Keratinization of the epidermal cells of the bovine claw generates the horn that gives the tissue its mechanical strength. Disruption of keratinization is likely to have a detrimental effect on the strength and integrity of the horn, and could lead to solar lesions and lameness. As part of a wider investigation of the cell biological causes of lameness in dairy animals, we have compared keratin synthesis and distribution in healthy bovine claw tissue with those in hooves with solar ulcers. Protein synthesis was measured by [35S]-labelled amino acid incorporation in claw tissue explant cultures. [35S]-labelled protein synthesis was higher in tissue from diseased claws than in healthy claws, and highest at the ulcer site. The identity of proteins synthesised in vitro did not differ between healthy and diseased tissue. DNA synthesis indicative of cell proliferation was also elevated in diseased tissue. Immunoblotting after one- or two-dimensional electrophoresis showed cytokeratins (CK) 4, 5/6, 10 and 14 to be amongst those expressed in healthy claw tissue. The relative abundance of these keratins was not altered in healthy regions of ulcerated hooves, nor at the ulcer site, but CK16, not usually found in healthy tissue, was detected in the sole of diseased claws. CK5/6 and CK14 were shown by immunohistochemistry to be present in the basal epidermis of healthy tissue, whereas CK10 was found in supra-basal layers. In healthy tissue from ulcerated claws, this distribution was unaltered, but at the site of solar ulcers, CK5/6 and CK14 were each found in both basal and supra-basal epidermis. The study suggests that solar ulceration of the bovine claw is not associated with gross alteration in the keratin composition of the tissue, but causes abnormal distribution of cytokeratins, perhaps as a result of loss of positional cues from the basement membrane. Ulceration did, however, stimulate cell repair involving epidermal protein synthesis (including keratins), and keratinocyte proliferation.

Phagocytic and bactericidal activity of polymorphonuclear neutrophil leukocytes (PMN) isolated from blood and milk, against Staphylococcus aureus, was compared between groups of six healthy dairy cows in early, mid- and late lactation using a bacteriological assay. PMN were isolated from blood with a high degree of purity, but the cells isolated from milk contained variable amounts of macrophages (MΦ) and lymphocytes (L). The results were therefore calculated using the percentage PMN in order to evaluate phagocytosis and killing by PMN only. Blood PMN phagocytosed 82% Staph. aureus and milk PMN 43% on average and there was no significant difference between the different stages of lactation. The bactericidal activity of blood PMN against Staph. aureus was 36±8% in early lactation (significantly different from mid lactation, P<0·05), 64±10% in mid lactation and 53±6% in late lactation. Milk PMN killed only 6±3% Staph. aureus in early lactation (significantly different from mid lactation, P<0·01), 27±3% in mid lactation and 20±9% Staph. aureus in late lactation. The ratio of the bactericidal activity of milk to blood PMN was 0·08, 0·43 and 0·22 in early, mid- and late lactation, respectively. In addition to the decreased function, the number of cells in milk (somatic cell count, SCC) was also 60% lower in early lactation than in mid lactation cows (P<0·01). Our results suggest an impairment of blood and milk-resident PMN bactericidal activity against Staph. aureus and a decreased number of milk-resident PMN in dairy cows at the onset of lactation.

An experiment using three New Zealand herds and a total of 632 cows, examined the effect of localised prophylactic treatments with antibiotic at drying-off on the incidence of new intramammary infection during the dry period and at calving. Antibiotic was infused either into the teat canal (0·22 g of dry-cow formulation) or the teat sinus (3·1 g of lactating-cow formulation) of uninfected quarters to eliminate any bacteria present in these locations at the last milking of lactation. These treatments were compared with a negative control (nil treatment) and a positive antibiotic control (infusion of 3·6 g of dry-cow formulation). All antibiotic formulations used the same active ingredient, sodium cloxacillin. No significant reduction in new dry period clinical mastitis was observed for the two localised treatments whereas the positive control treatment achieved 100% reduction in new clinical mastitis compared with untreated control quarters. A 41% reduction (P<0·05) in new Streptococcus uberis infections at calving was associated with the teat canal antibiotic treatment, compared with an 82% reduction (P<0·001) for the positive antibiotic control. Both localised treatments showed a reduced incidence of new intramammary infection (P<0·001) when pooled across periods and pathogens. Teats receiving either the teat canal antibiotic treatment or a full infusion of long acting dry-cow antibiotic had a lower incidence of open teat canals (P<0·05) at 3 weeks after drying-off.

