The action of rennet on homogenized milk was studied using turbidimetric and light scattering techniques, and compared with results obtained previously for skim milk. The time required for the onset of coagulation was shorter for homogenized milk than for skim milk. The rate of coagulation of fully renneted particles increased with increasing temperature, and with increasing Ca2+ concentration, but was only slightly influenced by changes in ionic strength. The von Smoluchowski rate constant for the coagulation reaction was two orders of magnitude smaller for homogenized milk than for skim milk. Results suggest that coagulation of homogenized milk is controlled in general by the same factors as skim milk, and that the reaction may be inhibited owing to a reduction in the amount of casein available for mutual interaction, rather than to disruption of the micelles on homogenization.

The C6–C11 2,4–dienals have been identified in distillates from skim milk with oxidized flavour. The C4–C11 2–enals were isolated from the same distillates in a previous investigation. The most abundant individual compounds in the two groups were 2–octenal, 2–nonenal, 2–4–heptadienal and 2,4–nonadienal. These compounds when flavour–tested in skim milk in dilutions of 10–7–10–9 closely resembled oxidized (cardboard) flavour. It is concluded that they are the main constituents of this flavour defect and that they originate from the oxidation of the more highly unsaturated fatty acids in milk lipids.

The fermentation products of Betacoccus cremoris in neutral milk are acetic acid and carbonic acid. In acidified milk or in mixed cultures of this bacterium and lactic acid streptococci the products are acetic acid, C02, diacetyl, acetylmethyl carbinol and 2–3 butylene glycol. The latter three substances may be called “C4 compounds”. Diacetyl is only formed when an oxidation with atmospheric oxygen can take place. Carbinol is found in aerobic and in anaerobic cultures. It may be reduced to butylene glycol. This reduction is more complete at lower acidity, but also depends on the strain of Betacoccus used.

All these substances are formed from the citric acid of the milk. However, small amounts of acetic acid may be produced from sugar.

From 1 mol. of citric acid are formed: 2 mol. of carbon dioxide, 1–1·5 mol. of acetic acid, 0·5–0 mol. of C4 compounds.

A reciprocal relation exists between the quantities of acetic acid and C4 compounds. When the amount of acetic acid is high the C4 compounds content is low. The higher the acidity of the medium in which the betacocci are cultivated the higher is the amount of C4 compounds. This means that the fermentation in neutral media is the extreme case of the fermentation process. Then the production of C4 compounds is minimal (0) and that of acetic acid is maximal (1·5).

Several milk components related to immune defences (lysozyme, lactoferrin and γ-globulins, γ-G) and to inflammation (somatic cell counts, SCC; N-acetyl-β-glucosaminidase, NAGase; albumin) were considered. Forty-one quarters and 685 samples of 24 cows were included in the study; among them 534 samples were defined as negative (78·0%), 93 as diseased (13·5%) and 58 (8·5%) as subclinical. The pattern of each milk component in quarters always negative during the follow-up period was evaluated by a mixed model. Statistical analysis showed that days in milk (DIM), age (primiparous, pluriparous), herd and the interaction between herd and days in milk significantly influenced all the markers, with very few exceptions. A subset of samples including the negative quarters before the first outcome of an infection or a subclinical mastitis and the samples from quarters always negative was also selected. The analysis showed that herd, DIM and health status had a significant influence on most markers. Overall, primiparous cows were confirmed to have higher levels of most of the markers than pluriparous cows. The presence of a herd effect on non specific immune defences in fully negative quarters implies that when the mechanisms behind their release are fully elucidated, it might be possible to modulate them. Udder tissues were confirmed as an important source of some immune components, as supported by the inconsistency between SCC mean values and NAGase, lysozyme and lactoferrin values. Overall, quarters with high levels of NAGase, lysozyme and γ-G, exposed to bacteria, did not develop subclinical mastitis. Hence, invading pathogens could induce the development of subclinical IMI when these components and γG are in low concentration.

