Strains of Lactobacillus bulgaricus and Streptococcus thermophilus isolated from yoghurt culture were used to study the cause of the synergistic effect on acid production by mixtures of the 2 cultures. The beneficial effect was essentially limited to the gradual accumulation of factors in the L. bulgaricus cultures that promoted more rapid acid production by Str. thermophilus. The active factors were identified as glycine and histidine.

Mastitis is one of the most costly diseases to the dairy farming industry. Conventional antibiotic therapy is often unsatisfactory for successful treatment of mastitis and alternative treatments are continually under investigation. We have previously demonstrated, in two separate field trials, that a probiotic culture, Lactococcus lactis DPC 3147, was comparable to antibiotic therapy to treat bovine mastitis. To understand the mode of action of this therapeutic, we looked at the detailed immune response of the host to delivery of this live strain directly into the mammary gland of six healthy dairy cows. All animals elicited signs of udder inflammation 7 h post infusion. At this time, clots were visible in the milk of all animals in the investigation. The most pronounced increase in immune gene expression was observed in Interleukin (IL)-1β and IL-8, with highest expression corresponding to peaks in somatic cell count. Infusion with a live culture of a Lc. lactis leads to a rapid and considerable innate immune response.

Treatment of unfractionated bovine casein with papain produced a digest which was bitter in taste. The bitterness was shown to be a property of a peptide originating only in β-casein and having an amino-acid composition consistent with its derivation from residues 53–79 inclusive of β-casein. The relationship existing between flavour and primary structure in this peptide is discussed briefly.

The synbiotic effect of the oral treatment of Swiss albino mice with milk-based diets supplemented with Lactobacillus helveticus M92 and various kinds of prebiotics was investigated. Survival, competition, adhesion and colonization, as well as, immunomodulating capability of Lb. helveticus M92, in synbiotic combination, in the gastrointestinal tract (GIT) of mice, were monitored. After the mice were fed with synbiotics, the lactic acid bacteria (LAB) counts in faeces were increased and reduction of enterobacteria and sulphite-reducing clostridia was observed. Similar results were obtained in homogenates of small and large intestine of mice on the 1st and 14th day, after feeding with synbiotics. After the mice were orally given viable Lb. helveticus M92 cells, alone or in combination with prebiotic, the concentration of faecal SIgA and total serum IgA antibodies from all immunized mice were higher compared with the control. The specific humoral immune response was not evoked after oral administration, therefore their synbiotic application is suitable. Among inulin, lactulose and raffinose, Lb. helveticus M92 in combination with inulin, has shown the best synbiotic effect on intestinal and faecal microflora and immune system of mice.

Agriculture and animal husbandry are important contributors to global emissions of greenhouse (GHG) and acidifying gases. Moreover, they contribute to water pollution and to consumption of non-renewable natural resources such as land and energy. The Life Cycle Assessment (LCA) methodology allows evaluation of the environmental impact of a process from the production of inputs to the final product and to assess simultaneously several environmental impact categories among which GHG emissions, acidification, eutrophication, land use and energy use. The main purpose of this study was to evaluate, using the LCA methodology, the environmental impact of milk production in a sample of 41 intensive Italian dairy farms and to identify, among different farming strategies, those associated with the best environmental performances. The functional unit was 1 kg Fat and Protein Corrected Milk (FPCM). Farms showed characteristics of high production intensity: FPCM, expressed as tonnes per hectare, was 30·8±15·1. Total GHG emission per kg FPCM at farm gate was 1·30±0·19 kg CO2 eq. The main contributors to climate change potential were emissions from barns and manure storage (50·1%) and emissions for production and transportation of purchased feeds (21·2%). Average emission of gases causing acidification to produce 1 kg FPCM was 19·7±3·6 g of SO2 eq. Eutrophication potential was 9·01±1·78 ${\rm PO}_{\rm 4}^{{\rm 3} -} {\rm eq}.$ per kg FPCM on average. Farms from this study needed on average 5·97±1·32 MJ per kg FPCM from non-renewable energy sources. Energy consumption was mainly due to off-farm activities (58%) associated with purchased factors. Land use was 1·51±0·25 m2 per kg FPCM. The farming strategy based on high conversion efficiency at animal level was identified as the most effective to mitigate the environmental impact per kg milk at farm gate, especially in terms of GHG production and non-renewable energy use per kg FPCM.

