1. A series of five experiments on the effects of variation in the concentrate ration of cows receiving normal diets of hay and grass silage are described.

2. Responses in milk yield to the feeding of additional concentrates occurred in all five experiments and were statistically significant in three of them.

3. Mean responses in four experiments with adequate statistical control ranged from 0·7 to 1·0 lb. milk/lb. additional S.E. at levels of feeding from 90 to 120% of the Woodman standard, and were not economic at prices ruling during the winter of 1955–56.

4. There were indications that the responses varied with the yield of the cow, and in two experiments there was clear evidence that the response to a second addition of 20% in the production ration was approximately half of that to the first.

5. The response to additional S.E. was appreciably reduced when normal protein standards were not maintained in the additional concentrates.

6. A limited substitution of hay for concentrates, which did not alter S.E. intakes appreciably, had no appreciable effect on milk yield.

7. Significant responses of solids-not-fat percentage to the feeding of concentrates above the normal standards occurred in two experiments, but not in two others where the control percentages were lower. The importance of factors other than energy intake in influencing this quantity was emphasized.

1. Rates of eating hay, kale and concentrates and responses to a 3 lb. increase in the daily concentrate allowances when roughage was rationed on a ‘group’ basis, were measured in fourteen Ayrshire cows and fifteen heifers.

2. There were significant differences between animals, between days, and significant cow × period interactions, in rates of eating in both groups. The cows were a more variable group and generally ate faster than the heifers. Although the rate of eating fresh kale tended to decrease with increasing dry-matter percentage, the rate of eating kale dry matter was positively and significantly related to the dry-matter percentage.

3. There were positive associations between the rates of eating of the three different foods, and of these with live weight, but no effects of milk yield or stage of lactation, and no marked effects of climatic conditions could be detected.

4. The errors in the determination of mean rates of eating were such that observations made on 4–5 days gave satisfactory comparisons of individual rates of eating.

5. Reponses in milk yield to additional concentrates were positively correlated with milk yield, and no independent effects of stage of lactation could be detected. Responses by the heifers were less then those of cows giving similar yields.

6. Responses in solids-not-fat percentage were greatest in those cows with inherently low percentages.

7. There was no relationship between rates of eating roughage and responses of milk yield to additional concentrates, but live-weight responses and, to a lesser extent, solids-not-fat responses were negatively correlated with rates of eating in the cows. It was concluded that the level of feeding, system of management and the roughage:concentrate ratio used were such as to eliminate the effects of rates of eating roughage upon milk yields, if indeed such effects exist.

This paper deals with an investigation on the influence of milking characteristics on lactation yield, maximum daily yield, and persistency carried out at the Institute of Animal Breeding and Genetics at the Agricultural College of Norway.

Data used for the analyses were collected from 57 heifers of Norwegian Red Poll and 111 heifers of Norwegian Red and White Cattle. The Red Polls were recorded at the Hafslund Progeny Testing Station, while the recording of the Reds and Whites were carried out by field control.

When the effect of the milk yield at the recorded milkings on the observed milking characteristics was eliminated, the milking character had no significant effect on the lactation yield, the maximum daily yield, or the persistency. This was the case when the effect of the milk yield at the recorded milkings was eliminated by correction as well as by using only those observations of milking characteristics that were taken when the milk yield was between 6·1 and 7·0 kg. Slow-milking cows are not, therefore, necessarily poor milk producers.

Simultaneous intramammary pressure recordings were made on pectoral and inguinal mammary glands of the sow. Oxytocin was injected via the ear vein and the nature of the pressure curves resulting from quantities of hormone above physiological level studied. The frequency of the periodic contractions of the mammary myopethelium under these conditions was measured and compared with human uterine responses under similar conditions.

The writer is indebted to Professor H. McK. Carey of the National Women's Hospital, Auckland for the intrauterine pressure graph shown in Fig. 3. Acknowledgement is also made of the technical assistance given during the experiments by Mr E. D. O'Reilly.

1. The mixed evening and morning milk from 360 cows, all sampled six times during their lactation, was analysed chemically and for its cell content. A total and a differential cell count were made. Similar analyses were made on 823 samples of farm milk taken at a receiving creamery.

2. The total cell counts varied from less than 10,000 to 5,000,000/ml. and there was considerable variation in the chemical composition of samples containing similar numbers and types of cells.

3. The proportion of polymorph cells in the total count increased rapidly with increasing total count.

4. Stage of lactation had little effect on the number of cells present in the milk, but samples from cows in very early and very late lactation had been avoided. The total cell count was lowest from the 70th to 130th day of lactation with a tendency to rise after the 130th day.

5. Both the total and the polymorph cell counts of the milk increased sharply with the lactation number of the cow until the seventh lactation and then remained at a fairly constant level.

6. As the total cell count increased to an average value of 500,000/ml. there was a fall in the daily yield of milk per cow and a marked fall (0·25%) in solids-not-fat content. The latter was the result of a steady drop in the lactose content, the casein content being affected only by counts approaching 1,000,000/ml. An increasing cell count was without effect on the fat content. Possible reasons for the relatively small effect on chemical composition of high cell counts in some milks is discussed.

7. It is concluded that the presence of subclinical mastitis, as evidenced by the cell count of the milk, leads to a lowering of the solids-not-fat content.

The authors wish to thank their assistants in the Technical Chemistry and Veterinary Pathology Departments, who did most of the practical work.

The C.O.B. test has been carried out at 15 min. intervals on raw milk samples stored at 20°C. to examine worker and replicate variability. Within experimental limitations, the differences between workers were not significant (P>0·05) and, in general, good agreement was found between the five replicates examined for each milk sample, coefficients of variation less than 4·0%. The change from absence to presence of a precipitate generally occurred with successive tests, but there were indications that the times to increased intensity of clotting differed with samples.

