The effects of level of fish oil inclusion in the diet on grass silage intake, and milk yield and composition of dairy cows offered either 5 or 10 kg concentrates/d were evaluated in a ten treatment, partly balanced, changeover design experiment involving 50 cows in early lactation. Concentrates were prepared to provide 0, 150, 300 or 450 g fish oil/cow per d or 300 g fish oil/cow per d from a premix when each animal was offered 5 kg/d. The fish oil was predominantly from herring and mackerel caught in the North Atlantic while the fish oil premix was obtained from a commercial source and used palm kernel expeller as a carrier. Increasing fish oil supplementation decreased silage dry matter intake and the concentrations of milk fat and protein, and increased milk yield and diet digestibility. There were significant interactions between concentrate feed level and level of fish oil for silage intake and milk yield. Other than for the concentrations of milk fat and protein, and 20[ratio ]4n−6 fatty acids, the source of fish oil did not affect forage intake or animal performance. Fish oil supplementation also decreased the concentrations of milk protein by 0·9 g/kg for each 100 g increase in fish oil supplementation, the depression being similar at each level of concentrate feeding. Supplementing the feed of dairy cows with 450 g fish oil/cow per d decreased the concentration of milk fat by 15 g/kg. This study also showed that feeding dairy cattle with fish oil is an efficient method of increasing eicosapentaenoic acid in the human diet through transfer into milk.

The progress of Staphylococcus aureus infection from inoculation to the early chronic stage was examined in 12 Israeli-Holstein cows (four primiparous and eight multiparous) for up to 48 d after inoculation. Before inoculation, the primiparous cows were free from any infection and the multiparous cows were infected by coagulase-negative staphylococci. Two quarters in each cow were inoculated intracisternally following milking with 2000 cfu of a local prevailing Staph. aureus strain, VL-8407. Infection was established in 21 out of 24 quarters. The control quarters remained free from infection during the study, with no significant change in function. No statistically significant differences were found between primiparous and multiparous cows in the responses examined. Somatic cell count (SCC) increased within 24 h of inoculation and remained high for the duration of the study. In the infected quarters mean ln (SCC) increased within 24 h from 9·9±0·5 before inoculation to 13·0±0·2 after inoculation; most of the cells were neutrophils. N-acetyl-β-glucosaminidase activity, expressed as ln (nnmol/min per l), was increased from 0·9±0·6 to 2·4±0·2 by inoculation, and was highly correlated with SCC. The Staph. aureus count fluctuated with no particular relationship with SCC. The phagocytic activity of neutrophils was significantly lower in the inoculated than in the control quarters and this difference increased with time after inoculation. CD8+ T lymphocytes were the main subpopulation of lymphocytes found in inoculated quarters. After inoculation, maximum but not minimum electrical conductivity (EC) recorded during milking increased significantly. The rises in maximum EC varied significantly among cows. The rises in SCC were associated with a persistent increase in EC in only one of the eight cows examined. No clinical signs were observed, and milk yield and composition were not affected during the study period. The results suggest that some strains of Staph. aureus may induce a relatively mild response in mammary glands of cows in mid lactation, and that the concomitant development of such chronic Staph. aureus infections in two quarters may not be detected by changes in the EC of composite milk and in the yield of the cow.

A kinetic modelling approach was developed and investigated with the aim of predicting the utilization of major substrates in the mammary gland and milk secretion rates in the lactating cow at varying concentrations of substrate in arterial blood. The model includes kinetic equations of transport and metabolism of glucose, acetate, free amino acids and free fatty acids in secretory cells and a phenomenological description of autoregulation of local blood flow, in which an energy criterion of control has been used. The predicted relationships between the rate of milk secretion and glucose levels in the blood are consistent with experimental results. Differential stimulation of α-lactalbumin synthesis causes increments in local blood flow and milk secretion rate in the model. The results of the study suggest that there is no simple relationship between the level of substrates in the blood and milk yield and contents of fat and protein in milk. This is because the effect on production of varying patterns of substrate concentrations in the blood is mediated by network interactions at the level of secretory cell metabolism and microcirculation. However, dynamic modelling provides a rational framework for developing such predictive tools.

