Mammogenesis and lactation were induced in five multiparous, non-pregnant goats by treatment with oestrogen and progesterone for 11 d, followed by dexamethasone for 3 d. Reserpine was administered during the last 5 d. All five goats lactated, although milk yield was less than had been achieved in previous natural lactations. Mammary development was assessed in vivo, using magnetic resonance imaging. Although parenchyma volume increased by more than 6-fold overall, only 25% of this increase occurred during steroid treatment. Most development took place after the cessation of treatment, when milking commenced. Maximum size was not achieved until week 8 of the induced lactation, and was only 70% of normal parenchyma volume. After 18 weeks lactation the activities of three key milk synthetic enzymes were very similar to values previously found in natural lactations, and secretion efficiency (milk production per unit volume of parenchyma) was also similar to that of natural lactations. We conclude that the lower than normal milk yields were associated with incomplete proliferation of mammary tissue, rather than inadequate differentiation of individual secretory cells.

The fatty acid content of triacylglycerols (TG) in arterial and mammary venous blood plasma has been analysed in five cows that were close to peak lactation. The fatty acids in arterial TG were extracted by the mammary gland in amounts 14:0 < 16:0 < 18:0and 18:0 > 18:1n – 9 > 18:2. The difference of extraction between palmitate and stearate was similar in different TG species. The fatty acid 18:1n – 7, which was largely the trans isomer, was extracted more than 18:1n – 9. Significant amounts of phytanic acid were acylated in plasma TG, but not extracted by the mammary gland.

Twin-bearing ewes were treated with epidermal growth factor (EGF) to determine its effect on mammogenesis and resultant milk production and composition. The EGF was infused intravenously at a dose rate of O5 mg/d in 300 ml saline between days 117 and 139 of gestation; control animals received placebo infusions of saline. All animals then received continuous infusions of 300 ml/d saline on days 139–144. Following parturition 1–5 d later, ewes were milked by hand for 10 d and thereafter were machine-milked until day 16 of lactation. At this level of treatment, EGF was not detected in the circulation during infusion and feed intake was not affected. All ewes gave birth to healthy twin lambs. There were no effects of EGF on birth weights of lambs, live weights of ewes or lengths of gestation. An EGF immunoreactive material was detected in the mammary secretions of control ewes at a mean concentration of 2 μg/l on day 1 of lactation. Two ewes had detectable levels on day 2, but none was found in the milk thereafter. In the EGF-infused group, concentrations of EGF in colostrum were ñ 10 times higher than in the control ewes on day 1 of lactation and EGF was detected in mammary secretions on day 2 but not in subsequent milk samples. A range of 0·3–0·5% of the EGF infused appeared in mammary secretions over the first 2 d of lactation. No other differences were observed for colostrum composition, subsequent milk yield or composition between the two groups of ewes indicating that mammary gland development and function were unaffected. The levels of EGF observed in the mammary secretions of treated and control ewes indicate that the mammary glands accumulate and store EGF in the pre partum period.

Milk quotas, based on an average fat content, severely limit milk production on UK farms. Predictions of the time-course of lactation are incorporated into most computerized herd management programs but these models take no account of food inputs, body weight change or milk composition. Dynamic models are generally used to simulate metabolic pathways and, as such, have little direct relevance to commercial milk production. Dynamic models can be converted to an adaptive-predictive model that partitions food energy into milk and non-milk constituents. This paper reports the development of an adaptive-predictive model to partition food into milk and non-milk components. Additional functions further partition milk energy into the principal constituents, fat, protein and lactose.

Four goats were studied from the end of their second lactation. One mammary gland of each goat was dried off just prior to the start of the third gestation, whilst the other gland was milked throughout gestation, with no dry period. At the end of gestation the continuously milked gland was significantly smaller than the gland that had been allowed a dry period. However, this difference did not persist beyond parturition and there was no significant difference between the milk yields of the two glands in the next lactation, although the continuously milked gland tended to have the higher yield. At 18 weeks of lactation, mammary parenchyma weight and secretory cell number were significantly greater in the continuously milked gland, but mammary enzyme activities did not differ between the two glands.

