Four different field studies including 64, 140, 850 and 180 herds were used to investigate the association between pulsator characteristics and udder health. The results indicate that the best udder health is found in herds with a d phase > 330 ms and a pulsation rate > 55 min-1. A d phase of < 250 ms was associated with significant elevation in bulk milk somatic cell count, a higher incidence of acute clinical mastitis and a higher frequency of cows having mastitis associated with major pathogens (mainly Staphylococcus aureus) as compared with a d phase of > 331 ms. There was also a significant positive association between a shorter d phase and a high incidence of teat lesions needing veterinary treatment. Herds having no such teat lesions had pulsators with significantly longer d phase than herds with teat lesions (300 ms ν. 288 ms). These results strongly suggest that in high-line milking machines the d phase should not be as short as 250 ms and should preferably be ∼ 300 ms, and the pulsation rate should be at least > 55 cycles min-1. There was a strong relationship between the effect of d phase and the rate of pulsation.

Six lactating dairy cows were used in a three period, part balanced changeover design experiment to investigate the effects of forage digestibility and concentrate composition on the efficiency of nutrient utilization in lactating dairy cows. Six treatments comprising three forage regimens and two concentrate types (starch υ. fibre) were examined in a 3 × 2 factorial design. The three forage regimens were high digestibility grass silage offered ad lib. (HA) or restricted to 6·5 kg dry matter/d (HR) and a low digestibility grass silage offered ad lib. (LA). Within each forage regimen animals were offered 10 kg·d of supplements containing either high-starch or high-fibre concentrations. Experimental periods lasted 28 d with a 10 d recording period, during which animal performance, ration digestibility and nitrogen and energy utilization were measured. Respiratory exchange measurements were made over a 72 h period using indirect open-circuit calorimetry. Throughout the experiment, there were no significant forage × concentrate interactions in any of the intake, production or nutrient utilization results. Milk yield was significantly influenced by forage regimen (24·1, 21·7 and 21·9 kg/d for HA, HR and LA respectively) and concentrate type (21·6 and 23·5 kg/d for high-starch and high-fibre respectively). Concentrate type also significantly influenced milk protein concentration (32·8 and 30·9 g/kg for high-starch and high-fibre respectively). Forage regimen significantly influenced the efficiency of utilization of metabolizable energy (ME) for milk production (κ1) with values of 0·62, 0·64 and 0·59 for HA, HR and LA respectively. Concentrate type had no significant effect on ME intake, heat production or κ1, although animals receiving the high-fibre concentrates synthesized proportionately 0·11 more milk energy per unit of available energy (ME intake – heat production) than those receiving the high-starch concentrates. Interpolation of the values obtained with the two high digestibility forage regimens indicated that at similar ME intakes there was a trend towards a higher κ1 with the diet based on high digestibility silage, and this was in line with the higher metabolizability of the overall diet with this silage.

The effects of the form in which amino acids are presented to the abomasum on the milk production of dairy cows receiving a basal diet of grass silage and a barley-based supplement were examined in two experiments. Effects of abomasal infusions of sodium caseinate were compared with the effects of corresponding levels of either an enzymic hydrolysate of casein (Expt 1) or a corresponding mixture of free amino acids (FAA; Expt 2). In Expt 1, although the yield of protein in milk increased progressively with each level of infusion, the yields of protein were greater for the caseinate than for the hydrolysate. Again, in Expt 2, for milk protein yield, sodium caseinate was superior to FAA at the lower level of infusion. In both experiments, the hydrolysate and FAA treatments were associated with higher concentrations of fat in the milk. There were indications of differences in the pattern of secretion of glucagon between the caseinate and FAA treatments. It is concluded that the differences between treatments relate either to the kinetics of absorption of amino acid residues or to the action of bioactive peptides released during digestion of casein.

