Analyses were made at the Institute chemistry laboratory over 2 dairy seasons of 900 composite milk samples prepared for routine fat testing at 2 dairy factories and held at ambient temperature. The composites, which were preserved with mercuric chloride, frequently had high free fat acidities and high bacterial and mould counts.

At one factory, where the composites were sampled at 85−90 °F, the samples contained incompletely dispersed fat. Werner Schmid fat values for 83 milks pipetted immediately after factory sampling were lower on average by 0·084±0·089% than values obtained for the same samples after high-speed mixing at 115°F. At the other factory, where the samples were mixed at 98–103°F, Werner Schmid tests on 56 milks showed a corresponding difference of only 0·033±0·047%.

For 273 factory composites, mixed at high speed, results by the Babcock test and by the Gerber test averaged, respectively, 0·015±0·019% and 0·059±0·054% higher than those by the Werner Schmid test.

High bacterial and mould counts in factory composites were attributed to contamination from unsterilized bottles and stoppers and to failure of factory staff to mix the contents of each bottle after the daily addition of milk. Low bacterial and mould counts and negligible increases in free fat acidity were found in composites made up from factory milk in the Institute laboratory in sterilized bottles, kept at ambient temperature and swirled daily. Composites made up from fresh farm milks and held at 38–40°F remained in good condition for sampling after warming to 98–103°F but showed wide variation in free fat acidity.

Rises in free fat acidity occurred only in composites preserved with mercuric chloride. Other preservatives, however, were less effective in preventing bacterial growth at ambient temperatures.

Increases in free fat acidity up to 10 (ml N alkali/100 g fat) had no effect on results in the Babcock tests but caused a slight rise with the Gerber tests. Acidities over 20 caused a decrease in Babcock and a further rise in Gerber values.

It is suggested that fat destabilization in composite samples could be minimized by avoiding rises in temperature during transport of fresh daily samples from farm to factory, by holding composites at 55–60°F and by mixing after each daily addition of milk.

Lactation was induced in 30 Holstein heifers by treatment with synthetic oestrogen only. The average age of the heifers at the start of treatment was 16·6 months and the average lactation yield 1072 kg of milk with a fat content of 3·43% given in 241 days. Subsequently, 22 of these animals gave a normal lactation starting at an average age of 31 months, with yields of 3980 kg milk with a fat content of 3·31% given in 294 days. The induced lactation was slightly associated with reproductive problems and growth of the animals was normal. There was a good within-cow correlation between the yield and composition of the milk obtained in the 2 lactations. The correlation coefficients between the total production of the milk in the normal lactation and the total yield and peak production in the induced lactation were 0·718 and 0·785 and that between the average percentages of fat in the milk obtained in the 2 lactations was 0·718.

It is possible to predict dairy performance from the performance during the induced lactation, but before the procedure can be recommended for general use the question whether it may induce reproductive difficulties requires further investigation.

When examined under the electron microscope, bovine casein micelles were seen as aggregates of spheroidal granules arranged in spherical symmetry. The granules were of 2 kinds—one transparent in the electron beam and the other relatively opaque. With increasing acidity of the milk the regular arrangements of granules tended to break down, and bridges composed of granules, formed between neighbouring micelles. The average diameter of the granules was about 8 mμ, from which a molecular weight of about 225000 was calculated. Evidence was adduced for the identity of these granules with the macromolecules of native casein in equilibrium with whey.

Human casein micelles showed the same structural features. The average diameter of the granules was about 6 mμ, from which a molecular weight of about 100000 was calculated.

With 10-day composite milk samples the effect has been investigated of various preservatives, of variations in the method of preparing the composites and of the condition of the composites at sampling on Milko-tester results for fat content.

The results for composites preserved with mercuric chloride agreed much more closely with the Werner Schmid results than did those for corresponding composites preserved with potassium dichromate, formaldehyde solution or paraformaldehyde.

In composites preserved with mercuric chloride, prepared and held at ambient temperatures at 2 dairy factories, a small proportion contained destabilized fat when sampled at 98–103 °F and gave very low Milko-tester results in comparison with the Werner Schmid and Gerber results. After high-speed mixing of the composites at 115 °F the Milko-tester results were closer to, but still lower than, the Werner Schmid results.