The physiological effects of intramammary infusions of recombinant bovine cytokines in six lactating dairy cows on the quality and yield of milk and the bactericidal activity of milk neutrophils were investigated. Recombinant bovine interleukin-2 (rboIL-2) and interferon-γ (rboIFN-γ) were produced in the yeast Pichia pastoris. Two animals were given rboIL-2 (2×105 units) in two quarters, two animals were given rboIFN-γ (6·5×105 units) in two quarters, and the other two cows received a dose of rboIL-2 in one quarter and rboIFN-γ in a second quarter. In addition, each animal was given phosphate-buffered saline (PBS) in the other two quarters as a control. Somatic cell counts and conductivity of the fore milk were monitored before and after infusion. Neutrophils were isolated from quarter milk samples 36 h after infusion of cytokine or PBS and their bactericidal activities against Staphylococcus aureus were measured in vitro with a colorimetric assay. Quarters infused with rboIL-2 or rboIFN-γ showed significant but transitory increases in both milk somatic cell counts and conductivity when compared with preinfusion values and with control quarters. There were minimal effects on daily milk yield. Neutrophils isolated from milk from quarters infused with rboIL-2 showed enhanced bactericidal activity against Staph. aureus. The bacterial killing from rboIL-2 treated quarters was significantly greater, with a mean of 63·5% compared with a mean of 5·4% for neutrophils taken from uninfected quarters to which PBS had been administered. The bactericidal activities for quarters treated with rboIFN-γ and infected quarters treated with PBS were 15·0 and 30·0% respectively. The results indicate that intramammary infusions of rboIL-2 and rboIFN-γ to lactating cows are well tolerated, and that rboIL-2 can activate milk neutrophils and augment their bactericidal activity.

The effects of cold storage at 4 °C for 12, 24 and 48 h on the physicochemical characteristics and renneting properties of ewes', goats' and cows' milks were compared. The most important changes were observed in cows' milk. Soluble calcium concentrations were not affected in ewes' milk but were increased by 10% in cows' milk and 7% in goats' milk. More casein was dissociated on cooling cows' (+300%) than goats' (+100%) milk, and there was no change in soluble casein in ewes' milk. The coagulation characteristics of cows' milk were more impaired by cold storage than goats' or ewes' milks. Coagulation times increased by ∼30% and whey draining capacity decreased by 40% after cows' milk was cooled, but there were no changes with ewes' milk and only a slight decrease in coagulation time with goats' milk. We propose an interpretation of these results based on the physicochemical properties of each type of milk.

Casein fractions and their breakdown products in Iberico-type cheeses made from the milk of cows, ewes or goats were analysed by capillary electrophoresis in order to characterize them. The actions of plasmin and chymosin on caseins were evaluated by comparing the electropherograms of caseins from milk and from cheese, both with and without treatment with plasmin. Characteristic capillary electrophoresis patterns were obtained for cheeses made from the milk of each of the three species, and the main components were identified. Caprine para-κ-casein and bovine β-caseins, eluting at the first and at the last part of the electropherogram respectively, were found to be indicative of the presence of the milks of these species.

Two new variants have been detected and characterized for the goat β-lactoglobulin gene at the cDNA level and confirmed at the genomic level. The two polymorphisms are located on exon 7 of the gene. One of the polymorphic sites is produced by a single nucleotide substitution in position +4601, allowing a polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) genotyping procedure to be developed using SacII restriction enzyme. The other polymorphic position contains a 10 bp long insertion at position +4641 that can be detected by capillary electrophoresis of the PCR product amplified with a fluorescent primer. The association of these two polymorphisms was also investigated, resulting in the description of two new alleles. Both of these contained the point mutation at the SacII site, with or without the 10 bp insertion at position +4641. The distribution of these new polymorphisms was studied in a population of males of four different goat breeds. The gene frequencies for these variants were similar in Spanish and French breeds.

