1. An experiment is described which assessed the effects on the production obtained from milking cows, of feeding a concentrate with a starch equivalent of 64 at four levels (0, 2, 4 and 6 lb./gal. of milk produced), in addition to a basal ration with limited amounts of hay and dried grass and with silage fed ad lib.

2. The total daily dry-matter intake of the cows increased from 2·2 to 2·7% of the live weight as the rate of concentrate feeding was increased from 0 to 6 lb./gal., despite a reduction in the amount of roughages consumed.

3. For each increase of 1 unit in silage dry-matter percentage, there were increases of from 1·18 to 0·42 lb. of silage bry-matter intake per cow per day as the level of concentrate feeding increased. For each increase of 1 lb. in silage dry-matter intake there was an increase of l lb. in total dry-matter intake per cow per day.

4. The average daily milk yield per cow increased from 22·2 lb. when no concentrates were fed to 27·6 lb. when 6 lb. concentrates were fed per gallon of milk produced. This is an increase of 0·9 lb. milk/lb. increase in starch equivalent intake. A significant difference in response was found between higher yielding and lower yielding groups of cows. The higher yielding group gave an increase of 1·1 lb. and the lower yielding group only 0·6 lb. milk/lb. increase in starch-equivalent intake.

5. At the general level of feeding and of milk yields obtianed in this experiment, no evidence of diminishing returns in milk production was detected when the rate of concentrate feeding was increased.

6. The content of solids-not-fat in the milk rapidly increased from 8·3% when no concentrates were fed to 8·6% when 4 or 6 lb. of the concentrates were fed per gallon of milk produced.

7. When concentrates were fed at the rate of 0 and 2 lb./gal. declines in live weight as well as in the yield and solids-not-fat content of the milk were noted, while at 6 lb./gal. there was an unnecessary gain in live weight. It is concluded, therefore, that with the particular animals and roughages used in this experiment, the optimal level of concentrate feeding was 4 lb./gal.

1. Under various feeding regimes the entire contents of the reticulo-rumen of fistulated Shorthorn cows were repeatedly removed, weighed, sampled and returned.

2. With cattle grazing grass/clover swards, but not with others grazing green cereals, there was a very marked tendency for less digesta to be found in the reticulo-rumen than with several winter diets.

3. An average fall of 71±24 lb. was found in the weight of a mixed herd of thirty-eight Friesian and Shorthorn cows when they were changed suddenly from winter diets to grazing. Simultaneous observations on three fistulated cows showed that 84% of such short-term variation in weight could be explained by variation in the weight of the digesta in the reticulo-rumen. It is likely that smaller, parallel variations in the weight of the contents of the remainder of the gut accounted for most of the remaining differences.

1. An experiment was carried out to study the effect on udder health and milk yield when half-udders of dairy cows were milked with either a moulded or an extruded teat-cup liner.

2. There was a higher incidence of mastitis in quarters that were milked with moulded than with extruded liners, but the incidence of new infection was similar for each group of quarters.

3. The types of liners used had no measurable effect on teat orifice erosion or leucocyte content of the milk, nor was the decline in milk yield with advance in lactation significantly different for the groups of quarters.

We wish to thank Dr A. T. R. Mattick and Mr A. S. Foot for advice and encouragement, and Miss H. R. Chapman for assistance in the cleaning of teat-cup liners. We are indebted to Miss M. S. Hawkins and Messrs T. M. Higgs and D. S. Simpkin for technical assistance.

An attempt to show the effect of temperature on the rate of growth of bacteria in milk was made by finding the generation times of Salmonella typhosa, Shigella dysenteriae, Streptococcus haemolyticus, Micrococcus pyogenes aureus, Lactobacillus acidophilus, Escherichia coli, Bacillus subtilis and Alcaligenes faecalis at temperatures ranging from 4 to 60°C. Growth was quantitatively measured by means of plate counts during the logarithmic period which was previously determined for each organism. The following is a summary of the results obtained:

At 4° C. none of the micro-organisms showed evidence of multiplication during the 6hr.incubation.

As temperatures of 5–45° C. were approached the generation time decreased until the optimum temperature for each organism was reached; beyond this point a slowing of growth was observed, until at 60° C. viability was apparently lost by all the organisms.