The modern food-processing industry is placing more and more emphasis upon the utilization of protein ingredients to provide specific functional properties to a wide range of formulated foods. Isolated milk protein products represent an important and valuable source of protein ingredients due to their recognized superior nutritional, organoleptic and functional properties. This paper provides up-to-date information on the quantities, production processes, composition, general properties, and specific functional properties of the major milk protein products, e.g. caseinates, co-precipitates, lactalbumin, whey protein concentrates and milk blends. The subject of chemical and enzymic modification to improve certain functional properties of milk proteins is considered briefly.

Thirty-nine British Friesian cows and 17 British Friesian heifers were used to measure the effects on milk yield, food intake and digestion, and N balance of increasing the protein concentration in the diet from 111 to 147 g crude protein/kg dry matter during the first 16 weeks of lactation. The comparison was made for animals given food either ad lib. or at a level which allowed them to gain 0·5 kg/d during the 8 weeks before parturition, and for animals given ad lib. diets of either 60:40 or 40:60 hay: concentrate ratio during early lactation. Milk yield was increased by a higher protein concentration in the diet (P < 0·01) and the increase was evident from the first week of lactation. Mean increases over the first 8 weeks of lactation were 3 kg/d for animals on the diet of high roughage content and 7 kg/d for animals on the diet of low roughage content. A higher crude protein content in the diet also increased food intake (P < 0·05) and digestion (P < 0·05), and the increases were greater for animals given the diet of low compared with high roughage content. Level of feeding before parturition did not influence food intake or milk yield and there were no differences between cows and heifers in their response to treatments. N balance over the first 10 weeks of lactation averaged –13 g/d for cows and 6 g/d for heifers (P < 0·025). and was not significantly altered by treatments. Mean N balance of all animals was estimated to increase from –37 g/d immediately after parturition to zero at 8 weeks of lactation. The results demonstrate that an increased protein concentration in the diet during early lactation is associated with increased food intake and digestibility of food, which are in turn largely responsible for higher levels of milk production.

A method for the partial fractionation of the αs-casein complex is described. It involves removal of κ-casein from iso-electric casein by the method of Zittle & Custer (1963) followed by fractionating the residue (αs- and β-casein) by the urea procedure of Hipp et al. (1952). αs0- and αs1-caseins precipitate from 3·3 M urea at pH 4·6, but much of the αs2-, αs3- and αs4-casein remains in solution and co-precipitates with β-casein from 1·7 M urea at pH 4·9. Chromatography on DEAE cellulose clearly separates β-casein from the αs2-, αs3- and αs4-caseins, which are not resolved by the conditions employed. The method is suitable for the fractionation of iso-electric casein into all its major components (i) κ-casein; (ii) αs0- and αs1-caseins; (iii) αs2-, αs3- and αs4-caseins; (iv) β-casein; (v) γ-casein.

1. Records were collected from a herd where many cows were producing relatively high daily yields of milk at the time of drying-off. Animals giving 7 lb. of milk or less daily were dried off by intermittent milking, and those giving over 7 lb. daily were dried off by ‘stop’ milking. The data from 113 dry periods were analysed so that a comparison could be made of the new infection rate in the early dry period according to level of production at drying-off.

2. The new dry-period infection rate was found to increase with yield at drying-off. This was not due to age differences between the groups of cows.

3. The rise in total infection rate with yield was due mainly to an increase in Str. agalactiae infections.

4. A high proportion of clinical quarters were detected in the dry period by the cowmen.

5. The yield in the lactation following the dry period studied was not related to yield at drying-off.

6. New dry-period infections were significantly (P <0·01) more numerous in quarters of cows that had been hand-stripped during lactation compared with quarters of machinestripped cows.

