Pituitary-derived bovine growth hormone (bGH) was administered to six lactating Friesland ewes for 7 d. There was no consistent galactopoietic response, with changes in milk yield varying from 0 to 33% during treatment compared with the pretreatment period. The major effect of bGH on the concentration of milk constituents was to increase fat by 14·2% (P < 0·05). Treatment resulted in significant increases in arterial plasma concentrations of growth hormone, insulin-like growth factor I and glucose, with decreases in the plasma arterial concentrations of acetate and certain amino acids. There was a marked reduction in haematocrit and in haemoglobin concentration which took at least 3 d to recover. The arterio-venous difference across the mammary gland decreased for O2 during treatment and the veno-arterial difference for CO2 decreased after treatment. Mammary respiratory quotient therefore decreased significantly after bGH treatment. The results suggest that bGH exerts effects at a number of separate loci.

Adding ammonium ferric hexacyanoferrate (AFCF) to cows' fodder produced after the Chernobyl nuclear accident prevented milk contamination by increasing the faecal elimination of 137Cs. Synthesis of ammonium ferric hexa[14C]-cyanoferrate (AF14CF) and its purification were performed for the study of the metabolic fate of this complex, and the evaluation of the possible release of cyanide. The stability of this colloidal product, tested by anaerobic incubation in rumen juice in vitro, showed no release of free cyanide from AF14CF, but hexacyanoferrate was identified in the rumen juice and 0·13% of the added radioactivity was converted to labelled CO2. AF14CF administered per os to two cows showed a nearly quantitative excretion of radioactivity in faeces during the first 3 d (91–95%). A very low but significant level of radioactivity appeared in plasma, blood cells, expired CO2 and was detected in organs taken 9 d after administration. Total cumulative radioactivity in urine and milk amounted to 0·19–0·47% and 0·068–0·071% respectively for the two cows. Labelled hexacyanoferrate and thiocyanate were identified in the urine and also in faeces. In spite of this relative instability of AFCF in the rumen of cows, the poor absorption of AF14CF degradation products showed that AFCF constitutes an efficient and safe food additive to prevent the absorption of radioactive caesium from ruminant feed and its secretion in milk.

Analysis of 448 milk samples (11 herds) from caprine udder halves showed that microorganisms were isolated from 21·8% of the samples. California Mastitis Test (GMT) and N-acetyl-β-glucosaminidase (NAGase) were superior to antitrypsin in detecting subclinical infections. Coagulase-negative staphylococci and micrococci were the main species isolated from halves showing no clinical disease. Coagulase-positive staphylococcal infections were associated with a significant increase of all inflammatory parameters. Significantly increased CMT and NAGase occurred when streptococci, other staphylococci or micrococci were present. Infection within one half was reflected as an increase in the inflammatory parameters in the milk of the infected half as well as a slight increase in the inflammation parameters in the adjoining half.

Lactating goats were given a close arterial infusion of [1-14C]leucine and [4,5-3H]4-methyl-2-oxopentanoic acid into one half of the mammary gland at 2–3 weeks and 34–39 weeks after kidding. Rates of protein synthesis, degradation and net output were determined from measurements of arteriovenous difference and blood flow using a model of leucine metabolism previously developed for muscle (Oddy & Lindsay, 1986). Protein leucine output in milk (Y μmol/min) correlated well with the difference between synthesis and degradation (X μmol/min) derived from the model:

There was substantial synthesis and degradation of protein within the mammary gland. Although only an approximate value could be obtained for the partitioning of protein synthesis and degradation between tissue and milk proteins, there was evidence of appreciable turnover of both. There was no significant difference between mammary leucine and protein metabolism in early and late lactation other than that imparted by a greater mass of mammary tissue in early lactation, although there was a tendency for greater oxidation of leucine in late lactation.

