The response of dairy cows to once a day (OAD) milking was investigated in four trials. Two trials involved Friesians (F) and Jersey cows selected for high (HP) or low (LP) milk protein concentration. Trial 1 compared 74 HP, LP and F cows milked either OAD or twice daily (TAD) for 2 weeks in both mid and late lactation. Trial 2 compared 98 HP, LP and F cows milked OAD or TAD for 12 weeks in early lactation. Trial 3 investigated the repeatability of production loss by milking identical twin cows either OAD or TAD during three 1 week periods. Trial 4 compared the time course of milk production in 32 cows milked every 12 or 24 h for 72 h. Cows milked OAD produced 10–28% less milk and milk solids in early to mid lactation and 9–13% less in late lactation than cows milked TAD. Losses in fat and protein yield were slightly lower than those of milk. HP, LP and F cows did not differ in percentage loss in milk and milk solids in Trial 1, except for loss in protein yield which was lower for HP than LP and F cows. In Trial 2 the losses in milk and milk solids were lower for HP cows than for F cows but the other differences were not significant. Milk storage ability of the udder (hours worth of secretion) was higher and productivity of the udder was lower for HP cows than F cows. Levels of residual milk did not differ among groups. The loss in udder capacity during lactation was greater for cows milked OAD than for those milked TAD. The correlations for repeated estimates of percentage losses in yields of milk and milk solids between successive OAD periods ranged from 0·29 to 0·49. Secretion rate of cows milked OAD was lower during the second 12 h than the first 12 h during each 24 h milking interval. Prediction of OAD performance based on milk composition and udder characteristics was poor. A high level of residual milk was the factor most consistently associated with high loss on OAD milking.

The effect of treatments designed to improve the efficiency of milk removal and minimize loss of production in cows milked once a day (OAD) was assessed in short-term trials involving Friesian and Jersey cows. Trial 1 involved 80 cows and compared twice a day (TAD) milking with OAD milking with the administration of 20 i.u. of oxytocin (OX), OAD milking with udder massage before and during milking (OS) and no treatment during OAD milking (OC). The OX and OS groups had increased yields of milk and milk solids when treatments were applied, though yields were not restored to previous TAD levels. The percentage increase shown by OX cows was greater than that of OS cows for fat yield. The level of residual milk in the udder after milking was lower for the OX group than for the OAD and TAD controls. In Trial 2, 12 cows were subjected to fast or slow rates of milking OAD in each of two periods. Losses in milk, fat and protein yields averaged 9·1, 9·9 and 1·0% respectively. Increased rate of milking reduced milking time and time to let-down but did not affect response to OAD milking. The results showed that treatments that increased the evacuation of the udder during milking and decreased the level of residual milk reduced losses in production that occur on OAD milking. Increasing the rate of milking was ineffective in reducing losses on OAD milking.

In the present study newly calved cows were tentatively classified as moderate and severe responders to experimentally induced Escherichia coli mastitis based upon the reactive oxygen species (ROS)-generating capacity of their blood neutrophils before infection. The groups differed in blood and milk composition prior to infection. This initial classification was supported by the corresponding variation in clinical symptoms and in the changes in milk production and composition measured during mastitis. Responses of newly calved cows to Esch. coli challenge varied from mild to severe symptoms of inflammation in infected glands and differed in the intensity of systemic disturbances and general illness. Losses in milk yield and compositional changes were most pronounced in inflamed glands and in severe responders. In inflamed glands milk yield and composition did not return to preinfection level in either moderate or severe responders. The yields of lactose, α-lactalbumin, casein and fat followed the same pattern as milk yield. It is concluded that the severe and long lasting systemic disturbances observed in severe responders can be ascribed to absorption of endotoxin from infected glands into circulation, indicating the important role of endotoxin in the pathology of coliform mastitis in periparturient cows. Evaluation of the ROS-generating capacity of blood neutrophils and blood and milk composition before infection might help to predict the cow's sensitivity to Esch. coli mastitis.

Two trials were conducted to investigate the effect of pre-milking teat dipping (PMTD) on mastitis caused by environmentally associated pathogens. The first trial showed considerable variation in effect between herds, so a second, larger trial was conducted. In this second trial a comparison of the rate of clinical mastitis was made between nine matched pairs of dairy herds over 24 weeks of the winter housed period. All herds were near the national average incidence of mastitis before the trial. One member of each pair used their normal method of udder preparation throughout the trial and disinfected all teats after milking with an iodophor disinfectant. In the other nine herds the preparation of all teats, at all milkings, included dipping in a 0·25% available iodine disinfectant, which was left on the teat for 30 s. Every teat was then wiped with a paper towel before cluster attachment. There was no difference in the overall rate of mastitis or the incidence of mastitis caused by any particular type or group of pathogens between the trial groups of herds. Both groups showed a reduction in mastitis compared with the previous winter. Although there were apparent benefits in some pairs of herds there was no overall benefit. In comparison with the previous winter the control herds reported a greater reduction in mastitis than the PMTD herds. The effect of trial supervision on normal practice gave a benefit which overwhelmed any effect of PMTD. There appeared to be no effect of PMTD on the total bacterial count, cell count or iodine content of bulk tank milk. There appears to be no justification for wholesale use of PMTD although most farms and risk groups could benefit from better attention to conventional mastitis control.

