A simple in-line filter is described which can be fitted into the milk tube of a. milking machine in order to detect clinical mastitis. It consists of a stainless steel mesh, on which the clots are retained, and it is fitted obliquely into a short length of clear plastics tube. The filter has been developed as an alternative to the fore-milk cup. Tests made over 9 months in a 60-cow herd show good agreement between the fore-milk cup and the in-line filter recordings. For general service production the filters are made by moulding.

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.

The distribution and activity of alkaline phosphatase (E.C. 3.1.3.1), acid phosphatase (E.C. 3.1.3.2), catalase (E.C. 1.11.1.6), xanthine oxidase (E.C. 1.2.3.2), aldolase (E.C. 4.1.2.7 and 4.1.2.13), ribonuclease (E.C. 2.7.7.16) and carbonic anhydrase (E.C. 4.2.1.1) were studied in the major components of bovine milk. Fractionation was accomplished by centrifugation of milk, skim-milk and buttermilk, and ammonium sulphate precipitation of skim-milk serum. The range of activities found for the enzymes studied are tabulated together with the activities of some of the enzymes in mastitic milk, and the significance of the results obtained is discussed. No carbonic anhydrase activity was detected in any of the samples tested. The other enzymes studied were found to have a greater proportion of their total activity located in the skim-milk fraction. However, all of these enzymes except ribonuclease had a higher specific activity in the fat fraction.

On the basis of complete permeability by high molecular weight reagents of casein micelles in milk and a uniform distribution of the 3 different casein subunits, a model of the micelle structure is proposed. It is composed of an average repeating unit of 1 κ-, 2 αs1;- and β-casein subunits assembled in a 3-dimensional network or branched polymer made of 130–130000 monomers, in which the trimers of κ-casein occupy the nodes and the copolymers of αs1;- and β-caseins make up the branches. All the associations between subunits are through non-covalent bonds. The chemical composition varies with the number of αs1;- and β;-casein subunits in the branches. This proposed structure is strongly supported by evidence from electron microscopy and a scale model has been made. It leads to an understanding of the role of κ-casein in micelle formation and opens new perspectives in explaining some properties of the caseins. It offers an interesting example of a new type of quaternary structure of protein subunits.

A method is described for canning and sterilizing concentrated whole milk containing 36·5% total solids. The product had acceptable organoleptic properties and did not form sediment or undergo age-thickening during storage. The method involved initially increasing the pH of the raw milk and forewarming. The product was not homogenized nor were polyphosphates added.

A description is given of a simple milking apparatus for collecting the yields of individual ewes, and of the milking procedure used in studies of lactation in ewes of ‘mutton’ breeds. The incidence of mastitis, level of milk yield, some of the non-nutritional factors affecting the milk yield and the coefficients of variation of milk yield and composition are discussed in relation to data from 6 experiments in which ewes of mutton breeds were machine-milked twice daily for 6–9 weeks of lactation.

The composition of ewe's milk during the first 4 days of lactation and on the 100th day of lactation was investigated. The total fat content was highest (17· 9%) on the day of parturition but decreased rapidly to reach a level on the 2nd day after parturition that was similar to that observed on the 100th day of lactation (9·9 %).

The concentration of octadecenoic acid, which was the major fatty acid of ewe's milk, was very much higher in early lactation than in late lactation. As the concentration of octadecenoic acid decreased the concentration of the shorter chain fatty acids (6:0−14:0) increased. The major octadecenoic acid was the cis-9 isomer. However, the proportion of the trans-11 isomer increased from 5·5 % of the total octadecenoic acid concentration in early lactation to 11·9 % in late lactation. Although linoleic acid remained a minor component of the fatty acids of the milk during lactation, its concentration increased from less than 1 % during early lactation to 1·4 % by the 100th day of lactation.

Electron microscopy was used to study the effect of addition of NaOH, forewarming, homogenization, concentration, and heat sterilization on the structure of whole milk during the production of 4 heat-sterilized concentrates that showed different degrees of physical stability. The samples were prepared for electron microscopy by adding fixative either to liquid or freeze-dried material, and then embedding for sectioning.

