When four goats were subjected to total water deprivation for 48 h once in early lactation and once in mid lactation and their voluntary food intake and effects on milk secretion were observed, milk volume decreased and lactose and fat concentration increased during both periods. However, when the goats were then fed the mean of their own food intake at the two previous water deprivation experiments, and were left free access to water, it was found that decreased food consumption had only a minor influence on milk secretion. When six goats were subjected to 48 h of food deprivation and six to 48 h of water deprivation, milk secretion decreased, but the reduction was delayed and of smaller magnitude during water deprivation. During food deprivation lactose concentration decreased and the milk protein and fat increased; the fatty acid composition changed from a greater proportion of short-chain to more long-chain fatty acids. During water deprivation milk fat and lactose concentrations increased, and only after 44 h did a change from short-chain to a larger proportion of long-chain fatty acids become evident. These experiments indicate that not only food intake, but also water intake are concerned with milk production.

Fenvalerate ear tags reduced fly loads on dry dairy cattle by 95% between July and September. Fly dislodging behaviour, such as ear flicks which correlated with numbers of Musca autumnalis on the face and stamps/kicks which correlated with numbers of Stomoxys calcitrans on the legs, was also significantly reduced. There was no significant difference between the tagged and untagged groups in the total time spent grazing each day. Milk yields were not statistically significantly different, but the tagged group showed a greater increase in milk yield between lactations, of 1·45 kg/cow daily in the first 12 weeks of the lactation.

TO test the potential for Cortisol to inhibit milk ejection directly, 18 Holstein cows were divided equally into control and treatment groups based on milk yields. For treated animals, a single injection of Cortisol was made into the saphenous vein 15 min before milkings. Increasing amounts of cortisol (0, 25, 50, and 100 mg) were injected for one morning and one evening milking, with the exception that the treated cows received only one 100 mg injection. Control animals received injections of 0·9% (w/v) NaCl. Cortisol injections had no effect on milk yields. However, a potential inhibitory mechanism might involve a delay, perhaps due to the necessity of synthesizing a regulatory protein. Therefore, to test the potential for increased cortisol over a period of hours to inhibit milk ejection, six of the nine cows in the treatment group were injected with 100 mg of cortisol at 3·25, 2·25, 1·25 and 0·25 h before sequential morning and evening milkings. In blood samples taken 1 min before and after injections, base-line cortisol concentrations averaged 10·2 mg/ml; after injection they were 984·1 ng/ml, and before subsequent injections they were 37·6 ng/ml. Again cortisol injections had no effect on milk yields.

Pregnant goats were treated with ACTH by intramuscular injection (1 mg/d for 2 d) at various stages of pregnancy to investigate its effect on initiation of mammary secretion. ACTH stimulated lactose secretion and increased udder volume at or after 84 d of gestation, when compared with untreated controls. Treatment with ACTH between d 109 and 127 of gestation increased circulating plasma glucose concentration, mammary blood flow and mammary uptake of glucose which returned to pre injection levels 6 d after treatment. Arterial concentrations of progesterone were not affected by ACTH but mammary progesterone uptake increased 2-fold. Pre partum milking alone stimulated mammary secretion in eight of 13 goats. Subsequent treatment with ACTH resulted in no further change in the composition of the secretion but increase in yield was maintained. ACTH stimulated mammary secretion in those goats which did not respond to pre partum milking. It was concluded that ACTH initiated mammary secretion in pregnant goats by mechanisms which interact with the stimulation of milking but which are independent of circulating progesterone levels.

As much secretion as possible was removed manually twice daily, from both mammary glands of 6 late-pregnant goats beginning on d 137 of gestation. Removing mammary fluid before parturition stimulated fluid secretion by different amounts in individual goats. The mean volume of fluid secreted pre partum by the goats correlated directly with their secretion of triglyceride and the percentage composition of C18 fatty acids in the triglyceride fatty acids; the volume also correlated with the concentration of progestins, but not prostaglandin F2α or oestrone sulphate, in the fluid.

A highly glycosylated phosphoprotein (HGPP) was isolated from a human casein fraction by reversed-phase high-performance liquid chromatography. This component contained carbohydrates to ∼ 38·2% (w/w) and phosphorus to ∼ 1·6% (w/w). The molecular weight of this HGPP as estimated by sodium dodecyl sulphate–polyacrylamide gel electrophoresis ∼ 41000. Ultracentrifugal analysis revealed that the sedimentation coefficient of the HGPP was 2·6S in a 10 mM-imidazole-HCl buffer at pH 7·0 and 27 °C, but this component interacted with human κ-casein and formed a complex with s = 10·4S.