The udder health of a research herd of between 160 and 220 Friesian cows run on a commercial basis has been monitored closely, including detailed bacteriological study, over 5 years. The five point mastitis control plan had been in use for several years prior to this study and was continued with minor alterations to the management of the plan, more detailed bacteriological monitoring and increased encouragement to apply it. It has proved possible to make a substantial improvement in the udder health of the herd. The percentage of infected cows fell from 21·9 to 12·0 and the percentage of infected quarters from 7·3 to 3·3. The main benefit has been a drastic reduction in the rate of clinical and subclinical mastitis caused by coagulase-positive staphylococci. However the total incidence of clinical mastitis did not change substantially, averaging around 30 cases/100 cows per year. This was largely because environmental mastitis organisms were responsible for 65 % of all clinical cases. The results showed marked differences in the patterns of infection due to the environmental mastitis pathogens, Gram-negative bacteria and aesculin-hydrolysing streptococci, suggesting different mechanisms of invasion of the gland.

Aseptic udder quarter secretion samples (n = 1112) from 200 mastitic and 65 non-mastitic control heifers from 160 different farms were collected for bacteriological examination and in vitro antimicrobial susceptibility testing. Coagulase-negative staphylococci (CNS) were the most frequently isolated bacteria (57·8%). The percentage of Staphylococcus aureus was 20·1, of streptococci 11·3 and of other pathogens 10·8. Staph. simulans, Staph. hyicus, Staph. xylosus and Staph. chromogenes were the most common CNS. Staph. simulans and Staph. hyicus were most frequently found in clinical samples after parturition, whereas other CNS were equally or more often found in control samples. Most CNS infections detected in the prepartum period were eliminated spontaneously or with antibiotic treatment during early lactation, but the infected quarters were more susceptible to new infection by other pathogens. Milk N-acetyl-β-glucosaminidase activities were measured to monitor changes in inflammation. Among the CNS infections, N-acetyl-β-glucosaminidase activities were highest for Staph. hyicus and lowest for Staph. xylosus in the lactating mammary gland of heifers. CNS were resistant to trimethoprim–sulphonamide, ampicillin and erythromycin. Staph. aureus was more resistant than CNS to β-lactamase-sensitive penicillins.

The antiproteolytic activity of selected proteinase inhibitors was studied in mastitic bovine milk and urokinase-activated normal milk using a caseolytic agar diffusion assay. The inhibition profiles of mastitic milk and urokinase-activated milk were compared with those of purified proteinases. The proteinase inhibition profile of mastitic milk did not resemble that of any of the pure proteinases, indicating a mixed type of proteinase system in mastitic milk. The trypanocidals diminazene (equivalent to Berenil®) and pentamidine (equivalent to Lomidine®), together with aprotinin (Trasylol®), showed most promise when considering possible applications in mastitis to break up the proteolytic cascade within the inflamed udder.

A comprehensive description of the health status of 2406 cows in 28 herds was used to study complex interrelationships between Staphylococcus aureus occurrence and potential risk factors at the cow level over a broad spectrum of production conditions. The objective of the study was to characterize those cows shedding Staph, aureus in milk and to provide indications of possible causal relations that should be further explored. The estimates are expected to aid in providing valid and precise evaluations of results from cross sectional microbiological examination of bovine (quarter) milk samples. Staph, aureus were isolated at microbiological examination of quarter milk from 5·2, 13·5, 17·9 and 22·0% of 1552, 490, 296 and 277 cows in lactations 1, 2, 3 and 4–9 respectively. Simultaneous isolation of other mastitis pathogens was not significantly associated with occurrence of Staph, aureus. Of the positive samples, 95% had a positive California mastitis test reaction. Among the clinical measures of udder health, only visibly abnormal milk combined with normal udder tissue was associated with increased occurrence of Staph, aureus, although not consistently. Prior antibiotic treatment for udder disorders was not significantly associated with Staph, aureus isolation. The occurrence of sole ulcers in multiple digits was consistently associated with Staph, aureus in the first lactation. Milk yield was involved in interactions with other pathogens isolated, prior veterinary disease treatment, body weight and season of calving. Strong herd-year effects were revealed. This, combined with the interactions, indicated that some herd-specific factors were major determinants of Staph, aureus occurrence. The study indicated which cow characteristics should be taken into account in epidemiological analyses and causal interpretations of data from cross sectional microbiological examinations of dairy herds.