About 10% of primiparous cows have no milk ejection during the first milkings after delivery. Therefore, 17 Brown Swiss dairy cows in their first lactation were used to evaluate the extent of disturbed milk let-down and the corresponding oxytocin (OT) plasma values in the 1st 5 days after delivery. The first milking was 9–22 h after parturition and served for classification of the cows to groups with inhibited (INH), bimodal (BIMO) or normal (NOR) milk let-down. The OT plasma levels before the start of manual teat stimulation and machine milking were comparably high during the first milking especially in NOR and BIMO cows. Ten minutes before the second milking (M2), 300 mg of the opioid antagonist naloxone was injected to test whether the disturbance was affected by the action of endogenous opioids on the neurohypophysis. The milk yield was not influenced by the naloxone treatment, and the INH cows had milk ejection only after a vaginal stimulation. Afterwards, the cows were milked twice every day, until the milk let-down and the OT release were unaffected (equal to control milking). Then, at the next milking, the cows were injected with 300 mg morphine 10 min before milking. The central OT release in response to manual teat stimulation and machine milking was completely blocked in all cows, but a vaginal stimulation was able to abolish this block, at least partially, in 16 cows. Thus, morphine produced a milk let-down characteristic as in the INH cows during the first three milkings. For the following milking, the cows were pre-treated with 300 mg naloxone (−15 min) plus 300 mg morphine (−10 min) before milking. The OT release and the milk yields were unaffected when compared with the control milking. This experiment demonstrates that exogenous opioids can affect the central release of OT in a naloxone-reversible manner even very soon after parturition. However, endogenous opioids are probably not the main mediators of disturbed central OT release and alveolar milk ejection in post-partum primiparous cows.

Two groups of 15 multiparous cows in mid-lactation were used in a Latin square design experiment with 4-week experimental periods. The genetic milk protein concentration level was high in the first group and low in the second. Each group of cows was given in a random order three feeding levels that covered 85, 100 and 115% of energy requirements and 90, 110 and 125% of nitrogen requirements, respectively. In both groups, increasing level of feeding induced a significant increase in milk yield (+2·4 kg/d between lowest and highest levels) and in protein concentration (+1·7 g/kg). The proportion of paracasein in total proteins was not altered by either genetics or nutrition. The proportion of casein in total proteins was slightly increased by 0·5 percentage points (P<0·05) with the intermediate level of feeding. Plasmin and plasminogen activities were not significantly modified by the genetic milk concentration level. Plasmin activity significantly increased with nutrient supplementation, but only in animals of low genetic potential (+21% between low and high levels, P<0·01). Casein composition was not significantly altered by the genetics or level of nutrition. Over the whole range of individual measurements taken (n = 90), the relationships between casein or paracasein and total protein concentrations were linear and very narrow (R2 = 0·92 and 0·95, respectively). The proportion of casein or paracasein in total proteins significantly decreased as plasmin activity increased.

β-Lactoglobulin (β-lg) is the main protein of ruminant milk whey. Although β-lg can bind in vitro to a variety of hydrophobic substrates, mainly retinol and long-chain fatty acids, its physiological function is still unknown. In Exp. 1, we investigated the effect of β-lg on the plasma retinol concentration in preruminant calves. Holstein male calves (n = 20) were fed Holstein whole milk at 40 g/kg body weight (BW) plus vitamin A acetate (500,000 i.u.) with or without β-lg (0·4 g/kg BW). The plasma retinol concentration of 10-d-old calves was greater (P<0·05) in the β-lg-fed group than in the control group during the period from 8 to 12 h and at 24 h after the feeding. The postprandial change of plasma retinol in 40-d-old calves fed milk with β-lg was higher (P<0·05) than that in the control calves only at 12 h after the feeding. In Exp. 2, Holstein male calves (n = 18) were used to investigate the effect of β-lg on plasma triglyceride concentration and fatty acid composition. Calves were fed Holstein whole milk at 40 g/kg BW plus milk fat prepared from whole milk at 2 g/kg BW with or without β-lg (0·4 g/kg BW). Plasma triglyceride concentration at age 10 d was higher (P<0·05) in the β-lg-fed group than in the controls during the periods from 1 to 2 h and from 7 to 11 h after the feeding. At age 40 d, plasma triglyceride in the β-lg-fed group was higher (P<0·05) than in the control group only at 9 h. Ratios of palmitic, stearic, and oleic acids to total plasma lipids were higher (P<0·05) in the calves fed β-lg milk than in the control calves at age 10 d. These results suggest that β-lg enhances the intestinal uptake of retinol, triglyceride, and long-chain fatty acids in preruminant calves.