Three microbial rennets, Noury rennet (Mucor pusillus, Lindt), Rennilase (M. miehei) and Suparen (Endothia parasitica), were assessed as calf rennet substitutes for Feta cheesemaking, in comparison with calf rennet. Cheeses prepared were all of good quality with similar organoleptic properties. Yield (referred to 55% moisture), moisture content, NaCl and protein content did not differ significantly. Different rates of proteolysis were observed in the cheeses, the highest of which was exhibited by calf rennet followed by Rennilase, Noury rennet and Suparen preparations. These calf rennet substitutes are well suited for Feta cheese manufacture.

The teats of 18 cows were externally exposed to infection with mastitis organisms by dipping them daily for 1 or 2 weeks in a mixed suspension of Streptococcus dysgalactiae and Str. uberis at the start, the middle or the end of the dry period. The teat sinuses of quarters which remained uninfected after external exposure at the beginning or the middle of the dry period were then infused with the same strains of streptococci. Of the 9 quarters infected following external exposure 8 occurred in animals exposed at the start and one in the middle of the dry period. Thirty-six new infections occurred after infusion of bacteria into the teat sinuses of 38 quarters. In a further trial with 10 cows, Staphylococcus aureus and Str. zooepidemicus were inoculated into the distal 3 mm of the streak canals of 5 cows immediately after drying-off and into those of 5 cows which had been dry for 28 weeks. Animals were slaughtered 48 h later and infection determined by teat puncture. Five infections occurred in cows which were at the start of the dry period and only one in the cows dry for 28 weeks. It is suggested that these differences in the rates of new infection between the early dry period and a very extended dry period are due to differences in the ease with which bacteria can penetrate the teat canal. At the later stage bacterial growth through the teat canal appeared to be inhibited.

Optimising the number of replacement heifers needed will have positive economic and environmental consequences on herds that rear their own young stock. The number of heifers needed to be kept is closely related with the number of culled dairy cows in the herd. This study therefore looked at the variation that exists in culling rate and herd level factors associated with it. A dataset from 1903 dairy herds available included information at animal level (dates of culling, slaughter/death) and herd level (characteristics of reproduction, performance, health) over the years 2007 to 2010. The average culling rate for slaughter/death was used and was defined for each year as percentage of the herd size that died within 30 d after they were culled. The analysis of the association between average culling rate for slaughter/death and the characteristics of the herd was performed using a mixed model. The results showed that the average culling rate for slaughter/death was 25·4% and varied between 23% (2007) and 28% (2010). More than 70% of the herds have an average culling rate for slaughter/death of less than 30%, showing that there is room for lowering the average culling rate for slaughter/death. A higher average culling rate for slaughter/death is associated with a longer average calving interval, a higher average 305-d protein production, a higher average somatic cell count (SCC), a higher percentage of new high SCC, a more than 5% decrease in herd size, and herds that bought more than 1% of animals per year. A lower average culling rate for slaughter/death is associated with a longer average age, herds that bought less than 1% of animals per year and a more than 5% increase in herd size. In conclusion, the average culling rate for slaughter/death is associated with fertility, udder health and openness of the herd.

Twenty-two Murciano-Granadina dairy goats were used to investigate the effects of organic Zn supplementation of a diet containing a high level of inorganic Zn. Goats were kept in pens, machine milked once a day throughout lactation and fed a diet based on a dehydrated mixture of whole-plant maize and alfalfa ad libitum, alfalfa pellets, barley grain and a concentrate mixture. Treatments were: (1) control, and (2) supplemented with 1 g/d Zn-Methionine (Zn-Met) included in the concentrate mixture. After parturition, goats were blocked in week 3 and dietary treatments were applied until week 23. From weeks 3–20, feed intake, milk yield, milk composition, milk somatic cell count (SCC), and udder health were measured. In week 21, all goats were injected intraperitoneally with 1 g/d DL-methionine for 5 d to establish the effects of methionine under the conditions of udder stress induced by hand milking on the second day. During weeks 22 and 23, diet digestibility, and N and Zn balance were determined. Dry matter intake, milk yield, and milk contents of total solids, fat, total and true protein, and casein did not differ between treatments, but whey protein and non-protein nitrogen contents were significantly lower for the Zn-Met group. Milk SCC tended to decrease as a result of Zn-Met supplementation but differences between treatments were not significant when halves with persistent infection were excluded. Hand milking increased SCC in both groups, but udders of supplemented goats showed a lower reaction. Apparent absorption of N significantly increased and Zn retention tended to increase in Zn-Met supplemented goats. We conclude that Zn-Met supplementation can enhance resistance to udder stress in dairy goats. Effects were attributed to the organic Zn and not to the methionine component. Zn retention and protein utilization were also improved by the Zn-Met supplement.

