Two fistulated adult bulls of the Zebu breed and 2 fistulated adult buffalo steers were given a diet consisting of concentrate mixture (rice bran and cotton-seed cake in equal portions +2% calcium hydroxide + 1% common salt) and straw. This was later changed to an all-roughage diet of first cut berseem (Trifolium alexandrinum) Samples of the rumen contents were taken for determination of protozoal differential counts, concentration and relative proportions of volatile fatty acids (VFA), rate of cellulose digestion, fermentation rate, and net growth of rumen micro-organisms. Further data were obtained for the 2 buffalo steers fed sweet Sudan grass. When the feed consisted of concentrate and straw there were significant differences in the numbers of protozoa and in volatile fatty acid concentration in the 2 species of animals. Higher protozoal counts were observed in the rumen of bulls (7·2−8·1 × 105 organisms/ml) than in the rumen of buffaloes (2·6−3·6 × 105 organisms/ml). Greater concentration of VFA was found in the rumen of buffaloes (5·3−11·2 mequiv/100 ml rumen liquor) than in bulls (4·8−10·4 m-equiv/100 ml rumen liquor). With berseem, the concentration of VFA in the rumen was generally higher (6·73−11·0 m-equiv/100 ml rumen liquor) and the protozoal counts were lower (2·8−5·2 × 105 organisms/ml) but there were no significant differences between bulls and buffaloes.

The rates of cellulose digestion and the maximum fermentation rates were similar in the 2 species indicating a microbial population of the same order. Higher rates of cellulose digestion and of maximum fermentation when the ration consisted of berseem than when it consisted of concentrate + straw indicated a higher concentration of micro-organisms, mostly bacteria.

The hydrolysis of κ-casein by a number of rennets and other proteolytic enzymes has been followed by measuring the increase in opacity due to the formation of insoluble aggregates of para-κ-caseins. The stability of these precipitates varied markedly, some being solubilized rapidly by the further action of the enzyme. The turbidity obtained with certain enzymes was dependent upon the calcium ion concentration, indicating that the para-κ-caseins produced were not identical for all enzymes.

For high concentrations of calf rennet, the rate of aggregation was linear with respect to time. With low concentrations of enzyme, increase in turbidity was preceded by a lag period which was lengthened by decreasing the enzyme concentration or increasing the κ-casein concentration. This increase in lag is favoured by a high κ-casein/para-κ-casein ratio, suggesting that the aggregation of newly formed para-κ-casein is prevented by the unchanged κ-casein. In addition, small amounts of αs1- or β-caseins present in the κ-casein also markedly affected the aggregation of para-κ-casein, indicating that all 3 major casein components can inhibit the aggregation of para-κ-casein in the absence of calcium ions. In the light of these observations the possible role of protein-protein interactions in casein coagulation by calf rennet is discussed.

An agar diffusion slide assay using a thin layer of calcium caseinate has been developed as a micro-method for the quantitative study of calf rennet and other proteolytic enzymes. The number and width of the precipitation zones formed as a result of proteolytic activity depended upon the enzyme used, the concentration of calcium ion, pH and temperature. The assay was highly reproducible and particularly suitable for the measurement of large numbers of samples. It was considerably more sensitive than the milk clotting technique and, in general, more sensitive than other standard methods for measuring proteolytic activity.

A re-investigation has been made of the nature of the tainting substances present in butterfat possessing the weed taint which arises through the ingestion of Lepidium spp. by dairy cattle. Some 0.5 ppm of skatole were isolated from Lepidiumtainted butterfat, along with 0.3 ppm indole. Flavour evaluation tests demonstrated that the skatole was principally responsible for the flavour defect, somewhat modifying the conclusions arrived at by earlier investigators.

Unheated Coronopus-tainted milk yielded butterfat from which benzyl methyl sulphide, benzyl isothiocyanate, benzyl cyanide, indole and skatole were isolated by high-vacuum distillation. The first 3 of these compounds were also isolated from the corresponding skim-milk, buttermilk and butter serum by vacuum steam distillation: identification was by gas chromatography and mass spectrometry.

The flavour threshold of benzyl methyl sulphide in milk and butter oil was found to be respectively, 1 part in 108 and 1 part in 107, whereas the amount isolated from butterfat was approximately 1 part in 106.

