The gastric emptying kinetics of peptides derived from milk protein were studied in vivo in preruminant calves by collecting and characterizing the whole effluent leaving the stomach for 12 h after ingestion of crude skim milk. Peptides were isolated by reversed-phase HPLC and identified. Particular attention was paid to biologically active peptides and to peptides that could be precursors of biologically active sequences. A gastrin inhibitor, the caseinomacropeptide, was emptied from the stomach only during the first 0·5 h of digestion and rapidly hydrolysed. Precursors of immunostimulatory peptides from αs1 - and β-caseins were emptied throughout digestion in the gastric effluent. A precursor of β-casomorphins (peptide 58–93 of β-casein) was emptied from the stomach 3·5 h after the meal when it was taken on an empty stomach. From this precursor, peptides that may be resistant to hydrolysis by intestinal peptidase were obtained after in vitro hydrolysis by pancreatic enzymes. A phosphopeptide (fragment 110–142 of αs1-casein) was also found in digesta after a few hours of digestion. When the meal was not taken on an empty stomach, these peptides were emptied in the first digesta at a low concentration. The potential activity of these peptides is discussed. The results support the hypothesis that active sequences could still be present in the gut after the action of pancreatic enzymes.

Twenty multiparous Jersey cows, paired according to previous lactation yield and expected date of calving, were given two diets in a cross-over experiment in early lactation. The diets had forage:concentrate ratios maintained at 3:7, the forage being wilted grass silage and the concentrate either a proprietary dairy cake or the same cake containing saliva salts (SS) at 40 g/kg dry matter. The SS diet proved acceptable to the animals and had no effect on gestation length or calf survival. Absolute milk yields were not affected, but the SS diet caused a significant increase in the proportions of milk fat, total solids (both P < 0·001) and protein (P < 0·05) and in the yield of fat-corrected milk (P < 0·001). Analysis of rumen liquor samples showed that giving the SS diet resulted in a significant increase in the molar proportion of acetate and a decrease in the proportions of propionate and to a lesser extent butyrate. Milk fat content showed significant correlations with ruminal acetate (r = 0·67), propionate (r = −0·59) and the acetate: propionate ratio (r = 0·64).

Lactating goats routinely milked twice daily were used. Starting at peak lactation, two groups of five goats were milked three times daily unilaterally (right gland) for 6 weeks, then one group received recombinant bovine somatotrophin (BST) by daily injection for 6 weeks, and finally both groups were returned to unilateral thrice-daily milking (left gland) for 6 weeks. Thrice-daily milking increased milk yield significantly by 10·4%. As thrice-daily milking finished and BST treatment began there was a small (2·7%) but significant increase in whole-udder milk yield in the treated goats and a decline in the control goats; throughout the BST treatment period treated goats produced 14·3% more milk than controls. The effect of BST was the same in glands previously milked thrice daily as in those previously milked twice daily. Milk yield declined as BST treatment finished, but this decline was less in the glands that then began thrice-daily milking. The effect of milking frequency was similar in this period to that obtained earlier in the experiment, and was not different between goats that had previously received BST and those that had not. The results are discussed in relation to the proposed modes of action of BST and frequent milking, and possible interactions between the two.

Fifteen lactating cows were milked throughout pregnancy, and the effects on milk performance were studied during this period and during the succeeding lactation, relative to 11 conventionally managed cows (2 months dry before calving) as controls. During the last 2 months of pregnancy, only nine cows did not dry off spontaneously. Protein and fat concentrations in milk increased rapidly, but the concentration of lactose, corrected for milk yield, did not change. The ratios of individual caseins to total protein decreased with the quantity of milk produced, but only for yields below ˜ 6 kg/d. The relative proportion of κ-casein tended to decrease in the last milkings. During the succeeding lactation (first 15 weeks after calving and first 6 weeks of grazing) continuously milked cows yielded 4 kg milk/d less than the cows of the other group. The protein content of their milk was higher (2–3 g/kg depending on the period) than that of the control group, and the lactose content tended (p < 0·10) to be lower. Changes in the relative proportions of nitrogenous fractions with time were not different in the two groups. Differences between the two groups in the concentration of protein in milk, and in the concentration of glucose and non-esterified fatty acids in the plasma, suggest a better energy balance for the continuously milked cows during the succeeding lactation.