Streptococcus haemolyticus and Micrococcus pyogenes aureus have a generation time of 37–23 min.

Salmonella typhosa and Shigella dysenteriae have a generation time of 50–26 min.

Escherichia coli and Alcaligenes faecalis have a generation time of 41–16 min.

Bacillus subtilis grows at about the same rate as Alcaligenes faecalis.

The slowest organism of all appears to be Lactobacillus acidophilus with a generation time of 52–125 min.

1. In testing the technique of using conversion factors (from determined concentration) for the calculation of the partial freezing-point depressions of lactose and chloride, regular weekly chemical analyses and freezing-point determinations have been made on the milk of one Jersey and one Friesian cow over a period of 7 months.

2. Relative constancy of freezing-point has again been noted, but slight though consistent differences were present between the milks of the two cows. No seasonal variations were observed, but changes in the freezing-point depression for the milk of one were generally associated with corresponding changes for the milk of the other.

3. Linear relationships were found and their adequacy tested between the partial depressions due to lactose and chloride for each animal. The relationships, though not statistically significantly different, differed considerably for each animal. It is suggested that formulae for the calculation of one of the constituents, lactose or chloride, from the determined amount of the other, need to be treated with caution in view of the results obtained for the two animals in this work.

For the Jersey milk it was found that 80% of the total freezing-point depression was due to the lactose and chloride content (on a fat and protein-free basis). For the Friesian milk, indications were that the lactose-chloride contribution was of the order of 75% of the total depression, but the result of statistical analysis was less satisfactory for this milk.

The co-operation of Mr J. McGibbon of the Hawkesbury Agricultural College is gratefully acknowledged. Thanks are due also to Mr J. V. Pascoe and the Dairy Farmers Co-operative Milk Co. Ltd. for their continued interest in the work.

Surface-active substances applied to the surface of whole milk may either bring fat globules, clumps, lenses and patches on to this surface, or sweep the surface clean of these fat forms.

In the homologous series of monohydric aliphatic alcohols, methyl and ethyl alcohols show a moderate rising action, whereas the other members from n-propyl alcohol to n-decyl alcohol are strongly active. There is only a slight difference in the activity of primary, secondary and tertiary butyl alcohols.

Ageing of milk slightly promotes the rising of fat globules on to the surface under the action of ethyl to n-amyl alcohols.

Alcohols, beginning with n-propyl alcohol, bring fat globules to the surface of milk much more strongly than does mechanical disturbance of the surface by touching with a platinum ring.

Glycerol, due to its three hydroxyl groups and a weak hydrophobic residue, is almost inactive, monobutyrin is strongly active in bringing the fat globules to the surface, while tributyrin sweeps the surface clean.

Spans and Tweens, sorbitan and polyoxyethylene sorbitan esters of higher fatty acids sweep the milk surface clean.

The author wishes to thank Mr G. Loftus Hills, Officer-in-Charge of the Dairy Research Section, C.S.I.R.O., Melbourne, for helpful discussion, and the Atlas Powder Company, Wilmington, Del., U.S.A., as well as its Australian representatives, Chemical Materials Pty. Ltd., Glebe, N.S.W., and Hardie Trading Ltd., Melbourne, for samples of Spans and Tweens.

Specific heat data have been obtained for separated milk, whole milk, cream (15% fat content) and the fat in cream, under certain well-defined experimental conditions. With standardized techniques of sample preparation, the results were repeatable within the errors of the experimental methods employed.

An examination of the effects on the specific heat curves of milk fat of different modes of thermal treatment has provided information on the melting and solidification behaviour of the fat. The degree of dispersion of the fat in cream has been shown to be an important consideration.

My thanks are due to Miss H. R. Chapman of the Institute dairy, for supplying milk and cream samples, and to Mr J. H. Prentice and other members of the Physics department for useful discussion.

The proportion of fat present in cream as small globules (approximately 1 μ and under) is estimated from the proportion of the total fat which remains in the serum when a sample of the cream, diluted to 10% fat, is centrifuged at 60° C. for 30 min. at 3000 r.p.m.

