Hispánico cheese, a semi-hard Spanish variety, was manufactured from a mixture of pasteurized cows' and ewes' milks (4[ratio ]1) using a commercial mesophilic LD-type starter comprising Lactococcus lactis subsp. cremoris, Lc. lactis subsp. lactis, Lc. lactis subsp. lactis var diacetylactis and Leuconostoc mesenteroides subsp. cremoris. Varying amounts (0–1·0 g/kg) of an Enterococcus faecalis INIA 4 culture in milk were added as a bacteriocin-producing adjunct. Differences in pH between cheeses manufactured with and without the bacteriocin producer did not exceed 0·11 pH units. Starter lactococci lost viability more rapidly in cheeses made with the bacteriocin producer, which reached counts of up to 6×107 cfu/g during ripening. Aminopeptidase activity in 1-d-old cheese made from milk inoculated with 1·0 g bacteriocin-producing culture/kg was twice that in control cheese. Degrees of overall proteolysis and levels of total free amino acids in 45-d-old cheese made with 1·0 g bacteriocin-producing culture/kg were 1·80-fold and 2·17-fold those in control cheese of the same age. Inoculating milk with 1·0 g/kg bacteriocin-producing culture reduced the level of hydrophobic peptides in the resultant cheese, increased the concentrations of 3-methyl-1-butanal, diacetyl and acetoin, and resulted in the highest scores for flavour quality and flavour intensity throughout ripening.

Whey protein hydrolysates were generated at different total solids (TS) levels (50–300 g/l) using the commercially available proteolytic preparation Debitrase™ HYW20, while enzyme to substrate ratio, pH and temperature were maintained constant. Hydrolysis proceeded at a faster rate at lower TS reaching a degree of hydrolysis (DH) of 16·6% at 300 g TS/l, compared with a DH of 22·7% at 50 g TS/l after 6 h hydrolysis. The slower breakdown of intact whey proteins at high TS was quantified by gel-permeation HPLC. Reversed-phase (RP) HPLC of hydrolysate samples of equivalent DH (~15%) generated at different TS levels indicated that certain hydrophobic peptide peaks were present at higher levels in hydrolysates generated at low TS. Sensory evaluation showed that hydrolysates with equivalent DH values were significantly (P<0·0005) less bitter when generated at 300 g TS/l (mean bitterness score=25·4%) than hydrolysates generated at 50 g TS/l (mean bitterness score=39·9%). A specific hydrophobic peptide peak present at higher concentrations in hydrolysates generated at low TS was isolated and identified as β-lactoglobulin f(43–57), a fragment having the physical and chemical characteristics of a bitter peptide.

Two methods were compared for the determination of free fatty acids (FFA) from acetic to long-chain acids in samples with a large excess of triacylglycerols (TG) (1[ratio ]200, w/w), such as cheese and other dairy products. In method 1, after fat extraction, FFA were separated from TG by aminopropyl-bonded phase chromatography, injecting the fraction containing FFA directly into the gas chromatograph. In method 2, extracted fat was treated with tetramethylammonium hydroxide, the methyl ester derivatives being formed in the injector. Cheese samples and standard mixtures of FFA and TG in different proportions were analysed by both methods. The cheese sample contained 2·4 times more FFA when analysed by method 2 as compared with the result obtained with method 1. The composition of the standard mixtures analysed by method 1 closely reflected that of the original mixture and gave 90–100% recovery of FFA, regardless of their chain length and the ratio of FFA[ratio ]TG (1[ratio ]1 or 1[ratio ]200, w/w). The composition of samples with a FFA[ratio ]TG ratio of 1[ratio ]200 (w/v) was severely distorted (as compared with the original composition of the sample) when analysed by method 2. Varying recoveries of FFA were also obtained, the largest differences being found for the shorter-chain components. We conclude that the FFA fraction should be separated from the TG fraction before derivatization and chromatographic analysis, particularly for samples in which the FFA represent a minor fraction of the TG.

Additions of urea progressively increased the heat stability of milk outside of its coagulation time (CT)–pH minimum. In the region of the CT–pH minimum larger amounts of urea were required before an increase in heat stability occurred. The effect of urea was observed over the temperature range 125–140 °Cfornaturalmilk, milk which had been dialysed against synthetic sera, and milk to which a sulphydrylblocking agent had been added. Urea additions did not affect the activation energy of the heat coagulation reaction or the stability of milk to rennet or ethanol.

