The nutritional quality of milk treated by 2 previously described processes for the removal of cationic fission products has been evaluated by the use of the baby monkey (Macaca irus).

The first process involves acidification of the milk to pH 5·2–5·3 and, when the treated milk was tested on baby monkeys, it was found to be nutritionally unsatisfactory. This result confirmed those previously obtained with baby pigs, from which it was concluded that the process cannot be recommended for the treatment of milk intended for young babies.

Two resin beds are used in the second process and no acidification is involved. Milk treated by this process was first tested on baby rats and pigs and then on baby monkeys. No change in the nutritional value of the milk was detected and it was concluded that this is the process which should be used if it should ever become necessary to remove fission products from milk intended for young babies.

Samples of the mammary gland were obtained by the freeze-clamping technique from heifers, lactating and dry cows. Levels of acetyl CoA, citrate, isocitrate and α-oxoglutarate were determined in extracts of the samples and calculated per g fresh gland and per mg DNA. All mammary metabolite levels were significantly higher in lactating cows than in heifers or dry cows. The accumulation in the lactating gland increased in the sequence acetyl CoA–α-oxoglutarate–isocitrate–citrate. NADP/NADPH ratios in cytoplasm, as calculated from the equilibrium of isocitrate dehydrogenase, were lowest in lactating glands. The activities of some enzymes were also determined in the cytoplasm and calculated per g fresh gland, per mg protein and per mg DNA. Mammary citrate synthase activity did not vary significantly between different groups of cattle, whereas mammary isocitrate dehydrogenase activity was higher in lactating cows than in heifers or dry cows. No activity of ATP citrate lyase was detected.

The fatty-acid composition of 17 samples of New Zealand milk fat obtained throughout one dairy season is reported.

The weight percentage of butyric (C4:0) acid was significantly correlated with that of caproic (C6:0) acid and that of caprylic (C8:0) acid. Percentages of C6:0 and C8:0 showed a highly significant correlation with each other and with weight percentages of capric (C10:0) and lauric (C12:0) acids.

There was a highly significant negative correlation between palmitic (C16:0) and stearic (C18:0) acids and between C4:0 and C16:0 acids. Oleic (C18:1) acid showed significant negative correlations with C8:0, C10:0, C12:0, myristic (C14:0) and C16:0 acids.

A method for obtaining distillates from whole Cheddar cheese is described. The distillate has an aroma at −80°C closely resembling that of the cheese before distillation. Gas chromatograms of the distillate were obtained by sampling the vapour over the distillate at −80°C, using both a 15-m Apiezon surface-coated open tubular column and a 1·5-m glass column packed with Porapak Q. The aroma of the effluent was evaluated and the chromatograms simultaneously recorded by passing the vapour through a splitting device before the flame-ionization detector of the gas chromatograph. The compounds responsible for the aromas detected in the effluent were identified using a gas chromatograph directly linked to a mass spectrometer. Of the compounds identified in the distillate, H2S, methanethiol, dimethyl sulphide and diacetyl had the most intense aromas, and these compounds are discussed in relation to their importance to Cheddar-cheese aroma.

A method for detection of proteolysis in milk was evaluated. Amino acids and peptides soluble in trichloroacetic acid were estimated by the Lowry–Folin procedure with expression of results in terms of colour yield equivalent to that of tyrosine (the ‘tyrosine value’ (TV)). Some variables and alternatives in the method of estimation were investigated.

TVs for milk freshly drawn from individual cows were extremely varied (0·31–0·92 mg/ml). TVs for samples of refrigerated milk from daily supply farms were in the range 0·40–0·58 mg/ml; no relationships between TV and bacterial counts were evident with these samples. With bulk refrigerated raw milk supplied to Brisbane for liquid consumption from country depots and local farms equipped with bulk vats, significant positive relationships were found between TV and total bacterial count (TBC) for supplies from some sources, but in no instance was a significant relationship found between TV and psychrotroph or proteolytic psychrotroph count. Significant positive relationships were found between TV of bulk milk supplies from some sources and atmospheric temperature, and between TBC of the supplies and atmospheric temperature. The significance of these various relationships for bulk milks is discussed.