One hundred and thirty-seven (Holstein (41), Montbéliarde (42) and Tarentaise (54)) dairy cows in first or second lactation received during winter one of two levels (high, H; low, L) of energy intake, and were later fed identically at pasture. Thrice in winter and twice at pasture, the chemical composition and coagulation properties of individual milks were measured. Milk from Holstein cows had lower casein and calcium contents, and poorer coagulation properties (curd firming time and curd firmness) than that from Montbéliardes and Tarentaises (P < 0·01). These differences practically disappeared when taking into account the distribution of the different κ-casein variants and milk casein content. κ-BB milks had coagulation properties 20–50% superior, according to characteristic, to those of AA milks. In the three breeds, animals from the H group had casein contents higher by 1·4 g/l than those of the L group, which induced a significant improvement in curd firming time, curd firmness and cheese yield. Turning out to pasture induced an increase of 0·02 in milk pH, and improved milk coagulation properties. These changes did not appear to result entirely from the parallel increase in milk casein content.

The interaction of sheep, horse, pig, human and guinea-pig whey proteins with fatty acids has been studied. Using gel filtration and autoradiography, it was found that sheep β-lactoglobulin and serum albumin from all species had the ability to bind fatty acids in vitro. Sheep β-lactoglobulin, isolated from milk, had ˜ 0·5 mol fatty acids bound per mol monomer protein, and albumin from sheep, horse and pig contained ˜ 4·5, 2·9 and 4·7 mol fatty acids/mol protein respectively. However, β-lactoglobulin from horse and pig milk had neither fatty acids physiologically bound nor the ability to bind them in vitro. Albumin was the only whey protein detected with bound fatty acids in these species as well as in human and guinea pig. This suggests that the ability of ruminant β-lactoglobulin to bind fatty acids was not shared by the same protein of non-ruminants.

25Mg, 43Ca and 31P NMR have been used to study the binding of Mg2+ and Ca2+ ions to β-casein A1. The concentration dependence of the line width of the 25Mg NMR signal shows that β-casein contains at least two different types of binding sites for Mg2+ ions, one with strongly bound, slowly exchanging ions and one with more weakly bound ions which undergo fast exchange. The strong Mg2+ binding site has an unexpectedly high binding constant, Kbstrong 104 M–1, which has not been reported earlier. Mg2+ and Ca2+ compete for the Ca2+ binding sites of β-casein, while Na+ does not compete for these binding sites under physiological conditions. The dependence of the 43Ca NMR chemical shifts on total concentration of Mg2+ and Ca2+, in the presence of β-casein, could be equally well fitted with a model assuming up to five identical and independent sites as with a model assuming five or more sites with negative cooperativity. The proton dissociation constant, pka, for the strongest Ca2+ binding site was found to be 7·1.

Defatted whey was obtained by aggregating residual fat to calcium phosphate precipitates and separating the precipitate by membrane microfiltration (pore diameter 0·2 μm). When ultrafiltering this defatted whey the performance of an inorganic membrane (molecular mass cut-off, 10 kDa) was limited by the large concentration of Ca and phosphates. Consequently, the influence of the aggregation pH (either decreasing or constant) on membrane fouling has been studied for ultrafiltration (UF) of defatted sweet whey and defatted whey UF retentates (protein content up to 30g l–1). In all experiments protein rejection was 100%. When pH was kept constant during the pretreatment, membrane fouling was significantly lowered. Hydraulic resistances ascribed to irreversible fouling were in good agreement with fouled membrane analyses performed by i.r. and X-ray photoelectron spectroscopies. They showed that provided a low Ca and phosphate content was maintained in the microfiltrate, which was achieved at constant pH, no apatite was detected within the membrane, and proteins were less fouling. On the other hand, the amount of fouling material depended on the transmembrane pressure gradient along the hydraulic path. On the membrane surface, the higher the pressure, the higher the fouling. In the membrane bulk, the fouling heterogeneity depended on the ability of the defatted whey to precipitate apatite. If it did, the higher the pressure, the higher the calcium phosphate and the protein fouling. With other phosphate structures, the bulk fouling depended on the barrier formed by surface fouling layers and the protein concentration polarization layer, which were more resistant to solute and solvent transfer under higher pressure, where they were thicker.

Whey protein solutions of different chemical compositions were filtered through a large pore size ultrafiltration membrane (molecular mass cut-off 100 kDa). The influences of pH, ionic environment and Ca chelation on the performance characteristics of the membrane (filtration rate, total and individual whey protein permeability) were examined. Increase in pH in the range 5·0-10·0 resulted in a gradual increase in filtration rate and individual whey protein permeability. The presence of Ca in the whey protein solution had a negative effect on the performance characteristics of the membrane. Addition of EDTA to protein solution improved the filtration rate but had no effect on the protein permeation. Fractionation of the low molecular mass whey proteins (β-lactoglobulin and α-lactalbumin) from high molecular mass proteins (bovine serum albumin, lactoferrin and immunoglobulins) was best achieved at pH 8·0.

Bovine colostrum contains transforming growth factor (TGF)-β-like activity. High levels of this activity are found in early colostrum (within 12 h after parturition); however, it decreases rapidly after 30 h. In this study, the activity in early colostrum was purified by a sequence of decaseination, DEAE-Sephacel chromatography, Sephadex G-100 gel filtration, precipitation at neutral pH, further gel filtration and reversed-phase FPLC. A homodimeric 23 kDa protein was identified that retained the TGF-β-like activity. Its activity was completely neutralized by a specific anti-TGF-β2 antibody. These results indicate that the TGF-β-like growth factor found in bovine colostrum is chemically and antigenically related to TGF-β2. The physiological roles of the TGF-β2-related growth factor are discussed.