The effects of 3 different thickening agents on the microstructure of yoghurt were examined by scanning and transmission electron microscopy. Unsupplemented yoghurt consisted of casein micelles fused together and linked in long chains; they seldom appeared in clusters. The addition of 0·5% gelatin caused no observable change in the yoghurt structure. Carrageenan (0·4%) formed a markedly fibrillar microstructure which connected large clusters of casein micelles. The fibres were thin and long and no free terminations were observed. Pregelatinized waxy maize starch (2%) appeared under scanning electron microscopy in the form of short fibres and sheets. The fibres frequently had free terminations and only some of them were connected with small clusters of casein micelles. Transmission-electron microscopy did not distinguish between pregelatinized starch and carrageenan additives.

Eight lactating cows were used in a Latin square experiment, to study the associative effects of level of energy and protein intake on milk yield and composition. Four diets were used, supplying 80 and 120% of estimated energy requirements and 80 and 120% of estimated protein requirements. The level of energy intake significantly affected milk yield, milk energy output, percentage butterfat, ash and non-protein nitrogen. The level of protein intake only significantly affected milk energy output and the non-protein nitrogen content of the milk. Although only the interaction of the effects of energy and protein intake on the milk content of solidsnot-fat (SNF) and ash was significant, it was evident that the effect of each of these factors on milk yield or composition was related to the level of the other in the diet.

Input-output relationships within each protein level were used to compute the response in milk energy output and bodyweight change to a change in energy intake. These showed a greater partitioning of additional energy toward milk energy output with the high than with the low protein level. Multiple regression analysis within each level of protein intake was used to partition energy intake between that used for maintenance, milk energy output and liveweight change. The results showed efficiencies of utilization of metabolizable energy for milk output of 63 and 50% on the high- and low-protein diets, respectively.

Nitrogen balance data are presented.

Sediment formation was investigated during UHT treatment of goats' milk, subjected to indirect treatment at 140°C for 2 s, with upstream homogenisation. Stabilisers evaluated were sodium hexametaphosphate (SHMP), trisodium citrate (TSC), disodium hydrogen orthophosphate (DSHP), and sodium dihydrogen orthophosphate (SDHP). With no added stabiliser, goats' milk produced a heavy sediment on UHT treatment. Addition of SDHP reduced pH, had little effect on ionic calcium and did not substantially reduce sediment. However, addition of SHMP, DSHP and TSC each reduced ionic calcium, increased ethanol stability and reduced sediment. Following stabiliser additions, there was a good correlation between ethanol stability and ionic calcium (R2=0·85) but not between ethanol stability and pH (R2=0·08). Overall, reducing ionic calcium reduced the amount of sediment formed for all these three stabilisers, although there was no single trend line between sediment formation and ionic calcium concentration. Sediment formation was not well correlated with pH for TSC or for SHMP, but it was for DSHP, making it the only stabiliser where sediment formation correlated well both with ionic calcium and pH, which might account for its effectiveness at higher ionic calcium levels. Sediment was much reduced when the temperature was reduced from 140°C to 125°C and 114°C. There were no further changes in sediment on storage for two weeks. Analysis of the sediment showed that it was predominantly fat and protein, with a mass ratio ranging between 1·43:1 and 1·67:1. Its mineral content was usually less than 5% of dry weight. The maximum amounts of P and Ca were found to be 2·32% and 1·63%, respectively.

The effects of feeding lactating cows a daily supplement of 1 kg formaldehyde-treated casein–safflower oil (1:1, w/w) on the milk composition are reported. Three breeds, Jersey, Sahiwal and Sahiwal × Jersey crossbred were used.

The formaldehyde treatment not only eliminated the suppressing effect on the milk, fat and protein yields and on the fat and protein contents usually encountered when such a level of unsaturated oil is fed to lactating cows, but also resulted, on the average, in 15 and 6% increases in the fat and protein contents respectively.

The formaldehyde-treated dietary supplement also caused a decline of 5% in the solids-not-fat content, presumably due to a decrease in the lactose content.

It is suggested that the formaldehyde treatment protects the casein from the ruminal proteolysis and this in turn prevents the encapsulated unsaturated oil from biohydrogenation and eliminates the diverse effects on rumen microflora and environment.