Natural variation in TV imposed limitations on reliability of the method to provide an index of proteolysis; in general the results indicated that its application was restricted to bulk milk cold-stored for at least 3 days.

The kinetics of the primary phase of rennin action on casein micelles and on total casein prepared by ultracentrifugation have been studied. It was observed that the values of Km and V varied for the different casein samples. Addition of whey proteins to the reaction mixture or variation of the concentrations of Na+ and K+ had no effect on Km and V and V, but there was a consistent increase in the values of both these parameters when κ-casein was added. It was concluded that these changes were due to an increase in the accessibility of the κ-casein resulting from the rearrangement of the casein micelles. These results are in agreement with our earlier conclusion that the Km for rennin action on casein is dependent on the carbohydrate composition of the molecule.

When heat treatments of the same sporicidal effectiveness were given, directly heated ultra-high-temperature sterilized milk gave twice as much sediment as indirectly heated milk after storage at room temperature for 100 days. Both types of process reduced the rate of clotting of the milk with pepsin and rennin, but the effect of the indirect process was markedly greater than that of the direct process.

Results are presented demonstrating quality control of the analytical procedures used during the application of metabolic profile tests to dairy herds over a period of 3 years. The significance of analytical variance is discussed in relation to the average population variance in dairy herds.

It is concluded that analytical variance can be restricted to reasonable proportions providing that careful quality control is continuously employed.

A study is reported of the effect of preincubation of raw and laboratory pasteurized bulk milk samples on the tyrosine value (TV) of milk and its relationship with bacterial populations. For raw samples, mean TVs before and after preincubation for 20±2 h at both 25 and 30 °C differed (P < 0·001). After preincubation at 30 °C, the TV of 47 % of raw samples exceeded that considered to represent the upper limit of variation in the TV of a normal bulk milk supply. At this temperature, however, there was no indication that proteolytic psychrotrophs were a major contributor to increased TV. With preincubation of raw samples at 25 °C, an increase to above the upper limit of variation occurred in only 20 % of samples; however, proteolytic psychrotrophs appeared more active at this temperature. In similar samples preincubated after laboratory pasteurization, large increases occurred in TV after 20 ±2 h at 30 °C, while at 25 °C the increases were much smaller and of the order found for preincubated raw samples. The results showed, however, that nonpsychrotrophic bacteria were also the principal source of proteinase giving rise to increased TVs in laboratory pasteurized samples.

A study was made, using Holstein cows, of the relationship between (1) the dose of oxytocin administered; (2) the time between milking and intravenous (i.v.) injection and (3) the time between injection and withdrawal of residual milk. Effectiveness of each dose for removal of residual milk was expressed as the percentage of residual milk in the quarter which was withdrawn by a test milking. The total amount of milk in the quarter was determined by giving a large dose of oxytocin and a second test milking, which then indicated the volume of milk missed by each combination of dose and delay times. It was found that delay before injection had no consistent influence on the effectiveness of the test dose; however, an increased delay after injection required an increase in the test dose for removal of a constant percentage of residual milk. The mean dose required for 75% removal increased from 6·3 mu/kg bodyweight to 57 mu/kg bodyweight as the time from injection to removal of residual milk increased from 5 to 30 min. The doses which produced removal of 75% of the residual milk in at least 50% of the quarters tested were 5, 10 and 40 i.u. for delays between injection and removal of residual milk of 5, 15 and 30 min respectively.

The setting rate of butter during the first 5 h after manufacture was found to be increased by a higher maximum temperature during working, e.g. 15 as compared with 12·5 °C, or by a temporary rise in temperature to 18 °C for 30 min after working. A temporary lowering of temperature to 7 °C for 30 min, however, had no effect. The amount of working did not affect setting rate except where more prolonged working resulted in a higher final temperature in the butter.