This evidence, together with the similarity in flavour of the Coronopus taint in milk and butter oil with that of untainted milk and butter oil to which had been added respectively, 1 part in 107 and 1 part in 106 of benzyl methyl sulphide, demonstrates that benzyl methyl sulphide is a principal contributor to the flavour defect. A hypothesis is proposed to explain the origin of the sulphide and related components in the milk. The possibility remains that in commercial weed-tainted butter, which is made from heated cream, other compounds may be present.

A study was made of the effects of the hormones, prolactin and cortisol acetate, on the activities in the mammary gland of the pseudopregnant rabbit of the enzymes concerned with lactose biosynthesis and glucose 6-phosphate metabolism, namely: UDP-glucose pyrophosphorylase, UDP-glucose-4'-epimerase, phosphofructokinase, phosphoglucomutase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. Significant increases in enzyme activities were observed in rabbits examined 3 or 4 days after receiving a mammary intraductal injection of prolactin. The activities were not significantly increased at examination 2 days after injection of prolactin. Rabbits receiving cortisol acetate each day for 3 days also showed no significant increases in mammary enzyme activity. However, when prolactin and cortisol acetate were given simultaneously over a period of 3 days, increased enzyme activities were found suggesting synergistic action of the hormones.

Experiments with continuously made curd leading to the use of a 4-min scalding period at 48°C for Cheddar curd-making are described. The short time at 48°C had only a slightly adverse effect on the starter, and the moisture content of the drained curd was within the range usually found in conventionally made curd at the same stage. The starter was allowed to grow in the drained curd during cheddaring. After 3–6 h the pH and moisture content were the same as those of normal cheddared curd.

Aseptically drawn milk was made into small cheeses (100 g) under aseptic conditions. The influence of the cow's feeding régime on the composition of the cheese fat, and the hydrolysis of the cheese fat and protein by bacterial and native milk enzymes, was studied.

In the absence of a strongly lipolytic bacterial cheese flora, the free fatty acid (FFA) content of cheese appeared to depend on several variables:

1. The initial FFA content of the milk varied according to the mode of milking (the lowest was obtained by cannulation of the udder) and the feeding régime of the cow. When one of a pair of monozygotic twin cows was maintained on pasture and the other on winter feed (hay and concentrates), the cheese made from the milk of the latter contained less FFA than did that from the former.

2. The major changes in the composition of the milk fat of the cows on winter regime were an increase of myristic and palmitic acids from 8 to 11% and 21 to 28%, respectively, and a decrease in stearic and oleic acid from 11 to 7·5% and 38 to 28%; minor changes in the other fatty acids were also observed.

3. The milk lipase in raw milk cheese liberated substantially more FFA than did the weakly lipolytic lactic acid streptococci. Milk lipase was active at the low pH value of cheese, but was inactivated when the milk was pasteurized at 63°C for 30 min.

4. Although rennet did not produce any amino acids in the mature cheeses it hydrolysed some of the cheese protein to nitrogen soluble in water (WS), trichloroacetic acid (TCA-S) or phosphotungstic acid (PTA-S). Some of the WS-N appeared to be utilized by the lactic acid streptococci. The native milk protease resisted the heat treatment used and liberated amino acids at the low pH value of cheese, but its contribution to the proteolysis was relatively less important than the contribution of the milk lipase to the fat breakdown in cheese.

5. The free amino acids of the milk, which appeared in the whey, were not recovered in the cheese. The cheese made from unheated milk with δ-gluconic acid lactone contained low amounts of free amino acids apparently due to the action of milk protease. The proteolytic activity of the lactic acid bacteria increased the amino acid content appreciably.

The isoprenoid fatty acid 4,8,12-trimethyltridecanoic acid has been isolated from butterfat and identified. This acid was found to be a DD diastereoisomer, and was thought to have been derived from the phytol moiety of chlorophyll. It was estimated that in the sample of butterfat investigated, 4,8,12-trimethyltridecanoic acid constituted about 0·005% of the total weight of fatty acids.

An antibacterial agent is produced by ultraviolet (UV) irradiation of Streptococcus cremoris strain C11–56. Its production is accompanied by cell lysis and it attacks the strain C11–56 which produces it as well as a number of other Str. cremoris strains. A correlation between sensitivity to the antibacterial agent and sensitivity to trypsin has been demonstrated. Electron micrographs have shown the presence of particles resembling phage heads, most of which are empty, and of only very few intact phage-like particles in the lysate. The active agent in the lysate is associated with a particle of M > 100000. The evidence suggests that the activity of the lysate may be due to the presence of a defective phage or of a lethal component of it.