Proteolysis was measured quantitatively in normal bulk milk, either raw, pasteurized or heated (95 °C, 15 min). During incubation at 37 °C for 24 h, about 0·7 mM of peptide bonds were split in raw milk, and 1·8 mM after activation of the zymogen with urokinase. The same values were observed in pasteurized milk, and no significant activity was present in heated milk. When compared with a commercial plasmin preparation, these levels correspond to about 1·4 and 3·6μg/ml of plasmin respectively. Most of this activity was separated in the micellar fraction, and it was suppressed by addition of soyabean trypsin inhibitor (SBTI). The remaining activity in the serum phase was not inhibited by SBTI and gave a rather non-specific breakdown with few well-defined casein fragments being produced. Upon further incubation, after the first 24 h, the activity increased, indicating that activation of the zymogen (plasminogen) occurred spontaneously. The rate of this activation was independent of the addition of more plasminogen and was higher in pasteurized than in raw milk. In pasteurized milk, all the native milk proteinase was in the form of the zymogen at the time of secretion. β-Casein was the preferred substrate for the milk proteinase (plasmin) and produced γ-caseins and proteose-peptone components 5 and 8-fast; other fragments were clearly visible on polyacrylamide gel electrophoresis, and included degradation products of αs1-casein. The formation of all these fragments was enhanced by addition of urokinase alone, or of plasminogen and urokinase, or by increasing the incubation time. They were also produced by incubating the micellar fraction alone, but not the serum fraction. Additional fragments were produced when porcine plasmin was added presumably due to differences in specificity between the porcine and bovine enzymes or to contaminating enzymes. Proteolysis induced by additions of plasminogen alone, or of plasminogen plus urokinase, was closer to that observed for the native milk proteinase, and must be recommended for future work in which it is desired to enhance the level of proteinase without altering breakdown patterns, unless a very pure bovine plasmin is available.

A number of endemic diseases of dairy cattle cause significant losses to the dairy industry in the mainland UK (England, Scotland and Wales), both in terms of the reductions in output levels or wastage of resources incurred and the resource costs of disease prevention and treatment (Esslemont & Spincer, 1993; Esslemont & Kossaibati, 1996). Various studies have estimated the costs associated with different diseases (Bennett, 1992). However, these studies use different methods of assessment, relate to different populations at risk, refer to different points in time and utilize different ways of measuring disease and valuations of the effects of disease on production. Thus, it is difficult to use these studies for any comparative assessment of the magnitude of output losses and resource wastage incurred as a result of different diseases. Such information is useful in exploring both the economic consequences of diseases and the potential benefits of research on improved disease control (Howe, 1991; McInerney, 1996).

This paper presents analyses of the impacts on production of five endemic diseases and conditions of dairy cattle in mainland UK: bovine viral diarrhoea (BVD), fasciolosis, lameness, leptospirosis and mastitis (including summer mastitis). These analyses follow from a preliminary economic study of the impacts on livestock production of some 30 non-notifiable diseases and conditions of farm animals (Bennett et al. 1997). The study was funded by the Ministry of Agriculture, Fisheries and Food in the UK, with the (eventual) aim of providing information to policy makers that might help them to reach decisions on allocating funds to research into livestock diseases. Full details of the analyses are available from the website address given at the end of this paper.

Two, 8-week experiments, each using 30 lactating Holstein cows, were conducted to examine performance of animals offered combinations of total mixed ration (TMR) and high-quality pasture. Experiment 1 was initiated in mid October 2004 and Experiment 2 was initiated in late March 2005. Cows were assigned to either a 100% TMR diet (100:00, no access to pasture) or one of the following three formulated partial mixed rations (PMR) targeted at (1) 85% TMR and 15% pasture, (2) 70% TMR and 30% pasture and (3) 55% TMR and 45% pasture. Based on actual TMR and pasture intake, the dietary TMR and pasture proportions of the three PMR in Experiment 1 were 79% TMR and 21% pasture (79:21), 68% TMR and 32% pasture (68:32), and 59% TMR and 41% pasture (59:41), respectively. Corresponding proportions in Experiment 2 were 89% TMR and 11% pasture (89:11), 79% TMR and 21% pasture (79:21) and 65% TMR and 35% pasture (65:35), respectively. Reducing the proportion of TMR in the diets increased pasture consumption of cows on all PMR, but reduced total dry matter intake compared with cows on 100:00. An increase in forage from pasture increased the concentration of conjugated linoleic acids and decreased the concentration of saturated fatty acids in milk. Although milk and milk protein yields from cows grazing spring pastures (Experiment 2) increased with increasing intakes of TMR, a partial mixed ration that was composed of 41% pasture grazed in the fall (Experiment 1) resulted in a similar overall lactation performance with increased feed efficiency compared to an all-TMR ration.