Oral tolerance to foreign enteral antigens is not fully developed in early neonatal life. Epidemiological evidence supports a role for maternal milk in the development of immune responses, including oral tolerance. Formula fed infants have an increased susceptibility to food allergy and the later development of autoimmune disease. This may relate to the lack in infant formula of growth factors found in maternal milk. Bovine milk contains proteins, growth factors and cytokines. Various studies have outlined the immune modulating potential of bovine milk-derived products. Fractionated whey extracts have therapeutic potential in disease states where there is an excessive inflammatory reaction, and disease preventive potential for infants who are not breast-fed. We have shown that daily oral administration of a growth factor-enriched fraction from milk whey to naturally suckling rat pups between days 4–9 postnatal can down-regulate immune activation to a specific orally administered food antigen, ovalbumin, assessed by lymphocyte proliferation. In addition, non-specific down-regulation in the intestine was observed as assessed by the expression of MHC I. Treatment of rat pups with whey extract at the time of oral sensitisation to ovalbumin also resulted in an increased secretion of TGF-β into the culture supernatant of spleen cells incubated with specific antigen. TGF-β is an immuno-down-regulatory cytokine involved in tolerance induction. Immune modulation by extracts derived from milk whey could be of potential benefit for formula-fed and pre-term infants in reducing susceptibility to inappropriate activation to food antigens.

The effect of milks fermented by Lactobacillus helveticus and its non-proteolytic variant on mucosal and tumoral immunity was studied. Milks fermented by Lb. helveticus wild type or its non-proteolytic variant were administered orally to mice for different periods (3, 5 and 7 d). The immune response was assessed by analysing the activity of the peritoneal macrophages, the number of cells secreting IgA associated with the gut-associated lymphoid tissue and with the bronchial-associated lymphoid tissue. The number of cells was determined by direct immunofluorescence. The antitumour activity was monitored by studying the regression of the subcutaneously implanted fibrosarcomas. After 3 d feeding of milk fermented by Lb. helveticus wild type, the number of sIgA increased significantly at both the intestinal and bronchial levels, indicating that a cellular migration had occurred. This effect was not noticeable when milk fermented by Lb. helveticus Protease (−) was orally administered. Both fermented milks (wild type or its variant) exhibited an effect on the activity of the peritoneal macrophages, which might be indirectly correlated to the regression of the fibrosarcoma. Although the mechanism by which the lactic acid bacteria enhance the immune system is not clear, this study clearly suggests that the bioactive compounds released during milk fermentation might contribute to the immunoenhancing properties of these products. By releasing biopeptide, lactic acid bacteria have important implications in modulation of the host's immune response, more specifically its cellular immune response.

The probiotic Lactobacillus rhamnosus HN001 is known to enhance immunity in animal models, following oral delivery. In this study, we investigated the immunoenhancing effects of HN001 delivered to mice in different milk-based substrates, including: whole (full-fat) milk supplemented with HN001; fermented milk supplemented with HN001; or whole milk which had been part-fermented by HN001. Direct oral feeding of mice with HN001 in whole milk was shown to enhance the phagocytic activity of blood and peritoneal cells. Similar effects on phagocytosis were observed when HN001 was offered to mice in the form of a milk- or fermented milk-based diet. The degree of immune enhancement conferred by HN001 was similar whether the probiotic was used as an additive or as a fermentative agent. These studies confirm that Lb. rhamnosus HN001, derived originally from dairy food, enhances immune function following oral delivery in different milk bases.

The effects of administration of Lactobacillus gasseri SBT0270 on serum lipids and bile acids, faecal bile acids and microflora were estimated in hypercholesterolemic rats. An effective dose of strain SBT0270 to exert its hypocholesterolemic effect was 109 viable cells/d. The dose of 109 cells/d did not affect the faecal coliform counts, but the number of faecal lactobacilli in rats fed this dose was significantly higher than that in the control group observed at the end of feeding period. Hypocholesterolemic effect of Lb. gasseri SBT0270 was attributed to its ability to suppress the reabsorption of bile acids into the enterohepatic circulation and to enhance the excretion of acidic steroids in faeces of hypercholesterolemic rats.