The effect of subclinical mastitis on levels of plasminogen and plasmin in milk from cows in a high-yielding herd was investigated. Comparisons were made with levels of milk Na, antitrypsin and N-acetyl-β-D-glucosaminidase (NAGase). In samples from mastitic quarters plasminogen activity, as measured after activation to plasmin, increased by only 21% and plasmin by 82%, while NAGase increased by 307 %. Plasminogen was the only component that was normally distributed, all other components showed more or less skewed distributions. Plasmin and plasminogen were significantly related to the other components. However, plasminogen plateaued when the other components continued to increase. There was thus no further increase in plasminogen with the severity of inflammation as with the other components. Plasmin showed a similar although less pronounced tendency. Results of treatment of mastitic whey samples with acid suggested that the non-linear increase in plasmin activity was due to interaction with acid-labile proteinase inhibitors. Mastitis led to dissociation of plasminogen and plasmin from the casein micelles. The degree of activation of plasminogen was higher with casein-associated than with soluble plasminogen in both healthy and mastitic milks. Plasmin was very closely related to milk Na, which is a sensitive indicator of epithelial integrity. It is suggested that plasmin contributes to Na leakage into milk by degrading membrane proteins of the epithelial lining. Plasminogen and antitrypsin, which are both plasma proteins, were not identically affected by stage of lactation, indicating nonidentical modes of transport from plasma to milk.

Fractions enriched with α-lactalbumin (α-la) and β-lactoglobulin (β-lg) were produced by a process comprising the following successive steps: clarification–defatting of whey protein concentrate, precipitation of α-lactalbumin, separation of soluble β-lactoglobulin, washing the precipitate, solubilization of the precipitate, concentration and purification of α-la. The present study evaluated the performance of the process, firstly on a laboratory scale with acid whey and then on a pilot scale with Gouda cheese whey. In both cases soluble β-lg was separated from the precipitate using diafiltration or microfiltration and the purities of α-la and β-lg were in the range 52–83 and 85–94% respectively. The purity of the β-lg fraction was higher using acid whey, which does not contain caseinomacropeptide, than using sweet whey. With the pilot scale plant, the recoveries (6% for α-la; 51% for β-lg) were disappointing, but ways of improving each step in the process are discussed.

Sixty female dairy calves (body weight, BW, 43·2±0·58 kg and age 9·8±0·61 d) were arranged in two groups to compare the short-term and long-term effects of an enhanced-growth feeding programme (EF) with those of a conventional-growth feeding programme (CF). After 1 week of adaptation to a milk replacer (MR), CF calves were fed 4 l/d of MR (25% crude protein, CP; 19·2% ether extract) at 12% dry matter (DM) from days 1 to 27 and 2 l/d at 12% DM from days 28 to 34, and the EF calves were offered the same MR at 18% DM: 4 l/d from days 1 to 6, 6 l/d from days 7 to 13, 7 l/d from days 14 to 20, 6 l/d from days 21 to 27 and 3 l/d from day 28 to weaning at day 34 of the study (50 d of age). Individual calf starter (20·7% CP) intake was recorded daily from the beginning until day 41 of study (57 d of age). Then, calves were placed in groups of six and they received a total mixed ration (TMR) containing 18·5% CP until day 56 d of study (72 d of age). Then, heifers were moved to larger pens and were fed the same TMR in both treatments at each subsequent stage of growth throughout the study. Calves were weighed weekly until day 56 of study and before every pen change (days 94, 149, 200, 387 of study). When heifers were 400 d old and weighed >380 kg, they were moved to a breeding pen where oestruses were checked three times a day. Heifers were inseminated 12 h after the detection of oestrus. One month before calving, heifers were returned to their original farm and milk yield at 305 days in milk was recorded from 28 cows. Starter intake was greater (P<0·001) in CF than in EF calves (0·79 v. 0·29±0·043 kg/d, respectively) during the preweaning period, but TMR consumption was similar in both treatments from days 42 to 56 of study. BW of EF calves was greater (P<0·01) than that of CF calves at weaning (76·4 v. 71·6±1·10 kg, respectively), but BW was not different at day 387 of study (405 d of age) (406·3 v. 401·3±4·05 kg, respectively). There were numerical differences in age at first breeding, fertility at first artificial insemination, age at pregnancy, and milk yield but some of these differences might have reached statistical significance with more replication.