The stability of the water-soluble B vitamins and the fat-soluble vitamins A and E of three liquid infant milks was followed throughout 12 months of storage at 20, 30 and 37 °C. Two samples were ‘follow-on’ milks from two different manufacturers and the other a ‘junior’ milk from one of these. The levels of water-soluble vitamins and vitamin E remained constant during storage at the three temperatures. In contrast, vitamin A decreased in samples from one manufacturer at all storage temperatures, and in samples from the other only at 37 °C. A kinetic equation was derived that made it possible to predict the influence of storage temperature on the shelf life of these kinds of products, together with the storage period during which levels of vitamin A recommended as adequate would remain.

To explain the limited nutritional value of milk cultured with proteinase-positive (Prt+) strains of Lactococcus lactis for the subsequent growth of dairy lactococci, we investigated further the time courses of modifications in the free amino acid and peptide contents of cultured milk. When growing in milk for up to 24 h, Prt+ strains of Lc. lactis progressively accumulated amino acids and casein-derived peptides. The growth of proteinase-negative (Prt−) wild-type strains and peptide transport mutants of Lc. lactis in cultured milk showed that casein-derived peptides could sustain growth up to 5×108 cfu/ml, depending on the extent of casein degradation during the preliminary growth of Prt+ strains and the Prt− strains. Of the casein-derived oligopeptides, <25% were transported into the cell and used for Lc. lactis growth. However, they played a prominent role, contributing 90% to growth. In contrast, di- and tripeptides did not contribute to growth, suggesting that either few were released from caseins or they did not supply essential amino acids.

The fatty acid composition and freeze–thaw resistance of eight strains of thermophilic lactobacilli were studied. Seven of these contained the same polar and neutral lipids, the five major components making up 90% of the cellular fatty acid pool being 14[ratio ]0, 16[ratio ]0, 16[ratio ]1, 18[ratio ]1 and C19 cyclopropane (cyc19[ratio ]0). Strain comparison by means of cluster analysis based on the fatty acid ratios using the overlap coefficient revealed two well defined clusters. One was formed by three strains of species Lactobacillus delbrueckii subsp. lactis and Lb. delbrueckii subsp. delbrueckii, the other included five strains of the species Lb. delbrueckii subsp. bulgaricus, Lb. acidophilus and Lb. helveticus. Resistance of strains with a high content of unsaturated fatty acids (66–70%) decreased with increasing cyc19[ratio ]0 concentrations. In contrast, in strains with a low concentration of unsaturated fatty acids (42–49%), increasing cyc19[ratio ]0 levels were associated with increased freeze–thaw resistance.

The respiratory burst activity of polymorphonuclear leucocytes (PMN) was evaluated in eight Holstein cows from 8 weeks before until 6 weeks after calving by chemiluminescence (CL). The CL response started to decrease 1 week before parturition, reaching a minimum during the first 2 weeks after calving. From week 3 of lactation, CL increased again and returned to original levels by week 6 of lactation. Plasma concentrations of 3-hydroxybutyric acid, total bilirubin and bovine pregnancy-associated glycoprotein started to increase before parturition to reach a maximum during the first or second week of lactation. The concentrations of glutamic–oxaloacetic transaminase, lactate dehydrogenase, non-esterified fatty acids and bilirubin increased after calving, reaching a maximum during the second week. A small decrease in plasma cholesterol during the week before and after calving was followed by an increase. The CL response of the PMN showed significant temporal relationships with the plasma concentrations of 3-hydroxybutyric acid, bovine pregnancy-associated glycoprotein, bilirubin, glutamic–oxaloacetic transaminase, non-esterified fatty acids; that with cholesterol was nearly significant. This means that the change in the CL response with time coincided with the changes in plasma concentrations of these substances with time and that these changes were significantly related with each other. The results of this study show that the decreased respiratory burst activity of bovine PMN around parturition may be related to the extent of the metabolic and hormonal changes. Although the causative relationships are not proven, these results support earlier results suggesting that 3-hydroxybutyric acid and bovine pregnancy-associated glycoprotein may directly affect neutrophil function, whereas non-esterified fatty acids, cholesterol, bilirubin, and liver enzymes may have potential as diagnostic markers of impaired neutrophil function and consequently increased disease risk around parturition.