The fat present as large globules (7 or 8μ and over) is estimated by finding the proportion of the fat which rises 1 cm. in 60 min. when the cream, diluted to 10% fat, is held at 60° C. in a modification of the Andreasen particle-size apparatus in which the jar is replaced by a conical flask and the tip of the sampling pipette is held 1 cm. from the flat bottom of the flask.

The thanks of the author are due to Dr F. H. McDowall for helpful advice and criticism and to Miss R. P. Johnson for assistance with the experimental work.

The effect of pH on the extent of splitting and clumping of globules in hot cream agitated by treatment in a Vacreator, by vigorous mechanical stirring or by simple aeration has been investigated. The size distribution of globules was determined in cream before and after treatment either by the microscopic method or by a rapid method involving separation of small and large globules by centrifuging and gravity creaming respectively.

It was found that at pH 8 splitting of globules was at a maximum and clumping at a minimum. As the pH of the cream to be treated was lowered towards pH 6, the amount of splitting decreased and clumping increased. The ‘clumping’ of globules in cream during single-stage homogenization was also increased as the pH was lowered.

Practical applications of the observations are suggested.

The thanks of the author are due to Mr J. A. Singleton, superintendent and Mr B. Le Heron, buttermaker of The Dairy Research Institute (N.Z.) experimental factory, for arranging and carrying out the Vacreator treatment of cream; to Dr F. H. McDowall for helpful advice and criticism, and to Miss R. P. Johnson for assistance with microscopic and analytical work.

1. The effect of the level of clover intake on the vitamin A potency of milk fat has been studied, using Jersey cows from the herd of the Dairy Research Institute (N.Z.).

2. In preliminary experiments in which composite bi-weekly butterfat samples were obtained from the whole herd of thirty-eight cows no relationship could be established between level of clover intake and potency of fat produced. This was assumed to be due to the rapidity with which the level of clover intake varied, since under normal grazing management the cows were moved to a fresh paddock (which was often of widely different botanical composition from that previously grazed) after every second milking.

3. In later experiments in which three pairs of monozygous twins from the herd were used, a clear-cut relationship was established between clover intake and potency of fat produced and between clover intake and iodine value, oleic acid percentage and tocopherol content. Diets high in clover tended to depress total potency, iodine value, oleic acid percentage and tocopherol content of the fat, while diets low in clover had the reverse effect. The clover used in these experiments was mainly an improved strain of white clover containing approximately 0·03% cyanide. Repetitive experiments using improved strains of red clover produced negative results.

4. The mechanism by which diets high in clover depress fat potency, iodine value, oleic acid percentage and tocopherol content is not clear. It is suggested, however, that it may be due to (i) the low tocopherol content of clover relative to grass, (ii) the high HCN content of certain species, and (iii) the possibly lower oleic acid content. The possibility is also considered that it may be due to some factor (or group of factors) associated with the stage of development of the pasture as a whole at a time when clover happens to be the dominant pasture species.

5. Drenching cows with thiocyanate, the probable detoxication product of HCN in the ruminant, could not be shown to have any effect on the levels of vitamin A alcohol, ester, carotene, or xanthophyll in the blood and milk fat.

Some of 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 M.Agr.Sc. 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 M. R. Patchell and farm staff of The Dairy Research Institute (N.Z.) for assistance in collection of milk and blood samples. The technical assistance of Miss Fay Frecklington is gratefully acknowledged.

1. The levels of vitamin A alcohol and ester, carotene and xanthophyll in the blood plasma of six cows, grazed out-of-doors on pasture under typical New Zealand conditions, have been followed throughout one lactation. The same constituents have also been followed in the milk fats of these animals and in commercial factory butters over the same season.

2. The seasonal trend in the vitamin A and carotenoid content of New Zealand milk fat is a reflexion of the changing level of these substances in the blood plasma.

3. The decreased level of carotene, xanthophyll and vitamin A ester in the blood plasma over the summer months is consistent with a decreased absorption or utilization of carotenoids over this period.

4. Throughout the year the vitamin A in the milk fat is predominantly in the ester form with no increase in vitamin A alcohol indicative of any increased utilization of hepatic vitamin A reserves.