Two experiments were conducted to investigate possible changes of milking-related oxytocin release (Expt 1) and of intramammary pressure and milking characteristics (Expt 2) throughout entire lactations in German Braunvieh dairy cows. Mean oxytocin concentrations after stimulation at onset of milking increased from 18·3 ± 15·9 to 30·7 ± 24·1 pg/ml in Expt 1 and decreased from 23·9 ± 17·6 to 15·4 ± 9·1 pg/ml in Expt 2, respectively, but remained above the level necessary to elicit complete milk ejection in both trials. Premilking baseline intramammary pressure had its maximum in early lactation until about month 4 and then decreased to ∼50% of its initial level. Ejection pressure followed a similar pattern, but dropped only to ∼75% of its maximum. This was due to the constant elevation of pressure increase, reaching its highest level in late lactation. Time from commencement of stimulation until maximum pressure exceeded 1 min in almost all instances even in early lactation and increased throughout lactation. Despite the normal decrease of milk yield average milk flow fell only slightly while maximum flow rate remained almost constant. Pressure increase, milk yield and milk flow were not different after 1 min and after extended stimulation. Thus there were no indications of a decreasing sensitivity of the milk ejection reflex during lactation, and milking characteristics were positively affected by intense teat stimulation. Suggestions for practical dairying are made.

Eighteen cows with a wide range of quarter peak flow rates (0·35–2·22 kg/min) were inoculated with Streptococcus agalactiae and Str. dysgalactiae 4 mm into each streak canal every 3 d for 12 d. Thirty of the 72 quarters developed intramammary infection. Mean peak flow rate and length of streak canal of those quarters that became infected were 1·26 ± 0·08 kg/min (mean ± SEM) and 11·47 ± 0·41 mm respectively, compared with 1·01 ± 0·05 kg/min and 12·05 ± 0·35 mm for those that remained uninfected. Logistic regression analysis showed that the probability of infection increased significantly with the increase in peak flow rate (P = O·O1). The influence of streak canal length on new infection, after allowing for the effect of peak flow rate, was not significant at the 5% level (P = 0·07), suggesting that there may be an inverse relationship between teat duct length and infection, but that it is of secondary importance to peak flow rate. If increased mass of milk distends the teat duct by raising intramammary pressure, then quarter susceptibility to infection is further compromised. These results strongly suggest that the benefits of reduced infection from mastitis control, achieved despite dramatic increases in milk flow rate and milk yield, are significantly underestimated.

C-reactive protein (CRP) and serum amyloid P component (SAP), which are known to increase in sera from humans and many other animals with acute inflammation caused by infection, toxic drug administration or injury, were previously purified from bovine serum. These serum levels were determined by enzyme-linked immunosorbent assay (ELISA) using specific antiserum to bovine CRP or SAP which was prepared by immunizing rabbits and goats with each purified protein. Among 68 healthy Holstein cows, 45 non-lactating cows had levels of CRP and SAP of 20·6±1·4 and 27·6 ± 1·3 μg/ml respectively; 23 lactating cows had higher levels of CRP and SAP (76·0±13·6 and 38·3±5·5 μg/ml respectively). In the latter group, there was a high correlation between milk yield and serum CRP levels (P <0·001). From these observations, it was assumed that lactation might stimulate CRP synthesis rather than SAP synthesis in bovine liver as an acute phase reaction, and that CRP might be called a lactation-associated protein.