We investigated effects of subclinical intramammary infection (IMI) on milk somatic cell count (SCC) and milk composition in udder halves of dairy goats. A total of 35 mixed-age Alpine does (70 udder halves; approximately 55 kg body weight) were rotationally grazed on a mixture of vegetative forages (wheat/berseem clover, sudan grass and cowpeas). Milk samples for bacterial analysis and SCC were collected monthly from both halves from April to September, 2001. Across stages of lactation, 19–31% of udder halves became infected. The prevalence of IMI exhibited quadratic patterns through multi-peaked responses within each stage of lactation. Higher rates of IMI were observed during the early stage of lactation (19% in May) and in the late stage of lactation (31% in September). Coagulase negative Staphylococcus (CNS, 43·7%), Staph. aureus (35·4%), and Pseudomonas aeruginosa (12·4%) were the most prevalent pathogens. Within single-strain IMI, log SCC (6·24) was lower (P<0·01) for CNS than those derived from IMI by Staph. aureus (6·49), Ps. aeruginosa (6·53) or Serratia spp. (6·90). Infected udder halves had a higher average SCC (4761 v. 2259×103 cells/ml; P<0·01) than uninfected halves, but uninfected halves often had similar levels of SCC to infected halves. Daily average milk production was not significantly different between infected and non-infected goats and the relationship between IMI and SCC was not always correlated. Effective mastitis screening requires bacteriological culture since SCC was not highly correlated.

Supplementation with a high dose (600 g/d) of rumen inert conjugated linoleic acids (RI-CLA) inhibits milk fat synthesis in total mixed ration (TMR)-fed dairy cows immediately post partum. However, effects of RI-CLA on milk fat and bioenergetic parameters during the transition period in grazing cows have not been investigated. Multiparous Holstein cows (n=39) grazing pasture were randomly assigned to one of three treatments: (1) pasture (PAS), (2) PAS+540 g/d Hyprofat (palm oil; HYPRO) and (3) PAS+600 g/d RI-CLA. HYPRO and RI-CLA supplements were isoenergetic, fed twice daily at 7.00 and 16.00 and provided 0 and 125 g CLA/d, respectively. Treatments began 27±10 d prepartum and continued until 36±1 days in milk (DIM). There was little or no overall effect of RI-CLA on content or yield of milk protein and lactose. RI-CLA supplementation decreased overall milk fat content and yield with RI-CLA-induced milk fat depression (MFD) becoming significant by day 3 when compared with PAS and by day 6 when compared with HYPRO. MFD continued to increase in severity during the first 24 d post partum after which MFD reached a plateau (~40%; RI-CLA v. HYPRO). Pasture-fed cows produced less milk (19·4 kg/d) than the lipid-supplemented groups and although there were no overall differences in milk yield between RI-CLA and HYPRO (22·3 kg/d) a curvilinear relationship (R2=0·57) existed between the RI-CLA-induced milk yield response and extent of MFD. RI-CLA tended to increase milk yield (1·8 kg/d) compared with HYPRO until MFD exceeded 35% (~day 21), after which point the positive milk yield response was eliminated. Milk fat trans-10, cis-12 CLA content averaged 0·25 g/100 g in the RI-CLA treatment, was temporally independent, and was undetectable in PAS and HYPRO treatments. Based on the milk fat 14[ratio ]1/14[ratio ]0 ratio, RI-CLA decreased the overall Δ9-desaturase system compared with PAS and HYPRO. Compared with HYPRO, RI-CLA had no effect on plasma glucose, insulin, leptin, or NEFA concentrations. Results indicate that a high RI-CLA dose decreases milk fat synthesis and tends to increase milk yield immediately post partum in pasture-fed cows; however, excessive MFD (>35%) appears to be associated with a diminished milk yield response.

