. The results have been expressed in terms of kinetic constants. The effect of concentration was investigated up to 3 times the normal total solids content, dialysis treatments were used to study the effect of non-protein constituents, and the effect of pH was studied at pH 4, 6 and 9. The results indicated that increased total solids (TS) concentration slowed the denaturation of β-lactoglobulin A and B (β-lg A, β-lg B) but hastened the denaturation of α-lactalbumin (α-la). However, increased lactose concentration slowed the denaturation of both α-la and β-lg, perhaps by preventing formation of heat-induced complexes. Increased Ca concentration, up to 0.4 mg/ml, tended to slow the denaturation of both proteins, but further increase in Ca up to 0.9 mg/;ml produced little effect. The rate of denaturation of both α-la and β-lg was slower at pH 4 than at pH 6 or 9, and was probably slowest at the isoelectric point. However, not all the changes associated with pH could be explained in terms of net molecular electrostatic charge. The genetic variants of ′β-lg showed different heat stabilities – below 90 °C β-lgA was more stable than β-lgB, but above 90 °C the situation was reversed at all TS concentrations, and pH 6. However, at pH 4 and 9, °-lgA was less stable than °-lgB over the entire temperature range at normal concentration.

Whey proteins have been isolated from cheese whey by complex formation with carboxymethylcellulose. The protein preparations form stable gels and foams when reconstituted in water. A study has been made of the effect of concentration, pH and temperature on the gelling behaviour of the whey protein isolates, and the conditions necessary for a standard gelling test have been defined. Proteose-peptones (p-p) have been prepared from a whey protein isolate which showed a strong tendency to gel, and also from heated and unheated milk. The gelling behaviour of whey protein isolates, which showed either no tendency or a strong tendency to gel, has been studied in the presence and absence of added p-p. The quantities added varied from 0·05 mg isolated from unheated milk to 15 mg from heated milk. No change in gelling time was observed, and it was concluded that p-p were not responsible for the gelling behaviour exhibited by whey protein isolates.

In the past the classification of ATCC 7962 as a strain of Streptococcus lactis has been questioned because it contains β-galactosidase and not β-phosphogalactosidase, and because all extracts do not react with group N antiserum. A comparison was made between ATCC 7962 and known strains of Str. lactis using physiological properties, some of the properties of the lactate dehydrogenases and percent guanine plus cytosine in the DNA. ATCC 7962 was distinguished only by its ability to ferment pentoses. The degree of hydribization between the DNA of ATCC 7962 and that of a typical strain of Str. lactis was 67 %. ATCC 7962 is an atypical strain of Str. lactis. The properties of a wild strain of Str. lactis isolated from radishes in Brunei which contains β-galactosidase and β-phosphogalactosidase, are given also. This strain ferments pentoses.