We have evaluated the usefulness in mastitis diagnostics of new diagnostic measures using the continuous nature of the variation in quarter milk samples of four inflammatory markers: somatic cell count, N-acetyl-β-glucosaminidase (EC 3.2.1.30), electrical conductivity and antitrypsin. A two-way analysis of variance was performed for each of the inflammatory markers on results from 273 cows sampled six times at 14 d intervals. Adjustment for the individual cow's mean removed approximately half the total variation for all four markers, indicating that comparisons in marker levels between quarters without taking the cows' overall level into account, as is done in diagnostic keys based on fixed threshold, is a rash procedure. After adjusting for the individual cow means, the total variation of the marker observations was partitioned in three sources of variation: between the four quarter levels, between different sampling days, and the experimental error, i.e. the variation within each quarter over-the study period. As expected, the variation between quarters accounted for the largest percentage of the variation (44–65%). In contrast the variation between days was only 16–34% and of the same magnitude as the experimental error. These figures can profitably be taken into account when designing experiments in future mastitis research studies. They imply that mastitis diagnostics based on quarter milk samples collected over time will be influenced only slightly by random biological variation and that the same relative differences that exist in marker levels between the four quarters of a cow as a rule will be disclosed irrespective of sampling day. Thus, the udder health state is relatively stable when determined by these inflammatory markers. In addition to simple correlations between markers measured on the same day, correlations of the logarithm of the interquarter ratios and of the experimental errors were computed. Stronger associations between the markers emerged and these correlations reflect more precisely than simple correlations the real diagnostic relations of the markers.

Three types of liner (wide bore tapered, wide bore and narrow bore) were compared in a change-over design experiment comprising three 3-d periods and using six lactating Holstein Friesian cows with a wide range in milk flow rate and teat dimensions. Vacuum levels measured within the liner showed a characteristic pattern of three distinct phases: 1, a mouthpiece chamber (MPC) vacuum that fluctuated with vacuum beneath the teat; 2, a stable MPC vacuum that coincided with the period of peak milk flow and 3, a MPC vacuum that fluctuated with pressure changes in the pulsation chamber and coincided with the period of no or reduced flow. Of the three liners examined, the Gascoigne 1030A (wide bore tapered) induced the highest MPC vacuum (29·4 ± 2·23 kPa, mean ± s.e.m), significantly higher (P < 0·01) than the Alfa-Laval 960000–01 wide bore (23·5 ± 2·32), regardless of teat size and milk flow rate. The Alfa-Laval 7275737–01 (narrow bore) gave a significantly lower value (16·5 ± 1·96) than either of the others (P < 0·001). It was not possible to link absolutely raised MPC vacuum to cow discomfort and teat trauma but circumstantial evidence encourages this view. Narrow teats in combination with slow flow rate appeared to exacerbate MPC vacuum and, because milking time for such animals was protracted, teats were exposed for longer periods.

In a series of short-term experiments cows were subjected to exaggerated bacterial challenge and accentuated milking machine conditions known to predispose to new mammary infection. The incidence of new intramammary infection was significantly greater in quarters with peak flow rates > 1·6 kg/min whether they were exposed to impacts (P < 0·05) or milking without pulsation (P <0·001). The infection rates were much lower (P < 0·001) in quarters milked with ‘pulsation and shields’ to protect against these two machine factors. Despite this, quarters with peak flow > 1·6 kg/min still showed a 12-fold increase in mastitis incidence compared with quarters with peak flow < 0·8 kg/min. Rates of milk flow have increased dramatically in the last 40 years through selection and breeding: whole udder peak flow rates in heifers have doubled from 1·9 to 3·8 kg/min. Increased emphasis, therefore, should be placed on hygiene, husbandry and milking techniques to minimize bacterial numbers at teat ends to control mastitis as the drive for higher flow rate and yield make cows increasingly more susceptible to infection. These results suggest that the benefits of reduced infection rate from mastitis control are significantly underestimated since animals are now considerably more susceptible than 40 years ago.

Concentrations of insulin-like growth factor 1 (IGF-1), insulin and growth hormone were measured in the secretion of the bovine mammary gland from day 70 ante partum until 6 d post partum. Highest levels were found during the last 2 weeks ante partum followed by a rapid decrease during the first milkings post partum. The association of IGF-1 with its binding proteins in milk was analysed and striking differences were found in the distribution of bound and free IGF-1. IGF-1 appeared mainly in the bound form (91%) at days 40–2 ante partum. Free IGF-1 preponderated in the first milkings post partum (73%) and changed again to about 85% in the bound form after day 4 post partum. A slightly acidic pH (6·3) of the secretion was correlated with high amounts of free IGF-1. Gel filtration experiments revealed a possible pH-dependent mechanism for the binding of IGF-1 to its binding proteins in milk.