The average Milko-tester result for 133 composites free from destabilized fat when sampled at 98–103 °F was 0–099 ± 0.055% lower than the average Werner Schmid result. Results for 133 duplicate samples, which were also free of destabilized fat at 98–103 °F but which had not been swirled after the daily addition of fresh milk, were on average — 0.158 ± 0.076% lower than the Werner Schmid result. The Werner Schmid and Gerber results agreed well. The lowering of the Milko-tester result in the ‘swirled daily’ samples was due (a) to the effect produced by dissolving mercuric chloride in milk, (b) to slight fat hydrolysis, and (c) to some other factor, possibly fat oxidation. The further lowering of the Milko-tester result in the ‘non-swirled’ samples was due mainly to greater hydrolysis of the fat with production of higher fat acidities. Other composites, which were swirled daily but which were held at 38–40 °F gave on the average higher fat acidities and lower Milko-tester results than the ‘swirled daily’ composites held at ambient temperatures.

A correction of +0.10% to the Milko-tester readings of all ‘swirled daily’ composites, preserved with mercuric chloride and in suitable condition for sampling at 98–103 °F, brought over 90% of the results to within ± 0.10% of the Werner Schmid results.

The Milko-tester (Foss Electric, Hillerød, Denmark) is already in use in a number of countries for the rapid estimation of fat in milk. The fat content is read directly by a photometric measurement of the turbidity due to the fat globules after heating, homogenizing and diluting the sample with a protein-dissolving versene solution. The instrument has been found satisfactory for the routine testing not only of fresh milks but also of milks to which preservative has been added (Černá & Písecký, 1966; Murphy & McGann, 1967). Grubb (1966), however, reported that Milko-tester readings for samples preserved with potassium dichromate were lower after 14 days' storage.

In the present paper the results are presented of an investigation into the suitability of the Milko-tester for fat testing of 10-day composite milk samples.

A high anti-O chaining titre against Salmonella pullorum-H can be obtained in colostral serum when the killed antigen is introduced into the mammary gland during the dry period. A significant titre, several times the normal level, is maintained in the milk serum for 3 weeks postpartum. There was a definite residual titre in the milk serum of non-infused cows against the O and H antigens of Salmonella typhosa and the O antigen of S. pullorum-H.

The effects of the isocaloric replacement of part of the dietary concentrate mixture by cottonseed oil on the yield and composition of the milk fat and on the pattern of rumen fermentation was investigated in 2 feeding experiments with a total of 8 cows in mid-lactation. The concentrate mixtures were given with high- or low-roughage diets that supplied 9·1 or 1·8 kg of hay/day.

In expt 1 the yield of milk fat was not altered by the addition of 10% cottonseed oil to the concentrate mixtures given either with the high- or with the low-levels of dietary roughage. On the low-roughage treatment, dietary cottonseed oil increased milk yield but reduced the fat content of the milk. The change from the high- to the low-roughage diets containing no cottonseed oil resulted in reductions in the yield and percentage of fat in the milk. In expt 2 the yields of milk and milk fat were similar irrespective of whether the concentrate mixture contained 5 or 10% cottonseed oil.

In expt 1 the inclusion of 10% cottonseed oil in the concentrate mixture reduced the yields and percentages of the medium-chain fatty acids (12:0, 14:0 and 16:0) and increased the yields and percentages of the C18 fatty acids in the milk fat. In expt 2, when the concentrate mixture contained 5% cottonseed oil, the yields and percentages of all the fatty acids in the milk fat were similar to the values obtained when the concentrates contained 10% cottonseed oil. For any given concentrate mixture, the change from the high- to the low-roughage treatments in both expts 1 and 2 resulted in increases in the percentage of oleic acid in the milk fat. The highest concentration of trans-octadecenoic acid was observed in the milk fat of the cows when they were given the high-roughage diet with the concentrate mixture containing 10% cottonseed oil.

In expt 2 the level of cottonseed oil in the concentrate mixture did not influence the pattern of rumen fermentation as measured by the concentrations of the various volatile fatty acids in the rumen liquor. However, the change from the high- to the low-roughage diets reduced the proportion of acetic and increased the proportions of propionic and n-valeric acids in the total volatile fatty acids in the rumen liquor.

Two experiments, one with 18 and one with 21 cows, were made to compare the feeding value for milk production of concentrates in which the nitrogen normally supplied by oil cake was completely replaced by either biuret or urea. In expt 1 the urea and biuret contributed 52% of the total nitrogen in the concentrate and in expt 2 they contributed 43%. Hay was fed as the sole roughage. The estimated energy intake in expt 1 was 102–104% of the Woodman standard and in expt 2 it was 108–109%.

