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.

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.

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.

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.

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).

Raw skim milk was diluted 1000-fold using distilled water or various salt solutions as specified. Smooth, hyperbolic profiles of coagulation rate v. pH for casein were calculated from recordings of turbidity (400 nm) with time. The effects of pH, cation type, anion type and cleavage of k−casein by chymosin (EC 3.4.23.4) were determined. The maximum of pH-coagulation rate profiles decreased by 63, 85 and 94% when the skim milk diluent was changed from water to salt solutions of NaCl (100 mM), CaCl2 (50 mM) or MgCl2 (50 mM). The maximum of the pH–coagulation rate profile was 15 times greater when the Ca salt was changed from CaCl2 to Ca(SCN)2 (50 mM). The highest pH at which casein coagulation occurred increased from 4·45 to > 6·0 when Cu2+ (1 mM) was included with casein micelles dispersed in CaCl2 solution (50 mM). The addition of chymosin to casein micelles suspended in CaCl2 solution (70 mM) eliminated the inhibition of casein coagulation by Ca2+ at pH 4·5. It is proposed that ions such as Mg2+, Ca2+, and Na+, which generally associate with casein phosphate and carboxylate groups, increased the H+ concentration required to initiate the coagulation of casein, because H+ must displace bound Ca2+, Mg2+ or Na+ to reduce repulsive hydration forces between casein micelles, allowing attractive hydration forces (e.g. hydrophobic phenomena) to cause casein coagulation. Furthermore, it is proposed that ions such as Cl−, Br−, and SCN− bind to lysine, arginine and histidine groups and thereby decrease repulsive hydration forces between cationic casein micelles.

Highly purified lactoferrin was isolated from ovine colostrum by sequential purification on CM-Sephadex C-50 and Blue-Sepharose, with overall yield of 55%. The ovine lactoferrin was characterized by SDS-PAGE, its amino acid composition and N-terminal sequence to residue 30. Homology with bovine and human lactoferrins was greater than 80 and 50% respectively. Antibodies to ovine lactoferrin were raised in rabbits and used to develop an enzyme-linked immuno-sorbent assay (ELISA). The antiserum was not cross reactive with other colostrum proteins.

Milk powders were subjected during manufacture to the following treatments: low-, medium- or high-heat, indirect or direct UHT preheat, or no preheat. The Ca2+ activity–pH profiles of reconstituted milks (9% total solids, TS) in the pH range 6·06–6·98 and reconstituted concentrated milks (19·6% TS) and recombined concentrated milks (26% TS, 18% SNF, 8% fat) in the pH range 6·27–6·69 were determined. Statistical analysis of the results using a (– In Ca2+ activity) transformation was used to quantify the effects of pH, preheat treatment and fat incorporation on Ca2+ activity. pH had a dominant effect on Ca2+ activity and the effects of preheat treatment and fat incorporation were small in comparison. Depending on the batch of milk used for preparation of powders, pH accounted for 98·8–98·9%, 96·4–96·7% and 93·7–97·3% of the total variation in Ca2+ activity in reconstituted milks, reconstituted concentrated milks and recombined concentrated milks. The corresponding contributions of preheat treatment to variation in Ca2+ activity were 0·26–0·47%, 0·34–1·67% and 0·24–0·40%. The addition of fat to reconstituted concentrated milk to yield recombined concentrated milk with the same SNF: water ratio resulted in 0·03–3·71 % variation in Ca2+ activity. The results suggested that differences in heat stability among powders subject to different preheat treatments are not likely to be linked to Ca2+ activity.

Six batches of Casar de Cáceres raw ewes' milk cheeses were examined throughout their ripening. Three were made in winter, the others in spring. The microbial counts in the interior of the cheeses were ∼1·5 log units higher in the winter cheeses for total viable counts, lactic streptococci and leuconostocs, and >2 log units higher for total enterobacteria, coliforms and faecal coliforms in the 60 d samples. Staphylococci were not detected after day 15 of maturation in spring cheeses, but reached 1 log unit at day 60 in the interior of winter cheeses. In the surface samples, differences in microbial counts were more marked. Values of some physicochemical indices, such as pH, % moisture content and % NaCl were also determined.

Volatile components of four batches of Manchego cheese were studied throughout their ripening process. Samples were submitted to a micro simultaneous distillation-extraction procedure, and then analysed by capillary gas chromatography (GC) and combined GC and mass spectrometry. Among other components, four homologous series of compounds were found: free fatty acids, methyl ketones, ethyl and methyl esters of even fatty acids. Ripening stage can be approximately estimated from the concentrations of some components.