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.

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.

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.

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.

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 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.

Analyses of the neutral volatile components from 3 Cheddar cheese are presented. Two were made aseptically in an aseptic vat, with and without starter culture; the third was made with starter culture in an open vat. Gas–liquid chromatography and mass spectrometry detected the same volatiles in starterless cheese having little or no Cheddar flavour as in cheese made with starter and having a characteristic Cheddar flavour. Methyl disulphide and dimethyl sulphide were the only compounds consistently detected in higher concentrations in the cheese made with starter than in the cheese made without starter. However, using a total trapping technique, it was found that the combination of components recovered from the effluents of the chromatographic columns did not have the cheese-like aroma of the distillate vapours that were injected. Reasons for this are discussed.

A laboratory method has been developed for studying the action of chemical disinfectants on milking equipment using a wet film and both metal and rubber surfaces. It was shown that milking machines may be soiled as effectively with fresh milk of low bacterial content as with aged milk of high bacterial content. When a single heat treatment preceded the soiling with milk and subsequent treatment with detergent and chemical disinfectant, a build-up of bacteria began on the third day. However, when the surfaces were heat treated daily 18 h before soiling, followed by cleaning and disinfection, no build-up occurred. These findings support the hypothesis that contamination of milk results from bacteria developing on the milking equipment and not merely from those added to it at each milking. The sites of bacterial contamination were shown to be the under surfaces of lid gaskets and the joints of the short milk tubes and the metal clawpiece nipples.

A pilot plant with a capacity of 2300 1./5 h day for the removal of cationic fission products from milk is described. The process involves the acidification of the milk with citric acid to pH 5.25 and its passage through an ion exchange resin charged with the ions of Ca, K, Na and Mg in the same proportions as those in which they occur in milk. The effluent milk is neutralized with potassium hydroxide. At the end of the day the plant and resin bed are washed and sterilized.

Two resin beds are provided and are used on alternate days, one being washed and regenerated while the other is in use. Regeneration is carried out with a solution which removes radioactive cations and restores the resin bed to its original ionic composition.

Bacteriological tests show that the method of cleaning both plant and resin bed is satisfactory.

Conclusions are drawn as to a suitable design for a larger scale plant.

AS previously described, the process consists essentially of the passage of milk at pH 5·2–5·25 through an ion exchange resin charged with a suitable mixture of the ions of Ca, K, Na and Mg.

When citric acid was used for reduction of the pH and 30 resin bed volumes (r.b.v.) were treated, the concentration of residual 85Sr was reduced to 2–4% whether it had been introduced in vivo or in vitro. There was no evidence that repeated use of the resin bed resulted in diminished radiochemical efficiency.

About the same efficiency of removal of 133Ba was obtained but this efficiency was achieved with 137Cs only if not more than 15 r.b.v. were treated. If 30 r.b.v. were treated the concentration of residual 137Cs was as much as 30%.

When hydrochloric acid was substituted for citric acid the residual concentration of 85Sr was 11%. Analyses of milks processed after adjustment of pH with either citric or hydrochloric acid showed the products to be satisfactory. The only important constituent lost was thiamine. Concentrations of heavy metals remained well below maximum values. Although the flavour of milk was detectably changed by the treatment it was still acceptable.

The results are discussed in relation to the problem of achieving maximum decontamination and to the design of a large scale plant.

Intramammary infection present in quarters of dairy cows, either throughout the dry period or originating in the dry period, reduces the milk yield after calving. Relative to the milk yield of equivalent non-infected quarters of the same udder the reduction was found in this work to be about 35%. The relative milk yield of quarters found infected in late lactation was depressed by 48% but if the infection was eliminated during the dry period, the depression in milk yield was only 11% after parturition.

Samples were tested for fat percentage from every consignment of herd bulk milk from 10 herds over a period of 12 months. The mean monthly within-herd variance was 0·043. Also, triplicate samples were taken from 8 herd bulk supplies for 8 days and tested in duplicate and an analysis of variance was applied to the within-herd fat percentage in order to find the contribution sampling, testing and biological variances. It is shown that when dealing with tanker-collected milk where composite samples are not used the testing accuracy is secondary to frequency of sampling. By combining the variances in the formulae given, the accuracy of different systems may be obtained and compared using either single tested or composite samples.

The chemical method of Tolle, Zeidler & Heeschen, (1966) for dispersing the fat in milk to allow electronic counting of the cells in suspension has been examined. The optimum conditions prescribed for obtaining the best estimates of cell counts were largely confirmed though inaccurate counts occasionally occurred. The reproducibility of counts made on the same milk samples was acceptable. For milk samples from individual quarters, cell counts determined after the chemical treatment and those after centrifugal separation of the fat could be related by a linear regression line of unit slope through the origin. The surface active liquid Lissapol NXP (I.C.I. Ltd.) appeared to be a suitable substitute for the Witopal CO (Chemischen Werken in Witten/Ruhr), an alkylphenol polyglycol ether, used by Tolle et al. (1966).

Factors associated with the milking cluster and the long milk tube which cause a diminished or a fluctuating vacuum within the liner of the teatcup assembly during simulated milking with an artificial udder fell into 3 groups. 1. Lower milk flow rates and admission of air at the clawpiece greatly decreased vacuum fluctuation within a pulsation cycle and increased the mean level of vacuum in the liner during that part of the cycle in which milk was flowing from the teat. 2. Larger bore of the short milk tube connecting the liner to the clawpiece, pulsation of the teatcup liners in pairs instead of all 4 together, and larger volume of the clawpiece bowl in the main decreased fluctuation in vacuum within the liner. 3. Larger bore and shorter length of the long milk tube connected to the clawpiece and decreased height above the outlet of the clawpiece to which the milk was raised mainly increased the mean vacuum in the liner during that part of the cycle in which milk was flowing from the teat.

In a milking experiment with 75 cows mean overall fluctuations in milking vacuum within the liner in a pulsation cycle at peak flow were 11·5 and 4·8 inHg and corresponding mean levels of vacuum during that part of the cycle when milk was flowing from the teat were 11·75 and 13·0 inHg. There were no differences in milking performance of practical consequence.