Noticeable structural changes occurred during forewarming of samples containing added NaOH, during homogenization, and during heat sterilization. Addition of NaOH and forewarming decreased the closeness of packing of the subunits in the casein micelles. Homogenization reduced the average size of the fat globules, and protein became attached to their surfaces. Heat sterilization caused coalescence of protein. In non-homogenized sterilized concentrate with added NaOH, protein bodies of about 100 times the volume of the original casein micelles were formed; these were free-floating and the concentrate was stable. In non-homogenized sterilized concentrate with no added NaOH the protein bodies were about 15 times the size of the casein micelles and bridged to each other, thereby forming a sediment consisting of large irregular particles. Very large protein bodies containing fat globules formed during heat sterilization of the homogenized samples, both in the presence and in the absence of NaOH, and were responsible for the formation of sediment in these 2 products.

Needle crystals observed in most samples were identifed as CaCO3. H2O by selected area diffraction; KC1 crystals were also detected.

A study has been made of the use of 2,6-dichlorophenolindophenol (DCP) and also of 2,4-dinitrophenylhydrazine (DNPH) with and without chromatography of the DNPH derivatives, for the determination of ascorbic acid (AA) and dehydroascorbic acid (DHA) in evaporated milks, and of AA in AA-fortified sterilized milks.

In the DNPH method, when interfering compounds were removed by the chromatographic separation of the DNPH derivatives, absorption curves typical of the pure DHA derivative were obtained.

The DCP method gave erroneously high values for the AA and DHA content, and the lower values obtained by the DNPH method with chromatography of the DNPH derivatives were judged correct. Thus for an evaporated milk, the values for vitamin C content (AA + DHA) were, in mg/100ml reconstituted milk, 0·88 (DCP method), 0·66 (DNPH method without chromatography), and 0·48 (DNPH method combined with chromatography). The AA contents (mg/100 ml) of the 2 fortified sterilized milks were 3·63 and 5·78 (DCP method); 3·01 and 4·28 (DNPH method combined with chromatography).

The AA contents of the 5 different evaporated milks, determined by chromatography of the DNPH derivatives, ranged from 0·07 to 0·63 mg/100 ml reconstituted milk. The DHA content was negligible.

As judged by the shape of the absorption curves after chromatography of the DNPH derivatives, it is concluded that this method is the most reliable of those studied.

A comparison was made of the effects of direct and of indirect ultra-high-temperature (UHT) processing of milk, under standardized operating conditions giving equal sporicidal effects, on some of the more labile water-soluble vitamins and on vitamin A and carotene. The effects of processing per se were negligibly small, and the method of processing was important only in so far as the presence of residual oxygen in the sterilized milk has been found to cause losses of folic acid and ascorbic acid during storage subsequent to sterilization. The incorporation of a de-aerator vessel, to reduce the oxygen level in the indirectly heated milk and so eliminate the adverse effects of oxygen during storage, had no effect on the vitamin loss occurring during heat treatment. It is concluded that milk produced by indirect heating plant incorporating a de-aerator should be similar in vitamin content to milk produced on a direct heating plant, both immediately after processing and after storage.

The milking characteristics of 4 transparent and 8 conventional rubber teatcup liners in new condition were compared for peak flow rate, machine time and strip yield, using 30 cows in two 15×15 Latin squares. The milking characteristics of transparent liners were similar to those of normal liners at the same cluster weight. The 4 transparent liners were then compared with 4 of the conventional liners using 16 cows in two 8×8 Latin squares, to observe the movement of teats within the liners throughout milking. The various analyses indicated significant differences between liners but the ranked liner mean values showed the transparent liners widely distributed in the range. It was concluded that findings from studies of teatcup action using transparent liners could be expected to apply also to conventional liners.

The conventional liners were selected to form groups differing mainly in one physical characteristic only (stiffness of the mouthpiece, wall thickness, bore and rubber hardness). Within groups, there were no significant differences in milking properties of practical importance, but between groups there were small differences in machine time and strip yield. Two properties of the liners which appeared important in controlling movement of the teat into the liner were bore of the barrel and friction, bore having the greater influence at the beginning and friction being the dominant influence at the end of milking. With the transparent liners it could be seen that the end of the teat was frequently bathed in milk. Both with transparent and with conventional liners it was surprising how often the teat penetrated so deeply that complete collapse of the liner in each pulsation cycle was prevented.