Four enzymes of citrate metabolism (viz. citrate lyase, acetolactate synthase, diacetyl reductase and acetoin reductase) were constitutively present in cells of several strains of Streptococcus lactis subsp. diacetylactis. In strain DRC1, which was studied in detail, diacetyl reductase and acetoin reductase were partly repressed and acetolactate synthase partly induced by growth on citrate. The stage of growth also affected the formation of each enzyme. The buffer species affected the activity of acetolactate synthase, diacetyl reductase and acetoin reductase.

A simple, rapid and sensitive spectrophotometric assay was developed and evaluated for monitoring proteolysis during cheese ripening, based on the fact that α-amino groups released by hydrolysis of cheese proteins react with trinitrobenzenesulphonic acid to form products that absorb strongly at 420 nm. A linear relationship was shown to exist between A420 and concentration of free α amino groups up to 0·5 HIM (r = 0·999, 38 df, P < 0·001). Repeatability of the method was satisfactory. The coefficient of variance was 0·53% for amino acid solutions and 1·19% for cheese extracts. Average recovery of glycine added to the cheese was 104 ± 2·9%. A comparison of the above method with that of determination of water-soluble N to total N ratio showed that there was good agreement between these two methods of assessment of proteolysis in cheese (r = 0·857, 32 df, P < 0·001). Mainly Feta and Teleme cheese were examined, but a similar correlation was obtained with hard Greek cheeses. Analytical conditions of the procedure are discussed.

Data are presented which show that the use of glucono-δ-lactone as a chemical acidulant in cheese manufacture results in a much more rapid decrease in pH than that occurring in biologically acidified cheese. One of the consequences of the excessive early acid development was a very marked increase in the level of proteolysis during cheese-manufacturing operations. Consequently, chemically acidified cheese, as manufactured by the technique of Mabbitt, Chapman & Berridge (1955) (expt 17), does not appear to be a suitable ‘reference cheese’, especially for studies in which proteolysis during ripening is under investigation. The technique of Mabbitt et al. Avas modified to simulate the pH development pattern of starter cheese more closely; the level of proteolysis in curd made by the modified method was approximately equal to that in starter curd.

An attempt was made to link the propensity to develop bitterness of cheese made with fast acid-producing cultures with excessive early proteolysis in such cheese. The results show that fast- and slow-culture strains differed significantly in their acid-producing capability only after the cooking stage and consequently such cheeses differed little with respect to early proteolysis. Further, cheeses made with 0·5, 1·0, 2·0 or 4·0% of ML8 culture which differed considerably in rate of acid development and consequently in the level of early proteolysis did not develop bitterness, even when 4·0% starter was used.

It is concluded that gross proteolysis and bitterness are not correlated.

The effects of stage of lactation and of age on milk and composition yield of cows kept under controlled conditions of feeding and management were investigated. Two groups each of 3 Friesian heifers were used: one group (A) was given a daily diet of 18 lb hay and concentrates at the rate of 3·8 lb/10 lb of milk and kept on experiment throughout the first 3 lactations; a second group (B) was given the same amount of hay and a constant daily amount of concentrates of 10·7 lb and was kept on experiment throughout the 1st lactation only.

The total yields of milk and peak yields for the 1st lactation were similar in both groups. In all the cows, fat content was high early and late in lactation and varied little throughout the mid-lactation period. With cows of group A, the content of solids-not-fat declined until about the 5th week of lactation and then remained steady until a marked rise occurred late in lactation. With cows of group B, however, the content of solids-not-fat was at a minimum between the 5th and 10th weeks of lactation and then increased progressively until late lactation when a more marked rise occurred. Lactose content increased rapidly in the first few days of lactation and then remained constant for several months, eventually declining late in lactation. Characteristic changes were also observed in the contents of total protein, and of the various protein fractions, and of the major minerals of milk.