In both experiments milk production was about 10% less on the urea and biuret treatments than on the control treatment. There was no significant difference in milk yield between the biuret and the urea treatments. The percentages of fat and protein in the milk from the urea and biuret treatments were higher than from the control treatment, but the weights of these milk constituents were slightly lower than from the control treatment. Liveweight changes and water consumption were not affected by the experimental treatments. In expt 2 an intake of nitrogen about 20% lower than is often recommended in the United Kingdom did not appear to depress milk yields. Three cows that had received biuret concentrates in expt 2 continued to do so during a nitrogen balance trial lasting 3 weeks. Each cow was slightly in negative balance, the average value being −4gN per cow per day.

Coagulation of rennin-treated casein was inhibited by treatment of the casein with dimethylaminonaphthalene sulphonyl chloride. The effect was caused by substitution on lysine side chains of the κ-casein fraction, and inhibition was complete when 2–3 lysine residues/molecule were blocked. This level of substitution did not affect other properties of the κ-casein, such as the release from it of non-protein nitrogen (NPN) by rennin and its ability to stabilize αs-and β-caseins in the presence of Ca++. The evidence suggests that lysine side chains on κ-casein take part in the coagulation of rennin-treated casein.

The effects of the addition of either 5 or 10% ‘oleic acid’ (78% pure) or 10% of a mixture of saturated fatty acids (64% palmitic acid, 31% stearic acid) to the dietary concentrate mixture on the yield and composition of the milk and milk fat and on the pattern of fermentation in the rumen were investigated in a feeding experiment with 8 cows in mid-lactation. The concentrate mixtures were given with a high-roughage diet that supplied 9·1 kg of hay/day.

The addition of 5% ‘oleic acid’ to the concentrate mixture resulted in increased yields of milk and solids-not-fat (SNF); the percentage of fat in the milk was decreased but the yield of milk fat was unaltered. The addition of 10% ‘oleic acid’ to the concentrate mixture decreased both the yield and percentage of fat in the milk. In contrast, the concentrate mixture containing 10% of the mixture of saturated fatty acids increased the yield of milk fat.

When the concentrate mixture containing 5% ‘oleic acid’ was given to the cows, the yields and percentages of the fatty acids from 4:0 to 16:0 (except 12:0) in the milk fat were decreased, but the yields and percentages of 18:0 and 18:1 were increased. Similar but more pronounced effects on the yields and percentages of the fatty acids from 4:0 to 16:0 (except 12:0) in the milk fat were observed when the cows were given the concentrate mixture containing 10% ‘oleic acid’, but under these dietary conditions the yield and percentage of only 18:1 in the milk fat were increased. The addition of the mixture of saturated fatty acids to the concentrate mixture decreased the percentages of the fatty acids from 4:0 to 14:0 (except 12:0) in the milk fat but decreased the yields of only 10:0 and 14:0; the yields and percentages of 16:0 and 18:1 were increased.

When the cows were given the concentrate mixture containing 5% ‘oleic acid’ there was a small but significant decrease in the acetic acid:propionic acid ratio in the rumen liquor. A similar but more pronounced change in the acetic acid:propionic acid ratio in the rumen liquor was observed when the cows were given the concentrate mixture containing 10% ‘oleic acid’, but in this instance there was a significant reduction in the concentration of total volatile fatty acids in the rumen liquor. Apart from a small increase in the relative proportion of propionic acid, the addition of the mixture of saturated fatty acids to the concentrate mixture had no effect on the concentrations of volatile fatty acids in the rumen liquor.

While using an acid degree value test during work on lipolysis in milk, difficulty was encountered in extracting the fat from the milk of certain cows, especially milk of high butterfat content and milk from newly calved cows. This difficulty was overcome by increasing the quantity of reagent used. A study was made of the quantities of reagent required for milks of different butterfat content and for colostrum. No effect on the acid degree value occurred as a result of increasing the quantity of reagent. A modification of the test is recommended, using an increased quantity of reagent.

The effects of the isocaloric replacement of part of the dietary concentrate mixture by 5% lauric acid (99% pure) or by 10% of myristic (95% pure), palmitic (96% pure) or stearic (94% pure) on the yield and composition of milk fat was investigated in 2 feeding experiments with a total of 10 cows in mid-lactation. The concentrate mixtures were given with a high-roughage diet that supplied 9·1 or 7·7 kg hay/day in expts 1 and 2, respectively.