A rapid procedure for isolating genomic DNA from milk samples has been devised, based on the use of Chelex resin. By using this protocol, genomic DNA was extracted from milk samples from 15 cows and 15 goats. The suitability of these DNA preparations as a template for performing the polymerase chain reaction (PCR) was tested by amplifying three different loci of the bovine genome: exon 4 of the κ-casein gene and the INRA5 and INRA23 microsatellites, together with two others: exon 19 of the αs1-casein gene and exon 2 and part of intron 2 of the DRB gene of the caprine genome. No amplification products could be obtained from any samples at 30 cycles. In contrast, at 45 cycles the number of amplified samples ranged from 86 to 100% and at 65 cycles all the DNA targets were amplified, indicating that the number of cycles was a critical factor to be optimized for obtaining the desired PCR target. These results suggest that this method may be a useful tool for analysing genetic polymorphism at the DNA level by PCR and relating it to milk composition and other traits of economic interest.

The objective was to measure the activities of all the enzymes essential for hepatic gluconeogenesis in dairy cows with induced fatty liver. We aimed to induce severe fatty liver in ten experimental cows by overfeeding them during the dry period while seven control cows were maintained on a restricted diet. To induce a marked negative energy balance, the experimental cows were deprived of feed for 8 h immediately after parturition. In addition, the experimental cows were given a restricted amount of diet during the first 5 d of lactation. Liver samples were collected 1 week before and 1, 2 and 4 weeks after parturition. Before parturition, liver triacylglycerol concentrations did not differ between the two groups. After parturition, the experimental cows developed marked fatty liver as indicated by a higher level of triacylglycerols in the liver compared with the control cows.

Before parturition, all gluconeogenic enzymes in the liver were lower in experimental cows than in control cows. Phosphoenolpyruvate carboxykinase, pyruvate carboxylase and propionyl-CoA carboxylase were significantly lower and fructose 1,6-bisphosphatase and glucose 6-phosphatase tended to be lower in the experimental cows. The activities of two crucial enzymes for gluconeogenesis in ruminants, i.e., phosphoenolpyruvate carboxykinase and propionyl-CoA carboxylase, remained low throughout the sampling period post partum. Activities of pyruvate carboxylase and glucose 6-phosphatase in the experimental cows post partum were upgraded to values similar to those of the control cows. The results showed that the capacity for hepatic gluconeogenesis before parturition was lower in cows with induced fatty liver than in control cows. After parturition, the low activities of crucial gluconeogenic enzymes indicated insufficient production of glucose. It is suggested that the low gluconeogenic capacity leads successively to low blood glucose concentrations, low insulin levels and high rates of mobilization of fatty acid, causing severe hepatic lipidosis.

Protein nanofibrils with 10–20 nm diameters were formed by heating whey protein solution at pH 2·0. Nanofibrils solution was deacidified slowly through dialysis followed by adding different amounts of CaCl2 (0–80 mM) into the dialysis water resulting in formation of a soft viscoelastic gel over time. The gel fabricated from the nanofibrils solution dialyzed against distilled water with 0 mM CaCl2 had zero ash content. Fourier transform infra-red spectroscopy revealed a change in the pattern of hydrogen bond formation in gel network by calcium chloride. The higher the ash content of gels, the lower was the storage modulus and fracture stress of samples. Gels with higher ash contents had a more porous microstructure which was attributed to the diminished hydrophobic interactions and hydrogen bonding among nanofibrils by the action of chloride. Higher ash contents also led to higher water holding capacity of gels which was attributed to the influence of the strongly hydrated calcium ions that interacted with the non-charged regions of proteins via site-specific interactions.

