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.

Six hundred and seventeen isolates of Staphylococcus aureus from sub-clinical mastitis cases in 63 dairy herds in Northern Ireland were typed using a set of 25 phages. Ninety-four per cent of the isolates were typable, with nine phages, predominantly from groups I and III, being responsible for almost all of the lysis. Although 68 phage patterns were found, six of them typed 47·2 % of the isolates. One strain accounted for 14·7% of the isolates, but the largest number of strains (44) was restricted to individual farms. The epidemiological significance of these findings for on-farm mastitis control is discussed.

Four vitamin B12 assays were compared using blood sera from Friesian cows on winter diets or grazing. In herd 1, ten animals were blood-sampled three times at monthly intervals and the vitamin B12 concentration of the sera determined by the Poteriochromonas malhamensis and Lactobacillus delbrueckii assays. At all three sampling dates the results produced by the P. malhamensis assay were significantly greater than those produced by the L. delbrueckii assay. Cows in herd 2 were divided into two groups, each of 30 animals. One group was given a soluble glass bolus releasing cobalt and the other was unsupplemented. Milk yields were recorded throughout the experimental period and herbage samples were taken at intervals for cobalt determinations. Blood samples were taken at intervals from January to September 1983 and the vitamin B12 concentration of the sera determined by four different assay methods: the P. malhamensis and L. delbrueckii microbiological assays and the Becton Dickinson and RIA Products ‘No-boil’ radioassays. The last of these failed to detect vitamin B12 in any sample. There was a significant difference between the results obtained by the three other assays, with the Becton Dickinson radioassay consistently producing the lowest result and the P. malhamensis assay the highest result of the three. There was no significant effect of cobalt supplementation on milk yield.

The magnitude of the forces causing closure of the bovine teat canal was estimated by measuring the pressure required to cause retrograde flow of milk into the canal from a manometer attached to the external teat orifice. Before milking, the hydrostatic pressure required to cause retrograde flow was 12 kPa or greater. Retrograde flow occurred at a pressure of 4–6 kPa once the teat canal surface had been wetted. This 2- or 3-fold fall in the closing forces presumably resulted from the combined effects of fracturing the teat canal epithelium and loss of initial resting tension in the smooth muscle fibres surrounding the teat canal. After milking, retrograde flow into any teat canal occurred at a pressure ∼ 1 kPa lower than the wetted, pre-milking value. This small drop, and subsequent recovery ∼ 30 min after milking, reflects the change in tonicity of the smooth muscle fibres which are stretched during milking. At hydrostatic pressures below 7–9 kPa, retrograde flow could be arrested momentarily by the occurrence of a teat contraction. At 4–7 kPa, the wave of contraction was also capable of expelling 4–14 μl milk from the teat canal indicating the outwardly directed, peristaltic nature of the phasic muscular activity.

Levels of free fatty acids (FFA) were determined immediately after milking (initial FFA), and after 22 h storage at 4 °C, either without (FFA-22) or with a mechanical induction of lipolysis (FFA-22I), in milk from Friesian and Montbéliarde cows in the same herd, at identical stages of lactation and pregnancy and receiving the same feeding regimes. There was no difference between the two breeds in initial FFA and FFA-22 contents whatever the lactation period. This was also true during late lactation when lipolysis was further increased after feeding a poor quality grass silage. The observation that milk FFA-22I content from the Montbéliarde cows was higher than that from Friesian cows in summer, but not in winter, requires cautious interpretation as the activation treatments were not comparable, owing to the different ambient temperatures during activation in these two periods.

In order to standardize a radioimmunoassay of milk progesterone as a routine method for confirmation of oestrus and diagnosis of pregnancy in water buffalo, monoclonal antibodies against progesterone were produced. Hybridomas were prepared by fusing spleen cells from a Balb/c mouse immunized with progesterone 11α-hemisuccinate–bovine serum albumin conjugate with the mouse myeloma cell line NS-1. Thirty wells out of 94 secreted anti-progesterone antibodies. Of the ten independent hybridomas derived, one (AF65) was suitable for the quantification of milk progesterone by radioimmunoassay. The tracer used in the assay was progesterone-11α-hemisuccinate ([2-125I]iodohistamine). The sensitivity of the assay was 50 pg/tube. The mean progesterone concentration at oestrus was 0·8±0·2 ng/ml increasing to 8·5±0·8 ng/ml 24 d later in pregnant animals.