In experimental small-scale manufacture of Cheddar cheese a study was made of the movement of lactose, lactic acid, calcium and phosphorus between curd and whey, and of the effect of high acidity developed in the curd before whey separation, on the pH and physical properties of the cheese. It was found that while the curd particles remain in contact with the whey, the lactose fermented in the curd is replaced by lactose diffusing from the whey. Lactic acid produced in the curd diffuses into the whey rather slowly.

When a high lactic acid level is attained rapidly the curd does not cheddar well, the pH of the cheese is low, the flavour is sour and bitter, the body is crumbly and the cheese is bleached. When a high lactic acid level is reached slowly, the curd also does not cheddar properly but the pH of the cheese may be within normal limits up to 3 weeks, at which age its body is coherent and its colour is normal. However, on maturing, the cheese becomes acid, the body crumbly and liquid separation occurs even at 2 months of age. This points to a risk in grading cheese at an early age.

It is suggested that the abnormal behaviour in cheddaring of ‘high-acid’ curds is connected with an excessive loss of calcium. When high acidity is developed over an extended time in the whey, the curd retains more lactose but loses more phosphorus so that its buffering capacity is reduced. Cheese made from such curd becomes highly acid at maturity and this leads to the development of a bitter flavour.

It is, therefore, concluded that both the rate of development of acidity, and the time the curd is in the whey, are critical factors in controlling the quality of Cheddar cheese.

Differences in milk-fat composition in summer and winter have been demonstrated and related to feeding for an autumn calving Friesian herd and an Ayrshire herd in which calving was equally divided between spring and autumn. The observations are in agreement with previous results obtained for milk fat in the Northern Hemisphere.

Summer milk fat contained more C18 acids and less C4–C16 acids than winter milk fat, the effect being particularly marked for the autumn calving herd.

Changes in the pattern of feeding altered the fatty acid composition of milk fat from both herds, and abrupt changes in feeding were clearly reflected even at times when stage of lactation effects were greatest.

The method of Gaitonde (1967) was adapted for the measurement of cysteine and cystine in acid hydrolysates. Analysis of 3 different casein preparations indicated the presence of both cysteine and cystine in whole casein in the proportions of 1:1 by weight and in the molecular ratio of 2:1. If all the cysteine and cystine is associated with κ-casein then it appears that one mole of the latter contains 2 moles of cysteine and 1 mole of cystine. The sulphydryl group in whole casein appears not to be highly labile.

Details are given of a histochemical technique suitable for the identification of lipoproteins in cheese based on their property of forming insoluble complexes with sulphated polysaccharides.

As previously described, the process consists essentially of the passage of milk at pH 5·2–5·3 through an ion exchange resin charged with a suitable mixture of the ions of Ca, K, Na and Mg.

The nutritive quality of plant-treated milk was assessed in feeding experiments with weanling rats and 1- to 2-day-old piglets.

No deleterious effect was found with rats, but tests with piglets indicated that the nutritive quality of the milk was impaired as evidenced by a higher mortality.

Post mortem examinations revealed no specific cause of death.

The use of hydrochloric acid instead of citric acid resulted in a lower mortality, though not as low as that found in piglets receiving untreated milk.

The difference in mortality between animals receiving treated and untreated milk was not consistent and was not found in some experiments.

It is concluded that the milk is unsuitable for piglets and that its suitability for human infants remains in question.

Total carotenoids, β-carotene and α-tocopherol concentrations were determined in serum from healthy dairy cattle of various ages, grazing good quality pasture, in different areas of New South Wales. The relationships of these components with each other and with age of the animal were examined.

Mean serum β-carotene concentrations for heifers and cows were 0·68 and 1·20mg/100ml, respectively. These concentrations were somewhat higher than those found for calves (0·20mg/100ml) and weaners (0·37 mg/100 ml). Total corresponding carotenoid values were generally about 20% higher than those for β-carotene for herds.

Mean serum α-tocopherol concentrations for heifers and cows were 0·54 and 0·90 mg/100ml, respectively. Again, these values were higher than those found for calves (0·22 mg/100 ml) and weaners (0·37 mg/100 ml).

There was a close relationship between serum α-tocopherol and β-carotene (r=0·90), between serum α-tocopherol and total carotenoids (r=0·92), and between serum β-carotene and total carotenoids (r= 0·99).