At atmospheric pressure, inactivation of lactoperoxidase (LPO) in milk and whey was studied in a temperature range of 69–73 °C and followed first order kinetics. Temperature dependence of the first order inactivation rate constants could be accurately described by the Arrhenius equation, with an activation energy of 635·3±70·7 kJ/mol for raw bovine milk and 736·9±40·9 kJ/mol for diluted whey, indicating a very high temperature sensitivity. On the other hand, LPO is very pressure resistant and not or only slightly affected by treatment at pressure up to 700 MPa combined with temperatures between 20 and 65 °C. Both for thermal and pressure treatment, stability of LPO was higher in milk than in diluted whey. Besides, a very pronounced antagonistic effect between high temperature and pressure was observed, i.e. at 73 °C, a temperature where thermal inactivation at atmospheric pressure occurs rapidly, application of pressure up to 700 MPa exerted a protective effect. At atmospheric pressure, LPO in diluted whey was optimally active at a temperature of about 50 °C. At all temperatures studied (20–60 °C), LPO remained active during pressure treatment up to 300 MPa, although the activity was significantly reduced at pressures higher than 100 MPa. The optimal temperature was found to shift to lower values (30–40 °C) with increasing pressure.

Chemical and microbiological composition of four Argentinean kefir grains from different sources as well as characteristics of the corresponding fermented milk were studied. Kefir grains CIDCA AGK1, AGK2 and AGK4 did not show significant differences in their chemical and microbiological composition. In contrast, protein and yeast content of AGK3 was higher than in the other grains. Although grain microflora comprised lactobacilli, lactococcus, acetic acid bacteria and yeast, we found an important difference regarding species. Lactococcus lactis subsp. lactis, Lactobacillus kefir, Lactobacillus plantarum, Acetobacter and Saccharomyces were present in all types of kefir grain. While Leuconostoc mesenteroides was only isolated from grains CIDCA AGK1 and Lactococcus lactis subsp. lactis biovar diacetylactis, Lactobacillus parakefir and Kluyveromyces marxianus were only isolated from CIDCA AGK2 grains. All grains produced acid products with pH between 3·5 and 4·0. The apparent viscosity of AGK1 fermented milk was greater than the product obtained with AGK4. All fermented milks had inhibitory power towards Escherichia coli but AGK1 and AGK2 supernatants were able to halt the bacterial growth for at least 25 h. Grain weight increment in AGK1, AGK2 and AGK3 during growth in milk did not show significant differences. Despite their fermenting activity, AGK4 grains did not increase their weight.

Fermentation of deproteinised whey with kefir grains CIDCA AGK1 was studied focusing on polysaccharide production from lactose. Kefir grains were able to acidify whey at different rates depending on the grain/whey ratio. During fermentation, kefir grains increased their weight and a water-soluble polysaccharide was released to the media. Exopolysaccharide concentration increased with fermentation time, reaching values of 57·2 and 103·4 mg/l after 5 days of fermentation in cultures with 10 and 100 g kefir grains/l, respectively. The polysaccharide fraction quantified after fermentation corresponded to the soluble fraction, because part of the polysaccharide became a component of the grain. Weight of kefir grains varied depending on the time of fermentation. Polysaccharide production was affected by temperature. Although the highest concentration of polysaccharide in the media was observed at 43 °C at both grain/whey ratios, the weight of the grains decreased in these conditions. In conclusion, kefir grains were able to acidify deproteinised whey, reducing lactose concentration, increasing their weight and producing a soluble polysaccharide.