Milk ultrafiltrate and milks of varying protein, citrate and phosphate concentrations were heated in sealed containers. Protein was found not to be involved in the mechanism of formation of lactulose, but increasing the protein content of milk reduced the concentration of lactulose after heating. This was considered to be due to increased condensation of lactose and lactulose with amino groups of the protein, Less lactulose was formed in milk ultrafiltrate than in skimmed milk accorded the same heat treatment, which was attributed to the buffering capacity of the milk protein in skimmed milk. Activation energies for lactulose formation in skimmed milk and in ultrafiltrate were 128 and 131 kJ/mol respectively. Citrate and phosphate catalysed the formation of lactulose. It is proposed that the formation of free lactulose in heated milk and ultrafiltrate proceeds exclusively by the Lobry de Bruyn-Alberda van Ekenstein transformation with the naturally occurring phosphate and citrate acting as base catalysts.

Skim milk samples from 126 Friesian and 147 Jersey cows in eight commercial herds were preheated at 85 °C for 30 min and concentrated to 200 g l−1 total solids. A heat coagulation time–pH curve was determined at 120 °C for each treated sample. Heat coagulation times ranged from 1 to 50 min at the non-adjusted pH and 1 to 60 min at the pH of maximum stability. The following statistically significant effects were found. Maximum heat stability was affected by genetic variants of κ-casein (B > AB > A; P < 0·001) and β-lactoglobulin (B, AB>A; P < 0·05) whereas natural heat stability was affected only by κ-casein genetic variants (B > AB > A; P < 0·001). Maximum and natural heat stability were corre-lated positively with β-casein and κ-casein concentrations and were negatively correlated with αs1-casein and β-lactoglobulin concentrations. Milk from Jersey cows had greater maximum and natural heat stability than milk from Friesian cows. Differences were found between herds within breed for natural heat stability, but not for maximum heat stability. Maximum heat stability declined with age of the cow. The heat stability of skim milk samples taken from 40 Jersey cows in one of the herds was determined at 140 °C. A considerable variation was found in the coagulation time–pH curves. There was a difference in natural heat stability between κ-casein variants (B > AB; P < 0°05). Natural and maximum heat stability were correlated positively with urea concentration. No relationship was found between the heat stability of preheated concentrated skim milk and the heat stability of the original skim milk. The pH of skim milk samples was associated with αs1-casein genetic variant, age of cow, stage of lactation and concentration of γ-casein.

Heat stability profiles of a number of indigenous bovine milk enzymes were examined with the object of being able to monitor heat treatments slightly more severe than typical pasteurization conditions by measurements of residual enzyme activity after heating. Assay procedures were limited to simple fluorimetric, or preferably colorimetric, methods that would be most likely to form the basis of a quick, simple and inexpensive test. Both lipoprotein lipase and α-fucosidase were relatively sensitive to heat and were totally inactivated at temperature/time combinations below those of pasteurization, but the latter may be satisfactory for studying temperatures in the range 55–65°C. Rather more heat stable were N-acetyl-β-glucosaminidase and γ-glutamyl transpeptidase, which may be most appropriate for 65–75°C and 70–80°C respectively. Higher temperature treatments between 80 and 90°C could best be investigated by following α-mannosidase or xanthine oxidase activity.

A proteinase was purified from a cell wall extract of a culture of Streptococcus lactis NCDO 763 grown in skim milk. Being active at a low pH (at pH 4·8 on haemoglobin and pH 6·–6·5 on casein) and completely inhibited by diisopropylfluorophosphate, it was considered to be a serine proteinase partly inhibited by EDTA; the mol. wt was ∼ 80000.

Yogurt starter B3 was grown in cows' milk, goats' milk I (obtained 2–3 weeks after parturition) and goats' milk II (8 months after parturition), and a number of biochemical and bacteriological parameters were recorded at intervals during incubation for 8 h at 43°C. No appreciable differences between the milks were observed for total viable count, bacteriological ratio of rods to cocci, or decrease in pH. Production of acetaldehyde, however, was considerably lower in goats' milk I (6·2 ppm) and goats' milk II (8·9 ppm) than in cows' milk (18 ppm). Formation of diacetyl and acetoin showed similar patterns in all three milks. The highest production of α-acetolactic acid was observed in goats' milk II, apparently coincident with the highest production of CO2 in this milk.