In expt 1 the inclusion of myristic acid in the diet decreased the yields of milk and solids-not-fat (SNF), but increased the percentage of fat in the milk without altering the fat yield. When stearic or palmitic acid was included in the diet there was an increase in milk fat yield; palmitic acid caused the greater increase. In expt 2 the inclusion of lauric acid in the diet did not appear to affect the yields of milk or SNF but it caused large reductions in the percentage of fat in the milk and in the yield of fat.

In expt 1 the inclusion of myristic acid increased the yields and percentages of 14:0, 14:1 and 16:1 in the milk fat and decreased the yields and percentages of the short-chain fatty acids (4:0–8:0), 16:0, 18:0 and 18:1. When palmitic acid was included in the diet there were increases in the yields and percentages of 16:0 and 16:1 in the milk fat and decreases in the yields and percentages of 10:0, 12:0, 14:0, 18:0 and 18:1. The inclusion of stearic acid in the diet increased the yields and percentages of 18:0 and 18:1 in the milk fat and decreased the yields and percentages of 12:0 and 16:0. In expt 2 the inclusion of lauric acid in the diet increased the yield and percentage of 12:0, and in 1 cow the content of 14:0 in the milk fat; there were reductions in the yields and percentages of all the other fatty acids in the milk fat. There was no evidence of any marked elongation of the carbon chains of 12:0 and 14:0 in the mammary gland to form 16:0 or 18:0.

In expt 1 the incorporation of myristic acid in the diet decreased the concentration of total steam-volatile fatty acids in rumen liquor. The inclusion of either myristic, palmitic or stearic acid in the diet had little effect on the relative proportions of the individual volatile acids in the rumen liquor. In expt 2 the addition of lauric acid to the diet reduced the acetic acid:propionic acid ratio in the rumen liquor.

The effect on the chemical composition of rumen fluid of replacing oilcake nitrogen by either biuret or urea N in the concentrate part of the ration for cows has been investigated. The biuret treatment produced the highest concentrations of NPN and the lowest concentrations of ammonia N in the fluid, whereas the urea treatment gave rise to higher concentrations of NPN than did the oilcake treatment and the highest ammonia N concentrations of the 3 diets. It is unlikely, however, that the differences in either peak or mean ammonia concentrations between the biuret and urea diets, if they occurred in lactating cows receiving these diets, would be sufficient to affect milk production. The concentration of ammonia N in the rumen liquor of cows on the biuret diet increased progressively up to the 5th to 8th week of feeding this diet. The different dietary treatments did not result in any marked differences in the concentrations of total volatile fatty acids in the rumen fluids or in the proportions of acetic, propionic and butyric acids in the total fatty acids.

The viscosity index and adhesive strength of casein from the milk of 6 individual cows were determined on samples collected regularly throughout the 9-month dairying season. The viscosity index of the casein from each cow showed a seasonal decline while the adhesive strength showed a general increase during this time. Casein from one cow had a consistently low viscosity index attributed to the presence in it of a rare genetic variant of α-casein. It is suggested that the variations in viscosity index and adhesive strength are lactational rather than seasonal.

The apparent digestibility coefficients of the various constituents of diets containing myristic, palmitic or stearic acids have been determined in an experiment with 8 sheep.

The inclusion of myristic acid in the diet had no effect on the digestibility coefficient of total dry matter or crude protein, but it decreased the digestibility coefficients of crude fibre and nitrogen-free-extractives and increased the digestibility coefficients of fat and minerals. When palmitic acid was included in the diet there were decreases in the digestibility coefficients of total dry matter, crude fibre and nitrogen-free-extractives. The inclusion of stearic acid in the diet resulted in decreases in the digestibility coefficients of dry matter and nitrogen-free-extractives. There was an inverse relationship between the melting points and the digestibility coefficients of the added fatty acids.

The findings of this investigation are discussed in relation to the results of a previous study on the effects of these dietary fatty acids on the yield and composition of cow's milk.

A preliminary study has been made of some relationships between the relative conductivity of milk and its cellular content and 3 basic relationships subjected to an extensive computer analysis. The results suggest that relative conductivity can be used to detect about 3 out of every 4 cows yielding milk samples from one or more quarters with a cellular content greater than 500000/ml, and about 4 out of every 5 cows with a cellular content greater than 1000000/ml. Less than 1 in 20 cows would be incorrectly detected as having cell counts greater than 500000/ml in milk from any one quarter.

The physical effects of various cations in caseinate dispersions of high concentrations were investigated over a range of temperature and pH.

