This study reports the effect of feeding formaldehyde-treated or untreated spray-dried casein–safflower oil (1:1, w/w) particles on the fatty-acid composition of milk and plasma lipids of cows.

When the formaldehyde-treated particles were given to Jersey, Sahiwal and Jersey × Sahiwal crossbred cows (1 kg per cow per day) the linoleic acid (18:2) present in the safflower oil was not hydrogenated by the rumen micro-organisms and was incorporated into milk fat.

When the untreated supplement was fed, however, the 18:2 fatty acid was hydrogenated in the rumen and there was an increased proportion of octadecenoic acid (18:1) in the milk fat.

The increased proportions of 18:2 (treated supplement) and 18:1 (untreated supplement) were associated with decreased proportions of palmitic (16:0) and myristic (14:0) acids in the milk fat. All 3 breeds showed similar responses.

The fatty-acid composition of plasma triglycerides, which are an important source of long-chain fatty acids for mammary-gland lipogenesis, was similarly affected. Furthermore, there were significant changes in the fatty-acid composition of other plasma lipids (e.g. phospholipids and cholesteryl esters). The interrelationships between dietary, plasma and milk fatty-acid compositions are discussed.

Three hundred and fifty-one lactating dairy cows, which were between 40 and 100 d post-calving, were selected from cows sampled during metabolic profile testing of 21 herds. Blood samples were analysed for packed cell volume (PCV), blood glucose and haemoglobin, and serum urea-N, albumin, total protein, inorganic phosphate, Ca, Mg, Na, K, Cu and Fe. After adjusting for herd and date of sampling and each cow's age, stage of lactation, milk yield and interval from calving to first service, concentrations of albumin and K (P < 0·01) and PCV (P < 0·05) were inversely related and concentrations of globulin (derived as the difference between total protein and albumin) directly related (P < 0·05) to the number of services required for conception. Conception rates to first service were inversely related to lactation number but not to milk yield on day of sampling.

Lactoperoxidase (LP), thiocyanate (SCN-), pH and somatic cell counts (SCC) were measured in mammary secretions from 20 cows collected 14 d before drying-off, 7 and 21 d after drying-off, and 3–18 d postcalving. The inhibitory activity of the secretions on Streptococcus uberis was determined and the susceptibility of the udder to infection by this organism was tested by intramammary infusion of 250 colony forming units at the above stages. LP, SCN-, pH and SCO increased during involution and fell postcalving. The secretions collected before drying-off, 7 d after drying-off and postcalving inhibited growth of Str. uberis.; those collected 21 d after drying-off did not. Inhibitory activity in pre-drying-off secretions was destroyed by heating and restored by addition of LP, glucose and glucose oxidase, but addition of these substances to secretion 21 d after drying-off did not provide a full inhibitory system. The growth of Str. uberis in the secretions was correlated with intramammary susceptibility, since challenges with Str. uberis at 14 d before drying-off, at 7 and 21 d after drying-off and postcalving led to 43·8, 25·0, 81·3 and 37·5% of quarters becoming infected. It is suggested that the LP/SCN-/H2O2 system plays a role in protecting the lactating mammary gland from infection with Str. uberis but becomes ineffective as involution progresses.

The keeping quality of commercial HTST-pasteurized milk and laboratory pasteurized milk from a common bulk raw supply has been investigated for 5 dairies. Spoilage occurred at levels of total bacterial counts around 107 colony forming units/ml, but with a slightly higher off-flavour threshold for the commercial milks than the laboratory pasteurized milks. The predominant microflora at spoilage and the type of off-flavour produced differed between the 2 types of milk. Raising the storage temperature from 5 to 11 °C caused a slight shift in the spoilage microflora and led to an average reduction in the shelf life of the laboratory pasteurized milk from 28 to 6 d and of the commercial pasteurized milk from 13 to 5 d. Changes in the level of post-pasteurization contamination (PPC) were reflected in changes in keeping quality, particularly at 5 °C. However, the greatest improvements were found in the absence of PPC.

Compounds associated with the ‘gluey’ off-flavour in stored casein have been isolated and identified by a combination of gas chromatography and mass spectrometry. Most of the flavour was found in the non-acid steam-volatile fraction which contained many compounds including n-alkanals, n-alkan-2-ones, furfural and other furan derivatives, benzaldehyde, dimethyl disulphide and benzthiazole. No single compound had the typical gluey flavour, which must be a complex sensation in which the quantities of minor components may determine the specific gluey character. o-Aminoacetophenone was present in the casein in subthreshold amounts. This compound has some gluey flavour and may have a synergistic effect in enhancing the total flavour.