When temperature conditions during and after working were standardized, it was found that temperature of pasteurization in either a Vacreator or plate pasteurizer or the presence of clumped fat in the cream had no effect on setting rate. The setting rate, however, was increased by Vacreator treatment as compared with plate pasteurization of cream or by low-pressure homogenization of cream after plate pasteurization.

Microscopic examination of butter samples showed much fewer intact fat globules in butter from Vacreator-treated or homogenized cream than in that from platepasteurized cream.

It is suggested that Vacreator treatment or homogenization of cream affect the setting rate of butter by causing changes in the fat-globule membrane which, in turn, influence the type of crystallization in the fat globules and the stability of the globules.

Four experiments were carried out with Friesian cows in different stages of lactation to determine the influence of the crude-protein content of the diet on the digestibility and utilization of dietary constituents and on the cow's performance and milk composition.

The rations were composed so that they met the energy requirements of the cows, but crude-protein content was widely variable.

Our findings on the digestibility of the dietary constituents were in agreement with the data given in the literature.

The utilization of dietary N for milk secretion was influenced by the level of N intake only when the crude-protein content of the diet was lower than a limiting value, which varied according to stage of lactation. When this value was not attained the daily milk production was affected, but not the protein content of the milk.

The optimal crude-protein content of the diet was 15–16% (dry-matter basis) when milk production exceeded 20 kg/d, 12–13% for a production of 15–17 kg/d and 11–12% for cows giving less than 10 kg of milk daily.

The susceptibility of the components of various caseinate systems (skim-milk, β-casein-depleted milks, colloidal phosphate-free (CPF) milk, sodium caseinate and isolated β-casein) to proteolysis was investigated. Isolated αs1- and β-caseins were quite susceptible to proteolysis, but their susceptibility decreased in heterogeneous soluble systems and even more so in heterogeneous aggregated systems. In skim-milk and β-casein-depleted milks only about 50% of both αs1- and β-casein was hydrolysable by high levels of rennin, and in CPF milk all αs1- and 70% of the β-casein was hydrolysable. It is suggested that about 50% of micellar β-casein is firmly fixed within the micelle and is unavailable for proteolysis, while the remainder can dissociate from the micelle on cooling and is then readily hydrolysable.

The compatibility of the data with the various published models of the casein micelle is discussed, and a modification of Rose's (1969) model is proposed.

The development of a rapid, highly sensitive double antibody–solid phase (DASP) radioimmunoassay for ovine/caprine prolactin is described. The assay was applied to the measurement of basal levels of prolactin in the blood of 4 anoestrous lactating female, 4 anoestrous virgin female and 4 castrated male goats. For several hours after milking there was a chronic gradually decreasing release of prolactin in the lactating goats, such that the circulating levels of prolactin were, for 14–16 h of the day, at a much higher level than those in the virgin female or castrated male goats. The basal levels of prolactin in the castrated male goats (87–200ng/ml) were somewhat higher than those in the virgin females (47–77ng/ml). The effects of feeding and stress on prolactin levels are discussed.

β-Casein is highly resistant to proteolysis in Cheddar cheese. A decrease in NaCl concentration reduced its resistance, but even in the absence of salt the amount of proteolysis of β-casein was slight. Proteolysis in Cheddar cheese increased when the moisture levels were raised by adding water. The relative susceptibility of β-casein to proteolysis by rennin was reduced considerably when the concentration of a sodium caseinate solution was raised from 10 to 20%. Sequestering the Ca2+ by means of EDTA had no significant effect on proteolysis of β-casein. It would appear that the resistance of β-casein to proteolysis is due to the substrate rather than the enzyme and it is suggested that the reduced relative susceptibility to proteolysis is due to some concentration-dependent physical change in the casein molecule which renders the β-casein inaccessible. The salt concentration would also appear to influence this change.

