A cubed molassed sugar-beet product with added urea, dicalcium phosphate, trace elements and vitamins was prepared containing 17% crude protein and up to 0·53% P. The product was evaluated in 3 changeover trials with lactating cows and the treatments involved comparisons with a low protein (10%) concentrate and one supplemented with groundnut plus cottonseed meals. When the product was included at 35–62% in milk production diets the mean daily yield of about 15 kg was about 0·5kg less than when full supplementation was as vegetable protein. This was considered more likely to be associated with inefficient utilization of urea rather than because of an energy difference between molassed sugar-beet pulp and barley.

The rates of production of protozoa in the rumen of buffalo calves have been estimated using a single-injection isotope dilution technique. The calves were fed at 2 levels of crude protein, namely, 13% lower and 19% higher than that recommended by the National Research Council. The animals were given their rations at 2-h intervals for 3 weeks. Thereafter 14C-labelled rumen protozoa were injected into the rumen of each calf in a single injection. Samples of the rumen liquor were drawn at various time-intervals for 10 h and were analysed for the concentration of protozoa and radioactivity. The decline in the specific radioactivity of protozoa cells in the rumen as a function of time was used for calculating half life (t½). A mathematical equation was used to calculate the rate of production of protozoa. The average t½ was 1077 min for both groups and the rates of production of protozoa were 73·9 and 92·1mg/min in groups fed on low and high planes of crude protein respectively, showing that the production of protozoa is significantly (P < 0·01) higher in animals consuming a ration high in crude protein.

Two experiments were carried out with Friesian cows grazing improved winter pastures. In expt 1, 12 cows were fed 6·6kg/d of a barley-based concentrate containing either no N supplement, or supplements of casein, formaldehydeprotected casein or urea which provided 48 g N/d. In expt 2, 12 cows were fed 2·6kg/d of a barley-based concentrate containing either casein, formaldehyde-protected casein or equal mixtures of both, all of which provided 96g N/d.

In expt 1, although the production of fat-corrected milk was 7·1% higher and that of total solids 6·1% higher on the protected casein than on the casein diet, production of milk and milk constituents on the control and urea diets were similar to values obtained for cows fed protected casein. In expt 2, milk production and composition were unaffected by treatments.

The concentrations of amino acids in jugular plasma and mammary uptake per litre of plasma were not affected by the experimental diets in expt 1, and were unrelated to milk yield in either experiment. In expt 2 the concentrations of glycine, serine and threonine in jugular plasma were significantly higher in the diet in which none of the casein was protected. Mobilization of muscle protein may have been responsible for the elevated levels of glycine in cows fed this diet. Mammary uptakes of essential amino acids in expts 1 and 2 were respectively 47 and 42% of those available, whereas the uptakes of non-essential amino acids were respectively 24 and 17% of those available.

An attempt was made to determine the amino acids most likely to limit milk production. Milk:uptake concentration ratios were obtained using our values for amino-acid uptakes and values published previously for the concentration of amino acids in milk. The results of these calculations suggest that the amino acids most likely to limit milk production are threonine, phenylalanine and methionine.

A survey of the composition of the milk of individual cows in 6 commercial herds in the North of England was undertaken from October 1968 to July 1969. In all herds there was a decline in solids-not-fat (SNF) content; in 4 of the herds this was mainly the result of a fall in protein content, although in all herds there was a decline in lactose content in association with an increase in udder infection and an advance in average stage of lactation. Between-herd differences in the minimum value for lactose content were related to differences in udder infection, stage of lactation and lactation number.

Two of the herds were selected for further study from October 1970 to April 1971. After a preliminary period each herd was divided into 2 matched groups. One group received the usual management, and the other was subjected to remedial changes of supplementary feeding and antibiotic therapy and improved udder hygiene. In both herds, treatment reduced udder infection and improved lactose content and in one of the herds there was also an increase in protein content.

It has been claimed by Stewart, Puppione & Patton (1972) that milk is a valuable source of cell membrane in a ‘relatively pure’ state originating from shed mammary secretory cell microvilli and golgi vesicles. The morphological basis for this has been re-examined in this paper. It is shown that the vesicular and elongated membranous structures found in skim-milk are identical to structures present as part of the initial milk fat globule membrane (MFGM) of alveolar and expressed milk, and that both structures survive extraction with chloroform–methanol. It is therefore suggested that a major part of the skim-milk membrane is material shed from the freshly secreted milk fat globule and consists of a specialised derivative of the secretory cell plasmalemma, the initial MFGM.

The influences of different operating parameters upon the distribution of pressure across a simple homogenizing poppet valve have been investigated. Regions of contracted and separated flow were defined by detailed probing of static pressures and found to correlate well with the results from previous visual and photographic observations.

Direct confirmation was obtained of the conclusion, first reported by Loo & Carleton (1953), that fat globules in milk are disrupted chiefly in a zone between the valve and seating surfaces which is close to the seating inlet boundary. Progressive coarsening of the globule suspension was detectable in the flow downstream from this zone.