The magnitude of the cyclic load applied to the teat apex by the collapsed liner during milking was estimated by measuring the pressure required to cause retrograde flow of milk into the teat canal from a manometer attached to the external teat orifice. The study was extended by observation of the milk flow cycle within a transparent teatcup assembly and by pressure recordings within the teat canal using a catheter-tip transducer. The source of the force compressing the teat is the small airspace, within the collapsed liner, directly below the teat apex. The total force generated is determined mainly by the size of this airspace and the pressure difference (PD) acting across the opposing liner walls. When the PD reached 80–90% of the liner vacuum, the load was just sufficient to occlude the teat canal. Further increase in PD provided the compressive load capable of offsetting vascular congestion of the teat apex. Increasing liner tension increased the load applied. The narrow range of compressive loads applied by conventional liners (5–12 kPa above atmospheric pressure) may be sufficient to offset congestion and oedema in the teat. Loads greater than the mean arterial pressure within the teat apex might serve only to expose the tissues to non-productive compression.

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.

During the course of an acute, fatal mastitis in mice caused by intra-mammary injection of ∼ 105 cfu of Staphylococcus aureus, small numbers of staphylococci were detected in liver, spleen, kidney and heart. Transport from the mammary gland was by the venous blood system with no evidence of lymph node involvement. Intravenous injection of 100 times more staphylococci (∼107 cfu) than were fatal by the intramammary route failed to kill the mice and small numbers of staphylococci were found in the visceral organs. However, intravenous injection of ∼ 108 cfu of Staph. aureus was fatal and large numbers of staphylococci were found in the visceral organs. Treatment with cloxacillin (500 μg) by the intramammary or subcutaneous routes, or equally divided between these two routes, cleared the visceral organs of staphylococci; subcutaneous therapy had a limited and variable effect on numbers of staphylococci in the mammary gland while intramammary and divided treatments significantly reduced the numbers of staphylococci. Thus, staphylococci are disseminated to visceral organs during acute staphylococcal mastitis, but this makes a negligible contribution to the clinical disease.

The effects of αs1-, β-, κ-casein and β-lactoglobulin genetic variants on rennet clotting time, rate of curd firming and coagulum strength, measured on the individual milks of 306 Rendena cows by a lactodynamographic apparatus, were evaluated statistically, with simultaneous adjustment for environmental and physicochemical factors. The importance of genetic polymorphism was confirmed, especially for the main effects of casein loci: interaction among them was not found to be significant. For κ-casein, BB genotype showed the best coagulation parameters (lower rennet clotting time, a higher rate of curd firming and higher coagulum strength), with AB in an intermediate position for clotting time and rate of curd firming. However, for αs1-casein and β-casein, dominance and overdominance effects between alleles were observed. Herd by genotype interaction was also found to be significant (herd by β-casein) or close to significance level (herd by κ-casein). From the results of the analyses, suggestions for selection programmes have been made.

Levels of free fatty acids (FFA) were determined in milk from cows after 7 months of lactation and 4 months of pregnancy immediately after milking (initial FFA) and after 22 h storage at 4 °C (FFA-22). During the pre-experimental period, cows were at pasture. When housed indoors (experimental period) they were fed hay or grass silage for 3 weeks. Then all cows received grass silage for 3 weeks (post-experimental period). Feeding hay did not increase FFA-22 content in milk compared with pasture, but grass silage feeding enhanced FFA-22 content in milk compared with pasture (+130 %) or hay (+93 %). Increased lipolysis with grass silage was not due to underfeeding of the cows because grass silage and hay were both of high nutritive value. As pasture, hay and grass silage were of the same type (native mountain grassland), the high level of lipolysis occurring with grass silage probably resulted from the method of forage conservation.

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.

