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.

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.

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.

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.

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.

Significant effects of parity and stage of lactation were found on ATP content, somatic cell count and antitrypsin content when using morning milk samples from 39 cows over a period of 18 months. A close similarity was evident between variation in ATP and somatic cell count, except during the first 10 d after parturition when the variation in ATP was more pronounced. The same result was obtained in the whole material as well as in a healthy subset. This study shows clearly that parity and stage of lactation must be taken into account when establishing normal values for ATP as an indicator of mastitis.

Milk samples of four species of wild equids (onager, Equus hemionus onager; mountain zebra, E. zebra hartmannae; plains zebra, E. burchelli; Przewalski horse, E. caballus przewalskii) and two domesticated equids (ass, E. asinus; pony, E. caballus) were analysed. At mid to late lactation the milks of all species were very similar, containing on average 10–12% total solids, 1–2% fat, 1·6–1·8% true protein, 6–7% ‘lactose’, 0·3–0·5% ash, 0·08–0·12% calcium, 0·04–0·07% phosphorus and a calculated energy content of 2·0–2·4 kJ/g. Milk samples collected in the first 2 weeks after birth showed elevated levels of total solids and protein, and some had reduced ‘lactose’ levels, but there were no observable trends in milk composition during mid to late lactation (1–12 months post partum). It was concluded that these closely related species produce milks that are nearly identical in gross composition and that the domestic horse is a representative model for the study of equid lactation.

Mixtures of κ-casein and β-lactoglobulin (β-lg) were heated at 70 °C in 20 mM-imidazole buffer, pH 6·8 containing 20 mM-EGTA. Aggregation of the κ-casein/β-lg mixture occurred within 90 s and susceptibility to hydrolysis by chymosin decreased significantly within 180 s even though covalent interaction was not detected until after 4000 s. UV-absorbance indicated initial structural destabilization of the heated κ-casein/β-lg mixture followed by a return ( > 350 s) to a spectrum comparable to the native state, indicating molecular rearrangement. Apparent hydrophobicity of κ-casein decreased 80% within 250 s compared to a 38% decrease for β-lg. Under similar conditions, the κ-casein/β-lg mixture (1:1) showed a faster (2·5 times) decrease in apparent hydrophobicity than κ-casein alone with concomitant exposure of acidic (hydrophilic) groups. The results suggested that the driving force for the rearrangement was mainly hydrophobic, i.e. entropic in origin. The tendency of heated and subsequently cooled κ-casein/β-lg to aggregate reached a maximum after heating at 70 °C for 720 s.

An industrial refractometer connected to a microcomputer was used to study the rennet coagulation of milk. The amplitude of the refractometer's signal changes during coagulation was about 104 times more important than the resolution of the computerized refractometer. The signal v. time derivatives were calculated and the inflection point time (ti) was correlated with pH, Ca concentration and temperature. The inflection point time was inversely proportional to the rennet and Ca concentrations and the logarithm of the proportionality factor (k) was linearly correlated with pH. The relation between ti and temperature was curvilinear. It is concluded that the refractometer tested could be used for research on the coagulation process.

Cows were infused with Escherichia coli endotoxin to provide a pool of milks with high somatic cell counts (SCC). This was mixed with bulk tank milk obtained from either of two Institute herds, producing a range of milks containing 0, 10, 20, 30 and 100% high SCC (HCC) milk. Creams containing 38% fat were produced from these milks on nine separate occasions; five times from winter milks and four times from summer milks. The SCC of the milks, the free fatty acid concentration of the unwhipped creams and the whipping time, stiffness and overrun of the whipped cream were measured. Whipping time and stiffness increased and overrun (volume increase) decreased as the proportion of HCC milk in the mixture increased. However, these changes were statistically significant only when comparing the 100% HCC milk with the other treatments containing lower levels of HCC milk. Creams produced in the summer took less time to whip and were less stiff than winter creams but there was no change in overrun. The source of bulk milk supply affected the stiffness and overrun of the whipped creams. Free fatty acid concentration appeared to have no direct effect on whipping characteristics.

An extracellular metalloproteinase from Aeromonas hydrophila strain A4, isolated from milk, was purified by a factor of 300 by chromatogrpahy on DEAE-cellulose and Sephadex G-150. The enzyme had a mol. wt of 43000 and contained 2 g atom Ca/mol. It was active over a pH range 4·8–9·5 and had optimum activity on casein at pH 7·0 with Km = 0·17 mM. It was strongly inactivated by metal chelators and the apoenzyme was fully reactivated with Ca2+, Mn2+ or Co2+. Heavy metal ions such as Ag+, Hg2+, Fe2+, Zn2+, Cd2+, Ni2+ and Cu2+ totally or partly inactivated the enzymic activity at 5 mM concentration. The enzyme was not inactivated by diisopropylfluorophosphate, soyabean trypsin inhibitor or sulphydryl group reagents. It was optimally active at 45 °C; above 50 °C activity declined rapidly, but significant activity persisted at 4 °C. It was heat labile in phosphate or Tris-maleate buffer but exogenous Ca2+ afforded protection.