The concentrations of all major constituents in milk secreted from the 2nd–5th months of lactation tended to decrease from lactation to lactation.

The results are discussed in relation to the development of knowledge of the changes in milk composition throughout lactation.

In a national survey of US dairy operations, 1685 dairy operations reported 47057 new dairy heifers (either births or acquisitions) and 4427 deaths (9·4%) of preweaned dairy heifer calves over a 3 month period. Stepwise logistic regression was used to identify management practices associated with high mortality among preweaned heifers in dairy operations where at least three dairy heifer calves were born alive or moved on to the operation. Analysis was done twice: once by separating all operations by size into high or low mortality; again using only operations with <2 and >10% mortality to eliminate dairy operations with intermediate levels of mortality from the comparisons. Results were similar. Dairy operations in the West were more likely to fall in the high mortality category than dairy operations in the rest of the country. In addition, the following dairy operation characteristics were associated with high death levels in both models: rolling herd average milk production <7710 kg, preweaned heifers placed in groups of seven or more, a male having primary responsibility for the care and feeding of preweaned heifers, calves not receiving hay or other roughages until >20 d old, calves fed on mastitic or antibiotic milk after colostrum and calves not given whole milk after colostrum.

The specificity of chymosin on αs1-casein was shown to be dependent on the reaction pH and on the state of aggregation of the substrate. In aqueous solution αs1-casein was optimally hydrolysed to αs1-I at pH 5·8; if the casein was solubilized in the isoelectric region by the use of 5 M-urea, optimum proteolysis occurred at pH 2·8. Hydrolysis of αs1-I to yield αs1-II, αs1-III and αs1-IV occurred at pH values > 5·8 in the presence or absence of urea. In the isoelectric region αs1-II, αs1-III and αs1-IV were not formed in the absence of urea where the substrate was aggregated: instead a peptide αs1-V was produced; at the same pH and using urea as a solubilizing agent αs1-II, αs1-III and αs1-IV were formed together with a further peptide αs1-VI.

The interaction of κ-casein and β-lactoglobulin is fundamental to all heat-induced modifications of milk product functionality, such as the heat stability of concentrated milks. Purified native κ-casein B and β-lg A solutions were heated at 80 °C at pH 6·7 separately and in a mixture. The circular dichroism spectra in the near UV indicated irreversible changes in the disulphide bonding patterns involving both proteins. Alkaline- and SDS-PAGE of heated samples showed that, in the presence of κ-casein, less β-lg was converted into β-lg polymers and the rate of loss of native β-lg was greater. When κ-casein was added to previously heated β-lg and the mixture was heated, the κ-casein reacted with the heat-induced β-lg polymers more readily than with the β-lg native monomers. The formation of β-lg dimers, trimers etc. was diminished. It was concluded that, when β-lg and κ-casein were heated together, β-lg formed thiol-exposed monomers, which reacted with each other or with the native κ-casein depending on the relative concentrations of β-lg and κ-casein. The products of these reactions included some disulphide-bonded 1[ratio ]1 β-lg[ratio ]κ-casein complexes, some monomer κ-casein and a range of large aggregates held together by either or both disulphide bonds and hydrophobic association.

Hydrophobic and hydrophilic peptides in the water-soluble fraction of 20 batches of Hispanico cheese made from pasteurized and raw milk were determined by reversed-phase HPLC, with detection at 214 and 280 nm. Cheese flavour characteristics were evaluated by a sensory panel, and regressions of bitterness scores on levels of hydrophobic and hydrophilic peptides and their ratio were calculated. The best fitting relationship for pasteurized milk cheese was the linear regression of mean panel bitterness scores on hydrophobic peptides at 280 nm (r2=0·791). The determination coefficient for the regression of hydrophobic peptides at 280 nm on panellist bitterness scores (r2=0·356) was lower, owing to individual differences in the perceived intensity of bitterness. In the case of raw milk cheese, the respective determination coefficients were 0·203 for panel scores and 0·034 for individual panellist scores.