Intracellular peptidases of Lactobacillus helveticus may play a major role in the proteolysis of Swiss cheeses, provided that they are released through bacterial lysis. Experimental Swiss cheeses were manufactured on a small scale from thermized and microfiltered milk using as starters (in addition to Streptococcus thermophilus and Propionibacterium freudenreichii) one of two Lb. helveticus strains, ITGLH1 and ITGLH77, which undergo lysis to different extents in vitro. All the cheeses were biochemically identical after pressing. The viability of Lb. helveticus ITGLH1 and ITGLH77 decreased to a similar extent (96–98%) while in the cold room, but the concomitant release of intracellular lactate dehydrogenase in cheeses made with strain ITGLH1 was 5–7-fold that in cheeses made with ITGLH77. Protein profiles and immunoblot detection of the dipeptidase PepD confirmed a greater degree of lysis of the ITGLH1 strain. Free active peptidases were detected in aqueous extracts of cheese for both strains, and proteolysis occurred principally in the warm room. Reversed-phase HPLC revealed a more extensive peptide hydrolysis for ITGLH1, which was confirmed by the greater release of free NH2 groups (+33%) and free amino acids (+75%) compared with ITGLH77. As the intracellular peptidase activities of ITGLH1 and ITGLH77 have previously been shown to be similar, our results indicated that the extent of lysis of Lb. helveticus could have a direct impact on the degree of proteolysis in Swiss cheeses.

Volatile concentrates were obtained by vacuum distillation from both natural and creamy Gorgonzola cheese and isolated by continuous liquid–liquid extraction. Both were analysed by high resolution gas chromatography (HRGC), HRGC–mass spectrometry and HRGC–olfactometry. A total of 63 components were identified in the neutral extract of the natural type (21 esters, 13 ketones, 14 alcohols, 5 aldehydes, 1 sulphur compound, 7 aromatic compounds and 2 terpenes) and 52 in the creamy type (17 esters, 12 ketones, 10 alcohols, 5 aldehydes, 1 sulphur compound, 5 aromatic compounds and 2 terpenes). Ketones, whose major components were 2-nonanone and 2-heptanone, were the predominant constituents of the neutral fraction. By olfactometric analysis of the neutral extracts, 23 odour-impact compounds were found in the natural and 21 in the creamy Gorgonzola cheese. 1-Octen-3-ol, ethyl hexanoate, 2-nonanone, 2-heptanone, 2-heptanol, ethyl butanoate, 2-nonanol and 4-methylanisole were the key odorants of the natural cheese, whereas 2-heptanone, 2-heptanol, ethyl butanoate, 3-methyl thiopropanal and an unidentified constituent with a fruity odour were characteristic of the creamy Gorgonzola cheese. On the basis of high odour unity values, 2-nonanone, 1-octen-3-ol, 2-heptanol, ethyl hexanoate, methylanisole and 2-heptanone were the most important odorants of natural and creamy Gorgonzola cheese aroma.

Two common genetic variants of β-lactoglobulin (β-lg), A and B, exist as co- dominant alleles in dairy cattle (Aschaffenburg, 1968). Numerous studies have shown that cows homozygous for β-lg A have more β-lg and less α-lactalbumin (α-la) and casein in their milk than cows expressing only the B variant of β-lg (Ng-Kwai-Hang et al. 1987; Graml et al. 1989; Hill, 1993; Hill et al. 1995, 1997). These differences have a significant impact on the processing characteristics of the milk. For instance, the moisture-adjusted yield of Cheddar cheese is up to 10% higher using milk from cows of the β-lg BB phenotype compared with milk from cows expressing only the A variant (Hill et al. 1997). All these studies, however, describe compositional differences associated with β-lg phenotype in established lactation only. No information is available on the first few weeks of lactation, when there are marked changes in the concentrations of β-lg and α-la (Pérez et al. 1990).