Bovine mastitis reduces the yield and quality of milk and increases the rate of culling and veterinary costs. This reduces the profitability of farm milk production but the calculation of the extent of this economic loss is complex because of the many factors involved and deficiencies in the evidence on the relationship between the disease and various production factors. This paper examines the available evidence for the UK and provides a consistent analytical framework within which the benefits arising from reduced mastitis in dairy herds constrained by quota can be considered. It is estimated that since 1970 the farms that have followed the recommended control procedures have reduced the average annual number of cases of clinical mastitis from 135 to 40 cases/100 cows each year, while the quarters remaining uninfected for a whole year has increased from 65 to 80% of the total quarters. The costs of the main control procedures (e.g. £8–60/cow for dry-cow therapy and teat dipping or spraying) are broadly covered by the reduction in clinical mastitis, leaving the benefits of reduced subclinical infection (e.g. £3810 for a 100 cow herd unconstrained by quota and achieving the average reduction in infection) as a substantial bonus. The imposition of quotas reduces the financial benefit of mastitis control but it still remains a worthwhile investment. The results of this analysis can be used to suggest maximum costs of additional new control measures produced by research. It also indicates that there is considerable value in production research which gives more precise knowledge of production Systems, thus allowing producers to respond optimally to quota cuts.

A direct capture enzyme-linked immunosorbent assay (ELISA) was developed to measure elevated polymorphonuclear granulocyte (PMN) antigens using horseradish peroxidase (EC 1.11.1.7) conjugated rabbit polyclonal anti-PMN antisera and a monoclonal antibody specific for PMN cells. Optical densities obtained in the ELISA were used to predict the cell counts of milk samples. Predicted counts were not significantly different from actual somatic cell counts (SCC). In a total of 156 bovine milk samples the correlation coefficient between somatic cell counting, taking > 500000 cells/ml as being indicative of mastitis, and the assay was 0·94, yielding an assay sensitivity of 95·2% and a specificity of 97·3%. In further trials the ELISA could detect elevated PMN antigens in milk with SCC as low as 100000 cells/ml. The results indicate that the monoclonal antibody based direct ELISA has excellent potential in the detection and determination of bovine mastitis.

Lactating heifers were treated for 4 weeks with recombinant bovine growth hormone (bGH, n = 9) or were untreated (n = 9). In addition, two mammary glands of each heifer were milked four times daily rather than the normal twice daily for the same 4 weeks, and for the following 2 weeks. Over the 4 weeks, milk yield was increased 12·8% by bGH, 14·0% by frequent milking and 28·5% by the combined treatment. The effect of bGH as administered here was slower in onset than that of frequency, but eventually produced a higher peak yield. ANOVA revealed significant effects of each stimulus independently and an additive, but not synergic effect of the combined treatment. The effect of the combined treatment tended to persist beyond the end of treatment; most of this response was related to the milking frequency component rather than the bGH. Mammary differentiation was assessed in biopsies of mammary tissue obtained prior to and at the end of treatment. Mammary enzyme activities (expressed on a per cell basis) indicated minimal differentiative response to either treatment, but synthesis rates for lactose and casein determined in vitro were increased by bGH treatment. Histological examination revealed a stimulatory effect of milking frequency on epithelial cell size. The results indicate that these two galactopoietic stimuli operate through independent mechanisms, and neither stimulus alone is sufficient to maximize milk yield in dairy heifers.

Numerous attempts to develop in-line Systems for the measurement of the electrical conductivity of milk as an aid to the detection of mastitis have been described. The major technical problem of fouling of electrodes exposed to milk has been overcome in the sensor tested here by use of an inductive System of measurement. The practical application of this System in the milking parlour is reported. The novel mastitis sensor has been shown to detect incipient mastitis before there are visible signs of abnormal milk. Conductivity measurements have the advantage over other diagnostic procedures in that the information is available immediately without additional effort. Normalized conductivity and milk yield variation results indicate the potential for developing a practical, automatic System for mastitis detection.