High pressure processing was investigated for controlling Cheddar cheese ripening. One-month- or 4-month-old Cheddar cheeses were subjected to pressures ranging from 200 to 800 MPa for 5 min at 25 °C. The number of viable Lactococcus lactis (starter) and Lactobacillus (nonstarter) cells decreased as pressure increased. Subsequent storage of the control and pressure-treated cheeses at 10 °C caused viable cell counts to change in some cases. Free amino acid content was monitored as an indicator of proteolysis. Cheeses treated with pressures [ges ]400 MPa evolved free amino acids at significantly lower rates than the control. No acceleration in free amino acid development was observed at lower pressures. Pressure treatment did not accelerate the rate of textural breakdown compared with the non-pressure treated control. On the contrary, pressure treatment at 800 MPa reduced the time-dependent texture changes. Results indicate that high pressure may be useful in arresting Cheddar cheese ripening.

In a study of the evolution of conjugated linoleic acid (CLA) during cheese production, the influence of Emmental cheese processing on the CLA content and the CLA isomer composition was evaluated. The use of raw and thermised milk, changes of processing temperature and the effect of propionic acid bacteria (PAB) were investigated. The content of CLA in raw milk was 8·6±1·9 mg/g fat and in the ripened cheese at 70 d was 8·6±1·6 mg/g fat, under normal processing conditions. No changes in the CLA content and CLA isomer composition were observed during Emmental cheese manufacturing process. Changes in cooking and moulding temperatures did not influence the CLA content. CLA content of cheese made from microfiltered milk with two different Propionibacterium freudenreichii strains was very close to cheeses made without PAB. CLA levels seem to be stable in this type of dairy product under the conditions examined.

Discovery of an endopeptidase by gel chromatography and separation of 3 exopeptidases (a dipeptidase, an aminopeptidase and a specific carboxypeptidase) from Lactobacillus casei NCDO 151 by affinity chromatography is described. The 3 exopeptidases were strongly inhibited by the metal chelators EDTA and 1,10-phenanthroline but were reactivated with Co2+ and Mn2+. The pH optima for aminopeptidase, dipeptidase and carboxypeptidase activities were 6·5, 7·6 and 7·2, respectively. Maximum activity was obtained at 45 °C for the aminopeptidase, at 30 °C for the dipeptidase and at 40 °C for the carboxypeptidase.

The substrate specificities of the 3 enzymes were also studied. The properties of these 3 enzymes are compared with those of other bacteria.

The study was aimed at identifying the pathogens causing subclinical udder infections in representative Israeli dairy goat herds and determining their effect on milk quality. Five hundred goats in ten flocks of various breeds and crossbreeds were surveyed. Of the 500 goats, 13·4% were in their first lactation, 36·4% were in their second lactation and 50·2% were in their third or higher lactation. Percentages of udder halves with subclinical intramammary infection in the flocks ranged from 35 to 71%. The effect of the bacteriological infection on somatic cells count (SCC) was significant (P<0·001). Various species of coagulase-negative staphylococci (CNS), mainly Staphylococcus caprae and Staphylococcus epidermidis, were the main pathogens in infected udder halves. Lactation number did not significantly influence either infection rate of udder halves or SCC, although the percentage of udder halves with no bacteriological findings was higher at the first lactation than at the third lactation. Milk composition (fat, protein and lactose) varied among flocks, with lower mean total protein in uninfected halves than in infected ones and higher lactose in uninfected than infected halves.

Experiments were designed to determine the cisternal milk during machine milking in unfamiliar surroundings, which has previously been shown to inhibit milking-related oxytocin (OT) release and milk ejection. The first experiment was performed with 22 cows in early, mid and late lactation. After cisternal milk was removed, 10 i.u. OT were twice injected intravenously to remove the remaining milk. Total milk yield, cisternal milk yield, cisternal milk fraction (17 and 12% in early and late lactation) and the milk yield obtained in response to the first OT injection significantly decreased from early to late lactation. Cisternal milk yield was similar in front and rear udder halves. However, owing to higher total yield, the cisternal milk fraction was lower in rear than in front halves. Cisternal milk yield and cisternal milk fraction were smaller in primiparous than in older cows. In a further experiment milk distribution in the bovine udder was evaluated after preceding teat stimulation and milk ejection. Teats of 12 cows were manually stimulated for 1 min at 15, 60 or 120 min before milking. Total milk yield was not significantly different with or without teat stimulation. However, cisternal milk yield and fraction were significantly higher in teat stimulated cows than in unstimulated controls but were similar whether cows were stimulated 15, 60 or 120 min before milking.