Low somatic cell count (SCC) is a reliable indicator of high-quality milk free of pathogenic microorganisms. Thus, an important goal in dairy practice is to produce milk with low SCC. Selection for cows with low SCC can sometimes lead to extremely low SCC in single quarters. The cells in milk are, however, predominantly immune cells with important immune functions. To investigate the mammary immune competence of quarters with very low SCC, healthy udder quarters of cows with normal SCC of (40–100)×103 cells/ml and very low SCC of <20×103 cells/ml were challenged with lipopolysaccharide (LPS) from Escherichia coli. In the first experiment, SCC and cell viability after a challenge with 50 ng of LPS/quarter was investigated. In the second experiment, tumour necrosis factor α (TNF-α) concentration and lactate dehydrogenase (LDH) activity in milk, and mRNA expression of various innate immune factors in milk cells were measured after a challenge with 100 μg LPS/quarter. LPS challenge induced an increase of SCC. SCC levels reached were higher in quarters with normal SCC and maximum SCC was reached 1 h earlier than in very low SCC quarters. The increase of TNF-α concentrations in milk in response to LPS challenge was lower in quarters with very low SCC than in quarters with normal SCC. The viability of cells and the LDH activity in milk increased in response to LPS challenge, however, without a difference between the groups. The mRNA expression of IL-1β and IL-8 was increased in milk cells at 12 h after LPS challenge, whereas that of TNF-α and lactoferrin was not increased at the measured time points (12, 24 and 36 h after LPS challenge). No differences of mRNA expression of measured immune factors between normal and very low SCC samples were detected. The study showed that udder quarters with very low SCC responded with a less marked increase of SCC compared with quarters with normal SCC. This difference corresponded with simultaneously lower TNF-α concentrations in milk. However, the immune competence of the cells themselves based on mRNA expression of TNF-α, IL-8, IL-1β, and lactoferrin, did not differ. The results may indicate that very low SCC can impair the immune competence of udder quarters, because the immune response in udder quarters with lower SCC is less efficient as fewer cells contribute to the production of immunoregulators.

The hydrolysis of κ-casein by a number of rennets and other proteolytic enzymes has been followed by measuring the increase in opacity due to the formation of insoluble aggregates of para-κ-caseins. The stability of these precipitates varied markedly, some being solubilized rapidly by the further action of the enzyme. The turbidity obtained with certain enzymes was dependent upon the calcium ion concentration, indicating that the para-κ-caseins produced were not identical for all enzymes.

For high concentrations of calf rennet, the rate of aggregation was linear with respect to time. With low concentrations of enzyme, increase in turbidity was preceded by a lag period which was lengthened by decreasing the enzyme concentration or increasing the κ-casein concentration. This increase in lag is favoured by a high κ-casein/para-κ-casein ratio, suggesting that the aggregation of newly formed para-κ-casein is prevented by the unchanged κ-casein. In addition, small amounts of αs1- or β-caseins present in the κ-casein also markedly affected the aggregation of para-κ-casein, indicating that all 3 major casein components can inhibit the aggregation of para-κ-casein in the absence of calcium ions. In the light of these observations the possible role of protein-protein interactions in casein coagulation by calf rennet is discussed.

1. Storage tests on spray-dried full-cream milk powders prepared from milk preheated at 160,170,180, 190 and 200° F. for approximately 20 sec. and dried by the Krause process have been carried out at 47, 37 and 15° C. or room temperature. The storage tests were carried out independently at two different research stations. At the Hannah Institute the powders were packed in plain tin-plate containers as received from the factory. At Cambridge grease-free plain tin-plate and lacquered tin-plate containers were used. Deterioration was followed at both stations by a tasting panel and by determination of the amount of oxygen absorbed by the powder and of the accumulation of peroxide in the fat.

2. When fresh the powder pre-heated at 180° F. had the best flavour, followed in order of preference by those pre-heated at 190 and 200° F., which had a definite but quite pleasant ‘boiled’ or ‘cooked’ flavour, and by those pre-heated at 160 and 170° F. which had an incipient tallowy flavour, but were nevertheless still acceptable. The 200 and 190° F. powders gave a strong reaction for volatile sulphur, the 180° F. powder a much weaker but quite definite reaction, and the 170 and 160° F. powders a negative reaction. The copper content of the 180° F. powder which, with the 170° F. sample, was the highest of the group, may have been partly responsible for the weakness of the reaction for volatile sulphur given by this sample. The solubility of the 180, 190 and 200° F. powders was not adversely affected by the high pre-heating temperatures, and the moisture contents of all the powders were sufficiently low to prevent any obvious loss of solubility, which remained very good indeed throughout the storage tests.