Bacteriological analyses, cell counts using the Fossomatic method and California Mastitis Test were performed on 1523 goat milk samples taken aseptically at monthly intervals throughout lactation from three goat herds. Of the goat udders, 81·4% were infected, minor pathogens being the most frequent isolates (65·7%). Differences in the level of infection by minor pathogens were found betwccn herds. Cell counts were influenced by stage of lactation and intramammary infection. Cell counts < 106 cells/ml were found in 80% of milk samples infected by major pathogens and in 45% infected by minor pathogens. About 81% of udders infected with major pathogens gave California Mastitis Test scores of 2 and 3, compared with 20% for uninfected goats. A high proportion (65%) of udders infected with minor pathogens also produced scores of 2 and 3. A significant positive correlation was found between the California Mastitis Test and cell counts. The use of cell counts for the detection of abnormal goat milk is discussed.

A mathematical model of the interactions within a milking machine teatcup has been developed, which describes the relationship between liner wall movement, pressures and flow rate when milking without an air inlet. It is based on equations of motion for a column of incompressible fluid and requires a second-order, non-linear differential equation to be solved. Incorporating a non-return valve allows hydraulic milking to be modelled, and the comparison between predicted and measured pressures, flow rates and liner wall movement when milking hydraulically is shown. The model can be used to optimize milking conditions to reduce vacuum peaks, improve liner opening and thus maximize flow rate.

The hyperinsulinaemic euglycaemic insulin clamp technique was used to study the effect of insulin on the arterio-venous concentration differences of glucose and amino acids across the mammary gland in dairy goats. Insulin was given in conjunction with K to prevent insulin hypokalaemia. Appropriate amino acid infusion was used to blunt insulin-induced hypoaminoacidaemia or to create hyperaminoacidaemia and maintain this state under insulin treatment. Hyper-aminoacidaemia alone only stimulated mammary leucine uptake but did not significantly modify the net metabolism of other amino acids and glucose. Insulin infusion at physiological level in conjunction with glucose, KCl-NaCl and amino acids failed to alter mammary uptake of glucose and essential amino acids; occasional increase in arginine extraction and decrease in tyrosine extraction were exceptions. Thus these new experimental conditions did not reveal any galactopoietic effect of insulin.

This study was conducted to examine the effects of mastitis and stage of lactation on plasminogen activator (PA) activity in milk somatic cells. An assay System, which measures the plasmin-mediated hydrolysis of the chromogenic substrate D-valyl-leucyl-lysine p−nitroanilide, was used to assess PA activity present within milk somatic cells. Milk cell associated PA activity was increased (P < 0·05) by 50% in the presence of fibrin fragments. This suggests that milk somatic cells contain tissue PA which, unlike urokinase PA, is preferentially activated in the presence of fibrin fragments. An increase of the milk somatic cell count from < 5 × 104 to > 106 cells/ml resulted in an 8-fold increase in PA activity per cell. Elevated levels of PA activity were associated with milk somatic cells isolated from mastitic quarters obtained from cows in early (<4 months in lactation) or late lactation (>8 months in lactation). We conclude that PA activity is increased during severe mastitic inflammation. Although the physiological function of this enzyme is as yet unclear, we propose that it may be involved in the conversion of plasminogen to plasmin, contributing to the higher levels of plasmin occurring in milk isolated from mastitic quarters.

Machine-induced changes in teat thickness were measured in a randomly selected group of 22 cows from a commercial dairy herd consisting of 110 cows during an experiment lasting 1 year. Half the cows used were free from mastitis whereas the remainder had at least one quarter infected by environmental pathogens. Teats were classified according to a threshold change in teat end thickness of 5%. The relationships between quarter infection or teat duct colonization and teat end thickness changes induced by machine milking were investigated. Teats with > 5% change in thickness had significantly increased teat duct colonization and a slight, non-significant, increase in quarter infection. We conclude that machine-induced changes in teat end thickness are predisposing factors for teat duct colonization by environmental pathogens. This may provid: an increased new infection risk, especially when hygiene is poor.