Five lactating goats which had kidded normally in March were mated during seasonal anoestrus in May, at the time of peak milk production, after ovulation had been induced using gonadotrophin-releasing hormone (Knight et al. 1988). Milk yield was unaffected by the hormone treatment, and decreased at the same rate as that of control (non-pregnant) goats for the first 8 weeks of the pregnancy. Thereafter yield declined more quickly in the test goats and just before parturition (in October) was 57% of the control value. Following parturition in the test animals, yield rose rapidly as the second lactation was established. None became ‘dry’ at any stage. Yield continued to decline with advancing lactation in the controls, which were mated normally in October or November and dried-off in December. During their second (‘extra’) lactation in the winter the test animals produced 12% less than in a normal second lactation in summertime; during the year the extra lactation meant that the test animals produced 73% more milk than the controls. In some, a second concurrent pregnancy was established during the extra lactation, with the resuit that three lactations were obtained in the time normally taken for two. Mammary cell number and proliferation rate were both higher in the pregnant animals than in the controls in week 23 of the first lactation.

A milking machine claw incorporating valves to prevent movement of milk between teats during milking, and its contribution to the prevention of udder infection under experimental and field conditions, is described. Under experimental conditions a suspension of Streptococcus agalactiae and Str. dysgalactiae was introduced into the milking cluster during milking; 11 of 40 quarters became infected using a conventional claw piece whereas none of 40 quarters milked with the multivalve claw developed intramammary infection. In a 12-month experiment in ten commercial herds, each split into two equal susceptibility groups, the multi-valved cluster reduced the incidence of new infection with coliforms and Str. uberis by 17% (P < 0·1). The incidence of all new infections and new clinical cases was 14 and 25% lower compared to conventional clusters but these reductions were not significant.

Changes were made in milking conditions and vacuum levels to assess optimum parameters for hydraulic milking. A randomized block design was used for the trial, each result being the mean of data from four cows. The results confirmed that faster milking occurred at 50 kPa vacuum (pulsation and milkline) and showed that high vacuum levels created within the liner could be prevented by providing a higher vacuum to the pulsation chamber than the milkline (differential vacuum) without substantially reducing milking performance. The stimulation provided by hydraulic milking may be important in achieving rapid milking in the absence of udder preparation. Lipolysis of milk fat was reduced by hydraulic milking as was milk foam in the recorder jar, particularly when no air was admitted to the claw.

The effect of errors that occur in the diagnosis of intramammary infectious mastitis on the precision of experiments measuring the efficacy of mastitis therapy has been investigated. Diagnostic errors within the range found by experienced workers can create large biases in the apparent cure rate of therapy particularly at cure rates of less than 0·5. Using confirmed methods of diagnosis rather than single samples and reducing the probabilities of false positive and false negative diagnoses to 0·01 and 0·05 respectively, the biases in the apparent cure rates are reduced to acceptable levels. A method is given for calculating the rates of occurrence of false positive and false negative diagnoses from the results of trials using confirmed diagnoses. These errors cannot be calculated from therapy trial data when diagnosis is based on single milk samples.

Because the bias in the measurements of the cure rate is greatest at the lowest levels of elimination, estimates of spontaneous recovery in untreated quarters have the greatest error. For this reason experiments incorporating an untreated control group of infected quarters usually reduce the precision of the therapy trials. An experiment in which the efficacy of a test product is measured relative to a reference product has advantages. It minimizes the difficulties arising from scale of measurement, diagnostic errors and herd differences in response rate, and makes possible comparisons between trials. Further investigations are required on the importance of spontaneous recovery, particularly for studies of Escherichia coli therapy and dry period therapy. The results of this investigation have relevance to all types of mastitis investigation that measure the change in mastitis status of udder quarters, i.e. new infection rates.

Xanthine oxidase (XO) was demonstrated to be present in the teat canal and secretory tissue of the bovine mammary gland by histochemical techniques. Homogenates of these tissues were able to replace XO in an antibacterial assay with Streptococcus uberis. The action of XO on its substrate hypoxanthine was shown to provide an essential component for anti-streptococcal activity mediated by lactoperoxidase. A mechanism is proposed whereby the interaction of XO, lactoperoxidase and thiocyanate may provide antibacterial activity in the teat canal.