The author is indebted to the Department of Scientific and Industrial Research for a grant towards this investigation; to Mr M. R. Patchell and the farm staff of The Dairy Research Institute (N.Z.) for assistance in the collection of milk and blood samples; to Dr F. H. McDowall, Mr A. K. R. McDowell and the staff of the Chemistry Laboratory, The Dairy Research Institute (N.Z.), for the preparation of the fat samples and for the supply of factory butters. The assistance of Miss Fay Frecklington and Miss Jane Monroe with part of the experimental work is also acknowledged.

1. The effect of varying levels of vitamin A ester in the blood plasma of cows on the levels of vitamin A ester in their milk fat has been investigated.

2. The milk fat levels reflect plasma levels, but it appears that, irrespective of the immediate carotene or vitamin A intake of the animals or of their liver reserves, some of the milk fat vitamin A ester is derived from vitamin A of other than immediate dietary origin.

3. It is suggested that the bulk of the plasma carotene contributes little to the level of carotene in the milk fat. The latter derives mainly from the carotene of immediate dietary origin which, during transport from the intestines to the storage organs, is associated with dietary fat and vitamin A ester in the chylomicrons.

The author is grateful to the Department of Scientific and Industrial Research for a grant towards this investigation; also to Mr M. R. Patchell and the farm staffs of The Dairy Research Institute (N.Z.) and Massey Agricultural College for assistance with the feeding and dosing of the animals and the collection of milk samples. The assistance of Miss Fay Frecklington with some of the experimental work and of Mr A. C. Glenday with statistical examination of the results is also acknowledged.

1. Plasma levels of vitamin A and carotenoids prior to and following parturition have been followed in groups of cows and heifers maintained under typical New Zealand farming conditions.

2. Despite the high carotene intake prior to calving, the cows, and to a lesser extent the heifers, showed decreases in plasma vitamin A and carotenoid level at or near to parturition, the decreases in the levels for the cows being of the same order as those reported in Great Britain and the United States.

3. Although the concentration of vitamin A and carotenoids was higher in the colostrum of heifers than of cows, the total daily secretion of these components by the cows was much greater over the first few days of lactation.

4. Evidence is advanced to support the suggestion that the decrease in plasma components is related to the extra drain of colostrum synthesis rather than to any hormonal changes associated with parturition.

We are indebted to the following: the Department of Scientific and Industrial Research for financial assistance towards the cost of this investigation; Mr R. M. Patchell and the farm staff of The Dairy Research Institute for the collection of milk samples; Miss Fay Frecklington for help with much of the analytical work; one of us (S.Y.T.) to the Royal Society, the Nuffield Foundation, and the Board of The Dairy Research Institute (N.Z.) for a travelling fellowship during the tenure of which the work reported here was carried out.

The properties and composition of buffaloes' colostrum have been compared with those of cows' colostrum. The most significant differences found between the two may be summarized as follows:

(1) Buffaloes' colostrum was richer in total solids, lactose, total N, globulin N and proteose-peptone N than cows' colostrum.

(2) Buffaloes' colostrum had a much wider range of fat content than cows' colostrum. A distinct difference between the two colostrums lay in the fact that while buffaloes' colostrum was definitely poorer in fat content than normal buffaloes' milk, cows' colostrum was richer in fat content than is normal cows' milk.

Changes in buffaloes' mammary secretion during the transition period from colostrum to milk.

The following is a summary of the most significant trends in the properties and composition of buffaloes' mammary secretion during the transition period:

(1) The specific gravity, acidity and chlorine decreased until they reached a normal value at the fifth milking. This compares well with the trends reported in the literature for cows' mammary secretion during the transition period.

(2) The pH increased gradually until it reached its normal level before the fifth milking.

(3) The highest level of total solids occurred at the first and second milking, and dropped sharply at the third milking to the level normally found in buffaloes' milk.

(4) Changes in the lactose content from the second milking onwards were very slight. This contrasts with the known trend during the transition period in cows, when a gradual increase from a low level at the first milking to higher levels at the following milkings is noticeable.

(5) The total N, globulin N, albumin N and proteose-peptone N decreased from relatively high levels at the first and second milkings to lower levels at later milkings, and thus closely followed the trend shown by the total solids.

Buffaloes' mammary secretion may be considered comparable in its composition to normal buffaloes' milk and suitable for human consumption from 5 to 7 days after parturition.