With calcium and strontium the temperature-viscosity relationships of the caseinates were abnormal in that the viscosity decreased rapidly from 30 to about 40 °C and a gel formed at temperatures in the region of 50–60 °C. On cooling, the gel reliquefied. No gel formed with barium, aluminium or magnesium. On cooling, magnesium preparations separated into 2 phases.

The supernatant phase from the magnesium caseinate and a corresponding phase prepared by centrifuging the calcium caseinate showed depletion of α-casein and enrichment of κ-casein and β-casein. The supernatant phase from the calcium caseinate showed the reversible gel formation on heating. The magnesium supernatant phase did not. κ-Casein and a mixture of κ- and β-caseins gave reversible gels at similar levels of calcium and pH.

For reversible gel formation to occur, calcium caseinate was required to be in fairly high concentration, to have a calcium content of about 1·0% of the protein and to be within the pH limits 5·2–6·0. The temperature at which gelation occurred was affected by the concentration of calcium and protein and by pH.

The behaviour of the material was compared with that of methyl cellulose with and without addition of urea.

Some potential commercial applications of the findings on viscosity relationships are outlined.

The changes in the size of the milking and residual fractions following milking intervals of 4, 8, 12, 16, 20 and 24 h were investigated in 18 ewes receiving regular injections of oxytocin at each milking. The observations were carried out using a 6×6 Latin square design in which each treatment interval was repeated 4 times. The milking and the residual fractions were found to increase significantly with the lengthening of the interval. The amount of hand strippings was also related to interval length. When a given interval was repeated there were no changes in the relative sizes of the fractions. A change in the milking interval, however, caused significant changes in the various fractions. It is suggested that in the present experiment the milking fractions consisted in the main of milk that was present in the sinuses prior to milking.

The effects of the isocaloric replacement of part of the dietary concentrate mixture by either tallow or cottonseed oil on the yield and composition of the milk fat was investigated in 2 feeding experiments with a total of 26 cows in midlactation. The concentrates were given with high- or low-roughage diets that supplied either 9·1–9·5 or 1·8–3·2kg hay/day.

In expt 1, the addition of cottonseed oil to the high-roughage diet increased the yield of milk fat during the first 8 days but decreased it during the last 4 days of a 28-day feeding period. In contrast, the inclusion of tallow in the high-roughage diet resulted in an increased yield of milk fat that was sustained throughout the period of 28 days. In expt 2, the intake of dietary fat was less than it was in expt 1 and the inclusion of tallow or cottonseed oil in either the high- or low-roughage diets had little effect on the yield of milk fat.

The inclusion of either fat in the diet increased the yields and percentages of stearic and oleic acids and, in general, decreased the yields and percentages of the medium-chain fatty acids (10:0, 12:0 and 14:0) in the milk fat. The addition of tallow to the diet did not appear to alter the yields of the short-chain fatty acids (C4–C8, 4:0, 6:0 and 8:0) in the milk fat. When the low-roughage diets resulted in a decreased yield of milk fat, the secretion of all the fatty acids in the milk fat was reduced, but the reduction in the secretion of oleic acid was less than the reductions in the secretions of the other constituent fatty acids.

Hypersensitivity to cow's milk is not uncommon in humans, particularly babies and infants. Those afflicted may be found to tolerate goat's milk which, in this country, commands a considerably higher price than cow's milk. For economic as well as ethical reasons it is therefore desirable to ascertain that goat's milk offered for sale is free from admixtures of cow's milk. Tests should be sensitive to relatively minor admixtures, since even small additions of cow's milk may undo the benefit which hypersensitive subjects expect to derive from the consumption of goat's milk.

Some milk lipid materials representing the phospholipid protein complex—fat globule membrane from buttermilk (FGMI) and from butter serum (FGMII), intact fat globules (dialysed cream) and triglycerides (butter oil)—were subjected to copper-induced oxidation in systems containing distilled water, phosphate buffer of pH 6·60 or milk dialysate. These model systems usually contained 2% lipid material and were allowed to oxidize for 48 h at 3–5 °C. Oxidation intensity was measured by means of the 2-thiobarbituric acid test.

The oxidation intensity was dependent on the composition of the lipid material and of the aqueous phase. Ascorbic acid in absence of added copper catalysed the oxidation of the membrane materials and of globular fat. The oxidation intensity produced by FGMI (from buttermilk) differed significantly from that produced by FGMII (from butter serum) and the difference was well correlated with differences in their composition. Butter-oil preparations gave the lowest oxidation intensities, indicating that they are not the site for development of oxidative defects in aqueous media.