An experimental non-return valve was fitted in the short milk tube so that flow was permitted only in one direction, away from the teat. Liner movement was minimal because no air admission to the liner above the valve was provided. The extent of liner opening therefore depended on the amount of milk extracted within a pulsation cycle and on any air leakage past the liner mouthpiece. Milking experiments using four cows showed that the mean vacuum level in nominally open liners of valved teatcups during peak milk flow was 8·6 kPa higher than in conventional teatcups. Bench tests showed that the increase in liner vacuum (LV) depended on the nominal plant vacuum level, the pressure difference between initial LV and maximum pulsation chamber vacuum, the liner elasticity and mounting tension. The main source of energy available to raise LV above the nominal plant vacuum is the release of strain energy, stored within the liner during the collapse phase of each pulsation cycle.

Changes in the teat apex before and after different milking treatments were measured with a spring-loaded caliper device known as a cutimeter which could detect changes in thickness of the tissues of the teat end, presumably due to congestion and/or oedema, with a high degree of accuracy (± 2%) and repeatability (r = 0·99). Teat end thickness increased with increasing vacuum level. The mean increase immediately after milking with a conventional cluster was 2% for 24 teats milked at 30 kPa, 8% at 50 kPa and 21% at 70 kPa. At these vacuum levels, the mean increases for the same teats milked with an unconventional (PKME) teatcup were 10, 18 and 25% respectively. Cyclic application of 35 kPa positive pressure to the pulsation chamber of a conventional teatcup operating at 50 kPa reduced teat end thickness by 8% compared with the mean premilking value. Although most teats returned to within ± 2% of their premilking thickness values by 1 h after milking, differences were apparent between different milking systems for up to 4 h postmilking.

Milk samples from 250 Jersey and Friesian cows were collected and used to investigate the pattern of interrelationships between milk constituents and to test the effects of breed, sire, parity, stage of lactation, season of calving and milking time on them. Breed and sire effects were significant for all constituents. Overall Jersey cows produced significantly higher milk constituent concentrations except lactose, but the test-day yields in Friesians were significantly higher. Milk constituents had varying responses to parity, days in milk and season of calving. Correlation between different constituents and their regression on each other suggested antagonistic relationships. The pattern of association between constituent concentrations in Friesian cows was similar to that between test-day yields, indicating an equilibrium between volume and content of milk.

The levels of N-acetyl-β-glucosaminidase (NAGase) and acid phosphatase were analysed in tissue from the teat and lactiferous sinus epithelia of dairy cows at different stages of lactation. Enzyme levels were lower in the epithelia of the teat sinus than of the lactiferous sinus. For both enzymes, levels were highest in tissue from post-partum glands, lowest in those from dry and mid-lactation glands. In involuting glands the levels were high, but not as high as the post-partum glands.

The development of devices to sample milk at the clawpiece and at the end of the pipeline during milking are described. The results of tests to compare the bacteriological and compositional quality of milk collected from the sampling devices or from the recorder jar or milk cans were similar, demonstrating that the samples provided accurate and representative values. The use of the in-line sampling technique, whereby samples of the milk are taken at three points during its passage through the milking plant, to assess accurately the sources of bacterial contamination of bulk tank milk on farms is discussed.

Two light scattering methods for monitoring the precipitation of casein from skim milk (9% w/w) with mineral acid are presented. Experiments were carried out at precipitation temperatures in the range 25–53 °C and precipitation pH values in the range 3·9–5·1. The initial stages of precipitation were explored using a light fibre optics system attached to a closed-loop acid/milk mixing system. The later stages of particle formation and growth were examined using a laser doppler anemometer attached to an open-pipe flow system. It was found that there was a lag initially, followed by a period of rapid particle growth. During a third phase a dynamic equilibrium between particle growth, break-up and shrinkage was established. A model for isoelectric casein precipitation based on these observations is proposed and discussed.