1. An experiment is described which assessed the effects on the production obtained from milking cows, of feeding a concentrate with a starch equivalent of 64 at four levels (0, 2, 4 and 6 lb./gal. of milk produced), in addition to a basal ration with limited amounts of hay and dried grass and with silage fed ad lib.

2. The total daily dry-matter intake of the cows increased from 2·2 to 2·7% of the live weight as the rate of concentrate feeding was increased from 0 to 6 lb./gal., despite a reduction in the amount of roughages consumed.

3. For each increase of 1 unit in silage dry-matter percentage, there were increases of from 1·18 to 0·42 lb. of silage bry-matter intake per cow per day as the level of concentrate feeding increased. For each increase of 1 lb. in silage dry-matter intake there was an increase of l lb. in total dry-matter intake per cow per day.

4. The average daily milk yield per cow increased from 22·2 lb. when no concentrates were fed to 27·6 lb. when 6 lb. concentrates were fed per gallon of milk produced. This is an increase of 0·9 lb. milk/lb. increase in starch equivalent intake. A significant difference in response was found between higher yielding and lower yielding groups of cows. The higher yielding group gave an increase of 1·1 lb. and the lower yielding group only 0·6 lb. milk/lb. increase in starch-equivalent intake.

5. At the general level of feeding and of milk yields obtianed in this experiment, no evidence of diminishing returns in milk production was detected when the rate of concentrate feeding was increased.

6. The content of solids-not-fat in the milk rapidly increased from 8·3% when no concentrates were fed to 8·6% when 4 or 6 lb. of the concentrates were fed per gallon of milk produced.

7. When concentrates were fed at the rate of 0 and 2 lb./gal. declines in live weight as well as in the yield and solids-not-fat content of the milk were noted, while at 6 lb./gal. there was an unnecessary gain in live weight. It is concluded, therefore, that with the particular animals and roughages used in this experiment, the optimal level of concentrate feeding was 4 lb./gal.

The increase produced by formaldehyde (HCHO) in the heat stability of milk did not occur when milk was treated with HCHO at temperatures up to 60°C followed by dialysis at 5°C. However, the minimum in the heat coagulation time (HCT)–pH curve was irreversibly removed if the milk was preheated at 80–C for 10 min in the presence of 5 mM-HCHO. Although this treatment blocked the ε-amino groups of lysyl residues, the stabilizing mechanism is considered to be due to the cross linking action of HCHO which reduced the level of non-sedimentable, κ-casein-rich protein dissociated from the micelles on heating. The specific crosslinking agent, dimethyl suberimidate, modified the HCT-pH profile of milk in a manner similar to preheating at 80°C for 10 min with 5 mM-HCHO, supporting the crosslinking hypothesis. The results of this study appear to lend some support to the proposal of Kudo (1980) that the minimum in the HCT-pH curve of milk is due to the dissociation of κ-casein from the micelles on heating at high temperatures at pH values greater than 6η7.

Approximately 30% of the nitrogen of κ-casein was soluble at pH 4·7 after the protein had been treated with rennin at pH 7 while approximately 10% was soluble in 12% trichloroacetic acid (TCA). The material soluble in 12% TCA appeared at a slower rate initially than did the nitrogen soluble at pH 4·7 but as the reaction proceeded it was released more rapidly.

Treating κ-casein with urea, or repeated precipitation of the protein at pH 4·7, caused the formation of material insoluble at pH 7, apparently para-κ-casein. Both treatments appeared to free the same soluble fraction as does rennin acting in low concentration or for a short time.

Low concentrations of rennin (0·07 μg/ml) released only part of the available soluble nitrogen from 2% solutions of whole casein at pH 7. Heating the reaction mixture appeared to restore the casein complex, the restoration being less complete the longer the reaction had proceeded.

It is suggested that κ-casein is not a single protein but a complex, and that the action of rennin is first to open the secondary bonds responsible for the stability of this complex.