When a chromogenic Limulus Amoebocyte Lysate (LAL) assay and a tube gelation LAL assay were compared for the detection of Gram-negative bacteria, using a strain of Pseudomonas putida, the detection level (∼ 103 cfu/ml) and cost of the assays were approximately the same for both assays but the reading was more precise for the chromogenic substrate assay. A modified chromogenic assay was devised for detection of Ps. putida in milk.

Cultures of Pseudomonas P46 grown in whole milk to contain ∼ 2 × 107 or 1 × 108 viable cells ml−1 before ultra high temperature (UHT) treatment (140°C for 5 s) demonstrated near linear increases in the concentration of short-chain free fatty acids (FFA) during storage at 20°C. However with 5 × 106 cells ml−1 before UHT heat treatment there was no detectable increase in these FFA levels over a 6-month storage period. A novel heat treatment (140°C for 5 s followed by 60°C for 5 min) reduced the rate of production of volatile FFA to < 10% of the rates achieved after the normal UHT treatment.

Pseudomonas fluorescens strains 240 and 32A expressed cell-associated peptidase activity which was shown by subcellular fractionation to be primarily intracellular. Two peptidases were partly purified from strain 32A. One specifically hydrolysed N-α-benzoyl-DL-arginine-4-nitroanilide and was termed endopeptidase and the other hydrolysed L-lysine- and L-leucine-4-nitroanilide and was termed aminopeptidase. The endopeptidase had very low activity on bovine serum albumin compared with that of trypsin and probably was not a proteinase. The endopeptidase had a mol. wt of 33000 and a pH optimum of 8·0. The enzyme was stimulated by Ca2+ and Mg2+ and inhibited by Co2+, Mn2+, Hg2+, Zn2+ and leupeptin. Soya bean trypsin inhibitor and phenylmethane sulphonyl fluoride (PMSF) had no effect on its activity. The aminopeptidase had a mol. wt of 44000 and a pH optimum of 8·0. It was inhibited by all the metal ions mentioned above and by PMSF. Little proteolysis was found when ultra high temperature (UHT) sterilized milk was treated with cell-free extract from strain 32A. It was concluded that the cell-associated peptidases from Pseudomonas strains normally present in raw milk may not contribute significantly to the deterioration of UHT sterilized milk.

The clarification of milk by addition of solutions of Triton X-100 and EDTA after digestion of added Hide Powder Azure (HPA) was found to provide a simple method of determining the extracellular proteinase activity of Gram-negative psychrotrophic bacteria in pasteurized whole milk. The light absorbance of the clarified HPA digestion product was measured directly, after a brief incubation period, and was stable to storage of samples in diffuse daylight for at least 2 d. Proteinase produced by growth in refrigerated whole milk of as few as 2·5 × 106 cfu ml−1 of Pseudomonas fluorescens AR11 was detected.

Milks whose compositions had been altered by deliberate manipulation or by contact with various environmental conditions relevant to cheesemaking were treated with rennet in such a way as normally to give a constant coagulation time. Rates of curd formation and whey loss, curd structure and fat retention were determined. Ca depletion in concentrated milks reduced firming and syneresis rates and gave curds with finer protein networks. Increased temperature of curd formation increased the curd-firming rate and curd coarseness, but decreased the syneresis rate at 30 °C. Prior treatment of concentrated milk with rennet in the cold gave a much finer protein network which retained fat better than curd formed normally. Despite increasing firming and syneresis rates, acidified milk gave a slightly finer curd with a better fat retention than normal. Addition of cationic materials stimulated aggregation and the curd retained fat better than normal, although the curd structure was unaffected. The results indicate that the processes of firming and syneresis have related mechanisms, and that the curd structure is not simply dependent on curd-forming conditions, but on the number of aggregating particles and the forces between them.

Camembert cheeses were made with pasteurized skim milk or with ultrafiltered milk concentrated 2-fold, using either rennet or Mucor miehei proteinase as coagulant. Using rennet, the rapid acidification during cheesemaking increased enzyme retention and 55% was retained after 24 h. With the M. miehei proteinase, acidification had no effect and only 17% of it was retained after 24 h. The use of ultrafiltered milk resulted in less rennet being retained in the curd.