Captain H. Barkworth was responsible for the plan and design of these experiments which were carried out by members of his staff at Shardlow.

1. The results of an investigation into the efficiency of utilization by dairy cows of carotene from New Zealand summer pasture and from arachis oil are reported.

2. A 50-fold decrease in the intake of carotene from pasture over a short period was shown to have only a small effect on the vitamin A potency of milk fat, carotene content being reduced by approximately 2μg./g. fat and vitamin A ester by approximately 1·5μg./g. fat. No change was observed in vitamin A alcohol content.

3. Sample-to-sample variations in both the control and treated animals were observed in many cases to exceed the differences due to treatment except during the period of extreme carotene deprivation. Sample-to-sample variations of control and treated animals were also observed to be highly correlated, and it is suggested that variations in the external environment of the animal may have a marked effect on carotene utilization.

4. Carotene in arachis oil was shown to be relatively more effective in maintaining the vitamin A potency of milk fat than summer pasture.

The results of this investigation form a section of a thesis submitted by one of us (N.A.W.) in partial fulfilment of the requirements for the degree of Ph.D. of the University of New Zealand. The authors are indebted to the Department of Scientific and Industrial Research for a grant towards the investigation, and to Mr D. J. Dobson and the farm staff of The Dairy Research Institute (N.Z.) for assistance with the feeding and dosing of the animals and the collection of milk samples. The technical assistance of Miss Fay Frecklington is also thankfully acknowledged.

1. The distribution of carotenoids and vitamin A in milk-fat globules has been further investigated. The results obtained support previous observations that the carotenoid content of the fat obtained by solvent extraction from the smaller globules in milk is greater than in the fat obtained from the larger globules. It has also been shown that the vitamin A alcohol content of the extracted fat varies in the same way as the carotenoid content, but that the reverse appears to be the case for vitamin A ester.

2. It is suggested that these differences in concentration are not due to a surface layer of carotenoids and vitamin A alcohol on the fat globule but to the presence in mammary secretions, as in blood, of protein-bound forms of these substances. In support of this it has been shown that when fat is obtained by centrifuging rather than by solvent extraction, its carotenoid and vitamin A content appears to be almost independent of globule size. Furthermore, some vitamin A and carotenoids remained in the virtually fat-free serum obtained from normal milk, colostrum and pre-partum secretion and was precipitated with the various serum proteins, particularly the globulin fraction. The increased carotenoid and vitamin A alcohol content of mastitis milk may also be explained by the presence of abnormally large amounts of these protein-bound forms.

The author is grateful to the Department of Scientific and Industrial Research for a grant towards the cost of the investigation; also to the farm staff of The Dairy Research Institute (N.Z.) for assistance with the collection of milk and colostrum samples.

The processing of liquid milk, particularly sterilization ‘in-bottle’ or ‘in-can’, may cause considerable destruction of its content of vitamin B12. This loss can be greatly reduced by thorough deaeration of the milk before heating.

The author would like to thank Dr S. K. Kon for helpful advice and criticism.

1. Despite the presence of appreciable quantities of steam volatile fatty acids as glycerides in butterfat, no short-chain fatty acids with odd carbon number have been detected by gas-liquid chromatography of the acids.

2. Mild oxidation of butterfat for short periods of time produces steam volatile fatty acids with odd carbon number. A large proportion of these acids was formic, with smaller proportions of propionic, valeric and nonanoic acids.

3. The relative ease with which short-chain fatty acids are produced on oxidation of fats, points to the danger of contaminating naturally occurring fatty acids with extraneous acids.

4. A total analysis of the fatty acids of New Zealand butterfat by gas-liquid chromatography compared well with similar analyses carried out by previous workers by means of esterfractionation analysis.

The size distribution of fat globules was determined microscopically in cream samples taken from different parts of the Vacreator during treatment of cream.

A considerable increase in numbers of small globules (splitting) was found in samples which had passed the equilibrium valve. Smaller increases took place in the pasteurizing chamber and in the extractor pump. Increase in numbers of large globules (clumping) occurred in the cooler section.

Splitting of globules could be reduced: in the pasteurizer by reducing velocity of incoming steam; at the equilibrium valve by reducing the vacuum drop across the valve or by introducing part of the steam at the infuser instead of into the pasteurizer.

It is concluded that splitting of globules in the Vacreator is due to a homogenizing effect where steam and cream travel at a high velocity. Flash-boiling causes clumping but not splitting of globules. These conclusions should apply to any equipment for pasteurization or deodorization of cream with direct steam.

The thanks of the author are due to Mr J. Singleton (Superintendent) and Mr B. Le Heron (Buttermaker) of the Institute factory for arranging and carrying out Vacreator treatments of cream, to Dr F. H. McDowall for helpful advice and criticism and to Mrs R. P. Haverkamp for assistance in measuring fat globules.

The relationships between nineteen strains of Str. cremoris and nineteen phage races were investigated. It was found that in addition to clear-cut lytic reactions there were other actions between some phage races and bacterial strains whereby in some cases a phage could show adaptation to a strain and become changed in host range, and in other cases could inhibit growth of a strain without any phage multiplication.

There is some evidence to indicate that bacterial strains and phage races fall into family groups within which most of the phages act in one way or another on most of the strains. The suggestion is made that the strains and races in a group may have originated from a parent bacterial strain and parent phage race.

The selection of strains of Str. cremoris for use as cheese starters is discussed in the light of the findings reported in the present paper. The diffculty of isolating a large number of strains unrelated in every respect is indicated.