Cheddar cheeses were prepared from low somatic cell count (SCC) milks and from milks containing 10, 20 and 30% added high SCC milk to give modestly elevated SCC. Increased SCO in the milk were associated with a reduction in the coagulum strength and an increase in moisture content of the cheeses. Cheese texture was affected significantly as judged both by the findings of an assessment panel and by instrumental physical measurement. The panel scores for flavour were also slightly altered. It was concluded that even a small increase in SCC is detrimental to cheese composition and quality, although no significant effects on yield were detected. Relationships between cheese yield, composition and properties, coagulation properties and composition of the milk were also studied. Yield was related to the total solids and fat in the milk but not to the coagulation properties or the flavour or texture of the cheeses. Coagulum strength, cheese composition and cheese texture were strongly interrelated.

An attempt was made to partition changes in milk yield during lactation in the rat between changes in the size of the secretory cell population and changes in cellular activity. Groups of rats were studied on d 2, 7, 14, 21 and 28 of lactation. Milk yield increased between d 2 and 7, less markedly between d 7 and 14 and decreased between d 14 and 21. Milk secretion had apparently ceased on d 28. Total mammary DNA (DNAt) and RNA (RNAt) increased from d 2 to 14. It is concluded that of the increase in milk yield between d 2 and 14, an increase in cell population accounted for 75% and an increase in cellular activity for 25%. A decrease in activity appeared to be entirely responsible for the decrease in yield between d 14 and 21.

The mammary glands of conventionally reared cows, never exceeding a live weight gain (LWG) of 0·74 kg/d, weighed 39% more and contained 68% more secretory tissue than glands of rapidly reared animals grown at 1·1 kg/d. In 11-month-old heifers reared at 3 rates of LWG (L, 0·57; M, 0·76 and H, 1·18 kg/d) gland weight was related to LWG, but dissected mammary parenchyma was heavier in animals on treatment L than on treatment H and followed a quadratic relationship. Parenchymal composition on treatment H was correlated to both age and body weight at puberty. No similar trend was observed in treatments L and M although group L animals had more ductal tissue and less fat than those of group M. Heifers from treatment L were reared during pregnancy at either 0·68 or 0·84 kg/d LWG (treatments LL and LH respectively) and heifers from treatment H at 0·58 kg/d (treatment HL). Total gland weight was unaffected by treatment, but the percentage by weight of secretory tissue in the gland in treatment HL was less than for treatments LL and LH. These experiments confirm that mammary development is permanently impaired by high rates of LWG in the first year of life. There was no impairment of mammary development in heifers reared moderately in the first year and more rapidly during pregnancy.

A method for isolation, detection and quantification of cholesterol oxidation products based on solid phase extraction in combination with preparative HPLC and gas chromatography–mass spectrometry selected ion monitoring has been developed for dairy products. The isolation procedure had a high recovery and artifact formation was minimal, as shown by isotope labelling. The limits of detection ranged from 0.3 to 35 pg/μl of the isomeric forms of 7-hydroxycholesterol, 20α-hydroxycholesterol, the isomeric forms of cholesterol-5,6-epoxides, cholestanetriol, 25-hydroxycholesterol and 7-ketocholesterol corresponding to a limit of quantification of 2–6 ng oxysterol/g lipid in the dairy product, depending on the nature of the cholesterol oxidation product.

We partially sequenced the mitochondrial D-loop region in 47 individuals from eleven Spanish and foreign goat breeds. Phylogenetic analysis of these sequences allowed us to identify a particular D-loop haplotype shared by individuals from the Palmera, Majorera and Tinerfeña Canarian breeds. Genotyping of 281 goats from 17 different breeds by PCR-HpaII RFLP evidenced that the geographical distribution of this haplotype is restricted to the Canary Islands. This ancestral mitochondrial haplotype might originate in the domestic goat herds brought by the native Canarian inhabitants approximately 3000 years ago. Although we observed other miscellaneous D-loop haplotypes in the Palmera, Majorera and Tinerfeña breeds, any of them allowed us to group individuals from these three populations in a single cluster, a feature that suggests that these haplotypes might have diverse origins. The remarkable degree of phylogeographic structure of the Canary goat breeds with regard to other Spanish and foreign populations might be attributed to the isolation of these breeds in the Canary Islands for approximately 2500 years, without exposure to the migratory movements and commercial trading events that probably affected the genesis of most domestic goat breeds worldwide. The Canarian D-loop haplotype can be efficiently genotyped by using DNA isolated from milk and cheese samples, which paves the way for the future establishment of a Canary breed identity test for these dairy products.