Comparison of the primary sequences of bovine, ovine and caprine αs1-casein shows a deletion of eight amino acid residues in the ovine casein region 141–148, which is identical in the bovine and caprine proteins except for a single difference in position 148 (Q or E). Polyclonal antibodies raised in rabbits against the bovine casein sequence 140–149 (QELAYFYPEL) appeared monospecific for bovine αsl-casein, since no antibody-antigen complex was formed with homologous ovine or caprine proteins. These antibodies remained unable to recognize the caprine sequence in the native protein even after extensive tryptic proteolysis. The lack of immunoreactivity of the antibodies against synthetic caprine αsl-casein peptide 138–149 (VNQELAYFYPQL) suggested that the glutamic acid residue in position 148 is essential for the antigenic character of the bovine peptide. From these observations, the use of these antibodies for the detection and quantitation of bovine milk present in ovine dairy products could be extended to caprine products.

The heterogeneity of ovine β-casein, apparent after discontinuous gel electrophoresis at alkaline pH and gel isoelectric focusing either by staining with Coomassie blue or immunoblotting, was investigated in detail. Electrospray mass spectrometry was used to characterize ovine casein by direct examination of whole casein samples. β-Casein in individual milks consisted of several components which were characterized through the accurate determination of their molecular masses. It was demonstrated that protein species occurring simultaneously in individual ovine milks differed mainly in the number of phosphate groups.

A method for isolation, detection and quantification of cholesterol oxidation products based on solid phase extraction in combination with preparative HPLC and gas chromatography–mass spectrometry selected ion monitoring has been developed for dairy products. The isolation procedure had a high recovery and artifact formation was minimal, as shown by isotope labelling. The limits of detection ranged from 0.3 to 35 pg/μl of the isomeric forms of 7-hydroxycholesterol, 20α-hydroxycholesterol, the isomeric forms of cholesterol-5,6-epoxides, cholestanetriol, 25-hydroxycholesterol and 7-ketocholesterol corresponding to a limit of quantification of 2–6 ng oxysterol/g lipid in the dairy product, depending on the nature of the cholesterol oxidation product.

The type and relative amounts of plasminogen activator (PA) in different fractions of bovine milk obtained from 15 Holstein cows were examined. Raw milk was centrifuged to separate skim milk and a somatic cell pellet. PA was mainly localized within the casein fraction, being 42 times that in the serum, and in association with somatic cells. The predominant form of PA in milk casein was isolated from SDS-PAGE gel extracts and had a molecular mass of ∽75 kDa. Its activity was increased 41-fold (P < 0·01) in the presence of fibrin but was unaffected by the presence of amiloride, indicating that it was due to tissue-PA. The predominant forms of PA associated with milk somatic cells were isolated from SDS-PAGE gel extracts and had molecular masses of ∽ 30 and ∽ 50 kDa. The activity of both proteins was unaffected by the presence of fibrin but was dramatically reduced by the presence of amiloride, indicating that they represented urokinase-PA.

We have investigated the effect of culture temperature on the growth of Lactococcus lactis subsp. lactis biovar diacetilactis, on its acidifying power, on diacetyl and acetoin production, and also on the activities of the principal enzymes involved in the synthesis of these two compounds. The rates of growth and lactic acid production decreased by a factor of ∼ 2 when the temperature decreased from 30 to 18°C. At 18°C, the maximal concentration of diacetyl (0·3mM) was 1·7 times that at 30°C, while that of acetoin was unchanged (5·2 mM). These results are explained by the behaviour of the principal enzymes involved in pyruvate metabolism. The activities of lactic dehydrogenase and acetolactate synthase varied little for culture temperatures between 18 and 30·C. However, the activity of NADH oxidase for a culture temperature of 18°C was 3·7 times that for 30°C, while that of diacetyl reductase for 30°C was 2·7 times that for 18°C. The net effect of temperature on these two activities was an increase in diacetyl production at lower temperature.

Low-fat Gouda-type cheese (200 g fat/kg dry matter) was made on a pilot plant scale from cheesemilk to which heat-treated lactobacilli and/or Neutrase encapsulated in dehydrated rehydrated vesicles had been added. In cheese containing added Neutrase, there was increased proteolysis after the first day following cheesemaking. The cheese with added heat-treated lactobacilli developed increased amounts of amino N as well as increased amounts of acetaldehyde and other, unidentified, volatile compounds. The addition of heat-treated lactobacilli also influenced the texture of the cheese which was firmer but less cohesive.