Xanthine oxidase/dehydrogenase (XO/XDH) increases at mid gestation in mammary gland but not in liver of the mouse and remains elevated until the pups are weaned at 20 d post partum. The increase in enzyme activity is due neither to alteration in activators or inhibitors nor to a production of a variant enzyme with altered catalytic properties. The increase is preceded in vivo by a surge of prolactin-like activity (placental lactogen) in plasma, and prolactin is required for induction of XO/XDH in explant culture in vitro. Induction of XO/XDH in vivo and in vitro precedes the full histological differentiation of the gland. In addition, induction of XO/XDH in vitro occurs more rapidly and at lower concentrations of prolactin than does histological differentiation. Thus although XO/XDH is present in milk, increased XO/XDH activity is an early event in mammogenesis in vivo and in vitro rather than a terminal component of differentiation.

The performances of falling film evaporators used in the New Zealand dairy industry for concentrating skim milk, whole milk and buttermilk were evaluated by determining (1) the kg steam used per kg water evaporated, and (2) the heat transfer coefficient of each pass in the evaporators. A computer program was used to calculate the results. The heat transfer coefficients varied from 0·3 to 3·2 kW/m2 per °C and the steam consumption from 0·4 to 0·09 kg steam/kg evaporation. The viscosity of the feed and the momentum of the vapours passing down the tubes were found to be the main factors controlling the heat transfer coefficient. A correlation between the heat transfer coefficient and these factors is presented. Other factors likely to have an influence on the performance are discussed.

The effect of preheat treatment, evaporation and drying in a commercial plant on the denaturation of βlactoglobulin and α-lactalbumin, their incorporation into the casein micelle and the heat stability characteristics of the milks and powders were determined. Preheat treatments between 110 °C for 2 min and 120 °C for 3 min denatured between 80 and 91% of β-lactoglobulin and between 33 and 45% of α-lactalbumin. Evaporation increased the extent of denaturation but spray drying did not increase it further. The incorporation of α-lactalbumin and βlactoglobulin into the micelles was markedly less than the amount that denatured and was not a constant ratio to it. Heat coagulation times at 140 °C of milks, concentrates and powders diluted to the original milk concentration were measured as a function of pH. In general, the greater the collective heat treatment, the shorter the time required to achieve coagulation. Spray drying shifted the peak positions in the pH-heat coagulation time profiles. In contrast, heat coagulation times (measured at 120 °C) of concentrates and powders diluted to 20% total solids content increased with the severity of the preheat treatment. Surprisingly, spray drying markedly increased the heat coagulation times of the diluted concentrates.

Bacterial analyses were carried out of 2069 udder secretions, isolated from 1481 heifers with mastitis in eight veterinary districts in Sweden. Streptococci, e.g. Streptococcus dysgalactiae and Str. uberis, dominated the bacterial flora, being isolated from 34·4 and 19·5% respectively of heifers with clinical mastitis occurring from puberty up to 14 d post partum. Bacterial species generally regarded as important pathogens in the summer mastitis complex, e.g. Actinomyces pyogenes, Stuart–Schwan coccus and strictly anaerobic bacteria such as Peptostreptococcus indolicus, Fusobacterium necrophorum and Bacteroides melaninogenicus were isolated at low frequencies (13·2, 6·3, 9·4, 3·8 and 1·3% respectively). When the cases of mastitis studied were restricted to those appearing in heifers pre partum, May 15 to October 14 (summer mastitis), these bacterial species were isolated at higher percentages (27·1, 14·4, 21·4, 13·5 and 5·2% respectively). These figures were, nevertheless, still lower than those published in reports from other countries. Whether considered up to 14 d post partum or only pre partum, there were no significant differences in the frequencies of A. pyogenes isolated at different seasons. There were geographical differences in bacterial incidence, e.g. Staphylococcus aureus was isolated significantly more often in northern regions whereas Str. dysgalactiae was more common in the south. This and other Swedish investigations support the theory that A. pyogenes and strictly anaerobic bacteria are ‘secondary invaders’ that depend on Str. dysgalactiae to cause a primary infection. It is stressed that the udders of all heifers should be examined daily so that cases of mastitis can be treated immediately.