Teat and gland cistern of the mammary glands of five dairy cows, five goats and five sheep were scanned in a water bath during α- and β-adrenergic agonist and oxytocin administration. A 5 MHz linear array scanner was used to create vertical cut pictures with the scan plane longitudinally through the teat channel. The i.v. injection of the α-adrenergic agonist phenylephrine (30 μg/kg) induced diminution of the section area through teat and gland cistern by 38±17% on average within 1 min in all three species. In contrast, the i.v. injection of the β-adrenergic agonist isoproterenol (1 μg/kg) did not change the cisternal areas. The i.v. injection of oxytocin (2·0 × 10−3 i.u./kg) elicited an enlargement of teat and gland cistern area by 48±12% on average. Ultrasonography proved to be a valuable system for visualizing changes of the cisternal volume. Smooth muscle contractions in response to phenylephrine administration are thought to cause area reduction, whereas an expected smooth muscle relaxation after injection of isoproterenol could not be observed by ultrasonography. Milk ejection as induced by oxytocin administration caused dramatic enlargement of the cistern area in all three species.

Cleaning of inorganic membranes after ultrafiltration (UF) of skim milk has been assessed using hydraulic, physicochemical and spectroscopic (i.r. and X-ray photoelectron spectroscopy) measurements. A cleaning sequence using hypochlorite alone or hypochlorite followed by HNO3 restored the membrane hydraulic resistance, in contrast to cleaning with HNO3 alone. When using NaOH, addition of Ca complexants (EDTA, gluconate, tripolyphosphate) and surfactants was required to obtain similar results. Three types of criteria (hydraulic, kinetic, chemical) are available to assess the effect of the sequestrant and surfactant types. In all the cases studied, traces of protein and Ca were detected on and within the membrane after cleaning. Nevertheless, it was concluded that it is possible to develop a single-step alkaline product to clean inorganic milk UF membranes if suitable surfactants and Ca sequestrants are included in its formula.

The reaction of secretory epithelium and myoepithelial cells in the alveoli to hand milking and i.v. injection of oxytocin and catecholamines was studied in lactating goats. The reaction of secretory cells was assessed by changes in the transepithelial (blood–milk) potential difference (PD), and the contractile reaction of myoepithelial cells by the growth of intramammary pressure (IP). The initial value of PD was 24·6 ± 0·6 mV, that of IP 3·32 ± 0·08 kPa (24·9 ± 0·6 mmHg). Milking and oxytocin administration caused a rise in PD and an increase in IP. After noradrenaline and adrenaline injections two-phase PD changes and a short-term rise in IP were recorded. Isoproterenol, a β-agonist, caused a rise in PD but did not affect IP. Phenylephrine, an α-agonist, caused two-phase and one-phase changes in PD. Simultaneously, a rise in IP was recorded. The results show that the reaction of the mammary gland to the substances administered is complex. Myoepithelial and secretory cells respond differently to short-term rises in the level of mediators and hormones in the blood.

Milk flow in nine primiparous cows with disturbed milk ejection (D) and in six corresponding control animals (C) with normal milk removal was recorded during machine milking and blood samples were taken before and during milking to determine plasma oxytocin, vasopressin. prolactin, cortisol, oestradiol-17β, luteinizing hormone, progesterone and β-endorphin concentrations. Manual teat stimulation before milking lasted for 1 min. After milk flow had stopped, air was blown into the vagina for 2 min. When milk flow had stopped again, 1 i.u. oxytocin and finally 10 i.u. oxytocin were injected to remove residual milk. During and after teat stimulation, oxytocin remained basal in D, but increased in C, whereas prolactin increased in both groups. While 94% of total milk was obtained in C during this period, only 9% could be removed from D, indicating lack of alveolar milk ejection. During vaginal stimulation, oxytocin increased transiently in D and more than by teat stimulation in C. This allowed the removal of 75% of milk in D, whereas almost no more milk was available in C. After oxytocin injections, 3 and 16% of residual milk were obtained in C and D respectively. Basal oestradiol-17β concentration was higher in D than in C (11·6 and 2·0 ng/1 respectively), whereas β-endorphin level was lower (24·1 and 86·6 μg/1 respectively). Basal concentration of luteinizing hormone and progesterone, and concentration of cortisol and vasopressin before and during milking were comparable in C and D. We conclude that in cows with disturbed milk ejection afferent nervous pathways to the hypothalamus were intact, because prolactin was released by teat stimulation. However, oxytocin was only released by vaginal stimulation, i.e. milk ejection was centrally inhibited during teat stimulation.