Alkylation of whole casein samples by reaction with cysteamine and cystamine in a bis-tris-propane–urea buffer (pH 7·0) followed by fast protein liquid chromatography (FPLC) at 20°C on a Mono Q HR5/5 column in the same buffer and using a NaCl gradient led to good resolution of the whole casein into fractions representing (i) γ2- plus γ3-caseins, (ii) κ-caseins, (iii) β-casein, (iv) αs2-caseins and (v) αsl-caseins, together with small amounts of unidentified materials. Quantitatively the FPLC values agreed well with those for αs1-, β-, αs2- and γ2- plus γ3-caseins obtained by ion-exchange chromatography on DEAE cellulose, Whatman DE52 and with those for º-caseins obtained by gel-permeation chromatography on Sephadex G–150.

The heat stability of the milk supply to manufacturing creameries in south-west Scotland was examined over 15 months from Nov. 1975 to Jan. 1977. For all but 2 months of this period the heat stability of the milk was very highly significantly correlated with the naturally occurring level of urea. Between 72 and 90% of the variation of coagulation time (CT), measured at the natural milk pH, was accounted for by changes in milk urea alone. For a short period, in May and June, the CT of the milk at natural pH fell within the minimum of the CT–pH profile, but insufficient data were available to allow the occurrence of this phenomenon to be related to changes in milk composition.

Six lactating, non-pregnant Jersey cows were given subcutaneous injections of recombinantly derived bovine growth hormone for 7 d. Milk yield was increased by 4·5 kg/d on d 7, compared with the average yield of 10·7 ± 0·4 kg/d (mean ± s. e. m.) for the 7d preceding treatment. Concentrations of insulin-like growth factor I (IGF-I) in the milk increased from 0·44 ± 0·04 nmol/1 (mean ± s. e. m.) during the 7 d preceding treatment to 1·6 ± 0·2 nmol/1 on d 7 of treatment. Taking the increase in milk yield into account the total increase in the secretion of IGF-I into milk of one udder half was 6-fold. Plasma concentrations of total IGF-I rose from 15·5 + 1·3 nmol/1 (mean ± s. e. m.) on the day preceding treatment to 56·9 ± 3·6 nmol/1 (mean ± s. e. m.) on d 7 of treatment. Mammary plasma flow increased from 1·6 ± 0·09 to 2·2 ± 0·06 1/min udder half over the same time. Estimates of the amount of IGF-I that reached the mammary gland gave values of 24 and 116 nmol/min udder half before and during treatment respectively. IGF-I in milk of treated cows was associated predominantly with proteins ranging from 40000 to 150000 mol. wt, but a significant proportion (19%) of the total IGF-I was present in the free unbound form. IGF-I crosslinking studies revealed the presence in milk of one specifically labelled band at 31000 mol. wt.

Naturally occurring monomeric κ-casein and αs2-casein in bovine milk were purified by ion-exchange chromatography in order to localize potential intrachain disulphide bridges. Enzymic cleavage of the proteins followed by mass spectrometry and amino acid sequence analysis of cystine-containing peptides revealed the presence of an intrachain disulphide bond in both proteins.

Dynamics of micro-structural changes in milk during the renneting process were analysed using high-resolution ultrasonic spectroscopy in combination with dynamic rheology and NIR transmission measurements. Two independent ultrasonic parameters, velocity and attenuation were measured in the frequency range 2 to 15 MHz, as a function of time after addition of rennet to milk. The results show an initial decrease of 20 nm for the average diameter of micelles caused by hydrolysis of the κ-casein ‘hairy’ layer followed by an aggregation of the micelles into small clusters (effective aggregation number of 3) and then formation of the gel structure. It was found that evolution of ultrasonic attenuation in the renneting process could well be described by the scattering of the ultrasonic waves on aggregates. The evolution of ultrasonic velocity is well described by the scattering theory but deviates from the predicted curve at the gelation stage of the process, which shows the difference in propagation of ultrasonic waves in a gel structure compared with dispersions. Overall, we found high-resolution ultrasonic spectroscopy to be a powerful tool for analysis of microscopic processes in the formation of milk gel. It allows the characterisation of the pre-gelation processes, such as hydrolysis and aggregation, and the initial stages in the formation of the gel network as well as monitoring of the microscopic evolution in the gel at the post-gelation stage.