α-Adrenergic mimetics inhibit milk removal whereas β-adrenergic mimetics have a favourable effect upon milk removal in dairy cows. This work aimed to relate these effects to the milk ejection reflex mechanism and/or milk flow from the cisternal cavities only. The α-adrenergic agonist phenylephrine and the β-adrenergic agonist isoproterenol were injected prior to and after milk ejection. Applied after milk ejection, the phenylephrine treatment reduced intramammary pressure (IMP) and milk yield markedly. Phenylephrine application before milk ejection prevented IMP from rising during teat stimulation or after oxytocin injection. Milking produced small amounts of milk at minimal milk flow rates. The very different responses to phenylephrine application prior to and after milk ejection indicate separate adrenergic inhibitory mechanisms for milk ejection and milk flow. The application of the β-adrenergic agonist isoproterenol did not alter the IMP. Nevertheless, this compound improved milk removal by increasing milk flow. The observation of bimodal milk flow at milkings without preceding teat stimulation indicates a delayed milk ejection. Isoproterenol injection without teat stimulation enhanced milk flow rates, but the bimodality remained unchanged. We conclude that isoproterenol enhances milk flow without affectiiig milk ejection.

Naturally occurring disulphide-linked αs2- and κ-casein in bovine milk were purified by gel chromatography on a column of Sepharose CL-6B. Four fractions (A–D) were obtained by elution with ammonium acetate-urea buffer. Fractions A and B, identified by SDS gel electrophoresis and amino acid sequence analysis, corresponded to disulphide-linked κ-casein and αs2-casein respectively. Fraction C consisted of a mixture of αs1-, αS2-, and β-casein. Separation of fraction C into its components was achieved by reversed-phase HPLC. The stability of the disulphide bridges in αs2- and κ-casein was shown to differ with respect to reducing agents (dithioerythritol and 2-mercaptoethanol).

β-Casein amino groups were modified with aldehydes and dialdehydes via reductive alkylation at pH 8·0. The degree of alkylation was controlled by the amount of the alkylating reagent applied. The initial rates of α-chymotrypsin-catalysed hydrolysis of alkylated β-casein were inversely related to the size of the modifying group. Proteolysis of modified β-casein with trypsin (18 h) or with α-chymotrypsin (48 h) depended on the nature and size of the substituent applied. The measurements of tryptophan fluorescence indicate that the modifications also induced conformation change. Solubilities of methyl-, ethyl- or benzyl-β-casein slightly increased; solubilities of β-casein dialdehyde derivatives were significantly lower than that of native β-casein. Emulsion stability of methyl- or ethyl- β-casein was higher than that of native β-casein in the acidic pH range. After modification with glyoxal, the emulsifying activity and the emulsion stability of β-casein decreased. The emulsifying activity of benzyl- β-casein was lower than that of native β-casein. Phthalylated β-casein displayed the poorest emulsion stability.

The fouling of an inorganic microfiltration membrane with an average pore diameter of 0·2 μm obtained in static conditions with milk, acidified milk and acid coagulum was examined using scanning electron microscopy. The structure and porosity of external fouling related to the pH of the milk accounts for the performance and efficiency obtained in microfiltration. Electrophoretic analysis of permeate, characterized by lack of casein, shows that the deposit plays a fundamental role in mass transfer through filter layers. Variations in the physicochemical properties of casein as a function of pH at 50 °C were used to account for the development of the structure of fouling, which comprised three main states: (i) dense deposit of juxtaposed micelles, (ii) loose network formed by chains made up of bonded protein aggregate, (iii) irregular protein aggregate leading to high-porosity deposits. The presence of a protein film strongly adsorbed on the membrane layer of alumina particles is demonstrated.