Caseins constitute the main part of milk proteins. The genes for the four major types of casein (CN), αs1-CN, αs2-CN, β-CN and κ-CN, reside on < 220 kb of the DNA on bovine chromosome 6 (Threadgill & Womack, 1990). Two casein genes (Cn), β-Cn and κ-Cn, have been found to be associated with differences in milk production, cheese yield, protein content, quality and fat yield (Ng-Kwai-Hang et al. 1984). Lin et al. (1986) have estimated that the combined contributions of αs1-Cn, β-Cn, κ-Cn and β-lactoglobulin loci accounted for 8·9% of the total phenotypic variance in milk, 8·6% of that in proteins and 5% of that in fat yield. Six alleles of κ-Cn gene have so far been identified: κ-CnA, κ-CnB, κ-CnC, κ-CnE, κ-CnF and κ-CnG. The κ-CN protein is 169 amino acids long with varying regions at codons 136 and 148. The A variant has threonine (ACC) at codon 136 and aspartic acid (GAT) at codon 148, whereas the B variant has isoleucine (ATC) and alanine (GCT) at codons 136 and 148 respectively (Mercier et al. 1973). Milk containing κ-CN B was reported to yield more cheese than that with κ-CN A because it contains more casein and has lower fat loss. Several studies have shown that cows with the κ-CnBB genotype produced milk with a higher protein content than cows with κ-CnAA (Ng-Kwai-Hang et al. 1984; Ron et al. 1994).

During the manufacture of Swiss-type cheese varieties, such as Emmental, Gruyère and Comté, a high scald temperature is used, which inactivates the added coagulant, decreasing the primary proteolysis of αs1-casein during ripening and resulting in the development of the rubbery texture characteristic of this type of cheese (Kosikowski & Mistry, 1997). Swiss-type cheese may be made from raw, thermized or pasteurized milk, depending on the type of manufacture and the country (Beuvier et al. 1997).

The suitability of milk for cheesemaking is often assessed from the somatic cell count (SCC) of the raw milk, with increased milk SCC being linked to impaired cheesemaking properties and cheese yield potential (Barbano et al. 1991; Auldist et al. 1996). Late lactation milk, which often has elevated SCC, also yields poor quality cheese (Lucey, 1996). High SCC milk has elevated levels of the milk alkaline proteinase plasmin (EC 3.4.21.7), but its activity is not generally considered to be detrimental during cheese ripening (Farkye & Fox, 1992; Bastian & Brown, 1996). Milk somatic cells are themselves also associated with a number of proteolytic enzymes of differing properties, the activities of which are ill-defined in dairy products (Verdi & Barbano, 1991), with the exception of the acid proteinase cathepsin D, which has a chymosin-like activity towards αs1-casein (McSweeney et al. 1995). Preliminary evidence of cathepsin D activity in Swiss cheese during ripening has been reported (Igoshi & Arima, 1993; Beuvier et al. 1997).

In the present study the effect of milk SCC on the ripening of Swiss-type cheese was examined. Of particular interest was the role of polymorphonuclear leucocytes (PMN), the predominant cell type in high SCC mastitic milk (Heegaard et al. 1994) and late lactation milk, when the frequency of milking varies (Kelly et al. 1998). PMN possess a range of proteolytic enzymes, including cathepsin D (Verdi & Barbano, 1991) and plasminogen activators (PA; Heegaard et al. 1994). The experimental strategy chosen was to examine the effects on the quality and proteolysis during ripening of Swiss-type cheeses of adding high SCC milk, whose cell population is mostly PMN, to creamery milk.