The milking characteristics of conventional clusters were compared with individual teatcups or clusters fitted with valves in the short milk tubes without external air admission to the liners. Individual teatcups fitted with non-return valves had peak milk flow rates 13% higher than conventional teatcups. A daily cross-over experiment involving 36 cows compared clusters fitted with non-return valves to conventional clusters. Valved clusters milked 18% faster, showed significantly better teatcup stability and 3% higher machine milk yields, but 48% higher strip yields were recorded. Clusters with non-return valves were difficult to remove after milking because the valve closed when the vacuum supply was shut off, thereby maintaining the vacuum level under the teats. When the nominal plant vacuum level for teatcups with non-return valves was reduced by 10 kPa to compensate for the higher effective milking vacuum level, the valved teatcups had peak flow rates 20% lower than the conventional teatcups. Clusters fitted with a modified valve, which allowed some reverse flow when closed (a ‘leaky’ valve), milked significantly faster than conventional clusters, had 33% lower strip yields and were easy to remove after milking.

The variability of the erythrocyte concentration of the tripeptide glutathione was studied in four flocks of Massese sheep. A relationship was found between glutathione level and stage of lactation in which the second month showed the lowest content. Genotype at transferrin and haemoglobin loci was associated with glutathione levels. Homozygotes at the transferrin locus yielded higher levels, while the D allele at the same locus was associated with lower concentrations. Animals with haemoglobin AA showed higher contents of glutathione. Also, a negative correlation was found between daily milk production and glutathione level.

Changes with time in the distribution of milk between different storage regions of the mammary gland were studied in goats. Milk was allowed to drain from the gland through a catheter (catheter milk); the gland was then milked by hand, before (hand milk) and after the administration of oxytocin (alveolar or residual milk). The hand-milk fraction was of negligible volume. There was an essentially linear increase in the catheter- plus hand-milk fraction from 0 to 16 h. The alveolar fraction increased up to 6 h, but thereafter remained constant to 16 h. There was considerable but consistent variation between animals in the alveolar fraction as a proportion of total milk volume. The proportion of residual milk was inversely related to milk secretory rate per unit weight of mammary tissue. The hourly administration of oxytocin without milking had no apparent effect on the distribution of milk in the gland 1 h later.

Casein micelles separated by ultracentrifugation of raw skim milk were dispersed at a casein concentration of 2·5% in simulated milk ultrafiltrate and dialysed against 10 mM-imidazole buffer (pH 7·0) at 5 °C. The amounts of colloidal Ca and inorganic P decreased from 77 to 11 mg and from 31 to 2 mg respectively in 100 ml during 72 h of dialysis. Micellar casein content was reduced to 43 and 11% after 48 and 72 h of dialysis respectively. In high-performance gel chromatography of casein micelles in the presence of 6 M-urea, fraction 1, consisting of the casein aggregates cross-linked by colloidal Ca phosphate (CCP) decreased during dialysis and the retention time of the peak of fraction 1 was prolonged, suggesting that the cross-linkage between CCP and casein molecules was disrupted. The dissociation rates of the individual casein constituents from the casein aggregates cross-linked by CCP during dialysis were in the order β-> αs1 - > αs2-casein. The higher the ester phosphate content, the slower was the dissociation rate of the individual casein constituent. It is suggested that the strength of interaction between CCP and casein molecules depends on the ester phosphate content.

The partial pressure of O2 in milk from normal cows and from cows with mastitis was measured and the concentrations of O2 calculated. Oxygen levels of milk from normal cows were similar to those in venous plasma, but inflammation of the mammary gland led to a dramatic drop in O2 concentration to < 10% of control values. Intracellular survival of Staphylococcus aureus strain M60 in bovine neutrophils was greater under anaerobic than aerobic conditions. The implications of low O2 concentrations in milk from infected mammary glands for the bactericidal activity of bovine neutrophils is discussed.