Discontinuous PAGE at alkaline and acid pH, polyacrylamide gel isoelectric focusing, two dimensional electrophoresis and immunoblotting have been used to study the heterogeneity of sheep caseins. Three main phenotypes were selected either because of mobility at alkaline and acid pH of the individual αs components or because of their relative intensity. On electrophoresis at alkaline pH, one phenotype showed two distinct bands of lower electrophoretic mobility than β,- and β2-caseins. A detailed study of these components using immunospecific detection with β-casein antiserum showed that these minor components of ovine casein may have a polypeptide chain similar to that of β1- and β2-caseins. Complete electrophoretic patterns of the casein components in some individual milks are also presented.

The onset of copious milk secretion (lactogenesis II) in women occurs between 1 and 3 d after birth, and during this period the composition of breast milk changes. During the first 5 d of lactation we measured the concentrations of total, diffusible and ionized Ca (Catot, Cad, Ca2+), diffusible phosphate (Pid), diffusible citrate (Citd) and lactose in the breast milk. On day 1 after birth the concentrations (mean ± SEM) were Catot, 5·71±0·30 mM; Cad, 2·66±0·19 mM; Ca2+, 2·90 ±0·18 mM; Pid, 0·26±0·16 mM; Citd, 0·25±0·03 mai and lactose, 76±11 mM. Between day 1 and day 4 the concentration of Catot increased 1·7-fold to 9·56 ±0·39 mai, Cad increased 1·8-fold to 4·75±0·26 mM, Ca2+ decreased by 20% to 2·33 ± 0·13 mM, Pid increased 6·6-fold to 1·69±0·11 mM, Citd increased 20-fold to 5·06±0·21 mM, and lactose increased 2·3-fold to 173±4 mM. A high correlation has been found between [Cad] and [Citd] in the milk of both ruminant and non-ruminant species, which show a wide range in concentrations of [Cad] and [Citd], and the data fit a simple physicochemical model of ion equilibria in the aqueous phase of milk. The results of the present study confirm the relationship between [Cad] and [Citd] in human milk, even during lactogenesis II when the composition of the milk is changing very rapidly.

Whey samples were screened for the presence of the proteinase inhibitor α2-macroglobulin (α2M). From an enzymic test, α2M levels in normal whey varied in the range 0·49–0·84% of the serum level, whereas in mastitis whey the activity was markedly increased, reaching values between 0·91 and 138·5% (median 7·2%) of standard serum level. In mastitis milk samples but not in normal milk α2M was also detected by double immunodiffusion and Western blotting. The proteinase inhibitor was purified from a mastitis milk sample with high α2M activity (138·5% of serum level). In SDS-PAGE, native-PAGE and in double immunodiffusion analysis the inhibitor appeared indistinguishable from plasma-derived α2M. The α2M preparation from mastitis whey migrated essentially as native α2M, representing the ‘slow’ form of the molecule. Treatment with trypsin transformed the α2M preparation to the electrophoretic ‘fast’ form, but treatment with methylamine had only a minor effect. The receptor recognition sites were not exposed on the isolated α2M molecule but could be readily exposed by treatment of the proteinase inhibitor with trypsin, which further proved that the isolated α2M was in the entire native, functionally active state.