Permeation chromatography on porous glass was carried out with skim milk at 20 or 30 °C using CPG-10 (50 nm) or a dual column system of CPG-10 (50 nm) followed by CPG-10 (300 nm). On columns of CPG-10 (50 nm) casein micelles were eluted at the void volume and were rapidly and efficiently resolved from non-micellar protein without micelle dissociation. The dual column system resulted in the additional resolution of the micelles into different size ranges. Examination of the resolved micelle fractions by electron microscopy showed a gradual decrease of weight average diameter (Dw) from 228·4 nm in the void volume fraction to 86·3 nm in the smallest micelle fraction. The translucent upper layer of a micelle sediment obtained by ultracentrifugation of skim milk at 30 °C consisted of casein aggregates intermediate in size between monomeric protein and the bulk micelle fraction as shown by its elution behaviour on CPG-10 (50 nm). These aggregates were enriched more than 2-fold with κ-casein relative to skim milk, were devoid of αs2-casein and had an estimated value of Dw of 33 nm. The ultracentrifugate serum contained ∼ 2·5% of total milk casein which had the elution characteristics of monomeric protein on CPG-10 (50 nm). It was concluded that the translucent sediment consisted of the smallest micelle fraction of skim milk and represented the minimum size range for casein polymerization in the natural milk environment. Overall, the results show that porous glass chromatography is an effective and convenient tool for the isolation and study of casein micelles.

Addition of reducing agents such as 2-mercaptoethanol (2-ME), dithio-threitol and Na sulphite to milk markedly reduced its heat stability at pH values below 7·1. 2-ME reversibly destabilized milk or serum protein-free casein micelle dispersions and promoted the release of κ-casein-rich protein from the micelles. Reduction of either casein micelles or β-lactoglobulin (β-lg) with 2-ME and subsequent blocking of the newly formed –SH groups with N-ethylmaleimide irreversibly reduced the maximum to minimum ratio in the heat stability profile. 2-ME disrupted κ-casein/β-lg complexes and stripped κ-casein from the micelles on heating. The milk or caseinate systems were thus destabilized. Addition of KBrO4 or iodosobenzoate to milk at 5 HIM eliminated the minimum but destabilized milk in the region of the maximum. However, KIO3 at 5 mm had a strong stabilizing effect throughout the pH range 6·5–7·3.

Most (98%) of the fat in human milk is present as triglycerides. This paper describes the use of a clarification procedure that enables the level of human milk fat to be determined by measurement of glycerol released by enzymic hydrolysis of triglycerides. The method requires only 10–50 μl milk, thus presenting a possible technique for work with small mammals, and is suitable for use with autoanalysers, permitting rapid sample throughput.

Goats’ milk caseins were separated into four components in a single run using reversed-phase gradient high-performance liquid chromatography. The purity of the isolated components was checked by sodium dodecyl sulphate polyacrylamide gel electrophoresis, amino acid analysis and determination of the N-terminal residue. By a comparison with previously published results for goats’ milk caseins the four peaks were identified as κ-, αs1-, αs2- and β-casein. In order to confirm the existence of αsl-casein in goats’ milk, this component was sequenced for 44 steps, revealing a sequence homologous to bovine αsl-casein and almost identical to the N-terminal sequence previously published by Boulanger et al. (1984).

Skim milk was heated rapidly to 130 °C in stainless steel tubing, and was then held at this temperature for periods of up to 1 h in a stainless steel holding vessel. Samples taken at intervals during the holding period were analysed for cations, inorganic and organic phosphate and protein in the total sample and in the supernatant after centrifugation at 60 500g. The cation and total phosphate (organic+inorganic) contents of the sedimentable material remained constant throughout the heating, although the caseins became extensively dephosphorylated. Dephosphorylated protein dissociated from the casein micelles during the first 20 min of heating, after which its concentration in the serum began to decrease, perhaps indicating the onset of the heat coagulation reaction.

24 ultra heat treated (UHT) and 17 in-bottle sterilized milks prepared in commercial plants and of a similar age were presented to taste panels for assessment of flavour and colour. The colour was also analysed instrumentally and the lactulose content of the milks measured by an enzymic method. Flavour defects, other than the cooked flavour, were scored very low. The lactulose content of the milks was negatively correlated with the acceptability of the milks and positively correlated with the cooked flavour. Correlations were also found between the visual and instrumental assessments of milk colour and between some of the instrumental colour parameters and the lactulose content of the milks. UHT and in-container sterilized milks could not always be distinguished on the basis of their organoleptic qualities. The best distinction was observed in the scores for cooked smell and acceptability of taste. The usefulness of the lactulose content and/or the colour of the milks in discriminating between UHT and in-bottle sterilized milks was calculated. Using all the data, sterilized milk could be correctly identified in 96·7% of decisions. The lactulose content of a milk was considered to give a good indication of the organoleptic quality of the milk.

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.