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.

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.

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.

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 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.

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.

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.

A study was made of the formation of the extracellular proteolytic enzymes during the growth cycle of several species of Pseudomonas cultivated under different conditions of temperature and nutrition. Proteolytic activity was not proportional to growth. Expressed per unit of cell dry weight, the proteolytic activity showed a peak in the early logarithmic phase which was greater in cultures grown at 3 than at 28°C. Proteolytic enzyme was not formed in the absence of organic nitrogen. Of 16 organisms studied, Pseudomonas aeruginosa ATCC 10145 was the most prolific producer of proteolytic enzyme.

The proteolytic enzymes present in the culture supernatant of Pseudomonas aeruginosa ATCC 10145 were active in the pH range 5·5–9·0 with a maximum activity at pH 7·3. Heating for 15 sec at 72°C resulted in a 36% loss of proteolytic activity whereas heating for 30 min at 63°C resulted, in a 6% loss. Boiling for 2 min completely inactivated the proteolytic enzymes. At 2°C the proteolytic enzymes were stable for at least a month and casein was readily hydrolysed at this temperature.

In order to determine how bacteria pass through the teat canal into the teat sinus, milk samples were taken by syringe, through the teat wall, from 12 quarters of 7 cows, before and after each milking for up to 16 days. Three of the teat canals were naturally infected before the start of the experiment and the remainder were artificially infected with Staphylococcus aureus by the Hadley–Wisconsin swab technique. In 3 of the quarters the inoculum was introduced into the teat sinus through the teat canal by the inoculation technique although the swabs were inserted only 3–5 mm into the canal. The other 9 of the 12 quarters were milked a total of 149 times during the experiment but only once was a colony-forming unit of the bacterium present in a teat canal infection isolated from the milk taken from the teat sinus after milking. One quarter developed an intramammary infection, the bacterium first being detected in the teat sinus prior to the third milking after inoculation of the teat canal. The invasion of the bacteria into the teat sinus therefore occurred between milkings. Staph. aureus persisted in teat canals between 5 and 32 or more milkings after inoculation. The experiment showed that bacteria in the teat canal are seldom refluxed into the residual milk in the teat sinus during correctly conducted milking with an efficient machine.

The milk produced by old cows frequently contains a lower concentration of solids-not-fat (S.N.F.) than that of young cows, mainly because of a low concentration of lactose. This can result from mastitis or possibly from other factors associated with ageing. The composition of the milk of 2 groups of old cows has been compared with that of substantially disease-free first-lactation cows. A comparison has also been made between the milk from the 4 quarters of each cow.

The first part of the work was done with 8 old cows and 4 first-lactation cows, and the milk was examined bacteriologically, cytologically and chemically at frequent intervals throughout the lactation. There was strong evidence that most of the difference in chemical composition of the milk of the old cows compared with that of the young cows was the result of mastitis, mainly subclinical. The milk from the old cows had a higher incidence of infection, a lower concentration of lactose and casein, higher concentrations of serum albumins, globulins and proteose-peptones and contained more total and polymorph cells. There was also some indication of another effect, not directly associated with disease in the current lactation, that led to a decrease in the lactose concentration of the milk of the old cows after about 80–90 days in lactation.

In the second part of the work, the milk from 23 old and 8 first-lactation cows in 8 commercial herds was examined twice, once after 58 and again after 163 days in lactation. Milk of abnormal composition as a result of disease was produced by 30% of the quarters of the old cows at the first examination and by 62% of the quarters at the second examination.

Some indication is given of the probable loss of milk and milk constituents that can be attributed to disease.

An investigation was made of the death-rate of Bacillus subtilis spores in suspension in hydrogen peroxide concentrations of 10, 15 and 20% at 25, 50, 60, 70 and 80°C. Average logarithmic survival curves were plotted against normal time and death-rate constants and Q10 values were calculated from the graphically determined decimal reduction times. This treatment of the experimental findings was found to be warranted in the temperature range 60–80°C. The first-order death-rate constant was ∽ 0·1 s−1 for 10% hydrogen peroxide solution at 60°C and the Q10 was about 1·6. Increases in the concentration from 10 to 15% and from 15 to 20% each gave an increase of about 50% in the rate constant. The application of these data to commercial practice is discussed.

The flavour quality and stability of 3 different UHT creams are described. The rate of oxidation was measured by the thiobarbituric acid (TBA) and peroxide methods as well as by organoleptic assessment. Lipid oxidation developed in some UHT creams on prolonged storage, particularly in creams manufactured during the winter months and stored at 18°C, while little or no oxidation occurred at 4 °C. Creams manufactured during the summer months were most resistant to oxidation. Creams with no detectable oxidized flavour had TBA values ≤ 0·08; values ≥ 0·16 and peroxide ≥ 2·0 were associated with pronounced oxidized flavour. These relationships between the chemical and organoleptic assessments were highly significant (P < 0·01). Low peroxide levels (< 2·0) were not necessarily indicative of good flavour quality.

The detergents sodium dodecyl sulphate and octyl phenoxy polyethoxyethanol interact with casein and cause dissociation of the high-molecular-weight casein aggregates. It is presumed that the detergent binds with hydrophobic regions in the casein molecule. The size of the complexes formed between detergents and αs1-casein, β-casein and κ-casein, as estimated by gel filtration and sedimentation velocity experiments, suggests that the caseins were complexed as monomers.

During gel filtration under non-reducing conditions, detergent-κ-casein complexes were separated from other major components because of their conversion through formation of disulphide bonds into high-molecular-weight aggregates. This reaction, which did not occur in sedimentation velocity experiments, was presumably facilitated by the changes in the equilibrium between the individual caseins during gel filtration.

Sedimentation velocity experiments showed that a ratio of about 40 detergent molecules to 1 casein molecule was required to give the smallest casein-detergent complex.