Cheddar-cheese flavour is largely independent of rennet concentration and it is possible to manufacture cheese of satisfactory quality using half-normal rennet levels.

A relationship between the level of dissolved O2 in a product and the head-space volume of a sealed container after filling was derived. The validity of the relationship was confirmed by studies using both water and milk which had been subjected to ultra heat treatment (UHT), and stored in glass bottles. The relation held well for water, but some deviation was noted using milk. The relationship allowed selection of the processing conditions necessary for the manufacture of products with a desired dissolved O2 level.

As part of this study a device was developed which permits continuous monitoring of dissolved O2 in sterile liquids being pumped between a container and an O2 sensor. Only very minor problems were encountered with the device through biological contamination or entry of atmospheric O2.

A technique is described for preparing ultrathin sections from cheese for electron-microscopic examination. The internal structure of fresh Domiati cheese was found to be composed of a framework of large, spherical casein aggregates held by bridges and enclosing fat.

After pickling, the casein aggregates were partly disintegrated into small spherical particles forming a loose structure.

Comparison of the carbohydrates of κ-casein with those of the glycopeptides released by the action of rennin on whole milk showed that there are consistent differences between them, which are due to the presence of carbohydrates in para-κ-casein. d-Mannose, d-galactose, 2-acetamido-2-deoxy-d-galactose and N-acetyl neuraminic acid were invariably present in κ-casein. N-acetyl neuraminic acid was located almost entirely on the glycopeptides whereas the greater proportion of d-mannose was attached to the para-κ-casein. d-Galactose and 2-acetamido-2-deoxy-d-galactose were detected in both para-κ-casein and the glycopeptides. In the glycopeptides there are usually about 2 molecules of d-galactose to 1 molecule of 2-acetamido-2-deoxy-d-galactose. Carbohydrates are attached to only a proportion of para-κ-casein molecules. Carbohydrates could not be detected in αs- and β-casein.

Forty-five Friesian cows were assigned to one of 3 milking management treatments: (1) cows milked 14 times weekly, (2) cows milked 13 times weekly (Wednesday morning milking omitted), and (3) cows milked 12 times weekly (Tuesday evening and Wednesday morning milkings omitted). Cows were removed from the trial at the end of their lactations, and newly calved cows were added as they became available. The trial was continued for 12 months.

When one milking was omitted weekly, the total lactational milk yield was reduced by 3·5%, fat yield by 2% and protein yield by 1·5%. These reductions were not statistically significant. When 2 consecutive milkings were omitted, the yield of milk and of its main components was reduced by 14% (P < 0·001). The effects were greatest for highly productive cows in early lactation.

When one or 2 milkings were omitted the milk yield on the following day was nearly 50% greater than the mean daily yield. No increase in the incidence of subclinioal mastitis was observed in either milking omission treatment.

It is concluded that it is practicable to omit one milking each week though it is suggested that the technique should not be used in highly productive herds unless most of the cows are past the sixth week of lactation.

Forty-five Friesian cows were assigned to one of 3 milking management treatments: (1) cows milked 14 times weekly, (2) cows milked 13 times weekly (Wednesday morning milking omitted) and (3) cows milked 12 times weekly (Tuesday evening and Wednesday morning milkings omitted). The trial continued for 12 months.

Milking omission led to compositional changes in herd milk similar to those described for subclinical mastitis, including increases in pH, chloride level and cell count. Alterations in processing properties consistent with these changes were encountered. Heat stability and curd firmness were affected by extending the milking interval, but the magnitude and direction of the effects varied.

Where only one milking was omitted weekly, herd milk arriving at cheese or powdered-milk factories would not be expected to cause any serious technical difficulties. Omission of 2 consecutive milkings a week would cause processing difficulties where milk was to be condensed or dried, since the maximum heat stability obtained by pH adjustment was reduced.