Volatile sulphur compounds are major flavouring compounds in many traditional fermented foods including cheeses. These compounds are products of the catabolism of L-methionine by cheese-ripening microorganisms. The diversity of L-methionine degradation by such microorganisms, however, remains to be characterized. The objective of this work was to compare the capacities to produce volatile sulphur compounds by five yeasts, Geotrichum candidum, Yarrowia lipolytica, Kluyveromyces lactis, Debaryomyces hansenii, Saccharomyces cerevisiae and five bacteria, Brevibacterium linens, Corynebacterium glutamicum, Arthrobacter sp., Micrococcus luteus and Staphylococcus equorum of technological interest for cheese-ripening. The ability of whole cells of these microorganisms to generate volatile sulphur compounds from L-methionine was compared. The microorganisms produced a wide spectrum of sulphur compounds including methanethiol, dimethylsulfide, dimethyldisulfide, dimethyltrisulfide and also S-methylthioesters, which varied in amount and type according to strain. Most of the yeasts produced methanethiol, dimethylsulfide, dimethyldisulfide and dimethyltrisulfide but did not produce S-methylthioesters, apart from G. candidum that produced S-methyl thioacetate. Bacteria, especially Arth. sp. and Brevi. linens, produced the highest amounts and the greatest variety of volatile sulphur compounds including methanethiol, sulfides and S-methylthioesters, e.g. S-methyl thioacetate, S-methyl thiobutyrate, S-methyl thiopropionate and S-methyl thioisovalerate. Cell-free extracts of all the yeasts and bacteria were examined for the activity of enzymes possibly involved in L-methionine catabolism, i.e. L-methionine demethiolase, L-methionine aminotransferase and L-methionine deaminase. They all possessed L-methionine demethiolase activity, while some (K. lactis, Deb. hansenii, Arth. sp., Staph. equorum) were deficient in L-methionine aminotransferase, and none produced L-methionine deaminase. The catabolism of L-methionine in these microorganisms is discussed.

The taste-active compounds of a Camembert cheese selected for its intense bitterness defect were investigated. The water-soluble fraction (WSE) was extracted with pure water and fractionated by successive tangential ultrafiltrations and nanofiltration. The physicochemical assessment of these fractions led to the construction of a model WSE which was compared by sensory evaluation to the crude water-soluble extract, using a panel of 16 trained tasters. As no significant difference was perceived, this model WSE was then used directly or mixed with other cheese components for omission tests. Among the main taste characteristics of the WSE (salty, sour, umami and bitter), bitterness was found to be due to small peptides whose mass distribution was obtained by RPHPLC-MS (400–3000 Da) and whose taste properties are discussed.

Molecular biology techniques have been used for species identification in food of animal origin in relatively recent years. A polymerase chain reaction (PCR) based method, the multiplex PCR, was recently applied to species identification in meat and meat products. It allows co-amplification of separate regions of a single gene or specific fragments, each typical of a different animal species in a single PCR reaction, using different pairs of primers in the same reaction mix. In the present paper, the duplex-PCR technique is proposed to identify bovine and water buffalo DNA in a single PCR assay in milk and mozzarella cheese (a typical Italian cheese, originally made from pure water buffalo milk). Because of its lower cost, undeclared bovine milk is added to water buffalo milk for making different kinds of mozzarella cheese. The results of this experiment indicate the applicability of this method, which showed an absolute specificity for the two species and a high sensitivity even down to low DNA concentrations (1 pg). In bovine and water buffalo mixtures of both milk and mozzarella cheese, the minimum concentration tested was 1% of bovine in water buffalo milk and water buffalo in bovine milk. The importance of the somatic cell content in raw milk is also discussed with special reference to the evaluation of mixtures (milk or cheese) of the two species.

Milk ejection and milk removal is considerably influenced by the sympathetic nervous system. Stimulation of α-adrenergic receptors by administration of α-adrenergic agonists inhibits alveolar milk ejection and milk removal in dairy cows due to smooth muscle contraction (Blum et al. 1989; Bruckmaier et al. 1991). However, contraction of the teat in response to α-adrenergic receptor stimulation has no influence on milk flow as long as milk is available in the cistern (Bruckmaier et al. 1997). Therefore, α-adrenergic stimulation causes inhibition of transport of alveolar milk into the cistern. On the contrary, the stimulation of β-adrenergic receptors facilitates milk ejection and milk removal in dairy cows (Bernabé & Peeters, 1980; Bruckmaier et al. 1991) because of muscle relaxation. Therefore, the distribution of α- and β-adrenergic receptors plays an important role in the milkability of dairy cows. However, from these in vivo studies it is not possible to distinguish between the different α1- and α2- and β2-receptor subtypes owing to the non-specific nature of the pharmacological agents used.

To date, the precise tissue distribution of these different subtypes, in bovine mammary tissue, is unknown. Using molecular techniques, we were interested in the expression of genes that encode α1c and β2 as a preliminary study towards the understanding of noradrenergic receptor-gene expression and regulation in this important system.

In addition, α1c- and β2-adrenergic receptors were determined in front and rear quarters of the mammary gland to investigate differences in receptor distribution within the udder and possible relations between adrenergic receptor distribution and the higher milk flow rates in rear than in front quarters (Rothenanger et al. 1995).