The effects of sheep αs1-casein CC, CD and DD genotypes on milk composition and cheese yield were studied. Processed bulk milk was collected from three groups of 15 ewes, carrying αs1- casein CC, CD and DD genotypes. CC milk was higher in casein content than CD or DD milk (+3·5 and +8·6% respectively), and had a higher protein[ratio ]fat ratio and a smaller casein micelle diameter. In addition, DD milk had a significantly lower αs1-casein content. The main differences were in curd formation: CC milk had better renneting properties. Cheesemaking trials, carried out in a pilot plant, showed that CC milk had better cheesemaking characteristics than DD milk, while CD milk was intermediate. Both 1 d old and fully ripened cheeses had different fat[ratio ]dry matter ratios and αs1-I-casein electrophoretic mobilities: these were lower for DD cheese. As a consequence, these genotypes could be considered as markers of milk and/or cheese quality.

A detailed kinetic study of alkaline phosphatase, lactoperoxidase and β-lactoglobulin was carried out in the context of identifying intrinsic time–temperature indicators for controlling the heat processing of milk. The heat inactivation or denaturation of alkaline phosphatase, lactoperoxidase and β-lactoglobulin under isothermal conditions was found to follow first order kinetics. Experimental results were analysed using both a two step linear regression and a one step non-linear regression method. Results obtained using the two statistical techniques were comparable, but the 95% confidence interval for the predicted values was smaller when the one step non-linear regression method was used, indicating its superiority for estimating kinetic parameters. Thermal inactivation of alkaline phosphatase and lactoperoxidase was characterized by z values of 5·3 deg C (D60 °C = 24·6 min) and 4·3 deg C (D71 °C = 38·6 min) respectively. For the denaturation of β-lactoglobulin we found z values of 7·9 deg C (D75 °C = 49·9 min) in the temperature range 70–80 °C and 24·2 deg C (D85 °C = 3·53 min) in the range 83-95 °C. Dref and z were evaluated under dynamic temperature conditions. To estimate the statistical accuracy of the parameters, 90% joint confidence regions were constructed.

Mammary gland protein metabolism, determined by an arteriovenous difference technique, was monitored in four Holstein-Friesian dairy cows in response to supplemental dietary protein (provided as rumen-protected soyabean meal) during late lactation (weeks 24–30). Each cow was offered two isoenergetic diets composed of grass silage (170 g crude protein/kg dry matter) plus either a low (108 g/kg) or medium (151 g/kg) crude protein concentrate in a single crossover design involving two 21 d periods. On day 21, arteriovenous measurements across the mammary gland were made during a 13 h continuous i.v. infusion of [1-13C]leucine and with frequent (2 hourly) milk sampling during the final 6 h. Although total milk yield was slightly increased (+1 kg/d) by protein supplementation, milk protein yield was not significantly affected. Whole body protein flux (protein synthesis plus oxidation) was not significantly affected by supplementation. Total mammary gland protein synthesis (milk plus non-milk protein) was also not affected by supplementation but on both diets gland synthesis was always greater (by 20–59%) than milk protein output. The fractional oxidation rate of leucine by the mammary gland was significantly increased by protein supplementation (0·047 v. 0·136). Although the enrichment of leucine in secreted milk protein continued to increase, the final value (at 13 h) was 0·94 of the arterial plasma free leucine plateau value (not significantly different), suggesting almost exclusive use of plasma free leucine for milk protein synthesis. Based on current feeding schemes for dairy cattle, a fixed proportion (0·65–0·75) of the additional protein intake (+490 g/d) should have been partitioned into milk protein. Instead, leucine oxidation by the mammary gland was increased. Whether oxidation of other amino acids was also enhanced is unknown but if amino acid oxidation and the ‘additional’ non-milk protein synthesis occurring in the gland are not crucial to milk synthesis, then by reducing such activities improvements in the efficiency of converting absorbed amino acid into milk protein can be achieved.

The heat denaturation of α-lactalbumin (α-la) in NaCl and KCl solutions, milk ultrafiltrate and milk was studied using the method of micro complement fixation. It was established that this protein was very resistant to heat denaturation and that it was more stable in milk ultrafiltrate than in the other media studied at temperatures up to 70 °C. Of the various milk proteins added to α-la, only β-lactoglobulin (β-lg) formed a heat-induced complex with this protein. This complex was identical in milk ultrafiltrate or in milk and depended on the molar ratio between both proteins; it was not modified by any other milk proteins. The binding of a-la to β-lg changed the ability of the latter protein to bind κ-casein.