Coagulation time–pH curves with a coagulation-time minimum around pH 6·8 (type A curve) could progressively become type B (no minimum) as the heating temperature was decreased from 150 to 130°C. The short coagulation time that most milks have when pH is around 6·8 was found to be the result of a ‘premature’ coagulation, probably caused by calcium phosphate deposition on the larger caseinate micelles. This is followed by a second coagulation, not visually detected, that coincides with the coagulation time that would be expected if no coagulation-time minimum existed on the coagulation time-pH curve. The coagulation time of milks giving type A and type B curves may therefore not be comparable.

Forewarming milk for 30 min at 80°C can introduce or accentuate a coagulationtime minimum when the milk is subsequently heated at a higher temperature. The effects of adding β-lactoglobulin, copper and N-ethylmaleimide on the heat stability of milk were examined and explanations proposed for these effects.

Gel filtration on Sepharose 6-B was used to study the size distribution of sub-micellar casein aggregates in colloidal phosphate-free milk, and comparisons were made between the elution profiles obtained for fresh, heated, ultra-hightemperature (UHT) treated and stored UHT milks. Increase in length of storage of UHT milk gave rise to an increase in proportion of casein aggregates excluded from Sepharose 6-B, but no corresponding increase in size of included casein aggregates was observed.

It has been shown that the inhibition caused by heat treatment, of the primary phase of rennin action on casein micelles, is dependent on the presence of β-lactoglobulin. The degree of inhibition increased with increasing amounts of added β-lactoglobulin for both heated casein micelles and heated skim-milk to a constant value. The results are fully consistent with the hypothesis that the inhibition is caused by complex formation between β-lactoglobulin and κ-casein when milk is heated.

The complexing of whey proteins in hydrochloric acid whey by carboxymethyl cellulose (CMC) has been studied. The efficiency of precipitation of CMC (the ability to form insoluble complexes with whey proteins) increased with increasing degree of substitution (DOS) of CMC. At a DOS of greater than 1·4, efficiencies of precipitation of whey protein greater than 90% were achieved without the need for dilution of whey. CMC of high DOS would thus be useful in whey protein reclamation schemes. The amount of CMC necessary for maximum efficiency of precipitation also increased with increasing DOS. The composition of the CMC-protein complex varied little over the range pH 2·8–4·0. Under optimum conditions for binding, the complex contained 61–68% protein and more than 95% of the CMC originally in solution was precipitated in the complex.

A method by which it is possible to quantify with very high accuracy the levels of rennin, bovine pepsin, porcine pepsin and proteases from Mucor miehei (fromase) or M. pusillus (emporase) in a ‘commercial rennet’ containing some or all of these enzymes is described. The method employs chromatography on DEAE cellulose in piperazine buffer (0·02M, pH 5·3) to fractionate the enzymes into 2 groups: (peak A) rennin, emporase, and fromase, eluted at ∼0·2 m-NaCl and (peak B) bovine and porcine pepsins eluted at ∼0·4 m-NaCl. The rennin in peak A is selectively denatured at pH 9·0, 20°C for 60 min and the rennin plus emporase at pH 6·0, 60°C for 20 min, permitting the quantification of emporase and fromase (and rennin by difference) and fromase, respectively. The porcine pepsin content of peak B is quantified by selective denaturation at pH 7·0, 30°C for 3 min. A number of commercial rennet preparations were analysed using this method: full rennet contained 45–60% bovine pepsin and ‘half and half’ contained 20–25% rennin, 25–30% bovine pepsin and 50% porcine pepsin.

The development of structure in Cheddar cheese was followed using electron microscopy, of both thin sections and freeze-etched preparations. The casein micelles, at first separate, were seen to aggregate into a network, coalesce and finally form a granular mass. The fat globules, also separate at first, were gradually forced into clumps as a result of shrinkage of the casein network and incomplete fusion took place during ripening. Starter bacteria were seen trapped in the casein near the fat–casein interface, which was shown to be the region of highest water content in the mature cheese.

A method has been developed for the routine determination of acetic, propionic and butyric acids in cheese. The cheese sample is homogenized with water (1:2) at 40°C for 15 min and the slurry centrifuged at −5°C and 12000 g for 10 min. The free fatty acids in a portion of the aqueous centrifugate are adsorbed on to a column of anion-exchange resin in the hydroxide form. After washing the column with water to remove extraneous material the acids are eluted from the resin with aqueous formic acid. Amino acids in the acidic eluate which interfere with subsequent analyses are removed by a cation-exchange resin column in the hydrogen ion form. The concentrations of acetic, propionic and butyric acids in the cation-exchange resin eluate are determined by isothermal gas chromatography using a glass column (1·8m×2mm i.d.) packed with Chromosorb 101 (100/120mesh). Cheese oil-water partition coefficients are then used to calculate the concentrations of acetic, propionic and butyric acids in the cheese sample.