The goal of this study was to measure the economic impacts of reduced milk production associated with papillomatous digital dermatitis (PDD) in dairy cows in the USA, and of specific risk factors for PDD, in 1996. The method applied was an economic-welfare analysis of producer and consumer surplus, with the GUM Workbench used to analyse uncertainties in the measurements. Reduced milk production associated with PDD was found to reduce consumer surplus by $750 million±$580 million, and to increase the economic surplus of producers by $560 million±$470 million, with a net economic loss of $190 million±$130 million. An examination of the economic effects of specific epidemiologic risk factors for PDD showed that having dairy cows that were not born on the operation had important economic consequences associated with the disease, as did the type of land to which dairy cows had access during the winter months and the type of flooring on which cows walked. Washing hoof-trimming equipment between cows was an important biosecurity measure that was associated with reduced PDD. The epidemiologic model used also implicated hoof trimmers who trimmed cattle hooves on other operations as having an important economic impact associated with this disease, although this finding may have been erroneous.

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.

Carboxypeptidase A (CPA, mol. wt = 34600) and 1-dimethylaminonaphthalene-5-sulphonyl chloride (dansyl chloride, mol. wt = 270) were shown to react with the 3 casein subunits, αs1-, β- and κ-caseins, which constitute the micelle. Virtually all of the C-terminal amino acids were released by CPA from these subunits without disrupting the micellar structure.

It was verified that the rate of dissociation of the micelle into low molecular weight complexes is considerably slower than the rates at which these reagents act on micellar components. It is concluded that dansyl chloride, CPA, and probably also rennin, whose molecular weight is similar to that of CPA, are able to penetrate to the interior of the micelles. This was confirmed in a quite independent way with a non-reacting agent, myoglobin (mol. wt = 17000).

It is postulated that the casein micelle has a sponge-like structure in which the 3 different subunits are distributed fairly uniformly.

Micellar fractions obtained by differential centrifugation from skim-milk and colostrum were examined for their content of αs1-, β-, κ- and para-κ-caseins by the use of CPA as described by Ribadeau Dumas (1968). The results confirm that there is a real difference in κ-casein content of the micelles, according to their rate of sedimentation.

Organophosphorus pesticides (OPPs), widely used in agriculture, can cause toxic effects to humans and animals. The main purpose of the present work was to determine the contamination in raw milk by the main organophosphorus pesticides used in Italy and to evaluate the opportunity to start specific procedures of risk management along the milk production chain. The samples, collected in 4 Italian dairy plants directly from the tank trucks during the delivering, were representative of 920 tonnes of raw milk. The isolation of the OPPs (acephate, chlorpyriphos, chlorpyriphos-methyl, diazinon, methamidophos, methidathion, phorate, pirimiphos-methyl) was performed by liquid partition followed by clean-up with solid phase extraction. The analyses were carried out by dual column gas chromatography using two nitrogen-phosphorus detectors. Among the 135 samples analysed, 37 were positive in traces and 10 showed an OPP contamination ranging from 5 to 18 μg/kg. The higher results were recorded in the samples collected during the autumn-winter period. The main pollutants detected were acephate and chlorpyriphos. In every positive sample found, the OPP contamination was lower than the maximum residue level (MRL) fixed by the European Commission.

Strains of coryneform bacteria which produce methanethiol from L-methionine in laboratory culture have been isolated from Cheddar cheese and raw milk Many Gram-negative raw milk isolates including Pseudomonas fluorescens, Ps. putida, Ps. fragi, Ps. aureofaciens, Acinetobacter, Aeromonas and Serratia marcescens also produced methanethiol. Representative strains of coryneforms and pseudomonads produced methanethiol only from free L-methionine; glycyl-L-methionine and D-methionine were not degraded. The aerobic nature of the methanethiolproducing bacteria and the instability and alkaline pH-dependence of their thiol producing enzymes explained their failure to increase methanethiol concentrations in experimental cheese, even when large numbers (5 × 107/g milled curd) of pregrown cells were added. Other commonly occurring cheese bacteria such as starter streptococci, micrococci or lactobacilli either did not produce methanethiol or produced only traces. It is concluded that the methanethiol normally present in Cheddar cheese is unlikely to be the product of bacteria or their enzymes.